Showing papers on "Demodulation published in 1975"

Spread spectrum demodulator

Abstract: Demodulation of a wideband spread spectrum four-phase PSK (phase shift keyed) modulated carrier signal is accomplished by means of a correlator which phase shifts the modulated carrier signal as a function of a locally generated PN (pseudo-noise) sequence to provide a narrow band two-phase PSK modulated carrier signal. The two-phase modulated signal is fed to a matched filter wherein undesired signal components are removed so as to provide an IF (intermediate frequency) signal. A carrier recovery phaselock loop demodulates the two-phase modulated IF signal to provide a baseband signal. A timing recovery loop operates upon the baseband signal to provide timing signals for the locally generated PN sequence to synchronize the local PN sequence with the modulated carrier sequence. A bit timing loop and a sample and hold means operate upon the baseband signal to detect the modulating data to provide an output signal which is a function of the modulating data.

Methods and apparatus for reducing intelligible crosstalk in single sideband radio systems

Abstract: Intelligible crosstalk in microwave radio systems employing single-sideband modulation is substantially eliminated by phase-modulating the AM carrier-wave prior to its modulation by the baseband signal. The phase-modulation may comprise a periodic signal, such as a single sinusoidal tone or pseudo-random noise, or it may comprise an aperiodic signal such as a truly random noise. In this latter event, the coding signal is transmitted to the receiving location to ensure proper demodulation of the encoded signal.

Current carrier communication system

Abstract: A current carrier communication system for selectively transmitting binary electrical signals from a first location to a second location over the AC power lines in a AC power distribution network in a building comprising a first tone generating means operatively connected to a first source of binary electrical signals for generating a first tone signal at a first frequency, a second tone generating means operatively connected to a second source of binary electrical signals for generating a second tone signal at a second frequency, linear tone summing means operatively connected to the first and second tone generating means for generating a modulating signal output that is a linear sum of the first and second tone signals, a source of RF signals connected to said linear tone summing means to produce a modulated RF output signal modulated by the modulating signal output of the linear tone summing means to the AC power lines, receiver coupling means at said second location directly coupled to receive said modulated RF output signal therefrom, a TRF multi-stage receiver connected for receiving the modulated RF output signal from the AC power lines and producing an amplified modulated RF output signal corresponding to the received modulated RF output signal, demodulation means operatively connected to the TRF receiver for demodulating the received signal, a first phase locked loop detector connected to the demodulation means for detecting the presence of the first tone in the demodulated signal and a second phase locked loop detector connected to the demodulation means for detecting the presence of the second tone in the demodulated signal.

Compatible stereophonic receiver

Abstract: A compatible stereophonic receiver capable of receiving a monaural signal, 2-channel stereophonic composite signal and multi-channel composite signal transmitted in the frequency modulated form, which comprises a plurality of band amplifiers each having a bandwidth different from each other so as to amplify an intermediate frequency signal including any of the above-mentioned signals; a discriminator for determining whether the signal received is a monaural signal, 2-channel composite signal, or multi-channel composite signal; and means for selectively connecting a band amplifier which has a bandwidth corresponding to an output signal from the discriminator to a multiplex demodulator through a frequency modulated wave detector and controlling the multiplex demodulator to demodulate an audio signal from the output of the frequency modulated wave detector.

Remote ECG monitoring system

Abstract: A remote ECG monitoring and telemetry system for use in a hospital equipped with a master antenna television cable system comprising a portable patient sensor/transmitter unit for deriving ECG information and for transmitting a first frequency signal modulated with the ECG information; a receiver/transmitter unit positioned in the patient's room for receiving the first modulated signal and for coupling directly to the master antenna television cable a second frequency signal modulated with the ECG information; a converter/amplifier unit coupled to the master antenna television cable adjacent the head end thereof for receiving the second modulated signal and for coupling back into the master antenna television cable a high power, third frequency signal modulated with the ECG information; and a receiver/demodulator unit coupled to the master antenna television cable at a central monitoring station for receiving and demodulating the third modulated signal to derive the ECG information.

Universal automotive electronic radio

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.

