GB552462A - Improvements in frequency or phase modulation receivers - Google Patents

Abstract

552,462. Frequency and phase modulation. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Oct. 24, 1941, No. 13717. Convention date, Oct. 25, 1940. [Class 40 (v)] A frequency or phase modulation receiver is muted unless the receiver is accurately tuned to an incoming signal. The intermediate frequency is applied by tuned circuits 1, 2 to a limiter valve 3 which feeds a frequencydiscriminating detector network. This may be of the off-tune type as shown, or of the phasing type described in Specification 489,094. The demodulated output is taken across rectifier load resistances 9, 11 through a smoothing circuit 26 to a relay oil 22, so that while the tuning is inaccurate a direct current passes through the coil 22, attracts the armature 20 against the action of a spring 30, and holds open the contacts 40 so as to cut off the detector from the audio-frequency input line 50. Only when the tuning is accurate does the direct current fall to zero and allow the signal to pass to the audio-frequency circuits. Closure of the contacts 40 is assisted by a coil 21 which is connected to a condenser-shunted leak 4 in the grid circuit of the valve 3 and which receives maximum current when the set is accurately tuned. The coils 21, 22 may be connected as series coils instead of shunt coils, and the contact 40 may be across the audio-frequency input. The relay may operate by biasing an audio-frequency amplifier. The Specification as open to inspection under Sect. 91 refers to an electronic relay arrangement used in place of the electro-mechanical relay. This subject-matter does not appear in the Specification as accepted.