Harris Corporation

Scientific-atlanta, Inc.

Charles R Burr

George W Waters

David K Campbell

Charles W Richards, Iv

Ronald S Posner

Accurate tuning of a satellite system's burst demodulator to a signal which is subject to frequency offset in the course of its transmission over the satellite link is achieved without the use of high precision oscillators at remote sites, or the transmission of a dedicated pilot tone. Instead, a dedicated high precision clock is used for the purpose of establishing both the outlink carrier and the return channel carrier. The modulation of the data on the outlink carrier is also derived from the precision clock source. At each remote station, the outlink channel is monitored to recover the high precision clock. This recovered clock is then used as a reference for generating the return channel carrier. The burst demodulator equipment at the master station monitors both the outlink channel continuous carrier and burst mode transmissions from the remote stations. Each of the continuous and burst mode carriers, having been transmitted through the satellite, will undergo the same frequency offset or modification, so that the frequency difference between the outlink channel carrier and the return link channel carrier will always be constant. The outlink channel carrier, which is available on a continuous basis, is used to derive a local oscillator frequency reference for establishing the burst demodulator's local oscillator reference.

Mechanism for deriving accurate frequency reference for satellite

An apparatus for scrambling a television signal in which horizontal lines of the transmitted television picture are selectively inverted in accordance with the state of a pseudorandom noise generator. In order to permit correction of the throughput gain as well as the throughput offset at the receiving end of the communication link so as to obtain a desired level of picture quality, particularly in a satellite communication system, an analog calibration signal representing both black and white levels is inserted into a horizontal line of the vertical retrace interval at the transmission end of the link. This calibration signal is then detected at the receiving end of the link and the signal levels are adjusted as needed. In addition, a randomly-varying key code signal for resetting the pseudorandom noise generator is randomly inserted into another horizontal line of the vertical retrace period to control scrambling. The audio portion of the television signal is also scrambled by randomly shifting the audio carrier between first and second offset frequencies.

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Palm Bay, FL, United States of America

Charles R Burr