GB564014A - Improvements in phase modulation receivers - Google Patents

Abstract

564,014. Phase modulation. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. May 21, 1943, No. 8139. Convention date, May 23, 1942. [Class 40 (v)] Relates to phase-modulation receivers of the kind in which a filter is used to isolate the pure carrier from the received wave and a recombination is effected after a relative phase shift between the carrier and its side-bands ; and consists in interposing frequency-dividers in the path of the pure carrier wave and of the received wave, to enable a filter, e.g. a crystal filter, to be used which gives a phase shift greater than 90 degrees on each side of the mid-band frequency. As shown, a superheterodyne receiver S with local oscillator L feeds the phase-modulated intermediate frequency through a filter F and frequency divider D to the input of a balanced detector, energizing the diodes 5, 8 and load resistances 6, 7 in phase opposition. The-phase-modulated intermediate frequency is also fed through a similar frequency-divider D1 and a phase-adjuster P to energize the diodes 5, 8 in phase agreement. Deviation in the intermediate frequency causes an unbalance in the voltages across the load resistances 6, 7 which is applied through a smoothing circuit 11, 12 to a reactance valve R to apply a correction to the oscillator L. The demodulated signal may be taken to an audioamplifier across the resistances 6, 7 ; but, as shown, a separate balanced demodulator 17, 20 is used for the audio signal, and is fed in phase opposition at 15 from the output of the carrier filter F and in phase agreement at 16 through a phase adjuster P1 from the phase-modulated I.F. output of the receiver S. The frequencydividers may be of the multi-vibrator type, or of the kind described in Specification 556,171.