Abstract: An improved synthetic heterodyne demodulator circuit. The circuit is arranged to accept the output signal s(t) from an interferometric sensor with large amplitude sinusoidal phase modulation (phase-generated carrier). The phase modulation amplitude is adjusted such that a selected pair of odd and even carrier harmonics are equal. The quadrature signal components are first extracted from the phase-generated carrier using standard homodyne techniques. The quadrature signal components are then used to AM-modulate a pair of equal-amplitude quadrature carrier components at an arbitrary frequency .omega..sub.c, and summed. The result is a conventional PM modulated carrier which can be demodulated using standard FM techniques, followed by integration, to recover with high fidelity the sensed information.

Abstract: An interference canceller comprises a first input terminal (10) to which a combined signal and noise is supplied, and a second input terminal (12) to which a reference signal correlated with the noise is supplied. A subtractor (11) has a first input coupled to the first input terminal (10) and an output coupled to the output terminal of the canceller. An adaptive filter (13) has an input connected to the second input terminal (12) and an output connected to a second input of the subtractor (11). A detector (14) is provided for generating a signal representative of the magnitude of the output of the subtractor (11). A calculation circuit (17) is coupled to the detector for generating a signal that is inversely variable as a function of the output of the detector. A multiplier (18, 20) scales a stepsize with the inversely variable signal and multiplies the output of the subtractor with the scaled stepsize. The tap-weights of the adaptive filter (13) are controlled according to the multiplied signal.

Abstract: A direct conversion receiver having a tri-phase architecture including three separate baseband signal channels. RF communications signals which are being tuned by the receiver are split into three equal and in-phase components which are mixed with three equal but substantially out-of-phase injection signals on frequency with the communications signal. The resulting baseband component signals are independently filtered and amplified on the three signal channels. The baseband components are then directed to a signal processing unit which corrects the baseband components for gain or phase mismatch errors between the signal channels based on the information carried by the three components and thereafter demodulates the signals in order to acquire the information carried by the RF communications signal. An automatic gain control system and a signal filtering system adapted for use with direct conversion receivers are also disclosed.

Abstract: An active filtering mixer has a feedback arrangement, by means of which unwanted components in the output of the mixer are fed back, out of phase, to an input of the mixer for substantially canceling such components dynamically within the mixer, itself. In so doing, active filtering mixers in accordance with the invention largely avoid the undesirable effects these components can have on signal processing in downstream devices, and within the mixer. The feedback arrangement also stabilizes the mixer's DC operating point, and thereby can maintain the maximum dynamic range of the mixer. Preferably, the desired components of the output are also fed back, but to a substantially smaller degree than the unwanted components, thereby linearizing the in-band output of the mixer, and generallly improving the mixer's performance over the entire spectrum of its output.

Abstract: A radio sensitivity enhancer inputs an incoming radio frequency signal into two receiver strings. The first receiver string modulates the RF signal to a frequency which is passed by a filter to produce the desired signal plus a noise component. In the second receiver string, the RF signal is modulated to a frequency outside the frequencies passed by a filter to produce a signal with a noise component but without the desired signal. The desired signal with the noise component is then subtracted from the signal with only the noise component to produce a substantially noise-free desired signal.

Abstract: A TVRO receiver for the reception of frequency modulated satellite broadcast signals is provided with the capability of efficiently rejecting image frequencies generated as the received signals undergo intermediate frequency translation. A TVRO tuner, which includes a super-heterodyne circuit having a voltage-controlled oscillator (VCO), means for supplying a controlling tuning voltage to the VCO, and a mixer for combining incoming 1st IF signals with the output frequency of the VCO to reduce the frequency of the 1st IF signals to a selected 2nd IF frequency, is provided with a tracking filter which is adapted to pass only the incoming 1st IF signals and effectively reject any image frequencies generated at the received signal frequencies.

