Showing papers on "Noise measurement published in 1970"

Noise in amplifiers

Abstract: In practically every type of research program in the physical sciences as well as in sophisticated engineering analyses, very small electrical signals must be measured and, in general, the limit of attainable precision and detectability is set by noise. This is true for the physicist and chemist performing nuclear magnetic resonance or spectroscopy experiments, for medical and biological researchers interested in evoked potentials, for geologists measuring small remanent magnetic fields in rock samples, for the metallurgist making Fermi surface measurements, and for the engineer performing vibration analysis and sensitive bridge measurements. These are only a few examples of applications in which noise plays a critical role in limiting measurement precision and signal detectability. This article discusses some of the inherent problems and describes techniques for improving signal-to-noise ratio.

A further note on a general likelihood formula for random signals in Gaussian noise

Abstract: A general likelihood ratio formula of the author's for the detection of signals in independent white Gaussian noise is extended to allow a "one-sided" dependence in which only the future white noise is required to be independent of past signal and noise. The assumption of Gaussian additive noise is also somewhat relaxed. The proof is based on some recent martingale theorems and on the concept of the innovations process.

On the influence of hot carrier effects on the thermal noise of field-effect transistors

Abstract: The noise resistance of the field-effect transistor has been calculated taking into account high-field effects such as mobility saturation and hot carrier temperature upon the thermal noise. The result of the calculations can be represented by a practical formula. The calculated results have been compared with measurements of the noise of a junction gate FET and a MOS tetrode with short active channels. The agreement is reasonable. At room temperature the effect is moderate, but at low temperatures it is considerable.

Radio Noise Currents and Audible Noise on Short Sections of UHV Bundle Conductors

Abstract: After a brief review of the theory involved, results of some conductor radio noise research at Project UHV are presented. These tests are based on measurements of conductors in cages and on laboratory tests of short conductor sections. Radio noise in foul and fair weather is discussed, and the results are presented in terms of excitation function and surface gradient. The relation of the excitation function to the electric field near the conductor rather than the surface gradient alone is examined, and a simple theoretical approach is proposed. Some experimental data on audible noise are included, as are potential and gradient calculations for the environs of bundled conductors.

Apparatus for measuring frequency modulation noise signals and for calibrating same

Abstract: Apparatus is provided for the measurement of frequency modulation noise on the carrier signal output of a low-noise, low-power, high-frequency diode oscillator under test. An auxiliary injection phase-locked oscillator, driven by the oscillator under test, is used to provide a signal of sufficient level for operation of a high-frequency discriminator used for noise measurement. The auxiliary oscillator may additionally be used for calibration of the discriminator preliminary to taking noise measurements.

An introduction to the theory of the detection of signals in noise

Abstract: An introductory discussion is presented in the general field of detection theory, with particular emphasis on the problems of detecting signals in Gaussian noise and of estimating parameters of signals in Gaussian noise.

Surface and bulk effects in low frequency noise in NPN planar transistors

Abstract: Extensive measurements on present technology NPN planar transistors equipped with a gate electrode allow a better physical characterization of devices in terms of individual noise source. The actual importance of the burst noise has been found to be heavily dependent on surface potential and correlations have been experimentally established with the occurrence of surface defects. Planar transistors free from burst noise feature essentially a 1ƒ excess noise which mainly depends on surface potential and collector current. However, experiments on gated transistors and diodes show that normally the majority of the noise comes from the bulk and can be visualized as an excess noise current generator in parallel to the emitter-base junction. Noise measurement on devices connected as diodes and as transistors allow the localization of the individual noise sources. The major source of 1ƒ noise has to be ascribed to a minority carrier recombination process in the emitter region.

Determination of signal and noise statistics using correlation theory

Abstract: A seismic trace may be represented as the sum of a signal and noise series. Each of the series may further be represented by convolution of a finite wavelet and a random series. With this representation, and provided that the signal and noise are uncorrelated, it is possible, in theory, to extract signal and noise statistics from two adjacent traces of a reflection seismogram. Some experiments are shown on model seismic traces, and it is shown that within the time‐duration of the seismic wavelet, the estimates of signal and noise statistics are reasonable for low signal‐to‐noise ratio. There remains, however, the problem of determining the optimum time lengths of the estimates.

Noise exposure forecasts: evolution, evaluation, extensions, and land use interpretations.

