To Balun or not to Balun...

Ham radio is about learning, and sharing wut you learn, it's something I like to do. I hope this can help others who may be struggling with "hobby funding". Just keep in mind, sometimes the simplest answer, is the best answer.

For several years, I've used a simple home made dipole using a home made center insulator, electric fence "dog bones" and antenna wire from "the Shack"..
Everything worked fine.. But, all this stuff about baluns, coax, ladder line, etc made deciding how to make the best functional, low cost antenna a real chore....


Ok, my simple 126' horzontal dipole, (63 feet each side) center fed ( pvc pipe cap and plug with so-239 and screws ) with RG8-X ( so it would be light weight being end supported) worked fine from 6m to most of 160, it even found sweet spots on 2m. go figure.. I even put up some for my friends, all with close to the same good results.

Then it happened. My friend Mike K7JML, ( a victious name and call ) called, said his radio worked horribly, except on 80m, he was really frustrated. So after some research, checking coax, connections etc, I found he had modified the dipole we put up with a really nice new 80m BALUN..
Ok, new center insulator shouldn't make much differance, but it did. Now this simple, and very functional dipole, didn't function except on 80m. The really bothered me.. So I started asking questions, and got some really good answers.. this one I like best :
"Baluns: Some swear by them, others at them. Do you need one, Nope. "
Here are the answers I got..
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""""" Personally, I do not have a balun. What I did was (in fact all my antennas)
wind an RF Choke at the antenna end of the coax. Wind maybe 6-8 turns of RG-
213 (or whatever you are using) about a foot below the dipole center
insulator. If you make the 6-8 turns maybe 8-12 inches in diameter and tape
it together then let it drop down. Leave an extra 3-4 feet of coax in your
feed line and wind the coil. this is an RF CHoke. Some of the ARRL handbooks
show this also.

A Balun does not "eliminate" RF. What the balun does, as Glen (K9STH) and
other have pointed out is convert the unbalanced Coax to a balanced antenna.
In the process of conversion RF is Not really eliminated, just put somewhere
else.

A dipole is a balanced antenna. Period. However people for eons have used
coax to feed a dipole. A dipole, by definition is about 70 ohms. RG-8/58/213
is 50 ohm stuff. TV coax, RG-6/59 is 75 ohm and in reality is a better match
for a dipole than the 50 ohm stuff. But, that said, people for eons have used
50 ohm coax. The resulting SWR mismatch is on the order of 1.3:1 so....it can
be said also...so what. No big deal at all. It will work either way and work
just as well either way.

In older days, we used to feed a dipole with 72 ohm feedline (like a zip cord)
and then at the shack end, install a Heathkit Balun and then RG-8 to the
antenna relay. Most rigs did not have built in antenna changeover relays
until later on. 72 ohm coax, twin lead or any open wire feeder has its own
problems in mounting. You just don't mount it like coax, twisted to the mast
or antenna support. It has to be "stood off" from the mast and antenna.
Hence the name of "Stand Off's" that you see in pictures.

However, that is ancient history. Glen (K9STH) and many others on QRZ and QTH
as well, have tried to answer your questions about baluns. I think that Tex
(WA0KZL) did a pretty good job also. I have known Tex for years.

Do you need one. Nope. Some swear by them, others at them.

However....if you are running a single wire, and want it to operate multiband,
forget the balun. Period.

I run a dipole that has wires for 20/40/80 and it works just fine. No balun.
Period No Balun. I do have an RF Choke (Coil) but no balun. If you want to
run balanced line (450 ohm) then it would be desireable to have a balun, but
at the bottom end of the feed chain, not at the antenna.

73

Bill, W0LPQ """""
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I still run my ic-736, SB-220 with the same setup, but I now use 6 to 8 turns of 10" loop near the bottom of the coax, just before the shack. this seems to keep some of the transiant rf out of the shack, but still allows the coax to work with the antenna to provide a really wide functional antenna....

Hope this helps. gud dx, cul.
gn gb. 73's Dan KB7UXE
kb7uxe@yelmtel.com
3.696mhz

 

nice info
i have been using a high q baluns for many years and no trouble with them ,i have used them on g5rv antenna and trapped 5  band antenna as well, now using one inverted vee 1/2 wave on forty meters only and iam qrpping 2 watts output and getting good reports all over the place.
also have a beam up with a balun it has been up for 27 years . maybe just luck i guess. de ve3jev

 

