"Ian Spencer" <iansp...@hotmail.com
> wrote in message
> back in the day we did things like transmit and receive SSTV, RTTY and
> CW using just the cassette input and output ports of the Spectrum withut
> any additional hardware interface.
I remember that, but it didn't work very well for high impedence tube gear,
and there were some isolation boxes out there, like the one from Technical
Software somewhere in Wales, but that coimpany is long since gone
apparently. Even if it's not, googling "technical software" leads to a dead
end due to all the noise.