Abstract: : Part I describes the evolution of methods for relating aircraft noise exposure to community response in this country, starting with the original Composite Noise Rating (CNR) concept developed in 1952, and with applications specifically to aircraft noise in 1957 under Air Force sponsorship. The development of CNR procedures for civil and military aircraft in 1962 utilizing perceived noise level contours and the development of Noise Exposure Forecast (NEF) procedures in 1967 utilizing effective perceived noise level data are recounted and compared. Part II interprets the noise exposure due to aircraft operations, as expressed in Noise Exposure Forecast (NEF) values, in terms of estimated impact on land uses. Assessments of the land use compatibility with aircraft noise as a function of NEF values are given for a variety of land uses for the purpose of providing guides in land use planning, zoning and in land use development and building construction. (Author)

Noise in integrated-circuit transistors

Abstract: Recent noise measurement from 1 Hz to 5 kHz on integrated-circuit transistors have shown an anomalous burst noise in addition to the usual noise spectrum. The terminal characteristics of the burst noise are presented and a phenomenological noise-circuit model is developed.

Nonsingular detection and likelihood ratio for random signals in white Gaussian noise

Abstract: This paper is concerned with the mathematical aspect of a detection problem (a random signal in white Gaussian noise). Specifically, we obtain a sufficient condition for nonsingular detection and derive a likelihood-ratio expression in terms of least-mean-square estimates. The problem itself is old, and the likelihood-ratio expression is also well known. The contribution of this paper is a relatively elementary and self-contained derivation of the likelihood-ratio expression as well as the nonsingularity condition.

On system identification from noise-obscured input and output measurements†

Abstract: This paper deals with maximum-likelihood system identification when both the input and the output signals are corrupted by Gaussian observation noise. A derivation of exact maximum-likelihood estimation for this problem is included, but the difficulty of implementing it numerically precludes its practical evaluation at this time. A new approximate method is introduced, called the ‘output reference’ method, in which the input noise is referred to the output, and an iterative gradient search method used. This technique requires no a priori knowledge of the noise covariance matrix. The method of Koopmans—Levin, which does require knowledge of the noise covariance matrix, is then reviewed in detail, and experimental results are presented for the white noise case which indicate that the output reference method is more accurate.

The range and frequency dependence of VHF—UHF man-made radio noise in and above metropolitan areas

Abstract: The surface distribution of composite incidental man-made radio noise power in metropolitan areas displays frequency and range variations which are predictable from a knowledge of the propagation characteristics of irregular surface terrain for low-height antennas and the noise-source spectral power densities for a Poisson distributed random noise process. The observed frequency variation of composite surface noise power in the very-low-frequency (VLF) through the lower very-high-frequency (VHF) band is porportional to the product of 1) the inverse first power of frequency, introduced by irregular terrain basic path loss dispersion for low antennas, and 2) the inverse quadratic frequency dependence of the noise-source spectral density. In the upper portion of the VHF band and in the ultrahigh-frequency (UHF) range, the basic path loss dispersion remains unchanged while the emission spectrum of the surface noise sources asymptotically approaches that of band-limited white noise. The observed first-order surface range dependence for composite man-made noise within an urban area is predictable from the measured variation of irregular terrain basic path loss for low-height antennas and displays a somewhat smaller exponent than the free space propagation function. The general range function for composite metropolitan area man-made noise power displays a quadratic exponential variation with distance from the urban center. The level of man-made noise power, observed from 1 to 5 miles above metropolitan areas, can be related to the surface noise distribution, the radiation pattern of the receiving antenna, and the coordinates of the airborne detector, relative to the urban center. The noise level, the noise spectral density, and the position dependence of the airborne noise power are predictable from this information plus a recognition that, as the receiver field of view increases with altitude or beamwidth, the amplitude distribution of the surface sources approaches a unit normal distribution in conformity with the central limit theorem for multiple independent random sources. Tests of the validity of the theoretical predictions of the range and frequency dependence of both surface and airborne man-made incidental radio noise power in the VHF-UHF bands have been performed, using accumulations of both surface and airborne noise data obtained from measurements in and above urban areas in Europe, Asia, Australia, and North and South America. Theoretical and experimental comparisons have confirmed the validity of the noise generation and propagation models and support their use for calculating the deterministic characteristics of metropolitan area incidental man-made noise.

