Showing papers on "Radio wave published in 1979"

Jupiter plasma wave observations: an initial voyager 1 overview.

Abstract: The Voyager I plasma wave instrument detected low-frequency radio emissions, ion acoustic waves, and electron plasma oscillations for a period of months before encountering Jupiter's bow shock. In the outer magnetosphere, measurements of trapped radio waves were used to derive an electron density profile. Near and within the Io plasma torus the instrument detected high-frequency electrostatic waves, strong whistler mode turbulence, and discrete whistlers, apparently associated with lightning. Some strong emissions in the tail region and some impulsive signals have not yet been positively identified.

Numerical studies of current generation by radio‐frequency traveling waves

Abstract: By injecting radio‐frequency traveling waves into a tokamak, continuous toroidal electron currents may be generated. This process is studied by numerically solving the two‐dimensional Fokker–Planck equation with an added quasi‐linear term. The results are compared with the one‐dimensional analytic treatment of Fisch, which predicted a reduced plasma resistivity when high‐phase‐velocity waves are employed. It is shown that two‐dimensional velocity space effects, while retaining the predicted scaling, further reduce the ratio of power dissipated to current generated by about 40%. These effects enhance the attractiveness of steady‐state tokamak reactors utilizing this method of current generation.

Radio emissions from the aurora

Abstract: Observations are reported of radio waves in the range 2.5-6 MHz, emitted by the aurora. Two distinct types of emissions are seen: bursts, which are broad band emissions with a time scale of the order of .1 sec, and roars, which are narrow band (300 kHz) emissions with a time scale of ten minutes.

Remote sensing of ocean surface current and current shear by HF backscatter radar

Abstract: : The Doppler spectrum of radar return from the sea at HF contains two narrow lines displaced upward and downward from the carrier frequency, resulting from backscatter off ocean surface waves moving toward and away from the radar, respectively These Bragg lines indicate resonant backscatter which occurs for the ocean waves of length one-half the radio wavelength The phase velocity of these gravity waves consists of two components; the first is determined by the wavelength and the second by the current component in the direction of wave propagation averaged over depth with an exponential weighting function that has a characteristic scale proportional to the wavelength The Doppler shift of the radar carrier is determined by the wave phase velocity Its variation with carrier frequency is thus related to the vertical profile of the current component in the radar direction by a Laplace transform; therein lies the principle of radio measurement of ocean current and its vertical shear Radio backscatter experiments to verify the feasibility of such measurements were conducted using the radar operating at four frequencies covering the range from 3 to 30 MHz The depth-averaged radial current deduced from the centroid of the Doppler-shifted sea echo experiments at 68, 133, 217, and 298 MHz showed fluctuations on the order of 1 cm/sec superimposed on temporal trends that reached maximum values of about 40 cm/sec It is concluded that multifrequency backscatter ground-wave radar at HF constitutes a powerful technique for mapping current and its vertical profile in the top few meters of the ocean

Radio direction finding systems

Abstract: A radio direction finding system in which the angle of arrival of radio signals incident on a group of antenna elements is determined from the relative phase or phases of the radio signals incident upon two or more of said antenna elements. One of said elements is connected to a first radio receiver, while the other elements of the group are connected in turn to a second radio receiver, successive values of relative phase between signals received by the two receivers being utlized to derive a value for the angle of arrival of a radio signal relative to the antenna elements.

Observations of equatorial ionospheric bubbles by the radio propagation method

Abstract: Recent data collected near the magnetic equator depict one kind of ionospheric perturbation in the nighttime hours variously as bubbles or plumes. Theoretical studies show that the underside of the ionosphere is subjected to Rayleigh-Taylor instabilities which, when they are triggered, will cause a region of depleted ionization to rise as bubbles. When such regions are traversed by a probing radio wave, the associated Faraday effect is expected to show depletions of the electron content. This paper describes some experimental results obtained at Natal, Brazil (35.23°W, 5.85°S, dip −9.6°), by monitoring radio signals transmitted by the geostationary satellites Marisat 1 and SMS 1. Using ionization depletions as indications of bubbles, statistical studies of occurrence, size, and magnitude of perturbations are carried out. The most probable depletions for the propagation path under study have values in the range 1–4 × 1016 el/m², but depletions as large as 1.2 × 1017 el/m² have also been observed. The average durations for each observed bubble may vary from less than 2 to over 30 min with an average of 8 min. The experimental data further show that the scintillation rate may increase suddenly when these bubbles either form along or drift across the propagation path.

