Abstract: A modem is operated in a half-duplex mode having various elements which are trained on data and which are locked up while data is not exchanged, thereby eliminating the need for a preamble. A preamble is used only if the period between successive transmissions exceeds a preselected threshold.

Abstract: An apparatus and method is disclosed of an SMSK/2 device that provides an additional phase state, and having at least three phase changes possible per bit period, as compared with standard SMSK/2 devices. The additional phase state increases the bit time needed for the signals to remerge which increases the euclidean distance defined by the remergence paths. The increase in euclidean distance provides an improved power efficiency and bit error rate (BER).

Abstract: A digital minimum shift keyed modulator (MSK) has been described incorporating a code generator for generating a plurality of bits in series representative of a spreading function, an Exclusive OR circuit for multiplying two successive bits, a memory for holding predetermined constants, timing circuitry, a digital-to-analog voltage converter and a bandpass filter. The invention overcomes the problem of variations over frequency and temperature associated with previous MSK modulator designs.

Abstract: A minimum shift keyed reference signal generator is described (FIG. 3) incorporating a shift register, for holding a spreading function, a first and second memory for holding in-phase and quadrature weights, a counter for addressing the first and second memory and first and second Exclusive OR circuits for combining the weights when addressed by the counter with the spreading function held in the shift register. A minimum shift keyed correlator is described (FIGS.

Abstract: An ADM codec includes CVSD encoder and decoder circuitry having a syllabic filter responsive to the binary state of the ADM bit samples for changing the quantization step amplitude at a rate of change directly proportional to the rate of change of slope of the received voice signal.

Abstract: A bidirectional coupling circuit is provided for carrier based communication and control networks in which a coupling transformer is employed having relatively decoupled primary and secondary windings which are each tuned to the carrier frequency. Separate secondary windings are wound on the same core leg, one of these secondary windings being employed as a transmitter winding which is referenced to a positive supply voltage and the other winding being employed as a receiver winding which is referenced to ground. The coupling transformer is arranged to have a relatively high input impedance at the carrier frequency but due to series resonant effects has a relatively low impedance for undesired signals on either side of the carrier frequency. An operational amplifier is connected to the receiver winding to provide high gain amplification for a signal received from the common network power line without loading the other windings of the transformer.

Abstract: Data-aided equalization and cancellation in digital data transmission over dually polarized fading radio channels is disclosed. The present invention uses decision feedback structures with finite-tap transversal filters. Subject to the assumption that some past and/or future data symbols are correctly detected, formulas and algorithms for evaluating the least mean-square error for different structures are disclosed. In a sequence of curves, the performance of various structures for a particular propagation model and several fading events are evaluated and compared.

Abstract: An "avalanche" relay communication network is configured of a plurality of transceiver stations spread out over a geographic area of interest to establish multipath communication diversity among the stations. The transceiver equipment at each station has the capability of simultaneous transmission over the same frequency through a "common knowledge" network timing scheme such as TDMA and has the capability of taking advantage of received multipath signals. Communications between an originating station and an intended recipient station are achieved by the originating station modulating onto an HF carrier a digital packet formatted to contain the number of times the message is to be repeated and a means of establishing the quality of the received message. All stations which have correctly received the packet repeat that same message on the same carrier frequency at the same preestablished future absolute time (or times, based on the number of repeats).

Abstract: An RF pulse transmitter, for use in precision distance measuring equipment (DME/P) of a microwave landing system, includes appropriate circuitry to correct for incidental phase modulation (IPM). The pulse transmitter includes a modulation circuit for generating an RF pulse having a pulse peak. A reference phase control circuit is provided to generate a reference signal. A phase detector receives the RF pulse and the reference signal and in response thereto generates a phase error signal. The reference phase control circuit includes appropriate circuitry for adjusting the phase of the reference signal applied to the phase detector to thereby drive the phase error signal to a predetermined value at the pulse peak. A pre-distortion circuit generates a pre-modeled correction signal pulse for use in correcting for incidental phase modulation (IPM).

Abstract: A communication system for providing reliable transfer of digital data in such system as a security system between source of data 214 and user 213, and between user 213 and end use of data 215. When the false alarm rate requirement of the security system is specified in less than one in ten years, this tight requirement must also apply to the communication link even though the RF transmission path might use the very noisy 60 Hz power line. Digital data signals are transmitted only when a detection is made at source of data 214 or when user 213 outputs an action command to end of use data 215. Thus the communication system must maintain the low false alarm rate under two conditions: (1) where no data signal but noise and interference is received over long periods of time, and (2) where a data signal pulse noise is received.

Abstract: Adaptive filters are used to separate frequency hop signals to improve the detection and estimation of the frequency hop signals. In preferred embodiments, two or more adaptive filters (which can be connected in series or in parallel) exhibit different convergence characteristics to isolate a frequency hop signal.

