04737968 is referenced by 24 patents and cites 12 patents.

A system for transmitting digital data employs an angle modulated carrier signal having constant amplitude and a limited spectrum. The system comprises an offset quadrature phase shift key (QPSK) modulator with a "tracking filter" phaselocked loop at the output of the QPSK modulator. The phaselocked loop has a voltage controlled oscillator which produces a constant amplitude carrier signal at the output of the loop, and also has a low pass loop filter which reduces the spectrum of the phase modulated carrier signal. Additional spectrum shaping is obtained by connecting L-R-C circuits to the low pass loop filter to eliminate predetermined frequency components from the output of the loop.

Title
QPSK transmission system having phaselocked tracking filter for spectrum shaping
Application Number
6/791622
Publication Number
4737968
Application Date
October 25, 1985
Publication Date
April 12, 1988
Inventor
Martin H Beauford
Bartlesville
OK, US
Jerry J Norton
Caney
KS, US
Agent
G E Bogatie
Assignee
Phillips Petroleum Company
OK, US
IPC
H03C 3/02
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