Speech and signalling switching equipment in the Highgate Wood electronic telephone exchange

The paper gives details of the common time-shared paths used for the switching of speech connections, the transmission of tones and the transmission and detection of line signals for a 3200-line electronic exchange to meet the facility requirements for public service. The exchange will work with the existing telephone and bell and existing junction signals. Exchange lines of all types terminate on individual line equipments which are arranged in 800-line groups and provide access to the common 4-wire time-shared paths. Compatible timedivision-multiplex pulse techniques using 100 pulse channels per group are employed for the speech and signal paths and for the common control equipment. The speech-path pulses are voltage amplitude modulated by the speech signals. Details are given of the diode gates and amplified coaxial cable links used in the common speech paths, and the means of meeting transmission performance requirements, particularly with regard to crosstalk and gain stability. Crosstalk attenuation is limited by energy storage in switching diodes, highways, and paths interconnecting the main switching stages. Proposals are given for future developments aimed at reducing the size and power consumption and improving the reliability of the equipment.