Demodulators – Phase shift keying or quadrature amplitude demodulator – Input signal combined with local oscillator or carrier...
Patent
1988-10-27
1990-04-10
Laroche, Eugene R.
Demodulators
Phase shift keying or quadrature amplitude demodulator
Input signal combined with local oscillator or carrier...
331 4, 331 12, 331DIG2, 375 87, H04L 2722
Patent
active
049164058
ABSTRACT:
Apparatus is provided for locking onto a severe doppler shifted data modulated carrier signal. A phase lock loop of the type having a data detection branch, a carrier tracking branch and a voltage controlled oscillator branch is modified to provide a summing circuit at the input of the voltage control oscillator in the voltage controlled oscillator branch. A sweep control circuit is connected to the input of the summing circuit for sweeping the voltage controlled oscillator through a range of frequencies which encompass the doppler shifted carrier frequency. An automatic frequency control circuit is connected to the input of the summing circuit for automatically disconnecting the sweep control circuit from the summing circuit when the frequency of the voltage controlled oscillator reaches a predetermined value defining a window which encompasses only the center frequency of the doppler shifted carrier frequency. The automatic frequency control circuit is adapted to drive the output of the voltage controlled oscillator to the center frequency of the doppler shifted carrier frequency without overshoot and then enable the phase lock loop to phase lock onto the phase of the doppler shifted carrier frequency to provide a locked on condition.
REFERENCES:
patent: 4092606 (1978-05-01), Ryan
patent: 4814719 (1989-03-01), Guyer
Keate Christopher R.
Mac Thornock Jeffrey
Williams Bruce H.
Bramson Robert S.
LaRoche Eugene R.
Pascal Robert J.
Sowell John B.
Starr Mark T.
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