Importance

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Abstract

There is disclosed a control system for receiving multichannel frequency multiplex satellite communication signals with channel identification coding wherein a desired channel can be located and locked-on by its identification code without knowing the channel frequency, including a receiver for satellite signals feeding at least one and preferably three or more voltage tunable demodulators. Each tunable demodualtor has an audio output for voice or data to be utilized locally or retransmitted, and an AFC output monitored by the control system; a respective demodulator is normally tuned to keep the AFC output at approximately 90 percent of its maximum value thereby tracking a received carrier signal. A microprocessor is programmed to detect subaudible frequency or other coding in the audio signal and to produce a tuning voltage bump signal on detection of undesired-channel coding; it also generates a reset signal after tuning voltage has reached maximum value to return tuning voltage to minimum value. The control circuit for the tuning voltage includes a charge integrator charged up or down in response to signals from the microprocessor or the AFC output. A preferred embodiment has up to ten channels with subaudible frequency codes between about 25 Hz and about 100 Hz and the coding detector includes a square wave converter together with a microprocessor program routine for measuring the period of the square wave. The microprocessor compares the square wave period and stored data identifying the desired-channel wave period and, if the comparison fails, controls the tuner to resume scanning.

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First Claim