Showing papers on "Noise (radio) published in 1989"

Burgers equation with correlated noise: Renormalization-group analysis and applications to directed polymers and interface growth.

Abstract: The Burgers equation is the simplest nonlinear generalization of the diffusion equation. We present a detailed dynamical renormalization-group analysis of this equation subject to random noise. The noise itself can be the product of another stochastic process and is hence allowed to have correlations in space and/or time. In dimensions higher than a critical ${d}_{c}$ weak and strong noise lead to different scaling exponents, while for d${d}_{c}$ any amount of noise is relevant resulting in strong-coupling behavior. In the absence of temporal correlations we find two regimes for d${d}_{c}$: either the hydrodynamic behavior is determined by white noise and correlations are unimportant, or correlations dominate and the resulting scaling exponents can be obtained exactly. With temporal correlations present, the hydrodynamic behavior is much more complex, as renormalization predicts a complicated dependence of the effective noise spectrum on frequency in certain regimes. The relevance of these results to two interesting problems is discussed. One is the anomalous transverse fluctuations of a directed polymer in a random medium, and the other is a description of a growing interface. Various recent numerical simulations are reviewed in the light of these results. For example, we show that an exponent identity observed in all simulations so far follows simply from the Galilean invariance of the equation in the absence of temporal correlations.

A class of unusual lightning electric field waveforms with very strong high‐frequency radiation

Abstract: The first wideband dE/dt recordings have been obtained for the narrow bipolar pulses previously identified by Le Vine (1980) as “sources of the strongest RF radiation from lightning.” These dE/dt waveforms are dramatically different from those of other known lightning processes. A burst of high-frequency “noise” is superimposed on the slower bipolar pattern one might expect from the relatively smooth E waveforms. For 18 such pulses from an isolated thunderstorm cell at known range, the mean peak E and dE/dt, range-normalized to 100 km, were 8.0±5.3 V/m and 20±15 V/m/μs, respectively. Spectral analysis indicates that the sources of these pulses radiate much more strongly than first-return strokes at frequencies from 10 MHz to at least 50 MHz. Absolutely calibrated power and energy spectra are presented which are reliable from 200 KHz to perhaps 20 MHz. At 18 MHz the narrow pulses appear to contain nearly 16 dB more spectral energy than first return-stroke waveforms from the same range. Supporting evidence shows that they generally occur as isolated pulses in intracloud flashes but are not associated with K changes or other known phenomena. They can occur in either polarity.

Feasibility of the high Tc superconducting bolometer

Abstract: A design analysis is given for a bolometric infrared detector that uses the resistive transition of a high‐temperature superconductor as the temperature sensing element, and liquid nitrogen (LN) as the coolant. It is shown that for highly oriented c‐axis films, the measured low‐frequency noise causes little or no degradation of the performance. With the incoming radiation chopped at 10 Hz, noise equivalent powers (NEP) in the range (1–20)×10−12 W Hz−1/2 should be achievable. These values compare favorably with the NEP of other detectors operating at or above LN temperatures for wavelengths greater than 20 μm.

Bubble sources of the Knudsen sea noise spectra

Abstract: Single coherent bubble contributions to the incoherent underwater noise of spilling breakers have been studied in an anechoic laboratory facility. The waves are generated by a plunger, they propagate 17 m along a 1.2×1.2‐m water waveguide, and ‘‘spill’’ and create bubbles at the surface of a 3×3×3‐m anechoic cube of water. Several species of bubbles have been identified. In general, they act as transient dipoles of duration from 2 to several milliseconds, with peak axial source strength of the order of tenths of pascals, at 1 m. The noise is emitted when the bubble is within hundreds of micrometers or a few millimeters of the surface. Bubbles were observed in the 2 decades of frequency from 500 to 50 000 Hz. The average of the individual bubble events yielded a spectrum that slopes at about 5 dB/oct from 1 to 20 kHz, the same as the Knudsen wind noise spectra at sea. The magnitude of the laboratory breaker noise during continual wave‐breaking events was approximately 80 dB re: 1 μ Pa2/Hz at 1 kHz, which i...

