Showing papers on "Radio wave published in 1989"

The heating of the high lattitude ionosphere by high power radio waves

Abstract: The high power radio facility, built jointly by the Max-Planck-Institut fur Aeronomie, Lindau and the University of Tromso, at Tromso in Northern Norway, has been operational since 1980. Since that time an extremely wide range of ionospheric modification phenomena, induced by the powerful radio beam or pump, has been studied by a multitude of diagnostic techniques. This review is concerned, in particular, with the role played by the anomalous absorption of the high power wave. Anomalous absorption arises when the high power electromagnetic waves excite thermal parametric plasma instabilities in the diffusion dominated ionospheric F-region. This leads to the growth of plasma density irregularities, which are highly elongated along the geomagnetic field and which very efficiently couple electromagnetic and electrostatic plasma waves. The conversion of the electromagnetic modifying wave to rapidly damped electrostatic waves constitutes the anomalous absorption process which gives rise to strong plasma heating and the self extinction of the pump. After briefly reviewing some relevant results from earlier experiments carried out in the USA, a number of modification experiments undertaken at Tromso, using both HF diagnostics and the European Incoherent Scatter radar (EISCAT), are described in detail. These experiments were designed to investigate anomalous absorption processes, large scale plasma heating, pump self action and cross-modulation effects. The relevant theories required to interpret these experimental results are also presented. In particular, the relative importance of collisional and anomalous heating at the high latitude site is examined. The importance of the Tromso high power facility to aeronomical studies is also briefly discussed.

Airglow enhancements associated with plasma cavities formed during Ionospheric Heating Experiments

Abstract: Optical measurements made at the Arecibo Observatory during the 1987 heating campaign showed large temporal and spatial variations in 630.0-nm airglow enhancements during times of continuous power transmissions of high-power radio waves. Photometric data displayed fluctuations of 60 R or more in the red-line (630.0 nm) emission from atomic oxygen. These fluctuations were associated with heater-induced cavities which drifted and evolved in the modified ionosphere. Data from the Arecibo incoherent scatter radar were used in conjunction with airglow images to provide a physical interpretation of the modification process. Electrons were accelerated by large amplitude Langmuir waves excited by parametric decay instabilities occurring near the wave reflection points inside the density cavities. Inelastic collisions with oxygen atoms produced excited states which yielded enhanced 630.0-nm and 557.7-nm emissions. A numerical model has been used to relate the enhanced airglow intensities to the energy spectrum of the accelerated electrons. The measured airglow could have been produced by an isotropic source at 340 km altitude that accelerated 0.01% of the ambient electrons into a suprathermal Maxwellian distribution with a temperature of 2.05 eV. Experimental and theoretical studies suggest that airglow clouds were directly coupled to plasma density cavities because (1) these cavities trapped themore » HF radio beam and (2) electrons accelerated out into regions of reduced plasma concentration were less effectively thermalized and, consequently, were more effective for collisional excitation of neutral species.« less

A technique for separating the galactic thermal radio emission from the non-thermal component by means of the associated infrared emission

Abstract: The correlation between the IRAS 60-micron band emission from the galactic disk and radio continuum emissions measured at 11 and 6 cm is discussed. The contribution of the radio continuum at these frequencies from H II is determined. The 60-micron band is used to separate the thermal component of the radio continuum emission from the synchrotron component, and this method is applied to the identification of new SNR candidates.

On the frequency dependence of ELF/VLF waves produced by modulated ionospheric heating

Abstract: We present results of the local field strength and, for the first time, apparent source height as a function of frequency from 200 to 6600 Hz of ELF/VLF waves produced in the auroral D region through modulated RF heating using the ionospheric heating facility near Tromso, Norway. These data show, besides the normal amplitude peaks near 2, 4, and 6 kHz, the occasional presence of peaks at intermediate frequencies, especially in the right-hand circularly polarized mode. A comprehensive model has been developed to explain the data, using a full wave solution of the ELF/VLF waves produced by the self-consistently calculated source currents, and correcting for the effects of finite source current extent and multiple Earth-ionosphere reflections. The model can reproduce the amplitudes and source heights for typical sweeps. The irregular peaks occasionally seen can also be reproduced by invoking interference between the downcoming wave and a partially reflected whistler mode wave from sharp electron density gradients in the ionosphere such as sporadic E layers. The model seems to work well above about 600 Hz, but below that it increasingly underestimates the measured amplitudes.

Multipath propagation measurements on manufacturing floors at 910 MHz

Abstract: Measurements of propagation and time delay spread at 910 MHz on several different manufacturing floors are presented. The statistics of RMS multipath delay spread and the values of the distance/power law gradient are computed and compared for these experimental sites.

