Showing papers on "Noise measurement published in 1974"

Simultaneous Input Power Match and Noise Optimization using Feedback

Abstract: A method is presented for the design of an input stage such that the input admittance is the optimum for minimum noise conditions. Furthermore, this condition can be obtained for almost any chosen passive load. This has been achieved by means of 2 lossless feedback elements in a shunt and series configuration. Also presented are formulae for the noise parameters of a stage to which a rather general type of feedback has been added and the graphical representations of some noise and gain expressions.

Image Processing In Signal-Dependent Noise

Abstract: Image detection noise is a fundamental limitation in picture processing, whether analog or digital. This noise is characteristically signal-dependent and this signal-dependence introduces significant problems in the design of appropriate noise-suppression techniques. This paper outlines some recent results obtained by the authors in the optimum suppression of two types of signal-dependent image noise: film-grain noise and photoelectron shot noise. The work in grain noise suppression involves deriving the minimum-mean-square error Wiener filter for a new form of signal-dependent noise model suggested in earlier work by T. S. Huang. Implementation of these filters by either coherent optical or digital processing techniques is possible. Digital computer simulations of grain noise suppression using two particular cases of this additive, "signal-modulated" noise model were performed. They demonstrate the potential advantages of noise suppression filters which make use of a priori knowledge of the signal-dependent nature of the grain noise. The results of work on linear, unbiased restoration of images recorded in the presence of photoelectron noise are summarized. Additional work in both of these areas is suggested, with a particular need existing for correlating the properties of various models proposed for grain noise with experimental data obtained on emulsions using scanning microdensitome ters.

Design of a Sanguine Noise Processor Based Upon World-Wide Extremely Low Frequency (ELF) Recordings

Abstract: This paper describes the design of a candidate noise processor for the Sanguine receiver based on communication theory considerations and detailed experiments using wide-band recordings of extremely low-frequency (ELF) (3-300 Hz) atmospheric noise. This processor consists of the following elements: 1) a compensating (or whitening) filter; 2) nonlinear notch filtering at frequencies of manmade interference; 3) a post-notch filter nonlinearity; and 4) a phase coherent linear matched filter. Due to the impulsive non-Gaussian nature of the noise, nonlinear processing with a bandwidth considerably greater than the 40-80-Hz signal bandwidth is significantly better than a linear receiver (consisting only of a matched filter and appropriate whitening filters). Simulations using noise recordings from a number of widely separated locations in the world have shown improvements of 7 dB to 20 dB at times of high ELF atmospheric noise levels at the receiver input.

Measurements of amplitude probability distributions and power of automobile ignition noise at HF

Abstract: Measurements of the amplitude probability distribution (APD) of the envelope and measurements of other parameters of automobile ignition noise were made at frequencies between 24 and 30 MHz. The measurements were conducted at a quiet site where several single stationary vehicles were operated at engine speeds corresponding to idle and cruise. Measurements were also made at two distances near a freeway, for light traffic (approximately 20 vehicles per min) and for heavy traffic (approximately 45 vehicles per min). The principal instrumentation consisted of several phase-stable receivers with coherent quadrature detectors whose outputs were digitized at a rate of 200 samples per quadrature component per second and recorded on magnetic tape for computer processing. About 10 min of data (about 120 000 samples) were obtained during each measurement. The computer plotted the APD on a Rayleigh scale in dB relative to thermal noise and calculated the mean noise power available at the antenna terminals (related by a constant to the noise factor F a ) and V d --the ratio in dB of rms to average voltage. The average power of the ignition noise increases with engine r/min and V d usually decreases. Near a freeway, most of the noise is contributed by a small number of very noisy vehicles. The APD's for various situations are strikingly similar; all show that most of the noise envelope samples in a measurement are Rayleigh distributed. A small percentage of the noise samples do not follow the Rayleigh distribution, but are of higher amplitude. This percentage is higher for an engine at cruise speed than at idle speed, and higher for heavy traffic than for light traffic.

On sensitivity and roundoff noise in wave digital filters

Abstract: In a wave digital (WD) filter, attenuation, and thus attenuation sensitivity, can be defined in two different ways. The first type of sensitivity is of importance from the point of view of attenuation distortion and can easily be kept small. The second, which differs from the first at most by an additive constant, is important from the point of view of roundoff noise. Structures are discussed for which both definitions coincide, thus ensuring the possibility of keeping both sensitivities simultaneously low.

Handbook of noise ratings

Abstract: The handbook was compiled to provide information in a concise form, describing the multitude of noise rating schemes. It is hoped that by describing the noise rating methods in a single volume the user will have better access to the definitions, application and calculation procedures of the current noise rating methods.

