I'll take a quote out of the Antenna Handbook - "Please recognize that an antenna need not be resonant in order to be an effective radiator. There is in fact nothing magic about having a resonant antenna, provided of course that you can devise some efficient means to feed the antenna. Many amateurs use non-resonant (even random-length) antennas fed with open-wire transmission lines and antenna tuners. They radiate signals just as well as those using coaxial cable and resonant antennas, and as a bonus they usually can use these antenna systems on multiple frequency bands." Based on this video, I would submit this is also relatively true with high quality coaxial cable and ATU in the HF bands.
Mark, Thanks for clearing up the SWR and Other Myths. As a retired electronics tech., and long time Ham, many of the common explanations never rang true to me. A little Common Sense, backed by knowledgeable resources goes a long way. 73 mike 🍺🍻
Thanks for this video! I have tried to explain this to many a ham friend, but often I have to just say "what ever dude". So this was helpful! I use ladder line all I can btw. Great video!
Absolutely brilliant - you have a new sub. I like your direct manner and science based information. Really informative from a SME in your field. Thanks Mark
With frequencies at which cable losses stay moderate, the reflected power gets reflected again by the transceiver and eventually finds its way out the antenna. For example a cb radio may output 4W into a dummy load, which becomes an apparent fwd power of 5W+ when the SWR is moderate, showing that the finals are not just absorbing the initially reflected power. So roughly speaking, what matters is the difference between fwd and reflected power, and 5W-1W is roughly as good as 4W-0.
Walt Maxwell's book "Reflections II, Transmission Lines and Antennas" is one of my most treasured books. The title of chapter 1 says it all, "Too low and SWR can kill you". And from there on, it's all gold! But it's a little beyond most hams that have been fully fed the myth (among most all other amateur radio myths). Thanks for this great video.
Funny story I read on a ham forum. A guy had a copy of Reflections on his night stand and his wife wondered why Maxell wrote books "reflecting" on his past with antennas and transmission lines. LOL
I agree with 98% of this analysis. My small disagreement is the loss in the cable. SWR creates both voltage nodes and current nodes. Since power lost = I^2*R, the power loss due to the increased current nodes cannot be neglected. So power loss in the cable does increase with SWR. But the overall point of the tuner reflecting power back to the antenna is correct.
True power loss increases with SWR. So the radio operator has to decide how much he is willing to tolerate based on what he is trying to accomplish. You can buy RG-8X for 65 cents a foot or CommScope 1-5/8in HELIAX Standard Air Dielectric for $45 a foot.
it is radiated but just like AC power it cycles back and forth even with a perfect match the RF still returns to the transmitter but the reactance is matched so the power cycle of RF in the transmission line is so low its almost undetectable
VSWR does cause issues with repeater operation. The phase delta can wreak havoc on the receiver and kill its sensitivity while the standing wave is present.
Love the content, and delivery. From my bass guitar playing days, I understood that my amp needed to see an acceptable impedance range and to never go below it’s lowest rating (i.e., a 2-ohm load into a 4-ohm amp). I see no difference between a bass amp and a transceiver power section impedance requirements, losely speaking. I always tune my antenna looking at the impedance not SWR. Sometimes that is not 1:1. I have no Elmer to teach me, I just apply basic knowledge and listen to Hams who have been around the block more than me. Thank you.
In mismatch, the reflected power is not lost, but is not radiated either, easily measured with a field strength meter. Also, you need to measure the collector current in the finals and you will notice the collector current increases because the power is not transferred to the load (Maximum Power Transfer theorem). Depending on the design of the finals section, and more important, the maximum ratings of the components, so, some radios finals will go and others will not depending on the components and the overall design. Some radios, like the Yaesu 817 will burn the finals on a 5:1+ mismatch, and others, like the Xiegu G-90 can take up to 18:1 mismatch without failing, because of sturdier components.
Yes it is easily confirmed with a field strength meter that SWR DOES NOT affect radiated power, I have done it. Tuning a two meter mobile whip with both an SWR meter and field strength simultaneously monitoring power, the SWR can be brought from >3:1 to 1:1 match and no difference seen at all on the field strength. The reason you may see current increases in the output devices is more to do with the way some solid state transmitters controlled the output power with an ALC loop than the effect of reflected power in the output devices. These output ALC loops only correctly reported forward power with a good 50 Ohm match and SWR would cause the ALC to overdrive the output stage. 73 de G0AFV
@@gabrielsierra6890YES…. The power transfer theorem is in operation but when your xmitter looks into a tuned ATU/tuner/transmatch it sees a 50 ohm load as the ATU matches the impedance of the PA of your rig. So power goes thru and gets onto the transmission line.
It is a well known HAM fact that dust bunnies in the shack will nullify a poor SWR …. Therefore this test is null and void! 😂😂😂😂😂 73 and tu fer this information.
