Showing papers on "Interference (wave propagation) published in 1979"

A Comparison of Modulation Techniques for Digital Radio

Abstract: This paper describes and summarizes the characteristics of the modulation techniques most applicable to digital radio. The modulation techniques discussed are on-off-keying (OOK) with coherent and noncoherent detection, quadrature amplitude modulation (QAM), quadrature partial response (QPR), frequency-shift-keying (FSK) with noncoherent detection, continuous phase FSK (CP-FSK) with coherent and noncoherent detection, minimum-shift-keying (MSK), binary and quaternary phase-shift-keying (BPSK, QPSK) with coherent and differentially coherent detection, offset-keyed QPSK (OK-QPSK), M -ary PSK with coherent detection ( M = 8, 16 ), and 16-ary amplitude and phase-shift-keying (APK). Functional descriptions of these schemes are provided and their performance is compared in a series of tables summarizing the results of the literature of the past 20 years. The modulation schemes are compared with respect to ideal (white Gaussian noise) performance, spectral properties, signaling speed, complexity, and the effects on performance of interference, fading and delay distortion.

Error-rate performance of digital FM with differential detection in land mobile radio channels

Abstract: Error-rate performance of a digital FM with differential detection in the presence of both thermal Gaussian noise and cochannel interference is theoretically analyzed in the fast Rayleigh fading environment encountered in the typical UHF or microwave land mobile radio channels. The temporal correlation of the fades is included in the performance analysis. The error probability is presented by a simple closed form for the important situations where both effects of Gaussian noise and cochannel interference predominate in causing errors. Finally, a comparison with the other detection schemes, e.g., discriminator and coherent detections, is given.

Multireflection optical multi/demultiplexer using interference filters

Abstract: A multireflection multi/demultiplexer using interference filters is proposed. Light waves of different wavelengths are combined or separated while they propagate between two filter arrays. The insertion loss of the 6-channel demultiplexer was around 1dB.

Effects of atmospheric turbulence on the interference of sound waves above a finite impedance boundary

Abstract: The interference spectrum between direct and ground‐reflected sound waves is strongly influenced by fluctuations in their phase and amplitude induced by propagation through turbulence. Measurements of the interference spectrum at distances up to 45 m over a flat asphalt surface were shown previously to be in satisfactory agreement with a spherical wave theory that allowed for partial covariance between the phases of the interfering waves. The amount of covariance was claculated from simultaneous measurements of wind and temperature fluctuations in the atmosphere. This theory has now been extended to include propagation over ground of finite acoustic impedance and provides an explanation for measurements of jet noise over grass to a distance of 1100 m. Above 300 Hz the sound levels are up to 10 dB higher than predicted by coherent acoustic theory. The meteorological parameters were used as constants adjusted for best fit and agreement is obtained by assuming standard deviations in phase velocity of about 1...

Interference in Multiprocessor Systems with Localized Memory Access Probabilities

Abstract: Past studies of memory interference in multiprocessor systems have generally assumed that the references of each processor are uniformly distributed among the memory modules. In this paper we develop a model with local referencing, which reflects more closely the behavior of real-life programs. This model is analyzed using Markov chain techniques and expressions are derived for the multiprocessor performance. New expressions are also obtained for the performance in the traditional uniform reference model and are compared with other expressions-available in the literature. Results of a simulation study are given to show the accuracy of the expressions for both models.

Method of Calculating Retroreflector-Array Transfer Functions

Abstract: Techniques and equations used in calculating the transfer functions to relate the observed return laser pulses to the center of mass of the Lageos satellite retroflector array, and for most of the retroreflector-equipped satellites now in orbit are described. The methods derived include the effects of coherent interference, diffraction, polarization, and dihedral-angle offsets. Particular emphasis is given to deriving expressions for the diffraction pattern and active reflecting area of various cube-corner designs.

