Showing papers on "Radio wave published in 1992"

The Unified Radio and Plasma wave investigation

Abstract: The scientific objectives of the Ulysses Unified Radio and Plasma wave (URAP) experiment are twofold: (1) the determination of the direction, angular size, and polarization of radio sources for remote sensing of the heliosphere and the Jovian magnetosphere and (2) the detailed study of local wave phenomena, which determine the transport coefficients of the ambient plasma. A brief discussion of the scientific goals of the experiment is followed by a comprehensive description of the instrument. The URAP sensors consist of a 72.5 m electric field antenna in the spin plane, a 7.5-m electric field monopole along the spin axis of a pair of orthogonal search coil magnetic antennas. The various receivers, designed to encompass specific needs of the investigation, cover the frequency range from dc to 1 MHz. A relaxation sounder provides very accurate electron density measurements. Radio and plasma wave observations are shown to demonstrate the capabilities and limitations of the URAP instruments: radio observations include solar bursts, auroral kilometric radiation, and Jovian bursts; plasma waves include Langmuir waves, ion acousticlike noise, and whistlers.

Autoregressive modeling of wide-band indoor radio propagation

Abstract: Based on frequency domain measurements in the 0.9-1.1-GHz band, an autoregressive model for the frequency response of the indoor radio channel is introduced. It is shown that a second-order process is sufficient to represent the important statistical characteristics of the channel both in the frequency domain and the time domain where each pole identifies the arrival of a cluster of paths. A comparison is made between the statistical characteristics of the empirical data and of the channel responses regenerated from the second-order AR processes. Four methods to regenerate the indoor radio channel responses from a second-order AR model are proposed. The accuracy of the methods is examined by comparing the cumulative distribution functions of the RMS delay spread and the 3-dB width of the frequency correlation function with that of the measurements performed in global, local, and mixed indoor radio propagation experiments. >

Ulysses Radio and Plasma Wave Observations in the Jupiter Environment

Abstract: The Unified Radio and Plasma Wave (URAP) experiment has produced new observations of the Jupiter environment, owing to the unique capabilities of the instrument and the traversal of high Jovian latitudes. Broad-band continuum radio emission from Jupiter and in situ plasma waves have proved valuable in delineating the magnetospheric boundaries. Simultaneous measurements of electric and magnetic wave fields have yielded new evidence of whistler-mode radiation within the magnetosphere. Observations of aurorallike hiss provided evidence of a Jovian cusp. The source direction and polarization capabilities of URAP have demonstrated that the outer region of the lo plasma torus supported at least five separate radio sources that reoccurred during successive rotations with a measurable corotation lag. Thermal noise measurements of the lo torus densities yielded values in the densest portion that are similar to models suggested on the basis of Voyager observations of 13 years ago. The URAP measurements also suggest complex beaming and polarization characteristics of Jovian radio components. In addition, a new class of kilometer-wavelength striated Jovian bursts has been observed.

Wideband indoor radio propagation measurements at 58 GHz

Abstract: Wideband measurements of indoor radio channels operating in a 2 GHz frequency band centred around 58 GHz were performed using a frequency step sounding technique. The results are presented of cell coverage and RMS delay spreas under both line-of-sight (LOS) and obstructed (OBS) situations.

Precision measurements of pulsar dispersion

Abstract: Timing observations of eight pulsars over a frequency range from 25 MHz to 5 GHz were conducted to investigate possible departures from the v -2 dispersion law that applies to propagation of radio waves through the tenuous interstellar plasma. Apparent deviations from a cold plasma law were found at high frequencies (2-5 GHz) for two pulsars: PSR 0525+21 and PSR 1237+25. No such departures were detected in pulse arrival times at meter or decameter wavelengths, within measurement uncertainties of ∼1 ms

Radio controlled spraying device

Abstract: A power spraying device is disclosed for applying a liquid to a surface. The electronic control of the device is contained within the nozzle of the sprayer and emits radio wave signals to initiate operation of the device. The radio signals are detected by a receiver which converts the radio signals into control signals for a main pumping unit. The radio waves may also control the introduction of various chemicals into the liquid solution by the main pumping unit. The nozzle also contains a deadman's switch for turning off the flow of liquid in case the unit is accidentally dropped.

