One D-D-D-of-the-C-U-the-D-T search later, and I found this:
What a mess!
So this was the mixer method. All I remember is the cct was known locally as the Bury Radio Club circuit.
Let's see, an MC1496, normally used as a balanced modulator, a 7492 /12 counter, I know the other two things are miniature relays, what did they do? Transmit/Receive switching I suppose.
And if that's an oscillator in the middle where's the active device? I know from recent experience that the MC1496 normally has an external osc.
Must be over 30 years since I've seen this. Frightening.