Noise characteristics of a non-degenerate Optical Parametric Oscillator - Application to quantum noise reduction

Abstract: A semi-classical analysis of the noise characteristics of a non degenerate, above threshold, optical parametric oscillator is presented, yielding expressions for the quantum fluctuations of the output field intensities and phases. Particular emphasis is given to the study of the noise on the intensity difference between the two generated fields. The effect of losses, unbalance, detunings and excess pump noise is investigated. A significant quantum noise reduction is found over a broad domain of the parameter space.

Excess spontaneous emission in non-Hermitian optical systems. II. Laser oscillators

Abstract: When the Petermann excess-spontaneous-emission factor described in the accompanying paper [Siegman, preceding paper, Phys. Rev. A 39, 1253 (1989)] is taken into account, we find that the quantum-noise fluctuations or Schawlow-Townes fluctuations in the output spectrum of a laser oscillator will be multiplied by this excess noise factor. The excess spontaneous emission in a laser oscillator cannot be canceled by adjoint-mode-excitation techniques as it can be in a laser amplifier. The resulting noise enhancement can be very sizable (100 to 1000 times or more) in gain-guided laser oscillators, and especially in laser oscillators using geometrically unstable cavities with moderate to high magnifications and Fresnel numbers.

Low-noise thin-film TlBaCaCuO dc SQUIDs operated at 77 K

Abstract: We have made a series of single‐level dc superconducting quantum interference devices (SQUIDs) from 4‐μm‐thick TlBaCaCuO films with large grain sizes and operated them in liquid nitrogen. Although device characteristics could not be precisely controlled, some devices had white‐noise levels that approached thermally limited noise above ∼1000 Hz. In addition, devices with 5 and 80 pH loop inductances had 1/ f noise levels at 10 Hz of 2×10−29 and 5×10−29 J/Hz, respectively. The noise levels at these frequencies are comparable to commercial rf SQUIDs operating in liquid helium, but the hysteresis of the voltage‐flux characteristic of the high Tc SQUIDs remains large.

Wave propagation effects of broadband electrostatic noise in the magnetotail

Abstract: An analysis of the wave and particle data from ISEE 1 for 1978 yielded several examples of crossings between the lobe and the plasma sheet boundary layer (PSBL) which exhibited the signatures predicted by the theoretical analysis of the generation of broadband electrostatic noise (BEN) by ion beam instabilities. These signatures are a gradual rise in the upper frequency of BEN as the spacecraft approaches the plasma boundary layer, and a very rapid rise in the upper frequency near the crossing into the PSBL from the lobe. Several examples of crossings are presented that exhibit both signatures, as well as a case of crossings in which the gradual frequency rise signature is absent but the rapid rise is present. This case exhibits a BEN in the range expected for the low-frequency ion-ion two-stream and the high-frequency Buneman instability.

Broadband electrostatic noise due to field-aligned currents

Abstract: There are observations of broadband electrostatic noise in the plasma-sheet boundary layer that are associated with field-aligned currents (electron beams), which often have an upper cutoff frequency above the electron plasma frequency. In this paper linear theory and numerical simulations are used to study instabilities caused by an electron beam in a thermally mixed plasma. It is shown that two instabilities, the electron acoustic and electron-ion instabilities, can combine to form a broadband wave spectrum that rapidly destroys the electron beam.

Photon noise reduction by passive optical bistable systems.

Abstract: We show that when a coherent light beam is sent through a passive bistable device, the output beam may exhibit a substantial reduction of photon noise below the shot-noise level, within some frequency range of the noise spectrum. This effect is not limited to the case of a high-finesse cavity and is observable as soon as a bistability turning point is approached. Linear losses have the unexpected consequence of improving the noise-reduction factor at low frequencies.

Electron quantum interference and 1/f noise in bismuth.

Abstract: The $\frac{1}{f}$ resistance noise of thin Bi films of lateral dimensions 1-10 \ensuremath{\mu}m increases at low temperatures approximately as ${T}^{\ensuremath{-}1}$, and the noise at 1 K is larger than at room temperature The noise magnitude is reduced by a factor of 2 above a temperature-dependent characteristic magnetic field These phenomena demonstrate that below liquid-nitrogen temperature the $\frac{1}{f}$ noise in a weakly disordered metal arises from defect-mediated quantum interference of conduction electrons

Frequency-stabilized laser-diode-pumped Nd:YAG laser.

