I have researched this topic extensively and agree with what the host is saying. However, I highly recommend looking at a coax loss calculator, like what is found on KV5R website. Depending on the HF frequency, depending on the SWR and length of cable, dielectric losses can become fairly significant. Case in point -- Using 50 Feet of LRM 400 @ 10:1 SWR at the frequency of 28 Mhz will yield a 27% power loss (not radiated) when using 100 watts. In this scenario the "output" power would be 72.584%. Now that was for 10 Meters, 6 meters in the same scenario would have higher losses, and the opposite would be true for lower frequencies meaning lower losses. Over all I like what Mark is describing in the video and for the most part I wouldn't worry about SWR higher than 2:1 unless using an ATU. Lastly, I have tested power losses, and it does exist.. I have purposefully heated up coax with high SWR to illustrate the point. As Mark said, the power isn't lost, it is converted from one form to another, and in the case of losses, from RF to Heat. Hope that helps -
@@N1IA-4 Correct, and the same goes for RF power being converted into heat in coax dielectric. If RF power doesn't get radiated by the antenna we generally say it is "lost". Of course @lomgshorts3 knows that, but he just wants to say "Ah Ha, I found something technically wrong with your post". "Now I'm going to post a fact and rub your nose in it". Truth is, I can point this insight at myself, and I've been guilty of the same. However, over time I have tried to improve the way I say things and how I come across. I'm not always perfect, but I try to not be "that guy".
In the case of coaxial cable at HF, the dielectric loss (rf power dissipated in the dielectric) is very small compared to the copper loss (copper loss is the loss due to resistance in the conductors). The loss in a short piece of coaxial cable with high SWR where the load impedance is high can be less than the loss when the SWR is 1:1. The loss is concentrated mostly where the current in the cable is highest. If you feel along a cable that has been heated by rf power with high SWR present, you will find hotter and cooler areas alternating, with spacing from one hot area to the next hot area being a half wavelength in the cable. The graph that is frequently published showing the increase in loss due to increased SWR is fairly accurate when the line is a half wavelength long or longer, but the graph can be significantly in error for short lengths. Of course, for short lengths of cable, the loss is rarely a concern anyway.
Since power cannot be created from nowhere, it may be confusing to some that you are suggesting that 20W magically becomes 30W at the aerial, so it is worth pointing out that this APPARENT increase in power arises because of the difference in impedance that occurs at the ATU, i.e. the measurement is referenced to 50 ohms but is not ACTUALLY at 50 ohms (at an SWR of 2, it's actually 25 or 100 ohms). Most SWR meters work by being calibrated to the stated output power (e.g. 20W) and then reports what FRACTION of this power is travelling forwards or in reverse.
Actually, what really happens is that half of the power are 10 W. Does not make it to the antenna and get radiated right away. But eventually it's recycled back towards the antenna and radiated. As you say in this ping pong configuration, so it's not 20 + 10. It's only ten that gets to the antenna and the other ten eventually gets back to the antenna which does not make it thirty watts
@@Paddy_Roche Reflected power not on outside of coax. You're confusing it with common mode currents that occur on outside of coax due to an unbalanced feed.
You were doing good to the part you said that on the low bands the SWR does not matter. For short runs up to say what would be used in a car there is not that much additional loss. However with feedline loss when matched is getting to be around 3 db or more the additional loss starts to increase by a good bit as the SWR gets higher. You sure do not want a 10:1 SWR with 100 feet of rg-58. One other thing is that if running high power the coax can develop hot spots and melt or the voltage can arc over.
Good points Ralf. Yes 100 feet of high loss cable like RG58 with a high mismatch would be a bad idea. I didn’t try to cover every scenario so thanks for that input.
The meters power rating is only correct at 1:1 match. Anyone who doesn’t understand that an antenna that isn’t properly matched isn’t as efficient as one that is, doesn’t understand basic power transfer engineering concepts. I have an Electronics Engineering degree, this was taught in school. Any reflected power between say the transmitter and input of the ATU if the ATU cannot provide a 1:1 match is reflected back to the transmitter finals as heat. This is why protection circuits cut back output power if there isn’t a 1:1 match since the reflected power will add heat to the final components. So the power is lost. There is also the output of the ATU to the transmission line and antenna. If there is reflected power from the antenna and the transmission line combined, then transmission line and ATU absorbs the reflected power as heat. It’s lost power that doesn’t get radiated from the antenna. If it’s not a 1:1 match at the antenna, a signal will still be radiated from the antenna, but some power gets reflected is not radiated. So your antenna is not 100% efficient . Theoretically if you loose 50% of your power to coax and reflected power then you have lost 3DB signal radiated.
I appreciate the hard work you put into your education and taking the time to respond but you are not correct. ALL reflected power is reflected from the transmitter or tuner back to the antenna. The transmitter does not see reflected power. Also a low SWR is not an indication of antenna efficiency-it indicates a good match. I have a dummy load with a 1:1 SWR but it’s a lousy antenna. As for what heats up the finals with a high SWR I will save for a future discussion. Check out the writings of antenna engineer Walt Maxwell. www.k3emd.com/downloads/Reflect.pdf
ATU's do absorb power, as a matter of fact what destroys expensive roller tuned ATU's is burn marks on the inductors--this probably isn't from SWR but a good look at burned up ATU's could be interesting. In EE school the first thing they teach you is that all components absorb power/have losses/ and that there is no perfect component.@@NoMoreRadioMyths
Based on that theory we should all have antennas with 100:1 swr. Take a look at the article “ the lure of ladder line “ from QST that goes into coax loss absorption.
Sure ladder line has virtually no loss but it’s inconvenient for most people. Who has an antenna with a 100:1 swr? What are they using - a kitchen fork? Did you do any reading? www.arrl.org/files/file/Technology/tis/info/pdf/q1106037.pdf
100:1 is a bit much but it seems that some handheld radios that have no transmission line at all work fairly well up to a SWR of 20:1. Because there is no such broadband HT antenna that can span 136 to 174 MHz or 400 to 520 and maintain a low SWR over this range.
Again a good informative video. I have explained this so many times, even to other engineers. I have done detailed calculations of how power bounces back and forth from antenna to transmitter and back again! Essentially I can use a simple example of 100 watts and a coax with 3 dB loss to make the calculations easy. 100 watts leaves the transmitter initially. With 3 dB loss only 50 watts gets to the antenna. Let’s say half of that or 25 watts gets radiated and 25 watts reflected. The reflected 25 watts travels back to the transmitter where with 3 dB loss only 12.5 watts makes it back. At that point the whole 12.5 watts gets reflected back to the antenna. Now we appear to have 100 plus 12.5 watts going forward or 112.5 watts. Of that 12.5 only 6.25 makes it to the antenna where 3.125 watts is radiated and 3.125 watts is reflected. Half of that or 1.5 watts makes it back and is reflected again and then that 1.5 watts adds to the froward power making the total forward power as read by the meter just about 114 watts. The example with 20 watts turning into 30 watts indicates that the output is 20 watts, if the loss in the cable is small, as in good short cable we can have almost the complete 20 watts get to the antenna. Where 10 is radiated and 10 is reflected back. Then of that 10 watts essentially all reaches the transmitter. Then all 10 watts is reflected. Now we have the initial 20 watts going out and 10 watts added to that giving 30 watts going forward. This is how it works. Each trip down the coax there will be some loss That loss is the same in dB for forward or reflected power. That loss determines how much power reaches the antenna. How well the coax is matched to the antenna determines how much of that power is reflected. With each reflection at the transmitter that power is added to the forward power. This process continues until all power is either radiated or becomes heat due to loss in the coax. If properly tuned, all reflected power returning to the transmitter gets reflected again toward the antenna. Does any of this hurt the transmitter? That depends on if the output circuit of the transmitter is or can be tuned properly or not. The so called antenna tuner at the transmitter usually solves that problem. I did that real quick so I hope I did my math correctly, but that’s the process.
Definitely 100% correct about the strange beliefs and misinformation out there. It's ok for people to say "I'm wrong" because we are all usually right about that ;) Of course, Transmit is only Half the story. For Receive, you want a 1:1 SWR so max signal arrives at the receiver. Personally i don't use an ATU because the antenna system hits near 1:1 on all bands, but it needs manually adjusting for each band change. ea7knw
That makes sense that the reflected signals end up at the aerial in the end, but wouldn't there some kind of phase cancellation issues happening? That power might be getting out, but not necessarily "helping" the signal?
Not helping the signal. The point is that reflected power isn’t lost and your full transmitter output will be delivered to the antenna, minus some insignificant coax cable loss. This applies to the HF bands only.
@@NoMoreRadioMyths So when you have a high amount of reflected power, why does it upset the finals so much? There must be something happening there that causes them to pull more current when this is going on?
@@xanataph For two reasons: If your transmitter sees a high impedance in the antenna feedline the voltage will be high, your mosfets may not like this. At the same time when your impedance is low, let's say 25 ohms, your output current will be twice as high.
The antenna tuner changes the phase of the reflected power. This is a quote from "Reflections" by antenna engineer Walt Maxwell. "Tuning for maximum line current simply adjusts the phase of the reflected wave to rereflect down the line in phase with the forward wave."
@@NoMoreRadioMyths Thanks for that Mark, it makes perfect sense since the aerial tuner is a combination of capacitance and inductance and those components change the phase of a signal passing through them.
With a line power of 75W the reflected power also goes up, to 37.5W, which is matched by the tuner and sent back to the antenna. This increase in power in the line results in increased loss of power in the line! Yes, much of the transmitter power is radiated, but a high SWR does ultimately cause a loss of power. Best to keep losses low as is reasonably possible. No need to obsess over getting a 1:1 SWR, but closer is indeed better.
All true David. SWR causes additional line loss. But the published charts show that at HF frequencies it is not much unless you have a long line of high loss cable. Another issue I would like to make a video on is that obsession with SWR prevents the use of a wire all band antenna. I’m using a random length OFC dipole with a 9:1 unun. It covers 160 meters to 10 meters with an swr of no more than 3:1 at the ATU.
My experience is that it blows up the output stage (BLW33 or 587BLY) - from my pirate radio manufacturing days in the 1980’s. A big SWR is a tiny output.
It's the impedance that has been transformed at the radio end of feedline because of the reflected power that causes the problems as the reflected power will join the forward power back towards the antenna
Standing wave ratio, kept low, merely keeps the radio running cooler. It does not help transmission distance much, on sideband. It keeps things a lot cooler for AM and FM. But for distance, it does not help much. A large 50 ohm resister will accomplish a perfect standing wave ratio of 1:1. The transmitted distance is not very far at all. If one has a vintage vacuum tube driven radio, there is not much problems running it with high standing wave at all. The tubes are designed to run hot for them to fuction correctly. The amateur radio operator I know has an old Kenwood TS-820. He tuned the antenna once to just around below 10:1 and did not care to check again. Being curious, I pulled my traveling standing wave ratio meter out of my ancient Jeep and stuck it on the radio. He had 15:1 with about 255 watts out of the antenna port. He said, it never hurt it but he would not recommend keeping it that high for a radio with solid state final amplifiers. The heat would damage it. I, just being an electronics technician, do what those that hire me want done. If they want a 1:1 ratio, I will stride for lowest possible for them. If they do not specify a standing wave ratio for their station, I will set it to around 3.5:1 or lower. A low standing wave ratio at the radio cable connection output does not mean a low standing wave ratio at the antenna feed point. The sinewave nature will cause impedence to go up and down along the cable. I just adjust the length of the cable to protect the radio from excess heat. Cable length does effect standing wave measurement at the radio output connection, no matter what anybody says. It will not change it at the antenna, only at the radio output connection point..
@James-ci3lx You are right. The radio is only rated 200 watts. It was only running a little higher than half power. But, the owner wanted nothing changed. Granted, he was my friend. I set up that station years ago for him and did what he said. It was all done free. However, I am often paid to set up radio stations to specifications that would achieve a high standing wave ratio. I do what I am told. It is their equipment and their specifications. I have been repairing, modifying, converting radios to different services, making antennas, power supplies, manual antenna tuners, linear amplifiers, and basic repeaters for many years. But, without a license, I can only transmit into dummy loads. It is up to the owners of the radios to test out my homemade equipment, modifications, amplifiers, and the such. I know what looks great on paper will not always have perfect standing wave ratios, nor put out the power formulas will say an amplifier will put out.
Mark, I built a small L-match for my QRP rigs. When the impedance is matched, the received signal is greatly improved. I have an indicator that indicates the voltage going out the radiator is maximum when the match is best. As a new ham, I'm not sure how all of this fits together. I have great success with this set-up and will email info to you hoping you can clarify what i am experiencing. Thanks for your videos.
Mark, I could not find your Email so I am sending a link to the L-match tuner and the matching indicator that I use. ua-cam.com/video/JGVtgWXCFxk/v-deo.html ua-cam.com/video/NjHyXi1SrZs/v-deo.html
Thanks for explaining about the reflected power the way you did. I always knew that it was more a matter of keeping the final amp happy, and back when I started as a Novice in 1974 with tube equipment my SWR was not a huge issue to me. Nowadays my QRP station uses well trimmed dipoles for 40m and 15m but when using a EFHW +/- for 80m I still use a tuner to keep the little transistor happy ;-) 73, WA4JAT
The only part I winced at was your statement about the ATU providing an impedance match to make the transmitter happy. As an impedance matching device, the ATU's role is to match the source (transmitter) output impedance with the load (feedline + antenna) input impedance to maximize power transfer from source to load -- regardless of any effect this may have on the transmitter's impedance mismatch protection behavior.
Here's an important point. For a given frequency, standing wave Impedance (V/I) varies at different points along a feedline. Thus, for a given frequency and load mismatch, a certain length of feedline may serve as the sole matching device (impedance transformer) between a source (transmitter) and a load (antenna). But when any given feedline length does not present a match, then an ATU between the source and the feedline can be used to essentially add or subtract a phantom/virtual length of feedline (via variable lumped inductive and capacitive elements) to match the source's output impedance. Of course, this does nothing to change the impedance mismatch at the feedline to antenna interface, but it allows the source to transfer full power to its composite load (feedline + antenna).
yes, yes, and yes; preach it. I really wish we could find a new term to popularize, for the feedline-antenna matching device, and stop calling it an antenna tuner.....
After 40+ years of being in communications technology both as a Ham and Military, I see that what you say is TRUE. RF is never lost, it just goes somewhere. I have never worried about SWR, if it was below a 3:1 or slightly higher. Since everything became fixated on a 50 ohm load, resistive, capacitive, or inductive, everyone has been screaming about SWR. I have found that the older transmitters that are vacuum tube based, it doesn't care what the antenna reads in SWR because the PI network loading does much the same as an antenna tuner does - match the transmitter to the load. Now, with semiconductor finals, the only worry is to keep the transmitter 'happy' by reducing SWR to around 50 ohms, or a multiple of 50 ohms and using some sort of a matching device to, again, keeping the transmitter happy, but the antenna will radiate no matter what the SWR is. The great goal is to have the antenna load be 180° out of phase, and some of the reflective power is always there. And as stated, no power is really lost, it either becomes hest, or is radiated. No power is ever lost.
Great topic! The principle of this is true with a catch.. look up the work by W2DU. High SWR and the multiple reflections will lead to excessive heat loss in the feed line if it is coaxial. Twin lead doesn’t exhibit nearly the same degree of loss and can tolerate very high SWR without any significant loss of radiated power. Someone else mentioned to look at a feed line loss calculator that depends on SWR to see its impact. Operating a twin lead at 8:1 VSWR or so will show a fractional loss. 73s
Pardon my ignorance and newness, but wouldn't that summation of power only apply if the reflection is in phase? I would imagine it ends up as a function of length, at a minimum.. I envision in my head two out of phase magentic waves would have walking nodes and nulls at varies snaps shots in time
This same question has come up several times but I have not answered it yet but here it is. The antenna tuner changes the phase of the reflected power. This is a quote from "Reflections" by antenna engineer Walt Maxwell. "Tuning for maximum line current simply adjusts the phase of the reflected wave to rereflect down the line in phase with the forward wave."
@@NoMoreRadioMyths Thank you for the reply! ..but when you do make that adjustment of phase, isn't that the same effect as lowering SWR?.. only electronically lengthening instead of a physical one? I ask in good faith as I try to come up with the mental models.. I appreciate the video, btw, made me think.. So, thank you!
Thank u. So will my SWR meter work for my dual band handheld ham radio that I use for my CB radio in my truck I was just hoping I could get away with using my workmen SWR meter for this project thank you for your video
By "this project" do you mean duplicating my demonstration of forward power or just for checking SWR? If you want to duplicate the demo you will need a meter that reads forward and reflected power in watts. If you just want to keep tabs on SWR I'm sure the Workman is fine. They are not necessarily very accurate but close enough.
@@NoMoreRadioMyths thank u so much. I just wanted to keep tabs on SWR for uhf/vhf 136/520 Mhz Antenna I'm having a had time finding one that works good 👍
Christ this guy grabs you from the start like Paul Harvey and keeps your attention with his charisma and delivery like Art Bell. And makes you think to boot. How did I never stumble upon this channel? This, in combination with all the younger UA-cam channels, is what is needed in amateur radio. This is why the ARRL, and the tools like Dave Casler that they use, will always stumble to explain things.
@@daveN2MXX Same. Great voice, great face, fantastic style. Casler is not always right, but he's right a lot of the time. But he's never been this smooth.
