Showing papers on "Modulation published in 1973"

A Combined Coding and Modulation Approach for Communication over Dispersive Channels

Abstract: The concept of combining the design of the error-correcting-coding approach and the modulation format is treated in general terms and its effectiveness is demonstrated by a specific implementation referred to as Codem I. A new decoding algorithm is presented, which has the interesting property that the only channel measurement information utilized is the relative reliability of each received digit. The effectiveness of this decoding technique is demonstrated by computer simulation over three different channel models for dispersive channels. Comparisons of the performance of Codem I with the more conventional 16-tone (four-phase DPSK) HF modem are obtained by actual field results as well as by computer simulations. Improvement in error probability in the region of two orders of magnitude is demonstrated when both systems are operating under similar channel conditions and at equal data rates. A further improvement is demonstrated when channel measurement information is used to reject a small percentage (typically less than 3 percent) of codewords that are considered unreliable.

System for communication and navigation

Abstract: A radio navigation and digital communication system is used for the transmission of navigation modulation and digital data. A modulation locked loop, which may be constructed with three channels, is used to develop synchronization signals for the digital data signals and to ensure a high level of communication reliability and accuracy of navigation measurement using pseudo random navigation code.

Large-signal direct modulation of injection lasers

Abstract: Large-signal direct modulation of injection lasers is described with the aid of nonlinear rate equations. For periodic modulation of arbitrary amplitude, an approximate large-signal oscillatory solution is described. Large spiking amplitudes of the modulated photon density are generated near the resonance frequency of the system.

Acousto‐optic diffraction of guided optical waves in LiNbO3

Abstract: We report acousto‐optic diffraction modulation of a guided optical wave in LiNbO3 by an acoustic surface wave. 250 mW of acoustic power produces 100% modulation of the zero‐order beam.

Coding system for differential phase modulation

Abstract: This invention is related to a coding system for a differential phase modulation system in which an input signal is coded into a signal including an error correcting code, predetermined bits of the coded signal are used as one symbol, and the phase of a carrier is deviated in accordance with the symbol, said coding system comprising: series-parallel converter means for converting a series input signal into parallel signals, encoder means for encoding each of the converted signals into a signal including an error correcting code, and buffer means for dividing the coded signals into predetermined bits and providing them alternately each in the form of one symbol.

Sputtered ferroelectric thin-film electro-optic modulator

Abstract: The modulation of guided optical waves has been accomplished using an integrated ferroelectric thin‐film structure. LiTaO3 was rf sputtered onto 7059 glass in an argon‐oxygen environment. Electrodes for applying the modulation signal were formed by chemically etching an interdigital pattern in gold which was rf sputtered onto the LiTaO3. The observed modulation of guided waves launched in the ferroelectric film can be attributed to the linear electro‐optic effect.

Pulse quaternary communication means

Abstract: A pulse quaternary modulator especially to enable laser communication systems when working at high data rates to be able to operate on less laser power and on a modulation format that improves modulation efficiency. The subject modulation means can be used in transmitters and receivers and include means that make use of polarization changes in the modulator to create selective high speed electronically controlled optical time delays, and it also includes means for using a combination of polarization state and pulse position information to represent information choices. The subject means are also able to achieve M-ARY modulation when using as a source a mode-lock laser which produces output laser pulses.

A Spectral Theory for Hybrid Modulation

Abstract: Certain properties of periodic signals are defined in terms of the zeros and singularities of associated analytic functions of a complex time variable z . This algebraic approach is a generalization of analytic signal theory, and leads to the conception of hybrid modulation as the superposition of two z -plane zero-singularity (ZS) patterns associated with amplitude- and angle-modulating signals, respectively. It is shown that important spectral properties of the modulated signal, such as band limitation, are explicit in the resultant pattern. Signal design is then interpreted in terms of ZS manipulation and placement. The theory is applied in a unified approach to compatible singlesideband (CSSB) modulation systems. It is shown that two types of proposed CSSB systems give rise to essentially nonband-limited output signals. The relation between conventional and single-sideband (SSB) angle modulation is also discussed in terms of their characteristic ZS patterns.

Multiplexed communications system

Abstract: A pulsed optical communication system based on use of a pulse train generated, for example, by a Q-switched laser, is frequency multiplexed so as to contain generally upwards of 10 subchannels. Subchannels correspond with frequency spectral portions representative of natural laser modes and are processed by first separating the spectral content of a pulse envelope, for example, by use of a prism, and then modulating such portions individually. Modulation may take any of the usual forms-either quantized or analog. In the usual system, component pulses are reconstituted after modulation perhaps by introduction into a transmission line. Demultiplexing is accomplished by a similar procedure, i.e., by separating spectral components within a pulse envelope and by introducing such components into photomultipliers or other suitable detectors.

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.

