Abstract: A phase modulation modem providing switch selectable speeds on voice-band channels utilizes four phase, modified eight phase, and optimized eight phase, two amplitude modulation techniques. A binary equalizer automatically corrects for envelope delay and amplitude distortion of the carrier signal caused by the voice-band channel. Each symbol time, the X-axis error and Y-axis error for the received symbol is determined by comparing the received X and Y components with stored ideal X and Y components for that symbol. These error X and error Y values are used to modify primary and secondary equalization constants. The equalization constants, thus modified during this symbol time, are used on the next received symbol to correct for the phase and amplitude distortion measured during past symbol times. This sequence is repeated for each symbol time. Preselected equalization constants are utilized on the first symbol received.

Abstract: A data transmission system is provided with a double sideband suppressed carrier transmitter and receiver for transferring data between data processing apparatuses. The transmitter and receiver communicate over a telephone line which has physical characteristics which produce delay and attenuation distortion and phase jitter in the transmitted signal. The receiver includes a sampler for converting the transmitted signal into a digital signal, an automatic equalization network for correcting the delay and attenuation distortion, and a phase correction network compensating for frequency offset, phase offset, and phase jitter. The phase corrected and equalized signal is then detected and introduced to the data processing apparatus.An error signal calculator is responsive to the phase corrected signal and the detected signal to provide a system error signal for automatically updating the functions of the equalization and phase correction networks in accordance with the characteristics of the incoming signal.

Abstract: A system equalizer and a method of equalization employed in a repeatered submarine cable system, in which automatic gain controlled (AGC) submerged repeaters are employed to compensate for fluctuations of the cable loss caused by the temperature fluctuations in the surrounding environment of the repeatered submarine cable system. In a terminal equipment connected to the repeatered submarine cable system, the seasonal misalignment of the repeatered cable system is equalized by a switchable equalizer having a loss-frequency characteristic corresponding to the total of compensation errors in the AGC submerged repeaters. Short-term level fluctuations of the repeatered cable system are compensated by an automatic equalizer, which has a loss-frequency characteristic proportional to the square root of frequency f and is controlled by the level of a pilot signal transmitted through the repeatered submarine cable system. An unknown fixed deviation is finally equalized by a second adjustable equalizer.

Abstract: An automatic equalizer for calculating the equalization transfer function of a transmission channel and applying same to equalize received signals. The initial calculation as well as the equalization proper are conducted entirely within the frequency domain. Equalization coefficients are obtained using successive approximations approaching the desired values. The equalization coefficients may be adjusted independently from each other inasmuch as these coefficients are not interdependent. Successive approximations of the coefficients differ by fixed increments of the real or imaginary components. A feedback circuit is utilized in generating the successive approximations wherein sign or polarity information is used to determine the adjustment necessary for convergence.

Abstract: An automatic equalizer for calculating the equalization transfer function and applying same to equalize signals received from a transmission channel. Time domain equalization is achieved using a transversal filter whose tap weights are calculated in the frequency domain during an initial training period.

Abstract: An automatic and adaptive time-domain equalizer with a first transversal structure operating on received signal samples has its convergence properties improved by the addition of a second transversal structure operating on detected signal samples and having its tap-gain settings conjugate, i.e., reversed in time, with respect to those of the first transversal structure for effectively measuring the spread of tap gain values generated at the first transversal structure and a third transversal structure also operating on received signal samples but having its tap-gain settings determined by the spreading error. The matrix product of the spreading-error tap-gain values and received signal samples modifies the up-dating of the tap-gain values controlling the first transversal structure. The resultant faster convergence is particularly useful in the presence of severe amplitude distortion in the data transmission channel.

Abstract: In a Fermat representation of numbers, the imaginary operator j is a real number which is a power of two. This is applied here to the implementation of complex digital filters, i.e., filters deriving the real and imaginary components of the desired filtered signal y by processing the components of the input signal x. Let (xm, xm) and (ym, ym) be samples of the real and imaginary components of x and y, respectively. The samples xm are delayed to provide j xm in the Fermat system, then both xm and j xm are fed to digital adders to provide xm + j xm and xm - j xm, which are separately applied to the input of transversal digital filters. The outputs of said filters are combined in simple digital adders to provide the desired y components.

Abstract: System comprising an integrating digital signal processing device to which input signal samples x(nT) are supplied with a period T and which supplies output signal samples z(mrT) with a period rT. To this end in this integrating signal processing device consecutive groups having a period rT and consisting of r successive consecutive signal samples are processed beforehand in a non-recursive digital filter for generating auxiliary signal samples y(mrT) which occur with a period rT, the last mentioned samples being integrated in an integrating network for generating the output signal samples z(mrT).

