GB472520A - Improvements in or relating to radio and like receivers - Google Patents

Abstract

472,520. Wireless receiving circuits. MARCONI'S, WIRELESS TELEGRAPH CO., Ltd. Feb. 4, 1937, No. 3344. Convention date, Sept. 23, 1936. [Class 40 (v)] The tuning indicator of a wireless receiver is operated by potentials which vary with departure from exact tune and also with variations in received signal strength, the indicator showing both extent and direction of detuning. Fig. 1 shows a band-pass filter in the I.F. stage of a superheterodyne receiver, which is employed as a source of control voltage for a tuning indicator by applying the primary and secondary potentials to a rectifier bridge GG. At exact resonance the direct-current potentials across the arms AO and BO are equal and opposite; detuning causes the primary and secondary voltage phase relations to vary, and the resulting potential across AB varies in polarity and magnitude with the extent and direction of detuning. The dry rectifiers may be replaced by diodes, Fig. 3 (not shown). Fig. 4 shows the application of such a control circuit to a pair of discharge tubes in a common envelope. The rectifiers G also serve as signal detectors, the audio-frequency signal being taken in parallel from the anode circuits of a pair of triodes, mounted in a single envelope, through condensers C2. The difference in length of the two luminous columns of the discharge tubes is a measure of the detuning ; their mean length is a measure of signal amplitude. Instead of the discharge tube a cathoderay tube may be fed from the double triode, Fig. 5 (not shown), the tube having three deflecting electrodes whereby the position of the ray indicates magnitude and direction of detuning and also carrier wave amplitude. Specifications 456,928 and 472,739 are referred to.