Excellent stuff Mark! Thanks! I use matching networks (aka "tuners") on all my antennas, and have been for many years. Two multi-band parallel dipoles (kinda like a fan-dipole, but equally-spaced parallel wires), and a HyGain AV-680 vertical. My SWR is not terrible on most bands (typically
You have misrepresented one VERY IMPORTANT aspect. Although I have been preaching the same thing about VSWR for decades, THERE IS A LOSS that you failed to mention. That is the RADIATION that is lost by the coax cable RADIATING. If the coax cable has a mismatch to the antenna, YES, the signals get reflected back and forth and the actual resistance burns up some of the power as heat, but the COAX CABLE ALSO BEGINS TO RADIATE THE POWER OUT, SINCE IT IS UNBALANCED. The coax cable becomes part of the ANTENNA SYSTEM. Well balanced ladder line doesn't radiate, because both sides are BALANCED, while coax is inherently UNBALANCED. We used to use this principle to radiate two way radio signals inside tunnels in the communications industry. Nowadays there is leaky cable, but decades ago we used regulated mismatch to radiate where we wanted it. The problem with the coax radiating is that it can distort your antenna radiation pattern, if you are using a directional antenna. It's also a problem if you NEED all your power to be radiated by the ANTENNA and not by the coax, where it may even be buried, or attached to the tower leg where absorption loss is bad. Yes, having a mismatched, radiating coax, feeding a suspended dipole could improve your signal in the dipole nulls and by having a complex radiation pattern of both horizontal and vertical radiation, but for a lot of installations, this leaking radiation is very detrimental. So my point is that, yes, the mismatched radiation isn't technically "lost", it could very well be going where you DON'T want it to go. Professional radio communications would never allow mismatched coax and antennas in their normal operation, for a myriad of reasons. Hams don't have to be as critical, especially being overly critical about unnecessary things and may even use mismatch to their benefit, but we need to be aware of the negative side as well.
Coax cable does not radiate unless you have common mode current on the outer shield because no common mode choke, also called a balun, is being used at the feed point. "Most of the shield effect in coax results from opposing currents in the center conductor and shield creating opposite magnetic fields that cancel, and thus do not radiate. The same effect helps ladder line." Wikipedia. "Another related concept, popular, but also erroneous, is that when terminated in a mismatch, the coaxial feed line becomes part of the radiator, causing radiation from the feed line due to the standing wave (ref. Part 2 of this series, statement 18). This is untrue because the line voltages and currents, and the standing waves resulting from the mismatch, are entirely contained in and between the outer and inner conductors, inside the coax. No standing wave develops on the outside because of mismatch." Walt Maxwell - "Another Look at Reflections."
Not because coax radiates but because of common mode current flowing back down the outer shield of the cable into the shack because of skin effect. That can be stopped with a simple common mode choke at the feedpoint. Google - Does coax radiate? Everyone seems to know it doesn't except as I've described.
Now you are saying it could radiate, UNLESS you put a common mode choke on it. You never mentioned that in your original post. The coax could radiate unless you do something to prevent. I will cede that there is a way to prevent coax radiation, but the fact is, unless you make special provisions, the coax can radiate. That is a life fact, because "RF bites" and other issues with coax radiation has been around since coax came out.
Great video, I am now a subscriber. I agree with you 100%. I use a Chameleon EMCOMM III antenna which is a 130 ft end fed 'random wire' antenna with a 5:1 transformer. I feed it with 35 ft of LMR 400. SWRs are 2:1 to 3:1 across the spectrum from 160 to 6 meters. I have worked all HF ham bands with this setup. It works great. Robert K5TPC
Vy clear explanation Mark, tnx! I always prefer a good antenna with a bad swr than a bad ant. with a good swr. The most important is the radiation resistance of the ant. vs the losses. A good antenna tuner will always do the job to transfer the max pwr with an efficiency of at least 90%. The added losses on ladder lines with high swr is negligible. An interesting test would be with an infrared camera looking into the antenna tuner to observe the increasing heat caused by the losses. Therefore the Qu, unloaded Q from the ATU circuit must be as high as possible. 73s
Sometimes reflected power is reflected back, and I did some experiments where I was able to increase power by purposefully mismatching the antenna. I did this with an experimental 1 W amplifier, of course, at the cost of more heat and increased power consumption.
