Title: Phase comparison radio navigation system with time-sequenced transmissions from spaced stations using selectable phase memory oscillators in a receiver

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1. For use in a phase comparison radio navigation system of the kind in which spaced transmitting stations consisting of a prime station and secondary stations radiate phase-locked signals in a time-shared sequence, and in which, for selection of the radiated frequency or frequencies the prime station has an oscillator and a frequency synthesiser for generating the frequency or each of the frequencies to be used in the system, and in which the secondary stations have phase-lock means for locking their transmissions to the transmissions from the prime station; a receiver having means for receiving the radiated signals, oscillators that are each phase-locked to a separate received signal to provide a phase memory enabling comparison signals of the same frequency to be simultaneously available for phase comparison, said oscillators including a prime station memory oscillator, said receiver further including at least one frequency synthesiser fed from the prime memory oscillator for providing heterodyne signals and means for mixing said heterodyne signals with said received signals to convert the received signals to signals of a common frequency which is a sub-multiple of the oscillator frequency and wherein all the phase memory oscillators in the receiver are operated at the same frequency and have dividers for dividing the frequency down to the common sub-multiple frequency, said phase-lock means comprising a single phase discriminator in separate phase-lock loops for each of the phase memory oscillators with time-sequenced switching means switching the phase discriminator into said phase-lock loops in a time-switched sequence, and wherein the prime station memory oscillator is arranged to provide a signal of the oscillator frequency and a divided down frequency and wherein there are provided two or more display units, each display unit including a digital phase comparator having two inputs for signals to be compared and a counter and decimal digital display for indicating the phase relationship between two signals of the same frequency at two inputs to the phase comparator, and selector means arranged for connecting the two inputs to each of the phase comparators to the outputs of any of said oscillators to receive therefrom the signals of said divided down frequencies whereby the divided down frequencies are compared in phase in the display unit and wherein the prime station memory oscillator provides the higher frequency signal required by the digital counter phase comparator.

2. In a radio navigation system in which radio signals of a given frequency are radiated in time-sequence from spaced transmitting stations with the radiated signals being locked to one another in phase; a receiver comprising means for receiving the radiated signals, a plurality of oscillators with one for each received signals, said oscillators operating at a frequency substantially greater than said given frequency, phase-lock means responsive to the received signals phase-locking the oscillators with their respective received signals, a plurality of frequency dividers connected respectively to the oscillators dividing the oscillator outputs in frequency to a comparison frequency lower than said given frequency, a frequency synthesiser locked to one of said oscillators and arranged to provide a heterodyne signal, mixer means connected to said synthesiser and said receiving means to change the frequency of the received signals to said comparison frequency, at least two display units with each having two inputs and including a counter-type phase comparator and decimal digital display for displaying the phase relationship between signals at said two inputs, and selector means arranged to connect outputs from selected dividers to said display unit inputs.

3. A receiver as claimed in claim 1 wherein the selector means are manually operable selector switches.

4. A receiver as claimed in claim 1 wherein the divided down frequencies are each one hundredth of the associated oscillator frequency.

5. A receiver as claimed in claim 1 and for use in a radio navigation system in which two different frequencies derived from a frequency synthesiser are transmitted wherein means are provided at the receiver for obtaining coarse positional information with respect to two transmitting stations by determining the differences of phase measurements at two different frequencies which means comprises means to measure the phase relation using one frequency by counting into said counter and then to count down the same counter by an amount representative of the phase relation of the signals from the same stations on another frequency.

Other info:

Inventors: Phipps, Derek John (London, EN)

Application Number: 524198
Filing Date: 1974-11-15
Publication_date: 1976-08-10
Assignee: Decca Limited (London, EN)
Primary Class(es): 342/397
Other Classes:
US Patent Ref:

3689925	Sep, 1972	Hulland	343/105.
3852751	Dec, 1974	Wood et al.	343/105.

Other Refs:
Primary Examiner: Wilbur, Maynard R.
Assistant Examiner: Berger, Richard E.
Attorney: Connors; Edward F.