Special Problems in Transistorized Repeater Design for Long-Haul Systems

When the change is made from tubes to transistors, the repeaters can be buried in the ground, which makes temperature control possible such that after about ten temperature-controlled repeaters, a pilot-controlled repeater will be used. Although a system with buried repeaters makes it difficult to locate a fault, this can be done by a pulsed carrier operating above the useful band and returning to the input point at each repeater via special filters connecting both directions. When the power-feeding circuit is interrupted, the origin of the fault can then be tracked down by resistance measurement. Transistor repeaters require efficient protection with respect to induced extraneous voltages, e.g., by gas-discharge tubes and diodes.