Showing papers on "Signal-to-noise ratio published in 1973"

An adaptive array for interference rejection

Abstract: An adaptive array that rejects undesired or interfering signals is presented. The array pattern is controlled by an adaptive feedback system based on a steepest descent minimization of mean-square error. Error is defined as the difference between the array output and a locally generated reference signal. Minimization of mean-square error is closely related to maximization of signal-to-noise ratio (SNR). A two-element adaptive array has been built, and its experimental performance is discussed. Typical patterns for various desired and interfering signals are shown, as well as measured transient response. Finally, some experiments showing the array behavior with modulated signals are described. The results show that such an antenna system is capable of automatically rejecting interfering signals, subject only to certain basic constraints. No a priori information about the angles of arrival of the signals is required, Detailed knowledge of the waveforms of the desired and interfering signals is also not needed, although the spectral characteristics of the desired signal must be known.

Recent Psychophysical Experiments and the Display Signal-to-Noise Ratio Concept

Abstract: The objective of this book is to give the reader the ability to specify the parameters of devices for accomplishing a given visual task under given conditions, or to estimate the probability of a viewer accomplishing that task, given the conditions and the parameters of the visual aids.

Sharp error bounds for intersymbol interference

Abstract: Sharp upper and lower bounds of the Chebyshev type are established for the probability of error due to intersymbol interference and additive Gaussian noise in a digital communication system. The results are in relatively closed form, and the only statistical knowledge assumed about the interference is the peak eye opening and the variance. The bounds apply to correlated and uncorrelated signals and for any signal to noise ratio.

A magnetic recording tape based on iron particles

Abstract: Tapes based on acicular iron particles give an outstanding recording performance compared to γ-Fe 2 O 3 and CrO 2 tapes. Especially in the short wavelength region the signal to noise ratio is, respectively, 12 and 7 dB better, whereas the bias noise level is somewhat lower. The iron tapes have a high coercivity, between 80 and 90 \times 10^{3} A/m, and hence the required bias is about 9 dB higher than for γ-Fe 2 O 3 . The print through properties are excellent.

Adaptive array processor providing improved mainlobe maintenance

Abstract: In an AMTI adaptive array, each array antenna element is connected to an element circuit which multiplies the contribution of each antenna element to the total return by a weight. The element circuits and further signal processing circuitry comprise the array processor. The element circuits include well-known cross correlator control loops. In accordance with the present invention, a signal whose pulse repetition interval to pulse repetition interval doppler phase shift is 180* out of phase with clutter returns is supplied to a control loop. Thus even with clutter at or near the look angle, mainlobe gain is maintained. Consequently, a ''''two pulse'''' MTI circuit utilizing a single delay line in each element circuit may be utilized rather than a two delay line element circuit which would normally be required to provide a signal to noise ratio value indicative of mainlobe gain which would be required for compatability with further MTI processing circuitry.

Structures dans l'émission photonique de He provoquée par bombardement d'électrons monocinétiques dans la région de 60 eV

Abstract: By measuring the photon intensity emitted by He excited by electron impact in the 60 eV region as a function of the electron energy, with an apparatus capable of excellent signal to noise ratio and...

Dual beam absorption type optical spectrometer

Abstract: A spectrometer particularly useful for determining the concentration of atmospheric pollutants along a path of substantial length. A tunable laser and an optical parametric oscillator provide two laser signals having slightly different wavelengths that are directed to strike a detector. One signal is absorbed by any predetermined pollutant material between the source and detector and the other is not. The difference between the intensities of the first and second signals striking the detector indicates the concentration of pollutant material along the path travelled by the beams. The tunable laser operates in the pulse mode and provides high intensity output signal pulses to maximize the signal to noise ratio of the signals reaching the detector.

The Improvement of Signal to Noise Ratio Using a Pulsed Hollow Cathode Lamp and Gated Detector for Atomic Fluorescence Measurements

Abstract: An expression for the maximum increase in signal to noise ratio obtainable with a pulsed hollow cathode lamp as primary source for atomic fluorescence measurements is derived under certain assumptions. Experience with copper and calcium hollow cathode lamps showed that by using these lamps in the pulsed mode in conjunction with a gated detector, the increase in signal to noise ratios obtained are less than a factor of 5, due to self-absorption broadening of the primary source emission lines.

Apparatus and method for measuring the signal to noise ratio for a periodic signal

Abstract: Apparatus for measuring the signal-to-noise ratio of a television signal wherein the noise and signal level of the signal are derived from the on-the-air television signal horizontal sync pulses. The noise is derived by sampling the sync pulses and bandpass filtering the samples, while the signal level is derived by D.C. filtering the sync pulse samples. The signal-to-noise ratio is the ratio between the derived signals which ratio is provided by a suitably calibrated meter.

