Loran-C signal phase tracking apparatus

• US 4,774,518 A
• Filed: 05/09/1985
• Issued: 09/27/1988
• Est. Priority Date: 05/11/1984
• Status: Expired due to Fees

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Fukuhara, Hiroshige
• Primary Examiner(s): Blum, Theodore M.
• Assistant Examiner(s): GREGORY, BERNARR E
• Application Number:
  US06/733,052
• Time in Patent Office: 1,237 Days
• Field of Search: 343/388-390, 364/452, 342/388-390
• US Class Current: 342/389
• CPC Class Codes: G01S 1/245 Details of receivers cooperating therewith, e.g. determining positive zero crossing of third cycle in LORAN-C
• CPC Class Codes: H03L 7/0807 concerning mainly a recovery circuit for the reference signal
• CPC Class Codes: H03L 7/14 for assuring constant frequency when supply or correction voltages fail or are interrupted

Abstract

An apparatus receives Loran-C pulses and tracks the phase of each received Loran-C pulse received from master and secondary stations. The apparatus comprises: (a) a phase comparator (12) for comparing the phase of the Loran-C pulse received from each transmitting station with that of a comparison signal; (b) a phase locked loop circuitry (16) for generating the comparison signal at a given integral multiple of the repetition rate of the Loran-C signal; (c) an S/N ratio detection circuit (14) for measuring the signal-to-noise ratio of the received signal; (d) a loop filter (13) for correcting the timing at which the comparison signal is generated toward coincidence with the phase of the received Loran-C pulse when a given number of phase comparisons by the phase comparator (12) produce results of the same polarity; and (e) a sample number control circuit (15) for adjusting at least one of the given integral multiple and the given number according to the measured signal-to-noise ratio. The phase tracking can thus be achieved with high accuracy even at low signal-to-noise ratios and with far higher accuracy at higher signal-to-noise ratios.

Claims

1. An apparatus for receiving Loran-C pulses and tracking the phase of the received Loran-C pulses from master and secondary stations, comprising:

(a) first means for comparing the phase of the Loran-C pulse received from each transmitting station with that of a comparison signal;

(b) second means for generating the comparison signal at a given integral multiple of the repetition rate of the Loran-C signal;

(c) third means for measuring the signal-to-noise ratio of the received signal;

(d) fourth means for correcting the timing at which the comparison signal is generated toward coincidence with the phase of the received Loran-C pulse when a given number of phase comparisons by said first means produce results of the same polarity; and

(e) fifth means for adjusting at least one of said given integral multiple and said given number according to the measured signal-to-noise ratio.

2. The apparatus according to claim 1, which further comprises a quantizing circuit for producing a binary signal representing the polarity of the received signal at a frequency synchronous with the received Loran-C signal.

3. An apparatus for receiving Loran-C pulses and tracking the phase of the received Loran-C pulses from master and secondary stations, comprising:

(a) first means for comparing the phase of the Loran-C pulse received from each transmitting station with that of a comparison signal;

(b) second means for generating the comparison signal at a given integral multiple of the repetition rate of the Loran-C signal;

(c) third means for sampling the received signal a predetermined number of times and measuring the signal-to-noise ratio of the received signal;

(d) fourth means for correcting the timing at which the comparison signal is generated toward coincidence with the phase of the received Loran-C pulse when a given number of phase comparisons by said first means produce results of the same polarity;

(e) fifth means for adjusting at least one of said given integral multiple and said given number according to the measured signal-to-noise ratio; and

a quantizing circuit for producing a binary signal representing the polarity of the received signal at a frequency synchronous with the received Loran-C signal, wherein said fourth means comprises;

a random work filter having an UP/DOWN counter which increments its value in response to each binary output signal from said first means indicating phase advance and decrements its value in response to another binary output signal from said first means indicating phase lag; and

an N-reset circuit which presets said UP/DOWN counter to a value N, said UP/DOWN counter producing a first output signal when its value reaches 2N and a second output signal upon reaching zero, said N-reset circuit being activated by said first and second signals.

4. The apparatus according to claim 3, wherein said third means comprises:

(a) a first counter which counts the number of signals from said quantizing circuit representing positive polarity;

(b) a second counter which counts the number of signals from said quantizing circuit representing non-positive polarity;

(c) a subtraction circuit for subtracting the count value of said second counter from that of said first counter; and

(d) a signal-to-noise ratio calculating circuit for calculating the signal-to-noise ratio on the basis of the difference derived by said subtraction circuit.