Abstract: We describe a frequency-stabilized diode-pumped Nd:YAG laser that is actively frequency stabilized relative to a reference Fabry-Perot cavity using the Pound-Drever technique. We describe the servo loop and the measurement of its noise and gain performance and demonstrate its ability to reduce the laser frequency noise close to the shotnoise limit of 12.5 mHz/ radicalHz. This corresponds to a linewidth of approximately 1 mHz, well below the Schawlow-Townes limit of 0.13 Hz that applies for a free-running laser.

Very high power-added efficiency and low-noise 0.15- mu m gate-length pseudomorphic HEMTs

Abstract: 0.15- mu m-gate-length double-heterojunction pseudomorphic high electron mobility transistors (HEMTs) for which excellent millimeter-wave power and noise performance were achieved simultaneously are reported. The 50- mu m-wide HEMTs yielded record maximum power-added efficiencies of 51, 41, and 23% at 35, 60, and 94 GHz, respectively. Maximum output powers of 139 mW at 60 GHz and 57 mW at 94 GHz were also measured for 150- mu m-gate-width devices. Finally, minimum noise figures as low as 0.55 and 1.8 dB were measured at 18 and 60 GHz respectively. This is the best power and noise performance yet reported for passivated transistors at millimeter-wave frequencies. >

Total noise and nonclassical states

Abstract: The total noise of a field state is a measure of the fluctuations of the field amplitude. It is a minimum for coherent states. As the behavior of a state becomes more nonclassical, its total noise increases. This is shown first for several specific types of nonclassical states, among them squeezed and sub-Poissonian states. These results are generalized by using nonclassical distance to measure how nonclassical a field state is. A lower bound for the total noise is derived that is an increasing function of nonclassical distance. From it one can conclude that highly nonclassical states have large amplitude fluctuations.

Asymptotic theory of propeller noise. II - Supersonic single-rotation propeller

Abstract: This paper gives analytical formulas for the far-field harmonic components of the acoustic radiation from a B-bladed supersonic single-rotation propeller, in the asymptotic limit B —» °o. The dominant source, for radiation in a given direction, is identified as located at the Mach radius along the blade span, the radius that approaches the observer at precisely sonic speed, once in each rotation. Favorable agreement is found between the asymptotic prediction and the results of full numerical evaluation of the radiation integrals. Singular surfaces in the field are identified from the asymptotic formulas, which are extended to include chordwise noncompactness effects. These show, among other things, that supersonic propeller noise is an algebraically decreasing function of tip Mach number, once chordwise noncompactness effects are taken into account, in contrast to the exponential increase with tip Mach number of subsonic propeller noise.

Influence of coercivity squareness on media noise in thin‐film recording media

Abstract: Signal and media noise measurements have been made for a wide variety of Co‐alloy longitudinal magnetic recording media A strong correlation between media noise and the coercivity squareness, S*, is observed at high transition density The optimum ratio of isolated pulse amplitude to media noise is found for S*≂075 This behavior arises from reduced ferromagnetic exchange coupling between neighboring grains of the film which influence both the coercivity squareness and also the uniformity of the domain boundary at the recorded transitions The low‐noise characteristics of sputtered γ‐Fe2O3 also appear to correlate with low values of coercivity squareness This work confirms that for systems in which media noise is a limiting factor, optimum performance may require considerably lower values of coercivity squareness than commonly used, determined by the relative contribution of media noise to the overall system noise

Effect of plasma noise spectrum on stimulated scattering in inhomogeneous plasma

Abstract: The flux of radiation emitted from an inhomogeneous plasma by stimulated Raman and Brillouin scattering is calculated with a source that includes both bremsstrahlung and longitudinal plasma wave noise sources. Significant enhancement of the flux above that found for a bremsstrahlung source alone are found for stimulated Brillouin scattering and for nonthermal but stable velocity distributions.

Radio frequency suppression for fuel pump

Abstract: An end cap (10) for a fuel pump provides suppression of radio frequency noise generated by the motor of the pump. The unitary end cap (10) includes radio frequency suppression circuitry (20, 28) disposed therewithin and is configured so as to be a direct replacement for conventionally utilized end caps.