Thirty-plus years doing this has taught me a few things about baluns and dipoles. First of all, all baluns are NOT constructed the same. Your friend who put the balun in the antenna where it worked "awful on all but 80 meters" was likely using the dime-store voltage balun.... Choke baluns like the W2AU/W2DU or some Radio Works units would not have been as bad, but even those baluns are not designed for such high mis-matches.
One rule of thumb. THROW AWAY those Hi-Q baluns. They are "voltage" baluns and have a very limited application on the lower bands and their performance deterioriates badly above 20 meters even on a perfectly "resonant" antenna. They are very intolerant of mismatch and will saturate and overheat easily.
Using coax fed dipoles without a balun invites VERY high losses on some bands. Yes, you can get a tuner to work it out, and yes, I'm sure you could have worked ZZØDX on some rare occasion, but keep in mind, you'd have to lose 95% of your signal before your perceived signal would be significantly weaker. If you do the math you'd find a huge percentage of your signal being absorbed by even modest lengths of RG-8X on 40 meters. The reason that adding a balun to such an antenna ruined the performance on your friend's aerial is because the balun cannot tolerate such huge reactive components so it absorbs most of them. True current baluns in such an antenna would likely work "sorta okay" up to a certain power level. A Hi-Q voltage balun would get hot with 100 watts and would quickly imitate a roman candle with 500 watts or more going up the antenna.
If you're going to use one dipole to serve all bands you'd experience a huge increase in performance by feeding the dipole with open wire balanced line. Use coax out of the tuner for a short distance to get the cable out the window. Then install the Radio Works REMOTE BALUN and run ladder line from there. The Remote Balun is specially designed for all-band use and is very tolerant of high SWR situations. I've used them for years and recomended them to friends who have had tuning difficulties and RFI problems using the awful baluns that are installed in most antenna tuners. (Palstar is one notable exception in that regard, excellent balance in most of their tuners)
Finally, regarding the coax "choke balun".... they're a fair solution when dealing within a range of the HF spectrum. But, just coiling some coax up and taping it is a hit-miss approach. One that works fine on 20 meters would be completely useless on 80. Also, one made for 80 might even increase problems on 20 or 15. Coax choke baluns can be very good if wound on a large form in the proper way. Otherwise it's like throwing darts. Instead get a good ferrite sleeve balun (like a W2DU) and be done with it. They're cheap, fairly light, and don't add coax length to your system.
73,
Dennis
NØSP

 

Balun Balun who's got the balun...Anyhoo, I have no idea what to use for my own design...if I make a multiband, or even single band wire dipoles...(I will be finding out eventually). I do know however, that the Cable Xperts G5RV that I have came with the ladder line, a balun (what value I don't know anymore...4:1?), and 50 feet of RG8X mini. I have had nothing but excellent reports and such, so whatever setup and balun these guys used, it works very well. I have also used coax feed lengths of 25 feet to 125 feet with no trouble. I run an MFJ 949E tuner mostly, and on a good day I can even tune 160 on it without end feeding it...but the old FT-101 spits at me if I drive it too hard.

As far as a choke balun, maybe someone could steer me right here. I aquired a Cushcraft A-3 (10, 15, 20-meters) when I got my HF license in '95, and since then I just feed it with RG-8 or RG8X (braid tied to one side of the driven, and center to the other side)....I have heard that one should use a choke balun with this setup, but I don't know the number of turns, how large diameter is the coil, etc... I have had great luck with it the way I run it, but I am guessing it may help even more with the choke.

Dave...N9TTX

 

My experience with baluns tells me to just leave them alone. I have used them and not used them for 27 years of making dipoles. The antennas that worked the best were those made by feeding directly from the coaxial cable.

I had a good 40/80 dual dipole and then ruined it by adding a balun. I am going back and will throw that Hi-Q balun away.

Don/AD0K

 

Some people can tune a dipole and some can't. Sometimes a little adjustment is required! I run an inverted Vee with 4 different dipoles all hooked to a balun with great contacts. Two things have to be said...1) adjust your angle and 2) each leg will interact and may require a change in length.

 