The application of GTD and ray launching techniques to channel modelling for cordless radio systems

Abstract: Propagation characteristics play a fundamental role in the design and implementation of radio systems. The application of broadband digital data services within the cordless environment requires close consideration of the dispersive nature of radio channels. A prediction algorithm is presented such that the propagation characteristics can be estimated for small-cell high-data-rate systems. Through the use of geometric optics and geometric theory of diffraction (GTD) the algorithm performs ray launching techniques in order to evaluate reflected, transmitted, and diffracted rays from a simplified description of a given environment. Both modeled and measured results are presented, demonstrating the model's ability to predict typical RMS delay spread values. >

Narrow cyclotron harmonic absorption resonances of stimulated electromagnetic emission in the ionosphere.

Abstract: We present measurements of stimulated electromagnetic emission (SEE) excited in the ionosphere by a powerful high-frequency ordinary mode radio wave vertically injected from a ground-based transmitter, at frequencies f 0 near high harmonics of the ionospheric electron cyclotron frequency f c . A prominent lower-sideband SEE feature was found to be absent in an extremely narrow f 0 range of Δf 0 /f 0 ≃2×10 −5 . This absorption resonance width allows an estimate of f c with an accuracy of a few tens of Hz, corresponding to a magnetic field magnitude accuracy of about 1 nT

Radio environment measuring system

Abstract: A radio environment measuring system for measuring a propagation state of radio waves includes: a fixed radio apparatus provided in a base station; a mobile radio apparatus operatively connected to the fixed radio apparatus through the radio waves; the mobile radio apparatus having a repeater unit for receiving a transmission signal from the fixed radio apparatus and sending a returned signal to the fixed radio apparatus; and the fixed radio apparatus having a transmission/reception unit for sending the transmission signal to the mobile radio apparatus and receiving the returned signal from the mobile radio apparatus, and a measuring unit for measuring the propagation state of the radio waves, for example, a propagation distance, direction and reception intensity of the radio waves between the fixed radio apparatus and the mobile radio apparatus based on the transmission signal and the returned signal.

Investigation of strong Langmuir turbulence in ionospheric modification

Abstract: Recent results in the search for strong Langmuir turbulence effects during ionospheric modification experiments performed at the Arecibo Observatory are presented. Indirect evidence of Langmuir wave collapse is obtained through the observation of theoretically predicted “caviton-type” enhanced plasma waves spectra using the 430 MHz incoherent radar at Arecibo. A typical spectrum consists of a “free-mode” peak with a frequency that is significantly higher than the heater frequency, and a broad “caviton continuum” with frequencies below the heater frequency. Free modes are freely propagating Langmuir waves radiated by collapsing cavitons during collapse. The generation and dynamics of these “free modes” will be discussed. Asymmetries between the frequency shifts and strengths of the upshifted and downshifted free-mode lines and their dependence on the time delay following the onset of heating are explained in terms of the radiation of free Langmuir modes by cavitons and the subsequent propagation of free modes down or up the density gradient. Experimental results are compared with theoretical predictions. Results on the transition of “caviton-type” plasma line spectra to the commonly observed “decay-type” spectra will also be presented.

Galileo Radio Science Investigations

Abstract: The radio science investigations planned for Galileo’s 6-year flight to and 2-year orbit of Jupiter use as their instrument the dual-frequency radio system on the spacecraft operating in conjunction with various US and German tracking stations on Earth. The planned radio propagation experiments are based on measurements of absolute and differential propagation time delay, differential phase delay, Doppler shift, signal strength, and polarization. These measurements will be used to study: the atmospheric and ionospheric structure, constituents, and dynamics of Jupiter; the magnetic field of Jupiter; the diameter of Io, its ionospheric structure, and the distribution of plasma in the Io torus; the diameters of the other Galilean satellites, certain properties of their surfaces, and possibly their atmospheres and ionospheres; and the plasma dynamics and magnetic field of the solar corona. The spacecraft system used for these investigations is based on Voyager heritage but with several important additions and modifications that provide linear rather than circular polarization on the S-band downlink signal, the capability to receive X-band uplink signals, and a differential downlink ranging mode. Collaboration between the investigators and the spacecraft communications engineers has resulted in the first highly-stable, dual-frequency, spacecraft radio system suitable for simultaneous measurements of all the parameters normally attributed to radio waves.

