Abstract: An adaptive interference reduction system for removing cross talk from a dual polarization system comprising a first adjustable filter for varying the phase and the weight of a first input signal, a second adjustable filter for varying the phase and the weight of a second input signal, a first adder for adding this first input signal and the weighted and phase adjusted output from the second adjustable filter, a second adder for adding the second input signal and the weighted and phase adjusted output from the first adjustable filter, a first noise-to-signal measuring device for generating a signal proportional to the noise-to-signal ratio in the output signal from the first adder, a second noise-to-signal measuring device for generating a signal proportional to the noise-to-signal ratio in the output signal from the second adder, and a dither-type control logic for dithering in-phase and quadrature square-waves in accordance with the signals generated by the first and second noise-to-signal measuring devices

Abstract: A feedforward nonlinear signal (P(n)) is added to each sample of a linearly equalized received signal (Q(n)) to provide compensation for nonlinear intersymbol interference. The received signal is a modulated data signal impaired by linear and nonlinear distortion as well as phase jitter and additive noise. The feedforward nonlinear signal added to each sample is comprised of a weighted sum of products of individual ones of the samples and their complex conjugates. Each multiplicand bears a predetermined temporal relationship to the sample currently being processed. In an illustrative embodiment, compensation for second- and third-order intersymbol interference is provided by including two- and three-multiplicand weighted products in the feedforward nonlinear signal. Weighting coefficients for each product are adaptively updated in a decision-directed manner.

Abstract: Attenuation equalizer for correcting within a frequency range the temperature and frequency-depending attenuation variation of cables, comprising a cascade arrangement of a fixed and a variable attenuation correction circuit, connected to a control circuit, the variable attenuation correction circuit comprising a bridge-T network having a series arrangement, of two identical series resistors bridged by a variable bridging impedance and a parallel impedance connected between these two series resistors, the fixed attenuation correction circuit having a lower attenuation for higher frequencies than for lower frequencies, the temperature dependency of the cable being eliminated in the variable attenuation correction circuit and the frequency dependence being eliminated mainly in the fixed attenuation correction circuit for which purpose the variable attenuation correction circuit comprises only two adjustable components.

Abstract: In a long line transmission system, the signal level at the transmission station is pre-equalized by the value L.sub.s which is adjustable according to the signal level at the receiving station. The receiving station equalizes the received signal to the standard level at the output of the receiving station. The difference between the actual level L.sub.r at the input of the receiving station and the standard level there, is fed back to the transmission station through a return transmission line, and said difference is utilized to adjust the pre-equalization value L.sub.s at the transmission station. The ratio L.sub.s /L.sub.r is controlled to be constant by the operation of the pre-equalization level distributor installed at the transmission station.

Abstract: A transmitting station for wide-band signals at one end of a line such as a bifilar or quadrifilar cable includes a generator of test frequencies lying between several sub-bands--such as carrier-frequency telephone channels--normally used for message transmission. A pilot wave outside the range of message frequencies, generated at the transmission station, is modulated under the control of a transmitting-side programmer to indicate the start of a test sequence during which the several test frequencies are sequentially emitted, except when a message to be transmitted (e.g. a TV program) spans several sub-bands and requires suppression of the intervening test frequencies. At the other end of the line, a receiving station includes an equalizer with a number of individually adjustable stages pertaining to respective frequency bands centered on the several test frequencies.

Abstract: The invention consists in an equalization system with two sections, one at each end of a transmission channel. The section at the transmission end adds control signals to information signals to be transmitted over the line. The section at the reception end generates control signals identical to those added at the transmission end and in phase with the control signals received over the transmission channel, which are separated from the received information signals by means of a first transversal filter with controllable weighting coefficients, the reciprocal transfer function of the transmission channel being synthesized from the locally generated and the received control signals by means of a second transversal filter with controllable weighting coefficients, equalization being achieved by means of a third transversal filter with the same design and same weighting coefficients as the second transversal filter. The invention is applicable to the transmission of data over telephone lines.

Abstract: A system for transmitting data between distant locations comprises a modem at each location and a communication channel, typically a telephone line, whose transfer function has a principal component whose variation is slow and a second component whose variation is faster, but whose action is lesser. A correction device is located in the modem at the output of the channel and comprises an equalization filter constructed to compensate for the principal component and a digital adaptive network having a few coefficients and a low time constant, compatible with the frequency of the second component. The coefficients of the digital network may be adapted independently of those of the equalization filter.

