Abstract: An improved spread spectrum communications system is provided for establishing full-duplex voice/data radio communications within a single specified FCC ISM band. Spectrum spreading is performed relative to a plurality of sub-bands respectively defined about the lower and upper band-edges of the prescribed ISM band and having spectral roll-off characteristics which satisfy FCC requirements for radio frequency radiation outside the ISM bands on the corresponding band-edges thereof. Full-duplex operation is implemented by the use of digital MSK modulation and associated filtering in order to conserve available bandwidth and accommodate the filtered, modulated signal within the sub-bands defined in the prescribed ISM frequency band, and the system is capable of being easily interfaced to related digital communications services.

Abstract: A system for maintaining an accurate frequency source in a single sideband repeater employs an ultra stable station control reference (SCR) frequency generator. A first frequency synthesizer for a local oscillator of the repeater phase locks to the output of the SCR normally, but is free running upon failure of the SCR. A second frequency synthesizer for another local oscillator phase locks to the output of the first synthesizer. Upon failure of the SCR, the system of synthesizers can provide a satisfactory frequency reference for the repeater. Disclosed are phase lock loop filter time constant design considerations for achieving proper operation.