Showing papers on "Demodulation published in 1973"

FM demodulator circuits

Abstract: There is disclosed an FM demodulator including first and second phase locked loops for demodulating a first and second FM signal contained in a composite signal. The loops employ frequency feedback whereby one loop controls the input to the other loop and vice versa to assure that said first and second signals are separately demodulated relatively independent of their power ratio as present in said composite signal.

Sonobuoy receiver system, floating coupler

Abstract: A modulation-demodulation floating coupler for use in a Sonobuoy Receiver to perform the function of an isolation transformer operating over a wide frequency band with very little phase shift is disclosed. The coupler is responsive to a high frequency composite input signal having a carrier portion on which is modulated a baseband information portion which is to be coupled and includes a transformer for coupling the composite signal to a pair of demodulators, the first of which provides an output with no ground reference, and the second demodulator produces a local feedback signal for gain and distortion control.

Digital modulate/demodulate system

Abstract: A digital information signal modulating system is disclosed which increases the carrying capacity of a given designator band by approximately 2. The disclosure illustrates how a quadrature phase-shift keyed system having four signal states can be converted to a system having nine signal states.

Measurement of ST depression of electrocardiograms

Abstract: A method and apparatus for electronically determining the ST depression of an electrocardiogram waveform relative to the PQ level of the same waveform is disclosed. The analyzer and the associated method employ delta modulation and demodulation for processing information. By varying a weight signal in the delta demodulator in a predetermined manner, the average ST depression is obtained directly without the necessity of comparing a delayed version of the EKG with an undelayed version of the EKG to overlap the ST and PQ segments of interest. The method and apparatus disclosed can be used to determine the average difference between two segments of waveforms other than an electrocardiogram by adjusting the weight signal.

Interface system with two connecting lines

Abstract: In various locations in computer systems or data transmission systems, the number of transmission or transport lines are reduced by the use of a serially operating interface adapter. The adapter which uses a special modulator and demodulator and associated coding technique, simplifies the information transferred over a transport line. The modulator includes means for generating bit pairs having an even and odd state and having the pairs of signal elements being of alternating parity. This arrangement enables a simplified approach for determining the start and the end of a message without the use of additional characters not present in the code set. The adapter also includes a demodulator which is adapted to recover and detect four-bit-parity code signals for recovering start and stop signals of block information.

Color television receiver

Abstract: In a decoding system to receive PAL television signals, one reference sub-carrier signal is produced with the proper phase by controlling an oscillator with every burst signal and utilizing the time constant in the oscillator system to average the alternating phase of the burst signal. A second chrominance signal is demodulated by selecting alternate bursts and using them to control an oscillator to demodulate the chrominance signal along an axis other than the correct one. The resultant demodulated signals are properly combined in a matrix to separate the component color signals. Alternatively, burst-controlled signals with alternating phase can be vectorially added to burst control signals with the correct, fixed phase to produce reference sub-carrier signals of the correct phase and phase alternation for both chrominance components.

Electronic protection and sensing apparatus

Abstract: The apparatus comprises an electronic system including an antenna positioned about the equipment to be protected and coupled to a resistor-capacitor bridge, to which is coupled an oscillator. The output of the bridge is coupled through a differential amplifier to a demodulator, and the output of the oscillator is also coupled directly to the demodulator, The demodulator output is coupled through an amplifying system both to a display device, which is used to indicate the state of balance of the system, and to a control circuit for generating a signal which is coupled to the equipment to be protected to turn it off or to otherwise exert a protective control action when a certain level of unbalance in the bridge occurs.

Balanced correlated ternary coding system

Abstract: A balanced correlated ternary coding system including a modulator, a demodulator and an error detector. The modulator is designed so as to code a binary signal of level 0 or 1 into a ternary signal of level +, 0, or - according to any of the following truth tables:

On Optimum Sampled-Data FM Demodulation

Abstract: Since the introduction of large-scale integration (LSI) techniques, there has been a continuing effort to develop digitalization techniques for communication equipment amenable to LSI implementation. Hopefully, this will permit expanded capability in the equipment while taking advantage of the cost reliability attributed of LSI. In this paper, a digitalized or sampled-data FM demodulator recursive algorithm is synthesized and its signal-to-noise ratio performance compared with the optimum analog demodulator and the conventional limiter discriminator demodulator. The demodulator is shown to exhibit threshold extension capability and automatic time-varying gain (bandwidth) adjustments from acquisition through tracking of the incoming modulated signal.

