Showing papers on "Noise (radio) published in 1968"

Low frequency noise in MOS transistors—I Theory

Abstract: The low frequency noise voltage spectrum for a MOS transistor is calculated under the assumption that a time constant dispersion, giving a 1/ƒ- spectrum , is caused by tunneling of carriers at the silicon-silicon oxide interface to traps located inside the oxide. The magnitude of the noise from different trap distributions is calculated. The largest noise contribution is shown to come from traps near the quasi Fermi level of the current carriers in the channel. The influence of temperature and operating point on the noise is examined. The theoretically predicted noise magnitude agrees with the experimental results (presented in Part II). The theory presented describes qualitatively the shape of the low frequency noise spectrum.

Voltage Noise in Limulus Visual Cells

Abstract: Intracellular recordings from Limulus eccentric cells suggest that the generator potential arises from the superposition of numerous discrete fluctuations in membrane conductance. If this is so, a relation between frequency response to flickering light and noise characteristics under steady light may be predicted. This prediction is verified experimentally. If a discrete fluctuation model is assumed, the data indicate that increased light has two major effects: (i) the discrete events are strongly light-adapted to smaller size, and (ii) the time course of each event becomes briefer.

Interpretation of auroral hiss measured on OGO 2 and at Byrd Station in terms of incoherent Cerenkov Radiation

Abstract: A wideband noise known as auroral hiss is observed at very low and low frequencies at ground-based stations and on satellites at high magnetic latitudes. Several attempts have been made to explain this noise as incoherent Cerenkov radiation from energetic particles in the magnetosphere, but the conclusions were all negative, as the calculated power was several orders of magnitude below the observed power. The results of recent observations of auroral hiss and of the low-energy electrons with which this noise is strongly correlated suggest that unrealistic models were used in earlier calculations of the total power generated in the magnetosphere by an incoherent Cerenkov process. Therefore it is considered worthwhile to study the Cerenkov radiation again. This paper discusses a model for a region in space in which the auroral hiss is believed to be generated. It is shown that the total power generated in this region is comparable to the observed power, and it is concluded that auroral hiss may be generated by incoherent Cerenkov radiation from electrons with energies of the order of 1 kev.

Modes of Corona Discharges in Air

Abstract: Corona discharges in air exist under several distinctive forms, either pulsative or stable. The properties of different corona modes are analyzed as they appear in a cylindrical distorted field. Differences between dc and ac excitations are emphasized. Corona discharges may produce energy loss without detectable radio noise or high noise at low energy loss, depending upon their form of appearance. The different withstands of asymmetric gaps under different polarities also find their explanation in corona mechanism.

Low frequency noise in MOS transistors—II Experiments

Abstract: Noise measurements on a number of commercial MOS-transistors have been performed. The low frequency noise spectrum and the dependence of the noise on the temperature and the operating point of the transistor have been examined for frequencies between 30 Hz and 100 kHz and for temperatures between 77° and 373°K. It is found that the noise dependence on temperature is different for p -channel and n -channel MOST's. In a p -channel MOST the magnitude of the noise increases with temperature, while the magnitude of the noise decreases in a n -channel MOST. The experimentally found noise behaviour is compared with the theoretically predicted behaviour in Part I of this work.

Noise due to generation and recombination of carriers in p-n junction transition regions

Abstract: The theory for the current noise associated with carrier generation and recombination in a p-n junction transition region is presented. The noise model is derived directly from the SRH defect center model. In a reverse biased junction the noise from this mechanism varies from two-thirds to full shot noise, depending upon frequency, and in a forward biased junction the noise ranges from three-fourths to full shot noise, depending upon injection level. These results approximately agree with published experimental results, but the agreement is not conclusive, especially in forward biased junctions. The theory shows that the noise associated with transition region generation-recombination current is not particularly significant in bipolar transistors.

Analysis of irregular paths of lightning channels

Abstract: The tortuosities of a number of lightning stroke channels have been measured by a method similar to that used for determining the scattering of the track of a nuclear particle. The distribution of the direction changes of sections of the channels are found to be Gaussian, and they appear to be characteristic of a noise variation of the channel direction. For cloud-to-ground strokes the magnitude of the noise appears to be largely independent either of section length or total length of channel or of the particular locale of the stroke.

