Investigation of four-level PCM/FM for spectrum conservation

It is pointed out that secure telemetry requires Pulse Code Modulation (PCM) transmission. Bandwidth conservation may be required in future secure telemetry missions, especially those involving wide band analog data. The present investigation is concerned with tests which have been conducted to study four-level PCM/FM for bandwidth conservation. For effective bandwidth conservation, the spectrum occupancy of four-level PCM/FM should be approximately one-half that of binary PCM/FM or less. Attention is given to spectra and waveforms, the effect of IF and video bandwidths, and bit error rate (BER) test results. It is found that the spectrum occupancy can be reduced to 65 percent of binary PCM/FM at a carrier power cost of 4 dB.