Optical memory with improved signal-to-noise ratio

Abstract: The signal-to-noise ratio in an optical memory is improved by using separate write and read beams. The read beam has a larger diameter than the write beam at the final focusing lens so that the read beam is focused to a read light spot at the memory medium which has a diameter less than the diameter of the write spot.

Statistical noise processor

Abstract: A statistical processing device for improving the signal to noise ratio of signals and transients within a noise environment Samples of electrical signals indicative of ocean noise are applied to a calculator that obtains the mean, variance and third moment of the electrical signal A delay circuit delays the calculator output signal for comparison with later produced electrical signal samples A second calculator receives the outputs from the delay circuit and manipulates the difference between a first higher order moment signal to obtain an output signal having an amplitude indicative of a transient or target The output signal is displayed on a lofargram which provides an enhanced visual indication of the sampled electrical signal contents

RANDI: Research Ambient Noise Directionality Model

Abstract: : A computer model for calculating the vertical and horizontal directionality of ambient noise and some of the results which have been obtained are discussed. The model considers three sources of surface-generated anisotropic noise, one source of surface-generated isotropic noise and two sources of volumetric isotropic noise. Noise levels are obtained for various propagation conditions and for different sensor depths. Results agree well with experimental data, and it is shown that the model can be a useful tool in the planning of ambient noise measurement experiments and in the analysis of results.

Analysis of Signal-to-Noise Ratio of the Laser Doppler Velocimeter

Abstract: The signal-to-shot-noise ratio of the photocurrent of a laser Doppler anemometer is calculated as a function of the parameters which describe the system. It is found that the S/N is generally a growing function of receiver area, that few large particles are better than many small ones, and that generally the ‘fringe’ or ‘differential’ mode configuration is equal to, or better than, the ‘reference beam’ mode.

Velocimeter with improved signal to noise ratio

Abstract: An improved laser velocimeter in which both magnitude and sense of direction are provided and which has an improved signal to noise ratio is shown. To obtain sense of direction the conventional laser velocimeter which includes a transmitting beam and a receiver comprising a grating and a photo detector, has added to it a second grating and detector. The second grating being shifted one-quarter of a line pair from that of the first resulting in two outputs which are shifted 90 degrees from each other. This information is processed in a well-known manner to obtain an output indicative of sense of direction. To improve signal to noise ratio a grating is used with the transmitted beam to cause it to form three separate beams which when received through the receiving grating will be superimposed upon each other to cause a greater portion of the signal to be utilized by the detector.

Signal-to-noise ratio detector for automatic gain controlled receivers

Abstract: In an automatic gain controlled receiver for receiving alternating periods of signal and noise the transient response to the termination of signal reception is used to produce an indication of signal-to-noise ratio. The level of the gain controlled input is monitored and a charging circuit is used to delay the change of level which would otherwise occur as a step function upon termination of signal reception. The level monitored during signal reception is then compared with the peak of the level attained after termination and due to the delayed change, this difference is essentially proportional to the db signal-to-noise ratio. The resultant signal-to-noise indication, which may be quantized, can be used as the basis for selection among remote receivers in a diversity receiver arrangement.

Mutual Coupling in the Signal-to-Noise Ratio Optimization of Antenna Arrays

Abstract: In terms of network parameters defined at the input terminals, expressions applicable to any array configuration are derived for the S/N ratio. The formulation is made in such a way that it becomes possible to account for coupling effects that arise from the geometry of the array and the current distributions on the elements of the array. Since the S/N ratio consists of the ratio of two Hermitians forms, known techniques are used for its optimization. Comparisons with simplified theories are given that demonstrate clearly the importance of mutual coupling in many cases. Numerical results for a 4-element circular array are included for two idealized noise temperature distributions. Applications of this theory to EMC fields are also mentioned.

A Comparison of Optimum and Logarithmic Quantization for Speech PCM and DPCM Systems

Abstract: Two quantization rules, optimum (minimum mean-square error) and logarithmic companding, are compared for application to digital speech transmission. Comparison is made on the basis of signal-to-quantizing noise ratio (S/N), subjective quality judgments, idle channel noise, and dynamic range. These quantizers are considered in both PCM and differential PCM configurations. A computer algorithm is described that yields the optimum quantizer levels for a given speech record. It has been found that the improvement in S/N which optimum quantization affords over conventional logarithmic quantization is offset by the greater idle channel noise and smaller dynamic range (range of talker volumes handled with a lower limit on S/N) of the optimum law.

Signal-to-noise ratio for magnetooptic readout from MnBi films

Abstract: The signal-to-noise ratio in an optical memory has been analyzed and examined experimentally. A solid-state detector can be used with MnBi as the storage media, but for media with smaller magnetooptic rotation, a photomultiplier is considered necessary. Analyzer orientation and light beam intensity have been included in the analysis. Results with experimental apparatus employing a crystal beam splitter at 45° angle and solid-state detectors compares well with analysis.

