GB684658A - Improvements in frequency-modulation receivers with silent tuning - Google Patents

Abstract

684,658. Radio-receiving circuits. PHILIPS ELECTRICAL INDUSTRIES, Ltd. July 25, 1951 [July 28, 1950], No. 17618/51. Class 40 (v). In a frequency-modulation receiver provided with silent tuning, the muting voltage is derived from a rectifier coupled to a high-Q circuit which is bottom-capacity coupled to one of the tuned circuits of the discriminator. As shown, the frequency demodulator comprises a valve 1 of nonode type, in which two successive grids are coupled respectively to the primary and secondary of a pair of coupled tuned circuits 3, 5, both of which are tuned to the signal carrier frequency. In order to mute the receiver, a negative potential is applied to the inner grid 7 of the valve 1, being derived from a source 8. The muting is removed upon accurate tuning by means of a rectifier 9 coupled to a high-Q circuit tuned to the carrier frequency and comprising inductance 15 and capacity 16, being coupled to the circuit 3 by means of a common capacity 12 of large value. The smoothed output from the rectifier 9 is used to bias back a tuning-indicator tube 18; the resulting rise in anode potential is communicated to the grid 7 of valve 1 via a resistance 20 and counteracts the muting bias. In order that unmuting shall not occur, with an exceptionally strong signal, before the proper tuning point is reached, delayed automatic gain control is applied to the preceding I.F. stage 2 by means of a rectifier 24 coupled to the tuned circuit 3. Specifications 611,335 and 684,659 are referred to.