Complex Demodulation of Geomagnetic Data and the Estimation of Transfer Functions

Abstract: Summary Complex demodulation is a technique that allows the examination of the variation with time of the amplitude and phase of selected frequency components of a time series. Complex demodulates can form the basis for estimates of the power spectrum of the time series. They are computed most efficiently by the use of the Fast Fourier Transform. Two examples of the application of complex demodulation to the analysis of geomagnetic time series are given. In the first example, the technique is used to demonstrate the modulation of a periodic phenomenon, the daily variation, by mechanisms with apparent periods of 6 months and 27 days. The second example, discussed in greater detail, is an application to the calculation of Geomagnetic Deep Sounding transfer functions. The spectra of simultaneous records of variations in the three components (H, D and Z) of the magnetic field recorded at a single station are divided into bands, and each band demodulated in turn. The polarization azimuth of the horizontal field at each instant of time can be computed, and, for the example considered, the azimuth tends to be constrained to the north-south direction. The detailed response of the local conductive structure to different source field polarizations can be demonstrated. Everett & Hyndman's Unit Vector Method is used to investigate the effect of the observed bias in the azimuth of the source field on estimates of GDS transfer functions made by conventional methods. The demodulates can be used to devise criteria for selecting events according to their signal/noise ratio. The selection procedure is most useful when applied to records containing only sporadic activity in the frequency band of interest.

Demodulator for combined digital amplitude and phase keyed modulation signals

Abstract: A digital carrier signal demodulation circuit is used in the carrier digital transmission system utilizing a 16-ary APK (Amplitude and Phase Keying) signal produced by the vector superposition of a second path signal consisting of a four-phase shift keying signal upon each phase of a first path signal consisting of a four-phase shift keying signal, the level of the second path signal being lower than that of the first path signal. The received 16-ary APK signal is detected with the reference carrier extracted from the received signal, regenerated to reproduce the base band pulses of the first path signal. The recovered base band pulses remodulate the reference carrier to produce the first path signal. The phases of the recovered first path signal and received signal are compared to phase lock a voltage controlled oscillator thereby producing the reference character.

An Optimal Phase Demodulator

Abstract: : The paper presents the results of an investigation on the optimal performance of the phase demodulator using Bucy's non-linear filtering theory. A cyclically optimal non-linear phase estimation technique was developed for modular phase tracking. (Author)

Discrete frequency colorimeter

Abstract: A compact and portable colorimeter, including an integrally-formed probe having both a solid-state source of relatively monochromatic light and an optically coupled photodetector mounted therein. A power oscillator gating means is connected to the light source for pulsing same, to provide a chopped optical input. A demodulating circuit receives the output from the photodetector. The power oscillator gate signal is provided to a synchronous detector at the demodulating circuit, to synchronize detection with the chopping. The output from the demodulator is converted to a signal and read-out indicative of the concentration of that component of the sample which has absorbance characteristics correlated with the wavelength of the monochromatic source. The light source may comprise an LED, a laser diode or the like; and a tunable diode or array of LED's may also be used so as to enable a plurality of discrete frequency outputs, which outputs correlate with a plurality of chemical species the concentrations of which are to be determined.

Multi-phase and multi-amplitude level modulator and modulation and demodulation methods

Abstract: A multi-phase, multi-amplitude level modulation method, and modulator, is provided which produces a three-level, ten-phase modulated carrier. The carrier is modulated in three amplitude levels, viz., off, intermediate and high and in ten phase positions, to produce sixteen signal states, one state corresponding to the carrier being off, five intermediate amplitude level states having five equally spaced phase positions, and ten high amplitude level states having ten equally spaced phase positions. A number of different four digit binary coding schemes for the sixteen signal states are disclosed together with other different coding and modulation techniques.

On optimal soft-decision demodulation

Abstract: Wozencraft and Kennedy have suggested that the appropriate demodulator criterion of goodness is the cutoff rate of the discrete memoryless channel (DMC) created by the modulation system; the criterion of goodness adopted in this paper is the "symmetric" cutoff rate which differs from the former criterion only in that the signals are assumed equally likely. Massey's necessary condition for optimal coherent demodulation of binary signals is generalized to M -ary signals. It is shown that the optimal demodulator decision regions in likelihood space are bounded by hyperplanes. An iterative method is formulated for finding these optimal decision regions from an initial "good guess." For additive white Gaussian noise (AWGN), the corresponding optimal decision regions in signal space are bounded by hypersurfaces with hyperplane asymptotes; these asymptotes themselves bound the decision regions of a demodulator which, in several examples, is shown to be virtually optimal. In many cases, the necessary condition for demodulator optimality is also sufficient, but a counterexample to its general sufficiency is given.