Method and modulation system for ambiguity reduction in pulsed radar

Abstract: The modulation system of a pulsed radar includes a modulator having a generator for providing a radar pulse repetition frequency (PRF) signal and which pulse modulates a single frequency oscillator to develop a pulse modulated signal. The PRF signal also drives a divider circuit that creates a divided control signal in phase coherence with the PRF signal. The divided control signal enables a linear sawtooth frequency modulated (FM) oscillator to provide an FM signal having a modulation rate which is a submultiple of the PRF. The total deviation of the FM signal is a function of the PRF. A mixer circuit combines the FM and pulse modulated signals, and the sums of the frequency components thereof are selected by a filter to provide a modulated output signal which is suitable for being transmitted by a radar either directly or on a carrier. The modulated signal rotates the time-frequency plane of the pulse modulation ambiguity response pattern of the radar with respect to the amplitude axis so that unwanted ambiguities are shifted off of the time and frequency axes to facilitate velocity and range measurement.

The Properties of Phase Modulated Soliton Trains

Abstract: Using nonlinear LC networks which are equivalent to a one dimensional nonlinear lattice, the solitariness and the recurrence phenomena are experimentally investigated for a pair of soliton trains of which the phases are independently modulated. Using a phase modulation system, up to 30% modulation is obtained. This modulation ratio is about 3 time larger than that for an amplitude modulation system.

Communications system utilizing modulation of the characteristic polarizations of the ionosphere

Abstract: A system for high frequency ionospheric radio communication utilizing transmitting and receiving antenna polarizations which are adjusted to take into account specific properties of the ionospheric medium and comprising two sets of transmitters, receivers and antennas that send and receive polarized waves. Two channels of information can be received at a single RF transmitted frequency. An RF exciter circuit provides the excitation to two mixers each of which is driven by two signal sources. The outputs of the mixers are then amplified to drive the antennas.

Optical Communication System Performance with Tracking Error Induced Signal Fading

Abstract: System performance is determined for an optical communication system using noncoherent detection in the presence of tracking error induced signal fading assuming 1) binary on-off modulation (OOK) with both fixed and adaptive threshold receivers, and 2) binary polarization modulation (BPM). BPM is shown to maintain its inherent 2-3 dB advantage over OOK when adaptive thresholding is used, and to have a substantially greater advantage when the OOK system is restricted to a fixed decision threshold.

System for transferring wideband sound signals

Abstract: A system for transmitting wideband signals, for example speech, over a narrow band is proposed. Lower frequency range signals are directly transmitted and amplitude information of partial upper frequency ranges is transmitted on pilot frequencies. At a receiver, "equivalent" signals from oscillators having frequencies approximately equal to the mid range frequencies of the partial upper frequency ranges are modulated with the amplitude information of the corresponding partial upper frequency ranges to produce "synthetic" signals. The synthetic signals are modulated with narrow band noise to crreate a more pleasing and realistic sound. Means are provided for controlling at the pick-up end the "modulation factor" of the noise modulation at the reproducing end. This is achieved by controlling the level of the third harmonic of a sync signal transmitted from the pick-up end. The level of the third harmonic may be automatically or manually adjusted to conform to the type of sound being transmitted.

Small-signal design theory and experiment for the punch-through injection transit-time oscillator

Abstract: The small-signal theory of the punch-through ‘barrier-injection and transit-time’ (BARITT) diode is given and the physical mechanisms of device operation are described Both velocity modulation and charge density modulation components of current are included and the effects of carrier diffusion in the source regions of the device are taken into account by using an equivalent small-signal conductivity for the potential barrier which controls charge injection It is shown how carrier bunching in the source regions creates space-charge waves which propagate through the source-drain space and generate power as the associated component of current moves into anti-phase with the local electric field Theoretical curves are presented for a typical PNP silicon device and agree well with experimental measurements of series resistance and series capacitance A device of area 1·25 × 10−8 m2 (5 thou diameter) and source to drain spacing of 5 μm made in 5 Ω cm material was found to possess negative resistance over the wide frequency range from about 5 GHz to about 12 GHz with a maximum value of about — 5 Ω

A new method for reducing pattern effect in PCM current modulation of DH-GaAlAs lasers

Abstract: A new method for reducing the pattern effect in PCM current modulation of DH-GaAlAs lasers without superposition of dc bias current is demonstrated at 200 Mb/s. Also PCM current-modulation characteristics are analyzed by simulation using nonlinear rate equations.

Ternary code error detector for a time-division multiplex, pulse-code modulation system

Abstract: In a time-division multiplex, pulse-code modulation system, each sequence of four binary pulses representing information is converted to a group of three ternary pulses for transmission to a receiver. The conversions are made either in a positive mode if the prior net polarity is negative or in a negative mode if the prior net polarity is zero or positive. Use of the positive and negative modes insures that the net positive and the net negative polarities are kept within selected limits. At the receiver, a ternary code error detector is provided to detect if the net positive polarity or if the net negative polarity exceed the selected limits. If either selected limit is exceeded, the error detector produces an error signal which can be used in any way desired, such as to switch to other multiplexing equipment, or to switch to other transmission lines, or to produce any sort of desired alarm.

