From one grey bearded ham to another, "very well presented. Thanks." I'll be watching more. After almost 60 years in the field, and 40 years of not operating at all, baluns have always eluded my understanding of them. Hardly ever needed one but I'm back building antennas and I have no idea what I'll be trying next. Now with the internet sleep will be my only distraction. I finally picked up an MFJ Z-bridge like you show and that will be a lot of fun to play with. 73's OM.
I have a novice argentine license (LU5ARC), an extra american licence (AC1DM) and a foundation british one (M6UON) and only just now watching this video I understood choque baluns. Thank you Dave.
Thanks for breaking this down. I still want to learn more about baluns and ununs, but this video got me thinking about them in a different way. I understand so much more about antennas now.
My understanding is this; if an antenna is not balanced, current (or signal/RF/voltage it's all the same idea) flows back along the shielding of the cable (or one leg of a feedline) to the transceiver. This back flow produces a high SWR reading which can damage the receiver if not corrected. Makes sense so far? A balun which is an RF choke, a line wrapped around a toroid core, absorbs and dissipates this RF before it returns thereby producing an acceptable SWR reading. The reason there are different ratios of baluns is because the amount of turns, equaling RF absorption, is different depending on how unbalanced the antenna is. More unbalanced=more windings around the core=more RF absorbed. That's it!
Smart Man right here, reminds me of my Father silent key (k6hzh) who was also a amature extra and a radar engineer for Lockheed Aircraft from 54' to 78' these guys are the pioneers of the ham radio hobby!🇺🇸⚡
Thanks for the information. I use a 10 turn loop of coax at the junction of coax and ladder line of my 40 mtr G5RV and I wound a transformer/balun [49:1] for my EFHW 40-10 wire antenna.
Very nice presentation. I appreciated that you pronounced the word BALUN correctly. Sometimes they are called “balms” (that’s an ointment) or “balloons” which only adds to the confusion about these devices.
4:1 Baluns are useful between balanced lines for center fed Zepps, Off-center fed (OCF) dipoles with coax, G5RV antennas, full wave loops, NVIS dipoles that are close to ground and have impedance levels near 200 ohms or high impedance feeds for log periodic beams.
Dave - I think you should review your statements regarding coax starting around 2:30. The shield in fact is the second conductor in this RF AC circuit; you have to have at least 2 conductors in a circuit. You can't have a single conductor simultaneously being the supply and return path. RF current equal and opposite to the current in the center conductor does flow on the 'shield'. Ideally, the shield current will be confined to the inner surface of the shield due to skin effect- the surface that can 'see' the center conductor
Hi Dave, In your animation starting at 1:38, you show current flowing back and forth on the center conductor, but no current flowing on the shield. However, there is current flowing on the INSIDE of the shield, and it is equal and opposite to the current on the center conductor. So there should be two arrows going in opposite directions INSIDE the coax. There must be a return path somewhere, and we don't want it on the OUTSIDE of the shield. That's why we might want to use a choke balun. Keep up the good work! 73 de kc0tw.
This explains a lot for me and answers my questions. I'm building a 2m j-pole that I intend to mount on my semi (modern semi bodies are terrible for ground plane antennas. Not very flat and they have a LOT of fiberglass). Instructions I find say I need a balun just below my antenna, but no one seems to agree on how many turns or diameter. So I suppose I can just coil SOME coax a few turns? Anything is better than nothing?
Great lesson, pretty much serve the same purpose just a difference in winding. So, here's my question. When it is appropriate to use a current or voltage balun? What about a advantage and disadvantage between the two?
Ha ha. Yes I've used in the army a beer can as a form for a choke=6 turns then remove the can. tape down the coil and make fast to the mast. Off to the radio we go with tolerable SWR. TKS
Hi Dave, thanks for the video. I understand the need of impedance transformer what ever they call them. However, I'm not quite understand 1:1 balun. Based on this video they are two type, the transformer (1:1 transformer, of cause) and the choke balun. What is the different between them in term of function and performance?
Current doesn't always stay inside coax. It is best of it does and is called differential mode current, but sometimes a portion of it also flows on the outside of the coax called "common mode current". If a dipole exhibits an imbalance for some reason like one side somewhat closer to ground or close to metalic objects such as a metal roof, then common mode current can and will flow on the outside of the shield. Thats where a good, 1:1 current balun should be used!
Thanks Dave. I’m scratching my head while trying to match my 20m efhw vertical (SpiderBeam) antenna. Maybe I’ll jot you down a quick question and maybe you could make a video. All my best to your sound and camera person (XYL). She does an awesome job. I just watched your 1000th video. Congratulations. Keep up the good work. 73!
Hi Dave, great video which I really enjoyed. The only one thing I'm confused with is when or what antenna situation would you decide to use a 4:1 voltage or current balun? Say a Doublet for 80-10m, I would be very grateful if you could help me with this 'voltage or current' choice, does it depend on the type of open line balanced antenna? Many thanks for the informative video.
