PPM-AM telemetry

Sven Grahn, Sollentuna, Sweden

This type of telemetry was used by many types of automated and piloted spacecraft launched by the Soviet Union.

In this pulsed AM transmission 4 microsecond long pulses are transmitted every 80 microseconds. These pulses define words in the telemrty format. Within each such interval a word value pulse is transmitted. Its position in the 80 microsecond word interval defineds the particluar word value transmitted. Therefore the telemetry system is called pulse-position modulated amplitude modulation (PPM-AM). There is also a second mode of the telemetry system with word interval length equal to 96 microseconds. The figure below illustrates the pinciple. It shows a simplified sketch of the oscilloscope output from a Nems-Clarke 1302A telemetry receiver.

Spectrum...

View on SDU....