Abstract: An apparatus and method for performing digital image correction in a receiver. In one embodiment, a receiver circuit may include an IQ signal source configured to provide a digital signal comprising in-phase (I) and quadrature (Q) components, such as an IQ mixer in combination with an analog to digital converter, for example. The receiver circuit may also include an image correction unit coupled to the IQ signal source and configured to combine the digital signal with a complex image correction factor. The image correction unit may be implemented using a digital signal processor under the control of associated program instructions, for example. In one specific implementation of the receiver circuit, the image correction unit may be configured to combine the digital signal with the complex image correction factor using a cross-accumulation operation.

Abstract: A compensating part compensates for deviations on transmission paths, and a pre-deviation signal combining part or a post-deviation signal combining part combines signals on the transmission paths before or after having the deviations applied thereto, wherein the compensating part performs compensation for the deviations based on output of the pre-deviation signal combining part or post-deviation signal combining part and the signals on the transmission paths to be compensated.

Abstract: An active cancellation controller receives a signal strength indicator that indicates a power level of a coupled signal from a local wireless transmitter at a local wireless receiver. The active cancellation controller tunes an active cancellation circuit to reduce the signal strength indicator. The active cancellation circuit is to generate a cancellation signal to combine with the coupled signal at the local wireless receiver.

Abstract: A multipath noise reducer extracts a high-frequency signal from a demodulated signal obtained from a frequency-modulated signal, and generates a noise reduction coefficient from the extracted high-frequency signal. The demodulated signal is also separated into high-frequency and low-frequency components, the high-frequency component is multiplied by the noise reduction coefficient, and the resulting product is added to the low-frequency component. An output signal is thereby obtained in which the spike noise that characterizes multipath reception of a frequency-modulated signal is reduced with relatively little distortion of other parts of the signal, including the parts between noise spikes. The distortion can be further reduced by replacing the demodulated signal with an interpolated signal during noise spikes before the low-frequency component is separated.

Abstract: A method within and wireless communications unit (WCU) arranged to operate in a fixed wireless network including a transceiver for receiving and transmitting signals within the network; an antenna system having adjustable visibility to the fixed wireless network; and a controller, coupled to the transceiver and the antenna system, to control the transceiver and to adjust the visibility of the antenna system such that the visibility of the WCU to the fixed wireless network is adjustable.

Abstract: An RF circuit configured to inteface a balanced port (1, 2, 11, 12) with an unbalanced port (4, 14) by emulating the function of a balun. Reactive components (20, 30, 120, 130) in both branches of a balanced circuit form two resonant circuits by resonating with parasitic reactance. At a predetermined operating centre frequency, one of the two resonant circuits is above resonance and the other is below resonance, resulting in a 180° phase difference between the signals delivered by the two branches. When used to interface an unbalanced signal source (10) to a balanced load (40), the input impedance may be set to a real value matching the output impedance of the signal source by selection of the reactive component (20, 30) values.

Abstract: A method and apparatus for processing cochannel signals received at a sensor array in a cumulant-based signal processing and separation engine to obtain a desired set of output signals or parameters. For use in a signal recovery system, the output signals are recovered and separated versions of the originally transmitted cochannel signals. An important feature that distinguishes the cumulant-based system from other signal separation and recovery systems is that it generates an estimated generalized steering vector associated with each signal source, and representative of all received coherent signal components attributable to the source. This feature enables the invention to perform well in multipath conditions, by combining all coherent multipath components from the same source. In a receiver/transmitter system, the estimated generalized steering vectors associated with each source are used to generate transmit beamformer weight vectors that permit cochannel transmission to multiple user stations.

Abstract: Disclosed are systems and methods which utilize an image reject mixer in an out-of-band mixer application such as in a forward data channel frequency converter. For example, according to a preferred embodiment, an image reject mixer is utilized to provide a relatively high degree of image rejection with respect to an out-of-band signal, thereby relaxing the requirement for filtering in the signal path leading to the mixer circuitry. Preferred embodiments of the invention are substantially or fully implemented utilizing integrated circuit technology.

