Abstract: A store and forward receiver for a satellite communication system employs a multi-threaded command interpreter, and an associated reduced complexity audio control language (ACL) to define commands for controlling actions at different receiver sites, each of which is programmable for its own local programming purposes. Upon receipt of a relatively simple command from the headend, the interpreter accesses and executes an associated sequence of potentially locally unique, previously stored commands, causing performance of a sequence of actions, e.g., play back of potentially locally unique, previously stored information files, interleaved with portions of a headend-source commercial audio program being rebroadcast at the receiver site. This allows different affiliate stations to produce separate potentially locally unique complex sequences of actions from a single headend-sourced command for all receivers in a network grouping.

Abstract: A store and forward receiver for a satellite communication system employs a multi-threaded command interpreter, and an associated reduced complexity audio control language (ACL) to define commands for controlling actions at different receiver sites, each of which is programmable for its own local programming purposes. Upon receipt of a relatively simple command from the headend, the interpreter accesses and executes an associated sequence of potentially locally unique, previously stored commands, causing performance of a sequence of actions, e.g., play back of potentially locally unique, previously stored information files, interleaved with portions of a headend-source commercial audio program being rebroadcast at the receiver site. This allows different affiliate stations to produce separate potentially locally unique complex sequences of actions from a single headend-sourced command for all receivers in a network grouping.

Abstract: 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.

Abstract: In a time division multiple access satellite communications system having a master station and one or more remote stations, frequency offset through the translation oscillator in the satellite is corrected by transmitting a pilot frequency signal, reference to a high precision oscillator, through the satellite, so as to subject the pilot frequency signal to a frequency translation and monitoring the frequency translation of the pilot frequency signal as received at the master station subsequent to its transmission through the satellite. Signals to be transmitted over the satellite communications link from the master station to remote stations are subjected to a frequency translation that is effectively complementary to the monitored frequency translation.

Abstract: A sidelock avoidance scheme for preventing sidelock in a PSK demodulator's carrier recovery loop contains augmenting sweep control circuitry, including a frequency discriminator and an associated window comparator. The output of the frequency discriminator, which is low pass filtered to remove noise, is applied to the window comparator which compares any differential between the true carrier and the output of a carrier recovery loop to a preset reference threshold representative of a frequency error condition that may approach sidelock. When the output of the frequency discriminator is greater that this preset reference threshold, an augmented frequency control voltage is applied to the voltage control oscillator of the loop to drive the oscillator away from a possible sidelock condition and toward the true carrier. The augmented frequency control voltage may be derived from a frequency sweep generator or from the output of the frequency discriminator, depending upon a selected strapping option.

Abstract: A link performance indicator card analyzes incoming analog data from a demodulator on a bit by bit basis and compares the individual bit amplitudes with a fraction of the average bit signal levels. The data bits that lack sufficient amplitude to be clear-cut "high" or "low" pulses are detected as "pseudo-errors". A bit error rate gate signal controls the detectors in order that circuits operate for only one burst or part of a burst per frame always from the same earth station. A comparator is used for comparing the output of the averaged incoming analog signal with the instantaneous value of the analog signal. Alternate clocking signals are used to perform the averaging function and the comparison function of the average signal with the instantaneous signal. This alternation of the signals frees the comparison operation from the influence of any loading on the circuit. The sample points of the incoming analog signal are adjustable by use of delays on the clock signals fed into the circuits.

Abstract: A decision-directed Costas loop demodulator, rather than employing decision circuits, i.e. sample and hold circuits, in the path of each of the I and Q channels, contains a single sample and hold circuit at the output of the crosstalk measurement subtraction circuitry that drives the VCO. Functionally, the same decision-directed sampling process that is carried out by dual channel approach is achieved, yet because the decision/sampling circuitry is located downstream of the crosstalk measurement subtraction circuit, it operates on a relatively slowly varying error signal rather than on the rapidly varying I and Q channel signals.