Phase locked loop receiving system with improved signal acquisition

Claim 1

In a phase-locked loop receiving system having a tracking mode of operation for tracking a variable frequency received signal including an analog signal-controlled oscillator, means for comparing thE phase of received signals with the phase of the output of said controlled oscillator to generate a first error signal, and means responsive to said first error signal for generating and applying a tuning signal which is a function of said first error signal to said controlled oscillator to form a closed tracking loop, the combination comprising: a reference frequency source operating at a predetermined reference frequency within the range of expected frequency variation of said variable frequency received signal; means for comparing said reference frequency with said output of said signal-controlled oscillator to produce a second error signal; switching means arranged to substitute said second error signal in place of said first error signal to generate said tuning signal during a first predetermined time interval, thereby to establish a calibrating mode of operation; a periodic wave generator and means for superimposing the output of said periodic wave generator on said tuning signal beginning at the outset of a second time interval to initiate a corresponding searching mode of operation; and second switching means responsive to a predetermined condition of said first error signal during said second time interval, said predetermined condition corresponding to phase lock-on within said tracking loop, to remove said periodic wave from said tuning signal thereby to permit said loop to operate in phase lock.

Claim 6

A system for receiving an electromagnetic energy signal from a rising and setting satellite, said signal including a Doppler frequency component varying throughout the visible travel of said satellite and said receiving system including a phase-lock loop for frequency tracking said received energy signal, said system comprising the combination of: first means within said phase-lock loop including an oscillator controllable by an electrical control signal, means for comparing the frequency of said oscillator with the frequency of said received energy signal to develop and apply said control signal to said oscillator as a feedback signal to tend to bring said oscillator frequency into continuous synchronism with said variable frequency received energy signal; second means for superimposing a sweep signal on said control signal to cause said oscillator to sweep correspondingly in frequency for searching to acquire said received energy signal for frequency tracking; third means for providing a calibration mode, said means connecting an externally provided reference frequency signal to said first means in lieu of said received energy signal for presetting said oscillator to said reference frequency approximately the expected frequency of said satellite at said rising thereby to minimize the required excursion of said oscillator frequency sweep; and fourth means responsive to external timing control to enable said third means for a time preceding the expected time of rise of said satellite, to disable said third means and enable said second means at a time approximately corresponding to said satellite rise, said fourth means being also responsive to an external acquisition signal to disable said second means and permit said first means to frequency track said received energy signal.

Claim 7

A system for receiving an electromagnetic energy signal from a rising and setting satellite, said signal including a Doppler frequency component varying throughout the visible travel of said satellite and said receiving system including a phase-lock loop for frequency tracking said received energy signal, said system comprising the combination of: first means within said phase-lock loop including an oscillator controllable by an electrical control signal, means for comparing the frequency of said oscillator with the frequency of said received energy signal to develop and apply said control signal to said oscillator as a feedback signal to tend to bring said oscillator frequency into continuous synchronism with said variable frequency received energy signal; second means for superimposing a sweep signal on said control signal to cause said oscillator to sweep correspondingly in frequency for searching to acquire said received energy signal for frequency tracking; third means for providing a calibration mode, said means connecting an externally provided reference frequency signal to said first means in lieu of said received energy signal for presetting said oscillator to said reference frequency approximately the expected frequency of said satellite at said rising thereby to minimize the required excursion of said oscillator frequency sweep; and fourth means responsive to external timing control to enable said third means for a time preceding the expected time of rise of said satellite, to disable said third means and enable said second means at a time approximately corresponding to said satellite rise, said fourth means being also responsive to an external acquisition signal to disable said second means and permit said first means to frequency track said received energy signal.