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Antenna wiring question.

Mike S

Mike S

Senior Curmudgeon
I am installing a RAMI VOR antenna that I picked up from a fellow VAFer, and it is supposed to be hooked up using a "balun".

I have talked to our resident avionics guru, Stein, and he says it should be fine with just a ferrite loop or something along that line, and that some folks even just hook them up straight to the coax. Like shown here.

Anybody out there know the ins and outs of this "balun" stuff???

What have folks done out there with this issue?

Educate me, please.
 
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Balun: Balanced to Unbalanced

Think of a balun like a bell crank. On one side, you have a bowden cable with it's sheath secured to the structure, and it's center cable connected to one end of the bell crank. The output of the bell crank is two pull-pull cables. The input is unbalanced, the output is balanced. That's basically what a balun does electrically.

A dipole antenna has two symmetric elements and is by nature balanced. If you feed it with coax, which is unbalanced, you could affect the antenna's pattern, so you might have uneven reception depending on direction. In practice you may not notice.

Here's an article that Jim Weir published several years ago in Kit Planes:

http://www.rst-engr.com/kitplanes/KP9912/KPtext.doc

Make sense?

Paige
 
Thanks!!

Thanks for the replies folks, but near as I can tell, there are two different designs presented--------either that, or one of the drawings is not correct.

Anybody have actual experience with making, and successfully using one of these???

How about the setup using a ferrite ring?
 
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Mike, I've made 4 or 5 of these and always copied 43.13. The store bought ones have the same balun. The copper strip unit in my RV-10 roof has great reception. The 43.13 version as always worked fine. After you make it, Shrink tube the balun to the coax to decrease the lump size.
 
Dave, thanks for the reply, I also sent you a PM.

The 43.13 doesnt give a dimension for the length of the turnback ----just says 1/4 ( assume they mean quarter wave?).

What have you used as a dimension (in inches please) for the turnback portion of the balun?

Thanks much for the info:D

PS, pretty sure folks would be interested in your copper strip setup, got any photos and info on that??
 
Mike, I think that your actually seeing the greek symbol for frequency divided by 4 (didn't know greeks had radios). I think you could match the length of one radiator and be right on. They should be quarter wave length.
 
Strip antennae

This pic shows the VOR & glideslope antenna. You can see the balun wrapped with the coax. Terminal screws are bedded in the roof and the ends of the tape were built up with solder before drilling the screw holes.
13ynn28.jpg
 
Thanks!!

Dave, Gil, thanks mucho:D

Dave, that is a great idea for the antennas, wish I had seen it before putting in the headliner. Now, I am stuck with doing it the traditional way, going to go with the VOR antenna under the tail.

The VAF knowledge base comes through again.
 
Just to close the loop on this one, I did make the balun as shown in Nukols Aero Electrical Connection.

Works just fine.
 
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