Showing papers on "Modulation published in 1975"

Communication systems: an introduction to signals and noise in electrical communication

Abstract: 1 Introduction 2 Signals and Spectra 3 Signal Transmission and Filtering 4 Linear CW Modulation 5 Exponential CW Modulation 6 Sampling and Pulse Modulation 7 Analog Communication Systems 8 Probability and Random Variables 9 Random Signals and Noise 10 Noise in Analog Modulation Systems 11 Baseband Digital Transmission 12 Digitization Techniques for Analog Messages and Computer Networks 13 Channel Coding and Encryption 14 Bandpass Digital Transmission 15 Spread Spectrum Systems 16 Information and Detection Theory Appendix: Circuit and System Noise

Zero-modulation encoding in magnetic recording

Abstract: This paper deals with waveform encoding methods in which binary data are mapped into constrained binary sequences for shaping the frequency spectrum of corresponding waveforms. Short and long pulse widths in the waveform are limited by constraints on the minimum and maximum run-lengths of zeros in the coded sequences. These constraints reduce the intersymbol interference in magnetic recording and provide an adequate rate of transition for accurate clocking. Signal power at low frequencies is limited by means of a constraint on a parameter that corresponds to the maximum imbalance in the number of positive and negative pulses of the waveform. This constraint on the maximum accumulated dc charge also eliminates the zero-frequency component. Zero modulation is one such code thati s especially suitable form agnetic recording channels. The encoding and decoding algorithm is presented, A one-to-one correspondence between binary data and constrained sequences is established by creating data states that are isomorphic to the charge states having the same growth rate. Sequences with other values of run-length and charge constraint are examined as candidates for other codes with zero dc component.

Application de la modulation spectrale à la transmission de l'information

Abstract: It is shown, theoretically as well as experimentally, that a system of communication based on the modulation of the spectrum of a light source is feasible. A white light source has been used for th...

Power spectrum of a digital, frequency-modulation signal

Abstract: We present the power spectrum of a sinusoidal carrier, frequency modulated by a random baseband pulse train in which the signaling-pulse duration is finite and the signal pulses may overlap and have different shapes. Symbols transmitted during different time slots are assumed to be statistically independent and identically distributed. The spectral density appears as a Hermitian form suitable for numerical computation by a digital computer. Simple conditions in terms of the modulation parameters are given under which discrete spectral lines are present in the spectrum. Several examples are given to illustrate the method.

Tracking and position determination system

Abstract: A method and apparatus for tracking and position determination includes generating carrier waves in transmitters; radiating said carrier waves; receiving said radiated carrier waves; imparting or simulating a motion, or motions, to radiators, reflectors or/and receiving antennas, within the locality of each, in such a way as to induce direction-dependent frequency modulation in each signal delivered to the receiving detectors; detecting said modulation on each received signal; and using measured parameters of said detected modulation to track the location of one or more of the said transmitters, reflectors or/and receivers and determine the corresponding position coordinates thereof. The actual or simulated motion of the radiators reflectors or antennas may have a uniform velocity along at least two straight, non-parallel lines.

Multi-line, multi-mode modulator using bandwidth reduction for digital FSK and DPSK modulation

Abstract: A multi-line multi-mode modulator uses compatible digital modulation techniques for multifrequency (MF), frequency shift keyed (FSK) and differential phase shift keyed (DPSK) modulation to achieve a multi-line multi-mode modulator which is capable of handling a plurality of lines requiring a dynamic mix of the three modulation techniques. The compatible modulation techniques utilize bandwidth reduction schemes which enable the use of simple RC filters on each output line for the sole purpose of removing the quantizing noise introduced by the digital modulation technique.

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

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

Integrated electro‐optic intracavity frequency modulation of double‐heterostructure injection laser

Abstract: Integration of a taper‐coupled GaAs‐AlxGa1−xAs laser with a linear electro‐optic modulator permits efficient optical frequency modulation of the laser emission. The pulsed room‐temperature threshold current density of the device was 8 kA/cm2. Frequency modulation depth in excess of 15 GHz (corresponding to a wavelength shift of 0.4 A) was obtained with a reverse bias change of 20 V across the modulator. Conversion of frequency modulation into intensity modulation was demonstrated with a characteristic power P0 of 10 μW/MHz for 90% intensity modulation. It is shown that reduction of P0 by an order of magnitude is easily feasible.

Carrier-modulated coherency monitoring system

Abstract: A radio information system is described which uses the exact mathematical tios and the unique periodic angular coherence of the residual RF carrier and the digitally encoded modulation spectral components of the electromagnetic wave as emitted by a source transmitter (or transmitters) to enhance system performance and to provide new instrumentation and measurement capabilities at the receiver apparatus. The digital modulation synchronizing code occupies a wide frequency bandwidth and is encoded for precise repetitive transmission to provide, for example in a satellite navigation system, a means of accurate synchronization and measurement of time and range parameters. Many encoded sequences of either discrete or pseudo-random types may be used as the synchronizing code. However in the description herein the pseudo-random noise (PRN) codes are used for their added advantage in spread spectrum discrimination against intentional interference. The total or composite RF signal typically also includes non-interfering information or message modulation.

