Showing papers on "Demodulation published in 1969"

Apparatus for testing modulator demodulator units for transmission errors and indicating the errors per power of 10

Abstract: Test apparatus for testing and recording either accumulated errors or the probability of error for either synchronous or asynchronous digital data modulator/demodulator units (modems). The modem tester includes a test generator which under the control of a bit rate selector and a sequence mode selector generates a bit test sequence. The bit test sequence is modulated by the modulator portion of a modem under test and is then applied to the demodulator portion of either the same or a different modem under test. The modem tester further includes a reference bit sequence generator and a data synchronization network responsive to the bit test sequence after demodulation for synchronizing the reference bit sequence generator with the test sequence received from the demodulator under test. The received test sequence and the referenced sequence are compared with disagreements of the comparison being accumulated in an error counter. For testing asynchronous modems, a bit synchronization network is provided to maintain the sampling window of the comparator at substantially the middle of a bit period. In order to display probability of error, the mode sequence selector is settable to any one of plural total bits indicia expressed as powers of 10 on the display panel. A total bit counter responds to such settings to inhibit further operation of the error counter after a number of bit periods equal to the setting of the selector such that the total errors per power of 10 bits is displayed directly on the display panel.

Frequency-modulation demodulator threshold extension device

Abstract: OCCURRENCE OF A CLICK-TYPE NOISE IMPULSE AND SWITCHING THE FOLLOW AND HOLD CIRCUIT TO THE HOLD CONDITION, WHEREBY THE SIGNAL TRNSFERRED TO THE OUTPUT FILTER IS HELD AT THE LAST PREVIOUT NONCLICK VALUE DURING THE OCCURRENCE OF THE CLICK IMPULSE. A THRESHOLD EXTENSION DEVICE IS CONNECTED BETWEEN THE OUTPUT OF A FREQUENCY-MODULATION DEMODULATOR AND THE INPUT OF THE CUSTOMARY DEMODULATOR OUTPUT FILTER FOR PURPOSES OF MINIMIZING THE OCCURRENCE OF IMPULSE NOISE, USUALLY REFERRED TO AS "CLICK" NOISE, AT THE OUTPUT OF THE OUTPUT FILTER. THE DEVICE INCLUDES A CLICK-CLIMINATING SIGNAL TRANSFER CHANNEL HAVING A FOLLOW AND HOLD CIRCUIT. THE DEVICE ALSO INCLUDES AMPLITUDE-SENSITIVE CLICK DETECTOR CIRCUITRY FOR DETECTING THE

Data demodulator employing comparison

Abstract: Data demodulator which demodulates a received signal by means of comparing the received signal with itself delayed to produce a comparison signal having one amplitude value upon identity and another different amplitude value upon non-identity. The comparison is performed by a modulo two net-work herein illustrated as an EXCLUSIVE OR gate. The comparison signal is filtered by a digital filter which includes an UP/DOWN counter and associated control circuitry. The output of the digital filter is sampled by a JK flip-flop to provide the demodulated data signal.

Antenna array phase quadrature tracking system

Abstract: The system input signals on two separate antenna elements in an antenna array are combined to form two processed signals with one such signal representing the absolute value of the sum of the two antenna signals and the other representing the absolute value of the difference of the signals. The two processed signals are time multiplexed through a radiofrequency switch operating at 10millisecond intervals to form a single input signal to a receiver which in turn detects amplitude modulation in the multiplexed signal and forms an amplitude dependent signal to control a variable phase shifter circuit. The latter circuit automatically alters the relative phase between the two antenna signals whenever any amplitude modulation exists in the multiplex signal. Relative phase shift of the antenna signals stops when the absolute value of the two processed output signals are equal to each other which occurs only when the two antenna signals are in phase quadrature. The described procedure may be employed for any number of antennas connected in parallel to provide substantially omnidirectional antenna coverage and the time multiplexing and signal processing operations may be performed with stripline circuitry and techniques. For transmitting, a phase detector is employed to detect the phase modulation in the received multiplexed signal to establish and switch to the antenna in the array which will provide the greatest system gain for use while transmitting. The invention described herein was made by an employee of the United States Government and may be manufactured and used by or for the government for governmental purposes without the payment of any royalties thereon or therefor.

