Microdyne Corporation

Donald J Woodworth

Gregory Allen Magin

James B Grabenstein

Frank A Ziegler

A satellite signal identification system utilizes distinguishable unique coded identifiers impressed on a carrier sent from a transmitting ground station to be identified. The identifier is recieved and identified by the receiving station to specifically identify a particular underlying carrier signal for reception. The invention utilizes a data modem for transmitting to an earth relay satellite coded identification signals together with various data and error correcting information. An IF carrier signal may be combined with video and/or audio signals, such combined signals being relayed via satellite to the ground station. The MPU of a modem in the ground station finds its counterpart in the MPU of the downconverter that receives via a block downconverter the data, housekeeping and ID signals after the video has been removed. The downconverter first translates the satellite transponder frequency to an IF frequency and sequentially searches for a carrier and the PSK code. The MPU establishes bit sync using the PSK carrier and then searches for the ID signal. The downconverter frequency sweeps to locate a new carrier if the desired ID is not found. Once the desired ID is detected the receiver locks on the signal through the downconverter utilizing the ID signal via a long phase lock loop to cause the local oscillator to track the phase and frequency jitter introduced by an inexpensive downconverter. The MPU demodulates and separates all of the data and housekeeping signals, the latter utilized in an error correction scheme.

Satellite data transmission and receiving station

A dual conversion variable bandwidth telemetry receiver employs a phase locked loop which controls the second local oscillator to maintain lock on the carrier frequency; the phase locked loop employing a loop filter with a variable time constant integrator, the time constant of which can be varied as a function of receiver bandwidth and the integrator with its associated capacitor and resistor banks being employed in a sweep, i.e. search, oscillator circuit enabled when the carrier signal is lost. A coherent double-balanced mixer is employed to detect carrier lock and if lock is lost but the carrier is still detected, a rapid response anti-sideband circuit in the phase detector of the phase locked loop is employed to suppress the sidebands and greatly increase the probability of relocking on the carrier. A synchronous AM detector employs quadrature IF and reference signals at the same frequency to produce a dc signal when phase lock occurs; the signal falling rapidly upon loss of lock. The synchronous AM detector employs a variable time constant integrator for eliminating noise above a low frequency to accommodate carrier fading, said integrator being located in an AGC circuit of an amplifier feeding a balanced mixer to hold the IF at a constant level, thus permitting detection of carrier signals at a carrier to noise ratio as low as a -20 dB. The AM detector also produces a substantially exact reproduction of the AM signal for use elsewhere in the receiver.

Variable phase signal demodulator

A multiple bandwidth quadrature type FM demodulator employs a double-balanced mixer supplied with a frequency modulated IF signal directly and through one of a selectable plurality of bandpass circuits each having a different bandwidth, having a linear phase shift versus frequency characteristic and producing a 90.degree. phase shift at the IF frequency whereby to produce at the output of the mixer a signal level that varies as a linear function of frequency of the input signal, the demodulator including a bias control circuit for the mixer to establish a normalized output for all filters at full bandwidth modulation and further including circuits for establishing a signal balanced with respect to ground or other reference potential regardless of the filter employed.

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Ocala, FL, United States of America

Donald J Woodworth