With my older type transmitters I would operate with a 3:1 SWR and make plenty of contacts, at 5:1 the plates glowed a nice dark red color. I also found the shack was filled with RF. Got a couple of burned fingers and would light up my fluorescent desk lamp without turning it on, those were the days. The strangest one though I was at the repeater site one day checking the antenna with a directional watt meter. I noticed a significant amount of reflected power. I was like what went wrong with the antenna? The feedline was 1/2" Heliax. Getting onto the roof of the building was a pain. You had to notify security to unlock the door, then you had to notify the engineers at the TV station so they could turn down the power of the UHF station. Then dawn a protective RF suit that was in bad need of cleaning. All of a sudden I realized, wait; I'm seeing this and my transmitter is not transmitting. That is coming from someone else's transmitter. When we did get out on the roof, we found somebody had mounted a DB-408 on the same bracket about a foot and a half from our VHF antenna. The site manager got them to move. Believe it or not he loved us hams better.
Good video. This is a very much misunderstood topic. I agree with all you said and I have a couple points to add. All antenna books have a chart that will give additional loss due to SWR. It all depends on the loss in the coax under perfect matched conditions. For example, if your feedline loss is say 3dB with a 1:1 SWR then you lose half your power with a perfect match. What starts as 100 watts, ends up as 50 at the antenna with even a 1:1 SWR. However if there is a high enough SWR to reflect 50 watts, then half of that 50 watts gets lost on the way back to the transmitter. Only 25 gets to the transmitter and ALL of it is reflected back toward the antenna. But half of that is lost (always lose 3dB each time) so 12.5 gets back to the antenna where again half of that or 6.25 watts if reflected. Half of that is lost so this trip only 3.125 watts gets to the transmitter. All of that power or 3.125 watts is reflected at the transmitter. This goes on until all power is radiated or lost! So the key is starting with a low loss. All coax has increasing loss with frequency, so coax that has low loss on 80 meters may have excessive losses on 10 meters. I measure my coax loss at the frequency I plan to use it on ( usually close to the advertised figures) then use the chart in the antenna books to see what total loss will be at a given SWR. Remember loss will be given in dB per 100 feet. If you only use 50 feet the loss will only be half that. So with very short coax it usually does not matter what the SWR is because the additional loss due to SWR will be small. But with high loss or very long coax the additional loss due to SWR can be unacceptable on the high bands. I usually have my 80 and 40 meter antennas away from the house with long feedlines and my 10/15/20 meter antennas close with shorter cable. This is a link to the chart in one of my blog posts: antennatalkbydon.blogspot.com/2023/04/loss-on-short-coax-for-portable-or.html
New to ham here. Not an electrical engineer nor electronics tech either. Not going to build a radio, but I have built antennas. While studying for general, I accidentally took an extra practice exam. 14/50. Humbling. But even in the general pool, I have found questions that seem SO obscure to me that I wonder if most ham extras would find 25% of the content frivolous. I would like to know, if anyone cares to speak to it. Thanks
Has anyone studied the degredation of received audio by multiple waves nulling each other, like ripples on a pond from two stones tossed in the water. There has to be null points created, along with an echo effect that may not be perceived by the human brain.
Hi! Would you please make a video about Power vs Signal, and how much power is needed to increase the signal strength by an extra S unit on the other station?
I’m in the process of setting up my shack now. Mostly there. Need a power supply and an SWR meter. But I have been a sub to this channel less than 12 hours and I am already learning the good stuff before the myths and bad info get imbedded too deeply. I’m going to be running QRP on homebrew random wire and dipoles, with relatively short feed lines (20 to 25 feet or less) and with what I have seen so far on this channel, I’m starting to think that these nano VNAs and antenna analyzers are going to be a waste of money that would be better spent on radios.
I got a NANO VNA and found it very useful for building aerials, knowing at a glance if they were too long or too short. It took quite a while before with nearby objects affecting things and watching an SWR meter not knowing if I had made them too short before realising it. Too easy on 12m. Not cutting them of course. 5 attic dipoles for 20m to 10m, an outdoor inverted vee for 60m and a 4 element 2m collinear which would be too easy to miss the resonant point. My wire elements were longer than expected. I should now be able to check my low pass filters on my h/b radio. QRP here with nothing above 5 Watts. G4GHB.
I do not understand your explanation as to why received signals don't get reflected by the ATU too (but obviously they don't, otherwise I wouldn't hear a thing!). But what makes the difference between the reflected, transmitted power and the purely received power at the ATU location (apart from magnitude)?
Tube equipment is a lot more robust in a high mismatch one of the myths I’d like to see put to rest is the guys (mostly the CB crowd ) that say they run so much power the antenna tip glows .
@@NoMoreRadioMyths needs to be tried now i have had guys tell me they have had a longwire fail with high power but anything A truck driver tells me I take with a BIG grain of salt 😆
I agree with your analysis. Question, if I may: If you are using an antenna tuner, and the SWR of the antenna therefore doesn't matter (within reasonable limits, of course), then under what conditions would you ever need a Balun or Unun? BTW, I'm a newbie ham. Maybe there is still common mode current? Please explain! 🙂
If your antenna is a dipole and you are feeding it with coax you should use a balun because coax is unbalanced but a center fed dipole is. If you are feeding an off center fed dipole you will need an unun, because both the antenna and the coax are unbalanced. If you use an unun you will probably also need a common mode choke. Some unun's have them build in. Balun Designs, DX Engineering and Palstar Engineering are examples of where you can get them if you don't want to make your own and a good source of information.