An Overview of Electromagnetic Safety Considerations Associated with Magnetic Resonance Imaging

Abstract: The introduction of magnetic resonance imaging into the clinical patient care arena has enabled a marked expansion of the diagnostic capabilities of the radiologist. The field has continued to grow each year with significant improvements and advances in such areas as transmitter/receiver coil design, pulse sequence design and optimization, and technical advances in other MR-related hardware devices. This rapid growth, however, has not been accompanied by an equivalent dissemination and understanding of the potential, or real, safety considerations that might be associated with this modality. Although most who work in this environment are aware of the potential interactions between the magnetic field of the imaging system and ferromagnetic objects, there seems to be a relative lack of understanding of some of the other safety issues associated with the imaging environment and function of a magnetic resonance imaging system. The recent renewed awakening of public interest in safety considerations of electromagnetic fields in general and the recent appearance of several comprehensive MR safety review have increased the timeliness of such a safety overview regarding electromagnetic and magnetic fields associated with magnetic resonance imaging, angiographic, and spectroscopic systems. Clinical magnetic resonance imaging, as it is presently practiced, is associated with several types of potential health concerns that impact both the patient as well as the health practitioners themselves that work in and around this environment. These can be classified and subdivided into several major areas, with varying degrees of importance depending upon such issues as field strength, magnet design, etc. The more common issues include the following:

Radiation of whistler waves in magnetoactive plasma

Abstract: In this paper the radiation of ring electric and magnetic currents in magnetoactive plasma in whistler frequency range is investigated. Particular attention is concentrated on the problem of variation of the radiated power distribution over the spectrum of excited waves with variation of the radiator parameters. Attention is also given to the radiation pattern structure near the resonance cone and peculiar caustic directions corresponding to the conic refraction and the Storey angle. It is shown that for ring electric current the consideration of the inhomogeneity in its distribution along the ring can be of importance and can lead, in particular, to a large increase of the relative contribution of the quasi-electrostatic whistler mode waves to the total radiation power. Detailed numerical calculations have been carried out for the conditions close to ionospheric ones.

Exhibit explaining system activated by infrared signals

Abstract: An exhibit explaining system includes transmitters and a portable information playback device. The transmitters transmits, in a wireless manner, identification signals respectively assigned to exhibits individually arranged at predetermined spatial intervals. The identification signal may be transmitted using infrared light or radio waves. When receiving the identification signal, the playback device reproduces and outputs prestored explanatory information as specified by the identification signal.

Video transmission over a 40 GHz radio-fibre link

Abstract: Transmission of a 40 GHz radio signal carrying wideband FM video modulation has been demonstrated over 12.5 km of optical fibre and 1.0m of radio path. This has been achieved without the use of a millimetre-wave source for the optical link, and without up-conversion or electrical amplification at the radio transmitter

A method for characterizing transient ionospheric disturbances using a large radiotelescope array

Abstract: Radio interferometers have been previously used for study of wave-like disturbances in the overhead ionosphere. However, all such studies involved baselines (≤3 km) which were very short compared to the disturbance wavelength, so that meaningful lag information was unavailable, and hence the waves' phase velocity usually could not be measured. Recently we have employed the Very Large Array radiotelescope at 90-cm radio wavelength to study ionospheric waves possessing disturbance wavelengths >20 km, using baselines which extend to 35 km. We have developed an analysis algorithm which fits spatially monochromatic planes waves (e −ik.r horizontal spatial dependence of the plasma disturbance) for each angular frequency ω in the visibility-phase data

Covert communication system using ultraviolet light

Abstract: A covert communication system uses ultraviolet light rather than radio waves as a medium for communication. Suitable wavelengths are chosen by examining atmospheric penetration, attenuation by clouds, presence of interfering sources, and ease of generation and detection. The transmitted ultraviolet light may contain both voice information and other data, impressed upon the light by frequency or pulse modulation using a Pockels cell light modulator. A corresponding receiver can be arranged as a transponder to determine range by phase angle differences between transmitted and reflected waveforms. By using an appropriate lens, the receiver can also determine the angle of incidence of a detected ultraviolet signal, and therefore the bearing of the transmitter.

