Abstract: An I-Q channel adaptive line enhancer has bandpass filters with passbands that can be widened to well beyond the band that is actually being processed by the adaptive line enhancer. This eliminates the requirement of filtering one of the sidebands as is required in single channel adaptive line enhancers, in which the sum and difference sidebands are generated on up-conversion. Band limiting is done with lowpass filters, and the local oscillator may be made variable so that any part of the band that is passed by the bandpass filters can be processed by a single I-Q channel adaptive line enhancer. This type of I-Q channel adaptive line enhancer can process any one of a large number of possible bands without tunable bandpass filters, or without banks of adaptive line enhancers which have been preset to adjacent sub-bands.

Abstract: A line build out comprises a control voltage mechanism for applying a control voltage to a tuning diode or varactor. The control voltage is generated so as to be indicative of the length of a cable over which the signal has traveled. The capacitance of the tuning diode or varactor is changed according to the control voltage. A resistor is connected to the cathode of the tuning diode or varactor and a capacitor is connected to the anode of the tuning diode or varactor. A signal can be measured at the cathode which corresponds to the incoming signal and has been attenuated by frequency roll-off in accordance with the length of the cable over which the signal has traveled. In this way, attenuation for signals over cables of various length can be equalized in a manner which not only takes into account the length of the cable, but also the frequency of the signal.

Abstract: A circuit and method are provided to compensate for the non-linear delay characteristics of a digital audio system introduced by the systems anti-aliasing filter. The circuit and method provide for introducing time delay to the digital system at the low and mid range frequencies, and adding decreasing amounts of time delay at the high frequency ranges to produce an overall composite time delay for the digital system which is relatively constant over its operating frequency range. The delay equalizer used to achieve such delay compensation is made up of active delay equalizer sections which are non-interactive, and which are independently tunable in terms of each sections center frequency and Q. An active delay equalizer section with a second order bandpass transfer functions has been devised to achieve this capability. It is comprised of an operational amplifier having input resistance and feedback resistance connected to its inverting input and a twin-T network connected in its non-inverting input.

Abstract: An all rate equalizer provides direct equalization of a data signal which is automatically adjusted based on data rate and transmission line. The equalizer is embodied in a closed loop circuit in which the amplitude of the data signal is the controlled parameter. The DC amplitude of the data signal is restored by an adjustable gain circuit and the bandwidth of the data signal is restored by an adjustable frequency circuit. The signal processing circuits are adjusted by a control processor in accordance with pre-determined tables of control signals corresponding to frequency and gain values required to provide equalization of the data signal for virtually any given data rate and transmission line. The all rate equalizer thereby automatically provides equalization of the data signal that is optimized for any combination of data rate and transmission.

Abstract: A technique is disclosed for equalizing an incoming signal including quadrature-related carrier signals by forming the product of the incoming signal at at least one prescribed time and only one real-valued coefficient associated with each time. In one embodiment of the present invention, the equalized incoming signal is demodulated into a first pair of component signals. At least one of these component signals is then used to generate each coefficient. In another embodiment of the present invention, each coefficient is generated in response to at least one of the component signals in the first pair along with a second pair of component signals which are formed by demodulating the incoming signal. This technique can be advantageously adapted to incorporate a number of coefficient updating algorithms and is suitable for use in a number of modulation formats.

Abstract: In an adaptive filter a plurality of outputs (5, 7, 9, 11) of a delay circuit (3) are coupled via coefficient control circuits (21, 23, 25, 27) to a plurality of inputs (91, 93, 95, 97) of an adder circuit (89). The control signal inputs (29, 31, 33, 35) of the coefficient control circuits each receive a control signal via first integrators (37, 39, 41, 43) from first multiplier circuits (53, 55, 57, 59). A further output (85) of the delay circuit (3) controls a further input (87) of the adder circuit (89). The output signal from the adder circuit is controlled by a control circuit (121) which receives a control signal from a second multiplier circuit (103) via a second integrator (109) and a circuit having an exponential transfer function (113).