Compatible AM stereophonic receivers

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

Optical bar code scanning device

Abstract: An optical bar code scanning device for high data density bar code reading. The device utilizes a two channel arrangement for directing light reflected from the bar code being read onto two photodetectors in predetermined proportionate amounts. With a two channel system, it is possible to detect a bar edge independent of print contrast variations, resolution modulation or change of illumination by comparing the optical signal of one channel with the optical signal of the other. The bar edge is represented by the crossover point of the normalized outputs of the two channels.

Spectrometer means employing linear synthesized RF excitation

Abstract: Broadband RF excitation for a Fourier transform spectrometer is obtained by synthesizing the time domain excitation from the desired frequency spectrum of RF excitation. Means are provided to Fourier transform the desired spectral data from the frequency domain into the time domain to obtain a modulation output for modulating an RF carrier signal to generate the desired sideband of RF excitation. In a preferred embodiment, the desired frequency domain data, as tabled in the computer, has a pseudorandom phase shift added to each component for scrambling the phases of the RF excitation. The excited RF resonance signals in the time domain are detected, time-averaged, Fourier transformed to the frequency domain and, in the case of phase scrambling, unscrambled by the pseudorandom phase angle sequence, and displayed.

Flux locked loop

Abstract: A flux locked loop, employing a squid in connection with the production of the locked-loop error signal, includes circuitry which renders the locked loop more immune to disturbance inputs such as a ground-loop noise and interference transients and which facilitates a scale factor adjustment of a sub-carrier drive signal for the squid. To minimize ground-loop noise disturbance effects, a portion of the circuitry in the feedback path of the locked loop includes a voltage-responsive converter circuit arrangement providing a current-drive feedback signal for coupling to the squid. To minimize interference transient disturbance effects, a portion of the circuitry in the forward path of the locked loop includes a circuit arrangement having a non-linear transfer characteristic defining opposed substantial attenuation regions separated by a generally linear gain region. To facilitate adjustment of the scale factor to a desired value, a portion of the circuitry provides for an open-loop operation in which a test-mode oscillating signal is coupled to the squid along with an operating-mode modulation drive signal. This causes a heterodyning process to take place such that the frequency spectrum of the electrical signal does not contain frequency components at or near the frequency of the test-mode oscillating signal under circumstances in which the modulation drive signal has been adjusted to the desired value.

Automatic one-per-rev control system

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

Digital transmitter for data bus communications system

Abstract: Disclosed is an improved digital transmitter for transmitting serial pulse-code modulation (pcm) data at high bit rates over a transmission line. When not transmitting, the transmitter features a high output impedance which prevents the transmitter from loading the transmission line. The pcm input is supplied to a logic control circuit which produces two discrete logic level signals which are supplied to an amplifier. The amplifier, which is transformer coupled to the output isolation circuitry, converts the discrete logic level signals to two high current level, ground isolated signals in the secondary windings of the coupling transformer. The latter signals are employed as inputs to the isolation circuitry which includes two series transistor pairs operating into a hybrid transformer functioning to isolate the transmitter circuitry from the transmission line. An effective increased amplitude, balanced, differential output signal is produced by the transmitter from the serial pcm input data to provide an improved transmitted signal to the transmission line.

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

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

Coupled mode analysis of light modulation in dielectric waveguides

Abstract: A detailed analysis of electrooptic light modulation in optical waveguides is presented. Several important problems of a waveguide modulator, such as the difference of waveguide axes from crystalline electrooptic ones, the distribution of transverse and longitudinal field components of light modes, and the traveling-wave property of the modulating field, are discussed. The analysis is based on the coupled mode theory, regarding the modulation as the coupling among sidebands of unperturbed waveguide modes. The coupled mode equation is derived for the modulation in optical waveguides. It can be solved if the normal modes of the waveguide are given. Actually the equation is solved for the modulation in dielectric slab waveguides and the mechanism of modulation is discussed. The results of the analysis are applied to designing two types of waveguide modulators. In an example (10.6 μm modulator with a GaAs slab waveguide) a new efficient crystal orientation is found. The calculated phase retardation with this orientation is 0.13 rad/(V·cm) with a 1 μm thick slab. Another example of a 0.633 μm modulator using a LiTaO3 crystal as a substrate is also described.

Modulation and Switching of Light in Dielectric Waveguides

Abstract: In this chapter, we will discuss methods of electronically controlling the flow of light in optical waveguides. We will restrict our attention to devices that may be called either modulators or switches. Some of these devices are capable of performing both functions.

