[Elecraft] Re: Spurious signal after k2 click mod

[Vic Rosenthal]

Wayne Burdick wrote:

> It sounds like sidetone energy is getting into the CW envelope. The circuitry
> for both sidetone and keying includes U8, U10 and RP3. At 600 Hz I wouldn't
> expect any conducted interference between the two, but a sharp edge from a
> digital waveform is a different story.
> 
> Do the sidebands go away completely if you set the sidetone amplitude to 0? Does
> their amplitude and frequency vary directly with the ST L and ST P settings?

You nailed it, Wayne!  The answers are Yes and Yes!

> Another experiment you can do: 
> 
> Set the sidetone level back to normal, then put a capacitor from pin 1 to pin 5
> (or pin 14) of the DAC, U8. This would tend to suppress the sharp edges coming
> out of the DAC -- it's the same pinciple behind putting C45 on the VPWR line
> (same as pin 2 of the DAC, U8). It reduces the slew rate. If edges in the
> sidetone waveform are causing the problem, this should help.

What value capacitor do you suggest?

-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco