This is my easy to build, homebrew sound card interface. This box allows me to chat with other hams over the air with my PC digitally (even with a rig that is now 30 years old). My first contact using the box was with the PSK31 digital mode. I chatted with another operator 1928 miles away in Montana on 10 watts (most night lights use 7 watt bulbs, but do not allow communication 2000 miles).
The box is very simple. It provides isolation and level control between the sound card in my PC to my Kenwood TS-520S transceiver. The PC is needed to make and interpret the tones on the radio. The schematic is taken from the universal sound card interface designed by S56AL on his site.
The performance of the box plugged into the phone patch in and phone patch out jacks on my TS-520S is acceptable. The receive audio on the 520's internal speaker can be a little louder than I like to get the correct audio levels for receive, but it doesn't bother me too much. I'm considering adding a second transformer or using one of the other taps on the one I've got to improve the receive audio performance. Transmit works very well. I use VOX to control transmitting on the rig and that seems to work just fine. I have gotten positive comments about having a clean, narrow PSK31 spectrum.
It took a few hours to build, but it is 100% junk box parts--new parts would not have cost much, and would have saved time scrounging; but I would have not been able to build it on a whim in the middle of the night either. It cost $1 to get the enclosure from Hamvention 2006. I wasn't sure what I would need it for until this week, but it was too cool of an aluminum box to pass up for a buck! Please check out the photos that follow. If you click the photos, you can get a really good close-up look.
Guts ready to go into the box -- The PCB I hot glued everything to came from the old modem that I pulled the isolation transformer from. The other transformer came from a 2nd old modem. The pots came from the junk box --- probably old TV adjustment pots. The cabling came from an old wall wart and dead headphones. The phono cable was laying around. The wooden strut was glued on to keep the guts from sliding around in the case. The stickers are placed strategically to hide extra holes.
The last image is the back of the unit where the cables exit though some existing holes:
Comments welcome -- 73, KB1KDW