An automatic gain control apparatus includes a variable gain amplifier 5 to amplify a signal with an amplification factor and a gain controller 6 to control the amplification factor of the variable gain amplifier 5. A gain limiter 7 is provided for restricting the magnitude of the amplification factor within a predetermined range. The amplification factor therefore does not vary largely, even immediately after the input signal level is suddenly changed due to a switching of a transmitter antenna or a carrier frequency. Thus, it is possible to quickly respond to the change of input signal without requiring a large dynamic range in the circuit following the automatic gain control apparatus.

A novel programmable digital gain controller is provided for the automatic gain control loop of a communications receiver. The digital gain controller comprises a pair of digital detectors coupled to the real and imaginary components of a data stream for providing digital data magnitude output signals which are coupled to an adder whose output is coupled to a first input of a comparator having a second input coupled to a predetermined reference level command. The output of the comparator generates a digital error signal which is coupled to the input of a programmable gain accumulator having a second input proportional gain command so as to provide at the output of the programmable gain accumulator a digital gain command which may be coupled to a variable gain controlled amplifier which is connected in the input data stream of the channel of a communications receiver to provide a predetermine amplifier output level.

A method for clipping a wideband signal in order to eliminate signal overshots having an amplitude above a predefined threshold before submitting the wideband signal to a power amplifier. The method subtracts, from the wideband signal, filtered pulses in phase with the wideband signal, each filtered pulse corresponding to an overshot, and the amplitude of each filtered pulse being dependant on the amplitude of the corresponding overshot and on the predefined threshold. The subtraction step is repeated at least twice on the wideband signal.

A spread-spectrum communication receiver uses two convolvers and a phase shifter to demodulate data from correlation outputs of the convolvers. The demodulated output is used to control the phase-shifting amount of the phase-shifter and gains of the correlation outputs.

A spread spectrum signal detector for sampling a modulated carrier employing a zero-crossing detection means having two independent control loops, a first loop for a zero-mean threshold control and a second loop for AGC control. An IF sampler quantizes the received spread spectrum signals at IF and provides high immunity to interference or jamming. The IF signal is sampled at a number of quarter cycle intervals to allow sampling in sequence of the in-phase (I) and quadrature-phase (Q) components. The output of the IF sampler is two bits, a sign bit and a magnitude bit. The zero-mean threshold control loop using only the sign bit of the I and Q samples sets a threshold level (T0) to detect the zero-crossings of a received waveform. Two magnitude threshold levels are set at fixed offsets from the T0 threshold level. A normalized statistical accumulator using the magnitude bits of the I and Q samples determines the AGC control level for a fixed percentage of outside threshold crossings of the most significant magnitude bit. The I and Q samples are aligned in time, and every other pair of I and Q samples are inverted for digital demodulation of the IF samples to baseband. The baseband samples are provided to a signal processor for generating range and range rate information.