Application of Compandors to Telephone Circuits

Prior to the war a compandor was developed for general use on telephone circuits of the Bell System. This equipment provides power range compression at the transmitting end and power range expansion at the receiving end of a telephone channel. The resulting crosstalk and noise reductions of about 25 decibels are large enough to make useful circuits out of channels which otherwise would be unworkable. This paper considers engineering problems in the application of compandors and describes the circuit principles involved in the equipment.