E

EAMPS: Expanded AMPS.

E&M signalling: A form of direct current signalling, which was developed 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 ...

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