Abstract: The present invention provides a dummy low noise amplifier (LNA) and an associated resistive network. Prior to DC offset correction, the primary LNAs are deactivated and the antenna is decoupled from the receive path leading to the inputs of the primary LNAs. A resistance is selected to provide a load at the input of the dummy LNA, wherein the load emulates the input load resistance seen by the primary LNA, which will be used to receive the incoming signal. Thus, the output of the dummy LNA emulates the performance of the primary LNA used to receive the incoming signal to allow accurate DC offset correction.

Abstract: The present invention discloses a method and apparatus for correcting the DC offset caused by self-conversion of the oscillator signal in an RF-to-baseband converter. The circuit comprises: a subtractor for subtracting an amplified DC offset signal from a filtered mixer signal to generate a corrected signal; a baseband amplifier coupled to the subtractor to receive the corrected signal to generate a baseband output signal; a low-pass filter coupled to the baseband amplifier to generate a DC offset signal representative of the DC offset; and a DC offset amplifier coupled to the low-pass filter and the subtractor to generate the amplified DC offset signal.

Abstract: A method and apparatus for balancing the forward link capacity of a wireless communication system with the reverse link capacity of the system is presented. Speech coders with selectable modes are implemented in both links so that a forward link speech coder will not be operating with a mode set that is identical to the mode set used by a reverse link speech coder. Since the reverse link has a higher user capacity than a forward link, the reverse link speech coder can operate with a higher average data rate. Hence, the mode set used by the reverse link speech coder can be implemented without low average data rate modes. Elimination of modes from the mode set reduces complexity of the speech coder.

Abstract: An apparatus for removing DC offset in a received data signal is presented. The apparatus measures the DC offset present in a data symbol and uses it to generate a compensation value which is then removed from a future data symbol. An enable signal is used to prevent updating of the compensation value during the reception of a data symbol.

Abstract: Downlink and uplink frequencies in a wireless access system are time-shared by adjacent sectors, but remain dedicated to downlink or uplink transmission and may utilize FDD-only bandwidth within the MMDS spectrum. TDD wireless access equipment need only be modified by introducing a frequency change at the normal TDD guard point, with respective downlink or uplink periods for adjacent sectors offset to form overlapping frames. Cyclo-stationary processing, block equalization, and burst timing coordination allow the boundary between downlink and uplink portions of both frames to be set dynamically, improving spectral efficiency. Fast frequency switching within an allotted physical slot enables synchronization of time-sharing the dedicated frequencies to be maintained among sectors and cells.

Abstract: The invention relates to a method and radio receiver for attenuating spurious signals when receiving (6 to 12) radio signals, when radio signals are mixed (10) to a second frequency, which may be the baseband frequency, for example. Spurious signals are caused by balance errors in the mixer (10) which result from component value fluctuations within tolerance limits. According to the invention, mixing is balanced by setting (12) variable-level bias voltages and/or currents to transistors in the mixer circuit (10). An advantage of the invention is that even-order spurious signals caused by balance errors in the mixing of a signal to a second frequency are considerably attenuated. The invention finds particular utility in a mobile communications device, for example.

Abstract: In order to increase accuracy of DC-offset compensation within radio receivers and to ensure that such compensation does not erode the dynamics of the decoders located within the receivers, the present invention separately performs mean value estimation and channel estimation. Additionally, a bias DC offset value caused by the use of a training sequence to perform mean value estimation can be corrected for in the channel estimator and equalizer.

