From: DL4YHF@aol.com
Message-ID: <72.19793e8e.29c8e9e6@aol.com>
Date: Tue, 19 Mar 2002 14:22:14 EST
Subject: Re: LF: Soundcard Mods
To: rsgb_lf_group@blacksheep.org
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<HTML><FONT FACE=arial,helvetica><FONT  SIZE=2>Hello Andy and group,
<BR>
<BR>
<BR>&gt; For LF use, how about an externally derived 1kHz sampling rate for input
<BR>&gt; from receivers using a narrow CW filter and BFO pitch set below 400 Hz ?
<BR>&gt;
<BR>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.
<BR>Surprisingly this is exactly what Alberto's PHD radio does, and what can be done with another program occasionally used by a few... &nbsp;:-)
<BR>
<BR>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.
<BR>
<BR>Regards,
<BR> &nbsp;Wolf &nbsp;&nbsp;DL4YHF.
<BR>
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