Showing papers on "Noise measurement published in 1975"

Adaptive noise cancelling: Principles and applications

Abstract: This paper describes the concept of adaptive noise cancelling, an alternative method of estimating signals corrupted by additive noise or interference. The method uses a "primary" input containing the corrupted signal and a "reference" input containing noise correlated in some unknown way with the primary noise. The reference input is adaptively filtered and subtracted from the primary input to obtain the signal estimate. Adaptive filtering before subtraction allows the treatment of inputs that are deterministic or stochastic, stationary or time variable. Wiener solutions are developed to describe asymptotic adaptive performance and output signal-to-noise ratio for stationary stochastic inputs, including single and multiple reference inputs. These solutions show that when the reference input is free of signal and certain other conditions are met noise in the primary input can be essentiany eliminated without signal distortion. It is further shown that in treating periodic interference the adaptive noise canceller acts as a notch filter with narrow bandwidth, infinite null, and the capability of tracking the exact frequency of the interference; in this case the canceller behaves as a linear, time-invariant system, with the adaptive filter converging on a dynamic rather than a static solution. Experimental results are presented that illustrate the usefulness of the adaptive noise cancelling technique in a variety of practical applications. These applications include the cancelling of various forms of periodic interference in electrocardiography, the cancelling of periodic interference in speech signals, and the cancelling of broad-band interference in the side-lobes of an antenna array. In further experiments it is shown that a sine wave and Gaussian noise can be separated by using a reference input that is a delayed version of the primary input. Suggested applications include the elimination of tape hum or turntable rumble during the playback of recorded broad-band signals and the automatic detection of very-low-level periodic signals masked by broad-band noise.

Signal processor method and apparatus

Abstract: Method and apparatus for processing input binary encoded analog signals to precisely determine the time occurrence of positive-going and negative-going transitions. Such digital signals result, for example, when bar codes (e.g. Universal Product Codes) are optically scanned. Transitions are determined by detecting the zero crossings, at selected gating times, of the second derivative of the input signals. The selected gating times occur whenever the first derivatives of the input signals exceed a threshold level. The threshold level is determined in one embodiment by peak-to-peak detecting the input signals and adding this value to a rectified noise measurement signal.

Applications of electrical noise

Abstract: The omnipresent noise in electronic circuits and devices is generally considered undesirable. This paper describes some of the applications to which it has been put. Short descriptions of a wide variety of applications are given together with references for further details. The applications fall in four categories: applications in which noise is used as a broad-band random signal; measurements in which the random noise is used as a test signal; measurements in which noise is used as a probe into microscopic phenomena; and the applications where noise is a conceptual or theoretical tool. Many examples of applications in each of these categories are given. Some of the applications included are only of historical interest now, and a few are, as yet, only proposals.

Stability Considerations of Low-Noise Transistor Amplifiers with Simultaneous Noise and Power Match

Abstract: Microwave transistor amplifiers may be simultaneously matched for optimum noise and input/output VSWR This paper demonstrates a combination of mapping techniques, computer optimization and stability considerations through two amplifier designs (70 MHz and 4000 MHz) to achieve these goals

Analysis and Digital Realization of a Pseudorandom Gaussian and Impulsive Noise Source

Abstract: This paper presents results on the analysis and digital hardware realization of a non-Gaussian impulse noise source which can be used to model the impulsive noise present in wide-band communications systems. The impulse noise appearing in practical systems is characterized by bursts of much higher amplitudes than would be predicted by a normal- or Gaussian-distribution law. A need exists for a better characterization of this non-Gaussian impulsive noise as well as actual noise generators which can be used for evaluation of present and future communications equipment under realistic system-operating conditions. The impulse noise model and the realization of the noise generator described in this paper are capable of producing Gaussian background noise, lognormal impulsive noise, and burst timing to set prescribed starting and ending times of the bursts and impulse density within each of the burst periods. The techniques used in this paper are based on first generating a basic pseudorandom binary sequence (PRBS) and then from this deriving the Gaussian background noise by adding samples from the PRBS generator. The lognormal noise is then derived from the same sequence by using an incremental exponential generator. The burst timing signals which realize an approximate Poisson distribution are obtained by observing the occurrences of specific subsequences from the PRBS generator.

