Abstract: In a circuit arrangement for sampling a ternary signal, this ternary signal is divided by amplitude decision circuits into two binary signals and the binary sub-signals are sampled at m-times the rate of the symbol clock. The binary samples of each sub-signal are shifted through a shift register having at least m stages and intermediately stored in a buffer store for one period of the symbol clock. With the aid of a logic circuit it is then determined in which regions of the buffer store accumulations of identical binary values occur. Regions in which the accumulations always re-occur--the number of occurrences is checked by means of counters--are considered to be eyes of the ternary signal. In each clock period of the synbol clock, a sample falling within the eye of the ternary signal is transferred from each buffer store at an output of the circuit with the aid of a gate circuit.
Abstract: Several forms of a novel amplitude-modulated (AM) signal format are disclosed. Circuits of several types for generating the desired special vestigial-sideband (SVSB) AM waveforms are discussed. The principal form of the SVSB modulation provides for a reduction in transmitted signal bandwidth compared with standard double-sideband techniques plus very linear amplitude characteristics with simple synchronous detectors. Circuits according to the invention may also include means for dynamically varying signal bandwidth to accommodate special applications.
Abstract: An improved transmitter circuit for rf modems usable for communication in local area computer networks is provided. The transmitter circuit includes a digital/analog conversion circuit for generating a frequency modulated carrier from an input data signal, and a switched linear amplifier for amplifying and controlling the frequency modulated analog signal under the direction of the LAN protocol. The conversion circuit includes a time balanced compensated switching circuit for maintaining duty cycle integrity, while the switched linear amplifier provides on/off carrier control and level adjustment with minimum signal distortion including switching transients, and with minimum spurious signal leakage when off.
Abstract: Methods for modulating and demodulating digital data streams utilize a quadrature-quadrature phase shift keying data transmission arrangement to achieve a 100% increase in the bandwidth efficiency over known systems, such as minimum shift keying. Known arrangements utilize two dimensional data transmission. However, Q.sup.2 PSK, in accordance with the invention, provides four dimensional transmission which doubles the rate of data transmission for a given bandwidth, at the expense of approximately 45% increase in the average energy per bit. The input data stream is demultiplexed to form four demultiplexed data streams which are formed of demultiplexed data bits. Each such data stream is combined with a signal having carrier and data pulse-shaping components. Additionally, the data pulse-shaping components have a quadrature phase relationship with each other, thereby adding the additional two dimensions of data transmission capacity.
Abstract: A stream of high-speed bipolar signals transmitted along standard twisted pair telephone wiring are detected by a circuit that includes a pair of differential amplifiers each having a signal input connected directly to one conductor of the twisted pair and a reference input connected through a peak voltage detector to the opposite conductor. The amplifiers function as an input signal comparator which generates a corresponding bit stream of logical ones in response to the bipolar signals that exceed 50% of the average peak voltage input. A threshold bias voltage corresponding to positive going signals on each conductor is generated by the detector and charges separate capacitors that connect each reference input to its conductor. The bias voltage and bipolar signals input to each amplifier are algebraically summed which doubles the differential input signal and results in an increased signal to noise ratio of about six decibels.
Abstract: A multiplex communication system comprises a central control unit, a plurality of local control units, an optical loop transmission path interconnecting the central control unit and the plurality of local control units by optical fibers in a loop-like configuration to thereby cause data transmission to be effected among the control units through the optical fibers, and an electrical loop transmission path for interconnecting the central control unit and the plurality of local control units by electrical signal conductors in a loop-like configuration to thereby cause data transmission to be effected among the control units through the electrical signal conductors, wherein the central control unit selects at least one of the optical loop transmission path and the electrical loop transmission path to be connected to the signal transmitter means in dependence on predetermined conditions, so that data transmission is conducted between the central control unit and the local control units through the selected loop t
Abstract: A PSK carrier recovery system has a frequency multiplier, a filter circuit and a limiter circuit for producing a double frequency signal from the incoming PSK signal. A pair of demodulators are supplied with the double frequency signal and with 0 and 90 degree phased reference signals of the same frequency to produce two output voltages representative of the phase of the incoming PSK signal. The output voltages are supplied through a pair of low pass filters at baseband frequency to a pair of remodulators which are also supplied with the reference signals. The outputs of the remodulators are added and applied to a filter, a limiter, a phase adjuster to compensate for processing delays and to a divide by 2 frequency circuit. The reconstituted signal has a frequency substantially equal to the incoming PSK signal and has a phase equal to one of the phases thereof. The incoming PSK signal is also supplied through a limiter to a demodulator circuit along with the reconstituted signal for demodulation.
