November 21012:

This interface came about as a consequence of the fact that the RA218 was never designed to provide direct audio output to a loudspeaker. Instead, as part of  the CJK configuration it was designed to deliver the baseband signal into a 600 ohm transmission line … although it does provide 1/4” jack sockets for local monitoring via headphones.

Concept block diagram

A Dedicated Interface for the RA17, RA17L, RA117 & RA218

Design considerations:

From each of the three receivers (RA17 MK1, RA17L & RA117), the interface requires a 100KHz output signal and a 3mW DSB baseband audio feed. The interface also serves to connect the aerial to which ever receiver is selected. A further function of the interface is to take the 1MHz reference from my MA259 and deliver it via cathode-follower buffers to up to four receivers.