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (N9TTX @ Feb. 20 2004,03:58)</td></tr><tr><td id="QUOTE">As far as a choke balun, maybe someone could steer me right here. I aquired a Cushcraft A-3 (10, 15, 20-meters) when I got my HF license in '95, and since then I just feed it with RG-8 or RG8X[/QUOTE]<span id='postcolor'>
Choke baluns are pretty easy to construct for HF. Take a length of 5 or 6 inch diameter PVC or plastic pipe. (not critical) Wrap about 15 to 20 feet of coax (close wound) around the pipe. Secure each end of the coax to the pipe in such a way that the cable remains tight and close-wound. Drilling some holes in the pipe and using tie-wraps works great. Or, you can run the cable ends back through to the center of the pipe through large holes and solder connectors on each end. You can use either large or small coax, but foam cables (like 8X) are not recomended since the soft dielectric can allow the center conductor to migrate over time. Of course using the larger RG-8 cables will need a longer piece of pipe than the RG-58 types. The only thing you need to remember is not to mount this balun up against conducting material. Keep it 6 inches away from metal.
Having said all of this, I might point out that such a device might be a bit clumsy mounted on a beam. Instead, Radio Works makes some nice compact, and inexpensive, baluns that work great for beams. (usually always better than what the antenna manufacturer provides)
At this point I should mention that a lot of people scramble-wind a hunk of coax and call it a balun. This is a shot in the dark. If early and late windings come close to each other dielectric losses increase dramatically and can even lead to inter-winding arcs with high power. Using a pipe evenly distributes the capacitance across all the windings and reduces the loss.
It's always a good idea to have a choke balun at the feedpoint of vertical antennas also. I had many RFI problems with my Cushcraft R-5 until I isolated the feedline with a choke at it's base. The neighbor's garage door stopped opening and closing as I transmitted and the ground-fault breakers around my house quit popping.
One more note to clarify an idea in my previous post. Any balun suggestions I made are with the assumption that you're feeding a near-resonant low impedence antenna!! Do not put baluns in single element dipoles that would be used for anything other than the frequency they're cut for or the appropriate odd harmonic. Multiple-element "fan" dipoles are great with a good balun. Always use current baluns. The ONLY exception to this are the Radio Works "Remote Balun" and another 4:1 balun called the "Centaur". I have not tested the Centaur but a friend used one with good results on a multi-band dipole with 1,500 watts. While these two baluns are generally useful over very wide mis-matches you should still approach with caution by using them only with a few feet of coax and then using ladder line out to the dipole. Use caution with high power by checking them for heating. If a balun is getting hot you should assume it's emitting harmonics. Some antenna/feedline combinations can result in extreme impedences at the balun... NO balun can expect to handle 5,000 ohms. Changing the ladder line length may be necessary to avoid these hot spots. A clue to this bad situation would be arcing in your antenna tuner or extremely touchy or unusually sharp tuning of your antenna tuner. (not to mention the inability to achieve a match)
The entire subject of baluns can get very complicated... many books have been written on the subject. The suggestions above will keep most of us safe.
73,
Dennis
NØSP

 

Balun or not -- first read the antenna books on theory, and understand the difference between BALANCED and UNBALANCED antenna feeds.

After the dust settles on your cranium, you will realize that coax isn't altogether that great of a feedline. I've always used ladderline or a random wire antenna on the HF bands, and used coax for antennas specifically designed for an unbalanced feed.

The magic comes in a box called an Antenna Tuner (and I don't mean those little components inside transceivers these days). A good tuner is worth its weight in gold, making anything that radiates look like a proper load to RG8 or other coax, period.

Look at the high power SW stations -- they use open wire feedlines feeding their antenna arrays. Yes, coax is nicer to install, but if you want performance, only use it in the shack, and on the VHF bands in short runs.

Gary Hildebrand WA7KKP

 

This is to N0SP
Good info. Thanks for no nonsense info.

 

Thank you all for the great replies.
My intention was not to say baluns are bad, or baluns are good,
but rather to get a more diverse understanding of how and why baluns work.
so I guess this is what i gather so far:

Baluns are good if:
you buy a quality balun,
use it for mono band only and don't want to use a tuner

Baluns are bad if:
You wish to use your single wire dipole on more than one band,
Don't usa a tuner,
Run more than a few hunderd watts,

I'm beginning to think ham radio is more like making soup.
"So just how big is a pinch of salt anyway ? "

Thanks again everyone for all the great information posted.

I'll see ya on 3.696mhz. evenings.
Dan kb7uxe.
kb7uxe@yelmtel.com

 

Whether or not your antenna is balanced or unbalanced, and whether or not it has to work with a feedline that is balanced or unbalanced, is not a question about whether or not you have the money to conform to the laws of physics.

Re-read W2DU's paper "some aspects of the balun problem"  He suggests looking at a doublet antenna as a "tripole" in which the coax shield is the third leg.  He suggests that to deal with a dipole as a balanced TWO-legged antenna, one needs to make the impedance of that "third leg" sufficiently high that the current that flows on it is negligible.

