[R-390] Synthesizer Phase Noise

[rbethman]

John,

You are correct!  I believe that most of the synthesized systems had 
very few sites involved.

I do know that this site was using diversity systems, and was only for 
"sniffing" what was in the ether!

Bob - N0DGN

John Vendely wrote:
> Hi Bob,
>
> You are confusing phase noise effects in receiver local oscillators with 
> that of thermal noise in RF amplifiers and mixers.  Front end thermal noise 
> can be overcome by added antenna gain, but phase noise certainly does not 
> become a "non-issue" with increased antenna gain.   In fact, large, high 
> gain antennas usually make the problem worse.  Large antennas often deliver 
> huge off-channel signals to the receiver front end, where reciprocal mixing 
> with L.O. phase noise sidebands translates this noise into the receiver's 
> IF.  Weaker signals can be buried in the translated phase noise.  This 
> effect is completely independent of the receiver's front end noise figure. 
> Of course, if the antenna is positioned so the offending strong signal is 
> off-axis, the effect can be reduced, but this is often not possible.  Often, 
> the whopper interferer and the weak desired signal are both in the antenna's 
> main lobe.  Consider the case of a station on the U.S. east-coast with its 
> high gain directional antenna facing Europe, attempting to receive weak 
> signals in proximity to an HF broadcast band.  The bigger than antenna, the 
> worse the phase noise effects.
>
> For such applications, receiver designers often trade off noise figure for 
> improved front end dynamic range, but L.O. phase noise cannot be 
> compromised.
>
> 73,
>
> John K9WT
>