Good morning.
I can add a little to this subject...
Being primarily a contester, there are times when a good F/B is necessary
and there are times when it is not wanted. Many of those who operate in the
Caribbean area know about the static crashes from lightning that are a
problem all night long. This is always an issue operating from Aruba,
Bonair, Curacao being close to the high mountains on the coast of Venezuala.
Without a directional antenna, the nights get very long and tiring.
Other times, when the conditions are very good, such as a path through USA
to Japan on the higher bands, a good F/B is not necessarily a good idea. One
can pick up additional Q's from SoAm off the back, maybe a multiplier or
two.
To fix this "problem", I have made several antennas that I called the
"tailgunner." They have a relay at the center of the reflector element. When
I want the best F/B, the relay is closed. When I want minimal F/B, the relay
is opened. The relay can also be keyed with the transmitter, so that the
antenna can transmit with minimal F/B and receive with best F/B.
The tailgunner is very nice for a multiplier antenna, as well as a runner.
This is not a simple design, as the antenna cannot change the feedpoint very
much for either condition. The two conditions are:
A) the regular antenna, complete with reflector
B) the regular antenna, but without the reflector.
If the feedpoint changes very much, amplifiers with VSWR sensors will trip.
Hope we get some good conditions for Field Day this weekend.
Have a good day and 73,
Tom, N6BT
Force 12 Antennas and Systems
(Home Page http://www.QTH.com/force12 )
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