At 08:50 AM 8/20/96 cst, sawyers wrote:
>Believe me, I am no expert at this, but I will pass on some stuff I was
>playing with and thinking about.
>
>I have been doing a bunch of modeling of a 114' tower with 127 to 132'
>active top guy wires for 160. My current inclination is to use switchable
>guy choice then connect the remaining two to the shield on the coax thru a
>20 uH physically large tapped inductor. This lets them work as a reflector.
>With the Yagi's on top, you get a 25-30 degree take off angle, about 3 dBd
>and a 120 degree pattern. The pattern looks like a lopsided donut laying
>flat on the table with the larger part of the donut in the direction of the
>chosen guy wire. Front to back isn't much, about 6 dBd, but the near
>vertical stuff (i.e. those stations just beyond ground wave range) are
>significantly attenuated. By changing the inductor and adding another
>tapped inductor to the driven element, it also plays on 80 and 40. On 40
>you are running it in a multiple wavelength mode and the results get rather
>impressive.
Alternatively, look at K3LR's article in the 8/94 QST. He uses 4x "lazy
vees" (top half could just as well be part of your guy wires), and uses the
feedline as the loading to turn the undriven elements into reflectors.
Depending on the operating and resonant frequencies, F/B as high as 25 dB
and gains ca. 4.5 dBi appear in the model. Note that this arrangement
requires an insulating box, floating coax shields from antennas to feedline,
and probably an extra relay to switch the shields around. but it looks like
it could be worth it. On your tower, a 40-meter version could work great -
I'm building mine for 80 on a 100-footer.
73, Pete Smith N4ZR
n4zr@contesting.com
LOUDER is gooder....
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