Electro-optical ranging system for distance measurements to moving targets

Abstract: An electro-optical ranging system for taking rapid measurements of the distance to a moving target object, such as a rotating log whose cross-sectional configuration is to be determined prior to the performance of a processing operation thereon. An electro-optical transceiver illuminates a small portion of the target object with a narrow beam of light modulated by a reference R-F signal. Light reflected from the target object is received by a telescope in the transceiver and focused upon a photodetector for demodulation to generate a detected R-F signal. The distance to the object is then determined by measuring the relative phase of the reference and detected signals. First, a preliminary measurement is made by adjusting the relative phase of the two R-F signals, using a calibrated, digitally-controlled phase shifter, until the output of a comparator circuit is as nearly null as possible without exceeding a digital input word to the phase shifter corresponding to a distance less than or equal to the target object. The average amplitude of the comparator output signal corresponding to the aforementioned preliminary digital word is determined, and the average comparator output corresponding to the preliminary digital word as modified by the arithmetic addition of one bit thereto is next determined. The actual distance to the surface of the target object is then calculated by interpolating between the two resulting digital words to find an equivalent digital word corresponding to a null phase-comparator output. Parallax error is minimized and the signal-to-noise ratio of the detected signal is maximized by transmitting and receiving the light along a coaxial path. Errors due to changes in the D-C offset of the comparator output are eliminated by A-C coupling the comparator's input and output utilizing a chopper stabilization circuit. Automatic calibration of the system is accomplished by an electro-mechanical shutter, which upon command cuts off the transmitted beam to zero the transceiver, and an electro-mechanical mirror which upon command deflects the transmitted beam through a fiber-optic tube of known optical length to the photo-detector for enabling a calibration factor to be calculated. Control of the operation of the transceiver and calculation of the measured distance to the object is accomplished by a digital computer.

Pulse width modulated signal amplifier

Abstract: A pulse width modulated signal amplifier system includes a signal input circuit, an amplifier for receiving an input signal from the signal input circuit, a pulse width modulator for receiving an output signal from the amplifier and producing a pulse width modulated signal, and a phase splitter for receiving the pulse width modulated signal and producing a pair of corresponding pulse width modulated signals having different polarities to each other. The system further includes a first demodulator for receiving one of the pair of pulse width modulated signals and demodulating a first output signal having one polarity and an amplitude in response to the input signal, a second demodulator for receiving the other of the pair of pulse width modulated signals and producing a second output signal having the other polarity and an amplitude in response to the input signal, a load supplied with the first and second output signals, an amplitude comparator for comparing the first and second output signals and producing a control signal in response to the comparison result, and a feedback circuit for receiving the control signal and applying it to the amplifier so as to balance the first and second output signal amplitudes.

Phase locked loop with circuit for preventing sidelock

Abstract: A side lock detector to prevent side lock in coherent PSK demodulation. For demodulation purposes it is necessary to recreate the carrier at the receiver. This may be accomplished with a phase-locked loop. However, with plural phase PSK modulation the input signal to the phase-locked loop has energy at side bands spaced at modulation rate intervals from the desired lock frequency as well as at the desired lock frequency. To detect side band lock, a band pass filter monitors the phase detector output of the phase-locked loop. The center frequency of the filter is equal to the modulation rate and the filter band width is very narrow. Only during side lock will significant amounts of energy pass the filter. This energy may be detected by a simple diode detector or the like. A lock inhibit means is provided, responsive to the output of the detector, to drive the voltage controlled oscillator out of a side lock condition.

Compatible AM stereophonic receivers

Abstract: Compatible AM stereophonic receivers for reception of a radiant energy carrier wave modulated with two stereo related signals (L and R), each appearing as a respective first order single-sideband. Receivers embodying the invention in general improve an optimize output stereo signal quality by quadrature demodulation of the carrier to derive the stereo difference (L-R) signal, together with in-phase detection of the stereo summation (L+R) signal, the L+R and L-R signals thus derived being placed in phase and combined through sum and difference circuits to obtain the stereo related (L and R) outputs. Demodulation distortion may be minimized by inverse amplitude modulation of the carrier wave with a portion of at least the envelope fundamental (and preferably also one or more harmonics thereof). The carrier wave is preferably enhanced prior to quadrature demodulation and preferably is also modulated with an infrasonic frequency (e.g. 15 Hz) signal indicating stereo signal presence, with such infrasonic modulation either amplitude modulating or phase modulating the carrier wave. Such infrasonic modulation is utilized to automatically switch receiver output mode and to visually indicate stereo signal presence.

