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!🇺🇸⚡
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
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.
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?
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.
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.
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)
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!
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.
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.
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.
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.
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
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?
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.
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.
Great discussion Dave. However, in this video and the other you did about "Do I Need a Balun?", you discussed that incident where you couldn't get the antenna to tune with the balun and when you removed it, it worked fine. You didn't explain why the balun didn't work in that case. Please explain.
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.
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.
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.
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?
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.
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.
You said that you don't know why the two to four ratio of ballon Transformer is used quite a bit, but I would guess that it's probably for the same reason high voltage power lines are used to transmit electricity across country. With a higher voltage, you lose less power to heat when they get put through the line.
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?
The resistance changes as you go up in frequency because the resistors you use are wire-wound type and they act as inductors when AC is applied to them. What you need is a "non inductive" resistor, ie carbon or metal film type.
Wow, I'm an EE and I've been wondering what all this talk of voltage balun vs current balun is all about. Translated back to conventional engineering lingo, I now know that this is just an autotransformer vs a conventional transformer with two isolated coils. I still don't quite get why this is called "voltage" vs "current" in ham land, but at least I know what they are now!
Yeah, I didn't spend a lot of time on voltage vs current. Basically a voltage balun balances the voltage at the output, and a current balun balances the currents regardless of the voltage.
In technical literature. a voltage balun would be different voltage and a current balun would make a different current. the impedance stays the same but multiple of the turns ratio time the inverse square so to speak. hope that helps some in understanding even tho this is not technical video. i mean that the only real change is in ohms law aspect of voltage and current. 73, ad0am
Excellent explanation. You're the first person who could actually succesfully explain baluns to me. For my own antenna, I'll stick with a choke as displayed at the end of the video (which is not really a balun, is it?).
while discussing current-baluns 11:35 he says: "If you want that kind of current, that's fine." and he leaves it at that. but i'm still studying for the technician class license and dont know that means? i was hoping to learn WHY a balun would be used in this situation but the discussion went in another direction. i must have missed something... i usually do:)
Baluns are used when transitioning between a balanced system (like a dipole antenna) and an unbalanced system (like a coax transmission line). Properly done, it keeps RF where it's supposed to be (inside the coax, and radiated only from the antenna).
The coax run to my Butternut HF9V vertical is grounded at both ends because the vertical itself is grounded. I found if I did not additionally ground it at the station end, I picked up gobs of local noise. I also have an MFJ hexbeam in the back yard about 20 feet up. I've not grounded the coax at the antenna end and it seems to work fine--pretty well, actually. So I guess it depends on the situation.
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.
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
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?
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?
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
Dave, great video. Can I check my understanding of something? I understand why coiling the coax works to create an inductor that prevents RF from coming back on the shield. Am I right to assume that the reason it doesn't prevent RF from moving to the antenna is because the center conductor is shielded, and therefore the center conductor is not also being turned into an inductor?
In coax what happens on the outside of the shield is different from what happens on the inside of the shield. Inside of coax is another world. Ideally, there is no radiation on the outside of the shield. In actual practice, the outside of the shield can carry radiation from the antenna back to the radio. Coiling it to create an inductor creates a reactances that is high enough to inhibit the radiation on the outside of the shield. Doing so does not disturb what's happening inside the coax.
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 ??
Newly licensed Tech and planning on taking my General next month, so forgive the basic question. Doesn't the extra 25' of coax that you used to make the inductor add to the losses in the feed line (due to the extra length)? Because of that, is it more beneficial to use the choke with the ferrite beads? Thanks.
Yes you are correct, in theory. It's a cost trade-off between the co-ax and ferrite beads. You can go either way. At HF the extra 25 feet of coax doesn't add that much loss
Thank you. Watched all of your tech exam videos prior to my test and got a perfect score. Just finished watching all of your general exam videos. Great stuff and much appreciated.
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
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.
This is the video that got me to connect the dots from my electrical knowledge to my lacking antenna/balun knowledge. Thank you sir.
Dave, you are a blessing! Thank you for sharing your experience and wisdom!
Dave, you are a real asset to Amateur Radio. N7KHH 👍🏾
Excellent work OG - I think your best work is with these advanced concepts, thorough and nuanced.
Fantastic video - I learned a lot - Thank you @David Casler - btw, animations that show what's happening 'in the wires' is really helpful!
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!🇺🇸⚡
I will definitely have to watch this one several times...
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?
Simply freaking awesome! I just learned a ton of new stuff!
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
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 ;)
4:1 is because TV's expect 75 ohms on the coax input, but TV antennas are usually 300ohm.
Nice presentation on a confusing subject to a lot of people. I like the , "if you need one they are great"!!!
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.
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.
Brilliant Dave - you make the subject matter real fun to learn. 73s GI8WFA.
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?
Thank you. You're the first person I've heard to give a good, coherent, understandable explanation of this whole topic.
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.
Dave is the best of Elmer's. 👷
Thanks for sharing. It really helps in understanding how balun worked in CCTV.
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.
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)
New subscriber and now working my way through every video. Awesomeness.
Welcome to the channel!
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!
Very well done, Dave!
Very well explained. Thanks again Dave!
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.
How do you determine how many turns of cable to make a choke on different bands...
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.
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.
A wealth of knowledge. thank you :)
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.
Great info Mister Casler, thanks a lot. Very Very helpful for us *hams* in EL81mt
Fabulous explanation - thank you.
Best explanation and diagrams I've found so far explaining baluns. Thanks for the clear explanations and examples!
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
The best explanation yet.
I love your videos. I feel like I'm learning from Obi-Wan himself.
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.
All of my questions answered. Thank you Sir. Steve GJ6WRI
Glad to help
Good Job! Congratulations!
