The Soviet/Russian telemetry
system employed since the mid-70's is a rather normal PCM telemetry frame.
The symbol rate is 256 kHz. The signal is frequency modulated on the carrier.
The modulation index is quite high and the received signal spectrum has
two distinct peaks about 125 kHz from the nominal carrier frequency. That
is why a sharp buzzing sound is heard on a narrow-band FM receiver on 165.875
MHz and 166.125 MHz when listening to telemetry from modern Soyuz vehicles.
This modulation system is
also used by satellites in the Foton series, transmitting on 239.5 MHz.
The image on the right shows the spectrum of the PCM-FM signal as picked
up by a Nems-Clarke 2501A receiver and displayed on the accompanying Spectrum
Display Unit 200-1.
Systems of Soviet/Russian manned spacecraft]
Copyright © 1996 Sven Grahn