Charged- and neutral-current interference in ν e -e scattering

Abstract: In the scattering of electronic neutrinos ..nu../sub e/ by electrons, charged- and neutral-current weak interactions can interfere with each other. According to all the popular gauge models that are consistent with neutral-current data, including the measurements of polarized-electron--deuteron scattering, this interference should be negative. The conditions under which a beam-dump experiment can be used to study charged- and neutral-current interference are studied in detail. It appears that if the interference is assumed to be present in the first place, then a 25% measurement of the integrated cross section will allow one to determine its sign. A greater accuracy is required to show that the interference actually does occur in ..nu../sub e/-e scattering. Tests for the presence of the helicity-flipping covariants S,P,T are also discussed.

Self-derived reference beam holography using a dove prism

Abstract: A method and associated system for providing interference patterns generated from light, including visible, ultraviolet and infrared, carrying desired information comprises the steps of and associated apparatus for modulating a light beam emanating from a suitable source, in accordance with the desired data or information or signal, splitting the modulated light beam into a pair of component beams, both thereby derived from the modulated beam, reflecting the resultant split beams towards each other so as to interfere optically. Advantageously, beam splitting and reflection may be effected by an essentially integrated, transparent element. Also advantageously, a recording of such interference is made by a positioning photosensitive medium at the point or in the plane of interference. Alternatively, an interference recording or filter may be positioned at the point or plane of optical interference, a blocking element positioned behind the splitting and reflecting element for blocking transmission of one of the split beams, and sensing apparatus positioned behind the recording on the line of transmission of the blocked beam to detect the re-occurrence of a signal corresponding to that contained on the recording.

Experimental Evidence for Interference Effect in K -Shell- Vacancy Sharing

Abstract: The impact-parameter dependence of $K$-shell-vacancy sharing has been investigated with collisions of H-like S (${\mathrm{S}}^{15+}$) on Ar. An oscillation of the vacancy-sharing ratio with impact parameter has been found which is due to the interference of components of the vacancy-sharing amplitude on incoming and outgoing parts of the collision.

Moiré interferometry with white light.

Abstract: While high-sensitivity moire interferometry requires monochromatic light, an auxiliary compensator grating removes the requirement. Experimental verification utilized white light for moire interference of sensitivity 0.833 μm/fringe. Configurations readily amenable to compensation include moire fringe multiplication by even factors and the minimum-deviation arrangement. Chromatic compensation is effective with virtual reference gratings as well as real reference gratings; in both cases the moire interference system becomes achromatic. Compensation provides the special quality of nearly zero phase difference—an actual range of ±π—between interfering beams. Potential applications include use of electrical spark light sources for high-sensitivity dynamic moire photography.

Carrier tracking loop performance in the presence of strong CW interference

Abstract: In a coherent data link, narrow-band radio frequency interference (RFI) near the carrier frequency can degrade the link performance by impacting the carrier tracking loop behavior and producing a partial or complete loss of coherence. If the RFI is strong enough, this effect can occur even though the frequency of the interference lies well beyond the carrier tracking loop bandwidth. In 1973, Bruno and Bianchard independently performed similar analyses of the response of a phase-locked loop (PLL) to a continuous wave (CW) interferor, and derived conditions under which the loop drops carrier lock and tracks the interference instead. This paper compares the contributions of these two analysts, and extends Bruno's closed form approximation for the loop phase error to the entire lock region.

Computer-controlled Fabry-Perot interferometer for Brillouin spectroscopy.

Abstract: Long measuring times are required to obtain an adequate SNR when recording weak intensity scattered light spectra with a Fabry-Perot interferometer. Drifts of laser frequency and mechanical and thermal instabilities of the interferometer, which affect the exact adjustment of the Fabry-Perot plates, are disturbing factors in the measurement. The system described here consists of a piezoelectrically scanned Fabry-Perot interferometer and a computer-controlled multichannel analyzer which uses the elastically scattered line (Rayleigh line) as a reference in order to compensate drifts of laser frequency and allow parallel alignment of the mirrors over long periods of time.

Design and Performance of an Adaptive Kalman Receiver for Synchronous Data Transmission

Abstract: A class of multilevel linear-modulation data-transmission systems, over unknown, slowly time-varying, and bandlimited channels is considered. It is shown how sequence estimation in the presence of Gaussian noise and intersymbol interference can be carried out by means of a discrete Kalman estimator. Moreover, the receiver can be provided with data-aided adaptive loops for performing channel identification, carrier recovery, and timing extraction. A computational method is presented to evaluate the average probability of error of the overall system in the presence of inter-symbol interference, additive noise, and phase-and sampling-synchronization errors. The method is based upon nonclassical one-and two-dimensional quadrature rules, which are outlined in the Appendix. As an example, numerical performance results related to a phase-shift-keying (PSK) system are given. The results are obtained by means of general-purpose and system-oriented computers.

