Receivers for phase comparison radio navigation systems

Claim 2

In a receiver for a phase comparison radio navigation system of the kind in which signals of different multiples of a fundamental frequency f are radiated in fixed phase relation from spaced transmitting stations, the transmitting stations normally radiating one signal at a time, but in which periodically the normal transmissions are interrupted and each station, one at a time in sequence, radiates all the frequencies to form a multipulse for lane identification, the multipulse being in a fixed cyclic time sequence from the various stations, and in which the receiver is of the heterodyne type for receiving signals from chains operating on different fundamental frequencies, the provision of a frequency synthesizer including a stable oscillator and divider chain for providing a plurality of selectable different frequencies for heterodyning the received signals whereby phase comparison means operating at fixed frequencies may be used irrespective of the actual radiated frequencies of the transmitting stations being used.

Claim 3

A receiver as claimed in claim 1 wherein there is provided a voltage controlled oscillator controllable over the range of required heterodyne frequencies and a phase comparator comparing the phase of the output of the voltage controlled oscillator with the selected output from the synthesizer to provide a control signal representative of the phase difference for application to said voltage controlled oscillator to phase lock the oscillator to the selected frequency.

Claim 4

A receiver as claimed in claim 1 wherein means are provided for deriving, from the frequency synthesizer, timing signals for providing outputs forming gating pulses during the successive received multipulse signals.

Claim 5

A receiver as claimed in claim 3 and for use with a navigation system in which the multipulse transmissions are signalled by an interruption in the normal transmission from one of the stations a short time before each multipulse transmission, wherein there are provided in the receiver means for detecting this interruption in the normal transmission and wherein timing means are provided using the divided down output from said divider chain to produce gating pulses at predetermined time intervals after the interruption is detected.

Claim 6

In a receiver for a phase comparison radio navigation system of the kind in which signals of different multiples of a fundamental frequency f are radiated in fixed phase relation from spaced transmitting stations, the transmitting stations normally radiating one signal at a time, but in which periodically the normal transmissions are interrupted and each station, One at a time in sequence, radiates all the frequencies to form a multipulse for lane identification, the multipulse being in a fixed cyclic time sequence from the various stations, and in which the receiver is of the heterodyne type for receiving signals from chains operating on different fundamental frequencies, the combination of a stable oscillator and divider chain, a frequency synthesizer matrix coupled to said divider chain for providing a plurality of selectable different frequencies, selector means for selecting one of said different frequencies from the matrix, frequency multiplier means for separately multiplying the selected frequency by multiplication factors corresponding to harmonic numbers of the radiated frequencies, a separate mixer for each received signal mixing the received signal with the corresponding multiplied selected frequency to heterodyne the received signals, means for selecting the lower side bands from the mixers and phase comparison means determining the phase relationships between the selected lower side bands.

Claim 7

In a receiver for a phase comparison radio navigation system of the kind in which signals of different multiples of a fundamental frequency f are radiated in fixed phase relation from spaced transmitting stations, the transmitting stations normally radiating one signal at a time, but in which periodically the normal transmissions are interrupted and each station, One at a time in sequence, radiates all the frequencies to form a multipulse for lane identification, the multipulse being in a fixed cyclic time sequence from the various stations, and in which the receiver is of the heterodyne type for receiving signals from chains operating on different fundamental frequencies, the combination of a stable oscillator and divider chain, a frequency synthesizer matrix coupled to said divider chain for providing a plurality of selectable different frequencies, selector means for selecting one of said different frequencies from the matrix, frequency multiplier means for separately multiplying the selected frequency by multiplication factors corresponding to harmonic numbers of the radiated frequencies, a separate mixer for each received signal mixing the received signal with the corresponding multiplied selected frequency to heterodyne the received signals, means for selecting the lower side bands from the mixers and phase comparison means determining the phase relationships between the selected lower side bands.

Claim 8

A receiver as claimed in claim 5 wherein there is provided a voltage controlled oscillator controllable over the range of required output frequencies from the matrix and a phase comparator comparing the phase of the output of the voltage controlled oscillator with the selected output from the synthesizer matrix to provide a control signal representative of the phase difference and means for applying the control signal to said voltage controlled oscillator to phase lock the oscillator to the selected frequency.

Claim 9

A receiver as claimed in claim 6 and for use with a navigation system in which the multipulse transmissions are signalled by an interruption in the normal transmission from one of the stations a short time before each multipulse transmission, wherein there are provided in the receiver break detection means for detecting the interruption in the normal transmission and wherein timing means are provided with timing control from the divided down output from said divider chain, said timing means being coupled to the break detection means to be responsive to the detected break to produce gating pulses at predetermined time intervals after the interruption is detected but during the multipulse transmissions and wherein digital phase comparison means are provided operating during periods controlled by said gating pulses to determine the phase relationships between signals derived from the received multipulse transmissions.