AN ORDER-WIRE FOR PCM SYSTEMS
RADIO CORP OF AMERICA NEW YORK DEFENSE ELECTRONIC PRODUCTS
Pagination or Media Count:
An experimental study of an amplitude modulated PCM order wire is described. Using a simulated 12-channel PCM pulse train and an ANGRC-50 transmitter and receiver, the following results were observed for 30 AM. In an order wire band, 300-2400 c, the signal-to-noise ratio for high RF signal levels was 33.0 db for full band, normal rate trains, and 28.0 db for full band, double rate biternary trains. At an error rate of 10 to the -6th power, a 1.5 db increase in RF signal power is required to compensate for the effects of 35 AM. Receiver noise in the order wire is 33 db below signal level using 30 AM, and operating at a PCM error rate of 10 to the -6th power. Several methods for detecting the AM order wire were tried. The best of these consists in subtracting from the AM-PCM train a delayed replica of the train and then applying half wave envelope detection to both positive and negative envelopes, using the average of the detected voltages for the order wire output. Theoretical analysis is given for the order wire noise caused by low frequency cutoff, intersymbol interference, and noise due to missing pulses. Theoretical and experimental results agree closely.