Method of recording a video signal

Abstract: Method of recording a video signal, in particular a colour video signal, on a record carrier, in which method a combined signal is produced which contains a carrier which is modulated in frequency by the luminance information, and a subcarrier which lies below the frequency band of this modulated carrier and is modulated, for example, by the colour information. The zero crossings of the ascending and descending edges of the modulated carrier are shifted in opposite dependence upon the modulated subcarrier and recorded on the record carrier as information-containing quantities.

Phase correction circuit

Abstract: A phase correction circuit for a demodulator for a phase-shift keying, suppressed-carrier communication system. The demodulator for such a coherent phase detector requires means for reintroducing the carrier in proper phase and frequency. To this end a phase-locked loop demodulator is conventionally used including a phase correction circuit sometimes called an I-Q multiplier. The invention provides an improved phase correction circuit which will generate a phase-corrected loop error signal to keep the phase-locked loop locked in phase even during the period when the input signal reverses its polarity. The phase correction circuit includes a reference oscillator and hence operates at an alternating-current signal rather than a directcurrent signal.

Phase control system for demodulation carrier in carrier band multilevel signal transmission

Abstract: In narrow band transmission by BSB and VSB modulation, phase distortion due to the transmission line occurs in the carrier signal, followed by a phase shift from accurate pulse response of the multilevel signal demodulated by the carrier signal subjected to the line phase distortion. A reference level signal having a predetermined level lower than the multilevel signal is inserted at a specified interval into the multilevel signal train to be transmitted. The intersymbol interference of the reference level signal is detected at the receiver, so that the phase shift from the accurate response of the multilevel signal is compensated by controlling the phase of the demodulation carrier signal to be supplied to the demodulator.

Multilevel code transmission system

Abstract: A multilevel code transmission system is made capable of transmission and reception of correct signals even if the demodulation carrier is 180 degrees out of phase by dividing the levels of a multilevel code to be transmitted into pairs and subjecting the transmission signal to differential coding, pair by pair. At the receiver, the levels are again divided into pairs, and the differentially coded signal is inversely converted.

Multichannel transmission system using clock pulses each occurring within a definite time position

Abstract: A multichannel transmission system comprising a generator for supplying to all the transmitters and receivers with a reference signal consisting of a plurality of clock pulse combined with a periodic sequential pulse signal. Each transmitter produces amplitude-modulated carrier pulses each occurring within a time position defined by the clock pulses in accordance with a given information signal to be conveyed. Each receiver opens its gate the same time position as the associated transmitter so as to receive and demodulate the carrier pulses from the transmitter.

Active frequency-responsive glass breakage detector

Abstract: The detector is primarily for detecting glass breakage and is constructed as an active device or system for detecting the breakage and generating an alarm signal The detector generally comprises a transmitter trandsucer of fixed first frequency below the frequency occasioned by breakage, a receiver transducer for receiving a signal which is a composite of the first frequency signal and the breakage frequency signal when a breakage occurs, a demodulator or mixer for obtaining the difference or sum frequency and alarm means for establishing an alarm condition upon detection of this difference or sum frequency

Frequency shift keyed demodulator

Abstract: A frequency shift keyed (FSK) modem (modulator and/or demodulator) utilizing a phase lock loop which modem may operate at any of several predetermined frequencies and whose output for the modulator section, is combined with a frequency shift keyed signal and the result passed through a low pass filter to provide a frequency shift keyed output. The phase lock loop also supplies signals to the receive or demodulation section. The use of a multiple frequency phase lock loop negates the requirements for a plurality of bandpass filters of different frequencies to be used with the frequency shift keyed source.

Digital demodulation of frequency-shift keyed data signals

Abstract: A digital frequency-shift keyed signal demodulator continuously measures the duration of successive cycles of a received data signal wave, compares pairs of duration measurements to determine the occurrence of a data-wave transition, and closely approximates the time of occurrence of the data-wave transition by linearly interpolating over the interval between successive duration measurements in accordance with their relative magnitudes. The interpolated interval value is applied as a time delay to the demodulated data wave to obtain a transition substantially free of phase jitter. The principle is applicable to single-channel cases directly and to multichannel cases through time-division techniques.