Abstract: A receiver for a quadrature amplitude modulated data signal impaired by linear and nonlinear distortion, phase jitter and additive noise includes circuitry which compensates for these impairments. In particular, the receiver includes a processor (FIG. 1 44; FIG. 2, 44')which subtracts a feedback nonlinear signal (FIG. 1, D(n); FIG. 2, D'(n)) from each sample of the received signal, either prior or subsequent to demodulation, providing compensation for nonlinear intersymbol interference. The feedback nonlinear signal subtracted from each sample is comprised of a weighted sum of products of individual data decisions and/or the complex conjugates of data decisions, each such product, in turn, being multiplied by a predetermined harmonic of the carrier frequency. In an illustrative embodiment, compensation for second- and third-order intersymbol interference is provided by including two- and three-multiplicand weighted products in the feedback nonlinear signal.

Abstract: A circuit for reproducing a signal from a moving record carrier includes a circuit input supplied with a signal read out from the moving record carrier, for example, a record disc having a spiral track in which the signal is recorded, and in which the signal has variations in its level due to the shift of reading out position on the carrier. The signal from the input is supplied to an automatic gain control loop including a gain control circuit and a gain control signal generating circuit connected to the output of the gain control circuit for producing a gain control signal varying in response to the level of the read out signal.

Abstract: An adaptive or self-adjusting corrector is provided for the correction or equalization of data signals formed with the primary value and a plurality of prior and subsequent oscillations. A plurality of delay members are provided for delaying the data signals. Members for multiplying the data signals by alterable coefficients are provided at outputs of each of the delay members. At least one adder connects with the coefficient members for summing up the multiplied data signals. Either a first coefficient member corresponding to the primary value of the data signal or a second coefficient member corresponding to a first subsequent oscillation of the data signal establish constant coefficients. Alternatively both the first and second coefficients may be made constant. Preferably the constant value is zero.

Abstract: A method of and apparatus for determining during an initial training period the initial values of the coefficients of a transversal equalizer in a data transmission system in which the transmission channel creates frequency shift. The received periodic training sequence is modulated by a time-domain window signal whose Fourier transform exhibits a relatively flat central peak and has comparatively low values in the vicinity of those frequencies which are a multiple of the inverse of the period of the transmitted sequence, and the discrete Fourier transform W.sub.k of the modulated signal is computed. The values of the coefficients of the equalizer are obtained by computing the inverse discrete Fourier transform of the ratio F.sub.k =Z.sub.k /W.sub.k, where Z.sub.k is the discrete Fourier transform of the transmitted sequence.

Abstract: The adverse effects of node slips on the operation of an adaptive equalizer are corrected by determining phase and amplitude errors in the received vector signal relative to phase and amplitude estimates, based on node decisions. The phase and amplitude error signals are aligned in a prescribed fashion with the tip of the received signal vector and, from this alignment, respective X and Y components of the error signals are obtained and fed back to the equalizer as projected X and projected Y errors for updating the equalizer weights.

Abstract: A cable equalizer is provided for automatically compensating a signal for cable attenuation as the length of the cable is varied. The circuit detects changes in a reference signal that is inserted in the signal being transmitted over the cable. Any deviation of the reference signal from its normal state at the receiving end of the cable causes the addition of a correction signal to the signal being transmitted so as to compensate the signal for the cable attenuation.

Abstract: An equalizer-dependent timing recovery system monitors the equalizer weighting coefficient pattern over the entire time span of the equalizer, and differential changes at opposite ends of the pattern are used as a basis for adjusting the receiver symbol timing clock. The magnitudes of a plurality of equalizer weighting coefficients at the beginning of the equalizer are summed and the total is compared with the summed magnitudes of a plurality of equalizer weighting coefficients at the end of the equalizer. Depending upon the sign of the difference between the two totals, the phase (or frequency) of the receiver symbol clock will be adjusted so as to shift the equalizer weighting coefficient pattern in a direction such that the magnitude of the weights at both ends of the equalizers are approximately the same.Circuitry for implementing the above scheme includes a pair of adders coupled to sets or plural weighting coefficient stages for opposite ends of the equalizer.