@davidgold He’s abs right except that Coax loss can be an issues at HF frequencies - but in most cases, good quality, coax, and short runs it’s not an issue. I have a masters in EE and Math and have researched this extensively. If you think the reflected power is not sent back to the antenna, where is it going? The tuner should be getting warm and it doesn’t. I’ve made great DX contacts by not worrying too much about the SWR
Hi,so are you saying that say a dxcommander all band vertical for example......if you cut your elements too short or too long so the swr is high,that rather than spending time trimming them to just hit the tune button n they will work exactly the same at say a 3.1:1 swr as they would being cut to resonance showing a 1:1 swr??? Many thanks new subscriber .73
A question I have is: How does this re reflection happen without an ATU.? Eg a 50ohm antenna , with an electrical half wavelength of say 600ohm Open wire tx line. (SWR 12:1) 50 ohms seen by the tx . Do the re reflections still happen from the final pa stage of the transmitter ? Another example may be 10m of 600ohm Tx line with an antenna impedance of 91-j998 at 3.6Mhz. (SWR = 70:1)giving very close to 50 ohms at the TX. Does the TX line "see" 50 ohms looking into the PA stage?
The impedance at any point along a transmission line is the instantaneous result of the voltage and current at that point on the line, not the "static" characteristic impedance of the line itself. Even though the transmitter output is nominally 50 ohms, the impedance on the line at the transmitter connection is very different than 50 ohms when there are standing waves on the line. When the reflected "wave" traveling back towards the transmitter reaches the transmitter, it sees a mismatch due to the difference in impedance and then the "wave" is reflected again back towards the load.
@@NoMoreRadioMyths Thanks. "When the reflected "wave" traveling back towards the transmitter reaches the transmitter, it sees a mismatch due to the difference in impedance and then the "wave" is reflected again back towards the load." What happens to any power not reflected in your explanation?(ie TX to feedline is minor mismatch))Does this power go into the PA stage ,causing damage ,even though the transmitter "sees "50 ohms?
Lets use an example for some clarity. A 50ohm Load(antenna) fed to the 50ohm transmitter with 291ohm Transmission line. (SWR = 5.82 : 1). An electrical half wavelength transmission line,and the line is lossless for simple math. The transmitter "sees" 50 ohms so can put 100watts into the feedline. Once the "power ' hits the 50 ohm antenna ,half is reflected due to the 5.82 : 1 SWR. The 50 watts reflected then makes its way back to the transmitter output. Of this 50 watts reflected power, does all of it get reflected again from transmitter towards the antenna? Half of it reflected towards antenna? What happens to the other 25 watts ?Is the reflection analysis only valid for the first split second of a transmission until a "steady state " analysis is more applicable?
Nice explanation of SWR, a very nice collection of theorical knowledge. I’ll go through my videos and show you the difference, in the same antenna, between swr 1.0 and 1.5. I just need some time to put it together since they are 6 hours long videos. The “myth” has context to it. Let me explain… if you are talking locally, example, someone from North America talking to another op in North America it’s rare that you feel the difference caused by swr. It starts to hinder your experience when you do true DX (12000 km +). Im Brazilian, from the south, and while I lived there this is the experience I had and every single other operator had (that’s why South American people care a lot about swr): I had a yagi with 1.7 swr and with 10w I had trouble talking to Easter Europe. Then I decided to flatten the swr and magically Eastern Europe was like talking to my neighbour, I started to reach china, South Pacific, etc… Then I started to build and sell yagis and cubical quad antennas. Once my clients installed them I’d ask for the swr. If they said more than 1.3 I’d ask them to keep a log of the qsos then I would go there and flatten the swr… guess? Magic… their reach for DX increased. Then I moved to Canada and I used a fishing pole to erect a efhw for 20 meters. If I changed the angle the antenna was erected I would change the swr (you can see this picture in my qrz page). With a xiegu x5105 I used to hear Qatar, Kuwait, Israel, turkey, etc.. swr 1.5 they never heard me. Swr 1.0 they would answer at the first attempt. Then I got a chameleon ss17 that I use as vertical, did the same test… same results.You don’t need to trust me, I’ll make a montage showing you. So when you simply say swr doesn’t matter you may be right and also wrong. One reason would be that in the process of lowering the swr you improve the other factors of the antenna. I invite you to do this: if you know those cb ops who have qsos with over 250 “dxcc” confirmed by qsl (I had 225 using a cobra 148gtl), ask them what’s the radio they use. If they answer of of those typical cb radio, look to know the output power (it’s probably very close to qrp). Then ask then what they think of swr. You explain swr very well and all the theory behind it, but forget that swr lives in a system. And sometimes the malfunction of the most insignificant part may cause the entire system to collapse. When a ham publishes a video like this he must be aware that there will be people that will just believe, without having any experience or experimentation. Nevertheless, great video! 73!
I believe in your example it's that you have tuned the antenna to be resonant to the proper frequency for best performance and not really the tiny difference in EIRP achieved by the better SWR. Just a thought.
This is the problem, real world examples just blow the "high swr doesn't matter" myth right out of the window. I think it is because these days we tend to have a single antenna working many bands that we don't really bother to do the work and just use an ATU. But I like you am also a big fan of learning from the CB guys, and one thing is for certain, with one antenna working on band they know full well the difference a high SWR can make. People can argue the science of why all they like, they can say it isn't because of reflected power but because of antenna resonance, it really does not matter why. Likewise because most radios do 100w, we don't really notice it as much, as we are just throwing 100w into a random wire and voila it works. It is of course the 100w doing the work and in reality the signal at the other end would be better if the antenna was resonant. Now I am not saying people should not use multiband single wire antennas. But I am saying that "high SWR doesn't matter" is the real myth.
@@wonderingworld119with a tuner into a dipole and open wire feedline high swr as 10.1 is more efficient than a resonant dipole with most coaxial cables as the feedline loss becomes a factor, there's alot more to it and the video abiet a little rough around the edges is a good starting point That's need to explain this subject, certainly alot better than most videos I've seen
@@paulm0hpd319 I agree ladder line straight to an ATU then a short run of coax to a radio is best. But, even with this setup, with 100ft of ladder in a perfect run, the losses at 10:1 on the ladder line would be 11% which is higher than 2% at 1:1 on the same run on 20 meters... I am guessing you didn't mean to imply that a high SWR was more efficient and you were trying to say ladder line is more efficient.
@@wonderingworld119 a resonant dipole would be around 1.5 swr with say rg58 that many use ,the dipole with the 600 ohm open wire into a tuner with 10.1 swr would indeed have more power at the antenna to radiate, all this said and done its highly unlikely the difference between the two would be noticeable on a received signal
Howdy. Great. My thinking too. The reflected power ping-pongs between the tuner and antenna. After every pong some of the previous wave reflected power is radiated alongside the new wave radiation. Technically the standing wave current nodes will produce ohmic losses at the nodes in the transmission cable. Technically there is a fire hazard at the nodes, but this is likely only running a 2 kW linear into a severely mismatched line. A 2 kW tuner is a monster. I assume not many have those. The fire hazard may be a good thing to keep in in mind though. Best regards.
the thing is... if your reflected power bouncing back and forth isnt the same harmonics as the outgoing signal then it would simply cancel in the system and not go out. if you have two sine signal colliding in a power line then they "short-circuit" in the line and cancels out. same thing is happening with radio. you cannot have a wave bounce back and ping pong back and forth forever without loss. it doesnt mean that this power is going out, as RF into air. it is mainly being cancelled in the system. this is why all power station in a country must be synchronized exactly. because the power going out would get short circuited in the line itself.
It's not just one burst of RF. It's continuous. So the wave is constantly replenishing itself as I see it. So you don't have just a single burst of RF wearing itself out. I'm going to refer you to antenna engineer Walt Maxwell, W2DU. "Reflected power does not represent lost power except for an increase in line attenuation over the matched-line attenuation. In a lossless line, no power is lost because of reflection. Onlywhen the flat-line attenuation and SWR are both high is there significant power lost from reflection. On all hf bands with low-loss cable, reflected power loss is generally insignificant, though at VHF it becomes significant, and at UHF it is of extreme importance."
@@NoMoreRadioMyths if you could help me a bit understand this. from my understanding if you have an *alright antenna with a SWR of 2:1* , using a theoretical loss-less cable and a 100W capable transceiver. lets say the "loss" is of 10% of power so 10W. where does those 10watt go? since the antenna isnt perfect, those 10W arent being emitted into the air, or converted into heat, because you wouldn't have an imperfect SWR reading then. i am starting to understand. maybe those 10watts arent necessarily being lost. because a dummy load (resistor) is wasting 100% of the energy in heat and give a perfect SWR. it would mean that the 10W are just not going anywhere and just causing a "blockage" of sort in the system? as you said bouncing back and forth until...? then if your radio is shooting 100W into a very very bad antenna, there does the reflected power go to dissapear? it would eventually go into heat because of the loss here and there? no?
With low loss coax in the HF bands only an insignificant amount of reflected power in a coax line is wasted as heat. It gets radiated by the antenna. Think about it. Why does an antenna radiate at all? Because of the RF energy has no where else to go. Remember the First Law of Thermodynamics: The amount of energy in a closed system remains constant. So energy has to go somewhere.
Agree with all of this as it is science based and true - but when pragmatic reality and life kicks in - instead of faffing about with antenna tuners, just tune the bloody antenna to start with. The correct length of coax is the distance from radio to antenna - as long as the latter is adequately tuned for the desired frequency. If wanting to use a random piece of wire - that's when the ATU is of use, as it matches both the antenna and the coax (because they collectively are the "antenna system" in this case.) I don't use an ATU for any reason because I have multiband antennas. Great video and thanks for this - it's about time!!
Hi Mark. Very interesting. I used to do comms gear (VHF/UHF comms) tests on military aircraft, and we used to check the SWR with an inline power meter (The famous Bird reflectometer) but there was no antenna tuner. Of course these were well-designed systems, and we were just checking for damaged cables or connectors, degrading system performance. I didn't delve too deeply into the theory at the time, but is this reflected power increase due to the antenna tuner circuitry? P.S. I'd like to do some reading about this as I'm getting into ham radio now. The links you posted in the description are truncated. Could you re-post them in a comment?
www.arrl.org/files/file/Technology/tis/info/pdf/q1106037.pdf That's a new one. Scroll down to "Does Higher SWR Lead to Lower Power Being Transmitted?" I think zs6wr goes into detail about why power is reflected back from the tuner. It's rocket science. zs6wr.co.za/documents/SWR.pdf www.k3emd.com/downloads/Reflect.pdf palomar-engineers.com/mlb-1-magnetic-longwire-balun/
Newbie question: If I have a resonant antenna, say at 28 MHz, perfectly tuned to 50 ohms, and I make my transmission on the 40-meter band, what will the SWR be like, considering there is perfect impedance matching but not resonance?
SWR will likely be through the roof. Trying to use an antenna cut for 10 meters on 40 will be a very poor antenna. There's no way to get around it - size matters.
@@NoMoreRadioMyths Yes, obviously, but I asked because if SWR is mainly caused by impedance mismatch, and in this case, the antenna-completely off in terms of size-meets the impedance requirement, where does this SWR come from? Is there a return due to the antenna's physical size being too short or too long? Thanks, you're so kind for answering!
If the antenna is too short, like trying to use a 10 meter dipole on 40 meters, I don't see how you could possibly have a good impedance match at the feed point. SWR is only determined by the match at the feed point. Too long is a different story. Antennas that are too long can work just as well as an antenna cut to a specific frequency. You would attach the coax somewhere there's a compromise impedance match. Look up information on off center fed dipoles for example. In your example, you could use an antenna cut for 40 meters on 10 meters but not the other way around. Make sure you have a decent antenna tuner. Don't be overly concerned about SWR unless you have a long feed line. For example, a 20 foot length of RG8X on 20 meters with a 10:1 SWR has a loss of less than 1 db. A shortened antenna is always inferior to a full size antenna.
@@NoMoreRadioMyths Aha! Now I perfectly understand that the antenna size also influences impedance matching, which is why I asked what happens if we use an 'antenna for 144 MHz, perfectly matched with the transmission line and equipment at 1.8 MHz.' I imagined an unlikely low SWR reading with extreme inefficiency. Thank you for your attention and patience.
Very true. 1:1 100% efficiency. Keeping the transmission line as short as possible between the trans-match and the radiator is good practice as the frequency goes up, balanced with the transmission line length/type/loss per ft. An antenna with a 10:1 match could be more radiationally efficient than a 1:1 antenna, just keep your finals happy. Thanks for making this video. I hope a ton of folks watch and learn. I am a short time op, but a long time AC theorist :) Edit: Word of the day: Recirculation.
The tuner does a little more than making the transmitter happy, in using capacitance and inductance to tune out the reactance of the system it creates a resonant system, the conjugate matching rectifies the mismatch to allow maximum power transfer to create reflection gain
A transmitter is almost never intended to be conjugately matched to its load. Instead, it is designed to deliver rated power at good efficiency into the intended load (typically 50 ohms). When conjugately matched, the output device or devices (transistors or tubes) may be overstressed, causing excessive voltage, current, or power dissipation, leading to premature failure. Fortunately, many modern transmitters will sense an overly stressful condition and reduce power or shut down to protect the output devices. We want our transmitters to deliver rated power with good efficiency for long life, not maximum power. Thus, we adjust the tuner so that the transmitter is terminated in 50 ohms (1:1 SWR). This is not the same as a conjugate match. In contrast, conjugate matching is often used in small-signal circuits where maximum power transfer is desired and where device dissipation and overstress are not issues.
@@paulm0hpd319 Mr. Walter Maxwell’s Reflections series is a great read for anybody interested in the subject. I concur with almost all of his points. I would describe the situation at the transmitter slightly differently, however. Mr. Maxwell’s point when discussing the transmitter is the desirability of tuning out any reactive component in the load impedance and I do fully agree with this. We need to keep in mind that the transmitter does not “know” what it is connected to. It only “sees” a load impedance. The transmission line concepts of forward and reflected power cease to have any useful meaning at the point of the transmitter. In the transmitter, we only deal with voltage and current, conveniently expressed as complex numbers as long as the waveforms are sinusoidal, and with their complex ratio: impedance (voltage/current), or admittance (current/voltage). We also have to keep in mind that the current and/or voltage at the active device or devices in the output stage is generally not sinusoidal. (Non-sinusoidal waveforms are present in all classes of amplifier that I can think of except for perfect class A, when free of distortion, and class A is rarely used in power amplifiers due to its relatively low efficiency.) A transmitter with a fixed-tuned output network is designed to work best into a fixed impedance (which is typically 50 ohms). Fortunately, variations from the design load impedance are usually of little consequence, up to a point. However, beyond some point the transmitter will experience stresses that will lead to premature failure or even immediate damage if the transmitter is not “throttled back”. Also, any variation in load impedance will affect the power output even when the transmitter is not “throttled back”. Just how the power will vary will depend on the specific design of the output stage and driver stage. The concept of forward and reflected power on the transmission line comes about as a result of applying the superposition theorem in one particular way to improve our understanding of the variations of voltage and current along the line. (If we merely thought in terms of voltage waves and current waves on the transmission line we might not have as many misconceptions.) We can derive those same voltage and current variations by applying the mathematics of transmission lines without ever dealing with forward and reflected waves per se. The superposition theorem enables us to formulate voltages and currents in an infinite number of mathematically equivalent ways. The engineers at our power companies often deal in real power (expressed in watts) and reactive power (expressed in vars, volts-amps reactive). This is a completely valid alternative way of looking at transmission lines. Yet real power and reactive power are not the same as forward power and reflected power. Using superposition, we could even do arbitrary formulations that don’t enhance understanding or ease calculations but would produce the correct result. My point is that the concept of forward and reflected waves is only one of many possible ways to view the situation on a transmission line. This concept can lead to improved understanding when applied within certain limits. When we extend it into forward and reflected power, we can be led into lots of confusion and misunderstanding, as we have seen in the ham community! Suppose we do the following tests that are conceptually very simple and fundamental to our understanding of transmission lines and power measurement. We begin with a two-wire transmission line that is being excited by some kind of electrical source such as a transmitter. (The transmission line could be parallel lines or a coaxial cable or another form.) We select one point along the line, and we designate one conductor, “A”, as the conductor to be measured and the other conductor, “B” as the reference line. We measure the instantaneous voltage of A with respect to B and simultaneously we measure the instantaneous conventional current on A. We multiply the instantaneous voltage times the instantaneous current to determine the instantaneous power. If the voltage is positive and the current is to the right, we conclude that the instantaneous power on the transmission line is flowing to the right. Likewise, if the voltage is negative and the current is to the left, we conclude that the instantaneous power is flowing to the right. In contrast, if the voltage is positive and the current is to the left, or if the voltage is negative and the current is to the right, we conclude that the instantaneous power is flowing to the left. We will reach the same conclusion about the direction of power flow regardless of which conductor is selected as A or B. Now we repeat this test many times at the same point on the transmission line. If the line is being excited by some ac or otherwise varying signal, we will in general get different readings for voltage and current each time we make the measurement. When we calculate the instantaneous power for each of the measurements, we will in general find different values for the power, and we may find that sometimes the power is flowing to the right and sometimes to the left. However, if we are dealing with a repetitive wave, and we happened to pick a measurement point where the wave impedance is real (where the voltage and current are either perfectly in-phase or perfectly opposite-phase), we will see that the power is always going in the same direction, even though its magnitude is varying from one measurement to the next. This remains true even though the transmission line may have high SWR! So, what happened to our reflected power? There is no reflected power when we view the line at this point in this fundamental way. We only get reflected power when we choose to apply superposition and treat the voltage and current as each consisting of two components heading in opposite directions and then we multiply only one selected voltage-current pair of components and call this reflected power. Now suppose we move to a new point on the line and once again repeatedly measure the instantaneous voltage and current. Calculations of instantaneous power at this new point may produce results that show power is going first in one direction and then in the other. These results are all valid at this new point, and if we calculated a long-term average power using these numbers and we compared to the long-term average power calculated at the prior point on the line, the result would be the same value (if the transmission line were lossless). While the power magnitude and direction would change at each measurement, each measurement would show the power going only one way at a time. We conclude by this method that the power never goes in opposite directions on the same line at the same time. We can only imagine that the power goes in opposite directions at the same time by applying superposition and saying the current is a summation of two particular currents and the voltage is the summation of two particular voltages and power in a given direction can be determined by multiplying only one voltage-current pair. It is important to remember that superposition is valid only for linear bilateral systems which, when they produce a result, f(x), for an input, x, and produce a result, f(y), for an input, y, they will also produce a result, f(x + y) for an input, x + y. Superposition is reasonably valid for passive transmission lines that are not being significantly heated by the transmitted energy. Superposition is not valid for active devices such as vacuum tubes or transistors, nor is it valid for other nonlinear devices such as incandescent lamps. It is also important to recognize that we can’t use superposition of voltages or currents to derive power via the formulas P = I squared x R or P = V squared / R because the squaring operation is nonlinear. Suppose we send power through the line one way that we will call the forward way and we measure the power loss in various short sections along the line. Then we turn around and send power through the line the opposite way that we will call the reflected way, and we make power loss measurements in the same short sections along the line. We then can’t sum the two power losses at any one section and expect that number to match the power loss we would see at that point if we arranged the line with generator and load such that the simultaneous forward and reflected powers at that point match the prior powers that were applied one at a time. In the simultaneous case (at least at frequencies below the upper microwave range), we know we will find hot spots of high loss in the sections with high total current and vice versa. I’m sorry for all this verbiage. This is just to illustrate that we must be careful to not overextend the use of superposition and the notion of forward and reflected power to reach conclusions that are not justified by the math. 🙂
@@paulm0hpd319 Mr. Walter Maxwell’s Reflections series is a great read for anybody interested in the subject. I concur with almost all of his points. I would describe the situation at the transmitter slightly differently, however. Mr. Maxwell’s point when discussing the transmitter is the desirability of tuning out any reactive component in the load impedance and I do fully agree with this. A conjugate match requires that at each junction the resistance looking to the right equals the resistance to the left and the reactance to the right is the same magnitude and opposite sign as the reactance to the left. Merely having equal and opposite reactance components is necessary but not sufficient. A conjugate match is used for maximum power transfer. A conjugate match requires that at least as much power is dissipated on the source side of the junction as on the load side. Thus, if we use a conjugate match, our final amplifier efficiency can never exceed 50%. (See, for instance, the textbook, "Electrical Engineering Circuits, Second Edition", by Hugh Hildreth Skilling, page 379.) A conjugate match works in both directions. Power flowing to the left is fully absorbed in the left side and power flowing to the right is fully absorbed in the right side. (We are assuming a bilateral network not containing devices like circulators or isolators.) We often use a conjugate match in small signal circuits where power dissipation is not an issue. If we try for maximum power transfer from the active device or active devices in our final amplifier, we will virtually always reach maximum voltage or maximum current or maximum power dissipation for the device long before we reach maximum power transfer. We don't want maximum power transfer in power circuits. Instead, we want to achieve rated power, or less, at good efficiency. (It looks like my earlier long reply post about superposition was deleted or not accepted. I must have been too long-winded!)