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.
That was super clear. Thank you!
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.
Great discussion Dave. However, in this video and the other you did about "Do I Need a Balun?", you discussed that incident where you couldn't get the antenna to tune with the balun and when you removed it, it worked fine. You didn't explain why the balun didn't work in that case. Please explain.
Another excellent video sir!
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.
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.
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.
Best video on balun ever ! Thanks, i'm in engineering school and i leearned so many things !!
Thanks !!
Excellent!! 73 to you..
Very informative, thanks for teaching complex subjects. 73 de N5EVD
A lot to take in but we’ll explained thank you
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! 🤦🏼♂️
Another great show Dave.
Thanks a lot!! Now I understand choke balinés from matching baluns. So a 1/4 vertical antenna is unbalanced, right?
Thank you Dave!
73's
KP4OSP
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?
Baught a qrp tuner kit wating for delivery. Have a few hand wound units. That was given by my Elmer. At W8FT.
Dave I should have added I am making 2 meter quad antennas so am using sleeve chokes due to light weight and less windloading.
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.
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.
Great video. Thank you.
You said that you don't know why the two to four ratio of ballon Transformer is used quite a bit, but I would guess that it's probably for the same reason high voltage power lines are used to transmit electricity across country. With a higher voltage, you lose less power to heat when they get put through the line.
Thanks!
Thank you for your financial support of this channel! It is greatly appreciated! 73, Dave, KE0OG.
Thanks Dave. I really needed that.
An estate sale yielded two baluns. A 1:1 and a 4:1
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They look identical but I'm not sure how they work..
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?
Wow, great job. Thank you. 73 Pascal VA2PV
The resistance changes as you go up in frequency because the resistors you use are wire-wound type and they act as inductors when AC is applied to them. What you need is a "non inductive" resistor, ie carbon or metal film type.
To a degree, yes. The resistor is composition, not wirewound, but there is inductance in the leads that makes a difference in frequency.
Perfect explanation on a rarely explained topic...73...Roger / NQ8RP
Thank you Dave 73's VK4FPKL
Wow, I'm an EE and I've been wondering what all this talk of voltage balun vs current balun is all about. Translated back to conventional engineering lingo, I now know that this is just an autotransformer vs a conventional transformer with two isolated coils. I still don't quite get why this is called "voltage" vs "current" in ham land, but at least I know what they are now!
Yeah, I didn't spend a lot of time on voltage vs current. Basically a voltage balun balances the voltage at the output, and a current balun balances the currents regardless of the voltage.
In technical literature. a voltage balun would be different voltage and a current balun would make a different current. the impedance stays the same but multiple of the turns ratio time the inverse square so to speak. hope that helps some in understanding even tho this is not technical video. i mean that the only real change is in ohms law aspect of voltage and current.
73, ad0am
Excellent explanation. You're the first person who could actually succesfully explain baluns to me. For my own antenna, I'll stick with a choke as displayed at the end of the video (which is not really a balun, is it?).
It's definitely a balun - converts balanced to unbalanced.
Thanks man, informative as always!
while discussing current-baluns 11:35 he says: "If you want that kind of current, that's fine." and he leaves it at that. but i'm still studying for the technician class license and dont know that means? i was hoping to learn WHY a balun would be used in this situation but the discussion went in another direction. i must have missed something... i usually do:)
Baluns are used when transitioning between a balanced system (like a dipole antenna) and an unbalanced system (like a coax transmission line). Properly done, it keeps RF where it's supposed to be (inside the coax, and radiated only from the antenna).
Great explanation of the topic. Even though I had a basic idea of the topic , I learned something. Thank you. David Byrd KN4BHS
Study coaxial cable! They are not grounded at both ends always. I have had trouble when there was a grounded at the far end!
The coax run to my Butternut HF9V vertical is grounded at both ends because the vertical itself is grounded. I found if I did not additionally ground it at the station end, I picked up gobs of local noise. I also have an MFJ hexbeam in the back yard about 20 feet up. I've not grounded the coax at the antenna end and it seems to work fine--pretty well, actually. So I guess it depends on the situation.
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.
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
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?
Get it well tightened down Dave, 3.5kW is a lot of current!!
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?
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
Thanks Dave for your contribution to the ham community. This was very helpful. KE8RWW. 73
Great video - thanks!
Dave, great video. Can I check my understanding of something? I understand why coiling the coax works to create an inductor that prevents RF from coming back on the shield. Am I right to assume that the reason it doesn't prevent RF from moving to the antenna is because the center conductor is shielded, and therefore the center conductor is not also being turned into an inductor?
In coax what happens on the outside of the shield is different from what happens on the inside of the shield. Inside of coax is another world. Ideally, there is no radiation on the outside of the shield. In actual practice, the outside of the shield can carry radiation from the antenna back to the radio. Coiling it to create an inductor creates a reactances that is high enough to inhibit the radiation on the outside of the shield. Doing so does not disturb what's happening inside the coax.
thank you for the video
This was excellent! Thanks so much
You're welcome
Great video, as always!
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 ??
Newly licensed Tech and planning on taking my General next month, so forgive the basic question. Doesn't the extra 25' of coax that you used to make the inductor add to the losses in the feed line (due to the extra length)? Because of that, is it more beneficial to use the choke with the ferrite beads? Thanks.
Yes you are correct, in theory. It's a cost trade-off between the co-ax and ferrite beads. You can go either way. At HF the extra 25 feet of coax doesn't add that much loss
Thank you. Watched all of your tech exam videos prior to my test and got a perfect score. Just finished watching all of your general exam videos. Great stuff and much appreciated.
Would it make a difference if you used Carbon composition resistors for your tests?
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