Posted by
Vic K2VCO on
Jul 25, 2006; 3:39pm
URL: http://elecraft.85.s1.nabble.com/Clean-CW-signal-tp392446p392448.html
Geoffrey Mackenzie-Kennedy wrote:
> Although this might not be the cause of the modulation that you hear,
> the sidetone generator, the BFO varicap tuning and receiver IF filter
> varicaps circuits all share the Quad DAC chip U8 on the Control Board.
> Ideally each DAC should be completely isolated from the others, but in
> practice this is not the case which results in some sidetone signal
> hopping across to the BFO varicap circuit U10D during transmit,
> modulating the BFO.
As Geoff knows, I had this problem. I was alerted to it by someone whom
I was working who could hear the sidebands. They were 50-60 db down,
but as everyone knows even QRPp gets out! I tried various things
suggested by Elecraft but finally the solution turned out to be to
replace U8.
The way to check for this is to listen for sidebands +/- your sidetone
pitch on another receiver. If you hear them, try turning the sidetone
volume up and down and see if the strength of the sidebands varies. Of
course you have to be careful not to overload the other rx.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco_______________________________________________
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