Showing papers on "Noise measurement published in 1969"

The determination of device noise parameters

Abstract: A novel noise measurement technique is outlined which results in data that directly give the noise parameters of the test device when processed by a simple computer program.

1/|f| Noise in Physical Measurements

Abstract: The purpose of this paper is to provide an insight into low frequency divergent noises with spectral density |f|?, where ? ? -1, and into their effect on physical measurements, with special reference to 1/|f| noise. This class of noise is widespread in nature, and it presents unique limitations to the measurement accuracy. In an attempt to present a picture of this class of noise with regard to the measurements of observable physical quantities, the questions about generation of noise, its divergence, correlation properties and measurements of variance are discussed. A statistical model for generation of low frequency divergent noises is used to consider the divergence problem in both the frequency and time domain. It is shown that 1/|f| noise is "weakly divergent," and that power limitation presents no reason to impose a low frequency limit within time intervals observable in nature. Correlation properties are discussed in terms of the time-dependent correlation function, using an ideal impulse response which generates low frequency noise from white noise. Two general models for generation of 1/|f| noise are summarized and discussed. Generation of 1/|f| noise from white noise over a limited frequency range by distributed and lumped-parameter filters is described. It is shown that the variance (i.e. mean square noise) is determined by the frequency limits of the observation method.

An optical homodyne technique for measurement of amplitude and phase of subangstrom ultrasonic vibrations

Abstract: An optical homodyne technique is utilized to measure sub-angstrom dynamic mechanical deformations. For measurement in the frequency domain, where synchronous detection is used both the amplitude and phase of the mechanical signal can be measured with a high sensitivity; displacements less than 10-2A were measured with normal environment acoustic noise. Measurement in the time domain is also feasible with reduced sensitivity.

Amplitude distributions of telephone channel noise and a model for impulse noise

Abstract: The noise waveforms found on voice bandwidth telephone channels are generally recognized to be non-gaussian in their amplitude distribution. This paper presents data which suggests that a simple exponential is a good function to describe amplitude densities in the extreme tails. A comprehenisve model of impulse noise as viewed on trunk groups is then presented. The model relates the distributions of impulse noise levels and impulse noise counts.

Low sensitivity filters for state estimation in the presence of large parameter uncertainties

Abstract: Three minimax sensitivity criteria are used to synthesize filters for estimating the state of a simple first-order plant when large uncertainties in dynamic and/or statistical parameters of the plant and measurement system are present. Two design examples involving unknown plant bandwidth and unknown plant input noise covariance are worked out in detail. Graphical comparison of the error performance of the three minimax sensitivity filters with that of the optimal filter is presented for each case.

Correlation of Radio Noise and Quasi-Peak Measurements to Corona Pulse Randomness

Abstract: The quasi-peak readings of radio-noise meters have been generally accepted as an indication of the degree of nuisance to radio reception from ac and dc coronas. Simplified theoretical analyses were previously made to correlate the readings of radio- noise meters to some corona pulse characteristics.

FM noise reduction of Gunn-effect oscillators by injection locking

Abstract: FM noise spectra measurements were performed on a Gunn oscillator under injection-locked conditions. The experimental results have shown good agreement with the theory not only qualitatively but quantitatively.

On the Accuracy of the Envelope Method for the Measurement of Doppler Spread

Abstract: The accuracy achievable by the envelope method in the measurement of the Doppler spread of a dispersive channel or, more generally, of any scintillating source that can be modeled as a Gaussian process is evaluated. Specifically, the effects of additive independent noise, finite sample size, and numerical differentiation are discussed, and analytical expressions are given for the resulting errors.

Sensitivity or noise level measurement circuit and method

Abstract: A device, such as a receiver, amplifier, active filter, etc. is tested for sensitivity or noise level by modulating an input signal source and switching the output of the device between two terminals in synchronism. Following signal detection and integration, the output of one of the terminals is connected to one side of a null detector while the output of the other terminal is connected through a resistance network and then to the other side of a null detector. The resistor network is adjusted so that when the input signal source is reduced to a level such that the output signal of the device is equal to the noise level within the device, the null detector indicates a null. The input signal level in dbm at this point is equal to the sensitivity of the device.