@@NoMoreRadioMyths yes, that's what I'm saying, but my mathematics were wrong. Round trip coax path length of 1, 1.5, 2.5, etc. wavelength yields zero output power if the CW reflection is very very strong.
With coax that long, hundreds of feet, yes, all of the power will eventually be turned into heat, especially with a high swr. The coax becomes a dummy load.
@@NoMoreRadioMyths the ohmic resistance is minimal, 1.50 Ω per 1k ft, but whatever. At 20 meters, a circulator would be 10 meters, with a 10% loss. I don't know what the loss is at 160/80 meters, probably zero. No?
Right to the point, I use 80ft Messi & Paoloni EXTRAFLEX BURY 10 /.400" (0.8db/100ft @50MHz) and I only try to keep SWR below 3:1 so I don't have to use external tuner.
SWR is an indicator that things are inefficient. Its not just cable mismatches. My good friend WA5FWC taught me years ago. spend time building antennas that are tuned to the frequency properly, and use quality components, and everything is efficient, long lasting and maximum sensitivity. I have no tuners attached to my rigs. I just use tuned antennas and proper coax, its easy!
I used perfectly tuned dipoles at low heights with limited success but my DX-Commander vertical works far better even with 1.5-2.0 SWR which is tuned with internal tuner. Ofcourse if everything is matched is better but the point of this video is that a little mismatch (which BTW is inherent to Verticals with 36 Ohms impedance) is not worth trying to eliminate.
Thank you for the video. As a physicist with some electrical engineering you are quite correct. This is why in some cases I just force tune a random vertical with short, high quality coax in the field even if the feed point swr might be 8:1. I’m not trying to have something perfect- just something that radiates. Example - 18ft RG-8X at 14mhz on a 14ft monopole at 8:1 swr only has 0.73 db loss or only 16% of my power (neglecting pure resistive and ground losses). Better coax would reduce those losses.
Why in a part of band, for example, 20 meters in the time of transmitting a transmitter (in this case, my Yaesu FT-991A) showed S=0.1 and SWR=1. Thank you and "73".
Several things I'll have to research. First the SWR meter he used to measure the power output to the antenna is not located at the antenna, it is located after the antenna tuner and before the coax leading to the antenna and it does in fact measure the power going out to the Coax a presumably another impedence matching balun or such not to the antenna. It would be nice to make some field strength measurements on the antenna itself to verify this presumption that what you see on the meter needles means what you think it does. It makes sense that the reflected power would effect that measured output power. So I question the assumption that that meter is measuring output of the antenna. Also my own experience of a manual tuner and the effect on reception (looking at the waterfall on my IC-7300) shows a dramatic change in the receiver picking up signals from the antenna. I would think then that when there is a mismatch then the same lack of resonance in the system would effect transmission power out. But interesting idea. I'll have to look at this more closely.
All you have to do is read some of the references I posted to see that forward power adds to source power in a mismatched transmission line. It's a fact, not some trick with an SWR meter.
The impedance mismatch between the feed and the antenna reflects the power back towards the transmitter. But there isn't any impedance mismatch at the transmitter. So that reflected power will not be reflected again back towards the antenna, and unless there's a circulator to steer the reflected power to a dummy load it will be dissipated as heat in the amplifier output stage and possibly destroy the transmitter.
The standing waves change the impedance at the transmitter, the feedline becomes an impedance transformer when there's an impedance mismatch at the antenna feedpoint, the tuner will also introduce a mismatch
So, looking at how a typical SWR meter works, why doesnt the detector on the antenna port end not pickup power from the transceiver port and vice versa?
An SWR bridge has directional couplers built into them one for forward power and one for reflected power, a directional coupler will only couple power flowing in one direction. Power entering the output port is coupled to the isolated port but not to the coupled port.
@@lifegettingintheway2710 ummm.... respectful... In every 'directional coupler'...there is a diode (signal detector)... and there is a resistor (signal termination) and a RF Coupling mechanism. Detector on one side of the coupler... termination other side... Just like a rhombic antenna... it is the termination that keeps the signal flowing in one direction. The orientation of the diode effects the polarity of the detected signal...
@@NoMoreRadioMyths pskreporter shows otherwise. Also breaking SSB POTA pileups is in my experience easier at the center, not edge, of tuned bandwidth. Still, for science I took a his/her pair of Ten Tec 238AB s and did AB testing to three remote SDRs. You are right one barely showed any difference, but the other two were far more weak the at higher SWR, one impacted most. I am now wondering if the reflected standing wave affects the radiation pattern and if that contributes to the debate.
You are likely experiencing minute by minute changes in propagation rather than changes in SWR as you change frequencies, unless the change is so extreme you experience a massive efficiency drop as with a small magnetic loop.
@@NoMoreRadioMyths of course not. i alternate and watch the trends and changes on both A and B as A/B compare. I try when band is hot and not. I make sure someone is not QRMing. It’s not easy.
it's not the lowest SWR that is the best match to the LOAD.......It's a complex situation that the reactances (capacitance and inductive) are reduced by the tuner the amplifier and the antenna.
Just learned something important from W6LG; lets say for the sake of argument someone is running higher SWR, using coax, because they "aren't worried about it"? Well, then you need to be more concerned about common mode currents. Not that you weren't before, but it seems running non resonant antenna's with coax can increase common mode currents which can cause other problems. Just another snippet of info to keep in the back of our minds as operators.
Yeah I saw his video also its a shame he spoilt it by saying high swr causes common mode current and that reflected power runs on the outside braid of coax
Look through the comments I did that for another guy. Here’s a good one that is not too technical. www.arrl.org/files/file/Technology/tis/info/pdf/q1106037.pdf.
So im new to this but, why do people use ladder line? I was under the impression it was less lossy than coax, and that coax used on non resonant antennas is extremely lossy. Maybe im confusing things but your video contradicts some of what i thought i knew.
it lets you operate on many other bands where the SWR might be way over 20:1. It has very little loss compared to coax in that situation. That's why a doublet fed with ladder or twin lead makes a better multiband antenna than the G5RV coax antenna.
Ladder line has virtually no loss. Good quality coax has some loss but not enough to worry about and is easier to use than ladder line. However in the VHF and UHF bands coax loss can be significant.
The only reason ladder line went out of favor is that it picks up noise: from the shack, power lines, and the wall warts in your home. Oh, and it is a neater install.
While the antenna tuner may "insulate" your power amplifier from the impedance mismatch it does not mean that the RF energy is radiated from the antenna. You will get voltage and current peaks on the feedline.. spaced in relationship to the wavelength (that is related to frequency and feedline velocity factor). If you had a thermal camera you would see hot-spots on the coax where the current is at a maximum as the RF energy is converted to heat. In other spots you would see very high voltages that might arc-over between feedline conductors. "Conservation of Energy" and the laws of thermodynamics.. energy is not lost but it can be converted to non-useful forms (heat). The bounce-back from the tuner and back in to the feedline/antenna does not suddenly arrive in-phase and end up as useful radiated energy at the antenna.
Don’t take my word for it. This is from the ARRL: The energy bounces back and forth inside the cable until it’s all radiated by the antenna for a lossless trans- mission line. An important point to realize is that with extremely low loss transmission line, no matter what the SWR, most of the power can get delivered to the antenna.
I concur. I absolutely cringed when FloridaMan uttered the phrase "SWR gain". (There is no such thing. Conservation of Energy is a real thing.) Cringed again when he (repeatedly) pointed out the power meter reading 30W. The only thing that meter demonstrates is the abuse that would happen to the transmitter's final stage if the transmatch was not in place. It would be sending out 20W, but would be dealing with the same amount of heat as if it was pumping 30W. So in the same setup, if the transmitter was cranked up to 100W, it would be trying to shed 150W of heat. That's when stuff goes "pop". There was a lot of good info in this vid, and the presentation style is absolutely fantastic. It just has a couple glaring flaws, that will lead gullible people astray. How very Florida, man.
Oh. One other point: depending on the length of the feedline, the reflected power could be 180-degrees out-of-phase, which could result in CANCELLING some portion of the energy at the antenna feedpoint from getting radiated, could it not?
@@kelvin0mqlNever said “SWR gain.” I said “reflection gain.” The SWR meter clearly shows an additional 10 watts of reflected power heading back to the antenna only to be bounced back again. In the end, almost all of the transmitter’s output power is delivered to the antenna. You don’t have to believe me or this from an ARRL paper on the subject: “The energy bounces back and forth inside the cable until it’s all radiated by the antenna for a lossless trans- mission line. An important point to realize is that with extremely low loss transmission line, no matter what the SWR, most of the power can get delivered to the antenna.“ You are also mistaken believing that reflected power destroys transmitter finals. But that’s for the next video.
@@NoMoreRadioMyths Yes, you’re right, I’d mis-remembered the phrase. I apologize for that. But it’s not really gain, at least not in the implied connotation. It’s merely an indication of the simplicity of the meter. (There are much better meters than anything MFJ makes.) If the transmission line is lossless enough, and exactly the right length to be in-phase by the time it arrives at the antenna feedpoint, then yes, you can get almost the entire 20W radiated. But if out-of-phase waves didn’t cancel, then phased arrays would not be a thing; they’d all be omni-directional. As for taking the ARRL’s word for it, no thanks. They’re a publishing house. They publish what will sell, whether it’s correct or not. Sure, they’d LIKE to be right all the time, but they’re just not. I take your point that people can waste time & money being overly concerned about a good match. But there’s also potential harm in being too unconcerned.
A good proof of this is in receive. Just as an experiment, find a weak dx station with your perfectly tuned antenna and then see how far you can de-tune the antenna before you start to loose signal and it will shock you (hopefully not literally) to see the results, especially with open wire feed line. I have many times before worked dx and didn't want to take time to tune the antenna as I have a manual matching unit. I just manually cut my power down to 40-50 watts and protect my radio that way. Also, when I used to operate mobile I used AM mode with no audio to tune my screwdriver antenna. AM mode automatically cuts the transmitter power to about a third (again NO audio) and zero beats the frequency so other stations are not even aware of your presence. NOTHING I hate more than people who for some reason use FULL POWER to match their antenna, and it always seems to be at an EAR PIERCING 3000 hz! Here in the shack, I turn my power down to just enough to move the meter to full scale, or even less, just enough to get a relative reading. When I can't match my antenna, I simply cut my power in half and I still make the contact! Back in the 70's Heathkit offered a two meter FM radio called the 2036 and claimed you could run it at "unlimited" swr. This was due to (in my opinion) the fact that the final transistor was only running at about half it's rated output and only put out about 12 watts. Great video man! 73's
The antenna tuner changes the phase of the reflected power. This is a quote from "Reflections" by antenna engineer Walt Maxwell. "Tuning for maximum line current simply adjusts the phase of the reflected wave to rereflect down the line in phase with the forward wave."
I've always being taught that any reflected power is simply converted into heat in the final stage of the antenna tuner or the transmitter. It seems to me that any reflected power then goes back into the antenna will be out of phase with the forward power causing a further loss of power transmitted
I'm not completely sure that the reflected power adds to forward power, or that the forward and reflective waves are even in phase, with no leads or lags, and if they are not, then there certainly is some cancellation going on. My understanding of an antenna tuner is that with it's combination of capacitors and inductors, what it does (and this is ONLY what it does) is cancel out inductive and capacitative reactance. (I read all three of "Kurt's" books when they were still in print.) Hopefully, what you have left then is pure resistance. Well we should probably call that instead hopefully "pretty low reactance" and not resistance, since we are discussing AC. As a subject, Cable loss is a VERY significant topic. Too many hams are connecting good radios to good antennas with crappy coax. While I can't prove it, I think that there is a lot of "milspec" Hucksterism going on. And yet? No Doubt, there's some ham attempting to use Heliax in a Liquid Helium environment to get rid of the resistance completely... 🤣 Finally, I observed with my own (Daiwa) cross needle meter, I observed that as I tuned and my SWR improved, as the "reverse" needle went down, the "forward" needle went UP. EVERY time. And, super finally, when I had a bad SWR before I knew what I was doing, the heat sink in my Ten Tec Scout got pretty hot with a bad SWR, so I MUST conclude that the reverse power was heating up the final, and so the reflected waves WERE NOT being broadcasted up the dipole, instead they were heating up my shack! And I couldn't match higher wattages at all. This was when I was still reading the radio mags with the linear amp and tower "centerfolds" and thinking I needed all of "that." But I got better, I went QRP and with an LDG auto tuner. Now, I just wait for the clicking to stop, and and I'm tuned and it's all rosy and peachy, with no credit account at The Candy Store! 😂
The antenna tuner changes the phase of the reflected power. This is a quote from "Reflections" by antenna engineer Walt Maxwell. "Tuning for maximum line current simply adjusts the phase of the reflected wave to rereflect down the line in phase with the forward wave."
Ok, I know I will regret this...I spent my formative years in the friendship of a ham who had a master's degree in electrical engineering. His reasoning always made sense, and I learned the hard way he was right. Reflected power does not simply disappear. It has to go somewhere. Some power is lost in ohmic losses in the transmission line (often coax). How much depends on the transmission line. The real problem is the so-called 'antenna tuner'. Its true name is 'match box', and it is meant as a convenient way to solve a complex problem. Reason? It does not tune anything! It simply makes your radio happy. It does not solve an SWR problem at the antenna. This is why I used to use 'tuners' at the antenna feed point (such as the SGC models and the Icom AH-4). They measure the SWR at the antenna feed point and adjust accordingly. Awesome devices when used correctly. If you use a coax choke at the 'matcher', you will also keep the radiated power at the antenna, and not on the outside of your coax where it can be carried back to your operating position. The boxes at the radio provide a 'conjugate' match. They do not correct a mismatch at the antenna. The 'loss' (the stuff NOT being radiated by your antenna) is still there. So where does the power go? The 'match box' simply shunts the power to the case or chassis of the box, and to the shields of all your coax, radio chassis, microphone, SWR meter, and anything else with electrical continuity to the chassis of the 'match box' become hot with RF. This is another reason why quarter-wave radials (counterpoise) are such a good thing on many antennas and grounding systems. They provide a low-impedance path for that 'lost' power to go and be radiated instead of filling your shack with RF. Of course, the best things to do are...1...properly match your antenna, and 2...learn how to use balanced line instead of coax, especially on HF. Balanced line has far less loss in a mismatched condition...almost lossless in both incident and reflected power conditions...and does not radiate power unless it is engineered to radiate. Not as easy to handle and use, but it sure works good on dipoles, loops, and other bigger antennas. Most of the long-timers I knew never used coax on HF. Good luck!