Nice video Dave! Explanation on choke balun needs more information. Winding few turns of the coax should add inductance on both inner and outer segments of the coax and that should act as common mode choke, which should be same as 1:1 current balun. Assume if it was adding only inductance on the outer braid, then that should be limiting the onward signal from the TX also.
No. What goes on inside the coax is independent of what happens on the outside. The signals inside the coax, going either way, are not affected by the coax loop. Only the current flowing on the outside of the coax is affected. The transmitted signal will not be on the outer braid. The ARRL Handbook and the ARRL Antenna Book both explain this in some detail.
Thanks for the great info. Just an FYI, when using an ohmmeter to test resistance values, touching the resistor legs and/or test terminals will vary the readings as our bodies create resistance as well. I am wondering if the coax loops or balun windings help at all with LED and fluorescent shop light interference? Thanks for the detailed video.
True. But a sweaty person will produce an ohmic resistance of no less than 200~150k Ohms (I've never had less than 300k myself) between hands. So any value below 1/5 of that shouldn't be significantly affected
Hi Dave, Is there a way to calculate how many ferrites are needed in a coax going to a 2m Jpole? I think this method would look cleaner than a bunch of loops of coax in my neighborhood. I am using RG-8X for a 40' run. Otherwise, barring this.. can one estimate the number of turns of 8X of, say 4-5" diameter ??
with reference to 8:17 I think the reason is same as why power lines use very high voltages. High voltage means smaller currents. With long cables the I squared losses will reduce the power to the end of line. But using a transformer to convert the signal to a high voltage means proportionally lower current, this 4:1 hence reduces those I squared losses. eg P=IxIxR. My guess is at the arial end, that 4:1 is simply converted back to 50ohms. It means you can have much longer cable as far less I squared losses will occur. But that is a wild guess as I know bugger all about transmission lines.
Some 50 years ago when I got my first call sign, we used to make baluns out of coil of coax. Why nobody uses them anymore? They were wideband transformers not dependent on the frequency and were capable to transfer kilowatts of power. Now with all these different ferrite toroids who knows what performance they'll have all over the spectrum and what loss of power is going to be transformed into heat?
@John Cliff No sir, I wasn't talking about the RF choke made of coax. Some almost 50 years ago, in our radio club YU5CEF back in Macedonia (Z37CEF now) Europe we bought a fabricated (I don't know who made it though) multiband antenna W3DZZ. It had a balun made out of coax to match the balanced dipole to the unbalanced coax. I remember bot hot sides of the coax loop were connected to both sides of the dipole while the connecting coax was connected to one side and the shield were all connected together. We were not aware of toroid baluns at the time. (de W5DMA)
I'm confused by the coaxial cable graphic where there is no current in the shield because it's ground...I thought ground serves as the return path...and hence the shield really does carry current...what am I missing?
Dave your doing beautiful job with your presentations keep up the good work. I have a question for you I can't figure out why all the articles I see for sleeve chokes tell me that the outside braid of a sleeve should be cut and allowed for the velocity factory from inside the coax when the whole idea for the sleeve on the outside at a quarter wavelength is to offer a higher impedance than the 50 ohm inside . I have made it both ways allowing for the velocity factor the coax which makes it much shorter and it doesn't seem to work as when I use it with open air frequency for outside braid that works . So are all these articles I'm seeing wrong? I put heat shrink on the outside of these chokes and if that has ,or the outside coax cover has an effect it can't be much because I tried to allow just a little velocity factor and didn't seam to matter ,guess it won't as long as the outside impedance is greater than the rg8x 50 ohm's.
I saw a video showing how to make an antenna that should cover 40 M through 6 M I think may have been just up to 10 M. But it had the wires out with 600 ohm ladder line coming down connected to RG8 and a coil of coax. I don't remember the length of the wires and the ladder line. But I was thinking that it would help if there was a balun in there to help change from the 600 ohm to 50 ohm. I am new to this and learning. But I think something like a 4:1 balun would make the ohms match better. If I wanted to make one of the antennas what would be a good balun to try in there? They say it isn't needed that the 600 ohm ladder line will make it 600 ohms to the antenna. I am new at this but I don't understand how that would work.
Dave you did a awesome job on a very complicated subject, l do however have a couple, dare I say, squabbles :o) , perhaps more like friendly advice. First, you should always use a 1:1 current balun when connecting an unbalanced radio to a balance antenna such as a dipole to prevent current from running back down the outside of your coax shield and the other was your advice on building your own. It is a little bit more complicated then just wrapping some wire around a big toroid. Peter from the TRX Bench did a wonderful 4 part series on Baluns, just search youtube for TRX Bench balun (videos 100, 101, 105 and 131) and if you want more information as to why the type of wire matters (actually it is the diameter) just do a wiki on telegraph equation. After viewing these videos you will be able to build a Balun better than anything you could buy at a fraction of the cost and you will be able to customize them to your needs. Peter has an awesome channel and his balun videos are must see for any ham. 73
Thanks for the TRX que. I'm currently building a 3 element yagi (my first antenna build. Also, the first time I've used a milling machine!) tuned to 144mhz. I was hoping I could use it for an experiment in RX on 143.050 and the lower end of the 2m band for TX. As I'm building it, I've been wondering about a balun. A yagi It is just a dipole with clothes on, but I've been scratching my head about how to implement it.