Abstract: In addition to an information signal subjected to a frequency dependent and a frequency independent loss component and delivered to an automatic equalizer through a transmission path which is typically a subscriber's communication path between a subscriber's terminal equipment and an exchange, an equalizer input signal comprises a pilot signal subjected to the frequency independent loss component alone. The equalizer comprises a first equalizer (26, 27, 36) responsive to a pilot signal component derived from the pilot signal for compensating for the frequency independent loss component. A second equalizer (31, 32, 37) compensates for the frequency dependent loss component in response to an information signal component derived from the information signal. The first and the second equalizers are cooperative in various manners in equalizing the input signal into an equalizer output signal. The pilot and the information signal components are extracted either directly or indirectly from the input signal.

Abstract: An adaptive transverse equalizer formed of delay elements, control elements and summers, and which is constructed in accordance with a serial-in/parallel-out or parallel-in/serial-out concept. Such an equalizer should be improved such that, given a simple structure, it exhibits a high equalizing performance and is particularly suitable for multi-stage digital radio link systems. For this purpose, an equalizer is provided as a linear transverse equalizer and having (n-1) positive and m negative coefficients set in accordance with a zero-forcing algorithm. A linear transverse filter is provided which supplies at least one additional, positive coefficient following upon an access region of the linear transverse filter and whose loop transit time corresponds to n-times or (n+i) times a symbol period.

Abstract: A post-equalizer and pre-equalizer circuit for use in communicating between nodes in a Pulse Amplitude Modulated (PAM) digital or analog communication system is described. The post-equalizer circuit comprises a first variable zero circuit, a second variable zero circuit, and a gain shaper circuit wherein the gain and frequency location of the zeros in the zero circuits combined with the gain of the gain shaping circuit are simultaneously controlled by a control circuit which generates a control voltage which is a monotonically increasing function of cable loss. In the case of a PAM digital communication system, the control voltage generates a signal equal to the difference between the equalized signal and the original transmitted signal which is used to vary the resistance of voltage variable resistors in the form of FET's in each of the zero circuits and gain shaper circuits.

Abstract: For compensation of the effects of multi-path reception, a cascade distortion corrector composed of distortion corrector blocks successively connected in series is provided for a digital FM demodulator that needs non-recursive filtering. Each distortion corrector block produces an increase of the phase rotation and of the propagation time as well as a reduction of the reflection factor of the input signal. The cascade distortion corrector leads to a significant reduction of the hardware expense compared to the previously used transversal type filter structures. Sufficient compensation of the multi-path reception effects can be obtained by connecting five or six distortion corrector blocks one after the other.

Abstract: A variable group delay equalizer comprises a delay portion and an amplitude correcting portion. In the delay portion, a group delay frequency response of an input signal is controlled. In the amplitude correcting portion, an amplitude distortion of the input signal caused in a delay portion can be corrected. A variable group delay equalizer with a wider variable range can be obtained by combining a fixed group delay equalizer.

Abstract: An equalizing circuit comprises a hopping-type amplitude equalizer (70) for changing the characteristics of burst signals inputted sequentially thereto to desired characteristics. The output of the equalizer (70) is distributed by a distributor (23) to a desired number of paths. Each output path of the distributor (23) is provided with a hopping switch (25a, 25b, or 25c), which is operated in synchronism with the amplitude equalizer (70).Consequently, even if the number of signal paths is increased, the number of equalizers required is smaller than the number of signal paths.

Abstract: The reference channel, the narrowband channel, and the error feedback channel are all constructed with analog components, while the adaptive processor is constructed with digital components. Unavoidable analog time delays in the narrowband and the error feedback channels are compensated for in the digital adaptive processor. The adaptive line enhancer described herein employs a local oscillator signal which is mixed with the input signal in a reference channel, which is subsequently converted to a digital signal. A digitized reference signal is supplied to an adaptive filter as an input signal. The adjustable weight values of the adaptive filter are adjusted by a feedback digitized signal. The output signal is derived from the subtraction of a narrowband analog signal, which is derived from the adaptive filter. The error feedback signal is split off of the output signal, mixed with the local oscillator signal, and supplied to the weight update mechanisms.

