Showing papers on "Demodulation published in 1979"

High speed modem suitable for operating with a switched network

Abstract: A high speed modem suitable for operating with a switched network and capable of achieving essentially 9600 bit per second information transfer rate through the switched telephone network. The high bit rate is achieved notwithstanding the variations in the characteristics of the switched telephone network by phase and amplitude modulating a plurality of sub-carriers (39) at a relatively low baud rate. Correlation detection (35) is employed at the receiver (33-38) to extract or demodulate the information contained in the various sub-carriers. To allow correlation detection with orthogonal signals, each of the sub-carriers is harmonically related to a fundamental which fundamental is, however, slightly higher than the baud rate. This allows the receiver (33-38) to delay correlation for a "gap" time, which reduces the effect of transients produced by modulation and also provides greater tolerance to inter-symbol distortion. Since the fundamental of all the sub-carriers is higher than the baud rate, the receiver "sees" orthogonal signals during the integration or correlation time which is maintained as the period of the fundamental. In addition to the information sub-carriers, a pair of unmodulated sub-carriers (36) are also transmitted to enable the receiver to maintain the correlation interval in proper synchronization with the transmitter, and to correct for phase distortion and frequency offset.

Baseband DC offset detector and control circuit for DC coupled digital demodulator

Abstract: The digital demodulator produces an information bearing analog signal which is controlled in peak-to-peak amplitude. The signal is coupled to a soft-decision demodulator which provides a multi-bit output representative of magnitude (polarity and amplitude) of the analog signal at a rate determined by the symbol clock derived from the digital demodulator. Logic means produces a logic signal of a first or second type in response to selected multi-bit outputs of the soft-decision demodulator. A logic output of the first type is produced if either the multi-bit output represents an analog signal of one polarity and amplitude greater than a predetermined amplitude, or if the multi-bit output represents an analog signal of the other polarity and amplitude less than an equal predetermined amplitude of the other polarity. The logic output is coupled to an integrating means which produces a control signal representative of deviations of the logic signal of the first type from 50% duty cycle. The deviation from 50% duty cycle determines the amplitude of the DC offset, and the polarity of the deviation determines the polarity of the offset. The output of the detector can be used in a feedback loop to eliminate the DC offset by coupling the control signal to a summing junction, to which is also coupled the analog signal.

Differential Detection of MSK with Nonredundant Error Correction

Abstract: A proposed scheme for differential detection of MSK with nonredundant error correction utilizes the output detected from the difference in phase between alternate signaling intervals, along with the output of the conventional differential detector, in accordance with the concept of a convolutional error correcting code. Theoretical analysis and experimental results show that the degradation from coherent detection is about 0.1 dB at a 10 dB signal-to-noise ratio.

Coherent phase shift keyed demodulator for power line communication systems

Abstract: An apparatus and method for coherent phase demodulation of a binary phase shift keyed carrier includes sequentially processing plus and minus polarity samples of plural carrier segments occurring within each carrier data symbol. The samples for each segment provide a binary coded signal for producing corresponding first and second relative phase angle vector signals. The second vector signals are summed over several data symbols to generate reference phase angle signal vector signals. Correlation signals are produced from phase comparison of each of the first vectors with the reference vector signals. The correlation signals are summed in a synchronized relationship for the carrier segments included in each data symbol. The sums of the correlation signals represent either positive or negative correlations with the one and zero data bits of the carrier data symbols.

Phased array radar

Abstract: In a phased array radar system with the radiating elements of the antenna are connected to associated r.f. transmitter-receiver modules. Each of the modules receives a transmitter signal and a local oscillator signal and delivers, upon reception of an echo signal via the antenna an i.f. signal. Furthermore a system of fiber optical waveguides is incorporated to distribute to the modules the transmitter signal and the local oscillator signal, both of which signals being modulated on carriers, which are frequency-matched to the system of fiber optical waveguides. Each of the modules comprises a demodulator to procure the transmitter signal and the local oscillator signal from the applied modulated signals.

QPSK Suppressed carrier with rotating reference phase

Abstract: A suppressed carrier signal is offset quadrature phase shift key modulated so the reference carrier phase is stepped 90° in the same direction in synchronism with sequential bits of a serial data stream and is further bi-phase modulated in response to the binary data source having first or second binary values. A coherent receiver responds to the suppressed carrier signal to establish an equivalent sequence of stepping reference phases at the carrier frequency. The reference phases synchronously rotate in 90° increments in the same direction as the suppressed carrier reference, being permitted a four-fold initial phase ambiguity (0°, 90°, 180°, and 270°). The rotating reference phase is compared in a bi-phase manner with the appropriate component of the suppressed carrier signal to derive sequential d.c. polarities indicative of the binary bit values during the sequential binary data bits.