Relation of Pure Tone Thresholds to Background Noise Level in the Atlantic Cod (Gadus morhua)

Abstract: A conditioning procedure was used to determine auditory thresholds of cod at frequencies 35.3, 70.7, 141, 283, and 400 Hz at four levels of background noise. The noise was produced in octave bands centered at the test frequencies, and ranged in level from −14 db to +4 db (re 1 microbar). Up to 283 Hz thresholds varied directly with background noise, and signal-to-noise levels at thresholds remained approximately the same at all background noise levels for each frequency. Thresholds at 400 Hz were much higher and showed no relationship to noise. Mean signal-to-noise levels are calculated.

Recent Research on the Magnetospheric Plasmapause

Abstract: The plasmapause is a three-dimensional field aligned boundary that divides the closed field-line portion of the earth's magnetosphere into two physically distinct regions. The boundary is asymmetric, usually exhibiting a minimum geocentric range near dawn and a maximum near dusk under conditions of moderate but steady geomagnetic agitation (Kp = 2 − 4). The mean equatorial radius of the plasmapause is typically about 4RE, but it may vary from about 5.5RE during periods of extreme quiet to the range 2 − 3RE during great storms. The approximately corotating thermal plasma within the boundary exhibits two types of radial drift motions. These may be visualized as: (a) slow “breathing“ motions that follow the radial variations in a fixed, asymmetric boundary; (b) more rapid, transient (1 − 2 hr) motions that occur when the boundary position varies, as is the case during a polar substorm. The plasmapause involves an abrupt change in electron density, in tube electron content above 1000 km, and possibly in plasma bulk velocity and mean thermal energy. To the ionosphere, the protonosphere inside the plasmapause appears as a large reservoir of thermal protons, while the region outside appears virtually empty. At the plasmapause, equatorial values of electron density change by a factor of 10 to 100 within less than 0.15 earth radii. Satellite VLF experiments suggest that the change may be far more abrupt than this, possibly on a scale of a few kilometers. Studies of the distribution of electron density along the field line in the plasmapause have shown that earlier empirical models of the type N ∝ R−3 are not, in fact, compatible with recent satellite data on topside electron concentrations. Instead, the theoretically palatable diffusive equilibrium model has been found to be an appropriate description for most of the plasmasphere, while a more rapidly varying model appears necessary to describe the tenuous outer region. Details of the latter distribution may vary in important ways as a function of local time. Many wave propagation phenomena of conjugate interest are strongly affected by the presence of the plasmapause. For example, satellites moving poleward through the boundary observe a cutoff in whistlers propagating from the conjugate hemisphere; a decrease in the intensity of fixed-frequency VLF signals propagating upward, and dramatic changes in VLF noise such as the lower hybrid resonance (LHR) noise. In ground recordings made at Eights (L ∼ 4) and Byrd (L ∼ 7) in the austral winter, four distinct magnetospheric regions of propagation may be identified: (I) the outer part of the plasmasphere; (II) the outer “surface” of the plasmapause; (Ill) a belt-like region extending 1−2 RE outward from the near vicinity of the plasmapause; (IV) a region beginning ∼ 1.5 RE beyond the plasmapause and extending several earth radii outward. Each region exhibits special properties with respect to the occurrence and spectral behavior of VLF noise, and, in particular, noise triggered by whistler components. The occurrence of one-hop whistlers propagating in the outer regions III and IV is relatively low, and is particularly low near midnight and in region III at all times except in the midafternoon. Whistlers propagating in regions I, III, and IV exhibit an abrupt half-gyrofrequency upper cutoff, whereas whistlers propagating in region II do not. The ground data on the occurrence of whistlers and noise are broadly consistent with recent surveys of magnetospheric noise carried out on satellites.

Shot noise in silicon Schottky barrier diodes

Abstract: Noise measurements have been performed on forward and reverse-biased silicon Schottky barrier diodes. Measurements were performed in the frequency range of 100 Hz to 50 kHz. Apart from excess noise observed for some diodes in a portion of this frequency range, the noise for the diodes was found to be in excellent agreement with shot-noise theory. Some refinements of the shot-noise theory have been considered, but the difference between the refined and the simple theories was not resolvable in our measurements. A useful noise-measurement technique is described.