Abstract: Predetection noise bandwidth reduction is effected by a pre-averager capable of digitally averaging the samples of an input data signal over a single symbol, the averaging interval being defined by the input sampling rate divided by the output sampling rate. As the averaged sample is clocked to a suitable detector at a much slower rate than the input signal sampling rate the noise bandwidth at the input to the detector is reduced, the input to the detector having an improved signal to noise ratio as a result of the averaging process, and the rate at which such subsequent processing must operate is correspondingly reduced. The pre-averager may form a data filter when the output sampling rate is reduced to one sample per symbol of received data.

Abstract: An image suppression harmonic frequency converter capable of operating in any microwave range is described. Frequency conversion is obtained by making use of a local frequency which is half that of a conventional converter. In particular, the radiofrequency reception signal is converted into an intermediate frequency signal with suppression of the converted image band. Similarly, the intermediate frequency signal to be transmitted is converted into a single side band radiofrequency transmission signal. The converter comprises two harmonic mixers, a first inquadrature radiofrequency hybrid coupler, a second in-quadrature intermediate frequency hybrid coupler, two appropriate duplexer filters, two low-pass filters, two matching circuits, and two decoupling circuits.

Abstract: A narrowband parameter estimator circuit is described which can be used to estimate the frequency and the relative power of narrowband interference tones which reside in a wideband information signal. A two-weight adaptive filter with a phase/frequency-lock loop circuit works in conjunction with a stepped synthesizer to lock onto the individual narrowband interference tones. A lock-detect circuit signals a digital logic unit to record the frequency of the stepped synthesizer and to measure the power in the adaptive filter output signal. This same output signal is used to cancel the unwanted tone in the wideband information signal being transmitted.

Abstract: A noise reduction circuit comprises a first circuit for extracting a relatively high frequency component of an input signal and amplitude-limiting a component of said extracted high frequency component exceeding a predetermined level, a second circuit for delaying said input signal such as a video signal by a predetermined time, and a third circuit for adding outputs of said first and second circuits and outputting an added result as an output of said noise reduction circuit.

Abstract: A simplified carrier phase control apparatus used in a modem for demodulating a quadrature amplitude modulated data signal, to correct phase jitters of a carrier signal due to a 50 Hz or a 60 Hz frequency of the commercial power supply, and its harmonic wave frequency components. The carrier phase control apparatus has a predictive filter for predicting a carrier phase jitter, the predictive filter composed of band-pass filters with center frequencies of 50 Hz and 60 Hz, and a circuit where the output signals of the band-pass filters are multiplied by the coefficients and added linearly.

Abstract: Asymmetric polyphase filer having first to fourth input terminals for applying thereto a 4-phase input signal including first to fourth signal vectors, respectively, which succeed one another in phase each time through 90.degree., first to fourth intercoupled identical filter sections, respectively, connected to the terminals, at least one of the odd and even filter sections being coupled to two output terminals, said filter sections having constant reactances.

Abstract: In a digital demodulation system (FIGS. 2, 3, 4, 7, 8) in a dual polarization radio system, having a first demodulator (4) and a first A/D converter (14) for a main signal, a second demodulator (5) and a second A/D converter (15c) for an interference signal (cross polarization signal), a transversal filter (18) for providing a compensation signal for cancelling an interference component in the main signal depending upon the demodulated interference component; the second A/D converter (15c) for providing the interference component in digital form is operated with a clock signal (102) regenerated in the main signal branch (4, 14) so that system operates correctly even when the main signal and cross polarization signal are in an asynchronous condition.

Abstract: A noise reduction apparatus in which an input signal is supplied to a first signal path (2) including a variable low-pass filter (2) and a second signal path (1), a control circuit (4) control is such that a cut-off frequency of the variable low-pass filter (2) is varied in accordance with a frequency of the input signal S(1), and an output signal is obtained from the first signal path when noise is generated and from the second signal path when noise is not generated.