Method and apparatus for demodulation of relative phase modulated binary data

Abstract: A phase modulated carrier wave, in which a phase reversal represents one of two binary values is demodulated by sampling at a rate f s greater than the frequency of the carrier, comparing the phase of each sample with a sample delayed a nominal bit period in one channel, a sample delayed less than the nominal bit period in a second channel, and a sample delayed more than the nominal bit period in a third channel to compensate for positive and negative Doppler shift of the carrier from its nominal frequency in the second and third channels, respectively. A code word is detected in each of the three channels by comparing each demodulated sample bit with a replica of the code word, and correlating the results separately for each channel. The channel with the highest correlation is selected as the one most closely tuned to the carrier frequency received.

Digital demodulator for differentially encoded phase-shift-keyed data

Abstract: A demodulator for differentially coherent phase-shift keyed data signals correlates samples taken in consecutive baud intervals. Depending on the results of at least two such correlations or lack thereof, counts are registered in unidirectional counters supplied with thresholds related to preassigned counts per baud interval. Bistable circuits respond to the attainment, or failure of attainment, of the threshold-count levels during each baud interval, after which the counters are reset to a reference level. The states of the bistable circuits directly represent binary data without further logic operations in the four-phase case particularly.

High-speed Manchester code demodulator

Abstract: A demodulator for decoding the Manchester code is described in which the bit rate is maximized by using a one shot set up for a pulse width less than one-half the bit period. Control of the one-shot is established so that it is clocked at the bit rate but not at twice the bit rate, in order to receive high data rates serially over a single fiber optic channel.

Automatic one-per-rev control system

Abstract: Vibration in the helicopter fuselage produced through the helicopter rotor at a frequency of one for each rotation of the rotor (commonly identified in the art as a one-per-rev vibration) is controlled by applying a correction signal to the primary cyclic control system of the rotor assembly. To generate the correction signal, a transducer responds to the one-per-rev vibrations to generate a signal coupled to circuitry for generating a vibration related signal dependent upon the amplitude and phase of the one-per-rev vibrations. The vibration related signal is applied to a sample and store network wherein it is demodulated by a reference signal related to the rotational speed of the helicopter to establish a control voltage which varies at a rate in dependence upon variation in the maximum amplitude of the one-per-rev vibrations. This control voltage is integrated and modulated by the reference signal thereby resulting in the correction signal for application to the primary cyclic control system. The reference signal for both the demodulation and modulation steps is generated by combining a reference pulse having a phase corresponding to a desired cyclic pitch generated for each revolution of the helicopter with a pulse train synchronized with the reference pulse at a repetition rate related to rotation of the helicopter rotor. In one embodiment of the invention a manually adjustable ride control voltage is generated that has a magnitude related to a desired vibration correction. This ride control voltage is switched alternately with the control voltage to be modulated by the reference signal.

System for generating an angular rate signal from an angular position signal utilizing a constant amplitude-variable carrier phase signal

Abstract: The instant invention relates to turn-rate signal generating circuitry for interrupting slaving of the directional gyro and roll erection of the vertical gyro in a heading, attitude and reference system whenever the turn-rate of the vehicle on which the system is mounted exceeds a predetermined rate. Cutoff of slaving and roll erection eliminates acceleration induced dynamic errors produced by excessive turn rates and is effectuated in response to a turn-rate signal (i.e., an angular rate signal) generated indirectly from angular position (i.e., shaft position) information. The angular position information is in the form of carrier signals amplitude modulated as a function of the sine and cosine of the angle θ. These signals are converted to modify the carrier phases so that they are respectively sinusoidal and cosinusoidal functions of the carrier frequency. The sinusoidal and cosinusoidally varying carrier signals are combined to produce a constant amplitude, variable carrier-phase signal, the phase of which is directly proportional to the shaft angle θ. The constant amplitude variable phase carrier is processed in a phase-to-pulse width converter to produce an output pulse which is proportional to the angle θ. This signal is differentiated and filtered to produce a varying DC signal proportional to the angular rate of change (dθ/dt). The rate signal is compared with a reference signal to determine when the rate of angular change exceeds a predetermined value to actuate turn-rate cutoff. By virtue of this novel arrangement, which does not require demodulation of the amplitude modulated carrier signal which represents angular position, the system is insensitive to variations in the excitation voltages for the electromechanical devices, such as synchros or the like, which produce the angular position signals.

A Digital Block-Processor for SSB-FDM Modulation and Demodulation

Abstract: A new algorithm is proposed for the digital implementation of the M -channel SSB-frequency-division multiplexing (FDM) modulator and demodulator, which is computationally attractive and inherently insensitive to parameter quantization.