Abstract: An equalizer for partial response signals is described which is constituted by a shift register and an analog adder, from the output of which a corrected signal is produced. Two of the switching stages forming the shift register have their outputs connected to inputs of an additional analog adder, and one of these shift register stage outputs is connected to the analog adder over an adjustable amplifier. The output of the additional analog adder is connected to a correlator, the value of the output signal of which controls the gain of the adjustable amplifier.

Abstract: An equalizer comprises a tapped delay line of a transversal filter and first equalizing means responsive to a short pseudo-noise train supplied thereto for adjusting tap gains so as to make the transversal filter output signals simulate a pseudo-noise train generated at the receiver with the pulse pattern of the supplied pseudo-noise train. Larger ones, in absolute values, of the adjusted gains are placed at the center of the delay line. Responsive to a subsequently supplied long pseudo-noise train, second equalizing means self-adaptively adjusts all tap gains. The delay line preferably comprises delay units, each for a half of a common clock interval of the supplied pseudo-noise trains and data signals.

Abstract: In a high speed QAM data communications receiver of the type adapted to receive bursts of signals having a bandwidth B Hz and sent at a predetermined rate of 1/T signals per second over a channel, wherein the receiver includes an automatic adaptive equalizer having taps spaced equally apart, tap coefficient circuitry for repeatedly multiplying the output of each tap by a respective tap coefficient, and adjustment circuitry for adjusting the tap coefficients, and output circuitry responsive to the equalizer for providing output signals at times kT + .tau., k = 0, 1, . . . , where .tau.

Abstract: An adaptive equalizer to compensate for the effects of frequency-selective fading on a microwave radio system. The equalizer includes two Bode-type bump networks and an AGC amplifier whose slope and gain are respectively controlled by pilot tones added to the message load. Importantly, the frequency characteristics of the two Bode networks are non-overlapping, thus ensuring stability.

Abstract: A communications receiver transversal filter equalizer is disclosed of the type using fixed increment tap weight adjustments involving use of amplitude data from the incoming signal in conjunction with tap weight adjustments.

Abstract: Utilizing a known equalizer and a single-sideband frequency transposition device, unitary construction is achieved by using a second series of output channels which, by a crosswise connection to the comparators already present in the control voltage generator, supplies a second equalized signal shifted in phase over .pi. /2 with respect to the equalized output signal of the first series of output channels. The output signals thus formed are used as input signals for a single-sideband frequency transposition device having two modulator stages which are also fed by two frequency transposition oscillations mutually shifted in phase over .pi. /2. In this way a unitary construction is realized which is especially interesting for integration and which distinguishes itself by an optimum frequency transposition quality as well as by a considerable saving in complex circuit elements.

Abstract: Incoming data pulses from a transmission channel are differentially combined with feedback pulses from the downstream end of a cascade of (N-1) delay networks to form an updating signal fed in parallel to a first set of multipliers for weighting with respective coefficients b.sub.1 - b.sub.N.sub.-1. These multipliers deliver optimized signal components to the inputs of respective delay networks of the cascade, through the intermediary of adders in each instance except for the first delay network at the upstream end; a further adder downstream of the last delay network may superimpose the updating signal, weighted with a coefficient b.sub.N by an N.sup.th multiplier of the first set, upon the feedback pulse issuing from the last delay network to generate an additional signal component. At least the more significant signal components, from the inputs of the delay networks located further upstream in the cascade, are weighted in a second set of multipliers with respective coefficients a.sub.1, a.sub.2 etc.

Abstract: Time base instability of signals in a train thereof is corrected by use of a frequency controlled delay device. As employed in the correction of time base instability of video signals, a charge-coupled delay device is used. The delay device is clocked by a frequency which is proportional to the reciprocal of the phase difference between a fluttering input signal and a reference synchronizing signal. This corrects errors caused by the nonlinear transfer characteristics of the delay device, i.e. the transit time through the device is porportional to the reciprocal of the frequency of the clock signal which controls the delay device.

Abstract: Equalizing system arranged for pulse transmission, adaptive equalization being achieved without the use of an additional periodic adjusting pulse pattern. For this purpose in a control voltage generator the sub-bands and the associated additional sub-bands of an equalized pulse signal processed by the phase and amplitude control circuits are used after pulse regeneration directly as a local reference signal and an adjusting signal respectively. The sub-bands and additional sub-bands are applied to the cascade connection of a comparator and a mean-value device for generating the control voltage which controls the phase and amplitude control circuits in a feedback mode.

