GB795098A - Telegraph apparatus employing a transistor amplifier - Google Patents

Abstract

795,098. Code telegraphy. STANDARD TELEPHONES & CABLES, Ltd (International Telephone & Telegraph Corporation). Sept. 25, 1956, No. 29242/56. Class 40 (3). [Also in Group XL (c)] A frequency shift telegraph receiver comprises a limiter-discriminator arrangement 12, producing double current signals which are fed to a transistor converting amplifier 13 supplying single current signals to the selecting magnet of a teleprinter 14, and a circuit 11 which biases the amplifier into the mark condition when the signal is absent. The output from the discriminator 12 is negative on marking signals causing an input transistor 41 to be cut off and parallel connected output transistors 53, 54 to be conducting so that current flows in the selecting magnet 61 of a teleprinter. Space signals are positive and these cause the input transistor 41 to conduct and therefore the output transistors 53, 54 to be cut off so that the selecting relay 61 is released. A capacitor, resistance arrangement 56, 57 improves the operation of the relay and a zenner diode 55 limits the voltage peaks when the relay current is interrupted. It is stated that the relay circuit 11 which bases the input transistor to the marking condition in the absence of an input signal could be replaced by a transistor circuit. In an alternative circuit (Fig. 2, not shown) the output transistors are replaced by a junction diode.