Abstract: A low-power, spread spectrum synchronized communication system employing a satellite which continuously and iteratively re-transmits a PRS signal PRS.sub.m from a master earth station having a chip rate C.sub.m and a bit rate B.sub.m and comprising a plurality of ground stations each including a transmitter for transmitting a first PRS signal (PRS.sub.G) unique thereto and having a first chip rate C.sub.G and a first bit rate B.sub.G and a receiver for receiving and identifying PRS.sub.G after being returned by the satellite as PRS.sub.Gr with a chip rate C.sub.Gr and a bit rate B.sub.Gr. Also provided is a phase difference detector responsive to C.sub.m and C.sub.Gr to periodically produce a signal representative of the change of phase difference thereof and a frequency changing circuit responsive to such signal to change the chip rate C.sub.Gr by an amount which will cause the phase of C.sub.Gr to approach the phase of C.sub.m at a given rate.

Abstract: A satellite communications system has a number of earth stations sharing an uplink carrier in a time division multiple access mode. One of the earth stations is designated as the master station for the carrier. The uplink transmissions from each station are synchronized by computing the time interval between the arrival at the satellite of the signal from the master station and the signal arrival from each of the other stations. The actual time intervals are compared to the optimum intervals for a properly synchronized transmission from each station. If the comparison indicates that a given earth station is not properly synchronized, that station's time of transmission is adjusted until the actual interval substantially matches the optimum interval.

Abstract: A transmitted signal includes a pilot signal at a given frequency and an information signal occupying a different band of frequencies. A noise reduction system for a signal receiver detects modulation on the pilot signal and generates a signal having a frequency that varies in response to the detected modulation. The system includes an apparatus for combining the received signal with the generated signal to produce a signal at another frequency with reduced frequency noise.

Abstract: An improved companded transmission system uses a transmitter having a first compressor for compressing a signal m(t) of bandwidth B.sub.1 to form a signal C[m(t)]. The transmission system has a bandwidth B.sub.2 where B.sub.1 .ltoreq.B.sub.2. A receiver having an expander to expand the received signal r(t) is provided to produce a signal m.sub.E (t). The improvement consists of a circuit for recovering the frequency components f.sub.L lost during transmission of C[m(t)] and includes a second compressor for compressing m.sub.E (t) in the same manner as m(t) was compressed to produce a signal C[m.sub.E (t)] which contains frequency components f.sub.c lying above B.sub.2. A filter which is responsive to C[m.sub.E (t)] generates (C[m.sub.E (t)]-f.sub.c), and, a subtractor subtracts (C[m.sub.E (t)]-f.sub.c) from C[m.sub.E (t)]. An adder adds f.sub.c to r(t), and, an expander expands the summed signal f.sub.c +r(t) to produce a signal m.sub.1 (t) which is a first order corrected approximation of m(t).

Abstract: A video scrambling device requires that a key signal be periodically inserted into a subscribers box, e.g. once a month. The key signal is a function of both the box number and the time, and thus once received must be inserted relatively quickly, e.g. an hour or two. If it is not inserted quickly, a new key signal must be obtained. This makes it extremely difficult for a pirate to distribute a key signal to his customers in time for it to be effective. The scrambling method can be pseudorandom line inversion and also audio scrambling.

Abstract: An improved automatic gain control system for a frequency modulated television (FM/TV) transmitter transmission system comprising a transmitter for generating and transmitting a television (TV) signal, a satellite repeater, and at least one receiver having a demodulator and which collectively form a transmission path having a certain frequency bandwidth with the transmitter comprising a pre-emphasis circuit for pre-emphasizing the TV signal and an FM circuit for frequency modulating the output of the pre-emphasis circuit. The invention provides a filter located at the transmitter for simulating the filter characteristics of the overall transmission path and responsive to the frequency modulated TV signal generated at the transmitter to produce a control signal in the event the spectrum of the frequency modulated TV signal exceeds the transmission path bandwidth.

Abstract: An improved automatic gain control (AGC) for a television transmission system comprising a transmitter for transmitting a TV signal via a transmission path to a receiver and having a certain bandwidth in which said transmitter includes a generator for generating a baseband TV signal which can be pre-emphasized, and a variable gain amplifier responsive to the baseband TV signal to produce an amplified baseband video signal. The AGC system comprises a band eliminating filter responsive to the baseband output signal to produce a control signal whose amplitude reflects the change in energy content of that portion of the TV output signal lying outside the allowed transmission bandwidth. The variable gain amplifier is responsive to the control signal to vary its gain substantially inversely as the out-of-band energy content varies. At the receiver a detector detects a component of the received TV signal which has known characteristics, usually constant, in the absence of the gain introduced at the transmitter.

Abstract: In a single-voice-signal-per-carrier communications system, means are provided for limiting the intermodulation distortion in a common amplifier of a plurality of talkspurt voice signals. Separate carrier waves and voice signals are applied to respective modulators. The voice-operated-switch signals associated with respective voice signals are applied through a limiter circuit to the respective modulators. The limiter circuit limits the number of modulators generating talkspurt signals at any instant to a number which avoids intermodulation distortion.

Abstract: A system to individually compress the volume range of each voice signal in a group of frequency-division-multiplexed voice signals, without frequency dividing the voice signals into separate channels, includes, in order: a sampler to sample the group of voice signals, an analog-to-digital converter to convert each analog sample a first fast Fourier transform processor producing coefficients, means to direct coefficients representing individual voice signals to respective individual signal channels in which the signal levels are compressed, a second fast Fourier transform processor, and a digit-to-analog converter and band-pass filter to produce an analog group of frequency-division multiplexed voice signals like the original signals but with each voice signal individually compressed in volume range.