Abstract: A radio transmission system a base station comprises a plurality of transmitters arranged to transmit from the same site and having substantially the same output power, each transmitting on an individual channel within a dedicated block of contiguous channels. Receivers tuned to channels within said block of channels therefore require a limited image and adjacent channel rejection, of the order of 30 db. The receiver is preferably a direct conversion phasing receiver which has a local oscillator which can be tuned to a frequency within the block such that an image of any channel also falls within the block of channels. The system is suitable for local area radio systems such as paging or cordless telephones.

Abstract: An improved noise suppression system (800) is disclosed which performs speech quality enhancement upon the speech-plus-noise signal available at the input (205) to generate a clean speech signal at the output (265) by spectral gain modification. The improvements of the present invention include the addition of a signal-to-noise ratio (SNR) threshold mechanism (830) to reduce background noise flutter by offsetting the gain rise of the gain tables until a certain SNR threshold is reached, the use of a voice metric calculator (810) to produce more accurate background noise estimates via performing the update decision based on the overall voice-like characteristics in the channels and the time interval since the last update, and the use of a channel SNR modifier (820) to provide immunity to narrowband noise bursts through modification of the SNR estimates based on the voice metric calculation and the channel energies.

Abstract: An improved decision feedback equalizer, which removes intersymbol interference from pulse transmissions having a desired period, includes an arithmetic circuit (9) for extracting a residual intersymbol interference signal from a residual signal and a delayed residual signal which is produced by delaying the residual signal. The residual signal is produced by a subtractor circuit (2) which subtracts an estimated intersymbol interference signal from the pulse transmissions. A pattern detector circuit (11) is also provided to detect a particular consecutive pattern from a demodulated data sequence produced by a decision or detection circuit (3) for demodulating the residual signal. The residual intersymbol interference signal and a reference signal are inputted to a selector (10) responsive to the output of the pattern detector circuit.

Abstract: An active polyphase filter arrangement in which asymmetric poles and zeros are obtained using feedback. In implementing the active polyphase filter arrangement there is provided a feedforward path comprising a first polyphase filter and a feedback path comprising a second polyphase filter. Both filters are preferably two phase filters. In operating the polyphase filter arrangement the loop gain at the unwanted "image" frequency can either be made much greater than unity thereby making the feed forward path insensitive to mismatching or be made much less than unity thereby making the feedback path insensitive to mismatching.

Abstract: A working on the zero IF principle is disclosed which contains a feedback circuit instead of a preselector for suppressing interfering signals. The interfering signals contained in the incoming signal (F.sub.E) are separated from the useful signal by filters in the baseband. They are then reconverted to the RF value, amplified, and substracted from the incoming signal (F.sub.E) by a subtracter (S1). In the steady state, the output of the subtracter (S1) provides the useful signal, which is converted into the baseband and then fed to a signal processor (SV).

Abstract: A noise reduction circuit for video signal comprises first through third circuits each for obtaining from an input video signal a high frequency component including a noise component and for limiting large amplitude parts thereof, where a filter part of the second circuit has an impulse response characteristic wherein an amplitude increases or decays with time and is complementary to that of a filter part of the first circuit and a filter part of the third circuit has an impulse response characteristic which is essentially a combination of the two impulse response characteristics, and a fourth circuit for carrying out a subtraction between the input video signal and an output signal of the first circuit so as to obtain a first signal which is substantially eliminated of the noise component except for a noise component and distortion remaining at parts in vicinities of rises and falls in the video signal caused by the amplitude limitation carried out in the first circuit, carrying out a subtraction between out

Abstract: A radio frequency tuning circuit, for use in a transmitter or receiver, which rejects image frequencies of the frequency band of a supplied RF signal to which it is tuned. The circuit comprises an N-path filter and a feedback loop connecting the output of such filter to the input of an RF amplifier to which the RF signal is applied. The filter includes a tunable local oscillator and a pair of quadrature related signal paths including mixers therein driven by such oscillator, the outputs of such paths being combined by a summing amplifier which produces the output RF signal. The output of the summing amplifier is also supplied to the feedback path, causing the center frequency of the transfer characteristic of the N-path filter to be displaced from the local oscillator frequency. The RF output signal thereby includes substantially only single sideband of the signals produced by the two signal paths.