Phase and amplitude modulated modem

Abstract: A method and apparatus for generating phase and amplitude modulated signals to be transmitted and for demodulating the transmitted signals with improved reliability and accuracy is disclosed. A modulator at the transmitter is adapted to continuously group digital data into multibit words of equal length. The modulator is responsive to predetermined multibit subgroups within each multibit word to differentially phase modulate a carrier signal during successive modulation periods. The modulator is further responsive to the remaining bits within each multibit word to amplitude modulate the carrier signal during successive modulation periods. A demodulator is provided at the receiver. A differential phase detection portion of the demodulator reconstitutes the multibit subgroup digital data phase encoded at the modulator. A variable gain amplifier at the receiver varies the amplitude of the received signal in accordance with derived gain selection commands. The gain selection commands are derived from an amplitude detection portion of the receiver. The amplitude detection portion also provides a digital output indicative of the remaining portion of the multibit words originally encoded. The derived gain selection commands vary the gain of the receiver amplifier to cause the output amplitude levels of the amplifier to accurately correspond to the originally encoded amplitude levels. The accurately corresponded amplitude levels insure correct amplitude detection at the receiver.

Phase locking as a new approach for tuned integrated circuits

Abstract: A new and practical inductorless solution to the integration of frequency-selective communication circuits will be described. The design and performance of an integrated phase-locked FM amplifier/demodulator will be discussed.

A stereophonic receiver muting means with substitution of a dc circuit for an ac circuit

Abstract: A silicon monolithic integrated circuit stereo multiplex receiver includes a gated symmetrical demodulator for providing the desired left and right audio output signals. A second demodulator is supplied with the same composite input signal supplied to the first demodulator, but substantially attenuated, with the second demodulator providing output signals 180* out of phase with the signal supplied by the first demodulator; and the outputs of the two demodulators are combined so that the crosstalk components are effectively eliminated. A provision also is made for interstation audio muting and for stereo muting by the direct substitution of equivalent DC loads for the AC amplifiers normally responding to the signals, so that transientless muting is achieved. In order to control the muting and to provide a driver for the stereo indicator lamp, trigger circuits having predetermined hysteresis of operation are formed as part of the integrated circuit. Improved symmetrical drive for the demodulator circuit is obtained by feeding the 19 k.c. pilot signal to the doubler circuit across a string of diodes which logarithmically compress signals that would tend to overdrive the doubler transistor amplifier. A filter at the emitter of the doubler amplifier establishes a DC level which is used to fire the indicator lamp trigger circuit to indicate stereo signals are being received and also serves to self-bias the doubler amplifier to further prevent its being overdriven.

Apparatus and method for the synchronous detection of a differentially phase modulated signal

Abstract: In a synchronous detector the carrier of a binary differentially coherent phase shift-keyed signal is recovered by decomposing the carrier information signal into its conjugate in-phase and outof-phase components which contain in their arguments a term delta (t) representing the phase difference between the carrier and a local oscillator signal. The conjugate components are multiplied to generate a product signal which is sampled every other time slot to produce an error signal proportional to sin(2 delta (t)). This signal is applied to the local oscillator to phase lock the local oscillator signal to the carrier of the information signal.

Fsk digital demodulator with majority decision filtering

Abstract: A digital FSK demodulator including frequency detecting circuits, temporary storage, and a majority detector. A plurality of the most recent data bits from the frequency detecting circuits are stored and an output is generated by the majority detector which is a mark if the majority of stored bits are marks, and a space if the majority of stored bits are spaces.

