An alternative to the SD interface is my PIC based one, which is
directly compatible and uses just two ICs one of them an op-amp.
Rik's idea of bypassing the card is another good solution.
One alternative that already exists is the VE2IQ interface. See
http://cafe.rapidus.net/bill1/bbs.htm and download SDPCX.ZIP .
This is a home brew Sigma-Delta A/D which drives a serial port.
Many PSK and CCW programs can use it, and it has also been
used with WOLF.
You can buy kits from Bill for US$54, or build your own from scratch.
Sample rate is a precise 7200 Hz. Resolution is only 8 bits,
but IMO that is plenty, unless the audio signal is dominated
by a strong interfering carrier. If most of the audio power is
random noise and/or static crashes, then even 1 bit is pretty good!
Steve VK2ZTO has shown impressive results sampling this way.
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