Conversion gain and noise in a Josephson mixer

Abstract: : Fundamental mixing at 36 GHz in non-hysteretic Nb point contacts has been observed with overall conversion efficiencies in the range 0.33 < or = eta < or = 4 and mixer noise temperatures in the neighborhood of ( Taub M) approximately 200K. The observed conversion efficiencies are in good agreement with the Resistively Shunted model. The observed noise can be accounted for by assuming that the Johnson noise in the shunt resistor is the only source of noise driving the junction. Somewhat larger noise is seen from resonantly coupled mixers than is seen when the mixer is driven from an rf current source. Fundamental mixing in hysteretic junctions is limited to a narrow if bandwidth and gives much larger conversion gain but also larger noise. Parametric amplification at the if frequency is seen in hysteretic junctions. Fourth order harmonic mixing with omega sub (LO)/2 pi at 9GHz has been achieved with performance almost comparable to fundamental mixing. Cavity mode mixing appears less promising. (Author)

Man-Made Radio Noise – Part 2: Estimates for Business, Residential, and Rural Areas

Abstract: The Office of Telecommunications, Institute for Telecommunication Sciences (OT/ITS), over the past several years, has accumulated a data base of man-made radio noise measurements in the frequency range from 250 kHz through 250 MHz taken in a number of geographical areas. This data base has been analyzed to provide estimates of the expected characteristics of man-made radio noise in business, residential, and rural areas. The parameters used are the average available power spectral density, the ratio of the rms to the average voltage of the noise envelope, and the ratio of the rms to the average logarithm of the envelope voltage. The variation of these parameters as a function of frequency, location, and time are shown and discussed. Examples of amplitude and time statistics of the received man-mad e radio noise process also are shown and discussed. The use of the estimates is shown (principally by references in Part II, Bibliography) in the solution of problems encountered in frequency management and telecommunication system design.

Optimization of digital filters for low roundoff noise

Abstract: This paper treats the problem of minimizing the roundoff noise in digital filters using fixed-point arithmetic under sinusoidal input. A basic assumption made is that of representing the roundoff error as white noise that is independent from sample to sample and from source to source. The minimax noise principle is introduced to serve as a guide in the filter design to optimize the structure for minimum noise. One application is illustrated through the design of low-noise cascade digital filters under dynamic range constraints. Numerical examples demonstrate the lower noise possible in comparison to other known designs and serve to verify the effectiveness of a design procedure based on the minimax concept.

A Model of HF Impulsive Atmospheric Noise

Abstract: Determination of optimal receiver or detector and suboptimal estimator in the presence of additive atmospheric noise depends on the application of a mathematically tractable model of noise. In the tropics the atmospheric radio noise occurring mostly in the burst form above a relatively small continuous background does not deliver energy at a constant rate. This type of noise is non-Gaussian and has a very large dynamic range. The noise bursts consist of a number of short impulses. They are modelled here as the product of a narrow-band Gaussian noise and the reciprocal of a non-Gaussian random process. This paper includes the derivation of statistical information for the above noise viz, the probability distribution of amplitudes, and of separation between pulses, required for determining the error probabilities using various digital methods. This information can be used in filter optimization in digital systems, where the error probability is to be minimized.

Noise generation by gas jets in a turbulent wake

Abstract: Radiated noise is generated when gas discharges from an underwater orifice into a turbulent wake. Few quantitative studies under controlled conditions have been reported, however, and the mechanism of this noise generation is not well understood. This paper presents measurements of noise radiated by gas jets exhausting into a turbulent wake under controlled conditions in the test section of a 48‐in. diam water tunnel. Acoustic‐measurements in the frequency range 6–45 kHz were made with a directional hydrophone mounted in a water‐filled tank attached to one side of the tunnel test section. A turbulent wake was generated by a water speed of 9.1 m/sec flowing past a strut‐mounted cigar‐shaped body. Nitrogen gas was discharged at various flow rates into the turbulence through two different nozzle plates attached to the aft end of the wake‐generating body. For the range of parameters used in these experiments, results indicate that radiated noise is primarily a function of orifice radius and the turbulence parameters, and only secondarily of gas flow rates. One possible mechanism for the generation of this noise may be related to a critical Weber number.

Measurement of Frequency Stability in Time and Frequency Domains via Filtering of Phase Noise

Abstract: A recently developed theoretical analysis has shown that it is possible to measure the Allan variance (a time-domain measure of frequency instability) without any statistical treatment of data from an electronic counter. The measurement is made via high-pass filtering of phase noise with a test set similar to the one used for frequency-domain measurements. The unique test set described in this paper relies on this principle and is capable of measuring the short-term frequency instability of the best quartzcrystal oscillators in both time and frequency domains.

