GB649262A - Improvements in or relating to noise limiter circuit arrangements - Google Patents

Abstract

649,262. Radio interference suppression circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Oct. 8, 1947, No. 27048. [Class 40 (v)] In a noise limiter circuit for a radio receiver having a rectifier associated with a time constant circuit such that it is blocked during the presence of steep noise impulses, the signal demodulator has its anode earthed, and the output is taken from the anode of the noise limiter rectifier, the cathode of which is conected to the demodulator load resistance. Fig. 3 shows part of a superheterodyne receiver in which intermediate frequency signals are fed to tuned circuit 3, and a demodulator diode 4 produces audio signals across the load resistances 5, 6, a positive potential being developed at the upper end of these resistances. Audio signals are applied through diode 10 and potentiometer 16 to the low-frequency output stages. The diode 10 is normally conducting due to the potential developed across resistance 5, but is associated with a time-constant network 11, 12, 13, so that diode 10 is rendered non-conducting during the presence of a steep noise impulse, thus interrupting the signal path and preventing the noise from reaching the output circuits. The addition of diode 18 improves the arrangement by providing a low-impedance path to audio frequency across the output circuit during noise impulses. The Specification acknowledges as known, a similar circuit, but in which diodes 1, 10 and 18 are reversely connected, the arrangement according to the invention resulting in reduced impedances between the cathodes of diodes 10 and 18, and earth, so that hum due to the diode filament alternating current supply is reduced.