Hi, Dave If I were to put up a shortwave dipole, each leg 12', without balun/transformer/impedance matcher, which bands should I expect to receive? Many thanks and 73 N4ANO
hi mr david am real new about the balum thing.. what you think here is my project 140 ft wire loop try ing to use it on cb band ch 20 and 7 meter 7263 balum 4.1 home made type best it will match is 2.1 swr need lower 1.2 is my desired swr what you suggest
Would it hurt anything to just wind a choke at the dipole connection regardless of whether you know if you have RFI or not? If not, are there specific ummm...Specifications of how many winds/how large of a loop for each band/meter?
Hi Dave, thanks for the fantastic videos. Could you give a little more detail on the matching of balanced feedline with a dipole, you mentioned feeding a dipole with ladder line in the video. For example if a dipole is 50 ohm at it's feed point but I connect 300 ohm ladder line for a 100ft run how would this change things viruses just sending coax up to the antenna. Thanks!
You would probably need a wide - range tuner with the open wire feed line. However, when all is said and done the total losses in the antenna system are lower with ladder line.
If your dipole is close to 50 Ohm, you would not use ladder line. You would simply put a 1:1 BalUn at the transition point. Ladder line is for the cases where you want to use a dipole for frequencies were it is not resonant. Here, the advantage of ladder line is lower loss, which is important, if the SWR on the line is high. So, you use ladder line and a balanced antenna tuner to transform from whatever to 50 Ohm unbalanced.
I made a 20M Dipole Antenna. I will not be using this 20M dipole for any other frequencies other than the 20M that it was made for. Is a balun needed for this a 20M Dipole antenna? Again I will not be using this 20M dipole for any other frequencies other than the 20M that it was made for. I also have an isolator. Would I need both? Do they pretty much do the same job?
Dave, can I use shielded cord for a feed in. I have some 18 AWG 2 conductor with a ground wire, shielded cord. It looks a lot the old rs-232 or centronics computer cord. This is going to be used for receiving only.
David, thanks for the video. I noticed that your explanation is in contradiction with the article by W7EL you are refering to. The current flows in both directions inside the coax cable, through the inner conducter and the inner surface of the shield, the same way it does in the symmetric feed. A balun prevents the current to flow on the outer surface of the shield. According to your video the current flows only through the inner conducter, which doesn't seem to be right.
In a proper coax, with all impedances matched, the current is unbalanced. The inner shield is ground, and the current on the inner conductor is AC, back and forth. If there is an imbalance, or impedances are not matched, then things change. I think what I've shown in the video is correct.
@@davecasler The fact that the shield is ground only means that we consider it a zero voltage reference. It doesn't mean that there is no current in it. The reason why bifilar 1:1 current balun works is that there are two currents with 180 degree shift flowing through it, one through the middle part of the cable and one through the inner part of the shield. Magnetic fields of these currents cancel each other, thus balun doesn't stop them. The current could choose to flow through the outher part of the shield (because from current's point of view there is no difference where to flow at the end of the cable - through the antenna or through the outer part of the shield). However this would turn the balun to the coil (choke) because now there is no opposite current to cancel the magnetic field. This fact creates high impedance for this patch.
Thank you for making this video. This has always been complicated for me to understand. In the video you use a transformer but I am seeing on utube that hams are using coax wrapped around a pipe calculating the turns for the center frequency. can you explain how this works instead of using a transformer, and where are these transformers found? Thanks George
Coax wrapped around something is called a "choke balun." Its purpose is to remove the RF from the outside of the coax shield so the signal you want stays inside the coax.
nuts dave now i need to learn more about it because now i want to see if a balun would improve my Rx antennas for fm radio on 3 meters and for aviation band and one for 1090mhz ads-b. the aviation band i made a Rx ground plane half wavelength, its real fun just to see the extra Rx range i get from home made antennas. the dutch government wants ham's to pay 35 bucks a year these days to just be a licensed ham so i will stay with Rx.
what would happen if you used a micro adjustable variable resistor/potentiometer in place of or in series with a fixed resistor to fine tune the ohm value?
No Dave! The coax MUST have return current on the inside wall of the shield! You see 1:4 baluns a lot because it just naturally comes out with 2 windings or 4 windings, as you showed.
The best SWR you can achieve without any balun. Say how to proper measure and calculate the CMRR of a 1:1 current balun with a two port VNA. The current balun itself is a three port device.