Depolarization of radio waves in jungle environment

Abstract: While propagating through a jungle environment radiowaves get substantially depolarized due to their scattering by the vegetation. Due to its conductivity, the foliage supports induced currents that tend to be randomly oriented and, therefore, they produce a depolarization of the overall field. Results of cross-polarization measurements in tropical moist deciduous and tropical wet evergreen forests in the VHF/UHF band are reported in this communication. It was found that vertically polarized waves suffer 5-15-dB higher depolarization than horizontally polarized waves. The crosspolarization discrimination is also found to be dependent on frequency as well as the separation distance between the transmitter and the receiver.

Radio wave generator for ultra-high frequencies

Abstract: An electron beam transmitted in the direction of an axis XX is subject to the action of a magnetic field, which is constant in time and directed along the axis XX, as well as to the electromagnetic field of resonant cavities placed along its path. These cavities are excited at the cyclotron frequency of the electrons in the field by a source coupled by an antenna. Output power, at a frequency which is near a multiple of the cyclotron frequency, is collected by a second antenna and coupled to a load. In one example, the cavities comprise a single guide, whose circular cross-section has been deformed so as to provide two extensions.

High Energy Astrophysics

Abstract: Information obtained by astronomers on the universe is no longer derived from observations using a tiny band of the electromagnetic spectrum. Radiation from radio waves to gamma–rays, cosmic ray particles and neutrinos are all being used, but some of the most rewarding investigations have been based on radio– and x–ray astronomies.

Generation of long‐delay echoes

Abstract: Long-delay echoes (LDE), defined as echoes received from a fraction of a second to several seconds after a radio signal is transmitted, have been observed off and on for about 50 years. A variety of explanations has been proposed in the past but none is completely satisfactory. The following models are presently proposed for LDE: (1) Radio waves of frequency less than about 4 MHz can become trapped in magnetic field-aligned ionization ducts with L values less than about 4. These waves after being trapped can propagate to the opposite hemisphere of the earth where they become reflected in the topside ionosphere. They can then return along the duct, leave it and propagate to the receiver. Delays of up to 0.4 s result and they probably account for most of the LDE at frequencies below 4 MHz with estimated delays of 1–2 s. (2) The signals from two separated transmitters T1 and T2, T2 transmitting a CW or quasi-CW signal, interact nonlinearly in the ionosphere or magnetosphere. If the wave vector and frequency of the forced oscillation at the difference frequency of the two signals satisfies the dispersion relation for electrostatic waves, such a wave would exist and begin to propagate. This wave could grow in amplitude due to wave-particle interaction. At a later time it could interact with the CW signal from T2 and if the wave vector and frequency of the forced oscillation at the difference frequency (frequency of T1) satisfy the dispersion relationship for electromagnetic waves, such a wave would exist and could propagate to T1, or some other receiving station tuned to the frequency of T1. Reasonable ionospheric and magnetospheric plasma parameters lead to delays of up to about 6 s with this model. (3) A large percentage of LDE have been reported with delays of tens of seconds. These delays could be explained if the model in (2) is applied to a magnetospheric ionization duct. Electrostatic waves could propagate for about 1000 km or more over the magnetic equator in such a duct and delays of about 40 s are possible. Dispersion for a finite frequency bandwidth would probably not be so large in cases (1) and (2) as to make voice unrecognizable. Dispersion in model (3) for delays greater than about 10 s would normally be too severe for voice modulation, but occasionally compensating effects might occur for which voice would be recognizable.

Optical information transmission system - comprising send and receive devices for difference pulse phase modulation

Abstract: Optical information transmission system consisting of a wave guide for radio waves in space or atmosphere or for optical fibre wave guides, has send and receive devices for the individual guides for difference pulse phase modulation (DPPM) which use similar multistep codes the sending devices being suitable for producing a wavelength of 1.06 mu. The beam sources for the atmospheric and space radiowave guides are solid laser cpds. of the following types: - Nd: YAG, ND: YALO, Nd: CdW. System permits cooperation between optical information transmission systems with various propagation media at low cost.

