GB1462227A - Distance measuring equipment a-branched aliphatic monocarboxylic acids and their preparation - Google Patents

Abstract

1462227 Radio distance measurement STANDARD TELEPHONES & CABLES Ltd 18 April 1974 16998/74 Heading H4D A distance measuring system includes; in an aircraft, a standard transmitter/receiver assembly 10, the transmission being sinusoidally a.m. modulated (e.g. at 3 kHz) and periodically keyed to give 100 m.sec. bursts; at a ground transponder, a receiver demodulator 20a, a phase locking 3 kHz oscillator 21 producing a C.W. signal, phased with the received modulation and a transmitter 20b replying to the aircraft with a 3 kHz a.m. modulated signal, said signal being received at the aircraft and phase modulated at 13 to give a signal which, after amplitude detection in the receiver 106, is periodically sampled and detected (e.g. every 10 m.sec.) at 14, to give a control signal for a phase shifter 12. This receiver, via ai calibrating phase shifter 17, the 3 kHz modulating signal, to give a phase shifted signal which is further phase reversed every 10 m.sec. in synchronism with the sampling at 14, before being applied as the modulating signal to phase modulator 13. The output of receiver 10b is thus a 3 kHz carrier, phase modulated by a 3 kHz signal, phase reversing every 10 m.sec. If, as desired for the distance between the aircraft and ground, the two 3 kHz signals are in phase quadrature, alternating in their lead/lag relationship, the amplitude of the signal at the output of receiver 10b will remain constant, detector 14 will give zero output and phase shifter 12 will not be adjusted. Otherwise said amplitude will vary with a p.r.p. of 10 m.sec., and phase shifter 12 will be adjusted by the detector's output to produce the phase quadrature relationship. The value of phase shifter 12 is then indicative of the distance. Calibrating phase shifter 17 is used to give a zero distance result when the aircraft is at a nominal zero distance from ground.