Abstract: Initial Adjustment of a receiver having an automatic adaptive equalizer in a modem communication system is accomplished by employing a data transmission rate lower than normal for an early segment of each burst of signals. At this lower rate, accurate reception is possible without complete adaptation of the equalizer. These same (early segment) signals are used to adapt the equalizer in a decision-directed mode. When the adaptation is completed the system switches to its normal higher rate of data transmission.

Abstract: Incoming data pulses from a transmission channel are differentially combined with weighted data pulses from preceding cycles to form an updating signal fed in parallel to a multiplicity of weighting circuits for digital multiplication with respective coefficients K.sub.1 - K.sub.N, the output signals from these weighting circuits being synthesized in staggered relationship to form a composite signal fed to a quantizing decoder. The weighting coefficients K.sub.1 - K.sub.N are continuously modified under the control of an error signal derived from a locally generated reference code during an acquisition phase and from the decoder output during an operating phase.

Abstract: An adaptive feedforward transversal equalizer acting jointly with a data decision-directed demodulating carrier recovery system to achieve substantially jitter-free passband equalization of a suppressed-carrier coherent data signal without the use of pilot tones is improved by adding a feedback transversal filter section operating on past demodulated data symbols. The weighted output of the feedback section is subtracted from the demodulated output output of the feedforward section to provide signals from which data decisions are made and common error signals are derived. Tap-gain coefficients for both feedforward and feedback filter sections and phase angle for the demodulating carrier recovery system are adaptively updated in accordance with the common error signal. Severe frequency offset and phase jitter are simultaneously compensated.

Abstract: Disclosed is a recursive circuit capable of serving as a signal detector or as a signal generator. The circuit comprises a shift register capable of storing multilevel signals, and a feedback network responsive to an input signal and to the output signals of selected stages of the shift register. In the feedback network, the output signals of the selected stages are each multiplied by prechosen integers, and then added with the input signal to form a sum signal which is applied to the first stage of the shift register. The sum signal is developed by nonmodulo addition, and the multiplying integers are prechosen to cause the characteristic function of the circuit to be a cyclotomic polynomial. Detection of the presence in the input signal of a signal having a chosen frequency is accomplished by the sum signal excluding a predetermined threshold level.

Abstract: Apparatus for accomplishing phase equalization between two signal components derived from a common source includes circuitry for generating the sum and the difference of the two signal components and for deriving an error signal from the envelopes of the sum and difference. The error signal is mixed in a first mixer with the envelope of the sum signal and mixed in a second mixer with an envelope of an original signal from which the two input signal components to be phase equalized are derived. The output of the first mixer is applied to a phase adjuster which adjusts the phase of one signal component to be phase equalized so that desired phase equality is maintained between the two signal components. The output of the second mixer controls the gain of an amplifier which amplifies the envelope of the original input signal. A particular application of the invention is in a LIND (linear amplification using nonlinear devices) amplifier such as disclosed in U.S. Pat. No. 3,777,275 issued Dec. 4, 1973 to D. C. Cox.

Abstract: A sample data filter using a delta modulator to feed a shift register of which selected outputs are pulsewidth weighted. Each of the coefficient multipliers include a flip-flop fed by one of the taps of the shift register and triggered by a clock. A synchronous counter, common to each of the multipliers, is fed to a NAND gate that clears the flip-flop. Interposed between the counter and the NAND gate are a series of switches, one for each stage of the counter. The flip-flop controls a switch to a source of reference voltage and the output of this switch controlled voltage from each of the multipliers is summed and fed to a demodulator.

Abstract: A receiver includes means for sampling and noncoherently demodulating a received signal to provide digital symbols in each of a first and second channel. An equalization network equalizes the incoming signal and a phase correction network corrects the phase of the equalized signal. In response to the transmission of a preamble in the first channel, a fast learn network derives the phase error by determining the arc tangent of a quotient formed by dividing the signal in the first channel by the signal in the second channel. A course phase jump can be made to insure that the arc tangent is not greater than unity. The timing error of the sampling means can be derived by determining the arc tangent of a quotient formed by dividing the present digital symbol in the one channel by the preceding digital symbol in the one channel.

Abstract: A digital filter for a plural digitally expressed pulse code modulated (PCM) signal utilizes a storage register to retain several samples of the signal and obviates the need for digital multiplication circuits by using a delta coding for the filter coefficients. Processing steps are at a multiple of the sampling rate and at each step, the value of one stored sample is combined additively or subtractively with previously stored sample values as determined by stored delta coefficient values. The summed values are periodically transmitted as output samples of a filtered PCM signal.