Abstract: A method and apparatus is provided for adjusting the tap coefficient of an adaptive automatic equalizer having a plurality of tap registers. An input signal is repetitively applied to a train of tapped delay elements and the sum of the weighted output of each tap output is obtained. An error output is obtained by taking the difference between the sum of the weighted output of each tap output and a reference signal, and a correlation value is obtained between the error output and each tap output of the delay elements. The improvement comprises storing the tap weights of each of the tapped registers and obtaining the total sum of each tap weight of one of the registers wherein the tap weight of a tap is the correlation value.

Abstract: An automatic equalizer for calculating the equalization transfer function of a transmission channel and applying same to equalize received signals. Equalization coefficients are obtained using a mean square error criteria for convergence to the desired values.

Abstract: In a delay equalizer having a plurality of quadratic all pass networks for equalizing the delay characteristics of a circuit, the automatic adjustment of the value of Q of each quadratic all pass network when calculated through the asymptotic formula ##EQU1## CAN PROVIDE PERFECT DELAY EQUALIZATION, WHERE Q.sub.i.sup.k is the value of Q of the i'th quadratic all pass network, and .alpha..sub.i is the step size parameter of i'th quadratic all pass network. Before applying said formula, the delay of the circuit to be equalized at the center frequency of each quadratic all pass network is measured, and said formula is calculated according to the result of the measurement.

Abstract: In a band division type equalizer having a plurality of equalizer sections, the adjustment of each of the equalizer sections is accomplished through measurement of characteristics of a transmission means to be equalized and calculation of the difference of the measured characteristics and the desired characteristics. Since all of the equalizer sections are adjusted at the same time according to the result of the calculation, the adjustment does not suffer from interaction among the sections. An adjustable variable, for instance, a variable resistor for each section is mounted in a single setting unit separable from the rest of the equalizer circuit. Thus, after completely adjusting the setting unit, the setting unit is connected to the rest of the equalizer sections, and then the desired delay characteristic can be obtained. The equalizer section is for instance a Moschytz type delay circuit.

Abstract: A Bessel function type automatic delay equalizer comprising a plurality of transversal filters each of which has an independent delay cosine equalization component having a predetermined period, and the superposition of those filters providing the desired characteristics, characterized in that, said equalizer further comprises a Bessel function generator for controlling the tap gain of said transversal filters.

Abstract: A non-recursive discrete filter for simultaneously realizing for example two band-pass filter characteristics starting from a given lowpass transfer characteristic, wherein one bandpass filter has an in-phase transfer characteristic and the other filter the quadrature transfer characteristic of this in-phase filter. The central frequency of these filters is f.sub.o and the output sampling frequency is f.sub.s = 8f.sub.o. This discrete filter comprises multiplying means in which input signal samples x(n) are modified by an associated filter coefficient a(i) for generating modified input signal samples z(n,i) = a(i)x(n-i). The coefficients a(i) are the same for both transfer characteristics and are given by: ##EQU1## WHEREIN H.sub.1 (I) REPRESENTS THE DISCRETE IMPULSE RESPONSE OF THE LOWPASS FILTER.To realize the in-phase transfer characteristic the samples z(n,i) are thereafter multiplied by a factor sgn[cos (.pi.i/4)] and the products thus obtained are accumulated.

Abstract: Digital signal processing arrangement such as a digital filter for computing output signal samples which are each equal to the sum of products of a given plurality of pairs (for example N) of input signal samples. One of the input signal samples of the pair is, for example, formed each time by a sample x(n) of a digital signal to be filtered, the other input signal sample of the pair by a filter coefficient z(n), wherein either the sample x(n) or the filter coefficient z(n) can assume only a limited number of values 0, .+-.A.sub.1, .+-.A.sub.2, . . . .+-.A.sub.M, M being much smaller than N. In the case x(n) can assume only this limited number of values, z(n) is first multiplied, owing to the x(n) belonging to the pair, by the sign of x(n) for generating a product of the form z(n). sgn [x(n)]. In-dependent of the magnitude of n(n) this product is applied to an accumulator which corresponds with this magnitude of x(n).

Abstract: An FDM/TDM transmultiplexer uses sampling rate multiplication to increase the sampling rate for time division multiplexed (TDM) to frequency division multiplexed (FDM) conversion and decrease the sampling rate for FDM to TDM conversion. The rate multiplication filters are realized digitally in order to exploit the computational advantage of Fast Fourier Transform (FFT) algorithm, and channel filtering is implemented by a single time-shared sixth-order elliptic digital recursive filter. A novel FFT processor and recursive filter are disclosed which may be used in the system.

