Showing papers on "Modulation published in 1972"

Current controlled two-state modulation

Abstract: In a current controlled two-state modulation system having a power switch and a low pass filter, a current sensor provides a current feedback signal representative of the current delivered by the power switch to the low pass filter The low pass filter also provides a voltage feedback signal that is combined with a reference signal to provide a combined signal A limiting amplifier amplifies the combined signal for further combination with the current feedback signal to provide a switching signal that is delivered to a circuit characterized by hysteresis This circuit determines the instant when the power switch is switched so as to maintain the output voltage provided by the low pass filter substantially constant so long as the load current is less than a predetermined limiting value determined by the limiting amplifier and thereafter limits the output current to substantially the predetermined limiting value

Cross modulation and intermodulation in amplifiers at high frequencies

Abstract: Cross modulation and intermodulation in amplifiers at high frequencies are investigated using the Volterra series approach. The general relationships between these forms of distortion are defined and the importance of phase in the specification of cross modulation is discussed. The use of feedback for distortion at high frequencies is investigated and it is shown that appropriate control of the feedback loop phase shift can result in substantial reductions in cross modulation over broad bandwidths. All theoretical conclusions are verified by circuit measurements at frequencies up to 200 MHz.

Data coding with stable base line for recording and transmitting binary data

Abstract: An improved method and apparatus for encoding and decoding binary data is disclosed. For improving data density for storage or transmission, the waveform has an upper frequency limit such that transitions in the encoded waveform occur no closer together than the time for one data digit. To provide suitable clocking for waveform detection circuits, the waveform has a lower frequency limit that transitions occur no farther apart than two data digit times. In addition, the waveform is symetrical about a zero signal level within narrow limits. The encoding is called ''''zero modulation'''' (or ZM) for zero direct component. Since the waveform has a constrained direct component, it can be used with circuit devices of the type that will not transmit a direct component. Circuits for detecting errors in the decoded waveform are also disclosed.

Pulse compression radar and method of operating such a radar

Abstract: A method is described for improving the operation of a digital pulse compression radar by compensating for amplitude variations in the modulation signal of the transmitted pulse. In the disclosed embodiment, the contemplated compensation is effected by modifying the stored complex conjugate of the frequency spectrum of the transmitted waveform.

Interdigital electro‐optic thin‐film modulator

Abstract: An integrated optical modulator is presented that achieved 50% depth of modulation. A double‐ended coupling prism allowed nitrobenzene to be used as the waveguide material. Also, an approximate theory of operation is developed.

High-Capacity Microwave System for Digital Data Transmission

Abstract: A nationwide data network is planned that will employ microwave relay networks for both long-haul and short-haul interconnection. A digital modulation technique has been developed that has the constant level advantage of frequency-shift keying (FSK) systems while retaining the error rate and threshold performance of coherently detected binary or four-phase phase-shift keying (PSK). Occupied spectrum and interference characteristics of a 21.5-Mbit/s data system are compared to the more conventional 600-, 1200-, and 1800-channel message systems.

A coupled-mode analysis of mode locking in homogeneously broadened lasers

Abstract: The coupled-mode equations are solved for homogeneously broadened lasers modulated near the axial mode separation frequency. The character of the oscillations changes rapidly when the modulation period is tuned through the round-trip delay at the group velocity. Specifically, this is the region in which phase modulation leads to pulsing and loss modulation leads to pulsing at normal power. The present method agrees with the results of Kuizenga and Siegman for this region, but gives a countable set of supermodes in addition. There is some reason to believe that these other modes have already been observed. When the group velocity condition is not satisfied, a more complete description is given than has been previously reported. Most importantly, the dependence of laser power on modulator drive and frequency can be predicted.

Phase-amplitude multiple digital modulation system

Abstract: A digital modulation system for modulating the phase and the amplitude of a carrier in accordance with multi-value digital code units so as to produce a phase-amplitude modulated wave, so that respective pointed ends of signal vectors corresponding to possible multi-values of the phase-amplitude modulated wave are positioned at respective centers of regular hexagons predetermined so as to correspond to possible multi-values of the multivalue digital code units from a plurality of regular hexagons, which are closely positioned to one another without leaving any space in a honeycombed fashion near the original point of a polar coordinate on the polar coordinate plane.

