Selective signaling in the bell system—Relay to transistor

Selective Signaling is used in Domestic Public Land Mobile Systems by many Telephone Companies to individually call vehicles equipped for mobile telephone service. Problems of reliability, speed, simplicity and number capacity, rule out many possible systems. A mechanical device used successfully for the past years is now proving both bulky and costly so that newer devices are under consideration. A description of the present day system is given in this paper inasmuch as any new equipment will be expected to perform in a compatible manner.