Telephone instrument transmit and receive circuit - uses amplifiers instead of induction coil located on diagonals of Wheatstone bridge network (NL 6.6.78)

摘要

The telephone instrument circuit replaces the usual ASTIC induction coil with a microphone transmit amplifier (AT) and a receiver amplifier (AR). Both amplifiers are placed on diagonals in a Wheatstone bridge network to prevent interaction. One arm of the Wheatstone bridge (Z3) is adjustable to balance the bridge with the subscriber line located in an opposite arm (Z4) of the bridge. Use of a transmit amplifier allows the carbon granule microphone to be replaced by dynamic and other inserts.