An antenna tuner tunes out the reactance of the antenna system to create resonance, the conjugate match corrects the antenna feedpoint mismatch to allow power transfer, reflected power does indeed have to go somewhere ,its either lost as heat within the transmission line if lossy or radiated at the antenna ,the tuner does not shunt the rf power to the braid of coax or chassis of equipment, the antenna is at fault for that ,may I guide you to Walt Maxwells books reflections he explains very in detail how it works
I've noticed that there's been some comments to my reply, I cant see them for some reason maybe been deleted ,if you have any questions to my comments I would like to respond to them ,so if Mark would allow please respond here with your questions
@@NoMoreRadioMyths I know it's a totally misunderstood subject, i try to help in group's to spread a greater understanding of the subject, I know your videos are a general overview on the subject I wonder if you could do separate videos going into detail with breaking each part down in separate videos, it may help others with understanding it a little better rather than getting negative comments and having to remove them ,I am surprised and disappointed that a couple of well known influencers that make educational videos don't fully understand this subject even though they make videos on the subject, what supprises me most is that most of these people have used the study books with this info in to obtain their licences ,keep the videos coming hopefully you will consider my suggestion ,cheers
Again, thank you @paulm0hpd319 for your help in trying to explain these things which can be complex. I am going to upload a new version of The Myth of SWR to add some clarifications and a better demo. When I put that first myth video together it was out of frustration for the amount of misinformation. I did not think anyone would look at it but that was sure wrong. I've been thinking it might be good to break these things down separately - SWR, reflected power, line loss and so on. This channel is all new for me. It's a work in progress. I will see what I can do. 73.
More likely due to heat generated by the relatively high resistance of the stainless steel wire used in WRC coil's construction and the relatively low melting temp of PVC coil form.
Thanks for this interesting video. I wonder why people are not more interested in radiated power which would be measured at some distance from the antenna. I realize that their are other factors involved here such as the angle or rather multiple angles of radiation which might be favorable or wasteful. An interesting article that I read 66 years ago in a CB magazine that bragged to have found the most amazing antenna anyone could build. It consisted of two equilateral triangles made from cardboard connect at their angular point facing away from each other. At the point of connection was a fifty ohm resister connecting to a coax. This article appeared in a CB magazine with no explanation other than it's SWR was the outstanding. I still wonder was this a joke or an attempt to ridicule the CB crowd.
The ZS5JF article is good reading and your demonstration shows the myth destroyed. QRP here using RG58 and I aim for below 2:1 SWR with 1.5 better. It doesn't take long to adjust my dipoles and inverted vee, are they too long or too short? Easy using my NANO VNA, unlike when I had only an SWR meter. C.B.'ers painstakingly trimming ½λ coax make me laugh. They can't seem to accept that by connecting an SWR meter their carefully trimmed ½λ coax joins to the jumper lead via the meter thereby making one coax so all their time consuming trimming is wasted. I've said this and they still say they want the thing which works best for them, i.e. trimming coax inch by inch. G4GHB.
Reminds me of years ago I was in a radio shop in Denver purchasing a two meter rig and a CB operator came in and told the store owner that his friend has an SWR of like 1.2 and was complaining that his was 1.5. 😅
Controversially there are times when an apparently matched antenna can benefit from being "detuned". For example a ground mounted quarterwave, if you had a perfect ground plane the impedance should be in the region of 35 ohms at resonance. However with a typical radial system with an impedance of about 15 ohms will create a nearly perfect 50 ohm match despite 30% of the power warming the ground. If you make the vertical slightly longer the feed impedance will go up accompanied by some inductive reactance. By raising the impedance of the vertical section you reduce the current in the ground system too raising efficiency. You can also get a better pattern. Obviously not all cases are equal, a typical coax needs derating for power handling when operated with a high VSWR. I kno this is the land of UA-cam but most of the obsession with low SWR is time badly spent, best make an antenna for efficiency and a good pattern and then figure out how to drive it. 73
As Engineers, we encourage use of the SWR meter because it is a simple method that can be used by someone with NO understanding of electronics, or transmission line theory, to get their Transmitter installed. These days, that is MOST Hams. Good luck trying to convince them. Most will never understand what is going on, which is why they spend a fortune trying to reduce their 2:1 SWR down to 1:1 . Despite this, they make hundreds of YT videos as "experts" because they really believe that their SWR meter is a high tech instrument. In a 50 year career designing communications equipment and antennae systems, I rarely even heard "swr" mentioned. These issues were usually expressed in more technically relevant terms. It is hard work being an Amateur, and a Professional. 🙂
Brilliant! I’m not an engineer but I can read and it disturbs me to see falsehoods spread. I think you would enjoy reading some of the papers of a fellow engineer - Walter Maxwell, who wrote a series of papers on this subject - “Another Look At Reflections.” It’s a good read. www.k3emd.com/downloads/Reflect.pdf
Yes, the SWR meter is an inexpensive addition to any station to tell the operator in a quick glance that the antenna and feedline are working today the same way they worked yesterday. In other words, that nothing has gone wrong. Unfortunately, since many operators have purchased SWR meters, low SWR has become an unnecessary obsession. The operator imagines that lower SWR has to be significantly better, since the meter scale often devotes a significant amount of space at the low end, expanding the scale there. If the SWR meters were redesigned so that 2:1 SWR was upscale just a few percent from 1:1 as compared to full scale, perhaps this would give a better indication of the relative importance of SWR, and there would be less obsession. 🙂
I didnt even watch the video but from reading the comments i know what its about. The transmitter output impedance is not actually 50 Ohm but something close to zero, and what's coming back from the antennna is reflected again, and this is what makes the power meter behind the transceiver show more power than the transceiver actually has. If cable dissipation can be neglected, then the antenna radiates about the difference of the "apparent" emitted power minus the reflected power. And yes, for a CB radio with 3m of RG58, it is about correct. With an antenna SWR of 3, the power meter shows then 5 W emitted instead of 4W, 1 W reflected, so it means the antenna still radiates its 4W. And really, a SWR of 3 is not as bad as many might think. Higher frequencies and longer cables makes it worse though.
Great comments, I'm inclined to believe that reflected power is not being radiated in a useful manner. I have no proof and have not researched the facts but I studied and bunch of physics and electronics and believe the power gets bounced back from the antenna and gets used up as heat in the ATU/Final and coax. Otherwise, the reflections would get radiated as noise, QRM, and be seen on a broadcast analyzer as a descending ghost signal that a TDR could measure to match the length of cable causing the delay. Again, maybe they do radiate and that is why some radios sound better than others? I'm sure a test could be devised using long lengths of cable and a top notch broadcast analyzer, TDR, bad antenna, and such--please let me know if this has been done.
Thanks Mark but, any good math guru can make anything they want to prove go their way--the answer may be if you just bought a $50,000 HF transceiver and hooked it up to a miss-matched antenna, would you crank it up and try to make contacts for 6 hours? I'm siding with JohnWallas74 on this one.@@NoMoreRadioMyths
What I fail to understand here is.. my understanding is, watts and watts. You deliver 20W into the antenna tuner. There is no additional energy being added anywhere, so how do we arrive at 30W forward power? Are you saying to interpret the reading, we have 20W forward + 10W reflected which eventually is more or less all radiated, so we read 30W forward, but in reality the total power coupled into the antenna is 20W after we take off the 10W reflected?
Yep. I know it's hard to wrap your head around. The bottom line is that no power is wasted, minus some usually minor coax cable loss. No new power is actually created. The law of thermodynamics says energy cannot be created or destroyed. Check the references in my description.
Thank you Mark, very clear and yes, not what I thought. It makes sense that we need to protect the transmitter (via a tuner). But based on this, I can put a bit more time on the air! N7DKE
The antenna tuner changes the phase of the reflected power. This is a quote from "Reflections" by antenna engineer Walt Maxwell. "Tuning for maximum line current simply adjusts the phase of the reflected wave to rereflect down the line in phase with the forward wave."
The standing wave is dissipated inside the output transistor. If the transistor (MOSFET nowadays) works in class C, with a circulation angle between 72° and 90°, it will have a very good efficiency and for 10 W output, it will draw 12 - 13 W from the power supply and therefore dissipate 3 W of heat. Now if the antenna is mismatched or broken, and half of the power is reflected back creating a standing wave, the transistor will have to dissipate 5 + 3 Watt. The heatsink may not be of the right size and after an hour or less of QSO, it will blow up. Newer radio use a temperature sensor which protects the entire circuit by reducing the output power...
Huh. I often wondered about swr "loss" since I could never see how the loss occurred. Good video & I will look into the references you mentioned. Thank you. K3EJP
very interesting video Mark. I ran simulations on my HF antennas here using the calculator that you mentioned. They are delta loops with an swr of 1.5:1 and indeed there is little to be gained by spending a lot of time readjusting wire lengths. It really shows that the obsession in getting a 1:1 swr gains just about nothing.
I agree with most of your video content right up to the point where you try to show and state that 20 watts out of the TX turns into 30 watts. Bad SWR does NOT increase the output power. The SWR meter may not accurately calibrated for that Freq. You can NOT increase power out by having bad SWR!! You will never get more than the 20 Watts to the antenna. What you are stating toward the end of your video is the holy grail of junk science! FREE ENERGY!! Just is not possible.
Never said that. SWR does not give you a power increase. Of course not. The point is that reflected power is not lost. Do some reading please. www.arrl.org/files/file/Technology/tis/info/pdf/q1106037.pdf
@@NoMoreRadioMythsI read the article. I wouldn't just assume because it was published by ARRL that is entirely correct. In the article he contradicts himself by stating that ladder line helps to radiate the reflected signals (radiating it away) but then in a coaxial example, he says it is "eventually radiated out the antenna" after going back and forth between the radio and antenna ---- but if that were the case, then we would never have overheating burned out transmitters from bad SWR. The reflected power is put back into the transmitter and is in the form of heat rather than transmitted. This part is where I believe he is incorrect.
@@NoMoreRadioMyths It would be very interesting to see a follow up video where the test is ran again with the external watt meter placed before the tuner such that when there is a perfect match to the TX, what does the watt meter show then? Would it still show 30 watts (indicating that the meter is poorly calibrated for that frequency) or would it now show just the 20 watts? And then if placed after the tuner would it then show the 30 watts?? I realize you are not so ignorant as to imply that there is "magic" power being generated, but the wording along with the display on the swr meter is confusing. Good video discussion overall. Cheers.
I think phase has everything to do with it. If reflected and and forward power where in phase it doesn't matter where in the transmission line you measure, it will always be the same. But it does matter where you put your power meter. Put your SWR meter somewhere else in the line and everything changes because you do not have standing waves. This is why the myth started that coaxlines should be a half wave length our a multitude of it. It should not. The length of the feedline does not matter if it is connected to an antenne with the same impedance as the feedline.
Can we please refer to antenna tuners at the transmitters as trans matches . As that is what they are . Unless you are considering your feedline as part of your antenna you are not tuning the antenna but matching the 50 ohm impedance of the transmitter to the feedline impedance
Transmatch is a better term but it also in effect tunes the antenna to resonance by cancelling the reactance. Check references I included in my description for a much more derailed explanation.
Reflected power still joins the forward power but the output will reduce to the difference of the reflected power, the tuner in line will allow the transmitter to produce its maximum power into the system
You are supposed to SUBTRACT Reflected from Forward; not ADD. If radio output set to 20W then no more than 20W can ever arrive where the coax joins the antenna. Even the greatest coax connected to the wildest tuner can not become a 10 Watt amplifier. There is no free 10 watts.
Look up "reflection gain" in a transmission line from a conjegate match. It's a scientific fact . That gain is then reflected back again at the load. No magic power increase being radiated and I never said there was. It's in the ARRL Antenna Book chapter 25.
@@NoMoreRadioMyths It can reflect back and forth alternatively between source and load but then its a wash and in reality its just knowledge of whats taking place but the power isn't changing. Maybe its just a case of semantics but I was led to believe you implied 30W output was being sent out of the antenna ultimately, when the source was 20W and that of course is scientifically not possible as that would require a steady non-alternating one-way addition of reflected power. - The subtraction thing I mentioned previously was in error.
Yes there is no magic power increase but the full transmitter output, not that plus the reflected power, is radiated. The reflected power basically stays in the line, bouncing back and forth, but eventually it gets radiated. It has to go somewhere. Many beleive that somewhere is the tuner or the transmitter but that's not true. It is totally reflected by the conjugate match at the tuner.
Do you know how many new operators you have sent into a tailspin? …. And antenna tuners only bullshit the radio and antenna tuner cannot make a antenna longer and it cannot make an antenna shorter. They cannot make an antenna. resonant at a specific frequency. It’s only bullshitting the radio no matter what. tune the antenna for resonance.on the frequency of operation.get the feed point matches close to 50 ohms as you possibly can, you will avoid a lot of heartache in the long run… tuna is not chicken.tuna is not pork.tuna is tuna……
One correction if I may. A tuner does in effect "tune" the antenna by canceling its reactance. It is resonant if the trans match is property adjusted. Please check the references in my description.
this is very interesting, but badly explained. not to insult. as they say "incredible claims need incredible proof" or something. i watched alot of your videos and still would have liked more explanation. it is hard to break the set thinking. i am beginning to understand the working of this. i think we are all using loaded and wrong terminology and it is causing most of the problems.
At resonance, my short, center-loaded vertical has an input impedance of about 12 ohms: 4:1 VSWR. In other words, antenna resonance does not necessarily equate to an impedance match.
Do you realise resonance doesn't guarantee efficiency, it doesn't guarantee its matched either but a tuner can deliver both resonance and matching for maximum power transfer
So what you are saing is that the higher the SWR the more power you will put out. If the Antenna had a 1:1 SWR then you only get 20 watts out. but since you have 3:1 SWR you get 30 watts out a bonus of 50% due to high SWR. Keep dreaming..... Keep dreaming.....
No you missed half of the process, which was clearly explained. The additional 10 watts is reflected back to the tuner by the antenna, giving you 20 watts radiated. There is no magic power increase. Click on the references in the description to learn more.
Thank God someone knows the ol SWR myth 👍 new sub from the UK
I have researched this topic extensively and agree with what the host is saying. However, I highly recommend looking at a coax loss calculator, like what is found on KV5R website. Depending on the HF frequency, depending on the SWR and length of cable, dielectric losses can become fairly significant. Case in point -- Using 50 Feet of LRM 400 @ 10:1 SWR at the frequency of 28 Mhz will yield a 27% power loss (not radiated) when using 100 watts. In this scenario the "output" power would be 72.584%. Now that was for 10 Meters, 6 meters in the same scenario would have higher losses, and the opposite would be true for lower frequencies meaning lower losses. Over all I like what Mark is describing in the video and for the most part I wouldn't worry about SWR higher than 2:1 unless using an ATU. Lastly, I have tested power losses, and it does exist.. I have purposefully heated up coax with high SWR to illustrate the point. As Mark said, the power isn't lost, it is converted from one form to another, and in the case of losses, from RF to Heat. Hope that helps -
I am surprised that with your learned post that you still state power is 'lost'. Read up on thermodynamics, will you?
@@N1IA-4 Correct, and the same goes for RF power being converted into heat in coax dielectric. If RF power doesn't get radiated by the antenna we generally say it is "lost". Of course @lomgshorts3 knows that, but he just wants to say "Ah Ha, I found something technically wrong with your post". "Now I'm going to post a fact and rub your nose in it". Truth is, I can point this insight at myself, and I've been guilty of the same. However, over time I have tried to improve the way I say things and how I come across. I'm not always perfect, but I try to not be "that guy".
correct. It's not LOST, but it isn't radiated either. You can't talk on heat@@lomgshorts3
He just means that it isn't being used for the intended purpose--it is lost to heat.@@lomgshorts3
In the case of coaxial cable at HF, the dielectric loss (rf power dissipated in the dielectric) is very small compared to the copper loss (copper loss is the loss due to resistance in the conductors). The loss in a short piece of coaxial cable with high SWR where the load impedance is high can be less than the loss when the SWR is 1:1. The loss is concentrated mostly where the current in the cable is highest. If you feel along a cable that has been heated by rf power with high SWR present, you will find hotter and cooler areas alternating, with spacing from one hot area to the next hot area being a half wavelength in the cable. The graph that is frequently published showing the increase in loss due to increased SWR is fairly accurate when the line is a half wavelength long or longer, but the graph can be significantly in error for short lengths. Of course, for short lengths of cable, the loss is rarely a concern anyway.
Since power cannot be created from nowhere, it may be confusing to some that you are suggesting that 20W magically becomes 30W at the aerial, so it is worth pointing out that this APPARENT increase in power arises because of the difference in impedance that occurs at the ATU, i.e. the measurement is referenced to 50 ohms but is not ACTUALLY at 50 ohms (at an SWR of 2, it's actually 25 or 100 ohms). Most SWR meters work by being calibrated to the stated output power (e.g. 20W) and then reports what FRACTION of this power is travelling forwards or in reverse.
There is no suggestion of magic. The original power is 20w. The reflected power is 10w. 20+10 is 30. Just regular math
Actually, what really happens is that half of the power are 10 W. Does not make it to the antenna and get radiated right away. But eventually it's recycled back towards the antenna and radiated. As you say in this ping pong configuration, so it's not 20 + 10. It's only ten that gets to the antenna and the other ten eventually gets back to the antenna which does not make it thirty watts
@@royfowler5637 thanks for being here. i was wondering how the reflected power on the outside of the coax made it back to the center conductor.
@@Paddy_Roche Reflected power not on outside of coax. You're confusing it with common mode currents that occur on outside of coax due to an unbalanced feed.