Abstract: The weights of least mean square (LMS) adaptive filter are updated with a different set of taps than are used to form the output of the adaptive filter in the adaptive processing device of the present invention. As a result of performing the multiplications and sums required for the filter operation simultaneously, an integral number of clock cycle delays appear in the narrowband and error feedback channels. The number of taps of the tapped delay line of the invention are increased, whereby the increased delay through the delay line may be used to compensate for a delay through the filter of an integral number of clock delay cycles. Instantaneous weight updating in accordance with the signal being utilized, may then be achieved at a clock rate frequency that is ten times or more greater than prior art adaptive filters.

Abstract: A demodulator for facsimile equipment in which there is provided a memory for storing equalizer coefficients of an automatic equalizer and a divergence detector for detecting divergence of the automatic equalizer, and in which equalizer coefficients of the automatic equalizer established at the beginning of transmission or reception are stored in the memory. In the event of divergence of the automatic equalizer during reception of a subsequent picture data message, the stored equalizer coefficients are re-set in the automatic equalizer.

Abstract: An autoequalizer having first and second data stores, first and second coefficient stores along with first and second multipliers for multiplying each stored data sample times its corresponding stored coefficient is disclosed. First and second accumulators accumulate the results of the first and second multipliers for an entire window of consecutive data samples. The results from the first and second accumulators are summed with feedback before being tested against various threshold values. In a preferred arrangement, for use with dual information channels, mirror image equalizer elements are connected in a feedback arrangement with each other.

Abstract: An adaptive equalizer for data signals is allowed to start up and train in a wholly decision-directed mode but is precluded from converging to an incorrect state by inhibiting equalizer updating for equalizer output values which fall within a predetermined null zone.

Abstract: Echo cancellation is carried out on a received demodulated analog signal. The apparatus comprises an analog transversal filter, a computing circuit for generating the direct coefficients a1 to ar and, eventually, feedback coefficients b2 to bm of an analog transversal filter. The input of a computing circuit is connected to the input of an analog transversal filter. The computing circuit is comprised of an analog-to-digital converter, whose output is connected to a self-adaptive digital transversal filter. The values of the digital transversal filter multiplication coefficients are applied, as coefficients, to the multipliers of the analog transversal filter. The optimization criterion is that of the mean quadratic error. The convergence algorithm is that of the gradient. The iterative correction may be carried out at each step on the digital transversal filter's group of coefficients. Or, it can be carried out cyclically of each of the digital transversal filter's coefficients.

Abstract: A technique for converging the tap-weight coefficients of an automatic or adaptive equalizer. The technique utilizes a training period during which time a plurality of identical signal sequences is transmitted. In the equalizer, during a training period, corresponding signal samples from the transmitted sequences are combined and used to generate the equalizer output and revise the tap-weight coefficients to their optimal values. Each combination of corresponding signal samples is an average or is a function which approximates an average.

Abstract: A receiving equipment comprises a modulator, a timing extraction unit, a PLL unit, an impulse recovery unit, a fix-equalizer, and an automatic-equalizer. A timing pull-in operation is performed, in one way, by phase-rotating a timing signal of the timing extraction unit and sends the signal to the PLL unit, and in another way, by introducing an input signal of the timing extraction unit from the equalized output of the fix-equalizer.

Abstract: In a line equalizer responsive to an input signal of a variable data rate for producing an equalizer output signal, a control circuit (12) supplies an equalizer circuit (11) with a selection signal (SEL) which is determined by the data rate and an output level of the equalizer output signal to select a frequency-gain characteristic that is matched with the line loss characteristic of a line. The equalizer circuit is implemented by a switched capacitor circuit and samples the input signal via a clock signal (CK) a clock frequency of which is varied by a clock signal controller (51) in consideration of the data rate. An additional equalizer circuit may be connected in cascade to the equalizer circuit and controlled by an additional control signal determined by the data rate and the output level. In this event, the selection signal may be determined only by the output level with the clock signal left out of consideration.

