GB505276A - Control device for radio receiver - Google Patents

Abstract

505,276. Wireless receiving circuits. MULLER, E. N. Aug. 3, 1937, No. 21440. Void. Convention date, Aug. 1, 1936. [Class 40 (v)] The invention relates to circuit arrangements for deriving control voltages actuating a utilization device of the kind described in Specification 500,111 or 503,217 whereby the receiver tuning shaft is arrested when exact timing with a desired station is obtained or the tuning gear ratio is changed thereby. An object of the invention is to prevent false actuation of the device by an interfering signal such as static. In Fig. 1, part of the output of the I.F. amplifier 5 of a superheterodyne receiver is applied to preliminary amplifiers 16, 19 and thence to a pair of rectifiers 46, 47 the outputs of which are applied in opposition to vary the bias on a D.C. amplifier 29 operating the utilization device 34. The input circuit 45 of rectifier 47 is flat-tuned to the I.F. and is magnetically coupled to circuit 41, while the input 43, 44 of rectifier 46 is sharply tuned and has a pronounced double-humped characteristic a few kc. on each side of the true I.F., by virtue of the series-resonant circuit 44. When a station is exactly tuned in the normal delay bias on 46 is exceeded, 46 then opposes 47 and the potential of line 50 falls to zero causing a sharp rise in the anode current of 29 which actuates device 34. An impulse due to static would not affect both circuits equally, as does a desired station, and the device would not be actuated. The amplifier 16 may be dispensed with and the circuits 43, 44 may be replaced by three parallel circuits connected in series in the anode circuit of valve 19, tuned respectively 2À5 kc. above, below and exactly to the I.F. ; the input of rectifier 47 is coupled to the first mentioned, 46 being connected to the common point of first and second, Fig. 2 (not shown). In Fig. 3, the rectifiers 46, 47 are fed from separate channels comprising amplifiers 193, 192. Their input circuit characteristics are as for Fig. 1, but the rectifier 46 opposes 47 by varying the grid bias of amplifier 192. The output of 47, as varied by 46, is applied to a D.C. amplifier 91, the anode circuit of which includes a neon tube 90. This tube strikes at a critical voltage corresponding to the in-tune position ; the resultant voltage drop across resistance 93 removes a prohibitive bias on the radio frequency amplifier 94 and renders the receiver and the A.F.C. system operative ; positive bias on 94 is prevented by the limiting diode 94<1>. The lamp 90 may also give a visual indication of tuning. The outputs of the two rectifiers 46, 47 mutually opposed, e.g. as in Figs. 1 and 2, may be applied to different grids of a hexode D.C. amplifier whose anode circuit includes a lamp such as 90, Fig. 3.