Showing papers on "Noise measurement published in 1968"

On state estimation in switching environments

Abstract: Work concerned with the state estimation in linear discrete-time systems operating in Markov dependent switching environments is discussed. The disturbances influencing the system equations and the measurement equations are assumed to come from one of several Gaussian distributions with different means or variances. By defining the noise in this manner, periodic step changes in the inputs which cannot be feasibly measured for economic or technical reasons can be detected and corrected. These changes can be in the amplitudes of the inputs or in the variances of stochastic inputs. A Bayes estimation procedure is applied to the problem of filtering the observations of the system so that an estimate of the system state is obtained. Computer simulations for the optimal and suboptimal estimators are also presented.

Restoration, Resolution, and Noise

Abstract: This paper treats the problem of restoring the detail to an optical image which has been degraded by diffraction and noise. The particular contribution of the paper is a more complete analysis of the effects of various types of noise on system performance than has been given previously. Background noise, measurement noise, and computer roundoff error are considered, and the errors in the reconstructed image caused by these noise processes are evaluated. Numerical results for the special case of a perfect one-dimensional slit aperture are obtained. A general conclusion is that the reconstruction technique described here is most useful when the smoothing is severe and when a modest improvement of resolution may be worthwhile.

Hazardous Exposure to Impulse Noise

Abstract: This paper presents impulse‐noise damage‐risk criteria based on conclusions of independent British and American studies and on the work of other research workers in this field. Most of the studies that led to this criterion were performed with noise from small arms, but the criterion is general enough to permit assessment of most other types of impulse noise. The variables that must be considered in determining the potential hearing hazard and in the practical application of the criteria are presented, and the parameters that must be measured are defined. The measurement technique and type of transducers to be used are discussed.

Optimum Signal-Processing for Pulse-Amplitude Spectrometry in the Presence of High-Rate Effects and Noise

Abstract: In this paper the idea of a general signal processing system which should satisfy various pulse rate and noise requirements is explored. Optimum processing functions (weighting functions) are considered for an ideal system, and for real conditions where effects like imperfect pole-zero cancellation are present. Time-variant filters of the gain-varying class are used to realize the required optimum weighting functions of finite width. It is shown how nonfinite-width weighting functions of some time-invariant filters can be modified into finite-width functions by switching. These switched-gain time-variant filters are somewhat limited in choice of weighting functions. A general processing system can be realized employing filters with continuously time-variant elements. In particular, a gain-varying element (i.e., an analog multiplier) can be used in conjunction with an integrator to realize arbitrary weighting functions, and therefore the theoretically maximum signal-to-noise ratio. The system is time-variant only for the noise and not for the signal, so that it does not require high precision of the time-variant element. The system output is independent of the gating interval, and does not require precise timing. A method for evaluation of such systems in terms of noise, ballistic deficit and sensitivity to parameter variations is given.

The Measurement of Near-Carrier Noise in Microwave Amplifiers

Abstract: This paper discusses the measurement of additive noise in microwave power amplifiers, under CW and pulsed condition. The introduction of a pulsed carrier cancellation principle permits, for the first time, an investigation of the additive noise of pulsed amplifiers down to the thermal noise level. The measurement apparatus consists of three channels fed from a common source. One channel contains the amplifier under test. The other channel is pulsed by a "noise-free" modulator with the same pulse parameters as those of the test channel. The two signals are algebraically cancelled in a hybrid circuit and the difference signal, containing only the noise sideband of the amplifier, is coherently detected with the signal in the third channel. Measurements made on klystron amplifiers indicate that the level of the power spectral density of the FM noise approaches the thermal noise level, and that it has nearly the same value for CW and for pulsed operation.

A Microwave System for Measurements of AM and FM Noise Spectra

Abstract: This paper describes a noise measuring system with a high degree of flexibility in regard to video frequency coverage as well as radio frequency coverage. Noise systems for S, X, and Ku-bands were constructed to obtain high sensitivity at spectral frequencies from several Hz to 30 MHz off the carrier. The measured limiting sensitivities of the X-band set over the video range 20 Hz to 325 kHz with an input power of 10 mW are --145 dB for AM noise and 0.02 Hz rms for FM noise in a 100-Hz measuring bandwidth.