Abstract: There is described a system and a process for reducing leakage of LO (LLO) in a system which converts the frequency of a first signal by mixing the first signal with a second supplied signal to a third signal having a frequency which is different from the frequency for the first and second signal, where the first signal is divided via a number of couplers into four part-signals which are phase-shifted relative to each other, and that each such part-signal is led through its respective transistor there being added via each transistor a second signal which is mixed with the first signal, and that the signals which pass through the transistors are modulated by a number of regulating means for each transistor, preferably one or two per transistor, and that the frequency-shifted part-signals are added to a third signal via a number of couplings after having been phase-shifted, the voltage regulators being adjustable so that the signals are modulated and LLO is reduced.

Abstract: A 2-way radio system for use by a driver of a vehicle such as a motorcycle, enables operation of the PTT (push-to-talk) switch to transmit voice communications, without requiring the driver to raise his/her hand to a PTT switch button on the 2-way radio and without requiring a cable connection. A self-contained separate PTT control unit (40) lies at the driver's finger for operation by the finger without taking the driver's hand off the steering bar (12). During operation, the unit transmits a short range radio signal (70) to a PTT receiver (90) on the 2-way radio to switch the radio to the transmit mode. The PTT control unit can be mounted on the driver's finger or on the steering bar.

Abstract: A system and a method for transfer of a digital information carrying signal 51 between an input of a transmitter and an output of a receiver. The information carrying signal is modulated in a modulator included in the transmitter 12, and the modulated signal is transmitted via a transmission medium 13 by transmission means 25 connected to the modulator. The transmitted signal is received by receiving means 41 included in the receiver, and the received signal is demodulated in a demodulator. The information carrying signal is modulated in the modulator with a predetermined first modulation index h0, adapted for efficient use of an available bandwidth of said transmission medium. In the receiver 14 a frequency signal 63 is created from the received signal. Further, the frequency signal 63 is amplified with a factor A, for creating a scaled frequency signal 64, from which a scaled phase signal 65 is created.

Abstract: An apparatus for reducing undesirable low-frequency distortion in a direct conversion communication receiver includes a signal generator to produce a first periodic signal and a second periodic signal. A merge circuit combines an input signal and the first periodic signal to produce a modulated signal with a polarity switched component. A frequency translation circuit converts the modulated signal into a baseband signal with a spectrum substantially equal to the modulated signal, but centered around a carrier frequency of approximately zero and including a low-frequency error component. An output modulator circuit combines the baseband signal with the second periodic signal to produce a modified baseband signal wherein the low-frequency error component is shifted to a high frequency spectrum position and the polarity switched component is eliminated.

Abstract: A communications receiver such as an integrated zero IF receiver comprises an input for receiving an input signal and a zero IF frequency down conversion circuit coupled said input and constructed to provide quadrature related signals (I,Q) at a substantially zero intermediate frequency. In order to balance the signal paths, at least one capacitance in each of the quadrature related zero IF signal paths of the frequency down conversion circuit comprises at least two integrated capacitors connected in anti-parallel. By fabricating the integrated capacitances in this way the symmetry of the circuit is maintained which enhances significantly the second-order inter-modulation performance.

Abstract: A normalization circuit for preventing divergence of the normalizing voltage of a coupler used for diversity operation in a communication system includes: a phase detector for generating a phase detection signal corresponding to first and second phase differences of the signals received from first and second inputs; a normalizer including a reference voltage generator for normalizing the phase detection signal so as to alternatively output one of either a constant voltage value, or a reference voltage value in the event that the constant voltage value is less than the reference voltage value; a phase shifter for multiplying and adding output of the normalizer by and with the first and second phase differences; and an adder for adding the output of the phase shifter to the signals received from the second input.

Abstract: A fading simulator for generating multipath-faded test signals which have attenuation notches of precisely controllable frequency position and attenuation depth from a modulated input signal of known bandwidth. The input signal is fed to a splitter that directs two in-phase components to a first path and a second path. The input to each path is divided by a splitter into in-phase and quadrature sub-signals having a quadrature phase relationship, each sub-signal being fed to a respective inverting attenuator, the outputs of the attenuators then being combined in a combiner and the combined output being passed through a variable delay line to generate the output of the respective path. The outputs of each path are then combined in a combiner circuit to generate the multipath-faded test signal. All four inverting attenuators are preferably substantially identical to one another so that the two paths have close to identical temperature-drift and other characteristics.