G9A02 (B) What is the relationship between high standing wave ratio (SWR) and transmission line loss? A. There is no relationship between transmission line loss and SWR B. High SWR increases loss in a lossy transmission line C. High SWR makes it difficult to measure transmission line loss D. High SWR reduces the relative effect of transmission line loss You would answer A? The correct answer is B. E9A09 (B) What is antenna efficiency? A. Radiation resistance divided by transmission resistance B. Radiation resistance divided by total resistance C. Total resistance divided by radiation resistance D. Effective radiated power divided by transmitter output You'd get this question wrong if you really believe what you said at 7:55 - "full transmitter power is radiated" because then total resistance would always equal radiation resistance.
@@NoMoreRadioMyths I would agree that in most cases, most of the power is delivered to the antenna. But check out KV5R's Coax Loss Calculator. Using Belden 8236 RG-8 with a 100 foot line, at 14 MHz, play around with SWR and you'll see that you'll double the non-transmitted power by going to 1:1 to 5:1. Will that alone make a meaningful difference? No, probably not: you've gone from about 85W out of the antenna to 70W out, and that's only about 0.8 dB due to the SWR. Most Amateur radios have built in SWR protection, and they will step back your power output if your SWR is too high in order to protect themselves because the reflected power manifests as voltage that, at sufficient level, can damage components. If it were as simple as "the transmitter has high impedance," then radio manufacturers would not worry about adding this feature. You're right about antenna tuners though: they do exactly what you need (to lower your SWR). Check out the video "standing up for standing waves" here on YT to see them in action. They're not just fooling the transmitter.
Next explain coax length, phase angles and impedance I have been playing with 2 verticals need 2 sections of RG11 75 ohm at quarter wave to combine them That is easy with single frequency antenna How does it work co phasing 2 log periodic that cover 50mhz to 1.2ghz? All equal length of 50 ohm coax and a combiner? So why my coax question
@@NoMoreRadioMyths I've watched that video Mark perhaps on another video put more emphasis on the phase angle and how the reflected power changes the impedance measured along the length of the line and that the actual length of the feedline does matter in this respect
No it doesn't make any difference. The same rules apply in ladder line vs coax.The losses in coax is not because of the copper wire. The losses because of copper is very low. Most of the losses in coax is because of the insulator between the two wires. Air is one of the best insulator
So, can it be said: the plate and loading controls of a transmitter are for matching the final to 50 ohm coax to the feed point of the transmission line. The ttransmatch is needed only if the transmission line is not matched (non resonant) .?
I'll take a quote out of the Antenna Handbook - "Please recognize that an antenna need not be resonant in order to be an effective radiator. There is in fact nothing magic about having a resonant antenna, provided of course that you can devise some efficient means to feed the antenna. Many amateurs use non-resonant (even random-length) antennas fed with open-wire transmission lines and antenna tuners. They radiate signals just as well as those using coaxial cable and resonant antennas, and as a bonus they usually can use these antenna systems on multiple frequency bands." Based on this video, I would submit this is also relatively true with high quality coaxial cable and ATU in the HF bands.
But you need to match impedance for maximum power transfer
Yup! True! @davidc5027
@@gabrielsierra6890 Right, that is what the ATU is designed to do. In some cases easier said than done.
My HF antenna is a "random length" wire, with a tuner of course.
Mark, Thanks for clearing up the SWR and Other Myths. As a retired electronics tech., and long time Ham, many of the common explanations never rang true to me. A little Common Sense, backed by knowledgeable resources goes a long way. 73 mike 🍺🍻
Thanks for this video! I have tried to explain this to many a ham friend, but often I have to just say "what ever dude".
So this was helpful!
I use ladder line all I can btw.
Great video!
Absolutely brilliant - you have a new sub. I like your direct manner and science based information. Really informative from a SME in your field. Thanks Mark
Awesome, thank you!
With frequencies at which cable losses stay moderate, the reflected power gets reflected again by the transceiver and eventually finds its way out the antenna. For example a cb radio may output 4W into a dummy load, which becomes an apparent fwd power of 5W+ when the SWR is moderate, showing that the finals are not just absorbing the initially reflected power. So roughly speaking, what matters is the difference between fwd and reflected power, and 5W-1W is roughly as good as 4W-0.
