Monday, 17 February 2014

El Cheapo soundcard - Modified

 A quick test of the 99p soundcard showed 2.2v DC on each headphone channel, which was easily solved using a small milling bit on my Dremel to remove the offending PCB trace.

A pair of 100uF 16v electrolytics were then soldered into place. As it turns out, on this board the silkscreening was correct, the + markers being in the right place.

The connections were probed again after modification with the card attached to my laptop. All seemed well so an audio feed was arranged from the FRG-100 tuned to the PSK sub-band of 20m, and FLDIGI started and configured.

The photo on the below shows FLDIGI running. Lots of nice clean decodes coming through. The level is a little high (the computers sound mixer is set to 0) but not a problem here.

I then switched to WSPR reception. The indicated audio noise level was too high, at 43dB, but I remembered what was needed to set up the other USB sound-card for WSPR, and found and switched off the cards AGC. Levels are now in the 20-21dB region. Im getting a lot of very nice WSPR decodes, including plenty of spots from across the pond.

Whats required now is to add the audio out feed and check performance on transmit. This is more awkward as I dont currently have a cable with the right inline socket to extend the Tx audio feed path.

No more radio play for now, its a boys day for me and Sam today and pictures and pizza await!

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