Abstract: An automatic balancing circuit for a radio frequency mixer which reduces LO-IF signal leakage, as well as minimizing second order harmonic distortion products is described. The circuit couples to in-phase and out-of-phase signal lines originating from the mixer, and comprises a differential gain network, a differential phase shift network and a combiner. The networks operate under the control of a microprocessor, which adjusts the networks so that the LO leakage signals, when combined, are almost completely eliminated.

Abstract: A balanced differential radio receiver (100) has an antenna (64) operative for receiving a modulated signal. A first pair of mixers (110, 112) each having an input that receives an output (106, 108) of the antenna (64) and each of the first pair of mixers (110, 112) having an output (118, 120). A second pair of mixers (114, 116) each having an input that receives an inverse output (108, 106) of the antenna (64). A resistive adding circuit (122, 124) having a pair of inputs (118, 120). The inputs (118, 120) coupled to the output of the first pair of mixers (110, 112).

Abstract: A mobile station, and a method for eliminating multiple-access interference in a CDMA cellular radio system having a plurality of cells each having at least one base station communicating with mobile stations residing in the respective cell and informing the respective mobile stations of at least one spreading code used in a neighboring cell, the mobile stations measuring the code phase and power level of a channel of the neighboring cell using the known spreading code. To reduce the effect of multiple-access interference, the signal received at the mobile station is utilized in the detection of the desired signal by using the code phase and power level of the measured channel using the known spreading code of the neighboring cell.

Abstract: Receiver section (200) includes a compensation network (202) which compensates for undesired effects caused by synthesized LO (204). Compensation network (202) substantially duplicates the amplitude and phase delay of synthesized LO (204) allowing for a substantially flat demodulated frequency response to be achieved at output (122) which is independent of the bandwidth of synthesized LO (204).

Abstract: Electronically adaptable polarization antenna feed apparatus for receiving any sense of linear polarization or for receiving either sense of circular polarization. The circuit makes use of variable gain amplifiers and/or variable attenuators in each of two orthogonally polarized paths. The signal to noise ratio of a desired polarization sense is maximized by adjusting the amplitude or gain in each path to a desired ratio. If desired, polarization components from the two probes may be combined so that orthogonal polarization senses from two frequency reuse signals be used simultaneously. The apparatus may be used with linearly polarized signals and with circularly polarized signals.

Abstract: Circuitry and concomitant methodology for demodulating Direct-Sequence, Spread-Spectrum Code-Division Multiple-Access (DS/SS CDMA) channel signal using multiple samples per transmitted symbol and a minimum mean squared error criterion to suppress interference. In one embodiment, a bank of cyclically shifted filters determined with reference to the conventional matched filter for CDMA is used to demodulate the channel signal. In another embodiment, a bank of sub-filters determined with reference to the conventional matched filter for CDMA is employed to demodulate the channel signal. In yet another embodiment, the output of a conventional matched filter is oversampled to demodulate the channel signal. Each embodiment utilizes a set of adaptive coefficients selected to minimize the mean square error between the transmitted symbol and detected symbol.

Abstract: To compensate the audio distortion resulting from amplitude and phase imbalance in the quadrature oscillator (103) and mixers (105, 115) in zero-IF downconverters (203), a balancing action is required. An apparatus for distortion compensation compensates for the amplitude and phase imbalance to reduce audio distortion. This is accomplished by determining (309) two gain values, which are combined (217, 227, 229) with the in-phase and quadrature components of the zero-IF downconverter (203) to compensate for the imbalance.