Equal gain diversity receiving system with squelch

Abstract: A pair of RF diversity signals are routed to separate channels and heterodyned to two IF signals having the same IF frequency. The IF signals are combined to provide a common IF signal for demodulation. An automatic gain control signal is generated from the common IF signal and is used to control the gain of each IF signal prior to combining to assure a constant amplitude, common IF signal. The common IF signal is also used as a reference signal for a phase comparator in each channel. Each phase comparator compares the phase of its associated IF signal to the reference signal and adjusts its associated IF signal for inphase combining thereof. A squelch diode is included in each channel prior to combining under control of a squelch circuit which responds to the automatic gain control signal and the relative carrier ratios of the two IF signals. The squelch diodes supply no attenuation when the relative carrier ratios are less than a predetermined value and the squelch diode associated with the weaker IF signal supplies substantial attenuation when one of the relative carrier ratios is equal to or greater than the predetermined value. An alarm/normal arrangement is driven by the squelch circuit to indicate critical signal levels for the IF signals.

Binary Decoding Extended to Nonbinary Demodulation of Phase Shift Keying

Abstract: The required energy per information bit E_{B}/N_{o} to achieve a specified error probability with a binary error correcting code is reduced by retaining partial knowledge of digit amplitudes. Quantization to three or four levels is the minimum step of demodulator complexity beyond hard decisions. A simple extension of binary decoding is described which achieves a large part of the maximum improvement theoretically available with unquantized demodulation. The usual decoding process is modified only to the extent that two decoding operations are performed, rather than one. Also, storage is needed to compare the two resulting words to select the preferred one. With four-level demodulation, an improvement of more than one decibel is demonstrated even for small code word lengths over a nonfading phase shift keyed (PSK) coherent channel with white Gaussian noise.

Color television signal demodulation system

Abstract: A silicon monolithic integrated circuit consisting of three sets of full-wave, synchronous, switched demodulators is used to demodulate the red, blue and green color signals present in a composite television signal. Each of the demodulators consists of two pairs of switching transistors with the transistors in each of the pairs being rendered alternately conductive by a reference signal derived from the reference oscillator in a color television receiver. The phase of the red and the blue reference oscillator signals are obtained in a conventional manner, and the phase for the green reference signal is obtained by adding a predetermined portion of the red and blue signals together in a resistive adder to provide the green oscillator signal. The color signals are supplied in alternate phase to the two pairs of switching transistors in each of the demodulators, and the brightness signal components are applied equally or push-push to the switching transistors of the demodulators through an input transistor for each of the demodulators. In order to provide the proper relative amounts of gain for three demodulators, the red and blue signal demodulators have shunting resistance circuits connected across the input transistor circuits; and the green demodulator has a shunt connected across equal taps on voltage dividers connected to the outputs thereof. Since the brightness signal components are balanced with respect the the shut devices, the brightness signal passes through all of the demodulators unaffected by the shunting circuits.

Amplitude demodulator using a phase locked loop

Abstract: An amplitude demodulator suitable for integration including a phase locked loop which provides a frequency equal to the carrier frequency of the amplitude modulated signal, in phase components of such two signals being multiplied together to provide, after filtering, the original modulating signal.

Digital differential angle demodulator

Abstract: A digital differential angle demodulator for use in a high bit rate digital data transmission system utilizing randomly selected voice grade telephone lines is disclosed The demodulator derives a clock signal from an information-representing phase shifted intermediate frequency modulated signal This clock signal is employed to synchronously gate a high frequency counter output into a detector circuit which samples a precise portion of an intermediate frequency signal containing the phase shift information to be ascertained The high speed counter is phase locked to the intermediate frequency carrier so that the zero crossing of the squared intermediate frequency signal will occur at an odd multiple of 225* in the phase value of the output of the binary counter Two separate storage registers in the detector circuit receive the most significant bits of successive counter output values depending upon the phase sampled from the precise portion of the information-containing signal A parallel adder determines the difference between successive counts, each count of which is characteristic of the information-representing phase change originally received during the interval in question Phase locking of the high speed counter assures that random phase changes caused by system noise will not adversely affect the detection operation An encoder converts the phase change signal as emitted by the parallel adder back to its original digital data level format