Abstract: A radio receiver gradually changes the phase of a regenerated clock when an abnormal receiving condition is detected. Since clock phase changes gradually, an equalizer which reduces receiving distortion and a discriminator are periodically synchronized. As a result, if receiving distortion is reduced at this time, the operation of the equalizer and discriminator are normalized and the normal receiving condition can be recovered quickly.

Abstract: An automatically variable all-pass circuit includes a variable impedance circuit for changing the shape of the phase characteristic of the output signal of the all-pass circuit as a function of the amplitude of the output signal of the circuit.

Abstract: In order to remove at least one of amplitude and delay distortions which tend to occur during signal transmission, the invention features circuitry wherein a received IF digital signal is fed through an equalizer circuit to a demodulator and wherein the demodulator outputs a series of data and error signals to a control signal generator. The control signal generator produces in-phase and quadrature control signals which are appropriately added and subtracted and subsequently averaged in an adder and subtracter circuit before being applied to a series of equalizers in the equalizer circuit.

Abstract: Equalizers, which provide distortion compensation for a modulated carrier signal having a time-varying signal envelope, are adjusted at selected times in response to the signal envelope and the data signals regenerated therefrom. Each selected time corresponds to a time when the signal envelope has a preselected value. Advantageously, the disclosed equalizer adjustment is unaffected by loss of receiver synchronization to the modulated carrier signal and is applicable to a variety of communications systems and modulation formats.

Abstract: A method of and an arrangement for determining the optimum position of the reference tap of a master adaptive equalizer which adapts itself to variations of the transmission characteristics of a transmission channel in a digital system for transmitting data which are in general complex, such adaptation being effected by modifying sets of coefficients of transversal filters which modify the transmitted symbols. Simultaneously with the operation of the master adaptive equalizer, and in consecutive analyzing periods, a selection is made in accordance with a selection algorithm of the optimum positions of the reference taps of transversal filters in a slave adaptive equalizer, the coefficients of which are adapted in accordance with an adaptation algorithm.

Abstract: In an equalizer for equalizing, by the use of zero forcing algorithm, an input signal obtained by modulating a carrier wave of a carrier frequency at a modulation rate, a specific one of complex control signals is modified into a modified complex signal and supplied to a specific one of gain control circuits of a transversal filter corresponding to a specific one of additional taps except a central tap. The modified complex signal is produced by rotating a phase of the specific complex control signal by a step equal to an integral multiple of .pi./2. Specifically, at least one of real and imaginary parts of the modified complex signal is inverted relative to those of the specific complex control signal. The real and the imaginary parts of the modified control signal are delivered to in-phase and quadrature portions of the specific gain control circuit in consideration of the step.

Abstract: A timing control signal generator used in a Teletext signal waveform equalizer to remove waveform distortions in a Teletext signal inserted into a horizontal scanning line for a vertical blanking interval of a television signal and arranged to generate timing control signals for controlling the operation of the waveform equalizer. The timing of each of the timing control signals, at which the level variation thereof occurs, is predetermined. To generate these timing control signals by a small scale circuit arrangement, a pair of counters and a pair of read only memories are used. The first counter is cleared by a field start signal and counts sample clock pulses synchronized with the Teletext signal. The first ROM stores information indicative of level changes of the timing control signals and is accessed by the first counter. The level change information read out from the first ROM is counted by the second counter.