Parametric amplification with self-pumped Josephson junctions

Abstract: The parametric nature of supercurrent in Josephson junctions may be exploited for amplification of high frequency signals in several modes of operation, where in each case the reactance variation is provided by the internal oscillations due to the average contact potential, a)One mode is negative resistance amplification with a single idler. This mode is entirely equivalent to that generally employed in conventional parametric amplifiers with varactor diodes. b)Negative resistance amplification with several idlers at further combination frequencies. This mode of operation is typical for the resistively shunted junction model, c)Amplification by upconversion, which is conceptually employed in the rf SQUID used in magnetometry. Experimental verifications of these various modes are described and their suitability for low noise amplification discussed. The upconverter experiment permitted the measurement of device noise by variation of the temperature of the input termination. An upper noise limit of 15°K is established. This experiment demonstrates that in high frequency application of active self-oscillating Josephson junctions the fundamental noise achievable is not greatly in excess of the thermal limit.

Noise characteristics of GaAs and Si IMPATT diodes for 50-GHz range operation

Abstract: Direct comparison of noise behaviors between GaAs Schottky-barrier junction and Si diffused p+-n junction diodes operating in the 50-GHz range is reported by using the same circuitry. In the oscillator operation, the GaAs diode exhibits excess "1/fm" noise near carrier, whereas the Si diode shows flat spectrum. Far from the carrier, and AM-DSB-NSR of -133 dB in a 100-Hz bandwidth and an FM noise measure of 27.1 dB are observed for GaAs diodes. Corresponding values obtained for Si diodes are -125 and 36.2 dB, respectively. As a reflection amplifier, minimum noise figures of 27.5 and 38 dB are achieved for the GaAs and Si devices, respectively. These results indicate that the GaAs IMPATT is superior in noise behavior to the Si diode also in the 50-GHz frequency range by about 10 dB. It is emphasized that the noise induced in the bias circuit of the IMPATT oscillator is a replica of the sideband noise of the output power and can be used as an indicator to obtain a low-noise tuning condition of the oscillator.

Numerical Results on the Convergence of Relative Efficiencies

Abstract: This paper considers the detection of a known constant signal in an additive non-Gaussian noise under the assumptions of discrete time and statistically independent noise samples. The objective is to determine how large sample size must be before the easily computed asymptotic relative efficiency becomes a valid measure of performance. The exact small-sample error probabilities are calculated for a Neyman-Pearson optimal nonlinear detector consisting of a zeromemory nonlinearity followed by summation and threshold comparison. "Large-tailed" noise having a double exponential distribution is used as an example. The exact distribution of the test statistics for a linear detector and for the Neyman-Pearson optimal detector are calculated. Then the relative efficiency of the Neyman-Pearson optimal detector, as compared to a linear detector, is computed in order to study the rate of approach of the relative efficiency to its asymptotic value.

Minimization of jet and core noise of a turbojet engine by swirling the exhaust flow

Abstract: A noise abating improvement for jet engines has been investigated and demonstrated using a full scale turbojet engine which provided the means for significant reductions in jet and core noise with minimal thrust loss. This was accomplished by controlled solid body rotation (swirling) of the flow in the nozzle and jet exhaust. Relatively moderate angles of solid body rotation in the presence of temperature, density, pressure, and velocity gradients were utilized. Of great interest was the finding that significant reductions of sound pressure levels and sound power were obtained with only a small percentage of the total primary mass flow swirling at the exit of the nozzle. Therefore, tradeoffs between noise reduction and engine performance can be optimized to satisfy aircraft performance and federal noise standards with minimal wasted rotational kinetic energy.

Interior noise levels of two propeller driven light aircraft

Abstract: The relationships between aircraft operating conditions and interior noise and the degree to which ground testing can be used in lieu of flight testing for performing interior noise research were studied. The results show that the noise inside light aircraft is strongly influenced by the rotational speed of the engine and propeller. Both the overall noise and low frequency spectra levels were observed to decrease with increasing high speed rpm operations during flight. This phenomenon and its significance is not presently understood. Comparison of spectra obtained in flight with spectra obtained on the ground suggests that identification of frequency components and relative amplitude of propeller and engine noise sources may be evaluated on stationary aircraft.