Morphognostic coils: a technique for transmitting several nearfield radio signals through the same space.

Abstract: ALL multielectrode neurological prostheses made in the past within this Unit have had many radio channels for conveying the stimulating signals. Either there has been one channel per electrode (BRINDLEY and LEWIN, 1968; FENXON et al., 1977) or, in visual prostheses (DONALDSON, 1973), a matrix coding has used (m-t-n) channels to excite (m • n) electrodes. In both cases, the large number of channels has made it necessary to have an array of small receiver coils in the implant, each inductively coupled to a corresponding transmitter coil of equal diameter outside the patient. Crosstalk between channels depends on:

Radio Wave Propagation in Structured Ionization for Satellite Applications

Abstract: : Methods are presented which permit the calculation of signal structure properties of satellite signals as they propagate through structured ionization. The primary parameters are the signal decorrelation time, the frequency selective bandwidth, the mean square log amplitude fluctuation, and the mean square arrival angle of the signal. The form of the generalized power spectrum, which characterizes the arriving signal as a function of frequency and delay, is specified in terms of the calculated signal structure parameters. Finally, methods are discussed to generate using Monte Carlo techniques signal structures from the generalized power spectrum.

On the apparent superluminal separation of radio source components

Abstract: It is shown that the differential bending of radio waves by an intervening galaxy, or by any other clumpy material en route, can give rise to an appartent superluminal separation of the components of a radio source. the merits and demerits of this idea are briefly discussed.

Environmental remote sensing. I. Methods based on scattering and diffraction of radio waves

Abstract: With recent advances in radio science and growing interest in environmental monitoring, the remote sensing of natural phenomena has become an important field of study. In this article remote sensing by the scattering and diffraction of radio waves is considered. This can provide information about the size, shape and distance of remote objects. Principles of radiowave surveillance are given and a target adaptive radar system under development is described

A Coherent Nonlinear Theory of Auroral Kilometric Radiation.

Abstract: : A theory of auroral kilometric radiation due to the nonlinear interaction between negative energy electromagnetic waves and coherent EIC waves is developed. The theory predicts that such radiation produced must have X-mode polarization and must have a frequency just slightly below the Doppler-shifted beam cyclotron frequencies. The basic requirement for free space accessibility is the presence of high-energy beams and a density cavity of the type observed by Isis I measurements. It is predicted that a harmonic band structure in the kilometric radiation may be observable.

Broad-band flux density variations of the extragalactic radio source 1611+343.

Abstract: A flux density outburst at low radio frequencies (less than about 1 GHz) has been observed in the extragalactic radio source 1611+343 (= DA 406). Observations in the period from June 1976 to September 1978 were made with several telescopes covering the frequency range from 0.325 to 15.5 GHz. The outburst appears to have been simultaneous at all observed frequencies and had a steep spectrum above 0.400 GHz. Some physical implications of these observations are discussed.

Fm-cw radar apparatus for automobile

Abstract: PURPOSE:To extract the necessary information alone by subdividing the beat frequency band corresponding to the detection distance covered by the radar so as to disintegrate the mixed beat frequency from several objects and the beat frequency is received independently separated from each other corresponding to the respective distance range. CONSTITUTION:Continuous radio waves modulated in the frequency are emitted from the antenna 5, while the radio waves reflected from the objects are received by the antenna 5 whereby a beat frequency of the received and transmitted waves is generated with the mixer 6. The beat frequency is transmitted to the channel divider 10 and the beat frequency signal analyzed in the frequency is transmitted to the filter 11 and the detector 12. The output of the filter gate 11 is sent to the frequency counter 8 to calculate the distance from the specified object and the relative speed with the signal processing apparatus 9'.