Digital communication systems

Abstract: The invention is particularly applicable to line telephony and relates to a method and apparatus for converting an isochronous baseband data signal into a diphase signal and vice versa. The diphase transmission is considered as a phase modulation or double-sideband suppressed-carrier in which the modulating signal switches the phase of a carrier whose fundamental frequency in hertz is the same as the modulation rate in bauds. The resulting modulated signal contains fold-over components which are used to advantage by introducing a 90* phase shift between the carrier and base band signals to reduce the line signal level at low frequencies where the line distortion is most severe and enhance the signal level at high frequencies where the attenuation is greatest. The need for line equalisation is therefore reduced.

Process of optical path modulation and modulator for implementation of the same

Abstract: The invention concerns a process and a device for optical path modulation. The process lies in modulating the optical path difference between both waves of an interferometer by alternate variation of the relative inclination of two components of the interferometer due to the action of a modulator producing an alternate flexure, in creating a modulated optical phase variation causing a change in the modulated light flux and in using the signal provided by a photo-sensitive receiver submitted to this flux for measuring or detecting a phenomenon producing an optical phase difference submitted to the action of the optical path modulator. The invention applies to metrology, ellipsometry, refractometry, polarimetry, etc.

Differential encoded quadriphase demodulator

Abstract: Coherent demodulation of differentially encoded quadriphase modulation is accomplished using initially a non-optimum passive delay line detector to derive a carrier component. The output of the delay line demodulator, comprising I and Q channel data of less than desirable error performance, is differentially encoded for correlation with the original quadriphase modulation resulting in reconstruction of the suppressed carrier frequency. The reconstructed carrier is supplied to a filter bank and frequency synthesizer for generating a synthesized carrier frequency. The synthesized frequency and the reconstructed carrier are supplied to a phase-lock loop which generates phase correction signals. The synthesized frequency is mixed with the original modulation and the resulting signal is supplied to coherent phase detectors, the latter also receiving the phase correction signals from the phase-lock-loop, and serving to optimally demodulate the quadriphase components, yielding I and Q data channels. Efficiency of demodulation is improved further by employing the phase detector acquired I and Q data for reconstruction of the carrier frequency, instead of the initial delay line demodulator source. Matched filter components, comprising bit synchronization and bit regeneration circuitry process the demodulator outputs and contribute accordingly to requirements for minimum error demodulation. Another measure of improved demodulation performance is afforded by weighted comparison of the redundant I and Q channels of data of the delay line demodulator and the coherent phase detectors.

Radar target simulator

Abstract: Apparatus is disclosed which simulates the operation of a plurality of radar transmitters so as to permit an evaluation of electronic countermeasure equipment The system generates sequences of pulsed radio frequency signals whose carrier frequency, modulation, amplitude and power lever are controllable to realistically reflect the signal conditions which may be encountered by an aircraft when a multiplicity of radar emitters are operating simultaneously in its vicinity

Several Modulation Techniques for a Pulsewidth Modulated Inverter

Abstract: Pulsewidth modulation of a six-step inverter can be accomplished in different ways. Comparisons between different modulation techniques are based primarily on harmonic content in the output waveform and circuit constraints imposed by semiconductor characteristics. Adaptive ratio is a modulation scheme which combines the beneficial features of several available techniques and makes the necessary compromises to optimize the operating characteristics of a modulated six-step inverter.

The Effect of Timing Errors in Optical Digital Systems

Abstract: The use of digital transmission with narrow light pulses appears attractive for data communications, but carries with it a stringent requirement on system bit timing. The effects of imperfect timing in direct-detection (noncoherent) optical binary systems are investigated using both pulse-position modulation (PPM) and on-off keying for bit transmission. Particular emphasis is placed on specification of timing accuracy and an examination of system degradation when this accuracy is not attained. Bit error probabilities are shown as a function of timing errors from which average error probabilities can be computed for specific synchronization methods. Of significance is the presence of a residual or irreducible error probability in both systems, due entirely to the timing system, which cannot be overcome by the data channel.

