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Title: Phase comparison radio navigation system receiver having phase memory oscillators for phase locking to time-sequentially received transmissions
Claims: I claim: 1. A receiver for a phase comparison radio navigation system wherein there is provided a phase memory for giving a continuous output signal having a phase locked to the phase of a received radio frequency signal, which phase memory comprises a controllable oscillator at a frequency much greater than the radio frequency to be received, said oscillator being controllable in frequency in response to a control signal, a frequency synthesiser fed from said oscillator to provide a selected heterodyne frequency at a frequency which is a multiple of a first sub-multiple of the oscillator frequency, a frequency divider coupled to said oscillator to provide an output which is a second sub-multiple of the oscillator frequency, said second sub-multiple being another multiple of said first sub-multiple, a mixer arranged for mixing the heterodyne frequency from the synthesiser with the received signal to give an intermediate frequency signal, a phase comparator arranged for comparing the phase of the intermediate frequency signal with the phase of the divider output to provide said control signal and means applying said control signal to said oscillator as a frequency control to phase-lock the oscillator with respect to the received signal. 2. A receiver as claimed in claim 1 and for receiving signals of a predetermined frequency wherein said frequency synthesiser is adjustable for setting to give a heterodyne frequency such that the intermediate frequency output of the mixer is of the same frequency as the divider output. 3. A receiver as claimed in claim 1 wherein said frequency synthesiser is adjustable in steps of 100 Hz. 4. A receiver as claimed in claim 1 and arranged for receiving a plurality of signals wherein a separate phase memory is provided for each signal to be stored. 5. A receiver as claimed in claim 1 and for receiving a plurality of signals of the same frequency wherein, for all signals of the same frequency, a single synthesiser, mixer and phase discriminator are employed, with, for each signal, a separate oscillator and divider, and wherein there is provided a timing circuit arranged to be controlled in synchronism with the sequence of transmissions from the stations so that each oscillator is phase-locked during the appropriate transmission. 6. A receiver as claimed in claim 5 wherein the frequency synthesiser is connected to be driven from the same oscillator. 7. A receiver as claimed in claim 1 and for receiving more than one radiated frequency wherein said synthesiser is arranged to provide a further heterodyne frequency or frequencies. 8. A phase comparison radio navigation system in which phase-locked radio frequency signals are transmitted from spaced stations, wherein one of the stations, hereinafter referred to as the prime station, has at least one frequency synthesiser and an oscillator providing an input signal to said synthesiser or to each synthesiser at a frequency many times greater than the required ratiated frequency or frequencies and means for radiating a signal or signals at a radio frequency or frequencies determined by the oscillator and synthesiser or synthesisers, and two or more secondary stations have means for receiving signals radiated by the prime station and for transmitting signals of the same frequencies or at least one of the same frequencies phase-locked to the corresponding frequency signals from the prime station and wherein at least one receiver for utilising signals from said spaced stations has means for receiving the radiated signals, a prime oscillator controllable in frequency in response to an input control signal, a frequency synthesiser for each frequency to be received, the frequency synthesiser having frequency adjusting means for setting an output frequency, the synthesiser further having the prime oscillator as a signal input source, a divider coupled to said prime oscillator to divide the frequency thereof down to a sub-multiple thereof, receiving means for receiving transmitted signals, a mixer arranged for mixing the output of the synthesiser with received signals from the receiver, a phase comparator arranged for comparing the phase of the output of the mixer with the output of said divider, means for setting the synthesiser ouput frequency so that the two inputs to the phase comparator for each received signal are of the same frequency, namely that of the divider output, means arranged for applying the output of the phase discriminator as a frequency control signal to said prime oscillator when signals of one frequency from the prime station are received, a plurality of other oscillators and associated dividers corresponding to each of the other transmissions from the spaced transmitting stations and switching means arranged for applying the output of the discriminator as a phase control signal to the appropriate oscillators during periods of reception of each of said other transmissions whereby the oscillators in the receiver are each phase-locked with the respective transmission. 9. A radio navigation system as claimed in claim 8 wherein indicator means are provided in the receiver for comparing and displaying phase relationship between any pair of oscillators forming memories of radiated signals of the same frequency so as to provide positional information. 10. A radio navigation system as claimed in claim 8 and wherein the transmitting stations are arranged to radiate more than one frequency in a time sequence and wherein the prime station synthesisers are arranged to provide outputs for mixing with a divided down output from the oscillator in the prime station to provide the required radio frequencies and wherein, in each of the secondary stations, there is provided a frequency synthesiser for each frequency to be radiated, a phase memory oscillator corresponding to the oscillator at the prime station, a transmission oscillator controllable in frequency in accordance with a control signal input, a divider arranged for dividing the transmission oscillator frequency and a mixer arranged for mixing the divided down frequency with the synthesiser output to provide the required radiated frequencies, phase comparison means arranged to provide a control signal in accordance with a phase comparison between the radiated signal and a signal from an appropriate memory oscillator, and phase control means arranged for phase control of the sequential transmissions by controlling the transmission oscillator sequentially in accordance with the control signal from said phase comparison means. Other info: Inventors: Phipps, Derek John (London, EN) Application Number: 524200 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:
Other Refs: Primary Examiner: Wilbur, Maynard R. Assistant Examiner: Berger, Richard E. Attorney: Connors; Edward F. |
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