Circuit for transforming rectangular coordinates to polar coordinates

Abstract: A circuit for transforming to polar coordinate form first and second binary number electrical signals representative of rectangular coordinates or quadrature components for a vector or phasor. The circuit utilizes a programmable memory in which values corresponding to the sine and cosine functions are stored. In the preferred form, the circuit utilizes binary number electrical signals of 10 bits. The most significant bit of the polar coordinate angle is found directly from the binary number representing one of the quadrature components, whereas the next two most significant bits of the angle are found using logic circuitry in association with the binary number signals representing the quadrature components. The remaining bits of the angle are found by use of a successive approximation technique in conjunction with the values stored in the memory. Once the angle is determined, the amplitude of the vector or phasor is determined by the use of the function P = Im(sinθ) + Re(cosθ) where Im and Re are the quadrature components. The coordinate transforming circuit is particularly useful in digital transmission and receiving systems in connection with modulation of transmitted signals and demodulation of received signals.

Multi-phase PSK demodulator

Abstract: A synchronized carrier recovery circuit for a PSK modulated signal includes a plurality of phase detectors supplied with the PSK input signal and phase shifted outputs from a voltage controlled oscillator. The detector outputs are rectified and alternately coupled to a pair of adders whose outputs feed a complimentary subtractor. The detector outputs are also converted to digital form and fed to an Exclusive OR circuit, whose output couples the appropriate subtractor outputs to the VCO to achieve phase locked synchronization.

Direction finding receiver

Abstract: A direction finding receiver contained in a hand held portable housing with a ferrite rod antenna mounted in and protruding through the housing so that when the antenna axis points to the radio frequency signal source to be direction found, a null is obtained in the signal level. The antenna is coupled to the receiver circuit which comprises a broadband fixed tuned radio frequency amplifier having low sensitivity, a modulation oscillator used to modulate the broadband fixed tuned rf amplifier by tone injection when a steady carrier is present, a demodulator for demodulating the rf signal, and an audio amplifier for amplifying the demodulated signal.

Noise-cancelling apparatus for FM stereo receiver

Abstract: A noise-cancelling apparatus for use in an FM stereo receiver. This apparatus blends the signals of the left and the right channels of the receiver with each other substantially evenly throughout the entire audio frequency range of such signals so that noise components are cancelled with each other and S/N ratio is improved. This blending is accomplished either by connecting the output terminal of the left channel to the output terminal of the right channel by a common resistor, or by causing a decay, through a filter, of those frequency components higher than the pilot signal frequency among the input signals of the multiplex demodulator provided in the FM stereo receiver.

Drop out compensation device

Abstract: A device for compensating dropouts in color television signal modulated by a carrier wave. The modulated video signal is applied to a first delay line, from whose output signal a luminance component delayed by one line period is derived with the aid of a demodulator, and is also applied through a second demodulator and a chrome separating filter to a second one line delay line. The sum of the delayed chrominance and luminance components are substitution for the demodulated color television signal during a dropout.

Transceiver having improved voice actuated carrier and echo suppression circuit

Abstract: A transceiver comprising a transmit circuit for receiving a transmit audio frequency signal from a voice input transducer and including a delay line for delaying the transmit audio frequency signal, a modulator for converting the delayed transmit audio frequency signal to a transmitable radio frequency signal and a first switchable attenuator responsive to a control signal and operative to selectively couple the radio frequency signal to an output terminal for transmission; a receive circuit for receiving a responsive radio frequency transmission and including a demodulator for converting the received radio frequency signal to a received audio frequency signal, and a second switchable attenuator responsive to the control signal and operative to selectively couple the received audio frequency signal to a voice output transducer; and a control circuit including a transmit detector for detecting the transmit audio frequency signal level, a receive detector for detecting the received audio frequency signal level, and a comparator for comparing the outputs of the transmit detector and receive detector and developing the control signal.

Double sideband transmission system

Abstract: An improved system and method for processing and amplifying double-sideband suppressed or reduced carrier waves using high efficiency amplifiers and not requiring frequency dividers. Typical practice of the invention involves generating a double-sideband suppressed carrier wave in a balanced modulator; for example, at a sub-harmonic carrier frequency and multiplying the frequency of the output of the balanced modulator by an odd multiplication factor greater than one in the modulated amplifier. The required envelope modulation (amplitude modulation) component is derived from the original balanced modulator output by use of an envelope demodulator and the component is used to modulate the modulated stage so as to reproduce the double-sideband suppressed carrier wave at a high power level. This invention may also be used in reduced carrier double-sideband transmitters; i.e., where the carrier is not fully suppressed but where the carrier is smaller in amplitude than the peak amplitude of the combined upper and lower sideband waves.