Signal processing utilizing basic functions

Abstract: The present invention relates to the analysis and synthesis of complex time-varying signals over a wide range of frequencies and amplitudes in terms of selectable sets of expansion functions. Analysis consists of gating a time-sampled representation of the input signal stored on capacitors, into resistor matrices, which compute other desired representations. Use of the Fourier series representation in the analysis produces Fourier phazor components, which are converted to resultant vector amplitudes and phases by carrier generation through modulation by the phazors of 90*-out-of-phase, very high frequency, reference oscillators. Synchronous carrier demodulation gives resultant Fourier amplitudes. Carrier phase, relative to one of the reference oscillators, being equal to the Fourier phase, is determined by time (between zero crossings)-to-voltage conversion. Analyzer tuning may be external, voltage-controlled, or phase-controlled. When tuning is phase controlled, phase computing circuits lock the analyzer frequency to that of the input signal. The analysis bandwidth may be absolute- or voltagecontrolled fractional, the latter being achieved by a variableduty-cycle time-sampling-filter method. Frequency-tracking-system control of the voltage for controlled fractional bandwidth gives the ability to analyze with narrow bandwidth while providing wide band frequency tracking. A slowly varying phase-time derivative, when present for an appropriate length of time, is used to test for input signal coherence. The test result is used to control frequency tracking to prevent erratic tuning during attempted frequency tracking of incoherent signals. Relative phase values over a range greater than the normal range of 2 pi radians are made possible by sensing the traversals of the phase cut. For synthesis, control signals are generated and applied to a transformation matrix which, via multiplexing of the matrix outputs gives the sequential representation of a signal. Curves used to derive control signals, on film are read at high speed using a flying spot scanner. Spot intensity differentiation with zero crossing detection gives extremely high accuracy independent of spot intensity. Fourier log or linear amplitude and phase curve values are serially converted to phazor components synchronously with scanning by gated excitation and gated dissipation of high Q LC resonant circuits. Appropriate final stage gating and filtering of the time-sample representation eliminates system transients and objectionable frequency components due to the quantization of the output signal.

Receiver circuit assembly

Abstract: THE PRESENT INVENTION PERTAINS TO AN RF RECEIVER CIRCUIT ASSEMBLY AND MORE PARTICULARLY TO A RECEIVER OPERATIVELY ASSOCIATED WITH REMOTE CONTROLLED HEATING AND COOLING SYSTEMS HAVING FANS AND ADAPTED TO DEMODULATE A COMPLEX RF SIGNAL HAVING AN RF COMPONENT, A MIDRANGE AUTDIO FREQUENCY COMPONENT AND A LOW FREQUENCY COMPONENT AND INCLUDING ASSOCIATED OUTPUT CIRCUITS OPERATIVELY CONNECTED TO THE RECEIVER WHICH ARE RESPONSIVE TO THE LOW FREQUENCY COMPONENT TO SELECTIVELY ACTIVATE SAID HEATNG AND COOLING SYSTEMS AND THE FANS IN A PREDETERMINED MANNER. THE PRESENT INVENTION IS DIRECTED TO A RECEIVER AND ASSOCIATED OUTPUT CIRCUITS FOR ACTIVATING HEATING AND COOLING SYSTEMS AND FANS CONNECTED THEREWITH IN RESPONSE TO BE RECEPTION OF A SELECTED TRANSMISSION TO SAID RECEIVER.

Frequency modulated optical spectrometer

Abstract: An optical spectrometer is adapted to provide differential wavelength modulation of a spectral signal by vibrating a photosensitive cell in the focal plane of the spectrograph. A synchronous detector is employed to demodulate the output signal of the photosensitive cell, and thereby provide to a recording device a signal that is the derivative of the spectral signal.

Phase-Locked-Loop Detection of Binary PSK Signals Utilizing Decision Feedback

Abstract: A modified quadrature channel phase-locked-loop demodulator for binary phase-shift-keyed signals is presented. The modification, called decision feedback, is a practical implementation of decisiondirected channel measurement. Noise analyses are carried out for both additive and phase noise. An optimum loop filter is derived and the analyses include determination of probability of error for the system. The results of an analog simulation of the decision feedback technique are also included.