TRX Bench #101 Balun part 2 describes the wire and Ferrite Toroid to use for an accurate Balun. Beware of the Ferrite Material being sold - I purchased what was to be an F114-43 Toroid Core after forming the Balun it only has a low SWR on the 13Mhz Frequency a true 43 Composition Ferrite Toroid will produce a low SWR on all bands when used with 18 Stranded Teflon Wire.
Just what I was looking for. Printed off the W7EL paper for bedtime reading. At my previous qth I had problems with rf in the shack from a dipole run along the edge of the roof, I used a dozen salvaged ferrites just threaded on the co-ax, worked a treat.
Minute 11:02 you show the phyiscal balun and i think you saybit matches the previous diagram you had. the physical one seems to have two separate loops? and has 8 turns each side. diagram was a single 4 turns. i am confused by this. Also why are you able has you said to operate a dipole with no Balun sometimes?
I have a 1-1 balun - 1 eye bolt on each side, one eye bolt on one end - then coax connector on other end.From 1 eye bolt to cb antenna, - top eye bolt for support - what size and type wire to use for connections balun to antenna ?
Balun=to a balanced antenna, UnUn=to an unbalanced antenna to start. The real mystery to me is the fact that twin lead has less loss than coaxial cable.
Hi Dave, great video about baluns. Thank's I have learned a bit more on the subject. I've made ones out of unmarked toroid material that has come from old power supplies and ones that I've bought at rallies. i.e take your pick from a big box. I've read and read scores of literature on the subject and am still confused about which material is best to use. Some advise on using dust iron verses ferrite due to saturation limits etc.-etc. I did get hold of a quite large toroid from a rally that had a light grey coating?. It was very heavy for the size. Ended up formed into a coaxial choke at the bottom of homebrew twin feed from a G5RV. It certainly anchored the twin feeder into a nice straight line if nothing else.It actually seemed to work ok into 75 ohm 1/2" dia. coax back to the shack. Got out well on 80 - 20m Plus 160 as a centre loaded T, from U.K to VK on a G5RV and some people say they don't work ???. Thank's again Dave. 73 de John-G0WXU.
The problem with toroid cores is that different manufacturers use different color codes for core type. And then none of the manufacturers put their name on the cores! So if you encounter an unknown core, it's anybody's guess.
Remembering Navy & college I got my Extra (AG7MW) on the first try. That doesn't mean I know something. I have a MFJ-9200 QRP with a SWR, tuner, then 50 feet of RG-8X going to an MFJ mini G5RV. I understood that I needed an isolation balun, so I did. Should I have gotten another? What tape do you recommend to keep the rain out of the connector? It might be too late.
Sounds like you have everything you need. Just add perseverance and you'll have lots of contacts! Re the rain, electrical tape is fine for the short term. Look at DX Engineering's web page for sealing tapes.
From one grey bearded ham to another, "very well presented. Thanks." I'll be watching more. After almost 60 years in the field, and 40 years of not operating at all, baluns have always eluded my understanding of them. Hardly ever needed one but I'm back building antennas and I have no idea what I'll be trying next. Now with the internet sleep will be my only distraction. I finally picked up an MFJ Z-bridge like you show and that will be a lot of fun to play with. 73's OM.
This is the video that got me to connect the dots from my electrical knowledge to my lacking antenna/balun knowledge. Thank you sir.
Fantastic video - I learned a lot - Thank you @David Casler - btw, animations that show what's happening 'in the wires' is really helpful!
Dave, you are a blessing! Thank you for sharing your experience and wisdom!
I have a novice argentine license (LU5ARC), an extra american licence (AC1DM) and a foundation british one (M6UON) and only just now watching this video I understood choque baluns. Thank you Dave.
Thanks for breaking this down. I still want to learn more about baluns and ununs, but this video got me thinking about them in a different way. I understand so much more about antennas now.
Excellent work OG - I think your best work is with these advanced concepts, thorough and nuanced.
Simply freaking awesome! I just learned a ton of new stuff!
My understanding is this; if an antenna is not balanced, current (or signal/RF/voltage it's all the same idea) flows back along the shielding of the cable (or one leg of a feedline) to the transceiver. This back flow produces a high SWR reading which can damage the receiver if not corrected. Makes sense so far?
A balun which is an RF choke, a line wrapped around a toroid core, absorbs and dissipates this RF before it returns thereby producing an acceptable SWR reading.
The reason there are different ratios of baluns is because the amount of turns, equaling RF absorption, is different depending on how unbalanced the antenna is.
More unbalanced=more windings around the core=more RF absorbed. That's it!
Awesome! Pure gold, thank you very much, now I finally understand what it is, what it's for and where/how to use one. 73 from NL
Very well explained. Thanks again Dave!
I will definitely have to watch this one several times...