A ray model for decimetric radiowave propagation in an urban area

Abstract: A ray-tracing model involving multiple reflections and diffractions is proposed to predict wideband decimetric radio wave propagation in an urban area. A computer code was developed in which only buildings close to the vehicle are considered. Wall irregularities and electromagnetic properties of material are taken into account by a constant reflection factor, while diffraction attenuation is computed from geometrical theory of diffraction results. Simulated channel path losses and complex impulse responses are compared with some measurements performed in Paris at a 900-MHz central frequency.

Auroral and polar-cap ionospheric effects on radio propagation

Abstract: Disturbances in the auroral and polar-cap ionosphere can have profound effects on radio signals traversing the high-latitude ionosphere (defined here as that latitudinal region poleward of approximately 55 degrees corrected geomagnetic latitude). Some effects of the high-latitude ionosphere on polar radio paths were documented as early as the 1930s, but intensive investigations of this ionospheric global region started during the International Geophysical Year (IGY) 1957-1959. Starting in the mid-1960s it was realized that high-latitude ionospheric anomalies could affect radio signals from ELF through VHF on terrestrial and earth-space paths, especially during sunspot maximum, disturbed periods. A considerable effort has been made in the last two decades to model and predict the salient parameters of the auroral and polar-cap ionosphere. A somewhat lesser effort has been devoted to develop HF propagation programs which included high-latitude ionospheric effects. Salient past results are briefly reviewed, and developments in this field for the period 1970-91 are presented. >

Laminated panel with low reflectance for radio waves

Abstract: The matter of concern is the reflection of a radio wave such as a television broadcast wave from a laminated panel having a substrate (10) low in reflectance for radio waves and a layer (12) relatively high in reflectance for radio waves. The reflection is greatly reduced by dividing the reflective layer (12) into a plurality of discontinuous segments (12a) by a series of relatively narrow slits (14) such that the width (L) of each segment (12a) in the direction parallel to the direction of the electric field of the radio wave is not greater than 1/3 of the wavelength of the radio wave. The invention is suitable for application to a heat reflecting glass with a heat reflecting film having a surface resistivity below about 500 Ω/□, and in that case it is preferable that the width of each segment of the heat reflecting film is not greater than 1/20 of the wavelength.

Magneto-acoustic resonance imaging

Abstract: A less expensive apparatus and associated method for Magnetic Resonance Imaging (MRI) of body tissues are disclosed. A physician uses an ultrasonic detector in combination with a weak magnetic field and pulsed, low frequency R.F. generator. The patient lies partially within the field of a magnet and receives low frequency radio pulses. As is shown below, ultrasonic waves are produced within the patient's body by the ordinary occurrence of nuclear magnetic resonance. For this reason, ultrasonic acoustic detection replaces the usual radio detection of the magnetic resonance induced spin echoes. The physician manipulates a hand-held ultrasonic detector with real time image feedback in much the same way that an ultrasonic transducer is used to provide the usual ultrasonic images. In the present case, however, no ultrasonic waves are emitted by the transducer; instead, the waves emitted by the "slice" selected by the radio frequency resonance with tissue protons are the source of the ultrasonic image produced. The MRI advantages of image production emphasizing longitudinal, T1, spin relaxation or transverse, T2, relaxation are retained. The usual problem that MRI has in low-noise measurement and location of spin echoes is obviated by the intrinsic ability to locate possessed by short wavelength ultrasonic signals. The need for very high magnetic fields in MRI to improve signal-to-noise ratio is removed in the present system. This removes a large capital expense. Another capital expense required by MRI is its complex magnetic field pulsing equipment. Such equipment is necessary to locate echoes using long wavelength R.F. detection. For a given frequency, of magnetic moment precession, the length of the acoustic waves, which are emitted at twice the precession frequency, are 100,000 times shorter than the length of radio waves, which are emitted at the precession frequency. Thus acoustic detection easily locates and measures the sources of magnetic spin echoes with a smaller burden of pulsed and steady magnetic fields.