Signal supplying circuit for a color picture tube

Abstract: In a signal supplying circuit for a color picture tube, the luminance signal component of a color signal is divided into a high-frequency component and a low-frequency component, the low-frequency component is supplied to a demodulator for the chrominance signal component of the color signal so that the output of the demodulator which is supplied to the output amplifier contains the demodulated chrominance signal component mixed with the low-frequency luminance signal component, and the high-frequency luminance signal component is separately applied to an input of the amplifier for mixing in the output of the latter with the chrominance signal component and the low-frequency luminance signal component so as to constitute therewith a complete color video signal for application to a color picture tube.

Voice transmission and receiving system employing pulse duration modulations with a suppressed clock

Abstract: A voice transmission system including coded voice information using pulse duration modulation (PDM) with a suppressed clock and wherein this suppressed clock pulse duration modulated voice signal is used to modulate a phase shift keying modulator (PSK). The receiver includes a phase shift keying demodulator which feeds a limiter having a wide bandwidth so as to achieve the highest possible processing gain. The receiver also includes a voltage controlled oscillator which is fed an error signal derived from an integrator so as to produce an output signal from the voltage controlled oscillator to replace the suppressed clock.

Frequency modulation signal demodulator

Abstract: In a data communication system a demodulator for use in detecting data information carried in a frequency modulated signal. A signal which had been modulated between upper and lower limits of frequency, in addition to other frequencies within or without the said limits for supervisory functions, would be received and by means of equalizers, a limiter, zero crossing detector, Schmitt trigger, and a low pass filter, the original data can be recovered from the received frequency modulated signal. Further, circuits are provided for providing phasing information and for detecting the presence or absence of the received carrier frequency signal.

Color television signal demodulation system with compensation for high-frequency rolloff in the luminance signal

Abstract: A silicon monolithic integrated circuit consisting of two sets of full-wave synchronous gated transistor demodulators is used to demodulate the red and blue color difference signals present in a composite television signal. Selected outputs of these demodulators are matrixed to provide the green color difference signal. The color difference signals are applied to the bases of emitter-follower output amplifiers which also are supplied with the brightness signals from an additional emitter-follower luminance amplifier, the output of which is coupled to the bases of the emitter-follower output amplifiers through coupling capacitors, which compensate for most of the high-frequency rolloff in the brightness signals and further provide filtering of carrier harmonics from the detected color reference signals. Collector current for the switching transistors in the demodulators is obtained from the emitter of the emitter-follower luminance amplifier, so that blanking may be accomplished by rendering the luminance amplifier nonconductive during the blanking intervals.

Automatic brightness control responsive to black level of video signal

Abstract: An automatic brightness control circuit in a color television receiver using direct demodulation of the color and brightness signals derives a brightness control voltage by comparing a reference signal, which is indicative of the cutoff or blacklevel condition of the cathode-ray tube, with the video signals supplied to the base of an NPN transistor output amplifier for the green output channel of the receiver. In one embodiment this is accomplished by the use of a differential clipper which is used to compare a reference voltage indicative of the desired black level with a voltage derived from the emitter of the green final amplifier stage during the scanning interval to provide pulses to an integrating circuit, the output of which is used to vary the DC operating level of the green, blue and red driver amplifiers in a closed-loop control system.