Method of and apparatus for transmitting and recovering offset QPSK modulated data

Abstract: Bit timing references are derived at a receiver for a carrier modulated by OQPSK. A carrier is transmitted with a constant reference phase modulation during a first interval. During a subsequent, second interval the carrier is transmitted with rotational phase modulation representing binary bit values so that orthogonal components phase modulate the carrier with a predetermined bit sequence. A receiver responds to the constant phase modulated carrier to lock the frequency and phase of a phase lock loop oscillator of a carrier recovery loop. Synchronization at the receiver is achieved in response to a reception of the rotational phase modulation, while maintaining the frequency and phase lock. A carrier recovery loop of the receiver is activated to a decision directed operation after bit synchronization has been achieved. Decision directed operation is achieved by sampling and comparing components derived in orthogonal channels of the carrier recovery loop while the receiver is responsive to the rotational phase modulation. The bandwidth of a filter used in achieving bit synchronization is reduced after there has been a decay of transients in the carrier tracking loop resulting from a transition between locking of the loop and initiation of the decision directed operation. Then the bandwidth of a filter in the carrier tracking loop is adjusted as a function of the quality of the received rotational modulated suppressed carrier.

On-line channel quality monitor for a communication channel

Abstract: An on-line channel monitor, for measuring E b /N O , measures the quality of a communication channel while the channel is in use. The channel monitor employs a soft-decision demodulator so as to compare analog signal levels of an AGC compensated signal in a demodulator with the desired signal level. Deviations, termed pseudo-errors, are counted and the number of counts integrated. The result is employed to drive a meter calibrated in terms of E b /N O .

Contention interference detection by comparison of transmitted and received signal information

Abstract: When a plurality of transceivers share a common communication medium or radio frequency channel, then collision interference will result when two or more transceivers transmit simultaneously. In order to detect this simultaneous transmission, an interference detector apparatus compares the received information after demodulation to that of the transmitted information before modulation. The classification of the distorted signals into either of the two decoded output states permits this interference to be detected with a comparison. The output from the interference detector is used to interrupt the transmitter when collision interference is present on the medium. It is also used to inhibit the receiver from generating erroneous data during the interference duration.

Digital coherent phase demodulator

Abstract: A digital system for demodulating coherent phase shift keyed signals. Maximum likelihood estimates of the unmodulated phase and rate of change of the unmodulated phase of the received signal relative to a local oscillator signal are used to improve the demodulation process. The maximum likelihood estimates are obtained from measurements of the phase of the received signal relative to the local oscillator signal over a predetermined set of keying intervals. The digital demodulation process permits rapid "lock-on" at low signal-to-noise ratios.

Interference eliminator in communication receiver

Abstract: In a communication receiver, a first mixing circuit, a first band-pass filter responsive to the output of the first mixing circuit, a second mixing circuit responsive to the output of the first band-pass filter, a second band-pass filter with a different center frequency from that of the first band-pass filter responsive to the output of the second mixing circuit, a first local oscillator, the output of which is applied to the first mixing circuit and a second local oscillator, the output of which is applied to the second mixing circuit. Various kinds of interference signals are eliminated by changing the output frequencies of the first and second local oscillators to thereby vary the effective bandwidth and center frequency of the signals which can pass through the receiver and thus eliminate interference. In addition, a third mixing circuit is responsive to the output of the second band-pass filter. The output of the third mixing circuit is applied to a notch filter, the notch frequency of which is effectively made variable by changing the frequency injected into the third mixing circuit and a demodulation circuit. Hence, by varying the effective notch frequency, further interference can be eliminated.

Color television receiver comprising at least one integrated circuit for the luminance signal and the chrominance signals

Abstract: A color television receiver is provided having a fully digital color demodulator wherein the luminance signal and the chrominance signals are separated and digitally processed prior to being converted to analog signals.

The Use of Synchronous Demodulation for the Measurement of Eye Movements by Means of an Ocular Magnetic Search Coil

Abstract: This paper describes an eye position monitoring system that can be built using inexpensive components for the demodulator. It uses a two-frequency (f and 2f) technique which provides excellent channel separation with a miinimum of adjustment and wide dynamic signal range. Phasing errors produce no crosstalk effects for a pure sine-wave signal. It should be noted that this system will also work as a single-frequency two-phase system, merely by changing the driver unit.

