A Bipolar Repeater for Pulse Code Modulation Signals

Abstract

Designed for use on unloaded exchange cable, this repeater was developed to satisfy the transmission requirements of an experimental PCM system. It utilizes a pulse repetition frequency of 1.544 mc, and 6000-ft repeater spacing. Functionally, the repeatered line transmits the PCM signal without appreciable degradation over distances up to 25 miles, a feat accomplished by retiming and reshaping the signal at each repeater point. Retiming is accomplished by means of a clock extracted from the signal; reshaping is accomplished by regeneration with positive pulse width control. Near-end crosstalk and pulse train jitter dominate the design parameters. Timing is made tolerant of near-end crosstalk by choice of bipolar transmission (where successive marks are of opposite polarity) with clock derived from the rectified and clipped signal. Tolerance in the decision circuit is obtained by automatic threshold control, spike sampling, and tight control of time and voltage parameters. Accumulated pulse train jitter is controlled to the extent dictated by the terminal equipment, principally through control of the bandwidth of the clock circuit. Seven diffused-base transistors and ten logic diodes are used in the oneway repeater circuit. A two-way repeater consists of two such circuits with a common power unit, utilizes 135 components, and is packaged in a can of $1{1 \over 16} x 3{1 \over 8} x 5{3\over 4}$ -inches outside dimensions. Accommodations are made for line-length and power options, as well as remote testing. Power for the repeater is transmitted over the signal pair. One watt is required for the two-way repeater.