Abstract: A beamforming adaptive control loop is simultaneously employed in combination with a null-steering adaptive control loop to enhance the signal/interference ratio resulting in an increase in the message quality. The loops employ spectral processing in which case bandpass filters and notch filters form separate loops which enhance the desired signals and cancel the undesired signals, respectively. The correlated output from the beamforming loop is added to the correlated output of the null-steering loop and mixed with the incoming signal.

Abstract: A canceller for eliminating the cross-polarization interference in incoming signals having polarizations which are orthogonal to one another is proposed. Each incoming signal is coupled to an associated adaptive filter. Each filter output is then summed with an associated one of the incoming signals which has a polarization orthogonal to that of the filter input signal. The signal sums formed are the canceller output signals. Adjustment of the adaptive filters so as to cancel the cross-polarization interference in each received signal is made in response to the incoming signals and the canceller output signals at selected times. During these times, circuitry for adjusting the adaptive filters examines spectral tones formed by the incoming signals and the canceller output signals.

Abstract: In a superheterodyne receiver, such as a typical television receiver, a radio frequency coupling arrangement includes a first resonant circuit coupled to receive the input signal and further coupled to a second resonant circuit by a first coupling. Both resonant circuits are tuned to the desired signal frequency. The capacitive branch of the first resonant circuit includes a circuit impedance for providing a neutralizing voltage, at least a portion of which is coupled by a second coupling to the inductive branch of the second resonant circuit. The circuit impedance is selected to cause cancellation in the inductive branch between image frequency components coupled by the first coupling and image frequency components coupled by the second coupling, without substantially affecting the desired signals.

Abstract: A variable-narrow-band rejection filter is inserted in a reception signal path for rejecting a jamming wave. Signals at input and output terminals of the narrow-band rejection filter are picked up by a pair of first and second bandpass filters each having a center frequency that can be passed thereby which is equal to a rejection frequency of the narrow-band rejection filter. A phase difference between outputs from the bandpass filter is detected by a phase comparator, and the detected signal is supplied through a switch to a hold circuit in which the supplied signal is held. The rejection frequency of the narrow-band rejection filter is adjusted into conformity with the jamming wave frequency by an output from the hold circuit. The levels of the output signals from the first and second bandpass filters are detected respectively by a pair of first and second level detectors, and the detected outputs are compared by a comparator.

Abstract: In an AM stereo system wherein a low frequency pilot tone is added to the difference channel signal before modulation of the carrier, "image shifting" and audio distortion in a receiver, due to residual pilot tone signal, are removed by separating out a portion of the pilot tone after it has been filtered and phase shifed for enabling the stereo mode of operation. The separated signal is then inverted and delayed appropriately for each of the PLL and audio circuits.

Abstract: A clock-controlled filtering arrangement for suppressing a number of interference frequencies related to a clock frequency, which comprises a time-discrete comb filter included in a negative feedback loop for a selective negative feedback of the said interference frequencies, which time-discrete comb filter is connected to an output of a clock generator for controlling the frequency location of the pass ranges of the comb filter. In order to avoid on the one hand the introduction of quantizing noise and the use of additional circuits, such as A/D and D/A converters, and on the other hand the occurrence of error cumulation while maintaining an adequate interference suppression, the time-discrete comb filter is of the switched capacitor N-path filter type.

Abstract: Methods for improving the availability of information derived from signals received from an object irradiated with coherent pulses of any form of radiation that exhibits a wave nature are disclosed. A method for reducing speckle derives separate component noncoherent signals from the received signals, and combines these separate noncoherent signals to form improved composite noncoherent signals. Weighting and processing of component signals can be applied as a function of time, frequency, and signal amplitude to optimize speckle reduction in all or a critical part of the signal by compensating for the range and frequency dependence of attenuation and the frequency dependence of scattering phenomena. In a method for enhancing resolution, separate component coherent signals are derived from the received signals, weighted and processed, and combined to form improved composite coherent signals; then noncoherent signals are derived from the improved composite coherent signals.

