Robert Tellefsen wrote:
To make antenna matching easier for the TX, I have a
homebrew relay box that adds in various lengths of more
450 ohm window line to bring the feedpoint reactance
down to close to zero. This gives the ATU a chance to
match easily and gives the best 2:1 swr bandwidth. The
single band antennas are coax fed, but still switched
through the relay box.
I do something similar, although I use inductors and capacitors rather
than pieces of line. This is very important to make a balun connected
between the balanced line and the coax efficient. I conducted a series
of tests in which I measured the temperature rise in the balun -- a sure
indicator of losses -- when the mismatch was primarily resistive or
reactive. Reactance is poison for balun efficiency!
And yes, you need a balun to reduce noise pickup, line radiation, and
rf-in-the-shack.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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