Walt Maxwell's book "Reflections II, Transmission Lines and Antennas" is one of my most treasured books. The title of chapter 1 says it all, "Too low and SWR can kill you". And from there on, it's all gold! But it's a little beyond most hams that have been fully fed the myth (among most all other amateur radio myths). Thanks for this great video.
Funny story I read on a ham forum. A guy had a copy of Reflections on his night stand and his wife wondered why Maxell wrote books "reflecting" on his past with antennas and transmission lines. LOL
I'm glad I found this channel. There is knowledge here.
Welcome aboard!
When you put power through a non-superconductor, some is it is lost in heat.
very very little.
@@ziggyinc just depends on ohms and how far (or how many times back and forth) you go. Loss can be very low or very high or in between.
I agree with 98% of this analysis. My small disagreement is the loss in the cable. SWR creates both voltage nodes and current nodes. Since power lost = I^2*R, the power loss due to the increased current nodes cannot be neglected. So power loss in the cable does increase with SWR. But the overall point of the tuner reflecting power back to the antenna is correct.
True power loss increases with SWR. So the radio operator has to decide how much he is willing to tolerate based on what he is trying to accomplish. You can buy RG-8X for 65 cents a foot or CommScope 1-5/8in HELIAX Standard Air Dielectric for $45 a foot.
@@NoMoreRadioMyths Unfortunately, I'm in the 65¢ range . . .
it is radiated but just like AC power it cycles back and forth even with a perfect match the RF still returns to the transmitter but the reactance is matched so the power cycle of RF in the transmission line is so low its almost undetectable
I have argued this point with several hams, and even pointed it out in the ARRL Antenna Book, but the myth still persists.
It's like people who believe conspiracy theories.
VSWR does cause issues with repeater operation. The phase delta can wreak havoc on the receiver and kill its sensitivity while the standing wave is present.
Love the content, and delivery. From my bass guitar playing days, I understood that my amp needed to see an acceptable impedance range and to never go below it’s lowest rating (i.e., a 2-ohm load into a 4-ohm amp). I see no difference between a bass amp and a transceiver power section impedance requirements, losely speaking. I always tune my antenna looking at the impedance not SWR. Sometimes that is not 1:1. I have no Elmer to teach me, I just apply basic knowledge and listen to Hams who have been around the block more than me. Thank you.
As an audiophile and guitar player I appreciate the analogy. Makes sense.
In mismatch, the reflected power is not lost, but is not radiated either, easily measured with a field strength meter. Also, you need to measure the collector current in the finals and you will notice the collector current increases because the power is not transferred to the load (Maximum Power Transfer theorem). Depending on the design of the finals section, and more important, the maximum ratings of the components, so, some radios finals will go and others will not depending on the components and the overall design. Some radios, like the Yaesu 817 will burn the finals on a 5:1+ mismatch, and others, like the Xiegu G-90 can take up to 18:1 mismatch without failing, because of sturdier components.
If it's not lost, where does it go? It has to go somewhere. Law of thermodynamics. So it gets radiated.
Yes it is easily confirmed with a field strength meter that SWR DOES NOT affect radiated power, I have done it. Tuning a two meter mobile whip with both an SWR meter and field strength simultaneously monitoring power, the SWR can be brought from >3:1 to 1:1 match and no difference seen at all on the field strength.
The reason you may see current increases in the output devices is more to do with the way some solid state transmitters controlled the output power with an ALC loop than the effect of reflected power in the output devices. These output ALC loops only correctly reported forward power with a good 50 Ohm match and SWR would cause the ALC to overdrive the output stage.
73 de G0AFV
If you don't match the impedance you can not have maximum power transfer, period.
@@gabrielsierra6890
You should probably invest in - and read - Maxwell's book "Reflections"...
@@gabrielsierra6890YES…. The power transfer theorem is in operation but when your xmitter looks into a tuned ATU/tuner/transmatch it sees a 50 ohm load as the ATU matches the impedance of the PA of your rig. So power goes thru and gets onto the transmission line.
It is a well known HAM fact that dust bunnies in the shack will nullify a poor SWR …. Therefore this test is null and void! 😂😂😂😂😂 73 and tu fer this information.
I should have dusted before filming. Too late.
@@NoMoreRadioMyths Radio is more important! My shack is an asthma attack in the making! 😀
New Subscriber
New Ham
SWFL based
THANK YOU for “Real” intel & frankly no bias in the information
Excellent stuff Mark! Thanks!
I use matching networks (aka "tuners") on all my antennas, and have been for many years. Two multi-band parallel dipoles (kinda like a fan-dipole, but equally-spaced parallel wires), and a HyGain AV-680 vertical. My SWR is not terrible on most bands (typically
Sounds like a great station and you certainly know your stuff!!
You have misrepresented one VERY IMPORTANT aspect. Although I have been preaching the same thing about VSWR for decades, THERE IS A LOSS that you failed to mention.
