To Balun or not to Balun...

As in many endeavors, ham radio is all about "The Art of The Possible". Operational imperatives must be balanced against aesthetic absolutes, or what model railroaders call "WAF (Wife Acceptance Factor)". My case is probably typical - ancient HyGain 80/40 doublet strung at about 25' diagonally across the lot, with a W2DU 1:1 balun in the center. From the balun there's about 60' of coax into the shack. Given the relative location of the shack in the house, about 25' of that coax run (all in the ceiling in the family room) is pretty much inescapable.

While I'm intrigued about the notion of running ladderline to feed the antenna, I'm not sure it'll be practical given the physical layout of the station. To run the ladderline directly to the tuner in the shack, I'd have to 1) lay a good bit of ladderline on the roof, 2) cross the aluminum flashing at the edge of the roof, 3) run through a drop ceiling for 20' , and 4) turn a couple of tight-space 90degree bends before emerging into the light of day at about floor level next to the radios.

The club to which I belong faces a similar constraint (shack is on 11th floor of a large hospital building; antenna feedlines run about 50 to 60 feet through a rather convoluted path out onto the roof). Our G5RV's ladderline is connected to 4:1 balun at roof level, then coax-fed the rest of the way into the shack. Seems to work ok, so long as you don't try to use the antenna on 6m .

Anyhow, would I gain anything, from a practical perspective, by feeding my aforementioned 80/40 doublet with ladderline as far as the entry to the house, then going through a balun and onto the coax? I'm not sure I would.

 

Thanks, KB7UXE, for a great thread.

It's wonderful to see Hams passionate about something that doesn't have anything to do with kicking each other in the groin.

Reading/responding in chatrooms is rarely better than radio, but sometimes the typed/printed word is worth reading just so you can learn something from your fellow Hams.  While I have my own opinions about Baluns that have already been posted here, I am THOROUGHLY enjoying hearing about everyone else's personal experiences.

Thanks again, KB7UXE.

 

Man, I wish I would have read this thread sooner.  I have a commercially-made (AlphaDelta DX-DD) dipole for 75/40m.  It has coils in it that shorten it to 41' per side and allow it to work on 40m quite nicely.  I assume that since there aren't any capacitors in the coils, there's enough internal C to make them act like traps.  The coils are about 36 feet from the center, with about 5 feet after them.  Does anyone have information to contradict this theory?

Next, they have their brand of balun in the center, but they include in their paperwork some instructions (as an option) to feed it with ladder-line by simply connecting it to the same terminals that the antenna wires attach to in order to bypass the balun.  So far so good...

I added a 20m dipole "fan style" below it and it works like a hose.  In fact, they make one like this that includes a 10m wire, and the 40m section works on 15m.  So my version actually works 15-75m (non WARC bands).  I measured the SWR on 10m, and it's a bit high (between 2:1 and 3:1), but I use it there, too.  I occasionally load my amplifier into it on 17m where the SWR is around 5 or 6:1.  No problem, but I realize that I have some loss in the coax (RG-213) due to the mis-match.  I can live with this.

All this to ask why that balun (which is sort of triangle-shaped and no more than 6 inches across) works fine there at close to legal limit power levels on all bands, even when the antenna isn't resonant??

Also, what do I have to gain by switching to say, 450 ohm ladder line and a short run of coax to a balun just outside the shack?  I've been thinking about doing that, but haven't pulled the trigger yet.

Oh, BTW, I let the output section in my amp (and vintage tube rigs) do all the tuning -- I've haven't used an "antenna tuner" in my life.  Always get good results and I was ONE SECTION away from sweeping the ARRL Sweepstakes contest using this setup.  Would you believe I only needed Quebec???

73 and thanks for an excellent thread!!
Joe,
N3JI

 

Heck with it, just feed it with twinlead straight to the tuner - that way you get vertical as well as horizontal polarization.

73 de
af0h - Rob

 

I have been considering a new inverted V, and I started a thread in "QUESTIONS AND ANSWERS" about whether or not to use a balun to connect coax to ladder line. The replies were great, and I am learning even more with this thread about baluns.

Great thread guys. It's nice to see hams working together for a change. Keep it going.

