GB445543A - Improvements in or relating to electrical high frequency oscillating circuit arrangements - Google Patents

Abstract

445,543. Valve circuits for wireless reception. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London, and RUST, N. M., 109, London Road, Chelmsford. Sept. 14, 1934, No. 26464. [Class 40 (v)] The natural frequency of an oscillating high frequency circuit of a radio receiver is automatically varied in dependence on departures from exact tuning by a reactance associated with the circuit, constituted by the Miller effect between two electrodes of a thermionic valve. In Fig. 1, the local oscillator of a homodyne receiver is constituted by the two grids 4, 5 and cathode of a heptode 1, the control grid 7 of which receives signal energy for frequency-locking purposes. The circuit 16 feeding the homodyne detector (not shown), is coupled to the frequency determining circuit 11, 12 of the oscillator across which is connected the control grid-cathode circuit of the pentode 31 constituting a variable reactance. The cathode circuit of the heptode 1 includes a low-pass filter 24, 26, 27, the output from which is applied through potentiometer 25 to the control grid of the thermionic reactance 31. A variable condenser 32 is connected between control grid and anode of 31. Beat frequencies due to frequency difference between the oscillator frequency of 11, 12 and the incoming frequency are applied to vary the reactance of valve 31 in such sense as to correct the frequency of 11, 12 until the beats disappear. The anode circuit of heptode 1 may be utilized to indicate beats for facilitating adjustment, by the dotted line circuit including an amplifier 41. In Fig. 2 part of the intermediate frequency energy of a superheterodyne receiver is applied to a double circuit A, B tuned as a whole to the intermediate frequency, branch A being tuned above and branch B below that frequency. The outputs from each branch are separately rectified at 46a, 46b and taken off from potentiometers 47a, 47b, the arrangement being such that when branch A is effective the point 49a is positive with respect to the cathode of the pentode reactance 31, while when branch B is operative 49b is negative. The reactance of the control grid-cathode circuit of 31 varies the frequency determining circuit of the local oscillator which is connected across terminals 13, 60. Instead of the rectifier arrangement shown in Fig. 2 a double-diode triode valve may be employed, but the remainder of the circuit is similar, Fig. 3, (not shown).