Abstract: A radio receiver for frequency modulated signals in which direct conversion techniques are used to provide zero I.F. quadrature baseband signals I & Q. The I & Q signals are limited (11,12) to form square wave signals and pulse forming networks (13,14) derive pulse sequences the frequencies of which represent the polarity changes in the square wave signals. Each square wave is multiplied (15,16) by the pulse sequence derived from the other square wave to produce a unipolar pulse train. The two unipolar pulse trains are combined (17) to give a digital output signal the frequency of which is equal to the sum of the frequencies of the two pulse trains. Low pass filtering the output signal produces a simulation of the original baseband modulation.

Abstract: A circuit is described for recovering binary data from an input signal which may be phase coded and received intermittently and nonsynchronously incorporating an edge detector for detecting transitions of the data from a 0 to a 1, a counter which may be reset upon detection of a data transition, a second counter which may be reset upon the first counter reaching a predetermined value, the second counter being permitted to free run up to a predetermined value, a circuit for generating data in synchronous with the output of the second counter, and a squelch circuit for inhibiting the output of the generated data in response to output of the counters.

Abstract: An adaptively tuned clock recovery circuit suitable for digroup terminal equipment comprises a reference pattern generator which generates two ones followed by fourteen zeros generated at the transmit clock rate. The pattern is applied to a tunable resonant circuit in the receive clock recovery circuit and the phase-difference between the free oscillations of the resonant circuit during the fourteen zeros and the transmit clock is detected. The resonant circuit frequency is automatically altered by switching capacitor in or out until the phase-difference is diminished to a predetermined value, whereupon the tuning process stops and the equipment is returned to normal operation.

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: A receiver for a Navstar satellite navigation system wherein the satellite signals are down converted into zero i.f. quadrature signals (70a, 70b) and digitized (71a, 71b). The digitized signals address a PROM (72) together with additional bits representing phase rotation information (74) and locally generated code signals (e,l,p). The PROM is loaded with data in the form of "look-up" tables incorporating combinations of all input signal conditions whereby the combined address signals effect correlation and phase rotation simultaneously of the received signals.

Abstract: Recovery from loss of synchronization of a synchronous serial receiver is assured by automatic reset circuitry described herein. In a synchronous serial data receiver, synchronization, data and fill characters are received from a synchronous signal transmitter. The synchronization character is provided at the beginning of each data record to establish receiver synchronization before control data is received. The fill character is used to maintain synchronization during data reception when no useful data is available for transmission. Detection of either of these characters indicates receiver synchronization with the received data. Failure to detect either of these characters during a predetermined time interval is sensed as an error indicating that the receiver has lost synchronization with the received data.

Abstract: An emergency transmitter provided with separate devices for the transmission of a first frequency and a second frequency. The transmitter is contained within a floatable housing. The transmission devices are connected via a switch to a battery. The transmission devices are comprised of a common quartz or crystal oscillator connected with frequency multipliers which are connected to drive stages and to high frequency final stages. The latter are connected to a transmission antenna which extends from the housing. Also provided is a signal generator for modulating the transmitted frequencies. A fixed-cycle control device is associated with the first and second transmission devices and alternately sets the two transmission devices into operation.

Abstract: Pulse Code Modulation (PCM) translator for translating a PCM input word into a PCM output word, one of said words being in accordance with a compressed code and the other with a linear code, characterized in that it is adapted to convert the binary bits of the input word into those of the output word in accordance with either the A-law or the mu-law. The circuit forms part of a telephone line circuit (LC) connected between a telephone line (LI) and a digital switching network (SNW) and comprising the cascade connection of a subscriber line interface (SLIC) able to perform line control and supervision, a digital signal processor (DSP) mainly adapted to execute analog-to-digital and digital-to-analog conversion operations, the above transcoder circuit and a dual processor terminal controller (DPTC) which deals with the general control of the line circuit. The DSP only processes linear PCM signals, whereas the DPTC solely operates on companded PCM signals.

Abstract: A synchronization detecting system for data transmission in which a two-dimensionally modulated signal is received by way of a demodulator. In a training sequence for a two-dimensional modulation modem, a point of transition from an alternation to a pseudorandom symbol sequence is detected by producing a sum of the vectors of two signals which are remote from each other by a period of two samples, or a difference therebetween. Whether the detection of the transition point has been correct is decided utilizing the alternation.

Abstract: The invention relates to a receiver circuit comprising a loop in which the oscillator frequency is controlled by the useful signal. The loop gain in the useful tuning range is negative and greater than unity. An attenuator is provided which is controlled by a control circuit so that larger deviations of the intermediate frequency loop from a target value result in the loop gain being reduced, improving the receiver tuning behaviour.