Theoretical design of guided wave structure for electrooptical modulation at 10.6 µm

Abstract: Two guided-wave structures for electrooptical modulation at 10.6-μm wavelength are proposed in this paper. They are structures that could be fabricated realistically by present technology. Theoretical design data on these two structures concerning their propagation wave numbers, attenuation rate, phase modulation rate, and dispersion characteristics are given so that an optimum design could be conceived before fabrication. In the two examples given, phase modulation rates of 3.75-9.3 mrad/V/cm can be achieved in these structures.

Extracting circuit for reproducing carrier signals from a multiphase modulated signal

Abstract: A carrier reproducing circuit for demodulating a signal transmitted by a pulse coded modulation-multiphase modulation system in which the output of a carrier extracting circuit is sampled by a clock pulse of a bit repetitive frequency in a sampling circuit and the sampled output is applied to a band-pass filter having a pass band of a carrier frequency to reproduce a carrier of reduced phase jitter.

Transmission system for a time-divisional multiplex psk signal

Abstract: A transmission system for a time-divisional multiplex PSK signal including a frame synchronization signal in addition to information channel signals, in which the number of quantum phase positions of the frame synchronization signal is smaller than the number of quantum phase positions of the information channel signals in the time-divisional multiplex PSK signal so that the frame synchronization signal and the information channel signals are transmitted by the same modulation rate.

Feedback modulation of exhaust gases in internal combustion engines

Abstract: A system for modulation of the amplitude of engine exhaust feedback to the engine induction system during engine operation. The modulation system includes means for varying the amplitude of exhaust feedback in periodic manner at a frequency which is substantially constant or which may vary as a function of an engine operating parameter. The amplitude may vary as a step function between predetermined levels or continuously and may have a duty cycle (length of time at a predetermined level) which varies as a function of an engine operating parameter, e.g. exhaust manifold temperature. The modulation envelope is controlled by a modulator circuit controlling a valve position in the feedback path. The frequency of modulation is controlled by a divider or multiplier type circuit coupled between a pulse source e.g. the distributor and the modulator circuit.

Application of a Wave-Length Modulation Device to Problems concerning Spectrometer Misalignment

Abstract: The use of wave-length modulation as a tool for minimizing spectrometer spectral misalignment is examined. A vibrating quartz plate is employed to repetitively scan a small wave length interval at the exit slit of a spectrometer. Increased latitude is thereby provided for any slit or wave-length misalignment of the spectrometer, as long as the correct signal detection system is employed. Investigation of the effects of wave-length modulation on a typical line spectrum has revealed signal averaging as the optimum detection system for this approach. From this, additional approaches are suggested for manual and automatic routine correction of spectrometer wave-length drift using existing optical systems. Also, a new technique is suggested for automatic feedback correction of the spectrometer using an on-line digital computer. Methods of implementation of all these procedures are considered and discussed.

Moving target indicator system and apparatus

Abstract: A moving target indicator system includes a signal source for generating an RF output signal, a code generator for generating a primary code train and a plurality of secondary code trains delayed relative to the primary code train, and modulator means responsive to the primary code train to modulate the RF output signal to produce a coded RF output signal. The coded RF output signal is transmitted and coded echo signals reflected by targets are compared with a selected secondary code train to produce a unipolar signal train with doppler modulation information if a matching relation exists between the coded echo signals and the secondary code train. The doppler modulation of the unipolar signal train is detected and a corresponding indicator is actuated.

Computer controlled rf noise and modulation analyzer

Abstract: A computer controlled test set capable of measuring FM and AM noise of an RF signal as well as the index of modulation, RF power level and the linearity of a ramped FM signal output from a microwave signal oscillator included in a unit under test.

System for discriminating between high and low speed targets

Abstract: The disclosed system distinguishes between high and low speed targets by the resolution of frequency ambiguities in return signals from a repetition rate coded transmitted radar signal. The return signals are processed through a passband filter; and logic circuits, which monitor the filter''s output, provide an indication of the speed range of the targets as a function of the presence or absence of modulation resulting from the repetition rate coding.