Abstract: An automatic equalizer is described including a first transistor to the input of which a cable is coupled and which is branched in common emitter configuration and a second transistor branched in common collector configuration a collector of the first transistor being coupled to the base of the second transistor and the emitters of the transistors being intercoupled through a positive feedback circuit. In variation by small variation of a variable which is substantially independent from active parameters of the transistors results in a gain variation which is independent of the cable length in the lower frequency region and utilizes no coils.

Abstract: A digital filter for pulse code modulation signals employs interpolation. A digital filter can handle a multiplicity of multiplexed pulse code modulation channels.

Abstract: An operational amplifier uses p- and n-channel enhancement type MOSFETs as variable input resistors on the inverting and non-inverting legs, respectively, of the amplifier, and the sources and gates of the MOSFETs are tied together. By using V.sub.S, the source-to-ground voltage, and V.sub.GS, the gate-to-source voltage, as input signals, the device will perform 4-quadrant multiplication at operating frequencies as high as 400MHz.

Abstract: A variable equalizer wherein a series circuit which consists of a voltage source and an impedance circuit having an impedance Z.sub.x is connected in parallel with a circuit for changing an input voltage into a current, and an impedance circuit having an impedance Z.sub.y is also connected in parallel with this current source. The voltage value of the voltage source is made one which is obtained by multiplying the current by a value proportional to 1/Z.sub.y, and the impedance circuit having the impedance Z.sub.y is endowed with a frequency characteristic.

Abstract: An automatic equalizer for calculating the equalization transfer function and applying same to equalize received signals. The initial calculation as well as the equalization proper are conducted entirely within the frequency domain. Overlapping moving window samplings are employed together with the discrete Fourier transformation and a sparse inverse discrete Fourier transformation to provide the equalized time domain output signals.

Abstract: The analogue filter system is constituted by first and second analogue filters having similar characteristics, a delay device connected between the first and second analogue filters and controlled by a timing circuit for storing the output of the first analogue filter and for producing an output with its time axis inverted, and a device for restoring the time axis of the output from the delay device.

Abstract: A method for determining the initial values of the coefficients of a complex transversal equalizer in a synchronous data transmission system employing Double Side Band-Quadrature Carrier (DSB-QC) modulation on a transmission channel having variable distortion from message to message is disclosed. The coefficients are derived from training sequences which consist of periodic pseudo-random sequences of complex numbers having a periodic autocorrelation function, all the coefficients of which except the first are zero. The amplitude of all complex numbers of the sequence is constant. Sequences with these characteristics are identified as CAZAC sequences. With the exception of a training sequence generator and a coefficient generator the system utilized is a conventional data transmission system utilizing the DSB-QC modulation technique.

Abstract: A transversal type automatic equalizer includes circuits for differentiating the equalized signal, sampling the equalized signal under the control of a timing signal, and generating an error signal from the sampled signal. The differentiated and error signals are multiplied together and a variable phase shifter phase shifts the timing signal in response to their product to provide optimum equalization.

Abstract: A weight multiplier for use in an adaptive processor. The input signal from a tapped delay line is split in a 3 dB hybrid into two equal level and equal phase signals. Each signal is fed to a mixer together with a signal performing the function of an oscillator signal. Output signals from the mixer are subtracted in a broadband hybrid. The result of this subtractor is then fed to a summer to supply a loop feedback signal.

Abstract: In an automatic equalizer for regenerating a received digital signal, comprising a delay element train with a plurality of taps, a coefficient matrix circuit and a group of variable coefficient units, the structure of said coefficient matrix circuit being considerably simplified by introducing a simple adder and/or subtractor at the input and/or the output of said coefficient matrix circuit.

Abstract: A receiving terminal for a switched analog data communications system is equipped with an adaptive equalizer which is adjusted on a single pass in response to a series of test pulses transmitted during a predetermined equalizer adjustment period.

Abstract: In a receiver, an analog-to-digital converter is adapted to sample a distorted analog signal to provide a plurality of distorted digital symbols separated in time by a particular interval. In an equalizer, taps are provided with variable multiplying coefficients which sequentially multiply the distorted digital symbols to provide undistorted digital symbols. A timing control network is responsive to variation in one of the multiplying coefficients to control the timing of the converter and hence the duration of the particular interval.