The audio frequency size effect seen in the modulation of the radio frequency size effect

Abstract: The modulation field used in the radio frequency size effect is screened by induced audio frequency currents. The incomplete penetration of the modulation field can be clearly seen in the phase lag of the Gantmakher resonance signal behind the signal due to surface bound states. A comparison of the phase lag as a function of modulation frequency with a simple theory leads to an estimate of the bulk electron mean free path. The influence of modulation field screening on measurements of the phonon limited mean free path and other applications are discussed.

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.

Laser pulse shaping due to self‐phase modulation in amplifying media

Abstract: It is shown experimentally that high‐power laser pulses amplified in ruby can display strong frequency‐modulated characteristics due to the refractive‐index nonlinearity of the medium. Theoretical calculations of the coherent pulse amplification under similar circumstances show that self‐phase modulation causes asymmetric pulse shaping due to adiabatic passage effects.

Digital Single-Sideband Modulation

Abstract: This paper considers digitized Weaver modulators for single-sideband modulation that can be used in radio communications and telemetering. A system of 12 such modulators to process 12 analog signals digitally is replaced by six multiplex modulators at the cost of additional computation at the input but with an overall reduction in computation time and a higher degree of accuracy. A unique digital filter is developed that can interpolate and output samples at multiples of the input sampling rate and exhibits a passband that occurs above the Nyquist frequency with no apparent distortion effects. A discussion of the Fortran simulation of a combined modulator-demodulator structure is included to verify the effectiveness of this scheme.

Compatible stereoscopic color television system

Abstract: A compatible stereoscopic colour television system with phasedifference quadrature modulation of the colour subcarrier by the chrominance signals of the first image of the stereo pair and transmission of the signals of the second image of the stereo pair on a subcarrier located in the frequency spectrum of the luminance signal, according to the invention, the system is characterized by the fact that the luminance signal of the second image of the stereo pair is employed for effecting additional modulation of the subcarrier so that the amplitude of the latter in one line is equal to the sum of the amplitude of the modulating signal and the square root from the amplitude of thel quadrature modulated subcarrier, whereas in the other line it is equal to the difference of these amplitudes; the additional modulation is carried out with conservation of the phase difference of the subcarrier in the adjacent lines; during the reception the chrominance signals of the first image of the stereo pair are separated by way of multiplying the delayed and undelayed voltages of the subcarrier directly for one signal and with an additional 90* phase shift for the other signal, the chrominance signals of the second image of the stereo pair being separated by way of detecting the delayed and undelayed voltages and obtaining the difference of their envelopes.

Fire detector responsive to amplitude modulation of a pulsed em beam

Abstract: In fire-detection apparatus of the kind in which a radiation receiver is exposed to a source of radiation through an intervening gaseous medium, the beam of radiation overlaps the receiver so that the beam continues to cover the receiver despite minor changes in beam direction due, for example, to movement of the surfaces supporting the emitter and receiver. Discrimination against ambient radiation is improved by causing the source, which is a solid-state emitter, to emit pulses of radiation and by having a frequency-selective circuit for selecting from the output of the radiation-sensitive device in the receiver a pulse signal resulting from the received pulses of radiation; an alarm circuit is responsive to an amplitude modulation in this pulse signal at a frequency which is typical of the modulation produced by a fire heating the gaseous medium between the source and the receiver.

Digital modulation generator with cylindrical antenna array system

Abstract: An antenna array for the TACAN navigational guidance system has a plurality of cylindrically arranged antenna elements. Each element is excited with a modulated radio frequency signal, the modulation pattern for each such element having a predetermined phase relationship with reference signals. The modulation signal for all antenna elements are stored in digital form in a memory which may comprise a "read only" memory. The memory is digitally addressed to successively provide outputs in binary coded form, these outputs representing the modulation signal for each of the antenna elements in sequence. The outputs of the memory are converted to analog form to provide modulation signals for each of the antenna elements in incremental steps.

Communications system using time position modulation and correlation slope demodulation

Abstract: An angle modulation radio communications system having privacy and security characteristics. The system utilizes two or more communication units, one at the transmitting terminal and the other at the receiving terminal of identical functional construction and each having a transceiver module, an antenna and a phase reversal modulator-demodulator module between the transceiver module and the antenna. Complex phase reversal modulation of the transmitted carrier is accomplished which produces a constant amplitude spread spectrum frequency-modulated carrier from which the modulation is not recoverable without a proper code in an autocorrelation process. The modulator-correlator module is bidirectional in operation, and because of its interposition between the antenna and the receiver module, the modulator-correlator spreads the spectrum of any electromagnetic wave signals supplied by it to the transmitting antenna and also spreads the spectrum of any signals received by the antenna not included in accordance with the proper code. Therefore, the units of the system present a very high degree of signal frequency selectivity and rejection of any electromagnetic wave radiation not having the proper code. Pseudo-random code phase reversal modulation suppresses the carrier and the intelligence signal power is in the form of frequency perturbations of the pseudo noise code modulation.