Inventors:
Charles A. Herbst - Palm Bay FL
Larry John Fruit - Melbourne FL
James Allan Wilkerson - Palm Harbor FL
Assignee:
Scientific-Atlanta, Inc. - Norcross GA
International Classification:
H04L 2720
Abstract:
Constant envelope angle modulation apparatus comprises a frequency synthesizer for outputting a stepped output waveform having a selectable precise output frequency. The output of the synthesizer provides an input to a mixer for O-QPSK modulating a received information signal. The O-QPSK modulated signal is then hard-limited, for example, via a series of hard limiting amplifier and filter circuits and a divider circuit. Preferably, a data stream for modulation may be filtered via a filter having an approximately 70-100% roll-off characteristic, such as a root raised cosine filter. A hard-limited, constant envelope angle modulated signal results that is easily frequency converted to, for example, microwave frequencies for landline or satellite applications via a simple multiplier circuit. The multiplier circuit preferably comprises a series of stage-filtered multipliers and band pass filters to achieve the desired output microwave frequency.