Some really great info here, and presented at a level that you don't need to be a Broadcast Engineer to understand. Well done and thanks from KM2U ;)
Dave, you are a real asset to Amateur Radio. N7KHH 👍🏾
Smart Man right here, reminds me of my Father silent key (k6hzh) who was also a amature extra and a radar engineer for Lockheed Aircraft from 54' to 78' these guys are the pioneers of the ham radio hobby!🇺🇸⚡
A wealth of knowledge. thank you :)
You don't say where it's better use a voltage or current balun, so if I understand correctly, it's a free choice. You just see what works best?
Nice presentation on a confusing subject to a lot of people. I like the , "if you need one they are great"!!!
New subscriber and now working my way through every video. Awesomeness.
Welcome to the channel!
Brilliant Dave - you make the subject matter real fun to learn. 73s GI8WFA.
Thanks Dave. I really needed that.
Thanks for the information. I use a 10 turn loop of coax at the junction of coax and ladder line of my 40 mtr G5RV and I wound a transformer/balun [49:1] for my EFHW 40-10 wire antenna.
Thanks for sharing. It really helps in understanding how balun worked in CCTV.
Great info Mister Casler, thanks a lot. Very Very helpful for us *hams* in EL81mt
Very well done, Dave!
Another excellent video sir!
Another great show Dave.
Great video, as always!
Thanks man, informative as always!
Best video on balun ever ! Thanks, i'm in engineering school and i leearned so many things !!
Thanks !!
That was super clear. Thank you!
Very nice presentation. I appreciated that you pronounced the word BALUN correctly. Sometimes they are called “balms” (that’s an ointment) or “balloons” which only adds to the confusion about these devices.
The best explanation yet.
Good Job! Congratulations!
Fabulous explanation - thank you.
4:1 is because TV's expect 75 ohms on the coax input, but TV antennas are usually 300ohm.
Great video - thanks!
Great video. Thank you.
4:1 Baluns are useful between balanced lines for center fed Zepps, Off-center fed (OCF) dipoles with coax, G5RV antennas, full wave loops, NVIS dipoles that are close to ground and have impedance levels near 200 ohms or high impedance feeds for log periodic beams.
This was excellent! Thanks so much
You're welcome
Thank you Dave!
73's
KP4OSP
thank you for the video
How do you determine how many turns of cable to make a choke on different bands...
Dave - I think you should review your statements regarding coax starting around 2:30. The shield in fact is the second conductor in this RF AC circuit; you have to have at least 2 conductors in a circuit. You can't have a single conductor simultaneously being the supply and return path. RF current equal and opposite to the current in the center conductor does flow on the 'shield'. Ideally, the shield current will be confined to the inner surface of the shield due to skin effect- the surface that can 'see' the center conductor
And all that aside, this was a very good presentation. Nicely done.
Thanks a lot!! Now I understand choke balinés from matching baluns. So a 1/4 vertical antenna is unbalanced, right?
Great explanation of the topic. Even though I had a basic idea of the topic , I learned something. Thank you. David Byrd KN4BHS
Hi Dave,
In your animation starting at 1:38, you show current flowing back and forth on the center conductor, but no current flowing on the shield. However, there is current flowing on the INSIDE of the shield, and it is equal and opposite to the current on the center conductor. So there should be two arrows going in opposite directions INSIDE the coax. There must be a return path somewhere, and we don't want it on the OUTSIDE of the shield. That's why we might want to use a choke balun.
Keep up the good work! 73 de kc0tw.
This explains a lot for me and answers my questions. I'm building a 2m j-pole that I intend to mount on my semi (modern semi bodies are terrible for ground plane antennas. Not very flat and they have a LOT of fiberglass). Instructions I find say I need a balun just below my antenna, but no one seems to agree on how many turns or diameter. So I suppose I can just coil SOME coax a few turns? Anything is better than nothing?
Great lesson, pretty much serve the same purpose just a difference in winding. So, here's my question.
When it is appropriate to use a current or voltage balun?
What about a advantage and disadvantage between the two?
Excellent!! 73 to you..
Thank you. You're the first person I've heard to give a good, coherent, understandable explanation of this whole topic.
Would it make a difference if you used Carbon composition resistors for your tests?
Can I see a Picture of a built Toroid with 200 ohm resistor please, Cant figure out where the resistor goes
Ha ha. Yes I've used in the army a beer can as a form for a choke=6 turns then remove the can. tape down the coil and make fast to the mast. Off to the radio we go with tolerable SWR. TKS
Very informative, thanks for teaching complex subjects. 73 de N5EVD
Hi Dave, thanks for the video. I understand the need of impedance transformer what ever they call them. However, I'm not quite understand 1:1 balun. Based on this video they are two type, the transformer (1:1 transformer, of cause) and the choke balun. What is the different between them in term of function and performance?
Current doesn't always stay inside coax. It is best of it does and is called differential mode current, but sometimes a portion of it also flows on the outside of the coax called "common mode current". If a dipole exhibits an imbalance for some reason like one side somewhat closer to ground or close to metalic objects such as a metal roof, then common mode current can and will flow on the outside of the shield. Thats where a good, 1:1 current balun should be used!
