Abstract: A receiver for FFSK modulated signals operating in the time domain so as to effect a rapid acquisition of the data signal and the generated clock signal and to maintain the synchronization irrespective of the data pattern. For that purpose the receiver comprises a zero-crossing detector and a window generator for selecting by means of this window generator from the zero-crossings detected by the zero crossing detector two consecutive zero-crossings of the lower frequency of the two signal frequencies of the FFSK signal for sychronization of the regenerated clock signal.

Abstract: In a serial binary digit stream, when a single bit follows at least two bits of the opposite polarity and is succeeded also by a bit of that opposite polarity, a comparator produces a correction signal which is combined with the first-mentioned bit so as to broaden it in time span. As a result, the amplitude of reception or reproduction of the broadened bit is enhanced so as to compensate for deficiency of amplitude which would result from the imperfection of the transmission channel or recording and reproduction process. The broadening of the critical bit pulse can be performed by a correction pulse that enhances its amplitude, followed by Nyquist filtering and then by amplitude limiting to the normal binary digit amplitude level, or else the broadening can be accomplished by providing a correction pulse shifted in phase by an adjustably shifted clock pulse or train.

Abstract: A telemetry system for sensing remote physical events and for transmitting and boosting a digital data signal representing the sensed events on a transmission line, which comprises a master clock and a plurality of sensing stations for sensing local data. The sensing stations inject local data onto the transmission line as a digital data signal, and a controller/receiver receives the digital data. The master clock initializes the system timing and generates a sync signal. Each sensing station includes a booster subsystem for receiving the local digital data and for injecting the digital data onto the transmission line as a digital data signal. During system start up, each booster subsystem claims a slot, in accordance with an organizational process, for injecting the digital data signal onto the transmission line. The booster subsystem in each sensing station further includes a booster circuit for boosting the digital data signals which are propagating on the transmission line, as well as the sync signal.

Abstract: The present invention features an ADPCM decoder of the instantaneous companding type which comprises two memory circuits (each preferably PROM). The first memory contains a plurality of differential values and the second a plurality of step size control codes. The memories receives ADPCM input codes which function as address signals. The memories are connected through an adder and a shift register feedback connected with the adder. The first memory receives two inputs, one of which is an ADPCM input code and the other is an input consisting of the sum of the current output of the second memory plus the previous value outputted thereby. The first memory produces a differential value on the basis of the two inputs applied.

Abstract: A multichannel time division multiplexed (TDM) bit stream has specific channels selected by gating selected channel bits out of a composite group of channels. The selected channel bits are spread spectrum coded as multiplexed noise codes which are then used to modulate a transmitter for communicating the codes over a transmission link. The noise codes are then automatically compressed back to original channel bits at a receiver to provide output signals which are totally non-interfering with each other.

Abstract: In an adaptive equalizer of the decision feedback type for reducing intersymbol interference in subscriber loops of a telephone system, the corrected digital signal is applied to means for detecting the occurrence in the signal of a zero state following a non-zero state. When that occurs, a correlator samples the signal during the "zero" bit period and applies the sample to an integrator. The integrator output varies the coefficients of the feedback signal applied to the input means for addition to the incoming digital signal to provide the corrected signal. The equalizer may have several stages, each for detecting a "zero" state in a different bit period following the original pulse. Also the circuitry may be duplicated for each polarity if the input signal is bipolar.

Abstract: Multilevel code mates A and B expanded in accordance with the expression , b.sup.K and B=a.sup.K, b are compressed to a lobeless basic mate pair by repeatedly compressing corresponding code mate pairs in successive stages to provide diminishing codes of half the code length by amplifying the code mates by a predetermined amplification factor and then adding and subtracting the code mates in accordance with the expressions A.sub.i-1 =A.sub.i +B.sub.i.sup.K.sbsp.i and B.sub.i-1 =A.sub.i.sup.K.sbsp.i -B.sub.i where i is the i.sub.th compression stage and K.sub.i is the amplification factor applied to the codes A.sub.i and B.sub.i.

Abstract: A quality measure of a signal received at a receiver of a two-dimensional linear modulation data communication system, is measured by using a phase controlled baseband signal (y.sub.k.exp(j.phi..sub.k)) obtained from the received signal and a reproduced data signal (x.sub.k) derived from the phase controlled baseband signal. That portion of the quality measure which is introduced into the received signal in a transmission channel for the received signal, is measured by estimating a data signal component (y.sub.k) which includes intercode interference, by subtracting the data signal component from the phase controlled baseband signal to produce a difference signal of a phase difference relative to the reproduced data signal, by giving the phase difference to the difference signal to produce a phase adjusted signal, and by calculating a mean square of an inphase component of the phase adjusted signal.

Abstract: Locations of a desired number of signal points for a double side band-quadrature carrier modulation system occupy the inner intersections of a multiplicity of concentric rings with a triangular grid. The signal point locations of the desired number on the outer partially occupied ring are provided with additional signal points at positions selected to provide that the centroid of the set of locations is at the center of the rings.

Abstract: FM-receiver for receiving an FM-signal with transmission identification. An aerial input is connected to a tuning unit (1) to which there are connected, in succession, an IF-unit (2), an FM-detection circuit (3), a pilot regeneration circuit (10) for regenerating a pilot, a demodulation arrangement (12) for demodulating the code signal which contains transmission identification information, and a clock regeneration circuit (18) which is connected to both the pilot regeneration circuit (10) and the demodulation arrangement (12). The clock regeneration circuit comprises a resettable phase search circuit (18') for producing a clock signal whose frequency is derived from the regenerated pilot and whose phase is derived from the demodulated code signal, a clock-controlled decoding circuit (13) for decoding the code signal and a clock-controlled signal processing unit (17).

