APPARATUS AND METHOD FOR IMPROVING SENSITIVITY OF NAVIGATION SYSTEM USING EARTH SATELLITES

• US 3,763,492 A
• Filed: 10/08/1970
• Issued: 10/02/1973
• Est. Priority Date: 10/08/1970
• Status: Expired due to Term

• Current Assignee: Roger L. Easton
• Original Assignee: Roger L. Easton
• Inventors: Easton, Roger L.
• Primary Examiner(s): Borchelt, Benjamin A.
• Assistant Examiner(s): Berger, Richard E.
• Application Number:
  US05/079,308
• Time in Patent Office: 1,090 Days
• Field of Search: 343/112D,1ST 325/346,381
• US Class Current: 342/458
• CPC Class Codes: G01S 11/08 using synchronised clocks

Abstract

An improvement to a navigation system which includes earth satellites that carry stable oscillators which are synchronized with a stable oscillator at the navigator'"'"''"'"'s station; the improvement consisting of means that improve system sensitivity and reduce the effectiveness of jamming by including in the receiver at the navigator'"'"''"'"'s station a tracking oscillator which is locked onto the carrier frequency received from the satellite. The tracking oscillator output is frequency divided down and phase locked with the multifrequency tone signals that are also received from the satellite and then phase compared with similar multifrequency signals which are derived from the stable oscillator at the navigator'"'"''"'"'s station.

Claims

1. A navigation system comprising:

at least one artificial earth satellite means, each of which broadcasts a carrier frequency signal that is modulated by a set of multifrequency tone signals, said carrier frequency signal and said set of tone signals being derived from the output of a very stable oscillator included in each satellite means;

reference tone producing means located at the navigator'"'"''"'"'s station for producing a set of reference multifrequency tone signals that are identical in frequencies to said set of tone signals produced on each of said satellites, said reference tone signals being derived from a very stable oscillator which is synchronized with said stable oscillator included in each satellite means;

receiver means for selectively receiving a modulated carrier signal braodcast by a satellite and for producing therefrom a set of pure multifrequency tone signals which are phase locked with the modulations of said received signal and are substantially free of the noise and jamming distortions which may be present in said received signal, and phase comparison means connected to receive said sets of multifrequency pure and reference tone signals and for indicating the phase difference between similar frequency signals of said sets of tone signals.

2. The navigation system set forth in claim 1 wherein said receiver means comprises:

an antenna;

a carrier frequency tracking filter connected to said antenna;

a variable frequency oscillator connected to be frequency locked to the output of said tracking filter whereby the output signal of said variable frequency oscillator is substantially free of the noise and jamming distortion which may be present in said received signal;

demodulator means connected to said antenna for producing from said received signal a set of multifrequency demodulated tone signals which may include noise and jamming distortions, and dividing and phase lock loop means connected to said variable frequency oscillator and to said demodulator means for producing said set of pure multifrequency tone signals.

3. A receiver for use with a navigation system that includes at least one artificial earth satellite which broadcasts a carrier frequency signal that is modulated by a set of multifrequency tone signals, said receiver comprising:

an antenna for receiving said broadcast signal;

a carrier frequency tracking filter connected to said antenna;

a variable frequency oscillator connected to be frequency locked to the output of said tracking filter whereby the output signal of said variable frequency oscillator is substantially free of the noise and jamming distortion which may be present in said received signal;

demodulator means connected to said antenna for producing from said received signal a set of multifrequency demodulated tone signals which may include noise and jamming distortions, and dividing and phase lock loop means connected to said variable frequency oscillator and to said demodulator means for producing a set of pure tone signals which are phase locked with said set of multifrequency demodulated tone signals and are substantially free of the noise and jamming distortions which may be present in said set of demodulated tone signals.

4. A receiver comprising:

an antenna for receiving a carrier frequency signal that is modulated by a set of multifrequency tone signals;

a carrier frequency tracking filter connected to said antenna;

a variable frequency oscillator connected to be frequency locked to the output of said tracking filter whereby the output signal of said variable frequency oscillator is substantiallY free of the noise and jamming distortion which may be present in said received signal;

demodulator means connected to said antenna for producing from said received signal a set of multifrequency demodulated tone signals which may include noise and jamming distortions, and dividing and phase lock loop means connected to said variable frequency oscillator and to said demodulator means for producing a set of pure tone signals which are phase locked with said set of multifrequency demodulated tone signals and are substantially free of the noise and jamming distortions which may be present in said set of demodulated tone signals.