Abstract: A fabric headband which incorporates a replaceable thermal cartridge and is integrated with a miniature radio set whereby when the band is worn about the head as a crown, it then provides beneficial thermal effects as the wearer listens to the radio through a pair of earphones which depend from the crown. The headband is constituted by a central pouch adapted to receive both the cartridge and a flexible card in front thereof having a metallized face, and a pair of hollow fabric wings extending from opposite ends of the pouch. When the band is encircled about the head and the wings are joined to define the crown, the cartridge in the pouch then lies in heat-exchange relationship with the brow of the wearer.
Abstract: An optical transmission network for transmitting information between two locations is disclosed. The transmission network comprises a collection of individual two-way links with all optical sources at one end.At a first location, the outputs of at least two lasers, operating at first and second wavelengths respectively, are multiplexed together, the resulting optical power being divided between a plurality of single mode optical fiber transmission paths. Each optical transmission path may include a wavelength selective modulator for modulating information onto the first wavelength for transmission from the first location to the second location.At the second location, the wavelengths are separated and the information modulated onto the first wavelength is detected. The second wavelength may be modulated with information to be transmitted back to the first location. No dedicated laser is required at the second location.
Abstract: In a local area network (LAN), of the Ethernet type, one of the segments, i.e. one bus, is replaced by a star coupler connected via optical fibre pairs to a number of stations. Each pair includes a GO fibre and a RETURN fibre. As in the usual Ethernet system, collision detection relies on measuring signal level on the medium, if it is too large then a collision condition exists.In an optical fibre system a similar collision detection technique is used. To detect collision, it is nescessary to be aware of the network's attenuation as "seen" by the station. To do this a low level pilot tone is sent from each station, each station having its own tone frequency. The amplitude of this tone when it returns to its own station indicates the system's attenuation, and this is used to detect collision.In an alternative the pilot signals are pseudo-random bit sequences.
March 7, 1985
Date of Patent:
February 3, 1987
International Standard Electric Corporation
Abstract: The apparatus includes circuits for detecting sequential carrier phases of a complex baseband signal and storing the detected carrier phases. A phase predictor is responsive to the detected carrier phases for producing a predicted carrier phase. A circuit is also provided for compensating for a carrier phase deviation of the complex baseband signal in response to the predicted phase. An error detector detects an error associated with data discriminated from the complex baseband signal and a controller controls the phase predictor to minimize the error.
Abstract: A framing code detector includes a shift register supplied with a received framing code and a number of EX-OR gates each having one input connected to a respective stage of the shift register and another input which is supplied with a respective bit of a stored pattern having the inverted form of the anticipated framing code to be received/ a counter is provided for counting the number of times all outputs of EX-OR gates become "1" during a predetermined period, and an identification signal is produced when the count value of the counter is greater than a predetermined value.
September 24, 1984
Date of Patent:
January 20, 1987
Hitachi, Ltd., Hitachi Video Engineering, Ltd.
Abstract: A hybrid ring mixer includes an annular conducting ring on a gallium arsenide substrate coated on the bottom with a conducting layer to comprise a strip transmission line. Three conductors spaced by 120.degree. extend radially outward from the annular ring to define local oscillator, signal input and i-f ports, respectively. A pair of conductors spaced by substantially 120.degree. extend radially inward to comprise diode ports. A conducting surface inside the annular ring is grounded and has circular sectors of different radius bounded by radii extending from the center of the ring and bisecting the signal and local oscillator ports, respectively. The sector of larger radius is located in the 120.degree. sector between the signal and local oscillator ports. Mesa diodes are connected between each of the diode ports and the sector of smaller radius.
