[Moon-net] Radio Drift problems

[Dave Anderson, K4SV]

Hi All,
 
Since I am new to EME JT65B  I have a question.  In trying to work some stations, can not decode,  I have noticed frequency shift of the center frequency. I tried one station for 40 minutes trying to decode.  As the data is sent the modulation extends higher in frequency and usually the center frequency is stable and lays in a straight line down the waterfall display.  On only a few stations have I noticed this drift.  It varies with successive transmissions.  It looks like a J or L and sometimes a S but each time my WSJT JT65B decoder can not decode this drifting signal.
 
I have a few questions
 
Can I do something to compensate for this drift on my end enabling an option or something?
 
Is this drift indicative of some transmitters?
 
Is this FSK of the FSK atmospheric?
 
Thanks in advance,
 
Dave Anderson, K4SV
Tryon, NC
828 777-5088
 
www.K4SV.com