Abstract: Apparatus and a technique for equalizing non-linear distortion in a received modulated data signal by (1) forming tentative decisions as to the values of data symbols represented by the signal preferably using a receiver including a conventional linear equalizer, (2) constructing a replica of the non-linear distortion in response to the tentative decisions, and (3) forming a final decision as to the data symbol values in response to signals including the replica. If desired, the final decisions can also be stored and fed back to the processor which forms the replica, so that the replica is a joint function of past final decisions and future tentative decisions regarding the data symbols represented by the signal samples. The present invention provides increased accuracy by using tentative decisions rather than input samples to form the non-linear distortion replica.

Abstract: The fading protection system protects against fading selectively occuring in a specific channel of a plural data transmission system. An equalizer is provided in each channel and adapted to equalize received data. An error correction mechanism is also provided for correcting errors of the received data in at least any one channel. A comparator associated with each channel is provided to deliver a first signal when the level of the received data in the associated channel has been reduced below a predetermined first threshold to indicate a level reduced channel. A controller operates in response to the first signal so as to deliver, as reference data, the correct data, after correction by the error correcting mechanism, to the equalizer provided in the level reduced channel.

Abstract: A listener echo canceller for a receiver made to receive data symbols a.sub.n transmitted at regular time intervals T. The received wave is first conventionally decoded to derive the received symbols therefrom, said symbols are the subjected to a bulk delay which has been determined for shifting the listener echo impulse response to the time reference origin. The delayed symbols are then processed to generate an echo replica which replica is then fedback to the decoder input for being subtracted therefrom.

Abstract: An equalization circuit with switched capacitor filters, each having variable filter characteristics, that is adapted to provide power equalization on digital transmission lines that are subject to power losses for high frequency signals. The power equalization is provided automatically by switching in or out of a filter one or more of its capacitors in response to detected variations in line power levels. Identical filters are connected in parallel and alternatively applied within the equalizer circuit, the capacitor switching occurring only in a filter circuit that is not actively applied within the equalizer circuit.

Abstract: Optimum tap coefficients corresponding to equalization characteristics are stored in a memory circuit and when an equalization characteristics is designated, an optimum tap coefficient is read out of the memory circuit and a transversal type equalizer is controlled by the read-out optimum tap coefficient. According to a modified embodiment, where a tap coefficient for a combined characteristic based on a combination of a plurality of transmission characteristics is necessary, a convolution operation of the tap coefficients for respective transmission characteristics is effected to determine a new tap coefficient which is used to set taps of the transversal type equalizer.

Abstract: Apparatus, and a related method, for fast carrier acquisition in a modem. The apparatus includes circuitry to speed carrier acquisition by the determination of which of two alternate phasors is being received during a baud synchronization period of a signal preamble before data transmission. Another aspect of the invention involves the use of a complex matched filter for the determination of the start of an equalizer training sequence in the signal preamble. The output of the matched filter exhibits a deep null at the start of the training sequence, since the beginning of the sequence bears an inverse relationship to the end of the preceeding baud synchronization period.

Abstract: The circuit (10) has a gain section which includes a first AGC circuit (12). The output of the gain section goes to a signal shaping section which includes a biquadratic filter (24), a summer (45), and a second AGC circuit (40). The two AGC circuits (12,40) are controlled by respective separate peak detectors (20, 50) and are noninteracting. For "short" cables, only the first AGC circuit (12) is active. For "long" cables, the first AGC circuit (12) is set at its gain breakpoint and the second AGC circuit (40) alone has active control. The shaping section includes a biquadratic filter (24) which is a tandem arrangement of a low-pass filter (26), an inverter (28), and an integrator (32). The low pass output (35) of the integrator (32) is connected to the noninverting (+) input of the a summing amplifier (45). The input (42) of the second AGC circuit (40) is connected to the band pass output (33) of the inverter (28), while its output (44) is connected to the inverting input (-) of the summing amplifier (45).