Superposition fringes as a measuring tool in optical testing.

Abstract: Superposition fringes are suitable for making highly accurate measurements of the thicknesses of air layers. A combination of a multiple beam interferometer (Fabry-Perot) and a two-beam interferometer is discussed. In this case the contrast degradation is small. Two possible applications are discussed to some extent: the first deals with the adjustment of air gaps between lenses or other optical elements, and the second is a special spherical Fizeau interferometer. This interferometer makes possible surface testing of spheres with the help of interference colors or rings as is usual with the proof glass method, with radius differences of several centimeters. The latter application seems especially promising.

Precise Optical Evaluation Using Phase Measuring Interferometric Techniques

Abstract: Fabrication of high quality optical surfaces requires both sensitive methods for measuring surface characteristics and delicate control of the fabrication process. Conventional metrology interferometers have been augmented with computer controlled interference phase measuring techniques to give greater accuracy and provide real-time data analysis. Key elements of a Phase Measuring Interferometer (PMI) system are a Twyman-Green interferometer; piezoelectric-driven reference mirror; image detector; and a minicomputer system with a graphic display, keyboard, and hard copier. Surface quality data is obtained by a direct measurement of intensity and computation of phase difference over an aperture containing a 32 x 32 element array. System functions include: isometric contour mapping at variable sensitivity, array subtraction, surface calibration, time averaging, determination of tilt and power over subapertures with respect to a clear aperture, and deconvolution of wavefront data to yield aberration coefficients. The system is being used to produce high-quality reflecting spheres, flats, mirrors, and refractive elements. A measurement uncertainty of <0.01A peak to valley and 0.001 Xrms has been achieved in the evaluation of a large spherical reflector.

Application of the FabryÁ-Perot Interferometer as a Refractometer

Abstract: A new method is used to determine the interference orders for various wavelengths in thick dispersive layers. The method is based on an order transformation in which the interference order is expressed in terms of a lower order representing the number of subtractive moire fringes which are producible along the interferometer axis with each spectrum doublet. Knowing the unambiguous value of the moire order, it is possible to deduce exactly either the absolute value of the interference order making use of a doublet with close components, or the difference of interference order in the case of a doublet with widely spaced components. The optical length can be determined accurately to the sixth decimal place of a millimeter. The refractive index of a layer of one centimetre thickness is determined accurately to the seventh decimal place. A new transformation of the Sellmeir dispersion formula facilitates the determination of the parameters of the atomic oscillators for glass.

Versatility Of A Microprocessor-Based Interferometric Data Reduction System

Abstract: The Zygo interference Pattern Processor was designed to evaluate either hard copy interferograms or real time interference patterns rapidly and accurately. Since its introduction one year ago, it has undergone an evolution leading t two new systems which shall be described here. In addition, continuing software development has led to a highly flexible operating system, satisfying many users requirements. These new features have been stimulated in the course of their development by various use requirements leading to the refinement and definition of the new systems. For those interested only in the basic analysis of an interference pattern, a minimum system has been designed and built. Those requiring not only the entire analysis capability but multiple systems can now time share one processor. Continuing developments for the reduction of very complex fringe patterns will on offer the industry a tool for measuring virtually all of its interference pattern's., Before providing more details of the nature of these new systems, a brief description of the basic system and its operation will be given first.© (1979) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Quasi-Molecular Interference Effects in Ion-Atom Collisions