Noise power spectral characteristics of an inductively coupled plasma mass spectrometer

Abstract: The noise power spectra of {sup 85}Rb{sup +} signal and {sup 93}Nb{sup +} signal from an inductively coupled plasma mass spectrometer were measured at the same plasma conditions as were those of Sr II emission from the plasma itself. Comparison of these spectra showed that discrete frequency noise in the emission at the mass spectrometer sampling orifice is nearly identical with that in the mass spectrometric signal and that white noise in the mass spectrometer signal was higher than that found in the emission signal. The dependence of noise frequencies on plasma operating conditions was generally the same for both measurements and was generally the same as that expected of emission from the plasma alone, i.e., when the plasma was not being sampled for mass spectrometry. However, discrete frequency noise in emission from the plasma alone differed substantially in frequency from that in the mass spectrometric signal. These results indicate that the plasma is the source of discrete frequency noise in the mass spectrometric signal and that the discrete noise frequencies can be affected by changes in plasma gas dynamics due to interaction between the plasma and the mass spectrometer sampling interface. The major source of signal instability in thismore » particular inductively coupled plasma mass spectrometer was found to be 1/f noise.« less

Role of pumping statistics in maser and laser dynamics: density-matrix approach

Abstract: We discuss in detail the influence that the statistical properties of the pump source have on maser and laser dynamics. We derive a general master equation for the radiation field that is valid for a wide range of different pump mechanisms. If the pump noise is eliminated, we find that the photon number noise in a micromaser and a laser can be significantly reduced below the shot-noise level. In contrast, the phase fluctuations for both maser and laser are unaffected by the noise contribution of the pump.

Transmission characteristics of a power line used for data communications at high frequencies

Abstract: The transmission characteristics of an installed power line used for data communication, and of a model of this actual line, were measured over the frequency range of 10 kHz-50 MHz. It was found that impedance characteristics were not greatly influenced by the working loads at high frequencies, but changed drastically at lower frequencies. For frequencies of less than 100 MHz, the transmission loss did not increase significantly with frequency. The effect of the length of the connections and variation in load impedance were both studied. It was found that for frequencies above 100 MHz, attenuation loss in the power line is divided into losses due to attenuation constant of the line and the loss occurring at wire connections located between the various wires in the wall sockets. The latter loss is proportional to the number of connections. When the transmission loss was measured by opening and closing the wire connections, the fluctuation in the loss was found to be smaller at frequencies above 1 MHz than at lower ones. The transmission loss at the higher frequency shows only fairly slight fluctuations to variations in working load on the power line. The intensity of the noise power spectrum shows a decrease of -40 B/decade. This degradation rate in the noise spectrum is greater than the rate of increase in transmission loss. The increasing transmission loss can be sufficiently compensated by amplification at the receiving end, but it is possible to keep the amplified noise below the level of disturbance. >

Apparataus and method for reducing radio frequency noise

Abstract: A device for filtering radio frequency noise emanating from one or more axially extending conductors. The device includes a conductive shell which is spaced axially from the conductor or conductors. A ferrite core is fitted intermediate, and in engagement with, both the conductor or conductors and the shell. The ferrite core, thereby, functions to provide substantially increased series impedance in the conductor or conductors and to concurrently provide a common dielectric for multiple distributed, bypass capacitors along the conductor or conductors.

Low magnetic flux noise observed in laser-deposited in situ films of YB2Cu3Oy and implications for high- Tc SQUIDs

Abstract: THE first device made from a thin film of a high-transition-temperature (high-Tc) superconductor was a d.c. SQUID (superconducting quantum interference device)1. Many applications of SQUIDs demand high sensitivity at low frequencies f( ≤1 Hz), and thus require films with low intrinsic '1/f magnetic flux noise2, 3. Although the level of 1/f noise in T2Ba2Ca2Cu3Ox SQUIDs4 is significantly lower than that in earlier YBa2Cu3O3, (YBCO) SQUIDs1, it remains higher than that in low-Tc devices. In post-annealed films of YBCO, the magnitude of the 1/f noise has been shown5 to decrease dramatically as the quality of the films is improved. Here we report measurements of flux noise in a film of YBCO grown in situ by pulsed laser deposition (but not patterned into a SQUID). The 1/f noise level was two orders of magnitude lower than in our best post-annealed film. Provided that it proves possible to fabricate suitable low-noise Josephson junctions, a d.c. SQUID made from a film of this quality and operated at liquid-nitrogen temperature (77 K) should approach the low-frequency performance currently achieved in commerically available Iow-Tc SQUIDs.