Abstract: A detector for detecting a valid synchronizing pattern in a data frame in which a synchronizing bit pattern is multiplexed including a first register to receive the data and the synchronization bits, a pattern detector connected to the first register for detecting the synchronizing bit pattern in the first register, a second register, a source of clock pulses coupled to both said first and second registers, the elements of the second register being set to a first binary state and a density detector coupled to the second register.

Abstract: A facility is provided for recovering the clock and data from a data stream transmitted in the bi-phase code even if the data stream contains no sync bits and if the transmission speed varies.For clock recovery, a nonretriggerable monostable multivibrator is triggered at each phase change, so that the inserted phase changes are rendered ineffective. The clock is used to control a memory which receives the valid data of the transmitted data stream at the correct instant and keeps this data constant during one clock period.

Abstract: A canceller for eliminating the cross-polarization interference in incoming signals having polarizations which are orthogonal to one another is proposed. Each incoming signal is coupled to an associated adaptive filter. Each filter output is then summed with an associated one of the incoming signals which has a polarization orthogonal to that of the filter input signal. The signal sums formed are the canceller output signals. Adjustment of the adaptive filters so as to cancel the cross-polarization interference in each received signal is made in response to the incoming signals and the canceller output signals at selected times. During these times, circuitry for adjusting the adaptive filters examines spectral tones formed by the incoming signals and the canceller output signals.

Abstract: A method of sending self-clocking data characters and control characters in a sequence from a first communications node to a second node includes the steps of: encoding each data character as respective code pairs of the form 0XX . . . X1 and 1XX . . . X0 where the X's are the zero and one bits of the data character; encoding each control character as respective code pairs of the form 0XX . . . X0 and 1XX . . . X1 where again the X's are the zero and one bits of the control character; and transmitting, for each character in said sequence, the particular code in that character's code pair whose first code bit is the opposite of the last code bit of the immediately preceding character in the sequence.

Abstract: A signal pre-processing method for detecting valid Manchester-encoded activity on a line carrying Manchester-encoded data signals to an inexpensive Manchester-decoding receiver. Detection is provided by monitoring both a positive-level presence and a negative-level presence to determine whether the received Manchester-encoded signal exceeds a predetermined positive voltage or falls below a predetermined negative voltage. Following detection of such line activity, the received signal is determined to be validly Manchester-encoded if it first crosses a predetermined positive level or a predetermined negative level after having first previously crossed the opposite level within a time interval of 3/4 to 11/4 of the inter-bit period of the received data signals.

Abstract: A dual tone multi-frequency receiver having an improved automatic level control is described. The level control is performed after the filtering operation instead of before the filtering operation as was done in previous designs. Separate channels are derived for each of the tone groups and are handled separately for automatic level control in feed forward responsive correction circuits. Improved responsiveness to twist distortion with a fast attack tracking and holding capability results.

Abstract: The output of a doubly-balanced mixer of a television tuner is terminated by a network which exhibits the characteristic impedance of the mixer for both the sum and difference frequency components. The difference frequency component termination simply consists of an inductor and a capacitor connected as a series-tuned circuit and a resistive element connected in series between the output of the mixer and signal ground. The inductor and capacitor are selected resonate at a frequency in the passband of the IF section and the resistive element is selected to exhibit the characteristic impedance of the mixer. The sum frequency component termination simply consists of a capacitor and a resistive element connected in series between the output of the mixer and signal ground. The capacitor is selected to exhibit negligible impedance just below the lowest frequency of the sum frequency component and the resistive element is selected to exhibit the characteristic impedance of the mixer.

Abstract: With such a circuit arrangement, the sampling clock is synchronized to the frame position and the phase of the characters of a received character stream containing a "unique word" at regular intervals. In a digital correlator (1), a crosscorrelation function is generated from a unique word stored therein and from the received, sampled character stream, and a frane detection circuit (2) derives a frame clock (RT1) from those maxima of the crosscorrelation function recurring at intervals of one frame period. To achieve synchronization at any polarity of the received character stream (i.e., even if the tip and ring wires of the subscriber line are interchanged), a second frame detection circuit (3) derives a second frame clock (RT2) from those minima of the crosscorrelation function recurring at intervals of one frame period. A clock selection circuit (8) determines which of the two frame clocks is received within a limited time interval.

Abstract: In a microwave mixer circuit, two diodes connected in series are formed in a semi-insulating semiconductor substrate. A power distributing circuit is connected across the series circuit of the diodes. One of the connecting points is connected to a first signal terminal. A line connecting the two diodes in series is connected to the second signal input terminal and through a low-pass filter element to an intermediate frequency output terminal.

Abstract: An all-channel television tuner includes a single 75 ohm input for receiving airborne signals and CATV signals. A single band high frequency section tunes frequencies from 370 to 806 MHz and a three band low frequency section tunes frequencies from 54 MHz through 370 MHz. Both sections are coupled to the 75 ohm input through signal diverting means. A channel selector provides tuning voltages and band switching voltages to the sections and to the signal diverting means as a function of the channel selected.