@@DaDitDaGood point. That’s something else some hams are confused about.
You were doing good to the part you said that on the low bands the SWR does not matter. For short runs up to say what would be used in a car there is not that much additional loss. However with feedline loss when matched is getting to be around 3 db or more the additional loss starts to increase by a good bit as the SWR gets higher. You sure do not want a 10:1 SWR with 100 feet of rg-58. One other thing is that if running high power the coax can develop hot spots and melt or the voltage can arc over.
Good points Ralf. Yes 100 feet of high loss cable like RG58 with a high mismatch would be a bad idea. I didn’t try to cover every scenario so thanks for that input.
The meters power rating is only correct at 1:1 match. Anyone who doesn’t understand that an antenna that isn’t properly matched isn’t as efficient as one that is, doesn’t understand basic power transfer engineering concepts. I have an Electronics Engineering degree, this was taught in school. Any reflected power between say the transmitter and input of the ATU if the ATU cannot provide a 1:1 match is reflected back to the transmitter finals as heat. This is why protection circuits cut back output power if there isn’t a 1:1 match since the reflected power will add heat to the final components. So the power is lost. There is also the output of the ATU to the transmission line and antenna. If there is reflected power from the antenna and the transmission line combined, then transmission line and ATU absorbs the reflected power as heat. It’s lost power that doesn’t get radiated from the antenna. If it’s not a 1:1 match at the antenna, a signal will still be radiated from the antenna, but some power gets reflected is not radiated. So your antenna is not 100% efficient . Theoretically if you loose 50% of your power to coax and reflected power then you have lost 3DB signal radiated.
I appreciate the hard work you put into your education and taking the time to respond but you are not correct. ALL reflected power is reflected from the transmitter or tuner back to the antenna. The transmitter does not see reflected power. Also a low SWR is not an indication of antenna efficiency-it indicates a good match. I have a dummy load with a 1:1 SWR but it’s a lousy antenna. As for what heats up the finals with a high SWR I will save for a future discussion. Check out the writings of antenna engineer Walt Maxwell. www.k3emd.com/downloads/Reflect.pdf
@@NoMoreRadioMyths Thanks for link. That is an excellent article.
ATU's do absorb power, as a matter of fact what destroys expensive roller tuned ATU's is burn marks on the inductors--this probably isn't from SWR but a good look at burned up ATU's could be interesting. In EE school the first thing they teach you is that all components absorb power/have losses/ and that there is no perfect component.@@NoMoreRadioMyths
I am amazed you are slating people who don't understand the rules of power transfer then proceed to admit you don't yourself
Based on that theory we should all have antennas with 100:1 swr.
Take a look at the article “ the lure of ladder line “ from QST that goes into coax loss absorption.
Sure ladder line has virtually no loss but it’s inconvenient for most people. Who has an antenna with a 100:1 swr? What are they using - a kitchen fork? Did you do any reading? www.arrl.org/files/file/Technology/tis/info/pdf/q1106037.pdf
@@NoMoreRadioMyths the higher the swr the higher the loss,apparently you didn't read the article.
100:1 is a bit much but it seems that some handheld radios that have no transmission line at all work fairly well up to a SWR of 20:1. Because there is no such broadband HT antenna that can span 136 to 174 MHz or 400 to 520 and maintain a low SWR over this range.
@@miker8379not necessarily if for example in the theoretical lossless feedline no power is lost no matter what the swr is
Again a good informative video. I have explained this so many times, even to other engineers. I have done detailed calculations of how power bounces back and forth from antenna to transmitter and back again!
Essentially I can use a simple example of 100 watts and a coax with 3 dB loss to make the calculations easy. 100 watts leaves the transmitter initially. With 3 dB loss only 50 watts gets to the antenna. Let’s say half of that or 25 watts gets radiated and 25 watts reflected. The reflected 25 watts travels back to the transmitter where with 3 dB loss only 12.5 watts makes it back. At that point the whole 12.5 watts gets reflected back to the antenna. Now we appear to have 100 plus 12.5 watts going forward or 112.5 watts. Of that 12.5 only 6.25 makes it to the antenna where 3.125 watts is radiated and 3.125 watts is reflected. Half of that or 1.5 watts makes it back and is reflected again and then that 1.5 watts adds to the froward power making the total forward power as read by the meter just about 114 watts.
The example with 20 watts turning into 30 watts indicates that the output is 20 watts, if the loss in the cable is small, as in good short cable we can have almost the complete 20 watts get to the antenna. Where 10 is radiated and 10 is reflected back. Then of that 10 watts essentially all reaches the transmitter. Then all 10 watts is reflected. Now we have the initial 20 watts going out and 10 watts added to that giving 30 watts going forward. This is how it works. Each trip down the coax there will be some loss That loss is the same in dB for forward or reflected power. That loss determines how much power reaches the antenna. How well the coax is matched to the antenna determines how much of that power is reflected. With each reflection at the transmitter that power is added to the forward power. This process continues until all power is either radiated or becomes heat due to loss in the coax.
If properly tuned, all reflected power returning to the transmitter gets reflected again toward the antenna.
Does any of this hurt the transmitter? That depends on if the output circuit of the transmitter is or can be tuned properly or not.
The so called antenna tuner at the transmitter usually solves that problem.
I did that real quick so I hope I did my math correctly, but that’s the process.
Another great post by @dandypoint. Guys who believe myths take heed!
Definitely 100% correct about the strange beliefs and misinformation out there.
It's ok for people to say "I'm wrong" because we are all usually right about that ;)
Of course, Transmit is only Half the story.
For Receive, you want a 1:1 SWR so max signal arrives at the receiver.
Personally i don't use an ATU because the antenna system hits near 1:1 on all bands, but it needs manually adjusting for each band change.
ea7knw
That makes sense that the reflected signals end up at the aerial in the end, but wouldn't there some kind of phase cancellation issues happening? That power might be getting out, but not necessarily "helping" the signal?
Not helping the signal. The point is that reflected power isn’t lost and your full transmitter output will be delivered to the antenna, minus some insignificant coax cable loss. This applies to the HF bands only.
@@NoMoreRadioMyths So when you have a high amount of reflected power, why does it upset the finals so much? There must be something happening there that causes them to pull more current when this is going on?
@@xanataph For two reasons: If your transmitter sees a high impedance in the antenna feedline the voltage will be high, your mosfets may not like this. At the same time when your impedance is low, let's say 25 ohms, your output current will be twice as high.
The antenna tuner changes the phase of the reflected power. This is a quote from "Reflections" by antenna engineer Walt Maxwell. "Tuning for maximum line current simply adjusts the phase of the reflected wave to rereflect down the line in phase with the forward wave."
@@NoMoreRadioMyths Thanks for that Mark, it makes perfect sense since the aerial tuner is a combination of capacitance and inductance and those components change the phase of a signal passing through them.
With a line power of 75W the reflected power also goes up, to 37.5W, which is matched by the tuner and sent back to the antenna. This increase in power in the line results in increased loss of power in the line! Yes, much of the transmitter power is radiated, but a high SWR does ultimately cause a loss of power. Best to keep losses low as is reasonably possible. No need to obsess over getting a 1:1 SWR, but closer is indeed better.
All true David. SWR causes additional line loss. But the published charts show that at HF frequencies it is not much unless you have a long line of high loss cable. Another issue I would like to make a video on is that obsession with SWR prevents the use of a wire all band antenna. I’m using a random length OFC dipole with a 9:1 unun. It covers 160 meters to 10 meters with an swr of no more than 3:1 at the ATU.
My experience is that it blows up the output stage (BLW33 or 587BLY) - from my pirate radio manufacturing days in the 1980’s. A big SWR is a tiny output.
It's the impedance that has been transformed at the radio end of feedline because of the reflected power that causes the problems as the reflected power will join the forward power back towards the antenna
Standing wave ratio, kept low, merely keeps the radio running cooler. It does not help transmission distance much, on sideband. It keeps things a lot cooler for AM and FM. But for distance, it does not help much. A large 50 ohm resister will accomplish a perfect standing wave ratio of 1:1. The transmitted distance is not very far at all. If one has a vintage vacuum tube driven radio, there is not much problems running it with high standing wave at all. The tubes are designed to run hot for them to fuction correctly. The amateur radio operator I know has an old Kenwood TS-820. He tuned the antenna once to just around below 10:1 and did not care to check again. Being curious, I pulled my traveling standing wave ratio meter out of my ancient Jeep and stuck it on the radio. He had 15:1 with about 255 watts out of the antenna port. He said, it never hurt it but he would not recommend keeping it that high for a radio with solid state final amplifiers. The heat would damage it.
I, just being an electronics technician, do what those that hire me want done. If they want a 1:1 ratio, I will stride for lowest possible for them. If they do not specify a standing wave ratio for their station, I will set it to around 3.5:1 or lower. A low standing wave ratio at the radio cable connection output does not mean a low standing wave ratio at the antenna feed point. The sinewave nature will cause impedence to go up and down along the cable. I just adjust the length of the cable to protect the radio from excess heat. Cable length does effect standing wave measurement at the radio output connection, no matter what anybody says. It will not change it at the antenna, only at the radio output connection point..
@James-ci3lx You are right. The radio is only rated 200 watts. It was only running a little higher than half power. But, the owner wanted nothing changed. Granted, he was my friend. I set up that station years ago for him and did what he said. It was all done free. However, I am often paid to set up radio stations to specifications that would achieve a high standing wave ratio. I do what I am told. It is their equipment and their specifications. I have been repairing, modifying, converting radios to different services, making antennas, power supplies, manual antenna tuners, linear amplifiers, and basic repeaters for many years. But, without a license, I can only transmit into dummy loads. It is up to the owners of the radios to test out my homemade equipment, modifications, amplifiers, and the such. I know what looks great on paper will not always have perfect standing wave ratios, nor put out the power formulas will say an amplifier will put out.
Mark, I built a small L-match for my QRP rigs. When the impedance is matched, the received signal is greatly improved. I have an indicator that indicates the voltage going out the radiator is maximum when the match is best. As a new ham, I'm not sure how all of this fits together. I have great success with this set-up and will email info to you hoping you can clarify what i am experiencing. Thanks for your videos.
Mark, I could not find your Email so I am sending a link to the L-match tuner and the matching indicator that I use. ua-cam.com/video/JGVtgWXCFxk/v-deo.html
ua-cam.com/video/NjHyXi1SrZs/v-deo.html
When the tuner is properly adjusted the entire system is resonate. That's why received signals come in better.
Thanks for explaining about the reflected power the way you did. I always knew that it was more a matter of keeping the final amp happy, and back when I started as a Novice in 1974 with tube equipment my SWR was not a huge issue to me. Nowadays my QRP station uses well trimmed dipoles for 40m and 15m but when using a EFHW +/- for 80m I still use a tuner to keep the little transistor happy ;-) 73, WA4JAT
The only part I winced at was your statement about the ATU providing an impedance match to make the transmitter happy. As an impedance matching device, the ATU's role is to match the source (transmitter) output impedance with the load (feedline + antenna) input impedance to maximize power transfer from source to load -- regardless of any effect this may have on the transmitter's impedance mismatch protection behavior.
Here's an important point. For a given frequency, standing wave Impedance (V/I) varies at different points along a feedline. Thus, for a given frequency and load mismatch, a certain length of feedline may serve as the sole matching device (impedance transformer) between a source (transmitter) and a load (antenna). But when any given feedline length does not present a match, then an ATU between the source and the feedline can be used to essentially add or subtract a phantom/virtual length of feedline (via variable lumped inductive and capacitive elements) to match the source's output impedance. Of course, this does nothing to change the impedance mismatch at the feedline to antenna interface, but it allows the source to transfer full power to its composite load (feedline + antenna).
yes, yes, and yes; preach it. I really wish we could find a new term to popularize, for the feedline-antenna matching device, and stop calling it an antenna tuner.....
@@dus777 Transmatch is the term I prefer; but the catchy acronym ATU has become commercially predominate and appears here to stay.
After 40+ years of being in communications technology both as a Ham and Military, I see that what you say is TRUE. RF is never lost, it just goes somewhere. I have never worried about SWR, if it was below a 3:1 or slightly higher. Since everything became fixated on a 50 ohm load, resistive, capacitive, or inductive, everyone has been screaming about SWR. I have found that the older transmitters that are vacuum tube based, it doesn't care what the antenna reads in SWR because the PI network loading does much the same as an antenna tuner does - match the transmitter to the load. Now, with semiconductor finals, the only worry is to keep the transmitter 'happy' by reducing SWR to around 50 ohms, or a multiple of 50 ohms and using some sort of a matching device to, again, keeping the transmitter happy, but the antenna will radiate no matter what the SWR is. The great goal is to have the antenna load be 180° out of phase, and some of the reflective power is always there. And as stated, no power is really lost, it either becomes hest, or is radiated. No power is ever lost.
Great topic! The principle of this is true with a catch.. look up the work by W2DU. High SWR and the multiple reflections will lead to excessive heat loss in the feed line if it is coaxial. Twin lead doesn’t exhibit nearly the same degree of loss and can tolerate very high SWR without any significant loss of radiated power.
Someone else mentioned to look at a feed line loss calculator that depends on SWR to see its impact. Operating a twin lead at 8:1 VSWR or so will show a fractional loss.
73s
This is correct, however if a very low loss feedline is used on lower frequencies that loss maynot be that significant
Pardon my ignorance and newness, but wouldn't that summation of power only apply if the reflection is in phase? I would imagine it ends up as a function of length, at a minimum.. I envision in my head two out of phase magentic waves would have walking nodes and nulls at varies snaps shots in time
This same question has come up several times but I have not answered it yet but here it is. The antenna tuner changes the phase of the reflected power. This is a quote from "Reflections" by antenna engineer Walt Maxwell. "Tuning for maximum line current simply adjusts the phase of the reflected wave to rereflect down the line in phase with the forward wave."
@@NoMoreRadioMyths Thank you for the reply! ..but when you do make that adjustment of phase, isn't that the same effect as lowering SWR?.. only electronically lengthening instead of a physical one? I ask in good faith as I try to come up with the mental models.. I appreciate the video, btw, made me think.. So, thank you!
Fascinating video. Many thanks for posting this. I think you proved your point. Well done and keep them coming.
Thank u. So will my SWR meter work for my dual band handheld ham radio that I use for my CB radio in my truck I was just hoping I could get away with using my workmen SWR meter for this project thank you for your video
By "this project" do you mean duplicating my demonstration of forward power or just for checking SWR? If you want to duplicate the demo you will need a meter that reads forward and reflected power in watts. If you just want to keep tabs on SWR I'm sure the Workman is fine. They are not necessarily very accurate but close enough.
@@NoMoreRadioMyths thank u so much. I just wanted to keep tabs on SWR for uhf/vhf
136/520 Mhz Antenna I'm having a had time finding one that works good 👍
Christ this guy grabs you from the start like Paul Harvey and keeps your attention with his charisma and delivery like Art Bell. And makes you think to boot. How did I never stumble upon this channel?
This, in combination with all the younger UA-cam channels, is what is needed in amateur radio.
This is why the ARRL, and the tools like Dave Casler that they use, will always stumble to explain things.
@@daveN2MXX Same. Great voice, great face, fantastic style.
Casler is not always right, but he's right a lot of the time. But he's never been this smooth.
@davidgold He’s abs right except that Coax loss can be an issues at HF frequencies - but in most cases, good quality, coax, and short runs it’s not an issue. I have a masters in EE and Math and have researched this extensively. If you think the reflected power is not sent back to the antenna, where is it going? The tuner should be getting warm and it doesn’t. I’ve made great DX contacts by not worrying too much about the SWR
Hi,so are you saying that say a dxcommander all band vertical for example......if you cut your elements too short or too long so the swr is high,that rather than spending time trimming them to just hit the tune button n they will work exactly the same at say a 3.1:1 swr as they would being cut to resonance showing a 1:1 swr??? Many thanks new subscriber .73
If you use an antenna tuner it will work just as well. Use good low loss coax.
True - but why not just tune the antenna properly? It is a multiband antenna for a reason. Still agree with you BTW!
A question I have is: How does this re reflection happen without an ATU.? Eg a 50ohm antenna , with an electrical half wavelength of say 600ohm Open wire tx line. (SWR 12:1) 50 ohms seen by the tx . Do the re reflections still happen from the final pa stage of the transmitter ? Another example may be 10m of 600ohm Tx line with an antenna impedance of 91-j998 at 3.6Mhz. (SWR = 70:1)giving very close to 50 ohms at the TX. Does the TX line "see" 50 ohms looking into the PA stage?
The impedance at any point along a transmission line is the instantaneous result of the voltage and current at that point on the line, not the "static" characteristic impedance of the line itself.
Even though the transmitter output is nominally 50 ohms, the impedance on the line at the transmitter connection is very different than 50 ohms when there are standing waves on the line. When the reflected "wave" traveling back towards the transmitter reaches the transmitter, it sees a mismatch due to the difference in impedance and then the "wave" is reflected again back towards the load.
@@NoMoreRadioMyths Thanks.
"When the reflected "wave" traveling back towards the transmitter reaches the transmitter, it sees a mismatch due to the difference in impedance and then the "wave" is reflected again back towards the load."
What happens to any power not reflected in your explanation?(ie TX to feedline is minor mismatch))Does this power go into the PA stage ,causing damage ,even though the transmitter "sees "50 ohms?
Lets use an example for some clarity. A 50ohm Load(antenna) fed to the 50ohm transmitter with 291ohm Transmission line. (SWR = 5.82 : 1). An electrical half wavelength transmission line,and the line is lossless for simple math.
The transmitter "sees" 50 ohms so can put 100watts into the feedline.
