<< When we started flying GELSA in Lakeland we had a similar problem,
>> reception OK but poor & intermittent transmit & yes it was an antenna
>> problem - clearly the antenna is required to handle much greater power
>> for transmitting.
>> We replaced the existing welding rods with copper tape in the fin close out
>> but were unable to obtain any ferrite torroids. I therefore made up a
>> "balun" from a loop of the RG58 cable from a published design which should
>> be available on the net somewhere. Goodness knows how this works but after
>> trimming the copper tape there was a sudden dramatic reduction in VSWR
>> reading and our radio performance was transformed. >>
>> It worked for us, just don't ask me why!
I am not an expert here, but I can quote others who are. If you swapped
copper
tape for welding rods, what you did was probably increase bandwidth, as I
would
understand from Jim Weir's explanation that accompanies his (RST Engineering)
copper tape/toriod core kits. In other words, you increased efficiency across
the band, and reduced it at its peak. Similarly, he also says that the
classic RG58 loop balun is more peaky that toroid cores, though. However, Bob
Archer (Archer Antennas) says that toriod cores are very "lossy." Maybe it's
a trade-off.
I was unable to prove this, as before I glassed in a nav antenna/toriod core
setup
onto a wing core, I took it to my other plane at the airport and got better
reception
(on the ground, VOR 20 miles away) than the bird-roost V-antenna on the plane.
I doubt, though, the power-handling capability was the problem, as welding rod
can handle the current easily. The tricky part is the radiating pattern and
as you
know, VSWR (related to bandwidth).
Regards,
Fred Fillinger, A063
Mentor, OH, USA
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