Synthesis of recursive digital filters using the FFT

Abstract: It has been shown that recursive digital filters can be synthesized using the fast Fourier transform. An algorithm for computer implementation has been developed and used in comparing the computation times and noise figures of filters synthesized in this manner with the computation times and noise figures of filters synthesized by recursion. A model has been proposed for analysis of noise in the two-pole filter. Predictions of this model have been found to be in good agreement with noise measurements.

A Test Set for the Accurate Measurement of Phase Noise on High-Quality Signal Sources

Abstract: The test set described here is capable of measuring the spectral density of phase noise on carrier frequencies from 1 to 500 MHz, for offset frequencies from 20 Hz to 50 kHz. Measurements to 50 MHz are described. The test set has a residual single-sideband phase-noise-power-to-signal-power ratio of -142 dB/Hz at 20 Hz offset from the carrier, which decreases to a floor of -172 dB/Hz at offset frequencies greater than 5 kHz. The estimated calibration accuracy achievable is ±0.8 dB, exclusive of random reading errors due to the Gaussian distribution of the phase fluctuations being observed. The estimated 1 ? repeatability of a measurement is 0.7 dB (70 percent of the observations on a given test will fall within ±0.7 dB of the average value). This test set is capable of characterizing the phase-noise performance of existing atomic frequency standards, crystal oscillators, frequency synthesizers, and other high-quality sources more accurately than has previously been possible. The increased accuracy has been achieved by a system design that minimizes readout fluctuations, allows for the accurate measurement of correction factors used to reduce systematic errors, and minimizes the possibility of operator error and bias.

A note on the analytical absolute stability test

Abstract: A simplified version of the conditions for the analytical absolute stability test is introduced. The absolute stability test requires that the polynomial

Computer-aided determination of two-port noise parameters (CADON)

Abstract: With a desk computer the noise and gain parameters of a two-port can be determined with high speed and reasonable accuracy from a well-known noise figure measurement process.

Noise considerations of optical beam recording.

Abstract: This paper reviews the signal-to-noise considerations of optical beam reading processes. It shows that, with a binary light signal system using level detection, it is preferable to consider the arithmetic sum of the noise terms of each level as the noise term in a signal-to-noise calculation, even though the sum of the gaussian noise terms for each separate level are summed as powers. For the case where gaussian and nongaussian noise terms are combined for one level, it is preferable to add the peak values of their envelopes rather than employ rms values. The importance of the magnitude of the common mode rejection ratio, when deciding whether or not to employ a differential light detection system, is considered. The specific case of a magnetooptical material that exhibits Faraday rotation is used to illustrate these points in a quantitative fashion.

Automatic joint probability calculation of noise corrupted process measurements

Abstract: A method for automatically calculating from a noise corrupted process measurement a quantity whose value is indicative of the probability that a process disturbance has occurred which caused the measurement to vary in such a way that it does not fit the statistical model for the expected noise at a particular reference level.

Masking of crosstalk by speech and noise

Abstract: We performed three laboratory experiments of crosstalk thresholds using simulated telephone conversations. Two of these experiments involved masking of crosstalk by noise; the third involved masking of crosstalk by both noise and primary speech. In this paper, we present intelligibility and detectability threshold data from these experiments and discuss the usefulness of the intelligibility threshold data for determining telephone crosstalk objectives. In general, the crosstalk threshold versus masking noise functions obtained from these experiments agreed fairly well with similar functions published earlier. These functions were found to be linear for high values of noise (about 20 dBrnC and higher) and markedly nonlinear for lower values of noise. For very low noise conditions (about 5–6 dBrnC or lower), crosstalk thresholds were almost independent of noise. Intelligibility thresholds were found to be 8–10 dB higher than the corresponding detectability thresholds and a difference of the same size was found between threshold values obtained (i) with background noise and (ii) with both background noise and background speech.

Error analysis of optimal filtering algorithm for colored noise

Abstract: Algorithms are developed for the error analysis of the optimal filtering solution for colored noise. The types of error sources considered are those both in the imprecise specification of the model and in the improper choice of the noise statistics. The matrix differential equations have been derived permitting the calculation of the actual error covariance and the additional error due to the preceding error sources. For a case where only the error source based on the incorrect choice of the noise statistics is present, a conservative design criterion has also been established, which makes it possible to prescribe the performance of the filter for colored noise. A simple example demonstrates the utility of these results.