Acoustic noise and vibration of rotating electric machines

Abstract: In recent years, with the growing public awareness of acoustic noise and current work towards International and British Standards concerned with noise from rotating electric machines, work on rotating-machine noise has progressed, from attempts at a qualitative explanation of the more obvious components of machine noise, towards the prediction of the complete acoustic spectrum from the design data This paper describes the ways, common to all machines, in which noise is produced by mechanical, magnetic and aerodynamic sources, and reviews methods used to determine the acoustic output and vibration of particular types of machine The measurement and analysis of machine noise is described, and some general rules for producing quiet machines are given A bibliography of the main work on machine noise is given

A computational comparison of several nonlinear filters

Abstract: Eight different filtering schemes, one linear and seven nonlinear, are applied to two nonlinear scalar dynamic systems which are forced by additive noise. The nonlinear measurement made of the state is corrupted by further additive noise. The various filters, derived using a continuous formulation, are simulated on a digital computer and are compared on the basis of their estimation-error history. In addition to the comparison, one system/filter combination is used to demonstrate the effects of varying the variance of the noise, of mismatched parameters, and of sampled measurements.

The Measurement of Oscillator Noise at Microwave Frequencies

Abstract: Improved measurement methods are presented for measuring both AM noise and FM noise from microwave oscillators, The Schottky barrier diode detector is used to measure AM noise 170 dB below the carrier in a 1 Hz bandwidth. A new discriminator is presented that has a measurement threshold below 0.001 Hz rms in a 1 Hz bandwidth. The use of a storage oscilloscope and wave analyzer to study noise modulation is discussed. The new discriminator and storage oscilloscope can be used for short-term stability measurements for intervals up to 100 seconds.

Speech processing in a high ambient noise environment

Abstract: Classical communication theory considers preprocessing of speech for more efficient transmission through a noisy channel. However, when a high ambient noise environment is present prior to modulation, conventional techniques break down. This paper discusses speech processing in a high ambient noise environment and how the intelligibility can be improved by using a discrete, adaptive filter whose parameters vary with the form of the speech signal. The intelligibility gain of processed speech over unprocessed speech ranges from 50 percent at very high noise levels to negligible gain at moderate noise levels.

Characteristics of optimum multichannel stacking filters

Abstract: A large class of seismic processing operations involve the linear combination of several traces in such a way that certain “signal” events are emphasized over other “noise” events. If the noise events are randomly distributed between traces, then simple addition of the traces represents the best possible technique for suppressing the noise. However, in many cases a noise event on one trace will also occur at relatively well‐determined points on other nearby traces. For these cases, multichannel linear filters offer better discrimination against organized noise than the straight addition of traces does. Such multichannel filters can be designed with only a knowledge of the relative times of the arrivals for the various signal and noise events but with no knowledge of the actual event shapes. In addition, the filter may be specified to allow for such contingencies as the presence of random noise, variable gain between traces, and random variations of the relative time of arrival between traces. Once these p...

Thermal Noise from a Passive Linear Multiport

Abstract: The thermal noise from passive multiports is discussed from fundamentals so that it can be understood, measured, or calculated by a microwave engineer The multiports are assumed to have a uniform temperature, but with no restriction on reciprocity or mismatch The noise temperature, T/sub N/, contributed by such a multiport is T/sub N/=A T where T is its physical temperature and A is its absorption coefficient An approximate method of measuring A, and a method of measuring an A as small as 0008 within 5 percent, are pointed out Also, exact and approximate expressions for A in terms of scattering matrix elements and termination reflection coefficients are derived Finally, the crosscorrelation of the noise from different ports is briefly considered

Lower order optimal linear filtering of nonstationary random sequences

Abstract: The following deals with the discrete-time linear minimum-variance filtering of nonstationary random processes. The dynamics of the signal and colored noise processes are represented by a combined random process model.[1] Some of the measurement elements contain additional white noise, others do not. Similar to the continuous-time case of Bryson and Johansen,[3] the white-noise-free measurements will be used to reduce the order of the Kalman filter,[1],[2].

Coherent optical noise suppression.

