I believe a good start is to leave the feed system with
the matching transformer in place and just cut the beverage
off, leaving only the vertical piece.>>
When the antenna wire is just hanging there it is so
reactive it could have a very wide range of matching loss
due to the complex interaction of the reactance and
transfomer reactance. When the T is added with the resistor,
we now have added 450 ohms of intentional loss resistance at
the same time we eliminate most reactance. I wouldn't even
try to guess what happens to mismatch loss without looking
at the impedance back into the transformer (the transfomer
might not be bilaterial, especially when misterminated
severely) and receiver and knowing the antenna impedance. We
can be pretty sure the radiation resistance of the vertical
wire increased by a factor of three or four due to current
distribution changing from triangular to nearly uniform, but
then we added losses with the resistor.
When I model a "T" wire as a termination to a six foot
vertical wire (easy to model) over average soil, the model
shows about 5-1/2 dB of directional pattern null from the
addition of the horizontal wire. This occurs at all low wave
angles.
In other words I have a six foot vertical wire. It has an
omni pattern, no null in azimuth pattern. I add a 250 ft
horizontal wire six feet high centered on the vertical, and
the pattern at low angles now models with about 5.5 dB of
directivity! A pattern like a poorly defined "figure
eight". Adding a resistor doesn't change the pattern of
course, only the sensitivity or "gain" and input impedance.
It isn't difficult to duplicate this model.
That very obviously indicates substantial radiation
(reception) from the horizontal wire. We should fully expect
this to occur because any groundplane with only two radials
spaced 180 degrees clearly shows effects of radiation from
the counterpoise....and in that case the vertical wire is
1/2 the physical length of the horizontal wire! Any book or
text telling us a "center tapped counterpoise" with a single
wire near 1/2 wl long from end-to-end doesn't radiate or
receive substantial signal when compared to a fractional
wavelength vertical wire is wrong, the only exception is
when that single wire is over and very close to perfect
ground.
I can't see why the counterpoise would behave differently
just because it is on a Beverage, but I'm open to correction
if I'm missing anything.
73 Tom
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