Abstract: A transversal filter which utilizes a charge transfer delay line in combination with a plurality of source-follower pairs or their equivalent to tap the delay line and a plurality of transistors fabricated and disposed to proportionately weight, polarize, error-compensate and differentially sum the tapped signals in a single operation.

Abstract: An electrical filter for removing noise from a voice communications signal in which, for example, seven sample values of the signal are obtained continuously updated and subjected to filtering. Filtering is accomplished by adding balanced, with respect to a mid-point sample, spaced pairs of the sampled values and then multiplying each pair by a selected filter constant. The signal products thus obtained are summed to provide a filtered version of the original signal.

Abstract: The feature of the invention is an adaptive equalizer for modulated carrier transmission systems in which a received signal is subjected to a Hilbert transformation to obtain a second signal having a 90.degree. phase shift for all components. The two signals are then passed through a pair of filters each and the outputs are cross-combined to generate the cartesian coordinate signals of an equalized signal. The coordinate signals are combined in a polar converter and are then decoded to detect the amplitude and phase data components of the received signal.The equalizers are made adaptive by determining at each sampling time, the phase and amplitude errors in the signal and using these errors to modify the coefficients of the equalizing filters. The phase and amplitude errors are recoded into Cartesian coordinates and multiplied by the values of the samples at each tap of the filters to generate four error signals for each tap.

Abstract: A multi-level digital filter system applicable to modems is provided. The incoming data is read serially into M shift registers and read out in parallel by M further shift registers under the control of an M-bit clock, where M=log.sub.2 N and N is the number of levels. After appropriate conditioning by a logic control circuit, the parallel outputs are filtered separately by M digital shaping filters. The shaping filters each comprise a chain of shift registers the outputs of which are weighted by a resistor network and summed to produce a desired time response, which in an exemplary embodiment is the inverse Fourier transform of an ideal low-pass filter. Summing of the filter outputs produces an N-level signal. Specific examples of three-, four-, five-, six- and eight-level systems are disclosed.

Abstract: A broad-band signal transmitting device including a signal transmitting transformer of the primary to secondary turn ratio 1 : N, comprising a first circuit for expanding the transmission band to low frequencies by decreasing the impedance as well as by decreasing the gain for the signal component in the primary circuit of the transmission transformer, a second circuit connected with the output side of the transmission transformer having an impedance larger than N.sup.2 times of the impedance of the primary side and smaller than the impedance exhibited by the stray capacitance of the secondary side at the upper limit of the transmission band, an amplifier for recovering the gain drop in the first circuit, and a low frequency compensating circuit for compensating the lack of low frequency transmission characteristic due to the transmission transformer.

Abstract: Apparatus for accomplishing amplitude equalization between two input signals includes circuitry for generating the sum and the difference of the two signals, mixing the sum and the difference and applying the low-pass filtered version of the mixed resultant as a feedback error signal of very low frequency to an attenuator associated with one of the two input signals. A hybrid combiner may be used to generate the sum and the difference from the two input signals. The phases of the two input signals are unaffected by the amplitude equalization. A particular application of the invention is in a LIND (linear amplification using nonlinear devices) amplifier such as that disclosed in U.S. Pat. No. 3,777,275 issued Dec. 4, 1973 to D. C. Cox.

Abstract: The invention relates to a device for the remote adjustment of a switchable network equipping an unattended station on a transmission line, by means of remote control frequencies emitted from a terminal station on this line. The device enables the remote control of a motor actuating a switch which operates said switchable network. The moving of the switch, and then the adjusting of the network, can be followed at the terminal station from the observing of the level of a return frequency sent back from the unattended station to the terminal station.

Abstract: A transmitter transmits data through a communication channel to a receiver and the communication channel provides the data with delay and attenuation distortion. The receiver includes an equalization network having taps with multiplying coefficients for correcting the delay and attenuation distortion of the data. In response to a special sequence of the data, either specially generated by the transmitter or detected in random data, the receiver generates signals for updating the multiplying coefficients of the taps and these signals are introduced to the equalization network through a gate enabled by a special sequence detection network. This apparatus provides for the adjustment of the equalization taps in an extremely short period of time such as 5.83 milliseconds.

Abstract: An automatic transversal equalizer is provided wherein the input signal is sampled and stored on a series of capacitors. The capacitor voltages are sequentially recalled for application to an analog multiplier which also receives a sequence of coefficient voltages which have been stored by a second series of capacitors. The single analog multiplier performs the functions of the plural voltage controlled attenuators of prior art equalizers.