Abstract: A circuit arrangement comprises a frequency response control circuit for controlling the level around a particular frequency of an input PCM signal in accordance with a control signal which is produced as a function of the difference between levels of positive peaks and/or negative peak corresponding to a logic bit pattern 1010 of a data synchronous signal of the PCM signal having a predetermined format. The level detection may be performed by a plurality of sample-and-hold circuits, and the difference is obtained by way of an adder-subtractor. The circuit may be arranged to constitute either a feedback loop in which level detection is effected by using a frequency response controlled PCM signal, or a feedforward system in which level detection is effected by using the input PCM signal whose frequency response has not been controlled. An output signal from the frequency response control circuit is then applied to two comparators of a conventional data acquisition circuit.

Abstract: A data terminal suitable for home use and having the ability to communicate in both bit synchronous and character asynchronous formats is provided. When a user places a call to a database, the terminal automatically detects whether the database is operating in the bit synchronous or character asynchronous format by examining the received signal for a specific character stream. In response to the presence or absence of this character stream, the terminal automatically configures its receiver and transmitter to communicate in the desired format. This frees the user from the task of modifying a synchronous/asynchronous setup parameter each time a different database is accessed.

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 data transmission system combines a near-instantaneous companding system with PCM or DPCM transmission data. In the transmitting side, lower bits are removed from an original data, to form transmission data and are accumulated in an accumulator. When a carry is caused as a result of such accumulation, the carry is added to the transmission data. Thus, total amount of the original data can be transmitted to the receiving side, thereby to improve a transmission quality and to reduce quantizing-noise. When the removed bits are subject to an addition, it is determined whether an overflow occurs. When the overflow occurs, the addition is not performed and such a logic operation as to prevent the overflow is performed.

Abstract: A portable transmitter for transmitting a magnetic signal is disclosed. The transmitter is provided with a transmitting coil for generating a magnetic signal upon receiving an electric current from a dry cell through an intermittently operating electric current supplying transistor. The transmitter further comprises a capacitor, a charging line provided with a diode, and a switching transistor. The switching transistor makes the induced current which is generated in the transmitting coil, flow into the capacitor by way of the charging line when the electric current supply to the transmitting coil is stopped, and supplies the electric current stored by the capacitor to the transmitting coil when the electric current supply to the transmitting coil is started.

Abstract: An encoder treats a block of b bits of binary data as a number N and encodes it into eight values S1, S2 . . . S8 identifying it. The eight values are each selected from positive, negative and zero integer values; and the values are chosen so that a set of eight consists of all even integers or all odd integers and so that the sum of the eight values is 0 modulo 4. In the transmitter these values are modulated on a carrier for transmission. A receiver detects the received versions of the transmitted values, determining the number N and reconstituting the block of b bits.

Abstract: A low power line driving transmission apparatus is described in which TDM signals are transmitted between points over a transmission line comprising a pair of conductors and in which the characteristic impedance of the tranmission line and the source impedance of the transmitters is matched and wherein the input impedance of the receivers is sufficiently high to present an effective open circuit to received signals. Under these conditions the transmitter dissipates power only during logical transitions of the input signals.

Abstract: A high frequency code division multiple access spread spectrum (CDMA SS) communications system includes multiple transmitters and their associated receivers, and a pilot carrier source. In order to reduce errors in the receiver IF frequency due to unavoidable differences between the desired transmitted carrier and receiver local oscillator (LO), the transmitted carrier ferquency is related to the pilot frequency. The receiver phase-locks the pilot carrier to the local oscillator, thereby providing an IF data signal with reduced frequency error. The IF data signal is multiplied by sine and cosine demodulating signals related to the local oscillator frequency to produce inphase (I) and quadrature (Q) components of the received data signal. The I and Q signals are applied to code matched filters, which produce filtered or decoded signals the amplitudes of which are related to the phase error between the demodulating signals and the IF carrier.

Abstract: Ordinary digital data is reformed and time shifted such that it may be broadcast over a radio link which periodically shifts its frequency. The system of this invention utilizes timing information obtained from a pre-existing frequency-hopping radio link in conjunction with its own buffer and control circuitry to accurately time-position discrete digital data packets within those time bands of the radio transmission wherein the frequency is not changing from one frequency to another. In the drawing, T.sub.H1 is a very short duration pulse which commands the AM frequency--hopping system to shift frequencies. The time period necessary for the frequency hop operation to settle down and attain a stable frequency is represented by the interval between T.sub.H1 and T.sub.1. The actual reception of the uplink message occurs in the interval between T.sub.3 and T.sub.4 ; transmission of the downlink signal from the system occurs in the interval between T.sub.5 and T.sub.6. The interval between T.sub.4 and T.sub.