Topband: Receiving on Directional Antenna

[Tom Rauch]

> It would be useful to use some black box where you use your Tx antenna
> as an alternative to the directional beverages even to the point where
> you could add them and use the omni directional in the background
> along with your beverages.  Alternately run a second receiver and mix
> the audio with stereo headphones so that you are not just listening in
> one direction but checking other azimuths at the same time in the
> other ear !!

Mixing in a signal from a different direction at audio is exactly like 
mixing it at RF! It decreases directivity and decreases S/N ratio of 
the system.

I can record in stereo WAV files with phase-locked receivers, and 
demonstrate that if someone has a web page. What you I find is 
this:

1.) If the signals are in phase and have nearly-equal S/N ratios and 
mixed to mono from widely separated antennas, I get substantial 
S/N improvement in the sum. But it is impossible to hold the signal 
in-phase for long and QSB makes the levels vary rapidly also.

2.) If I listen in stereo I get slightly less enhancement but QSB, 
phase and levels have less effect so the enhancement is more 
reliable.

3.) If I listen in two different directions, either in stereo or mono, it 
decreases S/N ratio a quite noticable amount. The change is about 
the same as just using a poorer receiving antenna.
    
73, Tom
(W8JI@akorn.net) 


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