GB1334103A - Telephone stations - Google Patents

Abstract

1334103 Substation equipment SIEMENS AG 7 Sept 1971 [8 Sept 1970] 41573/71 Heading H4K A portable substation incorporates a tone caller and an incoming speech amplifier whose gain is reduced so as to reduce the possibility of singing when the station is placed in its transmit mode by the operation of a transmit/receive switch (speak key). The latter Sp is effective when operated to remove a short circuiting capacitor C1 from the wiper of a potentiometer R1 so that the full track resistance thereof is incorporated in the emitter circuit of transistor amplifier T1. The potentiometer is adjusted for optimum received speech volume in the face of different length lines. The calling signal is of 1200 c.p.s. which is detected by an analyser B1200 that incorporates a threshold and a persistence circuit as well as a speech guard circuit. The latter includes an oscillator and a diode. The analyser closes a transistor switch which supplies power to a square wave low frequency generator G2 whose output chops a high frequency signal supplied by a generator G1 to a loud-speaker L so as to simulate a ringing signal. In order to transmit a calling signal, key R is operative to couple power to generator G1 via diode Gr1, to couple G1's output to line, to place T1 in its low amplification state and to prevent the analyser output from being effective. The station may be tested by operating keys R and P together so that the generated tone is now chopped by G2's output and applied to speaker L thus signifying correct operation of the generators and of the analyser. Power for the station is supplied by local battery U.