Electronic regeneration of teleprinter signals

On asynchronous or start-stop telegraph circuits of extended length it frequently becomes necessary to insert at repeater points signal regenerative devices to reduce the cumulative effects of fortuitous distortion. Regeneration is a process of signal scanning by a succession of accurately timed impulses whose phase is as nearly as possible independent of the phase variations of the signal impulses. In one form of a mechanical regenerator, reception of a start signal transition permits the engagement of a brush arm with a continuously rotating constant-speed shaft. The signal polarity then is determined at the instant of contact of the brush with commutator segments that are short in comparison with the signal period. Following retransmission of the signal the brush arm is disengaged from the shaft and held on a stop to await the arrival of the start transition of a second character. Mechanical regenerators have been developed to a high level of performance, accompanied by some complexity and the need for skillful maintenance. This paper describes an electric signal regenerator utilizing the time of delay of a recurrent filter network to generate the scanning impulses, which together with the electrical equivalents of the start and stop functions provide a regenerative repeater without mechanism. The composition of an illustrative teleprinter signal character and its peculiar susceptibility to interfering line currents is discussed. The development and the electric characteristics of the delay network are described, and an explanation of the regeneration of the signal character by the device is given.