Once the "power ' hits the 50 ohm antenna ,half is reflected due to the 5.82 : 1 SWR.
The 50 watts reflected then makes its way back to the transmitter output.
Of this 50 watts reflected power, does all of it get reflected again from transmitter towards the antenna? Half of it reflected towards antenna? What happens to the other 25 watts ?Is the reflection analysis only valid for the first split second of a transmission until a "steady state " analysis is more applicable?
@@2321brendanif the radio sees 50ohms and the antenna is 50ohms there is no reflected power
@@2321brendanif you have 50ohms antenna and 50ohms tx with half wave ribbon feeder,all power is transferred there is no reflections
Nice explanation of SWR, a very nice collection of theorical knowledge.
I’ll go through my videos and show you the difference, in the same antenna, between swr 1.0 and 1.5. I just need some time to put it together since they are 6 hours long videos.
The “myth” has context to it. Let me explain… if you are talking locally, example, someone from North America talking to another op in North America it’s rare that you feel the difference caused by swr. It starts to hinder your experience when you do true DX (12000 km +).
Im Brazilian, from the south, and while I lived there this is the experience I had and every single other operator had (that’s why South American people care a lot about swr): I had a yagi with 1.7 swr and with 10w I had trouble talking to Easter Europe. Then I decided to flatten the swr and magically Eastern Europe was like talking to my neighbour, I started to reach china, South Pacific, etc…
Then I started to build and sell yagis and cubical quad antennas. Once my clients installed them I’d ask for the swr. If they said more than 1.3 I’d ask them to keep a log of the qsos then I would go there and flatten the swr… guess? Magic… their reach for DX increased.
Then I moved to Canada and I used a fishing pole to erect a efhw for 20 meters. If I changed the angle the antenna was erected I would change the swr (you can see this picture in my qrz page). With a xiegu x5105 I used to hear Qatar, Kuwait, Israel, turkey, etc.. swr 1.5 they never heard me. Swr 1.0 they would answer at the first attempt.
Then I got a chameleon ss17 that I use as vertical, did the same test… same results.You don’t need to trust me, I’ll make a montage showing you.
So when you simply say swr doesn’t matter you may be right and also wrong. One reason would be that in the process of lowering the swr you improve the other factors of the antenna.
I invite you to do this: if you know those cb ops who have qsos with over 250 “dxcc” confirmed by qsl (I had 225 using a cobra 148gtl), ask them what’s the radio they use. If they answer of of those typical cb radio, look to know the output power (it’s probably very close to qrp). Then ask then what they think of swr.
You explain swr very well and all the theory behind it, but forget that swr lives in a system. And sometimes the malfunction of the most insignificant part may cause the entire system to collapse. When a ham publishes a video like this he must be aware that there will be people that will just believe, without having any experience or experimentation.
Nevertheless, great video! 73!
I believe in your example it's that you have tuned the antenna to be resonant to the proper frequency for best performance and not really the tiny difference in EIRP achieved by the better SWR. Just a thought.
This is the problem, real world examples just blow the "high swr doesn't matter" myth right out of the window. I think it is because these days we tend to have a single antenna working many bands that we don't really bother to do the work and just use an ATU. But I like you am also a big fan of learning from the CB guys, and one thing is for certain, with one antenna working on band they know full well the difference a high SWR can make. People can argue the science of why all they like, they can say it isn't because of reflected power but because of antenna resonance, it really does not matter why. Likewise because most radios do 100w, we don't really notice it as much, as we are just throwing 100w into a random wire and voila it works. It is of course the 100w doing the work and in reality the signal at the other end would be better if the antenna was resonant. Now I am not saying people should not use multiband single wire antennas. But I am saying that "high SWR doesn't matter" is the real myth.
@@wonderingworld119with a tuner into a dipole and open wire feedline high swr as 10.1 is more efficient than a resonant dipole with most coaxial cables as the feedline loss becomes a factor, there's alot more to it and the video abiet a little rough around the edges is a good starting point That's need to explain this subject, certainly alot better than most videos I've seen
@@paulm0hpd319 I agree ladder line straight to an ATU then a short run of coax to a radio is best. But, even with this setup, with 100ft of ladder in a perfect run, the losses at 10:1 on the ladder line would be 11% which is higher than 2% at 1:1 on the same run on 20 meters... I am guessing you didn't mean to imply that a high SWR was more efficient and you were trying to say ladder line is more efficient.
@@wonderingworld119 a resonant dipole would be around 1.5 swr with say rg58 that many use ,the dipole with the 600 ohm open wire into a tuner with 10.1 swr would indeed have more power at the antenna to radiate, all this said and done its highly unlikely the difference between the two would be noticeable on a received signal
Howdy. Great.
My thinking too. The reflected power ping-pongs between the tuner and antenna. After every pong some of the previous wave reflected power is radiated alongside the new wave radiation.
Technically the standing wave current nodes will produce ohmic losses at the nodes in the transmission cable. Technically there is a fire hazard at the nodes, but this is likely only running a 2 kW linear into a severely mismatched line. A 2 kW tuner is a monster. I assume not many have those.
The fire hazard may be a good thing to keep in in mind though.
Best regards.
@@stargazer7644 Howdy.
Yes. I believe You are correct.
Regards.
the thing is... if your reflected power bouncing back and forth isnt the same harmonics as the outgoing signal then it would simply cancel in the system and not go out. if you have two sine signal colliding in a power line then they "short-circuit" in the line and cancels out. same thing is happening with radio. you cannot have a wave bounce back and ping pong back and forth forever without loss. it doesnt mean that this power is going out, as RF into air. it is mainly being cancelled in the system.
this is why all power station in a country must be synchronized exactly. because the power going out would get short circuited in the line itself.
It's not just one burst of RF. It's continuous. So the wave is constantly replenishing itself as I see it. So you don't have just a single burst of RF wearing itself out. I'm going to refer you to antenna engineer Walt Maxwell, W2DU.
"Reflected power does not represent lost power except for an increase in line attenuation
over the matched-line attenuation. In a lossless line, no power is lost because of reflection. Onlywhen the flat-line attenuation and SWR are both high is there significant power lost from reflection. On all hf bands with low-loss cable, reflected power loss is generally insignificant, though at VHF it becomes significant, and at UHF it is of
extreme importance."
@@NoMoreRadioMyths if you could help me a bit understand this.
from my understanding if you have an *alright antenna with a SWR of 2:1* , using a theoretical loss-less cable and a 100W capable transceiver. lets say the "loss" is of 10% of power so 10W. where does those 10watt go? since the antenna isnt perfect, those 10W arent being emitted into the air, or converted into heat, because you wouldn't have an imperfect SWR reading then.
i am starting to understand. maybe those 10watts arent necessarily being lost. because a dummy load (resistor) is wasting 100% of the energy in heat and give a perfect SWR. it would mean that the 10W are just not going anywhere and just causing a "blockage" of sort in the system? as you said bouncing back and forth until...?
then if your radio is shooting 100W into a very very bad antenna, there does the reflected power go to dissapear? it would eventually go into heat because of the loss here and there? no?
With low loss coax in the HF bands only an insignificant amount of reflected power in a coax line is wasted as heat. It gets radiated by the antenna. Think about it. Why does an antenna radiate at all? Because of the RF energy has no where else to go. Remember the First Law of Thermodynamics: The amount of energy in a closed system remains constant. So energy has to go somewhere.
Agree with all of this as it is science based and true - but when pragmatic reality and life kicks in - instead of faffing about with antenna tuners, just tune the bloody antenna to start with. The correct length of coax is the distance from radio to antenna - as long as the latter is adequately tuned for the desired frequency. If wanting to use a random piece of wire - that's when the ATU is of use, as it matches both the antenna and the coax (because they collectively are the "antenna system" in this case.) I don't use an ATU for any reason because I have multiband antennas. Great video and thanks for this - it's about time!!
Hi Mark. Very interesting. I used to do comms gear (VHF/UHF comms) tests on military aircraft, and we used to check the SWR with an inline power meter (The famous Bird reflectometer) but there was no antenna tuner. Of course these were well-designed systems, and we were just checking for damaged cables or connectors, degrading system performance. I didn't delve too deeply into the theory at the time, but is this reflected power increase due to the antenna tuner circuitry?
P.S. I'd like to do some reading about this as I'm getting into ham radio now. The links you posted in the description are truncated. Could you re-post them in a comment?
www.arrl.org/files/file/Technology/tis/info/pdf/q1106037.pdf
That's a new one. Scroll down to "Does Higher SWR Lead to Lower Power Being Transmitted?" I think zs6wr goes into detail about why power is reflected back from the tuner. It's rocket science.
zs6wr.co.za/documents/SWR.pdf
www.k3emd.com/downloads/Reflect.pdf
palomar-engineers.com/mlb-1-magnetic-longwire-balun/
Newbie question: If I have a resonant antenna, say at 28 MHz, perfectly tuned to 50 ohms, and I make my transmission on the 40-meter band, what will the SWR be like, considering there is perfect impedance matching but not resonance?
SWR will likely be through the roof. Trying to use an antenna cut for 10 meters on 40 will be a very poor antenna. There's no way to get around it - size matters.
@@NoMoreRadioMyths Yes, obviously, but I asked because if SWR is mainly caused by impedance mismatch, and in this case, the antenna-completely off in terms of size-meets the impedance requirement, where does this SWR come from? Is there a return due to the antenna's physical size being too short or too long? Thanks, you're so kind for answering!
If the antenna is too short, like trying to use a 10 meter dipole on 40 meters, I don't see how you could possibly have a good impedance match at the feed point. SWR is only determined by the match at the feed point. Too long is a different story. Antennas that are too long can work just as well as an antenna cut to a specific frequency. You would attach the coax somewhere there's a compromise impedance match. Look up information on off center fed dipoles for example. In your example, you could use an antenna cut for 40 meters on 10 meters but not the other way around. Make sure you have a decent antenna tuner. Don't be overly concerned about SWR unless you have a long feed line. For example, a 20 foot length of RG8X on 20 meters with a 10:1 SWR has a loss of less than 1 db. A shortened antenna is always inferior to a full size antenna.
@@NoMoreRadioMyths Aha! Now I perfectly understand that the antenna size also influences impedance matching, which is why I asked what happens if we use an 'antenna for 144 MHz, perfectly matched with the transmission line and equipment at 1.8 MHz.' I imagined an unlikely low SWR reading with extreme inefficiency. Thank you for your attention and patience.
Very true. 1:1 100% efficiency. Keeping the transmission line as short as possible between the trans-match and the radiator is good practice as the frequency goes up, balanced with the transmission line length/type/loss per ft.
An antenna with a 10:1 match could be more radiationally efficient than a 1:1 antenna, just keep your finals happy.
Thanks for making this video. I hope a ton of folks watch and learn. I am a short time op, but a long time AC theorist :)
Edit: Word of the day: Recirculation.
The tuner does a little more than making the transmitter happy, in using capacitance and inductance to tune out the reactance of the system it creates a resonant system, the conjugate matching rectifies the mismatch to allow maximum power transfer to create reflection gain
@@N1IA-4 that's why I've said it does more than make the transmitter happy and described what it does
A transmitter is almost never intended to be conjugately matched to its load. Instead, it is designed to deliver rated power at good efficiency into the intended load (typically 50 ohms). When conjugately matched, the output device or devices (transistors or tubes) may be overstressed, causing excessive voltage, current, or power dissipation, leading to premature failure. Fortunately, many modern transmitters will sense an overly stressful condition and reduce power or shut down to protect the output devices. We want our transmitters to deliver rated power with good efficiency for long life, not maximum power. Thus, we adjust the tuner so that the transmitter is terminated in 50 ohms (1:1 SWR). This is not the same as a conjugate match. In contrast, conjugate matching is often used in small-signal circuits where maximum power transfer is desired and where device dissipation and overstress are not issues.
@@analog_guymay I guide you to the book reflections
@@paulm0hpd319 Mr. Walter Maxwell’s Reflections series is a great read for anybody interested in the subject. I concur with almost all of his points. I would describe the situation at the transmitter slightly differently, however. Mr. Maxwell’s point when discussing the transmitter is the desirability of tuning out any reactive component in the load impedance and I do fully agree with this.
We need to keep in mind that the transmitter does not “know” what it is connected to. It only “sees” a load impedance. The transmission line concepts of forward and reflected power cease to have any useful meaning at the point of the transmitter. In the transmitter, we only deal with voltage and current, conveniently expressed as complex numbers as long as the waveforms are sinusoidal, and with their complex ratio: impedance (voltage/current), or admittance (current/voltage). We also have to keep in mind that the current and/or voltage at the active device or devices in the output stage is generally not sinusoidal. (Non-sinusoidal waveforms are present in all classes of amplifier that I can think of except for perfect class A, when free of distortion, and class A is rarely used in power amplifiers due to its relatively low efficiency.) A transmitter with a fixed-tuned output network is designed to work best into a fixed impedance (which is typically 50 ohms). Fortunately, variations from the design load impedance are usually of little consequence, up to a point. However, beyond some point the transmitter will experience stresses that will lead to premature failure or even immediate damage if the transmitter is not “throttled back”. Also, any variation in load impedance will affect the power output even when the transmitter is not “throttled back”. Just how the power will vary will depend on the specific design of the output stage and driver stage.
The concept of forward and reflected power on the transmission line comes about as a result of applying the superposition theorem in one particular way to improve our understanding of the variations of voltage and current along the line. (If we merely thought in terms of voltage waves and current waves on the transmission line we might not have as many misconceptions.) We can derive those same voltage and current variations by applying the mathematics of transmission lines without ever dealing with forward and reflected waves per se. The superposition theorem enables us to formulate voltages and currents in an infinite number of mathematically equivalent ways. The engineers at our power companies often deal in real power (expressed in watts) and reactive power (expressed in vars, volts-amps reactive). This is a completely valid alternative way of looking at transmission lines. Yet real power and reactive power are not the same as forward power and reflected power.
Using superposition, we could even do arbitrary formulations that don’t enhance understanding or ease calculations but would produce the correct result. My point is that the concept of forward and reflected waves is only one of many possible ways to view the situation on a transmission line. This concept can lead to improved understanding when applied within certain limits. When we extend it into forward and reflected power, we can be led into lots of confusion and misunderstanding, as we have seen in the ham community!
Suppose we do the following tests that are conceptually very simple and fundamental to our understanding of transmission lines and power measurement. We begin with a two-wire transmission line that is being excited by some kind of electrical source such as a transmitter. (The transmission line could be parallel lines or a coaxial cable or another form.) We select one point along the line, and we designate one conductor, “A”, as the conductor to be measured and the other conductor, “B” as the reference line. We measure the instantaneous voltage of A with respect to B and simultaneously we measure the instantaneous conventional current on A. We multiply the instantaneous voltage times the instantaneous current to determine the instantaneous power. If the voltage is positive and the current is to the right, we conclude that the instantaneous power on the transmission line is flowing to the right. Likewise, if the voltage is negative and the current is to the left, we conclude that the instantaneous power is flowing to the right. In contrast, if the voltage is positive and the current is to the left, or if the voltage is negative and the current is to the right, we conclude that the instantaneous power is flowing to the left. We will reach the same conclusion about the direction of power flow regardless of which conductor is selected as A or B. Now we repeat this test many times at the same point on the transmission line. If the line is being excited by some ac or otherwise varying signal, we will in general get different readings for voltage and current each time we make the measurement. When we calculate the instantaneous power for each of the measurements, we will in general find different values for the power, and we may find that sometimes the power is flowing to the right and sometimes to the left. However, if we are dealing with a repetitive wave, and we happened to pick a measurement point where the wave impedance is real (where the voltage and current are either perfectly in-phase or perfectly opposite-phase), we will see that the power is always going in the same direction, even though its magnitude is varying from one measurement to the next. This remains true even though the transmission line may have high SWR! So, what happened to our reflected power? There is no reflected power when we view the line at this point in this fundamental way. We only get reflected power when we choose to apply superposition and treat the voltage and current as each consisting of two components heading in opposite directions and then we multiply only one selected voltage-current pair of components and call this reflected power.
Now suppose we move to a new point on the line and once again repeatedly measure the instantaneous voltage and current. Calculations of instantaneous power at this new point may produce results that show power is going first in one direction and then in the other. These results are all valid at this new point, and if we calculated a long-term average power using these numbers and we compared to the long-term average power calculated at the prior point on the line, the result would be the same value (if the transmission line were lossless). While the power magnitude and direction would change at each measurement, each measurement would show the power going only one way at a time. We conclude by this method that the power never goes in opposite directions on the same line at the same time. We can only imagine that the power goes in opposite directions at the same time by applying superposition and saying the current is a summation of two particular currents and the voltage is the summation of two particular voltages and power in a given direction can be determined by multiplying only one voltage-current pair.
It is important to remember that superposition is valid only for linear bilateral systems which, when they produce a result, f(x), for an input, x, and produce a result, f(y), for an input, y, they will also produce a result, f(x + y) for an input, x + y. Superposition is reasonably valid for passive transmission lines that are not being significantly heated by the transmitted energy. Superposition is not valid for active devices such as vacuum tubes or transistors, nor is it valid for other nonlinear devices such as incandescent lamps. It is also important to recognize that we can’t use superposition of voltages or currents to derive power via the formulas P = I squared x R or P = V squared / R because the squaring operation is nonlinear. Suppose we send power through the line one way that we will call the forward way and we measure the power loss in various short sections along the line. Then we turn around and send power through the line the opposite way that we will call the reflected way, and we make power loss measurements in the same short sections along the line. We then can’t sum the two power losses at any one section and expect that number to match the power loss we would see at that point if we arranged the line with generator and load such that the simultaneous forward and reflected powers at that point match the prior powers that were applied one at a time. In the simultaneous case (at least at frequencies below the upper microwave range), we know we will find hot spots of high loss in the sections with high total current and vice versa.