Abstract: A transmission system in which wide band electrical signals are transmitted along a transmission line has repeater stations located at intervals along the line for boosting and equalizing the signals. Each repeater station has an equalizer having a frequency response characteristic which generally complements that of the section of the transmission line which it covers. The frequency response characteristic of the equalizer is capable of adjustment to match the section of transmission line which feeds it. The adjustment required will vary when the section of transmission line feeding it has a length differing from that of a norm and where the line is subject to temperature changes. The repeater station incorporates a feedback chain which senses a pilot transmitted along the section of transmission line and responds to the monitored level of the pilot signal to automatically adjust the characteristic of the equalizer until it matches that of the transmission line section in question.

Abstract: A phase tracking network comprising a phase correction network for correcting at least some of the phase error of an input signal to provide a phase corrected signal having components in first and second channels and a detector responsive to the phase corrected signal for providing a detected signal having first and second components in the first and second channels. An error calculator provides a phase correction signal back to the phase correction apparatus which responds to the phase correction signal to correct the phase error of the input signal. The phase error signal contains substantially no noise from the first channel at least when the first component of the detected signal is zero and contains substantially no noise from the second channel at least when the second component of the detected signal is zero.

Abstract: The invention covers a precision digital filter for signal samples represented in a digital form. The flow of samples x.sub.o, x.sub.1, x.sub.2, . . . x.sub.n, of the signal is split into blocks of a fixed length which are simultaneously transmitted to two circular convolution generators operating to different prime number modulos. The outputs of the generators are each submitted to a correcting device and the corresponding corrected terms are added. The added terms are each then added to a delayed prior term to generate representations of samples of a filtered signal.

Abstract: Equalization apparatus for a communication system transmitting through a time or frequency spread medium. The message to be transmitted is partitioned and transmitted in burst or frame by frame form. Each frame comprises the message (unknown at the receiver) followed by a test signal known at the receiver. Time gaps are provided between the message and test signals to avoid overlapping of the received message and test signals due to time-spreading. The received mutilated signals are processed in the frequency domain to obtain a reconstituted version of the transmitted message in the frequency domain. This is re-transformed into the time domain so that the reconstituted message available at the receiver is a close replica of the message which was originally available only at the transmitter.

Abstract: Apparatus for correcting attenuation distortion in low frequency cable carrying a base-band signal from a transmitter to a receiver is described. A measuring device produces an indicating signal having a value dependent on the peak value of the base-band signal appearing in the region of the receiver. The receiver contains an amplifier, the gain of which is controlled by a RC element. The indicating signal is used to regulate the gain of the amplifier so that the cable and the amplifier together produce a substantially constant attenuation characteristic within a given low frequency range.

Abstract: A quadriphase shift keyed (QPSK) adaptive equalizer includes baseband inphase (I) and quadrature (Q) adaptive filters for receiving demodulated OPSK signals. The I and Q channel filters are designed to operate independent of each other and adapt their characteristics continuously in a predetermined manner in response to an incoming received QPSK signal, distorted in an unknown time varying manner.

Abstract: The sum and difference signals of a pair of data channels are applied to a pair of roll-off filters, respectively. The outputs of said roll-off filters are modulated by a pair of carrier signals which have the phase difference (.pi./2) to each other. The modulated signals are added to each other in an adder and a single output signal is provided from the output of said adder. Said output signal and another output signal relating to another pair of data channels, and some pilot signals are applied to an adder, the output of which is transmitted to a receiving station in the form of a multi-channel multiplex data signal. At the receiving station, the received signal is demodulated with the inverse process of the above modulation steps and the demodulated data signals are applied to an automatic equalizer. The present invention described above provides high speed data transmission through a narrow-band-line which has only almost the Nyquist band width.

Abstract: An adaptive equalizer for improving the quality of digital data contained in an electrical input signal supplied to the equalizer. The equalizer compensates for amplitude and delay distortion affecting the quality of the digital data contained in the electrical input signal. The equalizer includes a delay line having a plurality of discrete time delay elements and in a plurality of taps coupled to the delay elements. A clock circuit provides a plurality of clock signals of identical frequency but different phase, thereby, dividing a pre-selected time interval into a plurality of time-slots. A sequential switch controlled by the clock signals sequentially connects the delay line taps to a quality detector which also has as an input the equalizer output signal. The quality detector generates a signal, during each of the time slots, that represents the quality of the equalizer output signal.