Abstract: Publisher Summary A number of new fundamental phenomena have been discovered in atomic collision physics over the past ten years. One of these is quantum-mechanical phase interference between inelastic quasi-molecular channels. The coherent excitation of the inelastic quasi-molecular amplitudes and their interference result in an oscillatory structure in the energy dependence of the total cross sections of the inelastic scattering channels. This chapter reviews the experimental and theoretical studies where phase interference phenomena have been established and comprehensively investigated. The interference effects were first observed as a result of an investigation of spectral line emission originating during low-energy ion-atom collisions. The energy range of low-energy collisions is assumed to be comparable with the energetics of the outer-shell excitation for the atoms and single ions involved. In practice this means that the laboratory energy E of fast ions is less than 10 keV. Theoretical consideration of the interference effects follows the quasi-molecular approach to atomic collisions. According to this approach, the probability of an inelastic process and its dependence on the collision energy are determined by nonadiabatic transitions in a quasi-molecular system, i.e., dynamic processes in a two-atom molecule with changing internuclear separation. This chapter gives attention to experimental investigations where the phase interference of inelastic quasi-molecular amplitudes has been first observed and the qualitative interpretation has been given. The next section of this chapter deals with the studies of oscillatory structures of total cross sections of inelastic scattering processes. A new type of interference effect is discussed in next. This effect is responsible for regular oscillations in the degree of polarization of light emitted in atomic collisions. The importance of the interference phenomenon for atomic collisions is discussed in the final section of this chapter along with a brief review of recent atomic investigation where phase interference is found to be important.

Production of hologram wave front transducers

Abstract: PURPOSE:To achieve the improvement in photocoupling efficiency by using the hologram recorded by supersing the interference fringes by the interference of diffracted coherent divergent light and reference light and the interference frings by the interference of the coherent convergent light inthe same direction as this and reference light on the same recording material.

Interference effects between large cylinders in waves

Abstract: This paper describes interference effects between large cylinders in waves. Reliable predictions of wave-induced forces on large offshore structures are important from technical and economic standpoints. This paper offers a prediction method that reduces computer costs by a factor of several hundred when faced with the specific problem of two neighboring circular cylinders, rather than bodies of arbitrary geometry. Theoretical predictions were confirmed by experiments in a model wave basin.

Interferometric surface irregularity shape and sign determination - using polarised phase-shifted components forming line pair interference pattern

Abstract: The interferometric method of determining the shape and sign of irregularities or inclinations in a surface involves use of a measurement and a reference beam. The desired parameters are measured very accurately and rapidly and irrespective of all external influences. The results are evaluated quickly and with simple equipment. -The measurement or reference beam is polarised into two different components. One component is phase shifted by less than half a wavelength before combining it with the unpolarised beam. The two interference fields so produced are separated using polarising elements to produce two interference patterns. The two patterns are finally combined into a pattern of line pairs with relative positions defined by the phase difference impressed on the two components.

Radar interference eleimenating system

Abstract: PURPOSE:To avoid the interference with no allotment of the array of the repeating interval in the eliminating system for the mutual interference between the radar devices of the same specifications, by arraying the repeating intervals at random via a random number generator.

Data processor with interference suppression system - has clock pulses generated in random or pseudo-random fashion to reduce harmonics

Abstract: The data processor is designed to reduce the risk of interference to frequency-selective circuits and devices, such as radio receivers, caused by harmonics of the synchronising clock-pulse frequency, without the use of expensive filters. It has applications in computers used in aircraft. The clock-pulse generator built into or separate from the data processor is frequency or phase modulated by means of a noise generator to provide random or stochastic timing of the pulses. This can be achieved by using the output of a shift-register which has feedback. Random variation of the pulse-width of successive pulses may be employed as an alternative.

Photo coupling circuit

Abstract: PURPOSE:To simplify production by providing interference filters having frequency selectivity of light in fibers. CONSTITUTION:Interference filters 15, 16 having frequency selectivity of light are disposed in close contact between the optical fibers 11, 12 and 13, 14 which have the end faces having been cut at 45 deg. with respect to fiber axis. Then, out of the light of the frequencies f1 thru f3 having entered the fiber 11, only the light of the frequency f1 transmits through the interference filter 15 and propagates in the fiber 12 and the light of the frequencies f2, f3 reflects and propagates in the fiber 13, of which only the light of the frequency f3 is transmitted by the interference filter 16 and propagates in the fiber 14 and the light of the frequency f2 reflects and propagates in the fiber 17. Hence, the light may be branched by using the simple members for each frequency of light.