Initial results of the Pioneer 8 VLF Electric Field Experiment

Abstract: VLF electric field measurements from 1 AU heliocentric orbit, noting field oscillations in solar wind and large amplitude HF noise bursts

Some Observations and Analyses of Signal Generated Noise

Abstract: Summary The source and character of signal generated noise at Eskdalemuir array (EM) is demonstrated. Analysis of records elsewhere demonstrates the the site dependence of the phenomenon. Criteria for selecting sites for standard three component instrumentation are formulated on the basis of these observations. A plane P-wave front impinging on a plane free surface will be totally reflected as body waves, but if the surface is irregular part of the energy is converted to surface waves (Hudson, in press). We describe these surface waves as signal generated noise. They are impossible to identify on standard seismographs, and the magnitude of the effect escaped notice until large explosions were studied by means of large arrays of seismometers. Thirlaway (1966) discussed the experimental evidence for the hypothesis that between distances of 30-90" (the ' source window ') the P-wave initiated by an explosive source was recorded as a pulse which was undistorted during transmission. Carpenter (1966) showed that the pulse observed at these distances could be quantitatively derived from the known source function of explosions by assuming an Earth model in which the elastic parameters are a function only of the Earth's radius. This hypothesis is, apparently, not supported by the records at some standard stations. h these, the P-wave coda is unacceptably extended, and the coherence from station to station is low. We suggest that the presence of signal generated noise may be one reason for the inconsistency. Evidence for this came from a detailed analysis of explosion records from four U.K.A.E.A. type arrays. They are located at Eskdalemuir, Scotland; Yellowknife, Canada; Gauribidanur, India and at Tennant Creek, Australia. Each array consists two lines of vertical component seismometers at right angles, each line having instruments, with the exception of Gauribidanur, which at the time of this study, bad only half that number. The seismometers are spaced at intervals of 24 km except Eskdalemuir where the spacing is 896 metres. used to identify signal generated noise by measurements its origin, and by comparing the total delayed and summed ements in the array. In some cases particle orbits have been ee components. e reality of these P-generated surface waves, we searched for e examples in records of stations located in topographically rugged areas. (Records of explosion and deep focus earthquake signals at stations like La Paz, for example, display P-codas that are nearly always extended). Detailed analysis of

Mach bands in hearing.

Abstract: It is difficult to explain the extraordinary capacity of the ear in discriminating pitch without assuming the existence of laterally inhibitory neural nets fed by cochlear potentials. On such an assumption, we have sought to show edge effects in direct auditory masking analogous to Mach bands found in vision. Noise bands having theoretically infinite attenuation rates outside the passband were generated by computer from 56 sinusoids spaced randomly by frequency. Monaural pure‐tone‐masked audiograms were obtained for each of four subjects for each of two such noise bands (480–580 Hz and 960–1160 Hz) at sensation levels of 20, 30, 40, 50, and 60 dB. Edge effects, as measured by contours of threshold shift, were revealed for all subjects, at every loudness, and were similar for both noise bands. Sharpening was greater at the low frequency end of a band and grew nonlinearly with loudness, as did upward spread of masking. Sharpening was greater for an interrupted than for a continuous masked tone and may be maximal for relatively low interruption rates. The data are consistent with the existence of laterally inhibiting neural nets and are discussed in relation to their neural basis and to other phenomena such as the pitch of noise bands and the regions of increased sensitivity often found in abrupt hearing loss.

Injection-locked-oscillator FM receiver analysis

Abstract: The major components of an injection-locked-oscillator FM receiver are a linear mixer and a van der Pol type of negative resistance oscillator in a phase-locked configuration. In this paper the nonlinear differential equation describing the receiver output is solved and explicit expressions obtained for the output signal, noise, and controlling second and third order distortions. The input signal carrier is both amplitude and frequency modulated. Signal-to-distortion ratios have been computed and are presented for the case of a noise modulated FM input signal. The results indicate that excellent performance may be expected of such a receiver.

A comparison of photon counting and current measuring techniques in spectrophotometry of faint sources.

