The purpose of the Command Receiver and Decoder was to manage the power consumption of the "high power" HF transmitter by turning the transmissions on and off. The receiver was a superheterodyne receiver operating on 147.850 MHz in the 2 m amateur radio band.
The Command Decoder used three audio tones to determine the state of a bistable flipflop that controlled the transmitting state of the HF Transmitter. We can now reveal the Command System frequencies for the first time ever. The ON command required the Enable tone of 2,960 Hz and the On tone of 3,494 Hz to be transmitted simultaneously for several seconds. The OFF command required the Enable tone and the Off tone of 3,226 Hz to be transmitted. The bandwidth of each of the command tone audio filters was 30 Hz.
Frequencies were deliberately not published in the Users' Guide to ensure that valid commands were only sent by authorised stations.
It is interesting to see the Command Decoder photograph opposite where you can clearly see the capacitors and inductors of the resonant circuits for the three audio tones. No integrated circuits and gyrators in those days!