Investigation of the energy spectrum of electrons in vitreous and crystalline As2Se3 by modulation spectroscopy methods

Abstract: Absorption, thermo-absorption and electro-absorption in glass and moncrystals of As2Se3 were investigated experimentally. Modulation technique and phase-sensitive detection were used for measuring both thermo-absorption and electro-absorption. On the basis of data obtained the possible models of energy spectrum of the electrons in vriteous and crystalline As2Se3 were proposed.

Four channel stereophonic broadcasting system

Abstract: A broadcast system capable of transmitting and receiving a broadcast signal containing four discrete stereophonically related audio frequency inputs in which there is produced within the transmitter four matrix outputs, each of which is a function of one or more of the inputs. A main carrier wave is then frequency modulated with the first matrix output, with the sidebands of a suppressed first and second subcarrier which has been amplitude modulated with the second and third matrix outputs in quadrature relationship with each other, and with the lower sideband and a relatively small portion of the upper sideband of a depressed third subcarrier that has been amplitude modulated with the fourth matrix output. The modulation of the third subcarrier is limited to a maximum voltage level substantially below the highest level otherwise possible. The first, second, and third subcarriers are regenerated in the receiver and the four matrix outputs are detected. These outputs are then dematrixed to reproduce the four original inputs. The restricted sideband modulation associated with the third subcarrier and the amplitude limiting of its modulation signal maintain the out-of-band radiation of the transmitted energy within acceptable limits.

Pulse compression radar

Abstract: An improved digital technique for generating a chirp modulation signal for a pulse compression radar is shown. A stored set of digital numbers having a minimum number of different absolute values of successive samples of the desired modulation signal is processed through a logic circuit to derive a second set of complex digital numbers describing such modulation signal; such second set is then converted to an analog signal which is taken as the chirp modulation signal.

Medical data terminal for transmitting analogue and digital data

Abstract: Transmission means adapted for the transmission of medical data over a telephone transmission link to a remote centre for diagnosis, comprises a signal generator, modulation means by which the output of the signal generator can be modulated to transmit binary alphanumeric information over the transmission link, modulation means by which the output of the signal generator can be modulated to transmit non-alphanumeric information as an analogue signal over the transmission link, and coupling means by which the modulated output of the signal generator can be applied to the telephone transmission link.

Video signal processing system for facsimile transmission

Abstract: A facsimile transceiver for use with telephone line networks in which the original image is photoelectrically scanned to produce a video baseband signal, the baseband signal is shaped by a non-linear transfer network and converted into a relatively high frequency period-modulated signal, whose carrier frequency is outside the passband of the telephone transmission link and, after frequency division to a frequency within the passband, the low frequency components of the resultant carrier signal are emphasized. In addition, the signal is pre-equalized to partially compensate for the delay and amplitude characteristics of the voice-grade telephone line transmission facilities which carry the period-modulated signal to a receiving station transceiver. The non-linear circuit which shapes the video baseband signal adapts to the changing character of the video signal being sent, providing improved gray-scale reproduction of the facsimile copy while enhancing the resolution of detailed image segments through variable emphasis of the high frequency components of the baseband signal. In the receiver section of the transceiver, the incoming signal is de-emphasized and post-equalized for correction of delay characteristics of the telephone line transmission link after which the upper sideband is removed, and the resulting signal, which possesses a substantial A.M. content is passed through a first hard-limiter which in effect produces a double sideband carrier signal which is then post-equalized for correction of the amplitude characteristics of the telephone line transmission link whereupon the signal is again hard-limited before being passed to a period-to-amplitude demodulator whose output, after further amplification, shaping and emphasis, drives a stylus to produce a faithful replica or facsimile of the original image.

Phase derivative modulation method and apparatus

Abstract: A carrier frequency input is simultaneously applied to a pair of quadrature modulating paths or channels, each containing a pair of cascaded modulator or mixer circuits. In these two modulating paths, the quadrature components of the carrier input are multiplied or mixed with phase quadrature components of a modulating signal whose period is equal to twice the bit length of the input phase code data. The resultant or modulated signals are then additionally mixed with the input phase code data; the phase code input to one modulator path being shifted relative to the phase code input to the other path by one-half of the code bit length. The outputs from the two modulating paths are then recombined to produce an output signal containing no discontinuities in the time waveform.