Topband: Antenna Signal/Nosie

[Tom Rauch]

LAA26334
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Good work on the noise improvement Bill.

> Any omni ant    0 dB      0 dB
> 2 ele vert     -3.14     -4.15    Classic 90ºspace/90ºphase array
> My xmit ant    -5.28     -7.72
> 584' Bev       -6.31     -9.74
> 2 x 584 Bev             -12.25    Last year's 268º Beverage
> 881' Bev       -7.31    -12.65
> 2 x 881' Bev   -7.86    -14.84
> 3 x 881' Bev   -8.60    -16.97    Revision

Your figures agree with my experience, and my thinking. I'd like to 
add one additional comment.

I recently began adding a new group of Beverages 1000 feet back 
from my present arrays. Only under the most stable propagation 
conditions does the additional array improve S/N. That's because 
phase and amplitude vary considerably between the arrays, 
preventing them from being combined.

Also, mixing in a horizontally polarized phased array (a pair of 1/2 
wl high phased dipoles) with the vertical arrays (Beverages or 
phased verticals) causes severe problems with phase shift, and the 
result is virtually useless under most conditions.

This leads me to two additional conclusions. When conditions are 
not exceptionally stable:

1.) Arrays larger than two wavelengths spatial area will suffer phase 
shift and level problems that are associated with the area the array 
occupies, and the error won't show in a conventional model 
analysis, because the model does not include such effects. 

The effect of this is large arrays do not work as well as the model 
predicts.

2.) Mixing horizontal polarization and vertical polarization arrays 
causes an increase in fading, and a general overall reduction in S/N 
ratio unless phase and level is readjusted every 30 seconds or so.

The effect of this is antennas like four-squares can be combined 
with Beverages to improve S/N, but horizontal antennas can not 
(unless you are prepared to spend your life riding the combiner 
system controls).


73, Tom W8JI
w8ji@contesting.com



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