160 dilemma(?)

[Pete Smith]

OK, modeling and antenna-interaction gurus, I'm stuck.

My station has a single, 100-foot tower with a Force 12 C-4 on top.  I just
installed a K3LR-style parasitic array for 80m. consisting of 4 lazy-vees
strung from the 90-foot level on the tower, center fed with RG-8X , with the
lower ends of the dipoles brought back to the tower about 6 feet above
ground.  The unfed lazy vees are loaded to appear electrically longer
(reflectors) by the unconnected feedlines. It models great and, on limited
evidence, plays great too.

My next thought had been to install a single 160-meter inverted vee, also
strung from about the 90-foot level, bisecting the angles formed by the 4
90-degree-spaced elements of the 80-meter array.  Before I put it up, I
tried modeling it to get an idea of the interaction with the 80-meter array.
For simplicity, I left the two top "ends" of the inverted vee connected,
with no feedline (this may have been an error) and modeled the situation
feeding one of the lazy vees on 80 meters.  I was surprised to discover that
the presence of the 160-meter wire (really about 260 feet long) produced
massive distortion of the 80-meter pattern and gain.  The model shows a LOT
of current in the 160-meter wire.

Intuitively, I didn't expect the 160-meter inverted vee  to affect things
that much, since it's an even harmonic from 80.  Is that wrong?  Or is there
something wrong with my modeling approach?  Anyone out there understand how
to model a transmission line like the one that would be on my 160m. inverted
vee, roughly 85 feet long, with the shield grounded and the center conductor
floating when I'm on 80?  Do you treat it like a real open stub, or....?

I hate to forego 160, or try to put a 160 antenna somewhere else, but I'm
not about to compromise my 80-meter performance that much! I could sure use
some advice.  Direct replies appreciated - if anyone else cares, I'll gladly
summarize the advice I get.

Thanks, folks!  HNY!




73, Pete Smith N4ZR
n4zr@contesting.com 
West (bigawd) Virginia


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