Abstract: The component of dark noise produced by Cerenkov pulses in photomultipliers due to cosmic ray mu mesons is discussed It is shown by integration of pulse height spectra that this source of noise can be the limiting factor in dc measuring spectrophotometry of faint astronomical sources Direct current methods of photometry are compared with photon counting, and the advantage of photon counting is demonstrated under various operating conditions

A Method for Analysis of Radio Noise on High-Voltage Transmission Lines

Abstract: A technique is described for approximating the effect of various factors on the radio noise level, due to conductor corona, on EHV transmission lines. The technique is essentially one of comparison. Relations are given in the Appendix for calculating the conductor gradients and results are presented in curve form. The application is intended only for comparison of radio noise generated by conductor corona on ac lines, with conductors ranging only from 0.3 to 1.3 inches radius (1.5 to 3.3 cm) and for the frequency range from about 0.2 to 1.6 MHz. If an existing line has been evaluated statistically the technique can be used to approximate the radio noise level of another line. A relation is also given for obtaining curves of 3-phase voltage to conductor radius for the same radio noise generation. Because of possible conductor surface differences and environmental differences, which cannot be too accurately evaluated, care is necessary in any final estimation of the average radio noise level.

Radio Noise Measurements on High Voltage Lines from 2.4 to 345 kV

Abstract: This paper is based on radio noise measurements made near overhead power lines operating at voltages from 2.4 kV to 345 kV inclusive. Some of the measurements made are discussed and analyzed and used in a radio noise prediction technique for determining the location of communication and electronic sites with respect to high voltage overhead power lines. This paper is necessarily only a summary of the work which has been reported and detailed test results, calculations, appendices, and complete bibliography have been omitted.

Evolution of a q‐switched laser pulse from noise

Abstract: Q‐switched laser emission is calculated using a fluctuating dipole model of spontaneous emission. The emission pattern for a broadband noise source is a complicated quasi‐periodic train of short pulses.

Microwave Emission from Indium Antimonide Stimulated by Acoustic Wave Amplification

Abstract: A small‐signal theory is presented for the emission of microwave noise, stimulated by acoustic wave amplification, from n‐type InSb at 77°K in a transverse magnetic field, for electric drift fields below 25 V/cm. The acoustic gain at frequencies different from ω0, the frequency of maximum acoustic gain, is greatest at drift fields exceeding that required for highest gain at ω0. At these fields the gain becomes an extremely broad band phenomenon with substantial amplification occurring at frequencies an order of magnitude greater than ω0. The presence of a transverse magnetic field has been shown to enhance the acoustic gain of a high mobility piezoelectric semiconductor, over a certain range of drift fields, by effectively reducing the rf mobility by the factor 1/[1+(μB)2]. Experimental results obtained from 700 MHz to 12 GHz have shown good agreement with the small‐signal theory, which takes into account the electric field distribution within the crystal. In particular, the threshold curves obtained at X‐band indicate that a constant value of acoustic gain is required for the production of the emission. Receivers of sensitivities around − 105 dBm were used and could detect emission only for magnetic fields exceeding 1kG, oriented close to the exactly transverse direction. Threshold fields as low as 1 V/cm were measured for the inch‐long crystals used, for which μ=500 000 and n=1014 cm−3 at 77°K. The conclusions drawn are that this ``low field'' emission is acoustic in origin, requires the presence of a transverse magnetic field and is a one‐carrier type phenomenon.

Effects of radiated aerodynamic noise on model boundary-layer transition in supersonic and hypersonic wind tunnels

Abstract: : Boundary-layer transition and aerodynamic noise measurements were made on sharp leading-edge two-dimensional models in supersonic wind tunnels (1 ft to 16 ft). These data showed, conclusively, a significant and continuous increase in transition Reynolds number and a significant decrease in radiated aerodynamic noise (generated by the tunnel wall turbulent boundary layer) with increasing tunnel size. Results obtained in the AEDC-VKF Tunnel A from a shroud configuration placed concentrically around a hollow cylinder transition model and a flat plate microphone model further demonstrated the strong adverse effects that radiated aerodynamic noise will have on transition. A correlation of transition Reynolds numbers based on transition data from nine wind tunnels (3 or = M or = 8) was developed. The correlation was dependent only on the tunnel wall, turbulent boundary layer, aerodynamic noise parameters (displacement thickness and skin friction), and the tunnel test section circumference.

