METHOD OF AND APPARATUS FOR TRANSMITTING PHASE CONNECTIONS, IN PARTICULAR FOR THE OMEGA RADIO NAVIGATION-SYSTEM

• US 3,774,211 A
• Filed: 07/27/1972
• Issued: 11/20/1973
• Est. Priority Date: 04/20/1972
• Status: Expired due to Term

• Current Assignee: Christian Lamiraux, Georges Nard, Gerard Millot
• Original Assignee: Christian Lamiraux, Georges Nard, Gerard Millot
• Inventors: Nard, Georges, Millot, Gerard, Lamiraux, Christian
• Primary Examiner(s): Borchelt, Benjamin A.
• Assistant Examiner(s): Berger, Richard E.
• Application Number:
  US05/275,586
• Time in Patent Office: 481 Days
• Field of Search: 343/15R,112D,103
• US Class Current: 342/396
• CPC Class Codes: G01S 1/308 particularly adapted to Omega systems

Abstract

In a sequential-transmission phase measurement radionavigation system, such as the OMEGA radio-navigation system, phase correction signals are transmitted by a network of transmitting stations to provide phase corrections over a predetermined area. Each phase correction transmitting station compares the measured phases with preset theoretical phases and provides a phase correction signal for each measured phase. The phase correction signals are time multiplexed with a multiplex frequency between 10 and 30 times the repetition rate of each of the sequential transmissions of the radio-navigation system, the multiplexing being synchronous with the sequential transmissions. The multiplexed signal is phase modulated on a carrier with a low modulation index. At a receiver the multiplexed phase correction signal is demodulated and demultiplexed to provide the phase correction signals which are used to modify the measured phases at the receiver.

Claims

1. A method of transmitting phase corrections in a sequentialtransmission phase measurement radio-navigation system, comprising at a correction transmitting station, generating a plurality of phase correction signals repectively associated with selected sequential transmissions, and transmitting the phase corrections and at a conventional receiver of said radionavigation system, receiving said phase corrections for applying them to measured-phase signals associated with said selected transmissions and supplied by said conventional receiver, wherein the improvement comprises:

at said correction transmitting station, multiplexing said phase correction signals, the multiplex frequency being between 10 and 30 times the repetition rate associated with the average duration of the individual transmissions of the radionavigation system, said multiplexing being synchronous with the sequence of said selected transmissions, and modulating a carrier wave with said multiplexed phase correction signal; and

at said conventional receiver, receiving and denodulating said carrier wave, and demultiplexing said multiplex phase correction signal in a manner synchronous with the sequence of reception of said selected transmissions by said conventional receiver, to provide separate correction signals associated with said seleted transmissions and similarly modulated in phase in accordance with the corrections to be applied.

2. A method of transmission according to claim 1 wherein said modulation is a low modulation index phase modulation.

3. A method of transmission according to claim 2 wherein said low-index phase modulation comprises:

generating two sinusoidal signals the frequency of which is equal to one eighth of that of the said carrier wave, said signals being displaced in phase by a quarter of a period with respect to each other;

multiplying in amplitude one of these signals by said multiplex modulation signal;

adding in a balanced adder the other of said signals and said multiplied signal, the ratio of the maximum amplitude of said multiplied signal to said other signal being of the order of 0.1; and

multiplying the frequency of the signal obtained after said balanced addition by 8.

4. A method of transmission according to claim 1 including at said conventional receiver synchronously detecting said separate phase correction signals to provide continuous signals representing the phase corrections to be applied.

5. A method of transmission according to claim 1 entailing a plurality of correction transmitting stations, wherein the frequency of said multiplexed phase correction signal is the same for all said transmitting stations, and the frequencies of the respective carrier waves of the stations differ from one another by the same amount which is between about 5 and about 10 times said frequency of said multiplex phase correction signal.

