Topband: Center support on K9AY Loop

[Michael Tope]

Any suggestions for how to go about decoupling a nearby tower
from a K9AY loop array, Tom? My modeling suggests that this
may be a problem, but I am not sure if I trust my results. The amount
of pattern distortion shown in the model is a strong function of how
I model the ground connection between the tower and physical earth.
Since I can't make a direct ground connection in EZNEC, I put 8
radials under the tower 4" off the ground. With 8 - 8' radials under
the 45G the modeled interaction with the nearby K9AY loop array
seems to be pretty minimal. When I extend these to radials
to 33' the model shows strong coupling to the K9AY array. With the
long radials in the model, I can minimize the coupling by adding a gamma
arm to the tower and adjusting the series reactance (presumeably this
puts the gamma current in anti-phase with the tower current).

The real performance of the antenna suggests that something might
be going on with regard to interaction with the tower. Although
the arrays shows F/B on 160, it doesn't hear any better than the
TX antenna. I don't know whether this is a function of the
quasi urban environment with the accompanying isotropic noise
(we are up on a mesa with residential/commercial areas visible
over approximate 270 deg azimuth - not much to the north)
or mutual coupling with the TX antennas/nearby tower.
On 80 meters the antenna seems to really work (improved
SNR over TX antenna).

Any suggestions for troubleshooting this situation? I have
a feeling that we are still pretty deaf on topband, so
anything we can do to improve things would be welcomed.
(I would put the array further from the TX antennas, but the
geometry of the available real estate makes this impractical).

73 de Mike, W4EF...................