There are many different ways to do that.  Coils of coax and ferrites on the feedline are but two.  I don't know what kind of balun your friend tried, but if it was a transformer-type balun, the results are not surprising.  if it WAS a transformer-type balun, the fact that your friend's antenna showed unpredictable behavior on all but one band should tell you that transformer-type baluns are only predictable at certain frequencies.  Some simple coax-fed dipoles work.  Some don't.  I like to separate various problems.  Separating the balanced-to-unbalanced problem from any required impedance transformation is something that needs to be done before you do any further headscratching.

 

This from : Drew KD4QCX Midlothian, VA
I saw your post on QRZ.com; the following posts were exactly what I have been looking for, and hope these keep on coming.
I am considering using window line (300 or 450), with a remote balun, but as you know, you can have somewhere between 10-16 ft of coax to the transceiver. I am hoping that someone might give some comparative opinions regarding the use of each type of window line, and also using this straight to the tuner. My fear there has been that the RFI would get to the TV and computer, however I have never actually tried this. any experience with this Dan?
THX again for this important posting.. Drew KD4QCX Midlothian, VA
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Hello Drew.
Sorry, but I have no experience with "window line" (?)..
The only time I used ladder line was with an G5RV..
And I did find that the simple coax fed dipole seemed to work better everywhere I tuned to, and seemed to be easier to tune.
I live on acerage and have lots of trees. I have 3 center fed, end supported dipoles up now. So when I was compairing dipoles, it was simply a matter of turning a selector switch. All were about 75' above ground.

I hope someone else may have the information you need and will post it here..

Thanks all, please keep the information comming in.
Dan. kb7uxe
3.696mhz evenings.

 

Gentlemen, I wish to point out a few things which I did not see mentioned. First, A dipole has an impedance of 73 ohms under only a few conditions. They are: In free space. 2. At multiples of 1/2 wavelengths above a perfect ground. 3. At extreme heights above ground. None of these are likely to happen on our low frequency bands in our backyards. Our HF dipoles are generally quite low and therefore lower feedpoint impedance than 73 ohms. They are also often in the single pole support family called "inverted Vee", a misnomer but an accepted one. They are actually a bent dipole which is easy to match to 50 ohm line by adjusting the droop of the ends. I agree that the ground changes things but I am speaking in generalities here. Last but not least, all of the above only applies if we are speaking of a dipole operated on its fundamenetal frequency. The first references I ever saw to G5RV's specifically advised against using baluns. I dislike ferrites just a bit more than I dislike baluns. I NEVER use either. Actual measurements on these HF wire antennas are difficult and tricky. My advice: Copy the fellow who makes contacts when most others can not. This is a very good thresd. WA5SWD

 

Hi everyone, this from Chuck, WD4HXG

Hello Dan

The dipole antenna (not folded) when set at about 1/2 wavelength above ground and cut to resonance will exhibit a feedpoint impedance of 72 ohms resistive and no reactance. The antenna will exhibit a figure 8 pattern in the horizontal plane. That is true if there are no objects in the nearfield other then flat earth. (Nearfield is defined as the hemisphere dome within 10 wavelengths of the antenna.) I think it should be pretty obvious that very few hams have that luxury. Electric lines, phone lines, housewiring,
satellite dishes, automobiles and such distort this field. The distortions will cause reflection currents, the severity of which is dependent upon the proximity of the object, and size. Obviously the closer the object the larger the effect.

The imbalances can be mitigated by using a balun. Baluns can also function as an impedance transformer. Most ops are familiar with the 4:1 balun. It not only can restore balance but convert your feedpoint impedance by a factor of four. This may or may not be desirable. Usually when operating on a single band at 1/2 wavelength above ground the dipole is well behaved enough that a balun is not a forced issue. However if you measure the radiation pattern you will find nulls in the pattern and the ovals of the figure 8 will be at some angle other then 180 degrees to each other.

Do you have to use a balun? -NO!- Should you use a balun? It depends on what your intended communications requirement is. I personally say use a PROPER balun.
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Now the fly in oinment occurs when you try to use the resonant dipole with coax on multiple bands. The feedpoint resistance when operating off resonance will exhibit a resistance that is a function of the height and length. Along with that there is a reactive component. The reactive component is heavily governed by the length of the antenna. Using an 80 meter dipole on 40 will result in about 1000 ohms inductive reactance. The resistive component will be about 250 ohms. These are rough numbers but the end result is a VSWR of over 100:1 when using RG-8X.

