Abstract: Distortion due to transmission characteristics of a transmission medium is corrected by measuring leakage in a signal orthogonal to a received signal. The frequency response of an equalizer is adaptively adjusted until the measured leakage is at a local minimum.

Abstract: Distortion due to transmission characteristics of a transmission medium is corrected by measuring leakage in a signal orthogonal to a received signal. The frequency response of an equalizer is adaptively adjusted until the measured leakage is at a local minimum.

Abstract: Spurious frequency components from the output signal of a direct digital synthesizer are reduced with minimum degradation of the fundamental frequency of the output signal. The synthesizer has a phase accumulator for receiving digital multibit modulation data words from a source, a periodic wave function converter for converting the modulation data words into digital waveform data words and a digital-to-analog converter for converting the digital waveform data words into an analog signal which serves as the output signal. The output signal has a frequency and waveform dictated by the modulation data words. Reduction of spurious frequency components is achieved by generating a dither waveform representing a band limited waveform. The dither waveform is summed with the modulation data words prior to application to the wave function converter to provide a dither modulated analog output signal.

Abstract: An improved substantially "zero distortion" four quadrant modulator of the type including a pair of differential elements respectively coupled to the Y input port terminals of the modulator and exhibiting nonlinear amplitude transfer functions, includes the means for substantially linearizing the nonlinear transfer function. The means includes a pair of operational amplifiers, each having an input coupled to a respective terminal of the Y input port and an output coupled to the corresponding differential element so that the differential element is disposed in the feedback path of the operational amplifier.

Abstract: An improved substantially "zero distortion" four quadrant modulator of the type including a pair of differential elements respectively coupled to the Y input port terminals of the modulator and exhibiting nonlinear amplitude transfer functions, includes the means for substantially linearizing the nonlinear transfer function. The means includes a pair of operational amplifiers, each having an input coupled to a respective terminal of the Y input port and an output coupled to the corresponding differential element so that the differential element is disposed in the feedback path of the operational amplifier.An improved demodulator is provided by detecting the amplitude modulated signal with a first detector and applying the detected signal to one input of a signal comparator. A feedback loop couples the output of the signal comparator to its other input.

Abstract: A multiplier circuit for controlling gain amplification of an electrical input signal responsively to a control signal comprises log conversion means for producing a log signal as a logarithmic function of the input signal, means for producing a multiplier signal as a function of the sum of the log signal and the control signal and antilog-conversion means for producing an antilog signal as an antilogarithmic function of the multiplied signal. The improvement is characterized by the log conversion means and antilog conversion means each including passive elements capable of exhibiting log-linear and antilog-linear transfer characteristics. The passive elements are preferably in the form of diode elements connected in a diode bridge.

Abstract: An improved signal expansion system and technique is disclosed. The system comprises a detector for sensing an input signal and for producing responsively thereto a D.C. control signal having an amplitude as a function of the input signal, and a gain control amplifier for amplifying the input signal, the amplifier including means for controlling the gain of the amplifier as a function of the amplitude of the control signal. The improvement comprises means for varying the amplitude of the D.C. signal at least in part as a function of the time derivative of that amplitude.

Abstract: Homodyne automatic frequency control circuitry maintains the mean or center output frequency of a controlled oscillator, e.g., the output of a voltage controlled oscillator effecting frequency modulation, equal to the output frequency of a reference oscillator. The composite AFC circuitry employs ganged sampling switches and a common mode error obviating common frequency detector (e.g., a discriminator) to alternately store voltages representative of the reference and controlled oscillator frequencies in capacitors connected to the inputs of a difference amplifier. The difference amplifier acts through an integrator to supply any necessary correction potential to the control port of the controlled oscillator when the signals stored in the two capacitors differ, signalling that the mean output frequency of the controlled oscillator has departed from that of the reference oscillator.