Shifted sideband beamformer

Abstract: A fundamentally different time domain beamformer structure is described which can be used to process bandpass sensor signals efficiently. The beamformer operates directly on complex, frequency translated, single sideband representations of the input signals to obtain a similar representation of the beam output. Such representations are typically obtained by complex demodulation of the signals to facilitate the use of bandwidth sampling procedures. This new technique, which is referred to as the shifted sideband beamformer, is functionally a time-domain beamformer but it combines attributes of both time-domain and frequency-domain beamforming. Shifted sideband beam-forming has the advantage that beamformer vernier delay and throughput requirements depend on the frequency content of the translated band rather than of the original band. This paper discusses the potential hardware savings associated with shifted sideband beamforming in terms of analog to digital conversion, cable bandwidth, digital processing and, also, signal conditioning hardware. The impact of delay quantization on beam-pattern structure is compared for a shifted sideband and a conventional digital implementation. Beamformer throughput is also analyzed for both implementations. A further reduction in the beamformer throughput requirement is demonstrated by the use of digital interpolation in conjunction with the shifted sideband beam-forming concept.

IC engine knock detector circuit for capacitive sensor - compares filtered and unfiltered demodulator outputs and requires no tuning

Abstract: The device for the detection of knocking in internal combustion engines contains few and economical components and requires no ref. window. If a window is reqd. only one measurement window is necessary. The exact knock frequency does not need to be known for tuning purposes. The time history of the knock signal amplitude is obtd. via a demodulator circuit whose output is filtered by a low pass filter. The outputs of the demodulator and filter are compared in a comparator whose output is tested against an adjustable measurement window. A capacitive detector is used and its impedance may form part of a high-pass or band-pass filter. The low-pass filter and demodulator circuit ref. levels are adjustable. The demodulator may be a rectifier or squarer.

New demodulation scheme for laser-scanned acoustical-imaging systems

Abstract: Several acousto-optical imaging systems are described in the literature where the image information is obtained by scanning a focused beam over a flexible mirror located at the acoustical image plane. The small dynamic deformation of the mirror induces a shallow phase modulation in the scanning beam. This paper describes a time-delay filter that transforms the phase-modulated beam into an amplitude-modulated beam and compares the proposed method with other demodulation schemes described in the literature. Specifically, stability, resolution, sensitivity, and frequency responses are considered.

Electronic traffic control and warning system

Abstract: An electronic system provides traffic control and warning functions by radio transmission of signals to civilian vehicles from authorized mobile units, such as police vehicles and portable units at dangerous locations, such as the scene of an accident or road obstruction, etc., utilizing transmission within a police communications band. Transmitting circuitry carried within the mobile unit includes means for modulating the frequency modulation carrier signal radiated by an antenna with either a voice message or by preselected pulse messages. Receiving circuitry is carried within each of a plurality of civilian vehicles separate from the mobile unit, the antenna of such vehicles picking up the modulated carrier signal when the vehicle is within at least the general vicinity of the transmitting mobile unit. The receiving circuitry provides automatically selective response to the modulated carrier signal regardless of its frequency within the band and includes a demodulator and a pulse separator circuit responsive to a demodulated pulse message. A sequential switching arrangement and signalling devices interconnected with it provide visual signalling in different formats to the operator of the receiving vehicle. A further circuit is responsive also to operation of the sequential switching equipment to interconnect a transducer with the amplified output of the demodulator in response to the detection of a predetermined pulse message of a predetermined second type. Such arrangement allows the operator of the mobile unit, e.g., a policeman, to signal drivers of receiving vehicles by display of visual signals within such vehicles and also to speak directly to such drivers.

Remote telephone system

Abstract: This invention relates to a cordless telephone system which includes a radiophone having a radio transmitter and a radio receiver, and a radio station wired to a communication line having a ratio transmitter and a radio receiver. The radiophone is provided with a means which develops a pulse signal. The means may be a dial thereof, where the pulse signals is to be a dialing signal. The pulse signal is emitted to the radiophone on a carrier wave. The radiophone is provided with a means which detects and responds the pulse signal, and also a means which enables or disables a dialing signal demodulator therein as a function of the response of the means.

Carrier recovery circuit for use in a multi-level phase shift keying demodulator

Abstract: In a demodulator for use with a multi-level phase shift keying (p.s.k.) signal having N phase levels, the p.s.k. signal which includes a carrier signal is frequency multiplied by a factor N in a multiplier filtered and frequency divided by the factor N to enable the carrier signal to be reconstituted at a terminal. To enable the demodulator to work at different data rates, and to enable filters to have sufficiently precise characteristics, the received p.s.k. signal is initially converted to base-band in mixers to which is applied a locally generated signal nominally at the carrier frequency.