Abstract: A delay line circuit provides variable delay and phase shift to electric signals propagating along the delay circuit. The circuit is formed of a set of varactors constructed either as varactor chips or as a set of mesas upstanding from a gallium arsenide substrate. A ground plane interconnects bottom terminals of the varactor chips while a strip line conductor interconnects top terminals of the varactor chips. In the case of the mesa configuration, a metallized layer covers the regions between the mesas without contacting the base portions of the mesas. The strip line conductor makes contact with the respective mesas via a set of metallic posts upstanding from respective ones of the mesas. Dielectric material may be inserted between the strip line conductor and the metallic layer to position the strip line conductor relative to the metallic layer, which layer serves as a ground plane in a transmission line comprising the strip line conductor.

Abstract: An equalizer with two parallel branches for precursor and postcursor correction, receiving periodically incoming binary pulse samples, generates for each sample two purged symbols f, b at the outputs of these branches along with two decided symbols f and b, all of which are transmitted to a logic network checking whether or not the two decided symbols are identical. In the event of a disparity, the network produces an estimated signal s, calculates the absolute differences d.sub.sf, d.sub.sb between signals s and f, b, supplements them with further signals d.sub.f, d.sub.b representing the contributions of postcursors and precursors from one or more preceding and following samples, and compares resulting discriminatory signals D.sub.f and D.sub.b to determine which of the two decided symbols should be emitted as an output signal of the equalizer.

Abstract: An adaptive equalizer arrangement for digital transmission system comprises at the output of the transmission channel a first in-phase path and in parallel with this first path, a second quadrature path, both paths being of the non-recursive transversal filter type having n branches and (n-1) delay circuits between the inputs of these branches, each of these n branches comprising, arranged in series, a mixer, a low-pass filter, a multiplier, and having their outputs connected to an adder which is followed by a sampling circuit and thereafter by a comparator circuit to decide the symbols to be transmitted from the outputs of these paths. The arrangement also comprises a third control path which comprises two subtracting circuits to determine the differences between the signals before and after decision and a control circuit of a voltage-controlled oscillator, 2n phase shifters and 2n multipliers.

Abstract: A level comparator is used to check the incoming message header pulse amplitude and if it is of a level higher than an established level a signal is transmitted to update a digital counter whose digital output is converted by a digital to analog converter to establish an increased analog reference level. If the incoming message header is lower the counter is decremented to establish a lower reference level. Then the levels of any signals present at fixed intervals after the header or sync pulse are measured and recorded. These measured levels constitute the value of correction required for subsequent pulses and are added to or subtracted from following data pulses as required.

Abstract: A circuit arranged to measure and correct for transmission line induced disturbances at discrete intervals after receipt of a header pulse by recording the presence of any voltage deviating from a set level. These levels are registered and during receipt of the data pulses are utilized at times corresponding to the relative position of the preceding data pulses to modify subsequent data bits.

Abstract: The invention involves a self-adjusting equalizer configuration which automatically adjusts to the cable length. The equalizer configuration has band limitation for the transmission of digital signals and consists of an equalizing amplifier, a correction filter, and an amplitude control loop with a comparison of actual and nominal values. The object of the invention is to specify a circuit in which the correction filter is not located in the signal path. This object is achieved in such a way that the equalizing amplifier is located in the signal path, and the correction filter is placed in the amplitude control loop so that the output signal of this correction filter represents the actual value for the amplitude control loop.

Abstract: A block diagram and concept approach for use in conjunction in decision feedback equalization of providing positive decision feedback to enhance the amplitude of the present bit at the same time as delayed intersymbol interference feedback is provided to provide a larger eye pattern in the compensated and equalized output signal as compared to that obtained without the positive decision feedback pulse amplitude enhancement.

Abstract: Disclosed is a digital arrangement utilizing linear predictive coding for equalizing over a desired frequency spectrum the variable attenuation of a voice-frequency message signal transmitted on a communication line. The arrangement comprises a digital signal processor, program memories for storing program instruction sets, and a data memory for storing samples of a spectrally white test signal that has been variably attenuated by the line. Under control of one instruction set that incorporates linear predictive coding, the processor uses the stored test samples to calculate the reflection coefficients of the line that characterize the variable attenuation of a signal on the line. Under the control of the other instruction set, the processor functions as a digital inverse filter employing the calculated reflection coefficients for equalizing over the desired frequency spectrum the variable attenuation of a voice-frequency message signal transmitted on the line.

