Re: LF: Soundcard Mods

[DL4YHF@aol.com]

Hello Andy and group,


> For LF use, how about an externally derived 1kHz sampling rate for input
> from receivers using a narrow CW filter and BFO pitch set below 400 Hz ?
>
Instead of using the 1kHz reference signal as a sample clock for the soundcard (which may be a *very* tricky job), why not use 1kHz as a reference to determine the 'true' sample rate ? The software can do the rest, comparing the phase of the reference signal with a (software-based) NCO to find the 'calibrated' sample rate of the soundcard.
Surprisingly this is exactly what Alberto's PHD radio does, and what can be done with another program occasionally used by a few...  :-)

Regarding the 'AC-coupled' audio input: If only low bandwidth (a few hundred Hz) is required, the soundcard can be made 'DC-capable' with a simple chopper circuit (an square wave generator, an OPAMP as inverter and a CMOS 4066 analog switch can do the job). The software acts as synchronous rectifier to put the chopped pieces together again.

Regards,
  Wolf   DL4YHF.