GB555840A - Noise reduction signalling system - Google Patents

Abstract

555,840. Television. STANDARD TELEPHONES & CABLES, Ltd. March 28, 1942, No. 4156. Convention date, Nov. 1, 1940. [Classes 40 (iii) and 40 (v)] In television transmitting systems including a range compressor 11 at the transmitter and a corresponding range expander 42 at the receiver, a variable-gain amplifier for amplifying the compressed signals inversely in accordance with the maximum highlight and/or black peak amplitudes occuring within a stipulated period is inserted after the compressor at the transmitter or before the expander at the receiver. When the variable-gain amplifier is at the transmitter, an opposite variable-gain amplifier may be inserted before the expander at the receiver and control bias may be fed thereto from the variable-gain amplifier of the transmitter. This is shown in Fig. 1, where 10 is a picture signal generator, 11 a range compressor, 15 a variable-gain amplifier, 23 and 30 diodes arranged as shown to be influenced by the signal peaks to produce the variable bias for the amplifier 15, and 22 the final stages of the transmitter. The receiver includes a signal receiver 40 followed by a variablegain amplifier 45, a black-leveller diode 51, a range expander 42 and an image reproducer 58. The control bias signal transmitted from the transmitter is received by a signal receiver 60 and passed to a triode 62. which reverses the phase of the bias and applies it to the variable-gain amplifier 45. The variable-gain amplifiers shown in Fig. 1 have one stage only; but multi-stage amplifiers may be used instead.