Envelope-to: dave@picks.force9.co.uk
Delivery-date: Wed, 25 May 2005 12:35:25 +0100
From: "Mike Dennison" <mike.dennison@ntlworld.com>
To: rsgb_lf_group@blacksheep.org
Date: Wed, 25 May 2005 12:34:23 +0100
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Subject: LF: Reception with multiple antennas
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I have been following this interesting discussion, but I have some 
perhaps naive observations which could do with some expert answers.

Combining the output from two stations will give double the noise and 
double the signal - so no advantage there. I presume the fix is to 
make sure the two outputs are in phase, thus producing an improvement 
as the signals will be coherent but the noise will not. 

Plainly, there will be phase differences between the two receiving 
stations because of the different path lengths, and I suppose there 
would need to be compensation for this at the combining station.

I can see this being useful for point to point ground-wave links, 
where the relative phase between the two received signals can be 
predicted and is constant. But how can it work when the incoming 
signal is from an unpredictable direction, and the path length (and 
hence phase) of a sky-wave signal is varying all of the time?

At best you will have diversity reception (as described by Mal), but 
how do you keep two sky-wave signals in synch?

Mike, G3XDV
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