HYPERBOLIC RADIO NAVIGATION SYSTEMS OF THE PHASE COMPARISON TYPE

摘要

A receiver, for use with a hyperbolic radio navigation system in which synchronized signals of frequency pf and nf are radiated simultaneously from spaced transmitters, each frequency being radiated by only one station at a time, p and n being different integers greater than twelve and f a fundamental frequency, comprises an oscillator at a frequency mf where m is an integer greater than twelve (and may be the same as or different from p and n), means for synchronizing the oscillator with a received signal of frequency pf, a frequency divider providing a time index at frequency f and locked to the oscillator, and a timer responsive to the interval between the time index and a next succeeding time index locked to the nf signals. By integration ambiguities may be resolved. In one embodiment spaced transmitter signals on 1891f, 1887f and 1881f (e.g. f = 37À5 c/s.), Fig. 1, are phaselocked to respective oscillators 14, 15, 16 despite any interruptions in reception (e.g. the transmissions may be deliberately switched). Divider 20 produces an output at f with rectangular waveform and from which an index pulse, shorter than the duration of an R.F. cycle, is afforded by shaper 21 to start a counter 22. The counting is stopped by a squarer 24. Counter 22 is periodically interrogated and the changes in time difference are integrated. A second position line is given by operating switch 26. In another receiver, for stations transmitting on 57f, 56f and 54f, each channel has an oscillator operating at 55f, a gated discriminator controlled from a 55 times divider fed from one oscillator, and integrating meters comparing the phases of the oscillators in pairs, Figs. 2, 3 (neither shown). In a further receiver, Fig. 4, one oscillator only, 55, is utilized for systems in which the transmissions are effectively uninterrupted, phase quadrature outputs are obtained from circuits 60, 65 each of which may comprise the circuit, Fig. 5, which is stated to give substantially 90 degrees phase shift over a wide frequency range: it consists of a transistor 71 affording a constant current to the emitter of transistor 70 the latter being connected to a high input impedance transistor 72 and a capacitative load 73, the emitter of transistor 74 being fed from the collector of transistor 70 and a collector 74 voltage made equal by resistor 75 to that of the voltage at the emitter of transistor 70 but in phase quadrature therewith. Substantially equal amplitudes are obtained but to maintain this when a frequency is changed the magnitude of either load 73 or resistor 75 must be altered.