Experimental evaluation of trailing edge and incidence fluctuation noise theories

Abstract: Tests were conducted to evaluate conflicting theories for trailing edge noise and for incidence fluctuation noise. A flat-plate airfoil with flush-mounted surface pressure transducers was tested in an anechoic wind tunnel at velocities from 31.5 to 177 m/sec and nominal 4 and 6% grid-generated turbulence levels. In one series of runs, the airfoil was faired into the tunnel nozzle and extended beyond the nozzle lip for studies of trailing edge noise without a leading edge and with flow on only one side. Such noise was found to vary with velocity to the fifth power and turbulence level squared as predicted by Ffowcs Williams and Hall (1970) and by Chase (1972). Power spectral density at high frequencies decayed approximately inversely with frequency to the 10/3 power as predicted by Chase. The data were poorly predicted by Hayden's correlation (1969, 1972).

Nuclear Radiation Induced Noise in Infrared Detectors

Abstract: A model for calculating the rate and amplitude of gamma ionization events in infrared detectors is presented. Several simplifying approximations to the actual, complex physical situation are applied in the model, thereby allowing an exact analytical formulation of the problem. Experimental measurements of nuclear-radiation induced noise pulse-height distributions and event rates are compared to predictions made using the model. Comparisons of experiment and theory were made at several different gamma energies to provide confirmation of the model over the gamma energy range of interest of most application. The experimentally-confirmed model allows prediction of the noise response of photoconduction detectors for any specified detector material, geometry, surrounding material and incident gamma spectrum.

Accurate Measurement of Noise Parameters in Ultra-Low Noise Opto-Feedback Spectrometer Systems

Abstract: The accurate measurement of the basic noise parameters of ultra-low noise spectrometer systems has been developed in the frequency domain by spectrum analysis. This method overcomes some of the difficulties experienced in using cmventional techniques. An analytic and experimental comparison between 'time' and frequency domain techniques is carried out and the use of the latter as a method to develop extremely low-noise detector and FET packages is demonstrated. The origin of the remaining noise in high quality systems is traced to surface and gate junction generation through traps in the FET.

Measurement parameters for automobile ignition noise

Abstract: Peak-detector measurements of radiated electromagnetic noise from automobile ignition systems reveal detectable frequency components over a range to 7 GHz. Occasionally a very noisy vehicle will radiate noise over the entire frequency range in excess of 30 dB above the median observed noisy vehicle. Subjective evaluations indicate that the landmobile radio service may possibly by affected by automobile ignition noise. Automobile ignition noise is typically measured using a radio noise meter equipped with either a peak detector or a quasi-peak detector, and has also been measured using special equipment to produce the average rate of occurrence and strength of noise impulses. The result of the latter measurement is referred to as a noise amplitude distribution (NAD). Since the NAD method includes a measurement of the time variations of the ignition noise process, it is superior to the first-order amplitude measurements obtained by the peak or quasi-peak method for modeling the effects of ignition noise on communication systems. Ideal and practical modeling methods are discussed for determining the effect of ignition noise upon communication systems, with emphasis on voice communications. /Author/

On the evaluation of roundoff noise in digital filters

Abstract: The usual method of measuring the roundoff noise generated in a digital filter may lead, at least in case of sign-magnitude truncation, to an excessive result due to incomplete cancellation of the useful output signal. A simple method for determining a corresponding corrective term is presented.

Source Mismatch Effects on Measurements of Linear Two-Port Noise Temperatures

Abstract: A noticeable source mismatch occurs in measurements of noise parameters of a linear two-port, since an admittance-transformer network between the source and the two-port must be inserted. A generalized analysis of the source mismatch effects on noise measurements, which considers the dependence of the noise performance of the two-port on the input admittance, is presented here. On this basis, two types of noise generators are considered and compared with each other.

The development of experimental techniques for the study of helicopter rotor noise

Abstract: The features of existing wind tunnels involved in noise studies are discussed. The acoustic characteristics of the MIT low noise open jet wind tunnel are obtained by employing calibration techniques: one technique is to measure the decay of sound pressure with distance in the far field; the other technique is to utilize a speaker, which was calibrated, as a sound source. The sound pressure level versus frequency was obtained in the wind tunnel chamber and compared with the corresponding calibrated values. Fiberglas board-block units were installed on the chamber interior. The free field was increased significantly after this treatment and the chamber cut-off frequency was reduced to 160 Hz from the original designed 250 Hz. The flow field characteristics of the rotor-tunnel configuration were studied by using flow visualization techniques. The influence of open-jet shear layer on the sound transmission was studied by using an Aeolian tone as the sound source. A dynamometer system was designed to measure the steady and low harmonics of the rotor thrust. A theoretical Mach number scaling formula was developed to scale the rotational noise and blade slap noise data of model rotors to full scale helicopter rotors.