Abstract: The performance of coherent optical spatial filtering systems is often limited by lens noise. Imperfections in the optical components generate noisy diffraction patterns when illuminated by spatially coherent light. This random noise often masks useful signals in the output images. Coherent noise can be reduced by decreasing the spatial coherence of the illumination system. Unfortunately, reducing spatial coherence also reduces the frequency discrimination capabilities of the system; a filter cannot operate on a given spatial frequency without significantly affecting an adjacent frequency. This paper presents a technique for time averaging coherent optical noise without reducing the spatial frequency discrimination capability associated with a laser illumination system. Experimental results are given for noise suppression by both a reduction in spatial coherence and by the noise averaging technique. The improved frequency discrimination of the latter technique is also demonstrated.

On the Detection of a Known Signal in a Non‐Gaussian Noise Process

Abstract: In this paper, three receiver designs for the detection of a known signal in an additive non‐Gaussian noise process are considered. The noise process consists of white Gaussian noise modulated by a random‐spectrum level. The first receiver considered is an optimum (likelihood) processor and the remaining two receivers are suboptimum designs consisting of a cross correlator and a likelihood correlator. The basic processing operations of the three receivers are investigated and compared on the basis of their effects in observation space. The performance of each receiver is evaluated and presented in terms of ROC curves. A comparison of the performance curves indicates a loss in optimum performance as compared to the Gaussian noise case and a significant loss in performance of the suboptimum receivers relative to the optimum receiver.

Measurement of the Noise Temperature of a Mismatched Noise Source

Abstract: A method is suggested that can measure the available power (or the effective temperature) of a noise generator independent of its reflection coefficient. A system utilizing a compensation generator and a tuned three-port circulator is constructed at X-band and evaluated for a noise generator of about 10 000/spl deg/K. The error analysis and the experimental results indicate that the effective temperature of this generator, with a reflection coefficient of 0.5, can be measured within 0.6 percent in addition to the uncertainty of a standard needed to calibrate the system.

Aircraft noise evaluation

Abstract: : The Federal Aviation Administration, in response to Public Law 90- 411, has begun the rule making process leading to the certification of aircraft for noise. The basic element in the regulation criteria is the noise evaluation measure designated as effective perceived noise level, EPNL, which is a single number evaluator of the subjective effects of aircraft noise on human beings. Simply stated, EPNL consists of instantaneous perceived noise level corrected for tones and duration. The history of the development of EPNL is presented and a critical evaluation of its validity is made. The computational procedures are described in detail including both integration and approximate methods for calculating duration corrections. Examples are given in the appendices.

Position-Sensitive Semiconductor Particle Detectors Fabricated by Ion Implantation

Abstract: The advantages and problems associated with the use of ion implantation for the fabrication of position-sensitive particle detectors are discussed. Analysis of the noise and pulse risetime properties of such devices shows the desirability of using a high sheet resistance in the distributing resistive layer for optimum position resolution while restricting the RC of the detector to values approximately equal to the clipping times used in the measuring circuits in order to obtain good position linearity. From both detector noise and pulse rise-time considerations it is found desirable to use equal pulse shaping in the energy and the position signal measuring systems. Detectors were made by implantation of 60 keV boron and phosphorus ions into 4000 ohm-cm n-type silicon. Representative results are shown for a 4×32 mm2 one dimensional detector which shows integral and differential position nonlinearity of less than one percent and position resolution of less than 0.2 mm. Extension to one dimensional detectors up to 50 mm and to 10×10mm two dimensional detectors is discussed.

The Australian National Standards Laboratory X-Band Radiometer for the Calibration of Noise Sources

Abstract: The chief possible causes of error in the calibration of microwave noise sources are examined and a radiometer designed to minimize these errors is described. This includes a self-contained hot-load standard, facilities for measuring the hot-guide losses, a synchronously switched broad-band circulator, a switchable, high-stability attenuator, provision for measuring this attenuation, and a carbon-filament lamp reference noise source.

A Low-Noise Class-C Oscillator Using a Directional Coupler

Abstract: An oscillator using a directional coupler is proposed as a solution to the design of efficient low-noise high-power high-frequency oscillators. FM noise measurements are presented for microwave sources derived via varactor multipliers from several different transistor oscillators of this type. The design has an isolated port which can be used to achieve injection phase lock. This feature is used to point out some of the interesting FM noise properties of these oscillators, the knowledge of which is important in the design and application of solid-state microwave sources. Also, experimental results are given which show how a low-noise microwave source can be built using a low-frequency crystal oscillator followed by a high-order varactor multiplier.