Iterative guidance applied to generalized missions.

Abstract: Iterative guidance mode /IGM/ applied to effective gravity vector prediction, acceleration measurement of noise sensistivity and energy limitations

A derivation of the optimum continuous linear estimator for systems with correlated measurement noise

Abstract: Differential equations for minimum variance linear filter separating signals from additive correlated noise, using discrete time optimum formulas

Methods of measurement of acoustic noise radiated by an electric machine

Abstract: The acoustic field of an electric machine is described, and the basic measuring techniques and instrumentation for measuring noise are described. The results of sound-pressure measurements in free-field and semireverberant-field conditions, and measurements of sound pressure above a reflecting plane with various shapes of measuring surface are presented and discussed. From these measurements, the total sound power is calculated. The errors involved in using different numbers of sound-pressure sampling points in the power calculation, and of using approximate calculating procedures, are also investigated. Evidence is presented concerning the accuracy of methods of measurement and calculation.

On practical setting of detection thresholds

Abstract: In the practical setting of a threshold to implement the Neyman-Pearson criterion, the received noise power must be measured. The tradeoffs which take place between measurement accuracy, false-alarm probability, and detection probability are considered.

Radiometric Evaluation of Antenna-Feed Component Losses

Abstract: Low-noise antenna systems are frequently used in conjunction with measurements of atmospheric and cosmic background noise at microwave frequencies. The input transmission line losses of these receiving systems must be precisely calibrated to insure proper identification of the portion of operating noise temperature attributable to the external environment. Although most components in an antenna line can be calibrated by conventional insertion-loss measurements, many feed component losses must be evaluated by means of nonstandard techniques. This paper describes a radiometric method for calibrating the loss of multimode antenna-feed components in which the field is linearly or circularly polarized. The method consists of measuring operating noise temperature, first with the components under evaluation installed and again after substitution by a waveguide section of known loss. Calibration and error analysis equations are derived and discussed. Application of the radiometric method, for the calibration of a mode-generator and quarter-wave plate polarizing section, resulted in a loss measurement of (0.0069 ±0.0016 pe)/dB.

Phase Distortion in FM Satellite Communication Systems

Abstract: Wide deviation FM techniques employed in satellite communications require careful control of envelope delay distortion in the communications signal path to minimize phase distortion noise. This system impairment is more significant in satellite systems because of the high test tone deviations required. This paper highlights important characteristics of both terrestrial and satellite systems with emphasis on the latter. Methods for determining envelope delay coefficients and their conversion into picowatts of noise in frequency-division multiplexed (FDM) telephone channels and noise power ratio (NPR) amplitudes are included.

Prevention and Treatment of Noise in Control Signals

Abstract: Electrical control signals transmitted between two points usually arrive more or less distorted by noise. If proper control action is to occur, the information contained in the signals must be recovered and the noise must be rejected. This recovery and rejection are accomplished by invoking the principle of contrast, discriminating between useful information and noise as a result of some characteristic difference between them. Various practical means to effect and employ such contrast are examined, and a number of selected examples are presented. The role of proper wiring layout and grounding is stressed. High level noise can do more than obscure information in a signal. A number of instances exist in which actual equipment damage has been caused by noise. A brief description, with specific illustrations follows.

A double phase-sensitive detector for bridge balancing

Abstract: The general considerations involved in the design of low-frequency phase-sensitive detectors are reviewed. These include the equivalence of multiplier- and gating-type detectors, of pre- and postdetection filtering with regard to both signal and noise, and of half- and full-wave detection. The various configurations of full-wave chopper circuits using similar or complementary bipolar transistors are compared from the point of view of offsets. A question that has not been previously discussed?the degree of prefiltering needed to avoid noise saturation?is analyzed. These principles are applied to the design of a fixed-frequency detector that is especially adapted to bridge-balancing applications.