6. In a phase correction transmitting station for a sequential-transmission phase measurement radio-navigation system, comprising a system receiver to provide a plurality of measured-phase signals having the same frequency and modulated in phase in accordance with the measured phase which is respectively associated with them, and synchronisation information relative to the sequence of the corresponding transmissions, a modulating coding circuit for use with a transmission circuit for effecting a phase coRrection transmission, said modulating coding circuit comprising:

a plurality of preset phase shifters adapted to shift the phase of said measured phase signals in accordance with respectively preset values to supply phase correction signals;

a multiplexer for receiving said phase correction signals and said synchronisation information to provide a single signal multiplexed in synchronous manner for phase correction of the sequence of associated transmissions;

a circuit for changing the frequency of the single phase correction signal to provide a multiplexed modulating signal having a frequency between about 10 and about 30 times the repetition rate associated with the average duration of the individual transmissions of the system; and

a circuit for modulating a carrier wave of frequency Fo by means of said multiplex modulating signal.

7. Apparatus according to claim 6 wherein said modulating circuit is a low modulation-index phase modulator.

8. Apparatus according to claim 6 in which said modulating circuit comprises a pilot oscillator supplying a sinusoidal signal of frequency equal to one eighth of the frequency Fo of said carrier wave, a phase modulator modulating said Fo/8 frequency signal, and a multiplier of the frequency of the output of said phase modulator by 8.

9. Apparatus according to claim 8 wherein said phase modulator comprises a quarter-of-a-period phase shifter for the sinusoidal signal from said pilot oscillator, an amplitude multiplier for the quadrature component obtained in this way, and an adder for the signal supplied by said pilot oscillator and said signal modulated in this way, the ratio of the maximum amplitude of the latter to the maximum amplitude of the former being of the order of 0.1.

10. Apparatus according to claim 9 wherein said frequency multiplier comprises a circuit for shaping the signals of said adding circuit into square signals, followed by a monostable having a seven sixteenths form factor at said frequency Fo/8.

11. Apparatus according to claim 6 in a correction transmitting station comprising a system receiver equipped with a very stable clock supplying measured-phase signals and a reference phase signal derived from said clock and having the same frequency as said measured-phase signals, as well as a high-frequency signal likewise drawn from the said clock, wherein said multiplexer is arranged to supply said reference phase signal during an interval of time located outside those of said phase correction signals, and said frequency changing circuit receives said high-frequency signal to derive its heterodyne frequency therefrom.

12. Apparatus according to claim 11 wherein said interval of time located outside those of said phase correction signals corresponds to a transmission of the system which is not an object of a phase correction in a manner controlled by the synchronisation information.

13. A phase correction receiver for use with a conventional receiver of a sequential-transmission phase measurement radio-navigation system, which provides measured-phase information and synchronisation information associated with the corresponding transmissions, said phase correction receiver being adapted to receive the carrier wave of a correction transmitting station, said phase correction receiver comprising:

a circuit for receiving and demodulating said carrier wave; and

a demultiplexer receiving the demodulated signal and synchronisation information from said conventional receiver, to provide a plurality of phase correction signals similarly modulated in phase in accordance with the respective phase corrections to be effected.

14. Apparatus according to claim 13 comprising for each phase correction signal a demultiplexing and synchronous detection circuit associated with an integrating filter, to provide a continuous signal representing the corresponding phase correction to be effected.

15. Apparatus according to claim 14 for use witH a conventional system receiver supplying measured-phase signals in the form of sinusoidal signals the respective phases of which are in linear dependence on the associated measured phases, including for each measured-phase signal a phase shifter controlled by the associated continuous phase correction signal.

16. Apparatus according to claim 13 for use with a conventional receiver equipped with a very stable clock and intended to receive the carrier wave of a correction transmitting station, comprising means for supplying separately from said demodulated signal a correction signal for the phase of the said very stable clock of said conventional receiver with which it is associated with respect to that of the very stable clock of said system receiver located at said correction transmitting station.

17. Apparatus according to claim 13 for receiving selectively the carrier wave of one of a plurality of correction transmitting stations the carrier waves of which are distributed in equidistant fashion in a frequency band, wherein the receiving circuit comprises a wide-band high-frequency amplifier stage, a first frequency changing stage tuned to said frequency band, a second frequency changing stage with a heterodyne frequency adjustable by steps in controlled fashion in accordance with the frequencies of the different carrier waves capable of being received, having an almost rectangular pass band adjusted to the modulation spectrum, and a demodulating stage.