Subjective quality of television pictures impaired by sinewave noise and low-frequency random noise

Abstract: Transistorised amplifiers for video transmission over coaxial cables incorporate power units with d.c.-d.c. convertors that produce an aggregate effect similar to that of band-limited random noise at low frequency. The subjective effect of such noise, centred at 3.2 and at 7.5kHz, has been investigated. Tests were also made with sinewave noise at the frequencies giving the worst effect in the regions of 1 and 3.2kHz and 1 and 3.2MHz. Results are summarised in the form of signal/noise ratios for a series of `imp' mark points that has recently been introduced.

Applications and Analysis of Noise Generation in N-Cascaded Mismatched Two-Port Networks

Abstract: Generalized equations are derived for noise generation and its propagation in linear N-cascaded two-port networks with mismatches. The analytical method is applied to microwave measurements in low-noise technology; e.g., in determining the effective input noise temperatures of a cryogenic paramp and the noise temperature of a cryogenic noise standard in a mismatched system. This approach is also applicable to mismatched networks at different temperatures. Two types of thermal noise standards utilizing liquid helium or helium gas as a refrigerant are described. Either type can be mounted on the back side of antennas and switched into the microwave-receiver line. However, the noise standard with the helium-gas refrigerator has the advantage of operating without refilling or spilling its coolant as the antenna elevation is varied.

Effects of Noise on Transfer-Trip Carrier Relaying

Abstract: A test method is described for the measurement of the probability of error due to noise in transfer-trip (TT) relaying using power line carrier. Noise levels recorded on 230-kV carrier installations are given to permit the interpretation of the measured error probabilities in terms of reliability and security. Three possible applications of the method are demonstrated: 1) finding the required biasing for frequency-shift-keying receivers, 2) preservice checking of transfer-trip channels, and 3) comparison of different transfer-trip systems.

A Varactor Null Detector for Aduio Frequency Capacitance Bridges

Abstract: A two-varactor, double-sideband up-converter pumped at 30 MHz has been constructed Operated at room temperature with a signal frequency of 104 rad/s, the device has an optimum source resistance of 105 ohms and a minimum noise figure of 001 dB Immersed in liquid N2, minimum noise figures below 0001 dB referred to a room temperature source have been measured The device is particularly useful as a null detector for audio frequency capacitance bridges At 104 rad/s, a signal current of 10-14 amperes through a capacitance of 1000 pF can be detected in less than one second with this instrument Techniques for suppressing microphonics and other extraneous sources of noise are described

Effect of Signal Duration on Detection for Gated and for Continuous Noise

Abstract: A series of two‐alternative forced‐choice experiments showed that for short durations, the detection of a tonal signal in noise when the two are gated synchronously is superior to the detection of the signal in a background of continuous noise. The experiments also showed that for gated signal and noise, there is a steady improvement in detection as the duration is shortened, provided that highly practiced observers are employed in the task. Naive observers exhibit a similar trend, but their performance drops at the short durations (5 and 10 msec) where the listening task becomes very difficult.

Estimators for optimally sensitive systems

Abstract: The synthesis of an optimally sensitive controller is extended to the noisy case. A Kalman filter is used to estimate the uncertain parameter variations which are then used in the controller.

The Simultaneous Measurement of Gain and Noise Using Only Noise Generators

Abstract: The gain and noise of a linear two-port device can be measured simultaneously using two noise generators as the only signal sources. While this method is usable for measuring all linear two-port devices except those with high loss, it is particularly convenient for low-gain devices, for which it replaces three conventional measurements. The terms "minimum output temperature" and "standard output temperature" are introduced.

Digital analysis of current noise at very low frequencies

Abstract: Three methods of digital spectral analysis are compared, and their application to the investigation of current noise at very low frequencies is described. In each case periodic sampling of filtered noise voltages is followed by digital computation. Particular attention is given to the errors caused by aliasing in the determination of a power spectrum with the form characteristic of current noise.