ABSTRACT

EAMPS: Expanded AMPS. E&M signalling: A form of direct current signalling, which was de-

veloped in the UK by BT as DC5 signalling, for use on the PSTN. It is also used for tie line signalling through a PABX. Separate wires are used for voice and signalling, the signalling taking place on two wires, the E (ear) wire and the M (mouth) wire. The PABX sends signals on the M wire and receives signals on the E wire of another PABX (Figure E.1). The E lead has an earth potential applied from a contact and the receiving equipment has a battery connected relay as the receiving circuit. The same circuit is used in the opposite direction on the M lead, but in reverse. The impedance between sending and receiving ends is limited to about 140 ohms. The relay contact is pulsed at about 10 pulses per second from the PABX control system.