I’m sorry for all this verbiage. This is just to illustrate that we must be careful to not overextend the use of superposition and the notion of forward and reflected power to reach conclusions that are not justified by the math. 🙂
@@paulm0hpd319 Mr. Walter Maxwell’s Reflections series is a great read for anybody interested in the subject. I concur with almost all of his points. I would describe the situation at the transmitter slightly differently, however. Mr. Maxwell’s point when discussing the transmitter is the desirability of tuning out any reactive component in the load impedance and I do fully agree with this.
A conjugate match requires that at each junction the resistance looking to the right equals the resistance to the left and the reactance to the right is the same magnitude and opposite sign as the reactance to the left. Merely having equal and opposite reactance components is necessary but not sufficient. A conjugate match is used for maximum power transfer. A conjugate match requires that at least as much power is dissipated on the source side of the junction as on the load side. Thus, if we use a conjugate match, our final amplifier efficiency can never exceed 50%. (See, for instance, the textbook, "Electrical Engineering Circuits, Second Edition", by Hugh Hildreth Skilling, page 379.) A conjugate match works in both directions. Power flowing to the left is fully absorbed in the left side and power flowing to the right is fully absorbed in the right side. (We are assuming a bilateral network not containing devices like circulators or isolators.) We often use a conjugate match in small signal circuits where power dissipation is not an issue. If we try for maximum power transfer from the active device or active devices in our final amplifier, we will virtually always reach maximum voltage or maximum current or maximum power dissipation for the device long before we reach maximum power transfer. We don't want maximum power transfer in power circuits. Instead, we want to achieve rated power, or less, at good efficiency.
(It looks like my earlier long reply post about superposition was deleted or not accepted. I must have been too long-winded!)
The reflected power is out of phase with prior outputs, so if the wavelength is near the round-trip coax length, you output nothing?
Each time a reflected wave is reflected its phase is reversed.
@@NoMoreRadioMyths yes, that's what I'm saying, but my mathematics were wrong. Round trip coax path length of 1, 1.5, 2.5, etc. wavelength yields zero output power if the CW reflection is very very strong.
@@NoMoreRadioMyths that is exactly what a "circulator" does. QED
With coax that long, hundreds of feet, yes, all of the power will eventually be turned into heat, especially with a high swr. The coax becomes a dummy load.
@@NoMoreRadioMyths the ohmic resistance is minimal, 1.50 Ω per 1k ft, but whatever.
At 20 meters, a circulator would be 10 meters, with a 10% loss. I don't know what the loss is at 160/80 meters, probably zero.
No?
Nice job, Mark. I found a good book on the topic, Reflections III by M. Walter Maxwell, W2DU. A little long, but very detailed. Thanks again.
A must read 👍
Or, maybe a reflected power created a lot of harmonics and, that is why a transmitting power on at a certain frequency will be much less...
is reflected power in phase with forward power? ( reflected gain )
A properly adjusted antenna tuner reverses the phase of reflected power to be in phase with the forward power. That is called "reflection gain."
Right to the point, I use 80ft Messi & Paoloni EXTRAFLEX BURY 10 /.400" (0.8db/100ft @50MHz) and I only try to keep SWR below 3:1 so I don't have to use external tuner.
SWR is an indicator that things are inefficient. Its not just cable mismatches. My good friend WA5FWC taught me years ago. spend time building antennas that are tuned to the frequency properly, and use quality components, and everything is efficient, long lasting and maximum sensitivity. I have no tuners attached to my rigs. I just use tuned antennas and proper coax, its easy!
I used perfectly tuned dipoles at low heights with limited success but my DX-Commander vertical works far better even with 1.5-2.0 SWR which is tuned with internal tuner. Ofcourse if everything is matched is better but the point of this video is that a little mismatch (which BTW is inherent to Verticals with 36 Ohms impedance) is not worth trying to eliminate.
@@fwaynedavisAn antenna with a low swr is not an indication it is a good radiator. A dummy load has 1.1 swr
I agree with that statement! @@NoMoreRadioMyths
Thank you for the video. As a physicist with some electrical engineering you are quite correct. This is why in some cases I just force tune a random vertical with short, high quality coax in the field even if the feed point swr might be 8:1. I’m not trying to have something perfect- just something that radiates. Example - 18ft RG-8X at 14mhz on a 14ft monopole at 8:1 swr only has 0.73 db loss or only 16% of my power (neglecting pure resistive and ground losses). Better coax would reduce those losses.
Why in a part of band, for example, 20 meters in the time of transmitting a transmitter (in this case, my Yaesu FT-991A) showed S=0.1 and SWR=1. Thank you and "73".
What do you mean by S=0.1?
Several things I'll have to research. First the SWR meter he used to measure the power output to the antenna is not located at the antenna, it is located after the antenna tuner and before the coax leading to the antenna and it does in fact measure the power going out to the Coax a presumably another impedence matching balun or such not to the antenna. It would be nice to make some field strength measurements on the antenna itself to verify this presumption that what you see on the meter needles means what you think it does. It makes sense that the reflected power would effect that measured output power. So I question the assumption that that meter is measuring output of the antenna. Also my own experience of a manual tuner and the effect on reception (looking at the waterfall on my IC-7300) shows a dramatic change in the receiver picking up signals from the antenna. I would think then that when there is a mismatch then the same lack of resonance in the system would effect transmission power out. But interesting idea. I'll have to look at this more closely.
All you have to do is read some of the references I posted to see that forward power adds to source power in a mismatched transmission line. It's a fact, not some trick with an SWR meter.
The impedance mismatch between the feed and the antenna reflects the power back towards the transmitter. But there isn't any impedance mismatch at the transmitter. So that reflected power will not be reflected again back towards the antenna, and unless there's a circulator to steer the reflected power to a dummy load it will be dissipated as heat in the amplifier output stage and possibly destroy the transmitter.
I provided reliable references. Waiting for yours.
The standing waves change the impedance at the transmitter, the feedline becomes an impedance transformer when there's an impedance mismatch at the antenna feedpoint, the tuner will also introduce a mismatch
So, looking at how a typical SWR meter works, why doesnt the detector on the antenna port end not pickup power from the transceiver port and vice versa?
An SWR bridge has directional couplers built into them one for forward power and one for reflected power, a directional coupler will only couple power flowing in one direction. Power entering the output port is coupled to the isolated port but not to the coupled port.
@@lifegettingintheway2710 ummm.... respectful... In every 'directional coupler'...there is a diode (signal detector)... and there is a resistor (signal termination) and a RF Coupling mechanism. Detector on one side of the coupler... termination other side... Just like a rhombic antenna... it is the termination that keeps the signal flowing in one direction. The orientation of the diode effects the polarity of the detected signal...
I would say it's a totally overblown problem especially around the CB crowd.
I respectfully disagree. Can hit stations further with better SNR when the antenna reflection at the feed point is kept at a minimum
That would be true if the SWR is obscenely high. No one can hear the difference between 2:1 and 1:1.
@@NoMoreRadioMyths pskreporter shows otherwise. Also breaking SSB POTA pileups is in my experience easier at the center, not edge, of tuned bandwidth. Still, for science I took a his/her pair of Ten Tec 238AB s and did AB testing to three remote SDRs. You are right one barely showed any difference, but the other two were far more weak the at higher SWR, one impacted most. I am now wondering if the reflected standing wave affects the radiation pattern and if that contributes to the debate.
You are likely experiencing minute by minute changes in propagation rather than changes in SWR as you change frequencies, unless the change is so extreme you experience a massive efficiency drop as with a small magnetic loop.
@@NoMoreRadioMyths of course not. i alternate and watch the trends and changes on both A and B as A/B compare. I try when band is hot and not. I make sure someone is not QRMing. It’s not easy.
@@Aimsport-video The guy thinks an ATU solves losses because it tunes antennas. I think that should tell you what is wrong with his thought process.
it's not the lowest SWR that is the best match to the LOAD.......It's a complex situation that the reactances (capacitance and inductive) are reduced by the tuner the amplifier and the antenna.
one of the popular myths out there, especially on 80 meters, is you have to have a resonant antenna, cut for your favorite net.
Yes another ham radio myth.
Just learned something important from W6LG; lets say for the sake of argument someone is running higher SWR, using coax, because they "aren't worried about it"? Well, then you need to be more concerned about common mode currents. Not that you weren't before, but it seems running non resonant antenna's with coax can increase common mode currents which can cause other problems. Just another snippet of info to keep in the back of our minds as operators.
Use of a balun is always a good idea when using a coax feed line to prevent common mode current.
Yeah I saw his video also its a shame he spoilt it by saying high swr causes common mode current and that reflected power runs on the outside braid of coax
I enjoyed the explanation, subscribed.
Only one of the links in the description is complete. Can they be reposted in a comment?
Look through the comments I did that for another guy. Here’s a good one that is not too technical. www.arrl.org/files/file/Technology/tis/info/pdf/q1106037.pdf.
@@NoMoreRadioMyths I quickly browsed through it, so I’ll look a little deeper. Thanks
So im new to this but, why do people use ladder line? I was under the impression it was less lossy than coax, and that coax used on non resonant antennas is extremely lossy. Maybe im confusing things but your video contradicts some of what i thought i knew.
it lets you operate on many other bands where the SWR might be way over 20:1. It has very little loss compared to coax in that situation. That's why a doublet fed with ladder or twin lead makes a better multiband antenna than the G5RV coax antenna.
Ladder line has virtually no loss. Good quality coax has some loss but not enough to worry about and is easier to use than ladder line. However in the VHF and UHF bands coax loss can be significant.
The only reason ladder line went out of favor is that it picks up noise: from the shack, power lines, and the wall warts in your home. Oh, and it is a neater install.
While the antenna tuner may "insulate" your power amplifier from the impedance mismatch it does not mean that the RF energy is radiated from the antenna.
You will get voltage and current peaks on the feedline.. spaced in relationship to the wavelength (that is related to frequency and feedline velocity factor).
If you had a thermal camera you would see hot-spots on the coax where the current is at a maximum as the RF energy is converted to heat. In other spots you would see very high voltages that might arc-over between feedline conductors.
"Conservation of Energy" and the laws of thermodynamics.. energy is not lost but it can be converted to non-useful forms (heat). The bounce-back from the tuner and back in to the feedline/antenna does not suddenly arrive in-phase and end up as useful radiated energy at the antenna.
Don’t take my word for it. This is from the ARRL: The energy bounces back and forth inside the cable until it’s all radiated by the antenna for a lossless trans- mission line. An important point to realize is that with extremely low loss transmission line, no matter what the SWR, most of the power can get delivered to the antenna.
I concur. I absolutely cringed when FloridaMan uttered the phrase "SWR gain". (There is no such thing. Conservation of Energy is a real thing.) Cringed again when he (repeatedly) pointed out the power meter reading 30W.
The only thing that meter demonstrates is the abuse that would happen to the transmitter's final stage if the transmatch was not in place. It would be sending out 20W, but would be dealing with the same amount of heat as if it was pumping 30W. So in the same setup, if the transmitter was cranked up to 100W, it would be trying to shed 150W of heat. That's when stuff goes "pop".
There was a lot of good info in this vid, and the presentation style is absolutely fantastic. It just has a couple glaring flaws, that will lead gullible people astray. How very Florida, man.
Oh. One other point: depending on the length of the feedline, the reflected power could be 180-degrees out-of-phase, which could result in CANCELLING some portion of the energy at the antenna feedpoint from getting radiated, could it not?
@@kelvin0mqlNever said “SWR gain.” I said “reflection gain.” The SWR meter clearly shows an additional 10 watts of reflected power heading back to the antenna only to be bounced back again. In the end, almost all of the transmitter’s output power is delivered to the antenna. You don’t have to believe me or this from an ARRL paper on the subject: “The energy bounces back and forth inside the cable until it’s all radiated by the antenna for a lossless trans- mission line. An important point to realize is that with extremely low loss transmission line, no matter what the SWR, most of the power can get delivered to the antenna.“ You are also mistaken believing that reflected power destroys transmitter finals. But that’s for the next video.
@@NoMoreRadioMyths Yes, you’re right, I’d mis-remembered the phrase. I apologize for that.
But it’s not really gain, at least not in the implied connotation. It’s merely an indication of the simplicity of the meter. (There are much better meters than anything MFJ makes.)
If the transmission line is lossless enough, and exactly the right length to be in-phase by the time it arrives at the antenna feedpoint, then yes, you can get almost the entire 20W radiated. But if out-of-phase waves didn’t cancel, then phased arrays would not be a thing; they’d all be omni-directional.
As for taking the ARRL’s word for it, no thanks. They’re a publishing house. They publish what will sell, whether it’s correct or not. Sure, they’d LIKE to be right all the time, but they’re just not.
I take your point that people can waste time & money being overly concerned about a good match. But there’s also potential harm in being too unconcerned.
A good proof of this is in receive. Just as an experiment, find a weak dx station with your perfectly tuned antenna and then see how far you can de-tune the antenna before you start to loose signal and it will shock you (hopefully not literally) to see the results, especially with open wire feed line. I have many times before worked dx and didn't want to take time to tune the antenna as I have a manual matching unit. I just manually cut my power down to 40-50 watts and protect my radio that way. Also, when I used to operate mobile I used AM mode with no audio to tune my screwdriver antenna. AM mode automatically cuts the transmitter power to about a third (again NO audio) and zero beats the frequency so other stations are not even aware of your presence. NOTHING I hate more than people who for some reason use FULL POWER to match their antenna, and it always seems to be at an EAR PIERCING 3000 hz! Here in the shack, I turn my power down to just enough to move the meter to full scale, or even less, just enough to get a relative reading. When I can't match my antenna, I simply cut my power in half and I still make the contact!
Back in the 70's Heathkit offered a two meter FM radio called the 2036 and claimed you could run it at "unlimited" swr. This was due to (in my opinion) the fact that the final transistor was only running at about half it's rated output and only put out about 12 watts.
Great video man! 73's
Isn’t the reflected wave out of phase? Therefore the total effective power not increased?
There is no power increase. The point is that the reflected power is not “lost.”
I think that phase doesn't matter as RF is rectified and the resulting DC is measured by SWR bridge which is a directional coupler.
@@NoMoreRadioMythsIf it's not useful for making the transmitted signal stronger (weaker actually) then effectively it is indeed "lost".
Is it coming down to semantics of what we are defining of what we mean by "lost"?
The antenna tuner changes the phase of the reflected power. This is a quote from "Reflections" by antenna engineer Walt Maxwell. "Tuning for maximum line current simply adjusts the phase of the reflected wave to rereflect down the line in phase with the forward wave."
I've always being taught that any reflected power is simply converted into heat in the final stage of the antenna tuner or the transmitter. It seems to me that any reflected power then goes back into the antenna will be out of phase with the forward power causing a further loss of power transmitted
Who taught you that? It's just the opposite. See the references I posted.
I'm not completely sure that the reflected power adds to forward power, or that the forward and reflective waves are even in phase, with no leads or lags, and if they are not, then there certainly is some cancellation going on.
My understanding of an antenna tuner is that with it's combination of capacitors and inductors, what it does (and this is ONLY what it does) is cancel out inductive and capacitative reactance. (I read all three of "Kurt's" books when they were still in print.) Hopefully, what you have left then is pure resistance. Well we should probably call that instead hopefully "pretty low reactance" and not resistance, since we are discussing AC. As a subject, Cable loss is a VERY significant topic. Too many hams are connecting good radios to good antennas with crappy coax. While I can't prove it, I think that there is a lot of "milspec" Hucksterism going on. And yet? No Doubt, there's some ham attempting to use Heliax in a Liquid Helium environment to get rid of the resistance completely... 🤣 Finally, I observed with my own (Daiwa) cross needle meter, I observed that as I tuned and my SWR improved, as the "reverse" needle went down, the "forward" needle went UP. EVERY time. And, super finally, when I had a bad SWR before I knew what I was doing, the heat sink in my Ten Tec Scout got pretty hot with a bad SWR, so I MUST conclude that the reverse power was heating up the final, and so the reflected waves WERE NOT being broadcasted up the dipole, instead they were heating up my shack! And I couldn't match higher wattages at all. This was when I was still reading the radio mags with the linear amp and tower "centerfolds" and thinking I needed all of "that." But I got better, I went QRP and with an LDG auto tuner. Now, I just wait for the clicking to stop, and and I'm tuned and it's all rosy and peachy, with no credit account at The Candy Store! 😂
The antenna tuner changes the phase of the reflected power. This is a quote from "Reflections" by antenna engineer Walt Maxwell. "Tuning for maximum line current simply adjusts the phase of the reflected wave to rereflect down the line in phase with the forward wave."
Mark where is the link ive uploaded several times ,has it been deleted
I have never seen it. No idea.
@@NoMoreRadioMyths it's gone again
Ok, I know I will regret this...I spent my formative years in the friendship of a ham who had a master's degree in electrical engineering. His reasoning always made sense, and I learned the hard way he was right. Reflected power does not simply disappear. It has to go somewhere. Some power is lost in ohmic losses in the transmission line (often coax). How much depends on the transmission line. The real problem is the so-called 'antenna tuner'. Its true name is 'match box', and it is meant as a convenient way to solve a complex problem. Reason? It does not tune anything! It simply makes your radio happy. It does not solve an SWR problem at the antenna. This is why I used to use 'tuners' at the antenna feed point (such as the SGC models and the Icom AH-4). They measure the SWR at the antenna feed point and adjust accordingly. Awesome devices when used correctly. If you use a coax choke at the 'matcher', you will also keep the radiated power at the antenna, and not on the outside of your coax where it can be carried back to your operating position.