Abstract: An auto notch system which automatically "notch" filters up to four interference signals (interferers) in the band from 50 KHz to 150 KHz comprises a signal detector, an adjustable notch filter, a bandpass receiver and a digital controller, plus the software that runs in the digital controller. The signal detector circuit has an antenna, a preamplifier and a group of "fixed" filters. The adjustable notch filters are four circuits, each includes an active notch type filter stage with a DAC (digital to analog converter) in series with the input resistor to allow gain control and another DAC that controls the current through a diode that is optically coupled to a light dependent resistor pair. The light resistor pair is in the filter loop and as the resistance varies the frequency response of the filter changes. Thus the frequency response is controlled by varying the diode current.

Abstract: In an interference elimination device for use in a digital microwave communication system in which an interference component results from at least one different microwave communication system sharing a frequency band in common, a controller (21) controls a device input signal so that a controlled signal thereby produced may include a controlled component which is equal in amplitude to the interference component and be antiphase relative thereto. The controlled signal is subtracted from the device input signal to provide a difference signal which is free from the interference component. Together with the device input signal, the difference signal is supplied to a control signal producing circuit (41) for producing an amplitude and a phase control signal for the controller. Instead of the device input signal, an interference signal derived by causing the device input signal to pass through a narrow-band filter (11 or 12) may be delivered to the controller and the control signal producing circuit.

Abstract: A wide-band ghost reduction circuit apparatus for a television receiver comprises a ghost detector, two transversal filters having delay characteristics different from each other, a switch for selecting one of the filters and an automatic gain control circuit responsive to the output of the ghost detector for controlling the filters and the switch. Each of the transversal filters includes tap amplifiers whose gains are controlled by the automatic gain control circuit and having outputs connected, respectively, to tap inputs of delay devices formed of such as a CCD each provided with a tap and included in the associated transversal filter. Output end of one of the transversal filters having a smaller delay is connected to a selected one of the input tap of the other transversal filter through a switch so that input video signal components join together at every input terminal or every individual tap position of the delay devices.

Abstract: A system is disclosed in which signals are presented to a listener with a spatial impression in which the signal which is desired appears to be coming from a source in front of the listener while other signals appear to be coming from audio sources to the right and left of the listener. The same is achieved through a combination of a heterodyne type detector and a combination of high pass and low pass filters receiving the output of the detector. The outputs of the high and low pass filters are separately amplified and each sent to one ear of the listener.

Abstract: The fade character of a transmitted radio signal comprising an amplitude or phase modulated double-sideband signal is determined from the algebraic sign of the fade induced modulation and the location of the fade notch (.omega..sub.f) relative to the center (.omega..sub.c) of the double-sideband signal frequency spectrum. In the disclosed embodiment, the algebraic sign of the fade induced modulation is determined (e.g., 402, 403, 404, 405, 406, 409, 410, 411, 412, 413, 417) from the sign of the dc component of the product of the differentiated amplitude modulation and frequency modulation of the received signal. The relative location of the fade notch is determined by comparing the amplitudes (e.g., 402, 404, 405, 406, 415) of corresponding frequency components in each sideband of the received double-sideband signal.

Abstract: In a reception system which includes a receiver having a plurality of inter-connected stages and a demodulator, and where there appears at an input of the receiver a desired signal which occupies substantially a predetermined bandwidth, and at least one undesired signal which occupies a bandwidth different from, though partially overlapping the predetermined bandwidth, the improvement includes a signal selector coupled to receiver terminals upstream of the receiver demodulator for normally continuously selecting one of the signals appearing across the receiver terminals, a gain-controlled feedback stage connected with one input thereof to an output of the signal selector for negatively feeding back to the receiver terminals one of the signals substantially 180.degree.