Thanks Dave. I’m scratching my head while trying to match my 20m efhw vertical (SpiderBeam) antenna. Maybe I’ll jot you down a quick question and maybe you could make a video. All my best to your sound and camera person (XYL). She does an awesome job. I just watched your 1000th video. Congratulations. Keep up the good work. 73!
Thanks!
Wow, great job. Thank you. 73 Pascal VA2PV
Hi Dave, great video which I really enjoyed. The only one thing I'm confused with is when or what antenna situation would you decide to use a 4:1 voltage or current balun? Say a Doublet for 80-10m, I would be very grateful if you could help me with this 'voltage or current' choice, does it depend on the type of open line balanced antenna? Many thanks for the informative video.
I love your videos. I feel like I'm learning from Obi-Wan himself.
Nice video Dave! Explanation on choke balun needs more information. Winding few turns of the coax should add inductance on both inner and outer segments of the coax and that should act as common mode choke, which should be same as 1:1 current balun. Assume if it was adding only inductance on the outer braid, then that should be limiting the onward signal from the TX also.
No. What goes on inside the coax is independent of what happens on the outside. The signals inside the coax, going either way, are not affected by the coax loop. Only the current flowing on the outside of the coax is affected. The transmitted signal will not be on the outer braid. The ARRL Handbook and the ARRL Antenna Book both explain this in some detail.
Thanks for the great info. Just an FYI, when using an ohmmeter to test resistance values, touching the resistor legs and/or test terminals will vary the readings as our bodies create resistance as well.
I am wondering if the coax loops or balun windings help at all with LED and fluorescent shop light interference? Thanks for the detailed video.
True. But a sweaty person will produce an ohmic resistance of no less than 200~150k Ohms (I've never had less than 300k myself) between hands. So any value below 1/5 of that shouldn't be significantly affected
A nicely succinct video. Thanks. Glen, N0QFT
Hi Dave, Is there a way to calculate how many ferrites are needed in a coax going to a 2m Jpole? I think this method would look cleaner than a bunch of loops of coax in my neighborhood. I am using RG-8X for a 40' run. Otherwise, barring this.. can one estimate the number of turns of 8X of, say 4-5" diameter ??
All of my questions answered. Thank you Sir. Steve GJ6WRI
Glad to help
with reference to 8:17 I think the reason is same as why power lines use very high voltages. High voltage means smaller currents. With long cables the I squared losses will reduce the power to the end of line. But using a transformer to convert the signal to a high voltage means proportionally lower current, this 4:1 hence reduces those I squared losses. eg P=IxIxR. My guess is at the arial end, that 4:1 is simply converted back to 50ohms. It means you can have much longer cable as far less I squared losses will occur.
But that is a wild guess as I know bugger all about transmission lines.
Some 50 years ago when I got my first call sign, we used to make baluns out of coil of coax. Why nobody uses them anymore? They were wideband transformers not dependent on the frequency and were capable to transfer kilowatts of power. Now with all these different ferrite toroids who knows what performance they'll have all over the spectrum and what loss of power is going to be transformed into heat?
@John Cliff No sir, I wasn't talking about the RF choke made of coax. Some almost 50 years ago, in our radio club YU5CEF back in Macedonia (Z37CEF now) Europe we bought a fabricated (I don't know who made it though) multiband antenna W3DZZ. It had a balun made out of coax to match the balanced dipole to the unbalanced coax. I remember bot hot sides of the coax loop were connected to both sides of the dipole while the connecting coax was connected to one side and the shield were all connected together. We were not aware of toroid baluns at the time. (de W5DMA)
Thank you Dave 73's VK4FPKL
I'm confused by the coaxial cable graphic where there is no current in the shield because it's ground...I thought ground serves as the return path...and hence the shield really does carry current...what am I missing?
There is current on the inside of the shield. Hopefully it isn't also on the outside of the shield.
Dave your doing beautiful job with your presentations keep up the good work.
I have a question for you I can't figure out why all the articles I see for sleeve chokes tell me that the outside braid of a sleeve should be cut and allowed for the velocity factory from inside the coax when the whole idea for the sleeve on the outside at a quarter wavelength is to offer a higher impedance than the 50 ohm inside . I have made it both ways allowing for the velocity factor the coax which makes it much shorter and it doesn't seem to work as when I use it with open air frequency for outside braid that works . So are all these articles I'm seeing wrong?
I put heat shrink on the outside of these chokes and if that has ,or the outside coax cover has an effect it can't be much because I tried to allow just a little velocity factor and didn't seam to matter ,guess it won't as long as the outside impedance is greater than the rg8x 50 ohm's.
Hi Debbie, I'm a bit confused by what you're describing. Can you send me a drawing or photo to hamradioanswers@gmail.com?
