73091530
Jun 13, 1976
Dec 6, 1977
TEN-STATION INTER-COM UNIT, PROVIDING SELECTIVE SIGNALING AND INTER-COMMUNICATING CAPABILITY BETWEEN STATIONS ON CONVENTIONAL PUSH-BUTTON TELEPHONE KEY SYSTEMS, THE UNIT PROVIDING INDEPENDENT TALKING CURRENT AND DUAL TONE MULTI-FREQUENCY SELECTIVE SIGNALING IN SUCH SYSTEMS
Electrical and Scientific Apparatus