Detectability of emergency beacon

Abstract: This invention relates to a method for increasing the range of detectability of an emergency locator transmitter beacon, and for conserving transmitter power of the emergency locator transmitter, and to a transmitter and receiver for carrying out the method. In accordance with the invention, the carrier of the transmitter is amplitude modulated with a rectangular waveform whose frequency is a precise submultiple of the carrier frequency. A receiver for the system cross-correlates a received input with a reference signal which is a replica of the modulating waveform. The cross-correlator output indicates whether the received signal is identical to the reference signal, i.e., was transmitted by the transmitter. The reason for making the modulating signal a precise submultiple of the carrier frequency is that, for a correlator to work, the frequency of the correlated waves must be precise. As the carrier frequency of the transmitter is crystal controlled, it is most convenient to take off a submultiple of this frequency to control the modulator precisely. With a system in accordance with the invention, the signal to noise ratio is enhanced to thereby increase the range of detectability. At the same time, the transmitter is turned off cyclically so that transmitter power is conserved.

The Effect of Weighting upon Signal-to-Noise Ratio in Pulse Bursts

Abstract: The Doppler sidelobes of a received pulse burst may be partially controlled by varying the amplitudes of the pulses in the burst or sequence upon transmission and/or reception. When there is a peak power limitation, weighting the amplitudes produces a loss in signal-to-noise ratio. A general expression is derived for the loss factor under the peak power limitation, and loss factor formulas are given for the following cases: Case A: Full nominal weights upon reception. Uniform weights on transmission. Case B: Square roots of the nominal weights on both transmission and reception. Case C: Full nominal weights on both transmission and reception. These cases are listed in order of increasing loss. Numerical results are tabulated for regular spacings and for the following nominal weights: 1) Dolph-Tchebycheff, 2) Taylor, 3) Hamming, and 4) Hann.

System for detecting weak information signals in noisy receiver signals

Abstract: A system is provided which permits the detection of a useful signal in a received signal having a low signal to noise ratio. The system includes a band pass filter connected to receive the signal to be processed, an AGC amplifier, and a comparator which compares the output of the amplifier with a threshold or reference level and produces an output during the time this level is exceeded. The output of the comparator is converted into a train of rectangular pulses which are sampled at a clock frequency which is substantially shorter than the minimum duration of the useful signal. A circulating memory receives the samples which are arithmetically summed at each clock time, the arithmetical sum being then compared with a second threshold level to determine whether the received signal is a useful signal.

Image Processing Techniques

Abstract: The purpose of this paper is to describe the image processing research at MIT and to present some qualitative considerations about picture quality.© (1973) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Omega envelope capability for lane resolution and timing

Abstract: Reports on an investigation of the feasibility of using Omega pulse envelopes for resolving the Omega lane ambiguity--for sea-air rescue and other navigation and timing applications, Navy and civil. Pulse arrival time measurement accuracy is related to pulse rise time and signal-to-noise ratio (SNR). Required accuracies for three- and four-frequency transmission formats are determined and related to expected SNR. Lane resolution from pulse envelopes is shown to be feasible with a four-frequency signal format. Signal relay times of three minutes or less are required in heavy noise for 0.95 confidence of position location. Preliminary experimental results support calculations. (Author)

Summary Report, Phase I.

Abstract: : A computer program is described for calculating the signal to noise ratio at the output of vertically directional acoustic arrays in the ocean. The vertical array consists of one to four elements providing an omni-directional and four different types of null patterns. Provision is made for considering other patterns which may be found to be desirable. Multipath transmission is considered in computing signal level. The signal along each path is convolved with the array response for the arrival angle, and the multiple arrivals summed incoherently at the array output. The vertical directionality of the noise is considered and convolved with the array pattern to obtain the noise output. The noise can be partitioned into coherent and incoherent components. Provision is made to investigate the effect of array tilt. The purpose of the study is to compare the S/N ratios for various environmental conditions to determine the optimum pattern from among the available choices; this portion of the study has not yet been undertaken.

Signal-to-noise ratio as a predictor of speech transmission quality

Abstract: Signal-to-noise ratio expressed in decibels may be generalized to the form 10 \log S^{a}/N^{b} , where S and N are, respectively, signal and noise values expressed in power units. In the usual definition of signal-to-noise ratio, the exponents a and b both assume values of +1, that is, the ratio a/b = 1. This study was designed to examine the optimum value of a/b as a predictor of speech transmission quality using two sets of speech transmission quality data. Results of factor analysis, multiple regression analyses, and canonical correlation analyses showed that values of a/b greater than one were better predictors of transmission quality than a/b = 1.

A rapid scanning spectromerer and time averaging method for cathodoluminescence

Abstract: A description is given of a cathodoluminescence instrument and contol system. Study of signal to noise ratio. Improvement due to filter and use of a time averaging method. Luminescence spectra of CdS and HgS, illustrating the capabilities of the instument.