That is the RADIATION that is lost by the coax cable RADIATING.
If the coax cable has a mismatch to the antenna, YES, the signals get reflected back and forth and the actual resistance burns up some of the power as heat, but the COAX CABLE ALSO BEGINS TO RADIATE THE POWER OUT, SINCE IT IS UNBALANCED.
The coax cable becomes part of the ANTENNA SYSTEM.
Well balanced ladder line doesn't radiate, because both sides are BALANCED, while coax is inherently UNBALANCED.
We used to use this principle to radiate two way radio signals inside tunnels in the communications industry. Nowadays there is leaky cable, but decades ago we used regulated mismatch to radiate where we wanted it.
The problem with the coax radiating is that it can distort your antenna radiation pattern, if you are using a directional antenna.
It's also a problem if you NEED all your power to be radiated by the ANTENNA and not by the coax, where it may even be buried, or attached to the tower leg where absorption loss is bad.
Yes, having a mismatched, radiating coax, feeding a suspended dipole could improve your signal in the dipole nulls and by having a complex radiation pattern of both horizontal and vertical radiation, but for a lot of installations, this leaking radiation is very detrimental.
So my point is that, yes, the mismatched radiation isn't technically "lost", it could very well be going where you DON'T want it to go.
Professional radio communications would never allow mismatched coax and antennas in their normal operation, for a myriad of reasons.
Hams don't have to be as critical, especially being overly critical about unnecessary things and may even use mismatch to their benefit, but we need to be aware of the negative side as well.
Coax cable does not radiate unless you have common mode current on the outer shield because no common mode choke, also called a balun, is being used at the feed point.
"Most of the shield effect in coax results from opposing currents in the center conductor and shield creating opposite magnetic fields that cancel, and thus do not radiate. The same effect helps ladder line." Wikipedia.
"Another related concept, popular, but also
erroneous, is that when terminated in a mismatch,
the coaxial feed line becomes part of the radiator,
causing radiation from the feed line due to the
standing wave (ref. Part 2 of this series, statement
18). This is untrue because the line voltages and
currents, and the standing waves resulting from the
mismatch, are entirely contained in and between
the outer and inner conductors, inside the coax. No
standing wave develops on the outside because of
mismatch." Walt Maxwell - "Another Look at Reflections."
Look, in real life, we know that coax can radiate and rf in the shack can be a problem, along with rf bites.
Not because coax radiates but because of common mode current flowing back down the outer shield of the cable into the shack because of skin effect. That can be stopped with a simple common mode choke at the feedpoint. Google - Does coax radiate? Everyone seems to know it doesn't except as I've described.
Now you are saying it could radiate, UNLESS you put a common mode choke on it. You never mentioned that in your original post. The coax could radiate unless you do something to prevent.
I will cede that there is a way to prevent coax radiation, but the fact is, unless you make special provisions, the coax can radiate.
That is a life fact, because "RF bites" and other issues with coax radiation has been around since coax came out.
@jonizornes5286 coax radiation has nothing to do with swr ,common mode current has to do with antenna imbalance not feedpoint impedance mismatch
Great video, I am now a subscriber. I agree with you 100%. I use a Chameleon EMCOMM III antenna which is a 130 ft end fed 'random wire' antenna with a 5:1 transformer. I feed it with 35 ft of LMR 400. SWRs are 2:1 to 3:1 across the spectrum from 160 to 6 meters. I have worked all HF ham bands with this setup. It works great. Robert K5TPC
I'd call that an ideal antenna. What serves as the counterpoise?
Great video and thanks. “Mark the Ham…Good day!”
Same to you!
Just like tuning your coax for exact 50 ohms
thats ok with one frequency,
It all go out the window on wide band antennas
Vy clear explanation Mark, tnx!
I always prefer a good antenna with a bad swr than a bad ant. with a good swr. The most important is the radiation resistance of the ant. vs the losses. A good antenna tuner will always do the job to transfer the max pwr with an efficiency of at least 90%. The added losses on ladder lines with high swr is negligible.
An interesting test would be with an infrared camera looking into the antenna tuner to observe the increasing heat caused by the losses. Therefore the Qu, unloaded Q from the ATU circuit must be as high as possible. 73s
This is exactly right. A good tuner has a coil made of heavy wire. If not, that's where the losses occur.
Sometimes reflected power is reflected back, and I did some experiments where I was able to increase power by purposefully mismatching the antenna. I did this with an experimental 1 W amplifier, of course, at the cost of more heat and increased power consumption.
Interesting!
