I have a 131 ft crankup tower with a KLM 20m Big Stick antenna about 5 ft
above the tower top on a mast extending 15 ft. The 2 outer elements are
grounded to the boom and all others are insulated using the usual KLM
insulators. The boom has 3 truss guys, 2 side guys are Dacron rope and the
top guy is nr 10 copperweld wire. The top guy connects to the boom at the
usual attachment points and has a copper strip screwed to the boom. The
other end of the top guys is attached to the mast at about 5 feet above the
boom with sturdy insulators at the attachment point.
All of this was done in anticipation of loading the boom for a switchable
30/40m dipole. I have a number of vacuum relays which I expect to use to
switch matching networks for the 2 bands. I would like to have input on 2
topics.
1. The retracted tower height is 30 ft and that would put the beam at about
35 ft. I wish to tune the setup at the 35 ft height for obvious reasons. How
much will the resonance frequency increase when the setup is raised from 35
ft to 135 ft on each band? Our soil is fertile farm soil.
2. As I see it, I could use only one side of the truss guy for a gamma match
or omega match and ignore the other. I could instead feed both sides of the
truss guy with a balanced network via a balun. I could feed one side as a
gamma on 40 and the other side as a gamma on 30m.
Has anyone been down this road and has advice? I am familiar with the boom
matching schemes used by N4KG.
Tnx, Dan, N5AR
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