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Re: poor snr on ao 40 2nd note



Possible reasons for poor SNR vs. sun noise measurement.

The sun noise measurement is may be skewed by poor RF 
filtering and spurs in the local oscillator.  A simple system
with lots of local oscillator spurs and poor image filtering 
will often measure fantastically well when measured with
a broadband noise source, but perform poorly on the air.

The phase noise of the LO becomes a factor when attempting
to achieve high SNRs.  The downconverted phase noise may
actually mask weak signals.  One test is to listen to a clean
signal source and measure the achievable SNR.

73--Zack W1VT  
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