Abstract: A self-adaptive equalizer for use in a data modem for correcting in the baseband a received data signal. The equalizer comprises a difference circuit for determining the difference between a received signal and a correction signal formed at a sampling frequency by a transversal filter having adjustable coefficients, and which produces a corrected signal which is applied to a decision circuit which recovers the data signal. The output of the decision circuit is applied to the transversal filter, the coefficients of which are adjusted so as to minimize the mean-square value of an error signal. The error signal at each actual sampling instant is formed by deriving the algebraic difference between the value of the corrected signal at that sampling instant and the value thereof at a previous sampling instant, the latter value being first multiplied by the ratio between the value of the recovered data signal at the actual sampling instant and the value thereof at the previous sampling instant.

Abstract: Receipt of a training signal by a circuit wherein a demodulated data sequence is compared with a corresponding pre-recorded sequence and an impulse produced upon coincidence therebetween, is acknowledged by two consecutive signals occuring at a time interval corresponding to the period of the data sequence.

Abstract: An automatic equalizer comprises a waveform equalizer having a transversal filter connected to receive an input signal having a linear distortion, and having controllable tap gains; and a tap gain correcting means for successively correcting the tap gains of the transversal filter to take from the transversal filter an output signal from which the linear distortion is removed. In order to maintain the good convergency of tap gain correction control and prevent the excessive increase of the residual distortion, the tap gain correcting means is arranged to add a small leak to the correction control of tap gains. The magnitude of this leak is increased or decreased depending upon the sum of absolute values of the differences between the tap gains and their predetermined values to be set when the input signal contains no distortion.

Abstract: An automatic equalization device used in a data communication system includes a unit for extracting a single pulse from a training signal sent from a transmitter and initializing a tap coefficient using the extracted single pulse. The automatic equalization device also includes a first equalization circuit and a second equalization circuit. In the first equalization circuit, an auto-correlation series of the signal corresponding to the single pulse is calculated to provide a symmetric single pulse. In the second equalization circuit, an inverse matrix is calculated from the symmetric single pulse using the auto-correlational series of single pulses. By these calculations, the speed of the initial setting of the tap coefficient is increased.

Abstract: The present invention features an automatic adaptive equalizer which detects asynchronism in a demodulator coupled to the equalizer and intermittently generates a reset signal. This signal intermittently renders a transversal filter of the adpative equalizer operative during a period in which the filter is normally rendered inoperative by a control loop of the adaptive equalizer.

Abstract: Compensation for arbitrary combinations of linear and nonlinear distortion is provided by altering a received symbol value by a preselected amount. This amount is based on an estimate of the sequence of transmitted symbol values represented by the received symbol value at a sampling time and a number of received symbol values at other sampling times. The altered symbol value is then compared with the closest one of the possible transmitted symbol values to determine the difference, if any, therebetween. The closest one of the possible transmitted symbol values is then outputted if the difference meets a prescribed criterion. If not, the received symbol value is altered by a different amount in response to another estimate until the recited difference meets the prescribed criterion. In the disclosed embodiments, the foregoing technique is incorporated in a memory-based canceler or transversal filter.

Abstract: An auto-adaptive amplitude-equalizing arrangement for digital radio links having an intermediate-frequency signal input, a transversal filter and a circuit for the control of the filter. The transversal filter comprises a delay circuit providing, with respect to the intermediate-frequency signal input, a delay T equal to (2k-1)/4F.sub.c, where k is a positive integer and F.sub.c the center frequency of the intermediate-frequency signal, a first and a second multiplication circuit whose inputs are respectively connected to the output of the delay circuit and to the intermediate-frequency signal input, and an adder connected to the outputs of the multiplication circuits.