A theory of electron cyclotron waves generated along auroral field lines observed by ground facilities

Abstract: A generation mechanism for radio waves in the frequency range 150 - 700 kHz observed by ground facilities is suggested in terms of an electromagnetic electron cyclotron instability driven by auroral electrons. The excited waves can propagate downward along the ambient magnetic field lines and are thus observable with ground facilities. The trapped auroral electrons are supposed to play an important role in the generation process, because they give rise to a thermal anisotropy which consequently leads to the instability. The present work is a natural extension of the theory proposed earlier by Wu et al. (1983) which was discussed in a different context but may be used to explain the observed waves originated at low altitudes. This paper presents a possible wave generation mechanism valid in the entire auroral field-line region of interest.

Communication system for data transmission and reception using radio wave and optical transmission of message signals

Abstract: A radio communication system such as a radio paging system or the like, for data transmission and reception, which is comprised of a transmission device and a reception device. The transmission device comprises a modulation circuit, a radio signal transmitter for transmitting message signals, through air, after converting them into radio signals, and an optical signal radiator for radiating the message signals, through air, after converting them into optical signals. The reception device is capable of receiving both the radio and optical signals, combining these signals in order to reproduce the message signals, and demodulating the message signals from the combined signals.

Radiation field characteristic measuring apparatus

Abstract: A radiation field characteristic measuring apparatus comprises a rotating device for rotating a tested object through the total solid angle thereof, and a device for receiving electromagnetic waves radiated from the object, thereby measuring electromagnetic field characteristics of the object with respect to the total solid angle. According to the present invention, almost all the components of the rotating device are formed of a nonmetallic material, and spaces to allow the passage of the electromagnetic waves are formed in the components of the rotating device. Thus, reflection and scattering of the electromagnetic waves are suppressed, so that the radiation field characteristics of the tested object, with respect to the total solid angle thereof, can be obtained with high accuracy. Also, the effective radiated power is measured with use of the arrival probability density function of radio waves as a weighting function. By doing this, the evaluation index of an antenna best suited for the actual radio conditions can be obtained.

Jovian type III radio bursts

Abstract: Radio bursts have been observed in the Voyager plasma wave data from Jupiter that bear a striking resemblance to solar type III radio bursts. The emissions lie in the frequency range near 10 kHz, have durations of a minute or so, and occur in a set of periodically spaced bursts. The spacing between primary bursts is typically 15 min, but the bursts may have additional components which recur on time scales of about 3 min. The similarity with solar type III radio bursts suggests a source mechanism involving the movement of energetic electrons through a density gradient in the plasma surrounding Jupiter. The periodicity of bursts suggests Io may be involved in the generation of waves, since the timing is similar to the Alfven wave travel time from one hemisphere to the other through the Io torus.

Heater-induced cavities as optical tracers of plasma drifts

Abstract: A new technique is used to measure F region plasma drifts at night. The technique involves observing the motion of density cavities generated by high-power radio waves in the ionosphere. The airglow signature of the cavities is recorded and analyzed with a ground-based, low-light-level imaging system. The heater-induced cavity optical tracer method is capable of providing velocity information with an error less than 1 m/s and a time resolution better than 60 s.

Radio wavelength observations of the L134N molecular core

Abstract: A detailed study of the L134N dense molecular core through radio astronomical observations of spectral lines at millimeter and centimeter wavelengths is presented. The prototypical dark cloud was chosen for the following reasons: it is a nearby cloud at a distance of 160 pc, and thus radio observations have high spatial resolution; it resides out of the galactic disk, providing unobscured viewing along the line of sight; and it is known to be a rich source of molecular emission. The absence af any embedded infrared sources leads to the assumption that L134N is either in a stage of evolution prior to star formation or is a cloud in which internal support will prohibit a star from forming. A spectral line survey of 24 molecular transitions at up to seven positions in the L134N core, and observations of molecular emission from C18O, CSm, H13CO+, SO, NH3, and C3H2 are reviewed. Results indicate different spatial distributions for each species which may be attributed to variations in the excitation conditions for each transition or chemical abundance variations within the cloud core. Observational techniques and results are presented.

Transmission power control method and device for information transmission by radio waves

Abstract: In the process of obtaining an adjustment criterion from the received signal and transmission to the remote station for the purposes of adjusting the latter's transmission power, co-channel interference is not recorded. This, however, plays an important role, particularly in the case of cellular mobile radio networks, since it determines the re-usability of frequencies in other radio cells and thereby the important characteristic of frequency economy. To avoid power excesses and to record external interference, the transmission power control method according to the invention is designed so that a combination of reception level evaluation and quality evaluation via the phase jitter determined from the incoming signal is used as an adjustment criterion for controlling the transmission power of the remote station.

