Topband: Diversity receiving

[Tom Rauch]

I replied to Ford direct, but since people have a general interest in 
this....

> Space diversity meant two dishes separated by several hundred
> wavelengths. Obviously this is out of the question for topband.
> Polarization diversity would take very little real estate and should
> work very well.
> Those who have beverage farms might have further thoughts on space
> diversity.

Just from my experience here, since I have been trying this for a few 
years now.

Polarization diversity has been largely useless, because S/N is so 
much lower on a dipole at (any height) than a Beverage that the 
signal from the Beverage is almost always significantly better even 
in a fade.

I just can not get a very directional antenna that is horizontally 
polarized up, even with the real estate and towers I have. Even when 
I had two phased dipoles at 280 feet, the Beverages were 
significantly better 95% of the time.

Space-diversity does work quite well, but it takes about 2 or more 
wavelengths to be consistently effective. At 2 wavelengths it is 
almost impossible to keep two antennas directly combined in phase, 
because of the difference in fading and phase. The solution is to run 
stereo diversity with phase-locked receivers.

There is a profound difference when I use antennas 2500 feet apart, 
it is much less noticeable at 1750 feet, and rarely offers a 
noticeable improvement at 1000 feet. At less than that, I can 
directly combine antennas ahead of the receiver and pick up 
significant gain.

Keep in mind this is with fairly directional antennas, HPBW of about 
60 degrees or so. I'm not sure how it would work with less 
directivity in each "cell". It is sure worth a shot, no matter what 
the spacing.73, Tom W8JI
W8JI@contesting.com