Monroe Electronics 948A - Manual (Page 7)

6
OPERATION
The Model 3185E Dual Tone decoder monitors the audio at TB #1 pin 4 for the
specific four digit Cue Tone ‘ON’ code sequence to which it is programmed to respond.
When it receives the correct code, the 3185E’s relay energizes, which supplies ground
to the 3446A Relay card, energizing it’s relays. This switches in the alternate
audio/video program source.
The 3185E continues to monitor the audio at TB1 #4 and when it receives the correct
‘OFF’ code sequence, it de-energizes it’s relay and de-energizes the relays on the
3446A card. This returns it back to the main program source.
If the Model 3137B UAD has answered the telephone line, the above connection is
isolated, and tones supplied over the telephone line are used – as above – to activate
the device.