A note on Kalman-Bucy filters with zero measurement noise

Abstract: The limiting form of the Kalman-Bucy filter as measurement noise tends to zero does not, in general, correspond to the optimal filter derived assuming zero measurement noise. This may be considered to be due to a difference in initial conditions.

Radio Noise Meter Response to Random Pulses by Computer Simulation

Abstract: The radio interference from high voltage transmission lines is generally measured using either the CISPR or the ANSI type of instrument to give the quasipeak value and in some cases also the peak and average values, of the interference. However, because of the random and uncorrelated nature of corona generation on the transmission lines, the analysis of radio interference propagation can be made only in terms of rms quantities. In order to resolve this apparent inconsistency between the measurement and analysis of radio interference, the response of the conventional radio noise meters to random pulses is investigated using digital computer simulation. Some results are verified using a hybrid computer simulation, which represents more closely the detector output circuit of a radio noise meter. The results show that as the degree of randomness, both in amplitudes and separation intervals, of the pulses increases, the quasi-peak value becomes roughly proportional to the rms value. It is also shown that it is possible to predict, even with greater accuracy, the rms response of the radio noise meter from the measured quasi-peak and average responses.

Estimation of the Location of an Optical Object with Photodetectors Limited by Quantum Noise

Abstract: We study the maximum likelihood estimation of the location of an incoherent object, the light from which is distorted by an optical system and detected by photoelectric detectors with quantum noise. The noise is treated as a set of uncorrelated Gaussian variables with variances proportional to the signal plus background at their corresponding detectors. By the simulation of the noise, a large number of cases are tested and curves for the probability distribution of the error distance are obtained.

A new interpretation of noise reduction by matching

Abstract: The technique of noise reduction by means of a matching transformer is treated as a modification of the amplifier input noise sources, without resorting to the concept of noise figure. It is shown that matching is independent of the thermal noise of the source. The technique of noise reduction by paralleling input devices is also mentioned as closely equivalent to transformer matching.

Effect of cessation of late-night landing noise on sleep electrophysiology in the home

Abstract: Simultaneous measurements of noise exposure and sleep electrophysiology were made in homes before and after cessation of nighttime aircraft landing noise. Six people were tested, all of whom had been exposed to intense aircraft noise for at least two years. Noise measurements indicated a large reduction in the hourly noise level during nighttime hours, but no charge during the daytime hours. Sleep measures indicated no dramatic changes in sleep patterns either immediately after a marked change in nocturnal noise exposure or approximately a month thereafter. No strong relationship was observed between noise level and sleep disturbances over the range from 60 to 90 db(A).

Noise measurements in charge-coupled devices

Abstract: Measurements of the noise levels at the output of surface and bulk channel charge-coupled devices with three-phase overlapping polysilicon electrodes are presented. New schemes and input circuits for low-noise electrical insertion of the signal charge are discussed. Our measurements indicate that the noise levels due to the intrinsic noise sources (transfer and storage noise) agree with our physical understanding of the device operation. The noise levels due to the extrinsic sources (puiser noise and electrical insertion noise) are above the expected theoretical values.

Measurement of white and 1/f noise within burst noise

Abstract: A measurement method is described which enables the separate measurement of the power spectra of the normal noise (white and l/f) superimposed on burst noise. With this method the power spectra of normal noise can be determined for each burst noise level. It is found that the clean burst noise and the superimposed normal noise are generated by statistically independent processes. The fact that burst noise devices have a higher 1/f noise power content than devices without burst noise indicates that there exists a common condition for the generation of burst noise and 1/f noise.

Noise and bandwidth

Abstract: A discussion is given of the physical and mathematical properties of noise together with the concepts of noise bandwidth and system bandwidth. A general design procedure for measurement system is then outlined and illustrated by reference to a magnetometer developed by the author.

Theory of LDV Tracking Systems

Abstract: The application of frequency-tracking systems to the analysis of laser doppler velocimeter (LDV) signals degraded by background noise has been studied both theoretically and experimentally. Expressions are derived for both the correlation function and the expected value of the phase derivative in the general case of noise off center from the Doppler frequency, and these results are specialized to specific cases of practical interest. Laboratory measurements of output signal-to-noise ratio (SNR) and dc error, for varying input SNR and noise center frequency offset, show good agreement with the theoretical predictions.

