Topband: K9AY Center support

[Tom Rauch]

> My modeling exercises suggest that a grounded metal mast will 
> degrade the pattern significantly. It will still have some F/B, but
> the peak F/B in the null will be reduced. 

What spacing do you have between the mast and the antenna element, 
and how tall is the mast Gary? I've never seen that effect either in 
a model or in real-life antennas.

I just checked one random old model of mine using a 60 foot long 
antenna, and when I stay within the guidelines of Elnec I see a 
deterioration from 32.1 dB to 31.34 dB F/B when I add a 2-inch 
grounded metal mast that is within one foot of the #12 antenna wire. 

Tweaking the termination restored the insignificant change.

I'm puzzeled by the large reported change, since it also makes no 
sense from a theoretical standpoint unless the mast is a significant 
fraction of a wavelength tall, perhaps .1 wl or more. But then there 
is always something to learn, if you can get to the bottom of 
disagreements. 73, Tom W8JI
W8JI@contesting.com