 

I will try to pass on what I know to be true.
 Ladder line or open wire feeders are not a bad thing, matter of fact they are very good. The fear of running these feeders into the shack is unfounded, this type of feeder cancels, each leg cancels the other out and thus does not radiate in the shack in the sence I have read here. Coax (8X) is safe to 600 volts with a low swr much less as swr goes up, the open wire feeder will loaf at 12000 volts and does not really care about the swr that rides the wire. If equipment wasn't built the way it is today I would not use coax at all , but plain fact today some coax must be used to hook up your gear.
Look at loss figures for coax and open wire, would you put a part on your car that would make your gas mileage go down? No, so why use a feeder that eats your power?
    The balun is another link in the power eating chain.
you say the manufacturer says low loss, well that is the fact there is loss, small or large loss is loss, coated wire wound around a ferite core has no direct contact so there is loss, the balun depends on radiated power to change the condition to balanced.
    The balun can heat saturate causing damaging swr and rf to radiate all over the place, a balun is a bandage on wound, not a cure. G5RV Mr. Varney who designed this well used antenna states there is no benifit to using a balun, in fact decays the performace of the antenna.
    I run open wire right into my station. I have 2 computers a TV and a bunch of radio gear and I have no rfi, why? I insure that my station runs clean, and that is not hard to do, but it must be done.
    The trick is, and it is not a trick, just good radio theory is, I use a unbalanced to balanced tuner, not a un balanced to unbalanced tuner running thru a balun, big difference.
    I have not bought an antenna in 39 years, I build all my antennas.(all of them even vhf and uhf).
    Questions to ask yourself.
1. Why run coax to an antenna and run a tuner?
coax, about 68% of the power makes it to the antenna.
open wire, about 97% makes the trip, your running a tuner either way.(based on 100 ft + of feeder with 3 to 1 swr)
2.Why use a balun? I find that most who preach using a balun are those who sell them or don't know the difference or their buddy runs one.
3.Is it that hard to keep open wire 2 inches away from metal? no effort no station.
4.Why was coax invented? For mobile use,aircraft,military, it caught on for base stations because its easy, no work, you buy it not build it, offers 50 ohm for the solid state radio (doesn't make it he right choise)

   Having said all this, The proper place for a balun is the lowest voltage, current point, on a balance system a balun if used should be BEFORE the tuner or at the INPUT of the tuner,(inside the box) then you are tuning a balanced condition, the voltage and current are low and the swr the balun sees is low and 100% less chance of balun satuation and rfi and all the ills that go with it because the balun is not in heavy labor. A unbalance to unbalanced tuner can be modified to work this way with very little work at all.(this is done with a 1 to 1 balun).
   The last point, I own a amplifier, but find I use it very little, If I hear them I can work them with 100 watts, due to a antenna system with very little loss.

   Hope this helps someone.
73
Jim

Ride the Lightening

 

Wow Jim, That was a great reply! Just the information i'm looking for.
Thanks for the great input.
Dan. kb7uxe.

 

</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (kb7uxe @ Mar. 05 2004,00:02)</td></tr><tr><td id="QUOTE">Wow Jim, That was a great reply!  Just the information i'm looking for.  
Thanks for the great input.
Dan. kb7uxe.
[/QUOTE]<span id='postcolor'>
Your welcome Dan. If I can be of any help in the future, email me I am always happy to help a fellow Ham

73 Jim



Ride the Lightening

 

I NEVVER USE CENTER BALOON IN MY 55 YEARS OF HAM RADIO, I BUILD MANY DIPOLE AND YAGI ANTENNAS WITHOUT BALOON WITH EXCELLENT RESULTS. JUST COAX CENTER . IZ3DVZ / WP4NKF

 

I have just installed a super linear-laoded inverted V antenna multibanded for 80,40,20,10 meters. Apex of V is at 38 feet and 90 degrees seperation of legs. Feed with 29 feet of ladder line then a home made 4:1 balun wound on 1 1/2 " PVC pipe. Then RG8 into shack. All bands tune to less than 1.5 to 1 but most are flat. Used 15 meters with contact of 5.5 from Japan and 20 meters with contact in Brazil of 5.9. Legs of antenna are oriented east west. I am using a Kenwood TS180S that I have been working on during these tests and am extremely happy with the results. The specs for the balun I got from the internet by searching "amateur balun 4:1"

 

use ladder line the tuner has a 4 to 1 transformer to help with high impedance . i like the 300 ohm its lighter and provides a lower swr on the balun, and runs more quiet from local powerline hums ,it can operate nearer to metal objects with out becoming unbalanced.

if possible use resonate length of wire on the longest band you plan to use.

choke baluns are fine if you run a dipole for each band. but if you buy all that coax you may as well have bought a tuner.
km4gy
ps loops and folded dipoles dont need a balun. they are forced to be balanced.

 

We have to remember that, when a balanced antenna, as a center fed dipole, is used without a balun, due the difference of current distributions on both legs, the radiation pathern is different from that with a balun. So, it is possible that the signal strength in some direction is increased or decreased when one installs or uninstalls the balun, giving a false information about the radiation efficiency.
Another point is that a balun, strictly speaking, works fine ONLY when it is correctly matched with its own Zo.
Finally, an halfwave dipole antenna has its center impedance equal to 73 Ohm in the free space or at certain heights to the ground; normally below 1/4 wavelength high, the impedance is smaller (smaller the height, smaller the impedance).