Abstract: A distortion correction circuit having a mechanism for intercepting a distorted output signal from a receiver and for generating an Nth order signal. A circuit is provided to subtract the Nth order signal from the distorted output signal for providing a circuit output signal. Finally, a feedback loop is provided to feed back the circuit output signal for controlling the Nth order signal and for providing a distortion corrected circuit output signal. In a preferred embodiment, the distortion correction circuit includes a calibration circuit which provides a calibration signal employed to linearize a receiver channel. The receiver channel includes a plurality of receiver stages which receive the calibration signal and provide the distorted output signal which is intercepted and directed to a cubing circuit. The cubing circuit generates an error correction signal controlled by the feedback loop to cancel the distortion component of the distorted output signal.

Abstract: The gain of a recursive integrator is controlled so as to be adaptive to the quality of a received signal by comparing the magnitude of its emphasized information component with a reference voltage and controlling the gain of the integrator's feedback delay path in accordance with the difference between the peak value of the emphasized information component and the reference voltage. As a result, when the signal to noise ratio of the input signal is high, the gain can be reduced, so that the recursive loop will adapt quickly to changes in a multipath profile.

Abstract: A noise canceler for use in a CATV converter includes a keying pulse processing circuit for removing a noise signal from a keying signal. The keying pulse processing circuit includes a canceling signal generator for generating a noise canceling pulse signal, a delaying circuit for delaying the keying signal to produce a delayed signal, and a logic circuit including an AND gate for producing a noise canceled signal which is obtained by taking a logical product of the canceling pulse signal and the delayed signal. Since the noise pulse has a sufficiently small width when compared with the pulse widths of the keying signal and noise removing signal, the noise pulse is removed to obtain a noise canceled signal.

Abstract: A signal weighting system for associating a confidence level with portions of a communication signal transmitted upon a multipath channel and received by a receiver. A signal received by the receiver is equalized by an equalizer circuit, such as a maximum likelihood sequence estimator, and the equalized signal generated thereby is supplied to an adaptive filter which is synthesizes portions of the multipath channel. The signal received by the receiver is altered responsive to values of a filtered, equalized signal generated by the adaptive filter.

Abstract: An industrial measuring apparatus comprises first and second sensors having identical measuring characteristics and arranged close to each other and also close to a common subject of measurement, for measuring the same parameter, a transmitting unit having an adder and a first subtracter respectively connected the sensors through amplifiers, and a receiving unit having a second subtracter connected to the adder and the first subtracter through two transmission lines and constituting a noise canceling device in cooperation with the adder and the first subtracter. The second subtracter produces a receiving signal by subtracting the output of the subtracter representing the difference between the outputs of the first and second sensors from the output of the adder representing the sum of the outputs of the two sensors.

Abstract: A spread-spectrum noise canceller is provided for cancelling user code noise from a spread-spectrum communication channel. The spread-spectrum noise canceller including a receiver for receiving a spread-spectrum signal including a first and at least a second signal as well as a noise canceller operatively coupled to the receiver for reducing spread-spectrum noise in the first received signal by substantially processing the at least second received signal out of the received spread-spectrum signal.In addition a method is provided which cancels user code noise from a spread-spectrum communication channel. The method includes for receiving a spread-spectrum signal including a first and at least a second signal and subsequently reducing spread-spectrum noise in the first received signal by substantially processing the at least second received signal out of the received spread-spectrum signal.

Abstract: Undesired signals detected by a main antenna are cancelled by corresponding interference cancelling signals. The output of the main antenna is frequency converted to IF region and decomposed into first and second main baseband components. Decision circuits are provided for making a decision on whether each of the first and second main baseband components exceeds each of multiple thresholds and produces multibit codes as well as error signals. Auxiliary antennas respectively detect the undesired signals and feed auxiliary frequency converters for translating the frequency of the respective outputs of the auxiliary antennas to the intermediate frequency. Auxiliary quadrature demodulators are provided for respectively decomposing the output of each auxiliary frequency converter into first and second auxiliary baseband components. Correlations are detected between the first auxiliary baseband components and the first error signal and between the second auxiliary baseband component and the second error signal.