Envelope detection of a unit-index amplitude-modulated cartier accompanied by noise

Abstract: The facts concerning the relative merits of linear and square-law envelope detection of a sinusoidally modulated carrier accompanied by Gaussian noise are clarified in this paper. The comparison when the carrier is weakly modulated and has mean power substantially greater than that of the noise in the input circuit has been fully covered in prior technical literature. In this special case the signal-to-noise ratio (SNR) in the detected output is the same for the two methods, and the distortion of the signal is worse with square-law operation because of inherent second-harmonic production. Since noise in the detected output is typically measured in the absence of signal modulation, the fact that the relative performance changes when the index of modulation approaches 100 percent tends to be overlooked. It is shown in the present paper that the noise performance of the square-law detector suffers a penalty approaching 1.8 dB when the carrier is strongly modulated. Also, the distortion in the square-law case is characterized by a second harmonic only 12 dB down from the fundamental, while the second harmonic in the output of the linear detector is practically negligible. These results are important in the evaluation of techniques in diversity reception.

Reliability Prediction of Silicon Bipolar Transistors by Means of Noise Measurements

Abstract: The results of theoretical and experimental investigations on flicker-and burst noise are used in order to point out the relation between excess noise and the internal properties of the transistors. Noise is show to be a good means of characterization of the surface parameters. A HTRB step stress test and a complementary long time storage are described. It emerges from the results that previous excess noisemeasurements give a good prediction of the failures and that noisiness is a very sensitive degradation parameter, the increase of which can be, sometimes, the only indicator of an imminent failure. A screening method is deduced.

Coherent optical noise suppression device.

Abstract: In optical data processing the quality of the output image is usually degraded by diffraction noise generated by the optical components of the system. The suitability of previously suggested techniques to a dc spatial filtering processor is discussed. A new system is proposed that overcomes the problems of the previous noise suppression techniques. Experimental results of the new system are presented along with a determination of the resolution of the system. The errors and limits of the new coherent noise suppression system are discussed.

Noise limitations in digital recording

Abstract: Previous studies have shown that the tape limited signal/noise ratio (s.n.r.), which may be deduced from first principles, is in close agreement with practice on many modern recorders. This s.n.r. depends upon the medium properties and the recording format, in particular the trackwidth and bandwidth. Since the digital linear density usable is related to the bandwidth, it is possible to derive expressions linking the s.n.r., trackwidth, linear and area digital densities. It is concluded that the s.n.r. available at an area density of 107bits/in2, which is a factor of ten higher than present maxima, is still adequate to permit reliable digital recording.

Noise Cancellation in the Presence of Correlated Signal and Noise

Abstract: : A model for a multichannel array signal processor that performs a noise-cancellation function is specified. The performance of the processor is examined in terms of the output signal-to-total-background-noise ratio. The parameters of interest are the correlation between signal and noise, the number of noise sampling channels, the relative gain of the noise in the signal-plus- noise versus the noise-only channels, and the array input signal-to-noise and interference-to-noise ratios. An important practical implication of the results presented is that, in systems such as adaptive beamformers for arrays, system performance can be seriously degraded if the signal and noise waveforms are correlated over finite time intervals.

Judged acceptability of noise exposure during television viewing

Abstract: Noise masking of television audio signals by flyovers is the most frequently mentioned problem of airport neighbors. This problem was studied in the laboratory using artificial noise. Three studies varied the intensity, duration, and rate (noises per hour) of the noises. Acceptability was found to approximate a logarithmic function of noise energy for changes in intensity, duration, and rate. Thus, the equal‐energy principle, which has been generally observed in abstract psychometric experiments, was confirmed in this more realistic and representative task. A fourth study showed aircraft‐flyover recordings to be more acceptable than artificial noises even though they had equivalent peak levels and masking durations. This difference can also be explained by the equal‐energy principle, since the flyovers had lower average (or integrated) energy.

Measurement and prediction of sound inboard and outboard of ships as generated by cavitating propellers

Abstract: A survey is presented in which manner the noise, generated by a cavitating ship propeller, can be predicted based on either full scale or model scale experiments. Two sides of the problem are elucidated, i.e. the noise radiated from the propeller into the water and the noise inside the ship. For solving the first problem the model technique as used in the depressurized towing tank of the NSMB offers fruitful possibilities. Model rules for the noise-spectrum are given. Also the measuring set-up in this tank is outlined, together with some acoustical considerations about the acoustical properties of the tank. The second part of the paper concerns the problem of noise aboard ships. Most attention is paid to the description of the cavitating propeller as a source of sound. A new measuring technique for the measurement of the acoustical source strength of a propeller is outlined. Emphasis is given on the relation between the vibration problem and the noise problem aboard ships and on the possibilities of the depressurized towing tank in relation to these problems.