Combined coherent frequency and phase shift keying modulation system

Abstract: A system of modulation and demodulation for the transmission of binary data in the presence of multipath. The binary data modulates the phase of the carrier and the same binary data, after a delay of "δ" bits, also modulates the frequency of the carrier. Following reception, the binary data is obtained either by frequency demodulation or by a method of coherent phase shift demodulation wherein the mark or the space frequency is selected for detection of each bit in accord with the bit received "n" bits previously. The system selects between the demodulation methods to obtain one which operates satisfactorily in the instant electromagnetic environment.

Digital demodulator for phase shift keyed signals

Abstract: A digital demodulator for differential phase shift keyed ( PSK) signals (154) includes two pairs of 1-bit integrators (105, 106 and 107, 108) for continuously taking the phase difference between successive DPSK bits. Each DPSK bit is subdivided (100) into a plurality of bits, for example 15 bits. A weighted output signal having 4 bits is provided by each 1-bit integrator for each of the bits corresponding to a DPSK bit. The weighted output signals from each pair of 1-bit integrators are sine weighted and multiplied (118). The products are then added (120) together for application to a comparator (121). The comparator (121) compares the sum of the addition to a predetermined reference signal and provides a demodulated digital signal (155) having a logical state dependent on whether the sum is greater or smaller than the predetermined reference.

Video signal recording and reproducing device

Abstract: PURPOSE:To improve color reproduction in special reproduction by performing the angle modulation of a luminance signal and the low frequency conversion of a chrominance signal and also by recording signals so that a shift of the horizontal synchronizing signal on the adjacent track will be a multiple of one horizontal synchronizing signal interval. CONSTITUTION:A reproduced signal obtained from reproducing head 7 is extracted from a luminance signal through high-pass filter 8 and frequency demodulator 10. A color signal is restored to an original chrominance signal through low-pass filter 9 and frequency converter 11. This restored chrominance signal is applied to adder 12 as it is in normal reproduction. In special reproduction for slow motion, still pictures, etc., it is applied to adder 12 by way of 1H delay line 14. The reproduced signal from head 7 is also applied to flip-flop 20 by way of envelope detector 16, pulse generator 17, integrating circuit 18, and inhibiting circuit 19 and used there as a switching signal for change-over unit 21 to apply adder 12 with a 1H delay signal in the special reproduction. Consequently, the deterioration of reproduced- picture quality accompanying track switching is prevented.

Circuit for recovering the carrier of an amplitude modulated synchronous digital signal

Abstract: The present invention comes within the field of synchronous digital transmission. It relates to the recovering the carrier (which may be suppressed carrier) of an amplitude modulated synchronous digital signal. It provides a circuit which includes an oscillator (41) of adjustable frequency and phase to generate a local carrier, a demodulation circuit whose input(s) receives the local carrier (possibly phase shifted by ±Ψ (42,44,46,47) and the amplitude modulated synchronous digital signal e(t) and control means (48,49) which control the phase and the frequency of the oscillator from the signals delivered by the demodulation circuit and which comprise at least one sign coincidence autocorrelator. It advantageously applies to demodulating amplitude modulated single side band bipolar coded synchronous digital signals.

Universal automotive electronic radio with display for tuning or time information

Abstract: Selected radio circuits are fabricated on modules which plug into a "mother" board located in the radio chassis. The circuitry includes a plurality of RF front ends (including at least one AM and one FM front end), each tunable over a selected radio band by tuner circuitry. The AM front end includes a saturable core reactor whose tuning inductance varies as a function of the tuning current provided to it by a voltage-to-current converter in the tuner. Both AM and FM signals are translated by a frequency synthesizer to a common IF frequency, namely 10.7 MHz. The synthesizer employs a quartz crystal controlled oscillator feeding a phase lock loop whose frequency is varied via the tuning control. Quartz crystal filters for AM, and ceramic filters for FM provide required selectivity. As all signals are at the same IF, a common IF amplifier is employed. Further, a single phase lock loop is adapted to demodulate both AM and FM signals. The resultant demodulated signals are amplified, and tone shaped, via D. C. voltage controlled audio processor circuitry. The audio circuitry is adapted to accept auxiliary inputs, such as the output of a tape player. A digital display senses tuner status providing frequency read out. Additional provisions allow switching the display to read out tape player status, or to provide a time display from an electronic clock.

