Abstract: In a phase comparison radio navigation system in which a prime and one or more secondary transmitting stations radiate phase-locked signals of the same frequency in a time-shared sequence, phase locking at the secondary station or stations is effected by using a common phase comparator both for locking a phase memory oscillator to the received prime signals and for locking the secondary signals at the antenna with the phase memory oscillator.

Abstract: In a phase comparison radio navigation system in which phase-locked signals are radiated from spaced stations to be compared in phase in a receiver, the receiver has a separate phase memory oscillator for each received signal, the phase memory oscillators operating at the same frequencies (apart from differences due to Doppler shifts) and being locked to their respective signals from the transmitting stations and display units are provided each with selector means enabling any display unit to effect phase comparison between any pair of outputs from the memory oscillators.

Abstract: In a phase comparison radio navigation system in which spaced transmitters radiate phase-locked signals in a time-shared sequence, in order to enable a receiver to be operated on any selected one of a large number of different frequencies, a phase memory in the receiver for giving a continuous output representative of the phase of an intermittently received signal, comprises a controlled oscillator giving an output of a frequency much higher than the received frequency, a frequency divider providing a first sub-multiple of the oscillator frequency, a frequency synthesizer providing a heterodyne signal at a second sub-multiple and a phase comparator providing an output controlling the oscillator in accordance with the phase relation between the divider output and the output of a mixer mixing the received signal with a heterodyne signal.

Abstract: In a phase comparison radio navigation system using transmissions from spaced stations in a time-sequence, for synchronising the timing of the transmissions, and for synchronising switching in a receiver, the timing control means include digital counting means counting down from the output of an oscillator phase locked to one of the received signals, and a timing identification signal is transmitted from one station for initially synchronising the counter timing.