Measurements and analysis of aircraft airframe noise

Abstract: Flyover measurements of the airframe noise of AeroCommander, JetStar, CV-990, and B-747 aircraft are presented. Data are shown for both cruise and landing configurations. Correlations between airframe noise and aircraft parameters are developed and presented. The landing approach airframe noise for the test aircraft was approximately 10 EPNdB below present FAA certification requirements.

State Estimation with Coarsely Quantized, High-Data-Rate Measurements

Abstract: This paper treats the problem of estimating a signal corrupted by noise that is sampled and quantized at a high data rate. Local and global processors are proposed to achieve data compression that permits near optimal extraction of information. Two techniquesmaximum likelihood and minimum transform chi square, which are in the class of best asymptotically normal estimators- are investigated for the local processor. Simulation results are presented to demonstrate the feasibility of the approach.

Measurements of discrete vortex noise in a closed-throat wind tunnel

Abstract: Measurements are presented of the discrete vortex noise emitted by a thin airfoil. These measurements were made in a new wind tunnel designed specifically for aerodynamic noise measurements. The tunnel is an indraft type with a 25- by 35- by 100-cm testing section and a sonic-throat noise suppressor just downstream of the test section. Directivity and standing wave patterns are presented and compared with theoretical predictions. Frequency scaling criteria are developed and compared with other investigations.

On the estimation of uncertain signals using an estimation-detection scheme

Abstract: An estimation-detection scheme is proposed for the estimation of signals with unknown parameters. The scheme is illustrated by considering the case of a signal with unknown but bounded variance. Two sets of bounds are used to determine two regions of signal uncertainty, and different linear estimators are used for each region. A detector is then used to select the appropriate estimator. Since no a priori information is assumed on the unknown parameters a weighted minimax criterion is used to optimize the detector and the estimators.

Anomalous Noise in Schottky Diode Mixers at Millimeter Wavelengths

Abstract: Measurements on state-of-the-art 85 GHz mixers using GaAs Schottky-barrier diodes give high values of noise temperature ratio (~1.3) and loss temperature (~500/spl deg/K) despite low conversion loss (~5dB SSB) and input noise temperature (~600/spl deg/K SSB). The source of this noise has not yet been identified.

Optimum array detection in fluctuating ambient noise fields

Abstract: In practical underwater signal detection problems using an array, the statistics of the ambient noise field vary spatially and temporally. This paper considers the problem of detecting a farfield signal source of known location and waveform which generates a known signal field at an array aperture. The power of the ambient noise field is considered to be a random function of space and time and the Bayes approach is used to derive optimum receiver structures and their performance. For all cases considered, the optimum array processor either requires spatial filtering which is not accomplished by a beam former or requires spatial processing in addition to that provided by a beam former. The loss of detection performance due to uncertainty in the parameters of the ambient noise field is determined for several specific cases.Subject Classification: 60.20; 25.35.

Ignition Noise Measurements in the VHF/UHF Bands

Abstract: In the operational use of mobile communication terminals, it may often be unavoidable to park them in a location where they would be subject to ignition noise due to local traffic. This type of noise causes errors in digital systems. Since it is impossible to define a general model for impulsive noise, one must measure the necessary statistical paramaters to be used for calculating its effect on a communication link. Although these parameters vary for different types of links, peak amplitude distribution, time distribution, and duration of impulses at various amplitude levels should be known. In this paper noise amplitude distribution (NAD) measurements carried out on the VHF/UHF bands for ignition noise are explained. The information derived from the NAD is the peak amplitude distribution of the impulses; in addition, the average repetition frequency of the impulses is also obtained. An analytical expression is found for the probability density function of the idealized NAD.

The Effect of Radiation Damage on the Noise Performance of Fet's

Abstract: The gate noise from radiation induced defects in MOSFET's and JFET's has been studied for 24.8 MeV electron irradiations up to about 1 x 1016 e/cm2. The flicker noise increase induced in JFET's has been interpreted as due to the defect generation and recombination centers induced by radiation damage within the depletion layer. Finally, it is shown that the noise performance of JFET's is well applicable for high-intensity and high-level radiation detection.