Abstract: A radio frequency limiter having a radio frequency power divider having an input and a plurality of outputs; at least one diode connected in shunt with each one of the outputs of the power divider; and, a power combiner having an output and a plurality of inputs, each one of such inputs being connected to a corresponding one of the outputs of the power divider. With such arrangement, the insertion loss of such limiter is reduced compared to a limiter having a like number of diodes connected in shunt at a common point of a single transmission line. Therefore, the reduced insertion loss means that the impedance matching circuit required will not limit the maximum operating frequency to the degree an impedance matching circuit of similar complexity will limit the maximum operating frequency required for a limiter having the same number of diodes but using a single transmission line.

Abstract: A chirped backscatter filter 10 compares a received signal (RSIG) to a reference signal related to a transmitted signal (TSIG) and removes from RSIG the frequency component which is equal to TSIG in frequency. This removed frequency component corresponds to the frequency of the transmitter backscatter radiation. The filter of the invention adds a frequency offset (f.sub.n) to both RSIG and TSIG in mixers 12 and 14 before substracting one from the other in mixer 22. Thus, equal frequency components in both RSIG and TSIG, such as the backscatter radiation frequency component of RSIG, will equal f.sub.n. The frequencies resulting from this subtraction are thereafter passed through a notch filter 24 which is centered on f.sub.n and which passes all frequency components except f.sub.n. The output of the notch filter thus no longer has a frequency component associated with the backscatter frequency component.

Abstract: An FM signal obtained by modulating a carrier f.sub.c with a signal f.sub.s is demodulated by a frequency demodulator to obtain a demodulated signal which contains a lower sideband component as an undesired moire component. A moire component generator generates an mf.sub.c -nf.sub.s component (m and n: natural numbers) from the demodulated signal or generates an nf.sub.1 -(n-m)f.sub.c component (f.sub.1 : first lower sideband component of the FM signal) from the FM signal. A subtractor subtracts an output of the moire component generator from the demodulated signal so as to thereby eliminate the undesired moire component. Furthermore, to eliminate a cross-modulation moire due to crosstalk of a low-frequency signal f.sub.L, the moire component generator generates a 2f.sub.L component from the FM signal.

Abstract: Disclosed are a pulse cancellation system and a pulse cancellation method for enhancing the effect of a small pulse superimposed on a large pulse, in the context of processing video signals in a circuit employing a compression video amplifier. The original waveform is delayed by a selected interval which is short as compared with the expected duration of pulses of interest in it, and the delayed waveform is subtracted from the original one to cancel the effect of those portions of pulses which are longer than the selected delay interval. Excursions of the resulting waveform which are on a selected side of a selected baseline can be removed, if desired. Alternative embodiments provide for selectively bypassing the delay and cancellation circuits, to feed the detector output directly to the compression amplifier in some cases, and for placing the small pulse enhancing circuit before the detector.

Abstract: In a receiving station having an adaptive receiving antenna, a phasing system comprises a plurality of reception paths receiving telecommunications signals derived from the same useful signal combined in transmission with a disturbing signal having a frequency band outside the frequency band of the useful signal, via a plurality of primary sources of the receiving antenna. The phasing system includes a narrowband filtering circuit for filtering the overall telecommunications signal in one of the reception paths to derive a reference signal undisturbed by the disturbing signal and solely dependent on the useful signal. In phasing circuits respectively assigned to the reception paths, the useful signal alone is set to a phase as close as possible to the phase of the reference signal in order to obtain, after signal summing at outputs of the phasing circuits, a maximum power using signal mixed with an attenuated scrambling signal.