Analysis of a Signal Processor for an Antenna Array

Abstract: A signal processor that provides ratio-squared predetection combining, has been investigated for application in an adaptive antenna array. The analysis and experimental data presented here pertain to the signal processing gain when the antenna array is illuminated by a coherent signal source and a partially coherent noise source. For a noise source which is coherent, the processing gain depends on relative strength of the signal and noise, relative directions of arrival, and the usual "array factor." The array exhibits capturing effects much as in an FM receiver. The effective antenna pattern is a superposition of two beams of different magnitudes, one directed to the signal source and the other to the noise source. When the noise is partially coherent, the behavior of the signal processor is quite complex. Analytical prediction and experimental simulation measurement on a four-channel system indicate that the partially coherent noise may be regarded as the source of an incoherent noise component plus a coherent noise component with the magnitude of the latter determined by the coherence coefficient for the noise source.

Measurement of Self Cooled Transformer Sound Levels in Relatively High Ambients

Abstract: Measurement of the sound level of a self-cooled transformer can be made at high ambient levels provided the ambient contains little or no sound from other inductive apparatus at the transformer sound frequencies. By measuring the components of transformer noise through narrow pass-band filters that largely exclude broad-band ambient noise and making a true RMS summation of components mathematically, it is shown that useful measurements can be conducted in ambients as high as eight decibels above the transformer sound level. A beneficial by-product is the detailed description of the frequency composition of transformer noise made available to the designer and user.

Electron-radiation temperature measurements in a sealed-off CO 2 laser system

Abstract: Measurements of the noise temperature in the L band were used to investigate the effect of several constituents of the gas mixture on the discharge properties of the CO 2 laser. Addition of He and H 2 O to the discharge gives no significant change in the temperature. By contrast, addition of 4-torr N 2 to 2-torr CO 2 increases the noise temperature from 1.3 to 1.5 eV. Increase of the current in an optimum CO 2 -N 2 -He-H 2 O mixture leaves the temperature nearly constant (1.5 eV). This result deviates from that of Tyte and Sage, who found an anomalous rise of noise temperature with increasing current. Within the 5 percent experimental error the radiation temperature does not depend on laser action. A comparison of the present results with those of probe measurements is given. It is concluded that He has practically no influence on the average electron energy, which in turn controls the vibrational excitation. This and the observed behavior of the output power as a function of the partial He pressure give strong evidence that the major role played by He is cooling the gas in the discharge.

Standard L.F. noise sources using digital techniques and their application to the measurement of noise spectra

Abstract: Circuits of a random noise source and a pseudo-random noise source, both using digital techniques, are described and an account is given of their auto-correlation functions and power spectra. Their value as standard signal sources in noise power measurements is discussed and conclusions are reached about their relative merits.

An Alternate Approach to the Prediction of Polynomial Signals in Noise from Discrete Data

Abstract: When the problem of predicting the past, present, or future value of a polynomial signal or any of its derivatives is considered, where the signal is in white Gaussian noise, the standard approach has been to minimize mean-square-error with constraints by use of Lagrange multipliers. In this paper an alternate approach is described, using results of Rao and Bhattacharyya from the statistical literature, which reduce the specified prediction problem to a simple one requiring no formal minimizations and no use of Lagrange multipliers. It further has the advantage of yielding the covariances between estimates of the polynomial and its derivates. Useful engineering formulas for smoothing and prediction are developed in the main part of the paper. These include both filter and covariance expressions. A tutorial discussion of the theory is given in two appendixes.

A broad-spectrum pseudorandom Gaussian noise generator

Abstract: A new technique is described for filtering a pseudorandom binary sequence to produce pseudorandom noise that has a near-Gaussian amplitude probability density function. Its principal advantages are that the half-power bandwidth of the noise is approximately eight times that obtained with existing techniques, and the desirable autocorrelation properties of the binary sequence are retained. A practical design for a noise generator using the new technique is described. The results of simulation are given to substantiate the advantages claimed.

Capacity and noise relationships for major hub airports

Abstract: The conflicting goals of increasing capacity at an airport and reducing the noise exposure around that airport are examined. Basically, airport capacity is directly related to aircraft noise exposure such that an increase in capacity means an increase in the noise exposed area surrounding the airport. Several technological and operational noise reduction methods are discussed and it is shown that they can reduce the extent of exposure as capacity is increased. Using John F. Kennedy International Airport as an example, it is demonstrated that if these noise reduction methods are utilized, the capacity of this airport can be doubled and community noise exposure can be reduced below current levels.