Theory of the generation-recombination noise in mos transistors

Abstract: The theory of the generation-recombination noise of the insulated gate FET's is presented. This noise, similar to that in the junction-gate FET's, is generated from the charge fluctuations of the Shockley-Read-Hall centers in the depletion region between the conductive channel and the semiconductor substrate. The noise spectrum shows a flat plateau from some lower frequency, below which the 1 f surface noise dominates, and gives a f − n dependence with n between 1 and 2 beyond some corner cut-off frequency. The magnitude of this generation-recombination noise depends on the concentration of the SRH centers. The higher the concentration, the higher the noise generated and also the wider the frequency range of the flat plateau noise spectrum. For too low concentration, this noise may be overshadowed by the surface noise and disappear. The devices are gold doped purposely in order to give a better understanding about this noise mechanism.

A theory of 1f noise at semiconductor surfaces

Abstract: The 1 f noise at semiconductor surfaces can be explained by the model of slow surface states presented previously. According to this theory, the 1 f noise is produced by a modulation of surface recombination caused in the following manner. The chemisorbed molecules dissociate from their active centres and diffuse in the interface of the surface by Brownian motion until they are bonded again. During the removal of a chemisorbed molecule from an active centre, a chemical bond is interrupted and surface recombination is thus modulated.

Observations of noncollinear phase matching in optical parametric noise emission

Abstract: Measurements of optically excited parametric noise which demonstrate the importance of noncollinear phase matching are presented. The absolute magnitude of the emitted noise has also been measured and is found to be in excellent agreement with theory.

Noise and Equivalent Circuit of Double Injection

Abstract: Measurements of the high‐frequency noise of a silicon double‐injection diode result in 〈i^2〉 = α⋅4kT(1/r)Δf with α=1.04 and in agreement with the literature. A new interpretation demands Nyquist noise with α≡1 in these devices at high frequencies. This is in accord with an equivalent circuit derived for the double‐injection process. Speculations are made on the general validity of Nyquist noise in nonlinear devices at high frequencies. In addition, generation‐recombination noise is suggested as the prime source of the low‐frequency noise.

Helium Cooled Radio Frequency Preamplifier for Use in NMR

Abstract: A low temperature (4.2 K) radio frequency amplifier has been constructed using metal oxide semiconductor field effect transistors (MOSFET). Noise characteristics of the amplifier are compared to a model that includes two noise sources: shot noise and induced gate noise. The model is similar to models used to represent noise in vacuum tubes. Amplifier use for observation of low temperature nuclear magnetic resonance (NMR) signals is considered. Conditions for optimum signal‐to‐noise (S/N) are expressed in terms of the noise figure and are compared to those for room temperature vacuum tube amplifiers. Improvement of S/N by factors of 3 to 10 are readily obtainable. The S/N improvement with the low temperature MOSFET amplifier is demonstrated by observation of the NMR signal of 205Tl at 4.2 K at a frequency of 20 MHz.

Mode‐locked quieting of he–ne and argon lasers

Abstract: We report the suppression of low‐frequency noise in the He–Ne and argon lasers as a result of mode coupling by means of an internal phase modulator Suppression of off‐axis modes and 20 to 30 dB of low‐frequency AM noise suppression have been obtained in both FM and phase‐locked operation, with no loss of output power

City Noise and Its Effect Upon Airborne Antenna Noise Temperatures at UHF

Abstract: Results of an experimental program to determine the characteristics of city noise and its effect on airborne UHF antennas are presented. Coherent sources of energy from communications equipment, radar, navigational aids, etc. are not included in the analysis. Based upon the experimental data, a model of the industrial noise is presented in which an industrial area is considered as a uniformly distributed source of independent radiators. The magnitude of the power density distribution was computed to be 3×10-18 to 1×10-18 W/m2/Hz over the UHF band for all the East Coast cities measured, with the exception of New York City which was 5 to 6 dB higher. Relations have been derived and curves plotted to compute antenna noise temperature increase due to city noise, based upon the metropolitan area and its range from the aircraft.