The boxes at the radio provide a 'conjugate' match. They do not correct a mismatch at the antenna. The 'loss' (the stuff NOT being radiated by your antenna) is still there. So where does the power go? The 'match box' simply shunts the power to the case or chassis of the box, and to the shields of all your coax, radio chassis, microphone, SWR meter, and anything else with electrical continuity to the chassis of the 'match box' become hot with RF. This is another reason why quarter-wave radials (counterpoise) are such a good thing on many antennas and grounding systems. They provide a low-impedance path for that 'lost' power to go and be radiated instead of filling your shack with RF.
Of course, the best things to do are...1...properly match your antenna, and 2...learn how to use balanced line instead of coax, especially on HF. Balanced line has far less loss in a mismatched condition...almost lossless in both incident and reflected power conditions...and does not radiate power unless it is engineered to radiate. Not as easy to handle and use, but it sure works good on dipoles, loops, and other bigger antennas. Most of the long-timers I knew never used coax on HF. Good luck!
An antenna tuner tunes out the reactance of the antenna system to create resonance, the conjugate match corrects the antenna feedpoint mismatch to allow power transfer, reflected power does indeed have to go somewhere ,its either lost as heat within the transmission line if lossy or radiated at the antenna ,the tuner does not shunt the rf power to the braid of coax or chassis of equipment, the antenna is at fault for that ,may I guide you to Walt Maxwells books reflections he explains very in detail how it works
"Kurt Sterban?" Actually, "Kurt N Sterba", may he rest in peace since the demise of Worldradio mag.
Yes spell checker in my script got me on that one. My apologies.
I've noticed that there's been some comments to my reply, I cant see them for some reason maybe been deleted ,if you have any questions to my comments I would like to respond to them ,so if Mark would allow please respond here with your questions
@paulm0hpd319 Thank you for helping me banish these myths.
@@NoMoreRadioMyths I know it's a totally misunderstood subject, i try to help in group's to spread a greater understanding of the subject, I know your videos are a general overview on the subject I wonder if you could do separate videos going into detail with breaking each part down in separate videos, it may help others with understanding it a little better rather than getting negative comments and having to remove them ,I am surprised and disappointed that a couple of well known influencers that make educational videos don't fully understand this subject even though they make videos on the subject, what supprises me most is that most of these people have used the study books with this info in to obtain their licences ,keep the videos coming hopefully you will consider my suggestion ,cheers
Again, thank you @paulm0hpd319 for your help in trying to explain these things which can be complex. I am going to upload a new version of The Myth of SWR to add some clarifications and a better demo. When I put that first myth video together it was out of frustration for the amount of misinformation. I did not think anyone would look at it but that was sure wrong. I've been thinking it might be good to break these things down separately - SWR, reflected power, line loss and so on. This channel is all new for me. It's a work in progress. I will see what I can do. 73.
@@NoMoreRadioMyths sounds good I will look forward to them
This is why your wolf river coil burns up
More likely due to heat generated by the relatively high resistance of the stainless steel wire used in WRC coil's construction and the relatively low melting temp of PVC coil form.
Thanks for this interesting video. I wonder why people are not more interested in radiated power which would be measured at some distance from the antenna. I realize that their are other factors involved here such as the angle or rather multiple angles of radiation which might be favorable or wasteful. An interesting article that I read 66 years ago in a CB magazine that bragged to have found the most amazing antenna anyone could build. It consisted of two equilateral triangles made from cardboard connect at their angular point facing away from each other. At the point of connection was a fifty ohm resister connecting to a coax. This article appeared in a CB magazine with no explanation other than it's SWR was the outstanding. I still wonder was this a joke or an attempt to ridicule the CB crowd.
Radiated power measurements would really tell how well the antenna works and maybe some companies don't want us to know.
The ZS5JF article is good reading and your demonstration shows the myth destroyed.
QRP here using RG58 and I aim for below 2:1 SWR with 1.5 better. It doesn't take long to adjust my dipoles and inverted vee, are they too long or too short? Easy using my NANO VNA, unlike when I had only an SWR meter.
C.B.'ers painstakingly trimming ½λ coax make me laugh. They can't seem to accept that by connecting an SWR meter their carefully trimmed ½λ coax joins to the jumper lead via the meter thereby making one coax so all their time consuming trimming is wasted.
I've said this and they still say they want the thing which works best for them, i.e. trimming coax inch by inch.
G4GHB.
Reminds me of years ago I was in a radio shop in Denver purchasing a two meter rig and a CB operator came in and told the store owner that his friend has an SWR of like 1.2 and was complaining that his was 1.5. 😅
You did an excellent job explaining SWR. The preparation and research was obvious. You make the information easily understood. Good job.
Controversially there are times when an apparently matched antenna can benefit from being "detuned". For example a ground mounted quarterwave, if you had a perfect ground plane the impedance should be in the region of 35 ohms at resonance. However with a typical radial system with an impedance of about 15 ohms will create a nearly perfect 50 ohm match despite 30% of the power warming the ground. If you make the vertical slightly longer the feed impedance will go up accompanied by some inductive reactance. By raising the impedance of the vertical section you reduce the current in the ground system too raising efficiency. You can also get a better pattern. Obviously not all cases are equal, a typical coax needs derating for power handling when operated with a high VSWR. I kno this is the land of UA-cam but most of the obsession with low SWR is time badly spent, best make an antenna for efficiency and a good pattern and then figure out how to drive it. 73
Interesting!
@@NoMoreRadioMyths I think this is a good example when best SWR does not mean best efficiency.
I just get the screen down on my mobile hf so I don't have operate the manual atu . I suppose I could buy an auto atu but I'm too mean
As Engineers, we encourage use of the SWR meter because it is a simple method that can be used by someone with NO understanding of electronics, or transmission line theory, to get their Transmitter installed. These days, that is MOST Hams. Good luck trying to convince them.
Most will never understand what is going on, which is why they spend a fortune trying to reduce their 2:1 SWR down to 1:1 .
Despite this, they make hundreds of YT videos as "experts" because they really believe that their SWR meter is a high tech instrument.
In a 50 year career designing communications equipment and antennae systems, I rarely even heard "swr" mentioned. These issues were usually expressed in more technically relevant terms.
It is hard work being an Amateur, and a Professional. 🙂
Brilliant! I’m not an engineer but I can read and it disturbs me to see falsehoods spread. I think you would enjoy reading some of the papers of a fellow engineer - Walter Maxwell, who wrote a series of papers on this subject - “Another Look At Reflections.” It’s a good read.
www.k3emd.com/downloads/Reflect.pdf
Yes, the SWR meter is an inexpensive addition to any station to tell the operator in a quick glance that the antenna and feedline are working today the same way they worked yesterday. In other words, that nothing has gone wrong. Unfortunately, since many operators have purchased SWR meters, low SWR has become an unnecessary obsession. The operator imagines that lower SWR has to be significantly better, since the meter scale often devotes a significant amount of space at the low end, expanding the scale there. If the SWR meters were redesigned so that 2:1 SWR was upscale just a few percent from 1:1 as compared to full scale, perhaps this would give a better indication of the relative importance of SWR, and there would be less obsession. 🙂
I didnt even watch the video but from reading the comments i know what its about. The transmitter output impedance is not actually 50 Ohm but something close to zero, and what's coming back from the antennna is reflected again, and this is what makes the power meter behind the transceiver show more power than the transceiver actually has. If cable dissipation can be neglected, then the antenna radiates about the difference of the "apparent" emitted power minus the reflected power. And yes, for a CB radio with 3m of RG58, it is about correct. With an antenna SWR of 3, the power meter shows then 5 W emitted instead of 4W, 1 W reflected, so it means the antenna still radiates its 4W. And really, a SWR of 3 is not as bad as many might think. Higher frequencies and longer cables makes it worse though.
Great comments,
I'm inclined to believe that reflected power is not being radiated in a useful manner. I have no proof and have not researched the facts but I studied and bunch of physics and electronics and believe the power gets bounced back from the antenna and gets used up as heat in the ATU/Final and coax. Otherwise, the reflections would get radiated as noise, QRM, and be seen on a broadcast analyzer as a descending ghost signal that a TDR could measure to match the length of cable causing the delay. Again, maybe they do radiate and that is why some radios sound better than others? I'm sure a test could be devised using long lengths of cable and a top notch broadcast analyzer, TDR, bad antenna, and such--please let me know if this has been done.
If you look at some of the references I posted in the description your questions will be answered.
Thanks Mark but, any good math guru can make anything they want to prove go their way--the answer may be if you just bought a $50,000 HF transceiver and hooked it up to a miss-matched antenna, would you crank it up and try to make contacts for 6 hours? I'm siding with JohnWallas74 on this one.@@NoMoreRadioMyths
What I fail to understand here is.. my understanding is, watts and watts. You deliver 20W into the antenna tuner. There is no additional energy being added anywhere, so how do we arrive at 30W forward power? Are you saying to interpret the reading, we have 20W forward + 10W reflected which eventually is more or less all radiated, so we read 30W forward, but in reality the total power coupled into the antenna is 20W after we take off the 10W reflected?
Yep. I know it's hard to wrap your head around. The bottom line is that no power is wasted, minus some usually minor coax cable loss. No new power is actually created. The law of thermodynamics says energy cannot be created or destroyed. Check the references in my description.
Excellent explanation and spot on.
Excellent video. Most ham radio UA-camrs go off subject and waffle, making the video unwatchable. Thank you, Subscribed and clicked on the bell.
Thank you Mark, very clear and yes, not what I thought. It makes sense that we need to protect the transmitter (via a tuner). But based on this, I can put a bit more time on the air! N7DKE
This is excellent stuff! Thank you for this....
My first thought was "What if the re-reflected power is 180 degrees to the forward power"? Anyway, interesting indeed. 73
The antenna tuner changes the phase of the reflected power. This is a quote from "Reflections" by antenna engineer Walt Maxwell. "Tuning for maximum line current simply adjusts the phase of the reflected wave to rereflect down the line in phase with the forward wave."
The standing wave is dissipated inside the output transistor.
If the transistor (MOSFET nowadays) works in class C, with a circulation angle between 72° and 90°, it will have a very good efficiency and for 10 W output, it will draw 12 - 13 W from the power supply and therefore dissipate 3 W of heat.
Now if the antenna is mismatched or broken, and half of the power is reflected back creating a standing wave, the transistor will have to dissipate 5 + 3 Watt. The heatsink may not be of the right size and after an hour or less of QSO, it will blow up. Newer radio use a temperature sensor which protects the entire circuit by reducing the output power...
This is incorrect, reflected power joins the forward power, it's not absorbed within the transmitter outputs
Huh. I often wondered about swr "loss" since I could never see how the loss occurred. Good video & I will look into the references you mentioned. Thank you. K3EJP
very interesting video Mark. I ran simulations on my HF antennas here using the calculator that you mentioned. They are delta loops with an swr of 1.5:1 and indeed there is little to be gained by spending a lot of time readjusting wire lengths. It really shows that the obsession in getting a 1:1 swr gains just about nothing.
I agree with most of your video content right up to the point where you try to show and state that 20 watts out of the TX turns into 30 watts. Bad SWR does NOT increase the output power. The SWR meter may not accurately calibrated for that Freq. You can NOT increase power out by having bad SWR!! You will never get more than the 20 Watts to the antenna. What you are stating toward the end of your video is the holy grail of junk science! FREE ENERGY!! Just is not possible.
You might want to watch the video again
Never said that. SWR does not give you a power increase. Of course not. The point is that reflected power is not lost. Do some reading please. www.arrl.org/files/file/Technology/tis/info/pdf/q1106037.pdf
@@NoMoreRadioMythsI read the article. I wouldn't just assume because it was published by ARRL that is entirely correct. In the article he contradicts himself by stating that ladder line helps to radiate the reflected signals (radiating it away) but then in a coaxial example, he says it is "eventually radiated out the antenna" after going back and forth between the radio and antenna ---- but if that were the case, then we would never have overheating burned out transmitters from bad SWR. The reflected power is put back into the transmitter and is in the form of heat rather than transmitted. This part is where I believe he is incorrect.
Think you have misunderstood what he has said ,he doesn't say 30 Watts is radiated
@@NoMoreRadioMyths It would be very interesting to see a follow up video where the test is ran again with the external watt meter placed before the tuner such that when there is a perfect match to the TX, what does the watt meter show then? Would it still show 30 watts (indicating that the meter is poorly calibrated for that frequency) or would it now show just the 20 watts? And then if placed after the tuner would it then show the 30 watts?? I realize you are not so ignorant as to imply that there is "magic" power being generated, but the wording along with the display on the swr meter is confusing. Good video discussion overall. Cheers.
Sure... I have room for an expensive antenna tuner with my $300.00 CB... Sure boss.
Your reflected power is NOT in phase.......
I think that phase doesn't matter as RF is rectified and the resulting DC is measured by SWR bridge which is a directional coupler.
I think phase has everything to do with it. If reflected and and forward power where in phase it doesn't matter where in the transmission line you measure, it will always be the same. But it does matter where you put your power meter.
Put your SWR meter somewhere else in the line and everything changes because you do not have standing waves.
This is why the myth started that coaxlines should be a half wave length our a multitude of it.
It should not. The length of the feedline does not matter if it is connected to an antenne with the same impedance as the feedline.
@@maartenc6099 You should try to understand how directional couplers work, measuring forward power is not affected by reflected.
That's why the tuner is inline to correct the phase
Yes. Between transmitter and tuner. Not Between antenne and tuner
Can we please refer to antenna tuners at the transmitters as trans matches . As that is what they are . Unless you are considering your feedline as part of your antenna you are not tuning the antenna but matching the 50 ohm impedance of the transmitter to the feedline impedance
Transmatch is a better term but it also in effect tunes the antenna to resonance by cancelling the reactance. Check references I included in my description for a much more derailed explanation.
It tunes out the reactance of the entire system deeming it resonant ,Maxwell is happy with both names as they serve both purposes
All of what you said is correct only with an antenna tunner. connect the antenna directly to the transceiver and see what happens to the finals...
What burns up the finals is the impedance mismatch causing increased power dissipation - not SWR or reflected power.
Reflected power still joins the forward power but the output will reduce to the difference of the reflected power, the tuner in line will allow the transmitter to produce its maximum power into the system
Very interesting, thank you
Conjugately
You are supposed to SUBTRACT Reflected from Forward; not ADD. If radio output set to 20W then no more than 20W can ever arrive where the coax joins the antenna. Even the greatest coax connected to the wildest tuner can not become a 10 Watt amplifier. There is no free 10 watts.
Look up "reflection gain" in a transmission line from a conjegate match. It's a scientific fact . That gain is then reflected back again at the load. No magic power increase being radiated and I never said there was. It's in the ARRL Antenna Book chapter 25.
@val058 you have it wrong ,reflected power does indeed join the forward power
@@NoMoreRadioMyths It can reflect back and forth alternatively between source and load but then its a wash and in reality its just knowledge of whats taking place but the power isn't changing. Maybe its just a case of semantics but I was led to believe you implied 30W output was being sent out of the antenna ultimately, when the source was 20W and that of course is scientifically not possible as that would require a steady non-alternating one-way addition of reflected power. - The subtraction thing I mentioned previously was in error.
Yes there is no magic power increase but the full transmitter output, not that plus the reflected power, is radiated. The reflected power basically stays in the line, bouncing back and forth, but eventually it gets radiated. It has to go somewhere. Many beleive that somewhere is the tuner or the transmitter but that's not true. It is totally reflected by the conjugate match at the tuner.
@@NoMoreRadioMyths I get that now, thank you. interesting.
Nicely described, Thank you Sir ❤ #VU2XFD
Do you know how many new operators you have sent into a tailspin? …. And antenna tuners only bullshit the radio and antenna tuner cannot make a antenna longer and it cannot make an antenna shorter. They cannot make an antenna. resonant at a specific frequency. It’s only bullshitting the radio no matter what. tune the antenna for resonance.on the frequency of operation.get the feed point matches close to 50 ohms as you possibly can, you will avoid a lot of heartache in the long run… tuna is not chicken.tuna is not pork.tuna is tuna……
One correction if I may. A tuner does in effect "tune" the antenna by canceling its reactance. It is resonant if the trans match is property adjusted. Please check the references in my description.
Greetings KJ7JMP...
this is very interesting, but badly explained. not to insult.
as they say "incredible claims need incredible proof" or something.
i watched alot of your videos and still would have liked more explanation. it is hard to break the set thinking. i am beginning to understand the working of this. i think we are all using loaded and wrong terminology and it is causing most of the problems.
I suggest reading this: www.k3emd.com/downloads/Reflect.pdf
The videos are not meant to be highly comprehensive.
I'm the antenna tuner. Resonance or bust. Tuners are a waste of money.
At resonance, my short, center-loaded vertical has an input impedance of about 12 ohms: 4:1 VSWR. In other words, antenna resonance does not necessarily equate to an impedance match.
@@DaDitDaa mobile antenna guru once said that perfect SWR is a warning that you are not matched.
Do you realise resonance doesn't guarantee efficiency, it doesn't guarantee its matched either but a tuner can deliver both resonance and matching for maximum power transfer
So what you are saing is that the higher the SWR the more power you will put out.
If the Antenna had a 1:1 SWR then you only get 20 watts out. but since you have 3:1 SWR you get 30 watts out a bonus of 50% due to high SWR. Keep dreaming..... Keep dreaming.....
No you missed half of the process, which was clearly explained. The additional 10 watts is reflected back to the tuner by the antenna, giving you 20 watts radiated. There is no magic power increase. Click on the references in the description to learn more.
Haha listen carefully to what is being said ,at no point did he say there's more power than was originally generated radiated by the antenna