Precision test frequency generator

Abstract: A precision test frequency generator capable of selectively providing a sinusoidal output wave within a frequency range simulating the output of a flowmeter yielding a sinusoidal signal whose frequency is proportional to flow rate, the signal having a noise component superimposed thereon. The generator is constituted by a stable high-frequency standard coupled to a selectable output counter providing intermediate-frequency pulses whose repetition rate is a sub-multiple of the high-frequency standard and a predetermined multiple of the desired output frequency of the generator. The pulses are converted into a triangular wave whose frequency corresponds to the desired output frequency, the triangular wave having a staircase formation whose number of steps is determined by the multiple. The triangular wave is converted into a sinusoidal wave of the same frequency with a staircase modulation component simulating the flowmeter output signal.

Large-signal p.c.m. behaviour of injection lasers with coherent irradiation into one of their oscillating modes

Abstract: The effect of coherent irradiation on the modulation characteristics is investigated theoretically. A p.c.m. simulation has been performed using a multimode rate-equation model. A significant improvement in the modulation behaviour is predicted if the laser is subject to an external irradiation.

Pulse-code modulation communication system

Abstract: A pulse-code modulation transmission system having reduced redundancy and high transmission quality utilizes a variable companding law and variable number of bits per sample both of which vary in accordance with the type and/or short-time volume of the signal associated with a particular talker as well as with the type and/or short-time volume of all of the signals associated with all of the talkers handled by the transmission system. The system utilizes the envelope or modulating signal for the speech signal to provide a companding law which varies as the talker varies and, for a particular talker, as the short-time volume of that talker varies, so that redundancy can be reduced without impairing transmission quality. This companding law adapts itself to the vowels, consonants and syllables of the word in accordance with their volume in order to optimize the signal to quantizing noise ratio.

Receiver especially for use as a diversity combining receiver with channel selection capability

Abstract: A receiver especially for use as a diversity combining receiver is adapted to recover a single signal from among a plurality of cochannel signals transmitted from a plurality of sources. When recovering signals from a plurality of sources, the various sources transmit signals having PSK modulation and having, in addition, pilot tag modulation uniquely associated with each source. The output from each of the diversity branches is combined and the combined output is mixed with the output signal generated by a free-running oscillator to produce a loop signal uniquely identified by one selected tag. The processing is arranged so that when this loop signal is mixed with each branch input, the resulting sideband product of the loop signal and the one received signal having the selected tag contains a distinctive cophasing phase angle but is stripped of its PSK information and tagging modulation. However, the resulting sideband product of the loop signal and any unselected received signal contains some unremoved modulation or tagging and it is, therefore, distinguishable. Only the one modulation-free product derived from the received signal having the selected tag, is mixed with the total branch input and thus only the transmission having the selected tag contributes to the cophased combined output. The present arrangement provides a precise loop signal, and the loop will remain locked despite slight variations of either one or both of the input signal frequency or the injection frequency generated by the free-running local oscillator.

Visualization by ultrasonic detection

Abstract: A system for sensing by ultrasonic vibrational energy the shape and character of objects immersed in a visually opaque transmission medium is disclosed. Frequency modulated ultrasonic waves are projected to irradiate an object, with reflected energy from scattering points on the object being imaged on an ultrasonic image camera. The camera converts the received ultrasonic image to an electronic image which is electronically scanned to produce an output video signal having an amplitude and frequency which is a linear representation of the point-by-point interrogation of the image. The video signal is fed in parallel to an amplitude modulation detector, which produces a linear signal representing the video signal envelope, and a frequency modulation detector, which produces a constant amplitude reproduction of the original modulation signal, except for shifts in phase in accordance with the time delays of reflected ultrasonic signals reaching successive image points on the camera. The outputs of the detectors are processed and the resulting modified video signal and phase angle signal are applied to a visual display such as a cathode ray tube to provide a reconstituted presentation of the depth dimension of the object.

Digital signal synthesis system

Abstract: A process and an apparatus using an inverse discrete Fourier transform forynthesis of complex waveforms that have one or more sinusoidal components of arbitrary frequency, amplitude and phase. The component sinusoids are formed in segments of a predetermined period and modulated according to a preselected function. The modulation characteristic is compensated for by overlapped concatenation of adjacent segments.

Arrangement for compensating duty factor variations in an optical video disc

Abstract: Processing optical video discs may result in modulation of the duty factor of the pits and lands which constitute a spatial representation of a stored carrier signal frequency modulated with program information. Such modulation of duty factor introduces spurious components that are detrimental to image reproduction if the frequency of the stored carrier signal is not at least twice the highest video frequency component to be reproduced. A correction signal is developed and used to at least partially cancel the effect of such spurious components.

Audio frequency power line control system

Abstract: An audio frequency power line carrier control system utilizing an inverter as the carrier control transmitter with the output phase voltages of the inverter fed to a distribution network through a series inductance, a filter circuit and a current transformer in which a starting control is provided which modulates the audio frequency pulses at the beginning of clock pulses for transmitting data using a control signal which is pulse width modulated, modulation being terminated when the pulse width of the control pulse width falls below a predetermined minimum duration thereby permitting small series inductances to be used.