I saw a video showing how to make an antenna that should cover 40 M through 6 M I think may have been just up to 10 M. But it had the wires out with 600 ohm ladder line coming down connected to RG8 and a coil of coax. I don't remember the length of the wires and the ladder line. But I was thinking that it would help if there was a balun in there to help change from the 600 ohm to 50 ohm. I am new to this and learning. But I think something like a 4:1 balun would make the ohms match better. If I wanted to make one of the antennas what would be a good balun to try in there? They say it isn't needed that the 600 ohm ladder line will make it 600 ohms to the antenna. I am new at this but I don't understand how that would work.
Perfect explanation on a rarely explained topic...73...Roger / NQ8RP
Dave is the best of Elmer's. 👷
Dave you did a awesome job on a very complicated subject, l do however have a couple, dare I say, squabbles :o) , perhaps more like friendly advice. First, you should always use a 1:1 current balun when connecting an unbalanced radio to a balance antenna such as a dipole to prevent current from running back down the outside of your coax shield and the other was your advice on building your own. It is a little bit more complicated then just wrapping some wire around a big toroid. Peter from the TRX Bench did a wonderful 4 part series on Baluns, just search youtube for TRX Bench balun (videos 100, 101, 105 and 131) and if you want more information as to why the type of wire matters (actually it is the diameter) just do a wiki on telegraph equation. After viewing these videos you will be able to build a Balun better than anything you could buy at a fraction of the cost and you will be able to customize them to your needs. Peter has an awesome channel and his balun videos are must see for any ham. 73
Thanks for the TRX que. I'm currently building a 3 element yagi (my first antenna build. Also, the first time I've used a milling machine!) tuned to 144mhz. I was hoping I could use it for an experiment in RX on 143.050 and the lower end of the 2m band for TX. As I'm building it, I've been wondering about a balun. A yagi It is just a dipole with clothes on, but I've been scratching my head about how to implement it.
Thanks for the info.
Is all this applied to reception only antennas or only to transmision ?
All of this helps reception some. But the primary purpose of careful matching is for transmitting.
Hi, Dave
If I were to put up a shortwave dipole, each leg 12', without balun/transformer/impedance matcher, which bands should I expect to receive?
Many thanks and 73
N4ANO
hi mr david am real new about the balum thing.. what you think here is my project 140 ft wire loop try ing to use it on cb band ch 20 and 7 meter 7263 balum 4.1 home made type best it will match is 2.1 swr need lower 1.2 is my desired swr what you suggest
Would it hurt anything to just wind a choke at the dipole connection regardless of whether you know if you have RFI or not?
If not, are there specific ummm...Specifications of how many winds/how large of a loop for each band/meter?
Hi Dave, thanks for the fantastic videos. Could you give a little more detail on the matching of balanced feedline with a dipole, you mentioned feeding a dipole with ladder line in the video. For example if a dipole is 50 ohm at it's feed point but I connect 300 ohm ladder line for a 100ft run how would this change things viruses just sending coax up to the antenna. Thanks!
You would probably need a wide - range tuner with the open wire feed line. However, when all is said and done the total losses in the antenna system are lower with ladder line.
If your dipole is close to 50 Ohm, you would not use ladder line. You would simply put a 1:1 BalUn at the transition point. Ladder line is for the cases where you want to use a dipole for frequencies were it is not resonant. Here, the advantage of ladder line is lower loss, which is important, if the SWR on the line is high. So, you use ladder line and a balanced antenna tuner to transform from whatever to 50 Ohm unbalanced.
Beautiful..
Baught a qrp tuner kit wating for delivery. Have a few hand wound units. That was given by my Elmer. At W8FT.
I made a 20M Dipole Antenna. I will not be using this 20M dipole for any other frequencies other than the 20M that it was made for. Is a balun needed for this a 20M Dipole antenna? Again I will not be using this 20M dipole for any other frequencies other than the 20M that it was made for. I also have an isolator. Would I need both? Do they pretty much do the same job?
This was not the first video on this subject I should have watched-more confused now. I’m going to check out David’s earlier videos. Sheesh! 🤦🏼♂️
Dave, can I use shielded cord for a feed in. I have some 18 AWG 2 conductor with a ground wire, shielded cord. It looks a lot the old rs-232 or centronics computer cord. This is going to be used for receiving only.
For receive, you can pretty much use anything.
David, thanks for the video. I noticed that your explanation is in contradiction with the article by W7EL you are refering to. The current flows in both directions inside the coax cable, through the inner conducter and the inner surface of the shield, the same way it does in the symmetric feed. A balun prevents the current to flow on the outer surface of the shield. According to your video the current flows only through the inner conducter, which doesn't seem to be right.
In a proper coax, with all impedances matched, the current is unbalanced. The inner shield is ground, and the current on the inner conductor is AC, back and forth. If there is an imbalance, or impedances are not matched, then things change. I think what I've shown in the video is correct.