Electrochemical Noise Generation During Stress Corrosion Cracking of the High-Strength Aluminum AA 7075-T6 Alloy

Abstract: Electrochemical noise generation during stress corrosion cracking (SCC) of high-strength aluminum AA 7075-T6 alloy has been investigated in 3.5% NaCl solution under free corrosion potential. The electrochemical noise was observed as spontaneous potential fluctuations. The readings obtained were analyzed using the maximum entropy method. In the results, the power spectra densities were found to decrease with an increase in frequency. A low frequency (LF) noise was obtained with all the specimens tested and it characteristically indicated LF or “flicker” noise. The noise generated from the corroding specimen/bulk solution interface was found, generally, to increase with the degree of corrosion. The cracking of the specimen gave the highest noise amplitudes in most cases; the cracking is also indicated by the highest standard deviation peaks. The results obtained for this aluminum alloy further show the corrosion cracking behavior to be consistent with the film rupture/anodic dissolution mechanism.

Characteristics of Tip Vortex Cavitation Noise

Abstract: Tip vortex cavitation noise was experimentally investigated utilizing hydrofoils with an elliptic planform. The noise was monitored by an array of hydrophones. A variety of cavitating conditions were studied, including inception, fully developed vortex cavitation, and surface cavitation. An analysis of noise source distribution indicated that sound at cavitation inception is radiated from either just downstream of the vortex roll-up region or right at the tip of the hydrofoil where the vortex cavity intially develops

Volume and temperature dependence of the 1f noise parameter α in Si

Abstract: We present resistivity, Hall and noise measurements for p- and n-Si between 77 and 300 K. A 1f noise parameter α between 10-6 and 10-4 at 300 K and between 10-7 and 10-3 at 77 K is found in n- and p-Si. The α-value is independent of the effective volume. It is shown that 1f noise sources are located in the bulk. Hooge's empirical relation is confirmed in the case where an α-value of 10-6 is observed. The temperature dependence of the α-value is measured for n- and p-Si with doping concentrations between 1014 and 1018 cm-3. The magnitude of the α-value and its temperature dependence are related to the manufacturing process. Our measurements give no experimental support for the quantum 1f noise.

High-performance InP-based HEMT millimeter-wave low-noise amplifiers

Abstract: Quarter-micron InAlAs/InGaAs planar-doped HEMTs (high-electron-mobility transistors) lattice-matched to InP have exhibited state-of-the-art noise and gain performance at frequencies up to 94 GHz. Minimum noise figures of 0.5, 1.2, and 2.1 dB have been measured at 18, 60, and 94 GHz, respectively. Small signal gains as high as 15.4 and 12.0 dB have been obtained at 63 and 95 GHz, respectively. Using 0.25 mu m InP-based HEMTs, a V-band three-stage amplifier yields an average noise figure of 3.0 dB with a gain of 22.0 +or-0.2 dB from 60 to 65 GHz at W-band, a two-stage amplifier exhibits a noise figure of 4.5 dB with a gain of 10.2 dB at 90.4 GHz, and a three-stage amplifier shows a noise figure of 4.8 dB with a gain of 15.0 dB at 90.4 GHz. It is concluded that these results clearly show the great potential of InP-based HEMTs for high-performance millimeter-wave low-noise receiver applications. >

Photon noise reduction in lasers

Abstract: We consider the problem of reducing the contributions of pump and spontaneous-emission noise to the output noise of a laser field. We consider two models based on an atomic medium, one analytic, the other involving numerical simulation of a sequence of pump cycles. The predictions of both models are shown to agree. For regular pump excitation the intensity fluctuations of a laser well above threshold may be reduced to zero at the cavity resonance frequency if the ratio of the lifetimes of the upper and lower lasing levels is sufficiently large that spontaneous emission is suppressed. When the atomic lifetimes are comparable, spontaneous emission reduces the amount of noise reduction. For example, for equal atomic lifetimes regular pump excitation will result in a maximum noise reduction in the output field of one-half the shot-noise limit.