A simulator for hf atmospheric radio noise

Abstract: : Generally it is not feasible, or it is too costly, to conduct performance tests of a radio-communication system under the influence of actual atmospheric radio noise because of its nonstationarity and because of the difficulty in obtaining the desired noise conditions. Accurate simulation of desired conditions solves both difficulties. The device described here simulates HF atmospheric radio noise and is modeled after the available published characteristics of such noise, computer-analyzed samples, and empirical observations. The simulation is valid and accurate for the limited samples used. The basic concept of the device is sufficiently flexible that, with adequate statistical data, the several parameters could be adjusted so that the device could simulate any atmospheric radio noise condition likely to occur form ELF to VHF. (Author)

The effect of bandpass limiting on noise with a Gaussian spectrum

Abstract: The effect of limiting on the spectrum of Gaussian noise is computed where the noise has a Gaussian spectrum before limiting, and the output spectral density is plotted for various noise-to-limit level ratios. A decibel scale displays the spectral spreading due to limiting with an accuracy not available in previously published data. The results have application to radar and sonar signal processors which attempt to detect targets in clutter.

Digital simulation of low-pass Gaussian noise

Abstract: The acquisition and processing of data is often affected by randomly fluctuating variables with the result that the data values are a blend of signal and noise. Thus a realistic simulation of the physical system must also purposely add to the deterministic values of the signal an analogous amount and type of noise. Since the physical system which is being simulated passes only finite-frequency signals, the noise can be simulated as a low-pass pseudo-white Gaussian noise with a certain RMS value, sampled at certain (equidistant) intervals of time. This article describes a digital method of generating such a noise. The mathematical derivation of this algorithm is rather lengthy and can be found in references (1) and (2), which should be credited with its original derivation. All the author did was to realize the usefulness and the flexibility of this tool, check it out for validity by means of autocorrelation and power-spectrum-density analysis, and set it up in practical non-real-time as well as in realtime simulations. The source of the noise is assumed to be white Gaussian noise with the spectral density A 2 uniformly distributed over all frequencies, as in figure 1.

The White Noise Approximation

Abstract: It is proved that the random-variable coefficients of the orthonormal vector components of a Gaussian noise process converge to uncorrelated and identically distributed random variables as the power density spectrum of the process approaches a constant almost everywhere. An example is then given to suggest the rate of convergence and the ratio of noise bandwidth to signal bandwidth required for good approximation of the noise process by the white noise process.

Proposal on noise criteria for sea-going ships

Abstract: Noise criteria in terms of sound pressure levels and frequencies are proposed for the passengers and the crews accomodation, for the bridge and for the engine room of sea-going ships with respect to hearing conservation, audibility of whistles, speech communication, comfort and annoyance. It is shown that the NR-noise rating curves efficiently correlate with annoyance and that sound level A in contrast to industrial noise and road traffic noise is impracticable for ship noises. A survey of acoustical measures applied in existing ships illustrates that the proposed criteria can be met.

Circular-dichroism measurement system characterized by noise cancellation

Abstract: The disclosure concerns the provision of means for reducing problems associated with lamp intensity fluctuation and random noise in circular-dichroism measurement instrumentation.

Amplitude quantization: A new, more general approach

Abstract: From an unknown signal plus noise, we consider the difference in amplitude between the quantized output and the signal plus mean value of the noise. Whatever the width of the quantizer step and the probability density distribution of the noise, the probability density distribution of the final error is evaluated exactly.

Statistical Analysis of LF/VLF Communication Modems

Abstract: : This is a two-part technical report that considers the short-time statistical modeling of atmospheric noise at VLF/LF frequencies and applies a new noise model to the performance evaluation of various generic VLF/LF communication modems. In Part One atmospheric noise is examined mainly from a statistical point of view. Next, various statistical models for this type of noise are examined; finally, a new model is developed and compared with available data. In Part Two this noise model is applied to the evaluation of the error probability calculations of various generic VLF/LF modems. Much of Part Two, particularly in regard to a receiver system employing no clipping, is based on classical white Gaussian noise analysis applied in generic modems of interest. When nonlinear clipping is applied, the detailed statistical behavior of atmospheric noise becomes more important, and results depend on the detailed structure of the noise.