Impulsive solar wind‐driven emission from Uranus

Abstract: Several days prior to the Voyager spacecraft encounter with Uranus, the plasma wave and radio astronomy receivers detected extraordinarily narrowband bursty signals, the first indication of any radio emission from the planet. The characteristics of these signals were so unusual that their identity as a natural planetary emission was questioned at first. Subsequent analysis has shown, however, that the n bursts are modulated at the 17.24-hour Uranus rotation period and are, therefore, planetary in origin. It is shown, in addition, that the typical bandwidth and time scale for the bursts are about 5 kHz and 250 ms, respectively. The phase of the rotation modulation suggests a probable source for these events in the vicinity of the north (weak) magnetic pole. The waves are right-hand polarized and are therefore emitted in the extraordinary magnetoionic mode if the emission in fact originates above the north magnetic pole.

The magnetic resonance myth of radio waves

Abstract: An inaccurate description of magnetic resonance is current among those employing it in medicine and biology. The technique is purported to use radio waves for both stimulation of the sample and for reception of the ensuing signal. Arguments are presented which counter this myth, and using only magnetic fields, an accurate classical description of transmission and reception is given.

Radio wave absorber

Abstract: PURPOSE:To improve a radio wave failure of a television, a radio receiver or a radar due to a soundproof wall mounted on the side of a road or a railway line, the outer wall of a building or other construction wall by employing an absorber made of cement composition containing radio wave absorbing substance. CONSTITUTION:As a radio wave absorbing substance, conductive materials, such as aluminum, nickel, carbon or semiconductor silicon single crystal, etc., high dielectric materials, such as alumina or barium titanate, or a magnetic material, such as ferrite. After these materials are formed in powder or fibrous state, one or more radio wave absorbing substances are mixed with cement composition. This absorber is employed as a soundproof wall or a construction wall. Thus, radio wave failure, such as a television, a radio receiver and a radar, etc., can be removed, and radio wave absorbing effect is not reduced over a long period with high durability.

Solar wind interaction with the ionosphere of Venus inferred from radio scintillation measurements

Abstract: The observation of S-band (2.3 GHz) radio scintillations in the ionosphere of Venus by the Pioneer Venus Orbiter is reported. In situ plasma measurements and propagation calculations show that the scintillations are caused by electron density irregularities in the topside ionosphere of Venus below the ionopause. It is suggested that these topside plasma irregularities are associated with the penetration of large-scale magnetic fields in the ionosphere. It is found that the disturbed plasma and the scintillations are a manifestation of high-dynamic solar wind interaction with the ionosphere.

Device for auto-adaptive direction and polarization filtering of radio waves received on a network of aerials coupled to a receiver

Abstract: The apparatus is an antenna system for autoadaptive direction and polarization filtering of radio waves traveling through an HF ionospheric channel and generating an output signal for coupling to a receiver. First and second crossed loop antenna elements having first and second output terminals, respectively, are disposed around a common axis. A filar antenna element has a longitudinal axis along the common axis. The filar antenna element has a first end terminal situated at the same phase center as the first and second output terminals. A multiplier circuit multiplies each value output from the first and second output terminals and the first end terminal by a corresponding complex weighting coefficient. The complex weighting coefficients are adjustable as a function of variations of polarization of a radio wave, and azimuthal and site arrival directions of the radio wave. A summation circuit sums the output products from the multiplier circuit to form a resultant signal which can be exploited by a receiver with a maximum useful signal/noise ratio.

Millimeter–Wave Propagation in the Mesosphere

Abstract: At heights between 30 and 100 km above Earth, the oxygen absorption lines near 60 GHz together with the geomagnetic field cause the atmosphere to become an anisotropic medium This report discusses why this is so and how to compute the consequent effects It describes the computer program ZEEMAN, which allows the user to display in either graphical or tabular form many aspects of how radio waves propagate through this medium

The spectrum of coronal sources at millimetre and centimetre waves

Abstract: Recently recognized solar millimetre-wave off-limb sources are interpreted as a special phenomenon of long-duration post- and inter-flare emission at coronal altitudes. We present, for the first time, information about the brightness and polarization spectrum in the centimetre range for one such event of September 22, 1980 by means of RATAN-600 observations. The brightness temperatures observed favour the interpretation of the bulk of the emission by thermal optically thin bremsstrahlung. The degree of polarization measured (p ≈ 0.1–0.2 in the range 7.5–15 GHz) implies quite strong magnetic fields of about ≥300 ± 100 G at a height z > 3 × l04km above the photosphere and indicates a possible contribution of gyromagnetic radiation and/or optically thick bremsstrahlung at longer wavelengths.