Codan 7277-TB Options PCB

Before modifying of the Codan could take place, I needed to work out what had been fitted to it and what was surplus to my requirements.  The Codan radios where very popular for use with the Royal Flying Doctors service, which used an emergency tone alert when assistance was required.

This radio had two of these emergency call boards and also another undocumented one bolted to the front panel.

I posted a question on the Codan Yahoo Group if anyone knew what it might be.  Without the remote control radio head it made it very difficult to identify the purpose of the board. On removal of the board, the radio became silent.
Ken – VK6YKG closely inspected my photos of the PCB and came to the conclusion that it may have been used possibly as a tone squelch PCB given the use of the NE567 tone decoder IC. Maybe it was used for decoding FSK, RTTY or even WeFAX.
After working out that the board was intercepting the AF audio between the Mute PCB and Remote PCB, I have since removed it as it is surplus to my requirement.