Is there an expert out there who can explain how the Balun works!
There is no physical electical connection of the center wire
of the coax as explained in the Kitfox assembly manual and it
just does not look like it should work! The shield is split and
the VOR cat's whiskers are connected to each of the split ends of
the shielded wire.
There are three or four commonly used "balun" (short for balanced
to unbalanced) fabrication techniques using coaxial cable. You can
also do the job with little ferrite core transformers . . in fact
an antenna company in MO used to offer some antennas to amateur
airplane builders that used small transformers inside a molded
plastic center insulator on their products.
It's not easy to explain. Some excellent info on transmission line
theory and grass-roots practice can be gleaned from American Radio
Relay League's publications on antennas and feedlines for radio
amateurs.
I understand the purpose of the balun is to balance the impedance of the
feedline to that of the antenna.
Correct . . .
Is there another way to feed a VOR antenna?
Sure . . . hook the shield to one whisker and the center conductor
to the other whisker. Putting a balun in the system is a mixed bag.
It adds complexity . . . more solder joints . . . should be checked
with an antenna analyzer to see if everything is cut to proper
length . . . bottom line is that you'll not be able to percieve
any difference in performance by simply judging how well your VOR
receiver works. Other airframe effects such as electrical system noise,
p-static and atmospherics can have worse effects on VOR reciver performance
than the fact that you failed to "properly" terminate your coax cable
by hooking it to a balanced antenna.
There's a popular kit offered where ferrite beads or toroids are
slipped over the coax in immediate vicinity of the feedline attachment
to the antenna. I illlustrate this in my book's chapter on antennas
and feedlines. I've since learned (and seen demonstrated in the
lab) that a few toroids are not enough to make a difference. It takes
several dozen to equal the effects of a properly implemented balun.
VHF is line of sight stuff. If you can "see" the station you can
hear it or talk to it and a wet string would probably suffice for
an antenna. The ol' vacuum tube radios of yesteryear needed EVERY
advantage we could give them . . . modern solid state receiver
technology will work with very marginal signals compared to 40
years ago.
Make it easy on yourself. Hook 'er up, make sure you do a good job
with the connections and protect them from stresses of vibration
and environment and call it quits . . . it'll work just fine.
Bob . . .
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( Knowing about a thing is different than )
( understanding it. One can know a lot )
( and still understand nothing. )
( C.F. Kettering )
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