PSK31/SSTV Interface

The interface needs little more explanation than is provided by the circuit.  I preferred the interface to be electrically isolated from the PC when in use, so I employed line isolating transformers available from any number of mail order outlets for a £1 or so each to isolate the signal lines, and an optical coupler to isolate the RTS signal line, the 4N35 again available from mail order outlets for a few pence works fine.  The transformers are quite 'lossy' but in my case this turned out to be an advantage because the signal levels were just right for the Icom and I didn't have to put any further attenuation in the interface.   I also wanted the interface to be physically isolated from the PC when not in use, so as you can see from the circuit and photo, I have employed a rotary switch physically to break the signal and RTS lines on the radio side of the transformers and opto isolator.  The circuit shows connections for my Icom 720A, but all you need to do to adapt it for any other transceiver is identify where the transceiver's signal in, signal out and PTT auxiliary connections are and wire the interface accordingly.