Carrier regeneration circuit for polyphase modulation system

Abstract: An n (=8, 9)-valued polyphase modulation system having circuit construction for carrier regeneration in which not only correct phase demodulation is effected but also any AM components of the regenerated carrier wave are effectively compensated for and in which the decision circuit is adapted to produce a signal output having no phase ambiguity which is coupled to a π/4 phase modulator unit of the carrier generator to serve as a drive signal therefor.

Method and apparatus for detecting a fluorescent area on a sheet of paper

Abstract: Method for the detection, on a sheet of paper, of an area which becomes fluorescent when it is exposed to ultraviolet radiation, in which the paper sheet passing in front of a detector is illuminated by means of a source of ultraviolet light modulated by a frequency of between 1 and 10 KHz. The modulated fluorescent radiation is detected, amplified and demodulated by means of an amplification circuit and a demodulation circuit providing a first signal. The intensity of the ultraviolet source is measured by a photo-electric member associated with a detection and demodulation circuit supplying a second signal. This second signal is used to regulate the level of operation of at least one trigger which operates to provide an output, corresponding to the fluorescent radiation, when the level of the first signal supplied to the trigger is at at least the trigger operating level.

Electronic gear checker

Abstract: A functional gear checking machine for determining a number of gear characteristics from a composite input signal received from a linear voltage differential transformer is disclosed. The signal from the sensing transformer is coupled to a demodulation circuit which, in turn, is coupled to several types of signal processing circuits, each of which contains a memory, and each of which processes and separates the components of the composite signals in order to provide output signals that are indicative of the desired gear characteristics. The output signals that are developed are a function of the voltage between two reference levels, at least one of which is established by the associated signal processing circuit.

Security identification system using pulse code modulation

Abstract: A security identification system for telephone, teleprinter, computer, and similar communication applications comprising a plurality of transmitter station identification units, one for each transmitter station and each including an identification signal generator for generating a pulse code modulated identification signal, unique to the transmitter station, that comprises a repeating sequence of uncoded signal segments each including N pulse intervals of given duration alternating with coded signal segments each including M pulse intervals of like duration, coding being effected by the presence or absence of pulses in the coded signal segment intervals. Each pulse is transmitted as a burst of cycles of a carrier signal preferably having a carrier frequency above 3 Khz. The system further comprises a receiver identification unit at a receiver station, including a demodulator, an identification control circuit, and a visual display; the control circuit counts the pulse intervals in a demodulated uncoded segment of the identification signal to aid in identifying the beginning of each coded segment and decodes the coded segments, on a redundant basis, to actuate the display and afford a visual identification of the transmitter station.

Mobile radio space diversity system using optical fiber

Abstract: PURPOSE:To make space diversity of the mobile radio system possible by constituting the transmission line between plural base stations and line control base stations by optical fibers and by modulating the light by the carrier frequency or the intermediate frequency and transmitting the light CONSTITUTION:The signal from antenna 13 of mobile station 11 is acquired by antennas of radio base station 12a and line control radio base station 12b The signal acquired by base station 12a is amplified in 14 and is subjected to frequency conversion in 15 and becomes an intermediate frequency signal and is sent to light modulator 16 Light modulator 16 modulates the light by the sent signal and transmits the light signal to base station 12b through optical fiber transmission line 17 Base station 12b demodulates the signal from transmission line 17 by light demodulator 18 into an intermediate frequency signal, and this signal and the intermediate signal, which is acquired from the antenna and is subjected to frequency conversion in 15, are synthesized with the same phase by synthesizing circuit 19 The signal synthesized by circuit 19 is demodulated in 20 and is sent to sound circuit 21 Since receiving signals from respective base stations are synthesized in the intermediate frequency band with the same phase, frequency of level lowering dependent upon fading is reduced

Receiver for data-transmission system operating with single-sideband amplitude modulation

Abstract: A receiver for three-level data signals transmitted by single-sideband amplitude modulation with an attenuated carrier, including an amplitude demodulator driven by the extracted carrier, comprises a phase shifter in the carrier input of the demodulator controlled by a phase-error detector which compares the demodulated baseband signals with a pair of balanced voltage thresholds to correct spurious phase shifts between that signal and the carrier. The phase-error detector receives timing pulses from a sync extractor comparing the baseband signal with two other balanced voltage thresholds and summing the results to control a local oscillator with a phase-locking loop. The phase shifter may be manually precalibrated to maximize the amplitude of a synchronizing signal in the output of the summing circuit of the sync extractor, that amplitude being proportional to the width of an eye diagram obtained from the baseband signal.