Retrospective pulse modulation including bar coding and apparatus therefor

Abstract: Digital data in self-timing reference is free from error due to irregular data spacing because of variations in speed and/or direction of scan in manual or machine applications with a pulse modulation of retrospective nature. Initially reference data manifestations are established and thereafter digital data are established partly on the basis of preceding manifestations of the data. In a binary data translating system, for example, a pair of reference pulses are spaced apart by a given interval. A binary unit is thereafter manifested by a pulse following at the same or similar interval and a binary zero is manifested by a pulse following at a differing interval. Each manifestation of a binary number thereafter depends on the interval between preceding pulses. A principle advantage of retrospective pulse modulation lies in demodulation. Large variations in the spacing and relatively larger variations in the scanning speed are accommodated readily. Magnetic tape and like records can not only be addressed at conventional high speeds in searching and at conventional low speeds later used in reproducing but, also can be searched continuously as the change is made between those speeds. Adaptive rate communications are particularly enhanced by the principle. Optical scanning of bar codes is improved by differing the spacing of uniform width bars or with bars of differing widths and differing spacing. These arrangements are applicable to railroad car and like object identifying, label data processing, human identification, card data processing, graphic display data probing systems and many other uses. Synchronous and asynchronous capability permits input to almost any digital data processing system.

Syllabic adaptative delta modulation system

Abstract: A syllabic adaptive delta modulation system including a modulator and a demodulator. The modulator comprises a comparator having a first input connected to receive an input analog signal, a second input adapted to be connected to an integrator located in the conventional feedback loop of the delta modulator and a quantizing means for sampling the output of the comparator to generate delta modulated binary pulses of one polarity or the other as determined by the comparator. A syllabic filter is connected to the output of the quantizing means for filtering the low frequency components of the delta modulated pulses and a multiplier is also connected to the output of the quantizing means and responsive to the syllabic filter for modulating the amplitude of the delta modulated pulses with the low frequency components detected by the syllabic filter. The integrator is connected to the output of the multiplier for integrating the amplitude modulated pulses. The output of the integrator is applied to the second input of the comparator for comparing the output signal of the integrator with the input analog signal and generating a signal depending upon the difference between the two signals.

A Digital Demodulator for PSK Signals

Abstract: This paper describes a digital demodulator for phase-shift-keyed (PSK) signals in which the phase difference between the received signal and a carrier reference is found by measuring digitally the time interval between the zero crossings of the signal and the reference. In the case of coherent detection the reference is locked to one of the M possible phases of the signal. The advantage of this demodulator is that bulky low-pass filters and delay lines as well as critical threshold devices can be dispensed with. On the other hand, digital measurement of the phase and the use of a finite-width sampling window lead to degradation of the error performance. This degradation is theoretically analyzed for both coherent and phase-comparison detection. The quantizing error proves to be small enough when the phase difference is coded into a 6-b binary number, and the theoretical results are in good agreement with measurements taken from an experimental phase-comparison demodulator for fourand eight-level PSK signals. The experimental demodulator is also described in the paper.

System including a transmitter and a receiver for the transmission of binary signals located in periodical clock intervals

Abstract: A system for carrier synchronization in a multi-phase transmission system of synchronous pulse signals in which the multi-phase modulator at the transmitter end and the multi-phase demodulator at the receiver end are provided with orthogonal modulators. In order to recover the carrier at the recover end in the correct phase position under all circumstances while avoiding phase uncertainties, a clock interval is reserved for the transmission of a synchronizing signal which is transmitted at the transmitter end through a first channel of the orthogonal modulator while simultaneously the second channel of the orthogonal modulator is interrupted. For the local carrier recovery the receiver comprises a phase stabilization channel connected to the output of the modulator in the receiver channel corresponding to the second transmission channel, which stabilization channel incorporates a blocking circuit which for the purpose of phase stabilization is released by a switching signal at the synchronizing intervals originating from a synchronizing interval selector which for the purpose of selecting the synchronizing intervals of lower signal level is fed by the received phasemodulated oscillations.