February 8, 1985
Date of Patent:
January 13, 1987
Alpha Industries, Inc.
Ian Crossley, Daniel Donoghue, Steven Mittleman, Seth Nash
Abstract: An overload protector, using a power-dissipating element for receiving and dissipating excessive radio-frequency power, can safely transfer a signal from an input to an output. The protector also has a detector coupled to the input for providing a bias current in response to an input signal in excess of a predetermined magnitude. Also included in a diverter coupled to the input, the output, the power-dissipating element and the detector. This diverter can receive the bias current and can, in response, redirect power at the input from the output to the power-dissipating element.
Abstract: A phase-locked loop (PLL) for use in decoding MFM data recordings. The loop uses a counter to generate timing signals which divide bitcells into data and clock windows and which define times within these windows at which transitions in the MFM signal are expected to occur. Data and clock windows of differing relative size are readily accomodated. The PLL has two synchronization modes: one mode allows the PLL to take maximum advantage of both data and clock transitions which occur when reading actual data; a second mode is used during the synchronization period at the beginning of a data block and allows the PLL to lock quickly yet assure that it will lock to the bit frequency and not lock to harmonics or beat frequencies. A charge pump generates the PLL error signal by responding to pump-up and pump-down control signals which are set and cleared in response to the timing signals from the counter and in response to the detection of transitions in the input signal.
Abstract: A portable radio used with this invention has two different types of antenna, such as a monopole antenna and a loop antenna. The diversity reception system continuously selects that one of the antenna which provides the better received signal. Antenna selection is performed such that the received signal level is compared with two or more preset threshold levels, and antennas are switched when and only when the received signal level fails to satisfy certain predetermined conditions.
Abstract: This invention pertains to a method and system for transmitting high speed data from a transmitter to a receiver over several low speed data channels. At the receiver end the differences in the transmission times between data channels are detected and the signals from the faster data channels are delayed to insure that the output high speed data stream is correctly assembled. The differences in the transmission times are monitored during data transmission and if a change is detected the transmission is interrupted and retraining is requested.
Abstract: Disclosed is a digital phase-locked loop circuit for telecommunication circuits receiving bipolar codes. The digital phase-locked loop circuit includes a transition timer means for counting a transition duration between a high mark and a low mark in said bipolar code. A clock recovery signal is generated by dividing a transition duration by a value, such as two, to indicate an apparent zero crossing time, and comparing the apparent zero crossing time with the reference clock in the circuit receiving the bipolar code. The reference clock in the receiving circuit is adjusted in response to the clock recovery signal in order to maintain the reference clock substantially in phase with the incoming bipolar code.
Abstract: A squelch circuit in which a phase locked loop (PLL) (5) having a voltage controlled oscillator (VCO) (7) and a phase comparator (10) is used to detect the number of zero crossings, these being low for a speech signal and high for noise. The error voltage produced in the phase locked loop (5) is fed through a network (12) which ensures that the matching of the input signal to the oscillator is faster when the input frequency drops than when the input frequency rises. The input signal is clipped to enhance the frequency spectra of speech by using a limiting amplifier. The muting gate (2) output is derived from the VCO (7) control voltage of the PLL (5) to mute the output of the receiver when the VCO (7) output frequency is higher than a pre-set frequency for more than a pre-set time.
Abstract: A system for transmitting television signals on a radio link. The system includes a transmitter having a modulator for modulating a carrier signal to produce a vestigial sideband amplitude modulated signal for transmission. The modulator includes a first converter for converting the frequency of video signals to an intermediate frequency and a second converter for converting the intermediate frequency of the video signals to a radio frequency. The system further includes a receiver having a demodulator for demodulating a received vestigial sideband amplitude modulated signal. The modulator includes a Nyquist filter connected between the first and second converters, and the demodulator includes a filter having a rectangular characteristic for processing the signal to be demodulated.