Abstract: The fade character of a received double-sideband, phase coherent signal is determined from the location of the fade notch frequency, (.omega..sub.F) relative to the center (.omega..sub.c) of the received signal frequency spectrum and the phase between fundamental components of first (P.sub.1) and second (P.sub.2) product signals. These product signals are derived (401, 403, 411, 413, 419, 420, 421 or 801, 802, 803, 805, 811) using first (.omega..sub.1) and second (.omega..sub.2) spectral components that are symmetrically disposed about the center of the received signal frequency spectrum. The fundamental components of each product signal are at a common frequency.

Abstract: A narrow-band rejection filter inserted in a received signal path is arranged so that its rejection frequency may be changed by a control signal; the narrow-band rejection filter is controlled so that its rejection frequency may substantially coincide with the center frequency of a jamming wave; thereafter, the phase difference between signals on the input and the output side of the narrow-band rejection filter is detected; and the abovesaid narrow-band rejection filter is controlled by a signal corresponding to the phase difference so that its rejection frequency may automatically coincide with the center frequency of the jamming wave.

Abstract: The effects of crosstalk of an FM carrier from a first signal channel into a second signal channel are reduced by a variable-frequency notch filter coupled in the second channel. The frequency of the notch in the transmission characteristic of the filter is controlled to track the frequency of the FM carrier. Signals in the second channel at the frequency of the FM carrier are attenuated, and therefore the crosstalk signal is attenuated and its effects reduced.

Abstract: Effects of multipath fading and Doppler frequency spread in a single sideband radio communication system are largely overcome by separating (17) from a received signal spectrum, a pilot frequency component including those effects and using that component to accomplish both phase (36) and gain (38) corrections on an information-containing frequency component. Signals essentially free of those effects are provided (10) for controlling necessary frequency translations in the receiver. One illustrative embodiment (FIG. 4) is conveniently arranged for facilitating diversity signal combining.

Abstract: Adaptive suppression of narrow band interference is realized by a filter that automatically makes estimates of interfering signals in the frequency domain and separates the interference from the desired signal. Received analog signals are Fourier transformed in accordance with a CHIRP Z algorithm, squared, and filtered by an N point serial structural CCD to provide a smoothed power spectral density signal. The smoothed power spectral density signal is utilized to cancel interfering signals by any one of three mechanizations. One mechanization comprehends a threshold circuit that generates binary signals in response to the CCD output. The binary signals control a gate that gates strong frequency components (the estimates of the interfering frequency coefficient) from the Fourier transformer through to an inverse Fourier transformer. The inverse Fourier transformed strong frequency components are then subtracted from the delayed received analog signal.

Abstract: An acoustic transmission system for a gaseous or liquid transmission medium, in which the transmitting apparatus double-sideband amplitude modulates a carrier with the signal to be transmitted, the double-sideband amplitude modulated carrier is radiated acoustically over the transmission medium, and the receiving apparatus receives the modulated carrier plus noise introduced in the medium, rejects the superimposed noise by sampling and reconstruction means, and delivers the modulated carrier substantially free from superimposed noise.

Abstract: A channel level adjusting apparatus for equalizing the amplitude level of the received television signals of a plurality of channels. The channel level adjusting apparatus is designed so that when the input amplitude level of the television signals of a relatively small number or at least one channel is different from the more nearly equal or uniform input amplitude level of the television signals of the remaining relatively large number of channels, only the television signal or signals of the higher amplitude level are taken out, attenuated to a desired level and then combined, with a 180-degree phase difference, with the television signals of all the channels, thus making the television signal or signals of the higher input amplitude level more nearly equal in amplitude level to the television signal or signals of the lower input amplitude level and thereby generating the television signals of all the channels having relatively uniform amplitude levels.

Abstract: An FM wave received by an antenna is fed via an AGC circuit to a first FM demodulator and to a compensation signal generator which includes an envelope signal generator, a capacitor, a function generator, an analog multiplier, an SSB modulator, and a second FM demodulator so that the output signal of the compensation signal generator is added to the output signal obtained by the first FM demodulator to offset the multipath distortion contained in the received FM wave.