Abstract: A received analog signal applied to a data modem receiver is sampled and converted into a digital signal which is demodulated into a complex baseband signal. If the demodulated complex baseband signal is deviated in phase from a QAM signal point due to phase jitter, the phase error is detected, and a replica of the phase jitter is calculated and applied to impart phase rotation for canceling out the phase jitter that is contained in the complex baseband signal. In each sampling cycle, the phase error between the phase-rotated signal and the modem output signal is detected in order to correct equations for calculating the replica of the phase jitter in the next sampling cycle.

Abstract: A receiver array in accordance with the reception principle of synchronous demodulation, in which a controllable oscillator array is pre-synchronized to a set value for the oscillator frequency by a digital first control circuit having a reference frequency source during a pre-synchronization phase, and a heterodyne signal derived from the oscillator frequency is then synchronized with phase locking to the received useful signal by switching the oscillator control input to an analog second control circuit.

Abstract: Apparatus for demodulating information signals frequency-modulated on an RF carrier signal carrying spectral components within the audio frequency range, a pilot carrier signal having an imparted phase shift from the phase of the transmitted pilot carrier signal, and amplitude-modulated spectral components having another imparted phase shift in a subcarrier channel frequency range above the audio frequency range. The apparatus includes a demodulator for demodulating the frequency-modulated information signals to provide a detected composite signal which includes a detected pilot carrier characterized by an imparted phase shift due to the effects of multipath reception, and detected amplitude modulated spectral components exhibiting another multipath induced phase shift.

Abstract: Electronic receive arrangement for receiving a modulated carrier signal, which arrangement comprises a mixer/demodulator driven with the carrier frequency fc, at least one adder included in a closed signal loop, a low-pass filter, and a pulse shaper constituted by a sigma-delta (one-bit) signal converter and driven with the sampling frequency fs and also comprises a digital decimation filter. The signal loop includes the mixer/demodulator so that the modulated carrier signal is applied to the adder and the output signal of the adder is applied to the mixer/demodulator. The signal loop also comprises a second mixer driven with frequency fc, and the frequencies fs and fc present a common multiple.

Abstract: A communications receiver (103) comprising a carrier recovery apparatus having an adjustable response time loop filter (123) responsive to carrier signal parameters determined by a signal processor (141) is disclosed. Signal reception under fading conditions is improved by detecting the received signal parameters in an energy level determinator (207), a rate of change of energy level determinator (209) and a look-up table value (221) corresponding to a position of TDMA time clock (219).

Abstract: A system of transmission with amplitude modulation for the transmission of signals of all types, analog and/or digital, requiring high performance characteristics with respect to the noise induced by the transmission channel, comprising, at transmission, means for the suppressed carrier amplitude modulation of a useful signal and means for the amplitude modulation, in phase quadrature with said modulated useful signal, of a service signal, making it possible, at reception, to remove the ambiguity on the polarity of the demodulated useful signal. Thus it enables the transmission of signals in suppressed carrier modulation mode, hence with a good signal-to-noise ratio, without losing the polarity of the signal. The transmitters and receivers according to the invention also enable the transmission and reception of the signals modulated in SCAM, VSBAM or VSBSCAM modes.

Abstract: An infrared detector output of a radiometer is amplified and inverted to provide a first signal which is amplified to a predetermined level and a second signal which is inverted with respect to the first signal and amplified to a fraction of the predetermined level of the first signal. The first and second signals are alternately sampled to sample portions of those signals which occur when the detector of the radiometer is viewing the target and then viewing the reference. The signals are sampled once while the detector of the radiometer is looking at the target and twice occurring on each side of the target sample when the detector is looking at the reference signal. The first and second signals are separately integrated in accordance with a predetermined timing pattern determined by the sampling rate of the first (target) and second (reference) signals. The peak integrated outputs of the first and second signals are held then sampled to produce the demodulated output from the radiometer.

Abstract: A regenerating device for regenerating a signal from a composite input signal, provided with a phase-locked loop comprising a first phase comparison circuit 1, a first low-pass filter 2 connected to the output thereof and a controlled oscillator 3. The control input of said oscillator 3 is connected to the output of the low-pass filter 2 while its quadrature output 3a is connected to one input of the phase comparison circuit 1. The input of the phase comparison circuit 1 forms the input of the regenerating device and the in-phase output of the oscillator 3 the output. Furthermore a second phase comparison circuit 4 and a second low-pass filter 5 connected thereto are provided, which correspond to the first phase comparison circuit and the first low-pass filter respectively. The input of the phase-locked loop and the in-phase output 3b of the controlled oscillator 3 are connected to the inputs of the phase comparison circuit 4.

Abstract: A baseband carrier phase corrector is disclosed which permits rapid demodulation and demodulation of varying RF input signals. The baseband carrier phase corrector receives RF signals, or alternatively, IF signals, and converts the signals to baseband. An RF signal received by the baseband carrier phase corrector is split and multiplied with oscillating signals having a 90 degree phase differential. The resultant signals are baseband in-phase (I) and quadrature (Q) signals. The I and Q signals are filtered through low pass filters. The filtered I and Q signals are multiplied within a first complex multiplier with a generated phase error. The output of the first complex multiplier results in phase adjusted I and Q baseband signals. A symbol decision circuit estimates digital I and Q signals which are the allowed symbols closest in phase to the phase adjusted I and Q baseband signals. A second complex multiplier is coupled to the symbol decision circuit and to the outputs of the low pass filters.

Abstract: Coherent phase recovery in a time division multiple access (TDMA) system can be attained in a novel manner. After symbol-timing and frequency-offset are estimated, the stored received phase at the desired sampling instant is gated from memory and fed to the input of the carrier phase recovery circuitry. During a first half portion of a burst, the first half portion of the burst is stored, while the loops acquire lock. The first half portion is then fed to one of the loops in a reverse order of its reception. Demodulation is initiated as a common state of both loops in a mid-portion of the signal burst. The previously stored first half portion is backwardly demodulated by one of the loops, while the other loop demodulates the second half portion of the burst. The whole burst is recovered by storing the demodulated first and second half portions in random access memory, and then reordering the stored demodulated burst by reading the memory backwards for the first portion.