GB596662A - Arrangement for changing-over the speaking direction in two-way loud speaker telephone systems - Google Patents

Abstract

596,662. Loud speaking systems. AUTOPHON AKT.-GES. March 8, 1945, No. 5807. Convention date, Dec. 4, 1942. [Class 40 (iv)] In a system in which each subscriber is provided with a one-way amplifier, the speaking direction can be changed at will by either subscriber dialling 1. In the called subscriber's apparatus, Fig. 1, a call having been set up by means unspecified, relay E remains operated to switch in the amplifier V irrespective of the polarity of the D.C. current received from the centre tap of the coil Dr sent over the earth phantom from transformer Tr, Fig. 2, at the exchange via a<1>, b'. If negative polarity is received relay U operates to switch the amplifier V to the " receive " condition and indicator lamp SZ short circuited by a rectifier element does not glow. If positive polarity is received, relay U is short-circuited and switches the amplifier V to the " transmit " condition and indicator lamp SZ glows. At the same time the opposite polarities are sent out over wires a<2>, b<2> to the other subscriber to effect the appropriate changes in his amplifier. The polarities sent out at the exchange are dependent on the position of the stepping switch S, through whose coil successive impulses cause the reversal of the outgoing polarities to the subscribers. The impulses are given by the momentary falling back of relays J or Y in the subscribers' phantom circuits when one or other of the subscribers dials 1. On completion of the call slow release relay II falls back to ensure that the final position of switch S is such as to put the subscriber's amplifier into the " receive " condition.