Fine structure of the S-component spectrum of the solar radio emission in the frequency range 5.0–7.0 GHz

Abstract: Fine structure observations of the frequency spectrum of the S-component in the solar radio emission are described Measurements were carried out in August 1976 and August 1977 using a 22 m parabolic antenna and a radiospectrograph operating over the frequency range 50 to 70 GHz, with the resolution 60 MHz Measurement techniques are described Fine structures (150–800 MHz) as great as 20% of the local source radiation level were observed in radio emission spectra of a number of these sources The spectrum structures observed were changed in the process of active region development

Numerical simulation of type III solar radio bursts caused by high-density electron beam

Abstract: Numerical simulation for the type III solar radio bursts in meter wavelengths was made with the electron beam of a high number density enough to emit fundamental radio waves comparable in intensity with the second harmonic. This requirement is fulfilled if the optical thickness τ 1 for the negative absorption (amplification) becomes -23 to -25. Since τ 1 is roughly proportional to the time-integral of the electron flux of the beam, the intensity of the fundamental waves depends strongly on the parameters which determine the electron flux. Therefore, it is most unlikely that the harmonic pairs of type III bursts of the first and the second harmonics occur frequently with comparable intensities in a wide frequency range, say 200 MHz to 20 MHz, if we take the working hypothesis that the fundamental waves are caused by the scattering of electron plasma waves by thermal ions and amplified during the propagation along the beam. However, we cannot rule out the possibility that single type III bursts with short durations or group of such bursts are the fundamental waves emitted by the above mechanism, but only if the observed large size of the radio source can be attributed to the radio scattering alone.

Formation of radio signal spectral lines in propagation through circumsolar plasma

Abstract: The available experimental data on spectral line broadening for monochromatic radio waves propagating in the circumsolar plasma indicate the presence within the spatial spectrum of plasma inhomogeneities of an internal turbulence scale, the effect of which manifests itself in the finite values of the moments of the energy density distribution over frequency and in normatization of the spectral line form in the strong signal scattering regime. Theoretical analysis of line broadening produced by moving inhomogeneities in the solar corona has established a relationship between the second and fourth moments of the spectrum and the turbulence characteristics, permitting determination of the radial profile of the internal inhomogeneity scale for a known velocity of motion. According to Venera 10 data, the internal turbulence scale of the circumsolar plasma is of the order of magnitude of several km at distances of 5–10 solar radii and increases sharply with radial distanee. The change in the value of the internal turbulence scale with distance is of the same type as the dependence of ionic gyroradius on distance to the sun. Analysis of spectral broadening of radio signals is an effective means of studying such characteristics of inhomogeneities in the circumsolar plasma as the form of the spatial spectrum, the intensity of inhomogeneities, their rate of motion, the internal turbulence scale, and the radial profiles of these quantities. Simultaneously, the peculiarities discovered in the behavior of the spatial spectrum of the inhomogeneities require the completion of a stricter analysis of line broadening with consideration of radial variation of both the internal and external turbulence scales, a process which may explain other peculiarities of the spectral broadening of radio signals in the moderate and intense scattering regimes.

Low frequency turbulence in the solar corona and fundamental radiation of type III solar radio burst

Abstract: On the basis of the previous numerical simulations, a new mechanism for the emission of the fundamental radio waves of solar radio type III bursts is presented. This hypothesis is to attribute the fundamental radio emission to the coalescence of the plasma waves with the low frequency turbulence, whistler or ion acoustic waves, pre-existing on the way of the electron beam which excite the plasma waves.

On small-scale turbulence in cometary tails.

Abstract: Fluctuations in the intensity of radio waves during occultation by cometary tails indicate the existence of small-scale turbulence with wavenumber kapprox. =1.25 x 10/sup -8/ cm/sup -1/ in the comet's tail. We suggest that the turbulence may be attributed to the hydromagnetic Kelvin-Helmholtz instability due to a strong velocity shear. The excited waves are, in general, a mixture of Alfven waves and fast magnetosonic waves. We find that the instability may generate a turbulence spectrum with a peak at kapprox. =1.25 x 10/sup -8/ cm/sup -1/, which is consistent with observation. It is shown that the observed turbulence may scatter solar-wind protons, transfer momentum from the solar wind to the plasma in the comet's tail, and give an acceleration of aapprox. =30--300 cm s/sup -2/ for the cometary ions.