GB368597A - Improvements in or relating to apparatus for detecting frequency variations in alternating current - Google Patents

Abstract

368,597. Wireless receiving systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, London. -(Assignees of Hansell, C. W. ; Port Jefferson, Long Island, New York, U.S.A.) May 14, 1931, No. 14311. Convention date, May 14, 1930. Addition to 341,732. [Class 40 (v).] Changes in the frequency of received alternating current are detected by a valve oscillator 14 with its frequency fixed by a long line 18 to a value outside the frequency range of the signals, which are indicated by the changes in direct energy supplied to the valve. As shown, two oscillators 14, 16 have their frequencies fixed by long lines 18, 20 to values on either side of the frequency range and are coupled together to oscillate at a common frequency intermediate their natural frequencies, and the signals are applied by a coil 30 to force the common frequency of the oscillators to vary with the frequency modulation. The signals are passed through an amplitude limiter 6 before application to the oscillator. The oscillators may be arranged not to oscillate until signals are received, and a number of valves in cascade may be used. According to a modification, an aperiodic long line is used and couples tuned circuits in the anode and grid circuits of the oscillator, Fig. 2 (not shown).