A UHF mobile telephone system using digital modulation: Preliminary study

A UHF mobile telephone system using digital modulation is described. The system uses on-off keying of an 836-MHz carrier, the code being supplied by an adaptive delta coder with a clock frequency of 50 kHz. The maximum audio baseband signal-to-noise ratio is approximately 30 dB. The mobile receiver employs space diversity in a maximal-ratio combiner. Due to the use of amplitude modulation of the carrier rather than exponential modulation, the diversity receiver is very simple. The system was tested in the laboratory and in the field. Field tests were made in suburban and urban areas. For the four-branch system, threshold occurred at an average IF signal-to-noise ratio of approximately 12 dB.