Hi Steve,
The best antenna is one that makes the user happy, no matter how it really
works. With a few misused terms that sound official, like "critical
coupling" or "radiation resistance", an antenna can suddenly leap beyond
the tight grip of reality.
> This begs the question of using guy wires for slopers - an
occasionally
> used technique. Am I to infer that their performance is more a matter of
lucky
> placement than superior tower planning?
IMO, it's mostly luck. Especially since most modeling programs don't model
different diameters well when wires connect and few people would be able to
input all the data accurately anyway.
Can you imagine "typing in" a wire table that represents all the elements
and the boom of a TH7-DXX?? Or a stack of antennas of various types? It's
all part of the tower, and it all affects performance and optimum height.
One way to improve luck would be to install relays at the feedpoint and
ground all unused slopers to the shield and tower. That almost guarantees a
low impedance connection for the other half of the feedline (the shield)
and a decent SWR.
As an alternative you could put the relays 1/4 wl away on a transmission
line and open the unused antennas, but that results in high open circuit
voltages (into the kilovolt range) across the relay contacts in the open
position that might ruin the relays with high power.
Myself, I'd just use sloped dipoles (or ground-end fed slopers if the tower
was too short) if I was firmly convinced I wanted a vertical. Otherwise,
I'd use a regular dipole or Vee. W4EX had a system of inverted Vees using
his guy lines on 160 and 80, and he had a killer 160 and 80 signal and a
totally uncluttered yard. It allowed him to work DX like he was shooting
sitting ducks.
73 Tom
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