GB810698A - Radio diversity receiving system - Google Patents

Abstract

810,698. Automatic phase control systems. STANDARD TELEPHONES A CABLES Ltd. Jan. 11, 1957 [Feb. 14, 1956], No. 1148/57. Class 38 (4). [Also in Group XL (c)] In a radio diversity receiver the signal from two antennas 1, 2 are maintained in phase synchronism for maximum additive effect by automatically adjusting a phase shifter 13 preceding one input to the combiner 7. This may be done by amplitude modulating one input to the combiner 7 by a modulating frequency from source 6 so that, if the inputs are not in phase, the combined output is phase modulated at the frequency 6 and the latter may be detected by a frequency discriminator and filter 10 giving a variable-phase output of frequency 6 and of phase sense dependent on whether the input 4 leads or lags in phase the input at 3, which retroactively controls the phase shifter 13 until the inputs to the combiner 7 are cophasal. The modulator 5 may be a rotating variable attenuator or a ferrite modulator with attenuation dependent on an applied magnetic field. The combiner 7 may be a hybrid circuit or simple T-junction. The frequency 6 may be a frequency, e.g. 3500 c/s., in one of the guard bands of frequency multiplex telephone channels frequency modulated on a carrier, or for television, a frequency above the video band. In a modification the frequency 6 phase or frequency modulates the input 3 to produce from the combiner 7 an amplitude modulated output detected at 9 by an amplitude detector, the polarity, i.e. phase sense, of the detected output of frequency 6 being dependent on whether the input 4 leads or lags the input 3, as before its phase being detected by a phase discriminator 11 having a reference input from the modulating source 6. In a further modification the phase or frequency modulation is applied to a local oscillator beating with the input 3 and the output of phase detector 11 applied to adjust the phase of a second local oscillator beating with the other antenna input 4. In a still further modification a single local oscillator is used, its input to one mixer being frequency or phase modulated to produce from the combiner 7 an amplitudemodulated wave whose amplitude-detected output is compared in phase as before with the reference source 6 in a phase discriminator and its output applied to adjust a phase shifter between the local oscillator and the mixer for the other antenna input.