That level of mismatch will sacrifice 99% of your RF power in the feedline. That equates to 20 dB of loss. Since 1 S Unit is 6 dB you can see that level of mismatch will cause you in excess of 3 S Units reduction in your signal transmitted. THE ANTENNA TUNER
WILL NOT RECOVER THAT LOSS. No matter what you do in the shack with the antenna tuner, if you have that mismatch at the feedpoint the coax losses persist. NOTHING YOU DO IN THE SHACK can remediate the losses in the coax as long as the mismatch exists at the antenna. In order to keep coax losses down you have to match at the
antenna and provide the coax with an impedance that will keep the VSWR on the coax
below 10:1.
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Baluns come in several forms. Many are realized using coax. There is nothing wrong with coax baluns but they tend to be narrow in bandwidth. When I say narrow, they usually will cover a band or two in the lower HF and maybe three bands in the upper HF allocation. If you are trying to use a single antenna for multiband operation the coax balun can not provide the bandwidth you are seeking. When you move out of the operating frequency area of the balun you introduce a lot of new reactive components in the system.

To circumvent this many ops use a balun built with a ferrite core. The theory shows that a ferrite based balun can provide BROADBAND performance. It is feasible to build a balun with a ferrite core that will cover 80 through 10 meters and even 160 through 10 meters.
But the selection of the ferrite core material, the number of turns on the core and proper selection of the impedance of the line used in constructing the balun are critical to the wideband performance.

I have heard the comments on the use of voltage vs current baluns. I personally have concluded that the selection of voltage or current design is not critical, but rather the proper selection of core, turns on the core, the line impedance used on the core and the
impedance limits of the balun.

I would strongly urge you to buy the book "Reflections" by W2DU on the subject of lines, and baluns. He provides abundant information on this subject.
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Do not dismiss baluns! They are your friend when properly applied. They actually improve the antenna performance but if misapplied they can make matters worse just as putting the wrong fuel filter on a car can cause you heartburn.

If building your own balun with ferrite follow a couple of guidelines.

1 Use "Fair-Rite" Type 43 material in the core or equivalent for hf applications.
2 Do not use ferrite recovered from switching supply cores, tv flyback transformers or deflection yokes as these materials are optimized for the sub Megahertz frequency range.
3 Do not misapply the impedance spec on the balun. If it is a 4:1 balun for converting from 50 to 200 ohms or 200 to 50 ohms then don't try to use it to covert 12.5 to 50 or 50 to 12.5 ohms. I know that some have done it but it is hit or miss as to working properly.
4 Use a core of adequate size. Do not use cores that are only 1 inch in diameter, but rather 2.5 inch diameter minimum. A single 2.5 inch core for 100 watts will allow operation with 100:1 VSWR's without significant heating in SSB applications. If you run higher powr then stack the cores. I would estimate 4-5 cores stacked for legal limit operation. Do not tape the cores together. Use superglue to hold the cores together while winding. Tape will hold in any heat due to reactive losses when dealing with high VSWR's.
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Measure, Measure, Measure! Guessing the feedpoint impedance is a valid method of applying baluns but if it does not work as expected don't immediately conclude the balun is the culprit as the feedpoint impedance may be radically different then your guess.
The ARRL Handbook and Antenna Book both have excellent articles on building impedance measuring bridges which will provide you the resistive and reactive component values.
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If you are going to use an antenna for multiband operation then use ladder line or balanced line for the transmission line and feed the antenna at the center. The ladder line is much lower loss and will sacrifice only 5 or 6 dB vs the 20 of coax when used in mismatched
conditions. Feeding the dipole at the center insures near balanced operation, much more so then off center fed antennae.
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If you use a balanced transmission line then USE A BALUN or a BALANCED ANTENNA TUNER. If you directly couple to the balanced line with the 50 ohm unbalanced output of the rig or antenna tuner then you unbalance the ladder line and defeat the purpose. When starting out use a proven balun design. Again there is nothing wrong with coax but just remember it is only going to work on a single band or two at the most in the lower hf spectrum. I personally opt for ladder line connected directly to the dipole, which in my case is a shortened dipole on 80. I then use a 1:1 balun at the balanced
line end in the shack. Then I use a 1:4 transformer designed to convert from 12 ohms to 48 ohms. That connects directly to the antenna tuner.

I had operated with coax before and after switching to ladder line and the balun ops in a net I check-in on Saturday mornings commented that my signal had increased from S-5 to 10dB over S9. Proper selection of feedline, and attention to impedance matching
will give you a big signal even with 25 watts.

Walt, W2DU has some excellent info in his book and I would recommend raeding it. Jerry Sevick's Book on baluns is a must read for the op who is looking to properly apply baluns.
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73

Chuck WD4HXG
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Again, Thanks for all the good information..
Please, post your opinion on dripole buildin..
Thank you.
Dan kb7uxe.
3.696mhz evenings.

 

Interesting and worth giving it a try.

Any pictures you can share showing the finished product and how you have it mounted at your QTH?