5. The apparatus according to claim 4, wherein said second means comprises:

(a) a clock generator which generates a clock pulse with a predetermined frequency;

(b) a clock frequency multiplier which increases the clock frequency by a given integral factor selected according to the output signal from said S/N ratio calculating circuit; and

(c) a frequency divider for dividing the frequency of the output of said clock frequency muliplier by a predetermined division ratio and sending the divided clock pulse to said first means.

6. The apparatus according to claim 5, wherein said fifth means, in accordance with the detected signal-to-noise ratio and via said random work filter, changes the preset value N of said N-reset circuit and the given integral factor by which the clock frequency is multiplied.

7. The apparatus according to claim 6, wherein the reset value of the N-reset circuit is reduced as the detected signal-to-noise ratio increases.

8. The apparatus according to claim 6, wherein said given integral factor is decreased as the detected signal-to-noise ratio increases.

9. An apparatus for receiving Loran-C pulses and tracking the phase of the received Loran-C pulses from master and secondary stations, comprising:

(a) first means for comparing the phase of the Loran-C pulse received from each transmitting station with that of a comparison signal;

(b) second means for generating the comparison signal at a given integral multiple of the repetition rate of the Loran-C signal;

(c) third means for sampling the received signal a predetermined number of times and measuring the signal-to-noise ratio of the received signal on the basis of the sampled result;

(d) fourth means for correcting the timing at which the comparison signal is generated toward coincidence with the phase of the received Loran-C pulse when a given number of phase comparisons by said first means produce results of the same polarity; and

(e) fifth means for adjusting at least one of said given integral multiple and said given number according to the measured signal-to-noise ratio.

10. An apparatus for receiving Loran-C pulses and tracking the phase of the received Loran-C pulses from master and secondary stations, comprising:

(a) first means for comparing the phase of the Loran-C pulse received from each transmitting station with that of a comparison signal;

(b) second means for generating the comparison signal at a given integral multiple of the reception rate of the Loran-C signal;

(c) third means for sampling the received signal a predetermined number of times and measuring the signal-to-noise ratio of the received signal on the basis of the sampled result;

(d) fourth means for correcting the timing at which the comparison signal is generated toward coincidence with the phase of the received Loran-C pulse when a given number of phase comparisons by said first means produce results of the same polarity; and

(e) fifth means for adjusting at least one of said given integral multiple and said given number according to the measured signal-to-noise ratio, wherein said fifth means is responsive to said third means and adjusts at least one of said given integral multiple and said given number based on the signal-to-noise ratio measured by said third means.

11. An apparatus for receiving Loran-C pulses and tracking the phase of the received Loran-C pulses from master and secondary stations, comprising:

(a) first means for comparing the phase of the Loran-C pulse received from each transmitting station with that of a comparison signal;

(b) second means for generating the comparison signal at a given integral multiple of the repetition rate of the Loran-C signal;

(c) third means for sampling the received signal a predetermined number of times and measuring the signal-to-noise ratio of the received signal;

(d) fourth means for correcting the timing at which the comparison signal is generated toward coincidence with the phase of the received Loran-C pulse when a given number of phase comparisons by said first means produce results of the same polarity; and

(e) fifth means for adjusting at least one of said given integral multiple and said given number according to the measured signal-to-noise ratio, wherein said fifth means is responsive to said third means and adjusts at least one of said given integral multiple and said given number based on the signal-to-noise ratio measured by said third means.

12. For use with Loran-C receiver, an apparatus for tracking a phase of received Loran-C pulses from master and secondary transmitting stations, comprising:

(a) first means for comparing the phase of a specific cycle point of a carrier of the Loran-C pulse received from each transmitting station with the phase of a comparison signal;

(b) second means for generating the comparison signal at a given multiple of a repetition rate of the received Loran-C signal;

(c) third means for calculating a signal-to-noise ratio of the received signal; and

(d) fourth means for correcting the timing at which the comparison signal is generated toward coincidence with the phase of the received Loran-C pulse signal on the basis of the result of the phase comparison by the first means with an accuracy dependent on the calculated signal-to-noise ratio.