Method and apparatus of infinite q detection

Abstract: The method of maintaining positive locked-on detection with instantaneous locked-on filter tracking of a complex modulated carrier signal by instantaneous employment of the complex modulation content of the signal to respectively provide complexangularly locked-loop detection of any modulated carrier and exclude all other signals and noise not a part of the modulated carrier signal to provide detection of infinite Q capabilities and the structure thereof Locked-on tracking is obtained by instantaneously and continuously filtering the modulated carrier signal by synchronously filter-tracking the same with the modulation excursions thereof To maintain synchronization with the unfiltered modulated carrier signal, synchronous demodulation is preferred whereby a matched signal (matched to the filtered signal) is generated and synchronously demodulated with the filtered signal and the modulation excursion or content signals of both the filtered modulated carrier and the matched modulated carrier are used to produce output signal that is employed to instantaneously control the parameters of the tracking filter and the parameters of the matched signal generator, thereby maintaining synchronization in continuous tracking and positive locked-on detection (complexangularly locked-loop detection) The unfiltered modulated signal is filtered through a time variant filter to produce the carrier signal with its modulations alone The filter and the generator employed for producing the synchronized matched modulated carrier signal, are each preferably identical structures with the exception that the generator does not have an external input connection The filter and generator preferably include as one example embodiment, a connected closed loop series circuit having a multiple input inverter and a first and second integrator, each integrator having variable parameters that are controlled by the modulation content of the filtered signal obtained through a detection process

Am, fm, and fm stereo tuner having simplified am to fm switching means

Abstract: A tuner can be switched between AM, FM, and stereo modes of reception without any radio or audio-frequency band-switching, and without any changes being made in the tuning meter connections. Separate AM and FM radio sections have power terminals which are alternately connected to a source of power by a single pole, double throw AM or FM selector switch. The audio outputs of the two radio sections are fed into a mixing amplifier, and the mixing amplifier output is fed to stereo demodulation circuitry. A single tuning meter is connected between the FM section audio output and the AM section automatic gain control.

Demodulator for angularly related signals

Abstract: A demodulator for signals angularly related to the position of a rotor of a synchro or resolver uses, in one embodiment, only one transformer in a circuit for subtracting, adding, and phase shifting the signals to produce a single signal phase shifted in proportion to the rotor angle. In another embodiment, a transformerless circuit uses an operational amplifier to derive the phase shifted signal. The phase shifted signal is compared with a reference signal to produce a rectangular wave with a variable duty cycle, which is integrated to produce a DC voltage representing the rotor angle. A pair of the circuits are used in an altitude warning system connected to synchros for the actual altitude and the command altitude of an aircraft. The derived phase shifted signals from both synchros are compared to produce a rectangular wave with a variable duty cycle, which is integrated and compared with voltages representing preselected altitudes to indicate when the aircraft is at those altitudes.

An IC Approach to the Subcarrier Regeneration Problem

Abstract: A monolithic integrated circuit which performs the subcarrier regeneration task in a color television receiver is described. Differential amplifier configurations are used in a novel circuit concept which involves time-sharing and current switching techniques. The result is a realization of the design objectives with a relatively simple structure. The burst gate, phase detector and voltage controlled oscillator functions called for by the classical APC loop are provided. In addition, an in-phase detector for color killing and chroma AGC is included, as well as a novel DC controlled hue adjustment.

Pulse width signal demodulator

Abstract: A demodulator circuit for providing a DC output signal which is unaffected by variations in pulse amplitude or repetition rate of a pulse width modulated input signal. The demodulator comprises switching circuitry and a pair of integrators. The switching circuitry controls the integrators whereby they function as holding generators with a short time lag; input pulses being applied alternately to the integrators which in turn provide DC output levels which are alternately measured.

Television recording system with alternate period inversion and automatic frequency control

Abstract: The signal for every other line in a television signal is inverted, and the resultant signal is magnetically recorded and reproduced Reinversion (or demodulation) switching, to restore the played back signal to its original form for reproduction, is controlled by an automatic frequency control circuit to maintain switching synchronization through the vertical intervals and periods of drop outs and noise

Underwater temperature telemetry system

Abstract: A self-contained underwater telemetry system is provided for transmitting biophysical data from a freeswimming diver through the water to a receiving station. The system includes a pulse amplitude modulated FM transmitter carried on the diver and an FM receiver with an FM-to-pulse amplitude demodulation section. Also included are a precision oscillator whose frequency is controlled by sensor resistance; multiplexing circuits for monitoring several channels of biophysical information; an octal encoding system which generates the above-mentioned pulse amplitude modulated signal; a low drain voltage regulator; a hydrophonetuned amplifier combination; and a zero crossover-multivibrator demodulation section for the FM receiver.