GB490272A - Improvements in or relating to circuit-arrangements for facilitating correct tuning of radio receiving apparatus - Google Patents

Abstract

490,272. Wireless receiving circuits. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN. Oct. 30, 1937, No. 29722. Convention date, Nov. 2, 1936. [Class 40 (v)] An arrangement for facilitating correct tuning of a radio receiver comprises a device, e.g. a brake, the control of which is effected by an auxiliary alternating voltage combined with the high or intermediate frequency signals so that it only takes effect over a narrow frequency band adjacent the desired frequency. Low frequency currents are injected into the input circuit of the I.F. amplifier 13 from a source 38 which may be the supply mains. The output circuit of 13 is coupled to two tuned circuits 14, 19, the former feeding the signal rectifier 16 and the latter being highly selective and supplying a rectifier 21. The load circuit of diode 16 comprises resistances 17, 18 while that of diode 19 includes resistances 20, 18 and part of resistance 39. The input of the first low-frequency amplifier 25 can be switched at 23 to the load resistance 20 or to a tapping on 17, the switches 37, 22, 29 and 33 being simultaneously operated with 23. The switches are all shown in the tuning position, the loud-speaker 28 being then disconnected. When any station is being tuned in, the rectified voltage across resistance 18, due to diode 16 provides a delay bias for diode 21 which is thus inoperative until the voltage across the sharply-tuned circuit 19 is sufficient to overcome the delay ; this occurs substantially at the in-tune position. The injected. mains frequency from 38 is thus amplified at 25, 26, and applied to the tuned A.C. relay 30 which operates a brake disc 32 to render the tuning difficult or inoperative. At the same time the relay operates switches 37, 22, 23, 29 and 33, which latter applies a holding current from the mains for the relay. The receiver is now in normal receiving condition. The small additional delay bias on diode 21, obtained from part of resistance 39, prevents rectification in this circuit when the bias voltage across 18 has still a low value. The relay 30 may act so as to render operative the low-frequency portion of the set only when exact tune is reached ; or an optical indicating device may be similarly controlled. To tune to another station, the relay may be de-energised by a switch, associated with the tuning knob.