Abstract: A method for determining the initial values of the coefficients of a transversal equalizer for a synchronous data transmission system, wherein a training sequence is transmitted to allow the equalizer coefficients to be adjusted to optimum initial values. According to the method, a sequence (v.sub.i) of L elements v.sub.i, having a periodic autocorrelation function, only the first coefficient of which is not zero, is derived from a periodic binary pseudo-random sequence (u.sub.i) of L binary elements u.sub.i having a periodic autocorrelation function, the first coefficient of which is equal to L and each of the other coefficients are equal to -1. Then, the sequence (v.sub.i) is transmitted through the transmission channel and the initial values of the equalizer coefficients are derived from the received sequence.

Abstract: Disclosed is an automatic data communication system having communicating modems equipped with automatic equalizers. The equalizers respond to a first long equalization sequence automatically transmitted from another modem. In response to that long equalization sequence, the equalizer starts from a preset non-equalized condition and assumes a fully equalized condition. That equalized modem is also capable of automatically transmitting its own long equalization sequence to the other modem. Thereafter, second short equalization sequences are employed at the receiving modems to enable a memory storage associated with the automatic equalizers. The memory stores, in response to the long equalization sequence, signals which are indicative of the fully equalized condition. Accordingly, the equalizers do not have to start from a non-equalized condition for each new data message unless a dramatic distortion occurs.

Abstract: A real time digital filter with its transfer function being matched to a particular signal plus noise condition in a manner that causes the transfer function to adapt to changing signal plus noise conditions. A transversal type of digital filter is disclosed. A general purpose computer calculates coefficients of the filter by continuously monitoring the input signal plus noise in order to maintain the filter's transfer function at an optimum level in view of changing noise conditions.

Abstract: An equalizer for correcting distorted, received data signals, i.e., partial-response signals, is described. The equalizer is of the type which uses a multi-stage shift register and an analog adder, the latter of which emits the corrected signal. In the transmission path between the output of the analog adder and the first stage of the shift register a second analog adder is interposed. An output of one of the succeeding stages of the shift register is connected directly to a second input of the second analog adder. The output of the second analog adder is coupled either directly or indirectly to the first stage of the shift register.

Abstract: A signal processing means and method of adaptively filtering input signals received at a terminal means in which the input signals include pulse signals and noise, with the pulse signals occurring at unknown times and having unknown durations, which includes signal filtering means having a first input for receiving signals derived from the terminal means, a second input and an output, the signal filtering means having a controllable filter characteristic for passing signals from its first input to its output responsive to signals received at its second input, and a signal analyzing means having an input receiving signals derived from said terminal means and an output delivering signals which are responsive to signals received at its input, to the second input of said signal filtering means for controlling its filter characteristic, whereby the output of the signal filtering means delivers signals corresponding to the pulse signals of the input signals to said terminal means while minimizing delivery of noise

Abstract: An adaptive recursive filter is disclosed which, in a preferred embodiment, comprises first and second adaptive transversal filters selectively coupled together to minimize the mean square error of the output data of the recursive filter based upon observations of input data to the recursive filter. Each transversal filter includes a tapped delay line with a variable weight on each tap. The output data of the recursive filter is developed by combining the outputs of the first and second transversal filters. The input data is applied to the first transversal filter, while the output data is applied to the second transversal filter. The output data is also combined with a reference signal to provide an error signal. A function of that error signal is utilized to update the weights of all of the taps in both transversal filters in order to cause the weights to automatically adapt themselves to minimize the mean square error of the output data of the recursive filter.

Abstract: A method of adjusting and readjusting an automatic corrector for a data signal transmission system, the corrector serving to restore pulse-amplitude-modulated signals which have suffered linear distortions in a transmission channel. A transversal filter of the corrector receives during a first adjustment phase a reference signal sequence transmitted over the transmission channel and an identical reference signal produced at the receiving end to produce error signals which serve to adjust the transversal filter coefficients stored in the corrector. The filter coefficients are subdivided into at least two groups and during the first phase one group of filter coefficients is calculated with a more attenuated error signal than the filter coefficients of the other group.

Abstract: Passband equalizer in a system for data transmission by means of phase modulation. The equalizer comprises two filters in quadrature with adjustable coefficients. Difference circuits connected to the equalizer output form difference signals between the two quadrature components of the equalizer output signal and the two components of an estimated signal which is especially formed from phase jumps associated with the transmitted data signal. A pair of difference circuits is associated with each pair of corresponding coefficients of the two filters and forms difference signals from both components of the passband signals available in the two filters in places corresponding with the said pair of coefficients. The changes in the coefficients are calculated from the above said difference signals.