@@davecasler The fact that the shield is ground only means that we consider it a zero voltage reference. It doesn't mean that there is no current in it. The reason why bifilar 1:1 current balun works is that there are two currents with 180 degree shift flowing through it, one through the middle part of the cable and one through the inner part of the shield. Magnetic fields of these currents cancel each other, thus balun doesn't stop them. The current could choose to flow through the outher part of the shield (because from current's point of view there is no difference where to flow at the end of the cable - through the antenna or through the outer part of the shield). However this would turn the balun to the coil (choke) because now there is no opposite current to cancel the magnetic field. This fact creates high impedance for this patch.
Thank you for making this video. This has always been complicated for me to understand. In the video you use a transformer but I am seeing on utube that hams are using coax wrapped around a pipe calculating the turns for the center frequency. can you explain how this works instead of using a transformer, and where are these transformers found? Thanks George
Coax wrapped around something is called a "choke balun." Its purpose is to remove the RF from the outside of the coax shield so the signal you want stays inside the coax.
nuts dave now i need to learn more about it because now i want to see if a balun would improve my Rx antennas for fm radio on 3 meters and for aviation band and one for 1090mhz ads-b. the aviation band i made a Rx ground plane half wavelength, its real fun just to see the extra Rx range i get from home made antennas. the dutch government wants ham's to pay 35 bucks a year these days to just be a licensed ham so i will stay with Rx.
what would happen if you used a micro adjustable variable resistor/potentiometer in place of or in series with a fixed resistor to fine tune the ohm value?
You’d lose power to heat. Reactive components store and re-release energy but don’t dissipate it.
No Dave! The coax MUST have return current on the inside wall of the shield! You see 1:4 baluns a lot because it just naturally comes out with 2 windings or 4 windings, as you showed.
The best SWR you can achieve without any balun. Say how to proper measure and calculate the CMRR of a 1:1 current balun with a two port VNA. The current balun itself is a three port device.
TRX Bench #101 Balun part 2 describes the wire and Ferrite Toroid to use for an accurate Balun. Beware of the Ferrite Material being sold - I purchased what was to be an F114-43 Toroid Core after forming the Balun it only has a low SWR on the 13Mhz Frequency a true 43 Composition Ferrite Toroid will produce a low SWR on all bands when used with 18 Stranded Teflon Wire.
Just what I was looking for. Printed off the W7EL paper for bedtime reading. At my previous qth I had problems with rf in the shack from a dipole run along the edge of the roof, I used a dozen salvaged ferrites just threaded on the co-ax, worked a treat.
Minute 11:02 you show the phyiscal balun and i think you saybit matches the previous diagram you had.
the physical one seems to have two separate loops? and has 8 turns each side. diagram was a single 4 turns.
i am confused by this.
Also why are you able has you said to operate a dipole with no Balun sometimes?
I have a 1-1 balun - 1 eye bolt on each side, one eye bolt on one end - then coax connector on other end.From 1 eye bolt to cb antenna, - top eye bolt for support - what size and type wire to use for connections balun to antenna ?
I think most CB is vertically polarized. You can probably use just about any kind of wire you want.
Balun=to a balanced antenna, UnUn=to an unbalanced antenna to start.
The real mystery to me is the fact that twin lead has less loss than coaxial cable.
Hi Dave,
great video about baluns. Thank's I have learned a bit more on the subject. I've made ones out of unmarked toroid material that has come from old power supplies and ones that I've bought at rallies. i.e take your pick from a big box. I've read and read scores of literature on the subject and am still confused about which material is best to use. Some advise on using dust iron verses ferrite due to saturation limits etc.-etc. I did get hold of a quite large toroid from a rally that had a light grey coating?. It was very heavy for the size. Ended up formed into a coaxial choke at the bottom of homebrew twin feed from a G5RV. It certainly anchored the twin feeder into a nice straight line if nothing else.It actually seemed to work ok into 75 ohm 1/2" dia. coax back to the shack. Got out well on 80 - 20m Plus 160 as a centre loaded T, from U.K to VK on a G5RV and some people say they don't work ???. Thank's again Dave. 73 de John-G0WXU.
The problem with toroid cores is that different manufacturers use different color codes for core type. And then none of the manufacturers put their name on the cores! So if you encounter an unknown core, it's anybody's guess.
Hello sir,excellent video.By the way,my question is:
Where can I simulate a 4:1 balun(current)?I mean in which software?
You could try SPICE or something like that. I don't have an answer to your question. Perhaps another viewer does.
Remembering Navy & college I got my Extra (AG7MW) on the first try. That doesn't mean I know something. I have a MFJ-9200 QRP with a SWR, tuner, then 50 feet of RG-8X going to an MFJ mini G5RV. I understood that I needed an isolation balun, so I did. Should I have gotten another? What tape do you recommend to keep the rain out of the connector? It might be too late.
Sounds like you have everything you need. Just add perseverance and you'll have lots of contacts! Re the rain, electrical tape is fine for the short term. Look at DX Engineering's web page for sealing tapes.