GB777530A - Omni-directional radio beacon system - Google Patents

Abstract

777,530. Automatic phase-control systems. STANDARD TELEPHONES & CABLES, Ltd. (International Telephone & Telegraph Corporation). July 4, 1955, No. 19322/55. Class 38 (4). [Also in Group XL (c)] In a receiver for use in a phase comparison radio navigation system (see Group XL (c)), the received signal, Fig. 1B (not shown), comprises a pulse train of high recurrence frequency and two intercalated trains of N and S reference pulses 28 and 29, each of lower recurrence frequency, e.g. 30 c/s., the pulse signals being amplitude modulated at the frequency f and a harmonic thereof, e.g. 3f. The N and S reference pulses are extracted, Fig. 2 (not shown), and applied through a transformer 45 in opposite polarity to a sinusoidal oscillator 46 so that the output from oscillator 46 is synchronized with either one or both of the reference signals and in order to ensure exact synchronization the output from oscillator 46 is applied to the coincidence circuit 41, Fig. 2 (not shown), through a phase shifter 49 which is controlled automatically by a doublediode phase discriminator 50a, 50b. An output from phase shifter 49 is applied through an inverter 47 to the anode of diode 50a and the cathode of diode 50b and the reference signals are also applied to a thyratron 59 producing corresponding D.C. pulses which are coupled to the series connected primaries of transformers 60, 61 whose secondaries are so coupled to discriminator 50a, 50b that for each reference pulse a positive pulse is applied to the anode of diode 50a and a negative pulse is applied to the cathode of diode 50b, the amplitude of the applied pulses being greater than that of the peak amplitude of the sine wave from tube 47. The cathode of diode 50a is connected to the anode of diode 50b and the common junction is coupled to the phase shifter 49 over a pulsewidening network 55 having a time constant shorter than the periodic time of the sine wave. The phase shifter 49 is responsive only to voltages greater than the peak amplitude of the sinusoidal component of the output from the diodes. When correct synchronization obtains the reference pulses are coincident with the cross-overs of the sine wave output from phase shifter 49, the pulse outputs from the diodes cancel and no effective control voltage is applied to the phase shifter, but when this condition does not obtain then during one half-cycle of the sine wave the resultant diode output includes a pulse component of one polarity which adjusts the phase shifter 49 to reduce the phase error and in the next half-cycle the output includes a pulse component of smaller amplitude and of oppoaite polarity which adjusts the phase shifter in the reverse direction by a smaller amount, the process being repeated until synchronization is attained.