The following information has been excerpted from National Aeronautics and Space Administration. 1978. The Nimbus-7 User's Guide. C. R. Madrid, editor. Goddard Space Flight Center.
Command, telemetry, and ranging signals are handled by a unified S-band transponder. Stored data are played back to the ground station using the S-band links. Specifically, the telemetry system includes two transponders which are interlocked to prevent simultaneous transmission and also two wideband transmitters that are interlocked to prevent dual transmissions. Single or dual downlink transmissions may be commanded at the transponder downlink frequency of 2273.5 MHz or the wideband transmitter downlink frequency of 2211.0 MHz. Additionally, any combination of signals may be used to modulate one transponder and one wideband transmitter. One combination is an 800 kbs bi-phase PCM playback from any of the three on board tape recorders. When using this combination, the playback data may be either recorded digital information processor data or Coastal Zone Color Scanner sensor data. Another combination is an 800 kbs bi-phase PCM or real-time Coastal Zone Color Scanner sensor data.
The transponder modulation is baseband PCM/PM multiplexed with the VIP telemetry subcarrier. The wideband transmitter modulation is PCM/FM. The transponder can be phase modulated by ranging tones, by 800 kbs bi-phase PCM data or by 27 kbs bi-phase PCM real-time DIP data on a mutually exclusive basis, selected by command. Simultaneous commanding, range tracking and VIP telemetry transmission are possible with the selected baseband modulation signal.