I forgot to add that I use the rig's (ICOM 7300) 'antenna tuner' to get a good match at the radio. Robert K5TPC
With my older type transmitters I would operate with a 3:1 SWR and make plenty of contacts, at 5:1 the plates glowed a nice dark red color. I also found the shack was filled with RF. Got a couple of burned fingers and would light up my fluorescent desk lamp without turning it on, those were the days. The strangest one though I was at the repeater site one day checking the antenna with a directional watt meter. I noticed a significant amount of reflected power. I was like what went wrong with the antenna? The feedline was 1/2" Heliax. Getting onto the roof of the building was a pain. You had to notify security to unlock the door, then you had to notify the engineers at the TV station so they could turn down the power of the UHF station. Then dawn a protective RF suit that was in bad need of cleaning. All of a sudden I realized, wait; I'm seeing this and my transmitter is not transmitting. That is coming from someone else's transmitter. When we did get out on the roof, we found somebody had mounted a DB-408 on the same bracket about a foot and a half from our VHF antenna. The site manager got them to move. Believe it or not he loved us hams better.
Sounds like you had common mode current coming into the shack.
Good video. This is a very much misunderstood topic. I agree with all you said and I have a couple points to add. All antenna books have a chart that will give additional loss due to SWR. It all depends on the loss in the coax under perfect matched conditions. For example, if your feedline loss is say 3dB with a 1:1 SWR then you lose half your power with a perfect match. What starts as 100 watts, ends up as 50 at the antenna with even a 1:1 SWR. However if there is a high enough SWR to reflect 50 watts, then half of that 50 watts gets lost on the way back to the transmitter. Only 25 gets to the transmitter and ALL of it is reflected back toward the antenna. But half of that is lost (always lose 3dB each time) so 12.5 gets back to the antenna where again half of that or 6.25 watts if reflected. Half of that is lost so this trip only 3.125 watts gets to the transmitter. All of that power or 3.125 watts is reflected at the transmitter. This goes on until all power is radiated or lost! So the key is starting with a low loss. All coax has increasing loss with frequency, so coax that has low loss on 80 meters may have excessive losses on 10 meters. I measure my coax loss at the frequency I plan to use it on ( usually close to the advertised figures) then use the chart in the antenna books to see what total loss will be at a given SWR. Remember loss will be given in dB per 100 feet. If you only use 50 feet the loss will only be half that. So with very short coax it usually does not matter what the SWR is because the additional loss due to SWR will be small. But with high loss or very long coax the additional loss due to SWR can be unacceptable on the high bands. I usually have my 80 and 40 meter antennas away from the house with long feedlines and my 10/15/20 meter antennas close with shorter cable.
This is a link to the chart in one of my blog posts:
antennatalkbydon.blogspot.com/2023/04/loss-on-short-coax-for-portable-or.html
Good post.
No matter what, I still like your content 😎
Some of its a bit rough around the edges I guess.
New to ham here. Not an electrical engineer nor electronics tech either. Not going to build a radio, but I have built antennas. While studying for general, I accidentally took an extra practice exam. 14/50. Humbling. But even in the general pool, I have found questions that seem SO obscure to me that I wonder if most ham extras would find 25% of the content frivolous. I would like to know, if anyone cares to speak to it. Thanks
When I took the Extra exam some years ago there were a number of questions about calculating the discharge time of a capacitor. Completely useless!
Has anyone studied the degredation of received audio by multiple waves nulling each other, like ripples on a pond from two stones tossed in the water. There has to be null points created, along with an echo effect that may not be perceived by the human brain.
Hi! Would you please make a video about Power vs Signal, and how much power is needed to increase the signal strength by an extra S unit on the other station?
ua-cam.com/video/ufr1Nql62Og/v-deo.html
I’m in the process of setting up my shack now. Mostly there. Need a power supply and an SWR meter. But I have been a sub to this channel less than 12 hours and I am already learning the good stuff before the myths and bad info get imbedded too deeply. I’m going to be running QRP on homebrew random wire and dipoles, with relatively short feed lines (20 to 25 feet or less) and with what I have seen so far on this channel, I’m starting to think that these nano VNAs and antenna analyzers are going to be a waste of money that would be better spent on radios.
Good work. Knowing the truth about antennas and transmission lines will set you free from myths that are actually crippling.
I got a NANO VNA and found it very useful for building aerials, knowing at a glance if they were too long or too short. It took quite a while before with nearby objects affecting things and watching an SWR meter not knowing if I had made them too short before realising it. Too easy on 12m. Not cutting them of course.
5 attic dipoles for 20m to 10m, an outdoor inverted vee for 60m and a 4 element 2m collinear which would be too easy to miss the resonant point. My wire elements were longer than expected.
I should now be able to check my low pass filters on my h/b radio.
QRP here with nothing above 5 Watts.
G4GHB.
I do not understand your explanation as to why received signals don't get reflected by the ATU too (but obviously they don't, otherwise I wouldn't hear a thing!). But what makes the difference between the reflected, transmitted power and the purely received power at the ATU location (apart from magnitude)?