Converter for a line shared educational tv system

Abstract: An educational TV system features a converter for existing domestic TV receivers to enable reception and display of a multiplicity of pictures transmitted over a single TV channel using a line sharing principle. The converter includes a detector to demodulate a radio-frequency carrier signal having a plurality of n-separate pictures wherein every nth line of each of the pictures is transmitted beginning at a different line. In the converter, recovery of any one of the pictures is accomplished by selecting from the plurality of lines transmitted every nth line commencing at the preselected line, with the selected line being delayed by a medium having a bandwidth less than the bandwidth of the video pictures and recombining the undelayed selected line so that the selected one of the pictures is represented by subcarrier signals which are then modulated onto a radiofrequency carrier signal at the output of the converter. The converter output is then applied to the antenna terminals of a domestic type receiver where the carrier signal is demodulated and displayed on the receiving tube.

Method for demodulation of a differentially phase-modulated signal

Abstract: A method for demodulation of a differentially phase-modulated signal. The phase of a received signal is measured digitally during each information-transfer element in relation to an independent reference signal. The phase difference is stored in numerical form in a memory. The final demodulation is carried out by evaluating the difference between the measured phases of two adjacent signal elements.

Phase and frequency synchronizing circuit

Abstract: An inverter apparatus is disclosed for synchronizing a carrier wave form to a reference wave form to have a given frequency relation for controlling thyristor means. The carrier and reference frequencies are independently generated by a carrier generator and a reference generator to have a given frequency relationship. A detector determines the frequency difference of the carrier wave form from the given frequency relationship. An integrator interconnects the detector and carrier generator to modify the carrier frequency for resynchronization when the carrier wave form is leading or lagging the reference wave form at the given frequency relationship and for modifying the carrier phase when the carrier wave form is lagging the reference wave form at the given frequency relationship. The phase modification may include modifying the slope of the carrier wave form to contract a cycle thereof to phase synchronize the carrier with the reference wave form.

A New Digital Coherent Demodulator

Abstract: A coherent demodulator is described which is particularly well suited to digital implementation. Its important features are that no low-pass filter is required to eliminate double-frequency terms and that the passband signal need be sampled at only twice the highest frequency of the baseband signal, rather than at twice the highest frequency of the passband signal. A demodulator of this type will be useful in those systems that do not require passband digital signal processing for other purposes.

Method and apparatus for transmitting amplitude modulated signals

Abstract: Method and apparatus for transmitting information by means of an amplitude modulated carrier signal wherein the received signals and a carrier generated at the receiver are coupled to a demodulator. A test signal is generated having two equal valued amplitude extremes, and the test signal pulses are spaced in time at sufficiently great intervals that they cause no mutual interference. The test signals are applied to the modulator and transmitter when the latter are carrying no other signals. At the receiver, the test signal is demodulated, and a control signal is derived from the amplitude extremes of the demodulated test signal. This control signal changes the phase of the carrier generated at the receiver when the values of the amplitude extremes are dissimilar.

Phase shifting network

Abstract: Variable direct current control phase shifting networks are connected to supply reference signals with predetermined phases relative to the synchronizing signal. An I axis demodulator of a color television receiver is utilized to sense a component of color along the I axis and shift the phase of the reference signals to change the phase shift amount when a component is present on the I axis.

Method and apparatus for noise reduction in discrete phase modulated signals

Abstract: A method and apparatus for selectively reducing the phase shift contributions caused by transmission impairments such as noise and phase jitter, takes advantage of the fact that for phase modulated data signals capable of assuming one of M discrete values, when the noise phase shift due to impairment in transmission is less than pi /M in a system capable of discriminating between discrete data encoded phase shifts of 2 pi /M. Accordingly, each received discrete signal of phase magnitude theta is multiplied by 2 pi /M. The integral portion of the product represents the phase shift of data whereas the fractional value represents the phase shift caused by impairments. The fractional value is multiplied by a parameter Alpha and algebraically combined with a reference value. The reference value is subtracted from the discrete signal theta to reduce the phase shift of the transmission impairments. By varying the value of Alpha , the type of demodulation can be altered. For example, for Alpha 0, the demodulator is coherent, while for Alpha 1 the demodulator operates differentially. The reference value is in effect a predictor of the noise contribution and its magnitude is modified by the algebraic addition of the product of the fraction part and the parameter Alpha .