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An experimental digital repeatered line has been developed which transmits information at a rate of 224 Mb/8 as part of an experimental highspeed digital transmission system. The PCM terminals and time division multiplex portions were described by J. S. Mayo and others in the November 1965 issue of the Bell System Technical Journal. The repeatered line is described in this paper. The performance of this line is shown to be suitable for coast‐to‐coast operation. The line utilizes 0.270‐inch copper coaxial transmission lines and regenerative repeaters at one‐mile intervals. Ten repeaters have been operated in tandem to form ten miles of repeatered line. Each repeater uses 25 transistors, most of them a new germanium design with a cutoff frequency, ft, of 4 GHz. Esaki diodes provide the decision thresholds for the regeneration. Power to the repeaters is supplied by dc over the center coaxial conductor. The pulse transmission code is paired selected ternary (PST).

A 280-Mb/k 'dhital coaxial repeater employing h v v v g transmission_ with quantized feedback for dc-wander control has been designed and constructed. The linear channel forward path includes a 10-MHz low-frequency cutoff,.and the missing low frequencies are supplied by a filtered signal from the repeater output. This approach effectively removes dc wander without use of code restriction, making it possible to use two-level rather than three-level transmission without loss of information transmission. Eye margins ire consequently significantly greater than for previously designed 280-Mb/s three-level repeaters.The bandwidth ratio, or ratio of upper to lower 3dB down points of the signal transmission path, is only 10 for this approach compared to several hundred for the three-level bipolar approach (and more for codes with higher transmission efficiency), This results in greatly reduced susceptibility to interference from lightning, and power surges, elimination of preamplifier overload, and simplified repeater design.--

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