GB474771A - Arrangement for automatic tuning of radio receivers or the like - Google Patents

Abstract

474,771. Wireless receiving circuits. COLE, Ltd., E. K. May 7, 1936, No. 12848. Convention date, July 13, 1935. [Class 40 (v)] In a wireless receiver of the kind having automatic fine control of tuning, a mechanically variable impedance or network is associated with the fine-tuning device and is mechanically coupled in such manner to the manual control of the tuned circuit and/or the wave-range switch that the frequency range of regulation of the fine-tuning device is substantially constant irrespective of tuning frequency. In Fig. 1, the tuning circuit of the local oscillator 4 comprises inductances 9, 10 tuned by the condenser 11 and coupling condensers 12, 13. Fine tuning is automatically effected by an error detector 17 fed from the I.F. stage 5 and comprising two diodes fed from circuits 18, 19 tuned 8 k.c. above and below the I.F. The rectified voltages act in opposition on the moving coil of a voltmeter 16 which is mechanically coupled to a fine-tuning condenser 15 across condenser 11. To equalize the control range over a band of frequencies, a series condenser 22 is ganged with the condenser 11. Further to compensate for change of wavebands, an additional series condenser 24 is switched in circuit by switch 25 which is unicontrolled with the waveband switch 14. In Fig. 3, the fine tuning impedance is constituted by a variablemu valve 27 in series with condenser 28 across the tuning condenser 11, the grid bias of 27 being varied by the error detector 20, 21. An additional grid biassing source comprising battery 33 and potentiometer 34 is provided, the moving contact of the potentiometer being nnicontrolled with condenser 11 and with the series condenser 28 ; a section of the resistance may be short-circuited by switch 37, ganged with the wave-range switch 14. As an alternative to condenser 22 of Fig. 1, a potentiometer may be shunted across the tuning condenser 11, the moving contact being ganged with the tuning condenser; the fine-tuning condenser 15 is connected between the moving contact and one terminal of the potentiometer, Fig. 4 (not shown). Specification 378,256 is referred to. Reference has been directed by the Comptroller to Specifications 443,423 and 450,806.