Abstract
A communication system is described which enables three music circuits and an engineer's circuit to be combined. The combination is effected by using pulse time modulation in four time-division multiplexed channels. The purpose of the system is to enable a microwave link, intended for the transmission of television signals, to carry audio signals of broadcast-programme quality as an alternative. The radio equipment, primarily intended for television transmission, need not be specially designed for this particular service.Measurements of the performance of the equipment indicated very satisfactory signal/noise and signal/crosstalk ratios. When the terminals were directly connected the figures obtained were better than those recommended by C.C.I.F. When the terminals were operated in conjunction with a 25-mile radio link there was a 20dB margin in the signal/noise ratio over the recommended value. This margin was allowed for fading of the radio signal.The choice of time division as a multiplexing method is discussed, and the selection of the pulse repetition frequency, duration and time deviation is explained.A detailed description of the multiplexing circuit is given, and both the performance specification and actual measured performance figures are tabulated. Finally, the signal/noise ratio obtained with the radio link working over a 25-mile path is discussed, and the improvement which results from the use of pulse time modulation is explained.
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