Phase. It has a lot to do with the science.
@@NoMoreRadioMyths That doesn't make it clearer to me ☹️
Tube equipment is a lot more robust in a high mismatch one of the myths I’d like to see put to rest is the guys (mostly the CB crowd ) that say they run so much power the antenna tip glows .
I wonder if that’s true? I can only imagine the power some of them are running. And there is high voltage at the tip of an antenna.
@@NoMoreRadioMyths needs to be tried now i have had guys tell me they have had a longwire fail with high power but anything A truck driver tells me I take with a BIG grain of salt 😆
I agree with your analysis. Question, if I may: If you are using an antenna tuner, and the SWR of the antenna therefore doesn't matter (within reasonable limits, of course), then under what conditions would you ever need a Balun or Unun? BTW, I'm a newbie ham. Maybe there is still common mode current? Please explain! 🙂
If your antenna is a dipole and you are feeding it with coax you should use a balun because coax is unbalanced but a center fed dipole is. If you are feeding an off center fed dipole you will need an unun, because both the antenna and the coax are unbalanced. If you use an unun you will probably also need a common mode choke. Some unun's have them build in. Balun Designs, DX Engineering and Palstar Engineering are examples of where you can get them if you don't want to make your own and a good source of information.
@@NoMoreRadioMyths Thank you for your advice and explanation. I've also learned a lot from watching your videos.
Love this. Thank You
You are so welcome!
outstanding pesentation
Many thanks
G9A02 (B)
What is the relationship between high standing wave ratio (SWR) and transmission line loss?
A. There is no relationship between transmission line loss and SWR
B. High SWR increases loss in a lossy transmission line
C. High SWR makes it difficult to measure transmission line loss
D. High SWR reduces the relative effect of transmission line loss
You would answer A? The correct answer is B.
E9A09 (B)
What is antenna efficiency?
A. Radiation resistance divided by transmission resistance
B. Radiation resistance divided by total resistance
C. Total resistance divided by radiation resistance
D. Effective radiated power divided by transmitter output
You'd get this question wrong if you really believe what you said at 7:55 - "full transmitter power is radiated" because then total resistance would always equal radiation resistance.
Perhaps "delivered to the antenna" would have been more accurate.
@@NoMoreRadioMyths I would agree that in most cases, most of the power is delivered to the antenna.
But check out KV5R's Coax Loss Calculator. Using Belden 8236 RG-8 with a 100 foot line, at 14 MHz, play around with SWR and you'll see that you'll double the non-transmitted power by going to 1:1 to 5:1. Will that alone make a meaningful difference? No, probably not: you've gone from about 85W out of the antenna to 70W out, and that's only about 0.8 dB due to the SWR.
Most Amateur radios have built in SWR protection, and they will step back your power output if your SWR is too high in order to protect themselves because the reflected power manifests as voltage that, at sufficient level, can damage components. If it were as simple as "the transmitter has high impedance," then radio manufacturers would not worry about adding this feature.
You're right about antenna tuners though: they do exactly what you need (to lower your SWR). Check out the video "standing up for standing waves" here on YT to see them in action. They're not just fooling the transmitter.
Could "Reflected Power" alternatively be called "Recycled Power"?
I would say yes.
Next explain coax length, phase angles and impedance
I have been playing with 2 verticals
need 2 sections of RG11 75 ohm at quarter wave to combine them
That is easy with single frequency antenna
How does it work co phasing 2 log periodic that cover 50mhz to 1.2ghz?
All equal length of 50 ohm coax and a combiner?
So why my coax question
ua-cam.com/video/ysXPGRmFsjU/v-deo.htmlsi=n7mMgMRJ3Xbc1anE
@@NoMoreRadioMyths Thanks, I missed that video
6 months trying to figure it out, combine wide band antennas
@@NoMoreRadioMyths I've watched that video Mark perhaps on another video put more emphasis on the phase angle and how the reflected power changes the impedance measured along the length of the line and that the actual length of the feedline does matter in this respect
no difference... well a ladder line is balanced, but a coax isn't. Unless these don't make a difference for the purpose of your explanation.
No it doesn't make any difference. The same rules apply in ladder line vs coax.The losses in coax is not because of the copper wire. The losses because of copper is very low. Most of the losses in coax is because of the insulator between the two wires.
Air is one of the best insulator
Correct. No difference regarding reflected power.
@@maartenc6099 thank you!
So, can it be said: the plate and loading controls of a transmitter are for matching the final to 50 ohm coax to the feed point of the transmission line. The ttransmatch is needed only if the transmission line is not matched (non resonant) .?
I assume vhf and uhf would be the same?
Yes but coax losses are much higher.
@@NoMoreRadioMyths Thank you, for the information. You a great help to new hams KQ4ODA.