Abstract: FM receivers for communications at UHF frequencies often use automatic frequency control (AFS) or phase lock to precisely control a local oscillator. By causing the local oscillator to track errors and slow variations in the frequency of the received signal, these control loops suppress DC and low-frequency modulation components in the intermediate frequency signal and interfere with demodulation of low frequency information, such as digital signalling data. This invention permits recovery of the full modulation spectrum with flat frequency response. A conventional FM demodulator recovers the high frequency modulation components; the frequency control signal for the local oscillator provides the low frequency components. Combining the components with proper weighting produces recovered modulation with bandwidth limited only by the IF bandpass filter of demodulator.

Abstract: A 2.sup.n -level demodulated signal is resolved into 2.sup.(n+m) equal intervals by an (n+m)-bit A/D converter (12) and an (n+m)th significant bit is produced from the LSB output of the converter as a representation of an interfering signal contained in the demodulated signal, where m is equal to or greater than unity. A subtractor (5p, 5q; 32p, 32q) cancels the interfering signal with a cancelling signal supplied from a feedback control circuit (9, 11, 7; 16-19; 30-31) which derives it by controlling the amplitude of the (n+m)th significant bit in accordance with the amount of the interfering signal still present in the output of the subtractor.

Abstract: A signal detection apparatus wherein pulses of the reverse polarity to that of the signal pulse to be detected are detected from an input pulse signal, and thereafter the signal outputting path is cut off for a fixed period, so that noise pulses which have oscillating waveforms in both positive and negative polarites are segregated from the signal pulses which can be provided with a unipolarity, by making use of the difference in polarity, and thereby, the noise pulses are eliminated regardless of their pulse heights. Further, the signal input to the cut-off circuit is delayed for a fixed period of time so that the first peak of the noise pulses may be eliminated even if it is of the same polarity as that of the signal pulse.

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: A digital pulse detection apparatus for correcting a distorted serial digital signal by differencing the signal and a delayed version of the signal in a differential amplifier to obtain the slope of the digital signal. The output signal from the differential amplifier is applied to a voltage hysteresis differential amplifier which provides the corrected digital output signal.

Abstract: In a radio receiver in which the received signal is converted by mixing into an intermediate frequency signal and/or a baseband signal, the degree of distortion of received disturbance signals in the receiver is temporarily changed and a recognition circuit is used which recognizes from the change in the signal gaining demodulation, caused by the change in the degree of distortion, whether the receiver is receiving spurious interference signals falling into the useful channel, and which, in the event of such a disturbance signal reception, initiates a suppression or reduction of the spurious interference signals.

Abstract: A circuit receives either a composite voltage, which is the sum of a signal voltage and a noise voltage, or the noise voltage. A switching arrangement is used to charge a first capacitor to the composite voltage, and a second capacitor to the noise voltage. The opposite poles of the first and the second capacitors are connected after they are charged, to generate an output voltage which is proportional to the signal voltage alone.

Abstract: A radio receiver circuit which suppresses an interfering signal exhibiting an amplitude significantly greater than that of a desired signal and a frequency nearly the same as that of the desired signal is disclosed. A received signal is applied to a gain controlled amplifier and a limiter. The limiter provides a limited signal which reduces amplitude and power of the desired signal relative to the interfering signal. The gain controlled amplifier provides a constant amplitude signal at an amplitude where the interfering signal portion of the constant amplitude signal equals an amplitude of the interfering signal portion of the limited signal. The constant amplitude and limited signals combine through a subtraction operation resulting in a significant attenuation of the interfering signal while causing only a small attenuation of the desired signal. Switching and decision circuitry are provided to selectively utilize the interference suppression.

Abstract: A communication system transmits information which may be in the form of frames or bursts of suppressed-carrier data over a dispersive transmission path which introduces multipath distortion. Each frame is stored as it is received and processed by iteratively simulating the multipath distortion, subtracting the distortion from the stored frame to form a corrected signal, and evaluating the quality of the resulting signal. The quality of the resulting signal is determined by frequency multiplying the corrected signal and evaluating the total power of components other than the frequency multiplied carriers. The iterative procedure adjusts the phase and, if deisred, the amplitude of signals tapped from a delay line.