Abstract: A PSK modem has a transmitter for converting input digital data into corresponding PSK signals modulated on a first carrier for transmission out and a receiver for receiving PSK signals and for converting those PSK signals into corresponding digital signals wherein the receiver has a phase locked loop used in demodulating the input PSK signal. The phase locked loop includes a low pass filter and an integrator connected in a circuit configuration so that the low pass filter output overrides the integrator output even if the output of the integrator is equal in magnitude to either of its input signals, thereby allowing the loop to lock. The integrator then adjusts itself slowly to reduce the DC output of the low pass filter and the steady state phase to 0. This permits the loop to free run in the absence of an input signal without losing lock.

Abstract: A circuit for amplifying electrical signals, particularly for devices for transmitting frequency-modulated emitter coupled logic (ECL) broad-band signals by means of coaxial lines utilizes a plurality of ECL logic elements as amplifier stages. The input of each logic element is connected to a bias voltage and is charged by means of a coupling capacitor with the signal to be amplified. The circuit amplifies electrical signals to ECL level with an improved signal pulse duty factor.

Abstract: An automatic correction circuit is responsive to suitable bit patterns in a bit stream being received from a transmission medium, to generate an error amplitude map of signal distortion being introduced by the transmission medium. The error amplitude map is digitally stored or recorded. After each non zero bit occurrence in the signal stream a synchronized output signal corresponding to the recorded error amplitude map is generated and added to the bit stream being received to reduce signal distortion, whereby information recovery from the received bit stream is improved.

Abstract: A modem which utilizes a method and means for coding a data signal for transmission and reception which includes the steps of generating a prefix signal which is a train of pulses at a multiple or submultiple of a selected baseband frequency, then generating a data stream following said prefix with the data stream having one binary state transmitted at said baseband frequency and the other transmitted at another frequency. The data stream is terminated with a suffix having a waveform different from that of the two binary states. A separate receiver is provided for each of the redundant highways. The receivers utilize a clock circuit synchronized to the data and a timer responsive to the clock for establishing the bit time. The incoming signal is modified by a factor so that a single decoding circuit can be used to decode the prefix as well as the data. A prefix counter counts the initial incoming pulses and upon receiving the number in a prefix indicates to the circuit that a carrier has been detected.

Abstract: A method and apparatus for baseband generation of a spread spectrum reference signal for an LMS adaptive array processor is provided. An IF summed, weighted spread spectrum signal is output from the processor and translated to baseband to produce an I (in-phase) channel spread baseband signal and a Q channel (quadrature-phase) spread baseband signal. A baseband correlator receives the I channel and Q channel baseband signals and delayed versions of in-phase and quadrature-phase PN signals and produces despread I channel and Q channel baseband output signals. A baseband linear spreader receives the despread I channel and Q channel baseband output signals and the in-phase and quadrature-phase PN signals and produces respread I channel and Q channel baseband signals. A baseband modulator modulates the respread I channel and Q channel baseband signals with a phase-shifted local oscillator to produce the reference signal.

Abstract: A radio receiver for FM signals having a demodulation system to produce an approximation to an analog output by either measuring the time intervals between successive zero crossings in the I.F. (FIG. 1, FIG. 2B) or by filtering pulses produced at each zero crossing of the I.F. (FIG. 1, FIG. 2A). The demodulator includes two signal pathways in quadrature phase relation, the second signal either lagging or leading the first signal in dependence on whether the received signal frequency is above or below a local oscillator frequency. The modulation frequency can carry analog information separate and apart from the on-off (digital) information.

Abstract: A carrier and timing recovery technique is disclosed for combating the phase effects of multipath fading occurring during radio transmission. The technique is based on a known mathematical model of multipath fading. A test variable generator (26) develops a number of test variables whose relationship characterizes the multipath distortion. A processor (27) derives a plurality of coefficients of weighting measures from the test variables. The coefficients serve to adjust a matched filter (28) to provide greater use of those portions of the received radio signal yielding higher signal-to-noise ratios than those portions with lesser yields, as well as to compensate for multipath phase perturbations. The technique is also compatible with maximum-likelihood sequence detection techniques to provide further compensation for multipath fading effects.

Abstract: The radar trigger and pretrigger generator determines the inherent component time delay through the radar modulator and transmitter during a first cycle of operation. During the next cycle of operation a pretrigger pulse is generated after a time corresponding to the previously measured delay and a trigger pulse is generated after a time corresponding to an operator selectable delay. The trigger pulse is used to trigger the radar modulator, which in effect, permits the operator to control the elapsed time between pretrigger pulse and transmitter firing in a fashion which is completely independent of circuit delay variances through the radar modulator and transmitter.

Abstract: Expanded multiplexed noise codes including code mate pairs having autocoration functions which upon detectionprovides an impulse autocorrelation function are generated by delaying the inverse of one of the code mate pairs (code b) by a value .tau. and adding it to the other code mate pair (code a) to form a first expanded code mate (code A) while a second expanded code mate (code B) is generated by delaying the inverse of said other code (code a) also by a value .tau., forming the complement thereof and adding it to said one code mate (code b). Such an expansion enables each expanded code to begin with each different code of a mate pair.

Abstract: Precise phase acquisition and tracking of a data modulated pulse signal in order to recover the data in a low signal to noise ratio environment is achieved by a sample data phase locked loop that is adaptive, second order, and uses baseband polar coordinate processing. The circuit utilizes an adaptive second order loop where the loop bandwidth can be adjusted by a coherence measurement. This provides wide bandwidths during initial acquisition, medium bandwidths during acquisition/track transition and narrow bandwidth during tracking.