Continuum radiation in planetary magnetospheres

Abstract: With the completion of the Voyager tour of the outer planets, radio and plasma wave instruments have executed the first survey of the wave spectra of Earth, Jupiter, Saturn, Uranus, and Neptune. One of the most notable conclusions of this survey is that there is a great deal of qualitative similarity in both the plasma wave and radio wave spectra from one magnetosphere to the next. In particular, in spite of detailed differences, most of the radio emissions at each of the planets have been tentatively classified into two primary categories. First, the most intense emissions are generally associated with the cyclotron maser instability. Second, a class of weaker emissions can be found at each of the magnetospheres which appears to be the result of conversion from intense electrostatic emissions at the upper hybrid resonance frequency into (primarily) ordinary mode radio emission. It is this second category, often referred to as nonthermal continuum radiation, which we will discuss in this review. We review the characteristics of the continuum spectrum at each of the planets, discuss the source region and direct observations of the generation of the emissions where available, and briefly describe the theories for the generation of the emissions. Over the past few years evidence has increased that the linear mode conversion of electrostatic waves into the ordinary mode can account for at least some of the continuum radiation observed. There is no definitive evidence which precludes the possibility that a nonlinear mechanism may also be important.

Facility and method for the detection and monitoring of plumes below a waste containment site with radiowave tomography scattering methods

Abstract: An embodiment of the present invention is a toxic waste containment facility subject to leaking hazardous plumes into soils beneath and adjacent to the site. The facility includes a plurality of substantially horizontal underground drillholes adjacent to and below a waste containment pit. A radio transmitter and antenna are placed in a first underground drillhole proximate to a surface waste containment site. A radio receiver and antenna are placed in a second underground drillhole opposite to the first drillhole. A position indicator is used for gauging a plurality of locations of the radio transmitter and antenna within the first underground drillhole and the radio receiver and antenna within the second underground drillhole. A data processing unit analyzes data received from radio receiver and antenna and position indicator to measure radio signal attenuation between the radio transmitter and antenna and radio receiver and antenna. The transmitted signal from the radio transmitter and antenna are synchronized by a signal from the data processing unit. Fiber optic cables are used to couple signals between the radio transmitter and antenna and radio receiver and antenna with the data processing unit. Along each path, the operating frequency is increased until all of the transmitted energy is absorbed along the path to maximize resolution. Tomographic techniques are used to translate the data collected from a variety of transmitter and receiver positions into attenuation profiles that can image a toxic plume beneath the containment pit.

Cloud-to-stratosphere lightning discharges: A radio emission model

Abstract: Recent observations of rare cloud-to-stratospheric lightning discharges suggest the events are inherently 'slow-rising', with the emitted energy reaching peak values in about 10 milliseconds. Applying a dipole radiation model, it is demonstrated that the emitted radio wave energy from such slow-rising events is strongest below about 50 Hz, and possesses a significant rolloff at higher frequencies. In the analysis, various current distributions are considered in order to determine the effect on the radio spectrum. Near 10 kHz, the emission from cloud-to-stratospheric lightning is significantly reduced as compared to the typical cloud-to-ground return stroke, with amplitudes as much as 50 dB lower. This result may explain the lack of detection of VLF signals from recently observed long-lasting discharge events.

On some problems of the theory of radio wave propagation in a randomly inhomogeneous ionosphere

Abstract: In considering HF propagation in a random inhomogeneous ionosphere it is necessary to take into account regular and random caustics. Regular caustics connected with regular refraction of radio waves in the ionosphere form a skip zone and determine the maximum usable frequency (MUF) and the maximum of the oblique incidence backscatter sounding (OBS) signal. Random fluctuations of ionospheric radio rays “wash out” field enhancement in the vicinity of MUF and the maximum OBS signal. The presence of random caustics results in strong intensity fluctuations of ionospheric radio waves. The above mentioned problems are considered by the interference integral method. A scintillation index formula for strong fluctuations of oblique ionospheric radio waves is obtained. Average intensity and average pulse signal which form in the vicinity of MUF are investigated. The peculiarities of oblique multihop radio wave propagation, taking into account random ionospheric inhomogeneities, terrestrial surface roughness, and caustics focusing in skip distance are discussed.

Angles of arrival of indoor multipath

Abstract: Some preliminary results of the angles of arrival of multipath components in indoor radio channel measurements are reported. The results show that strong multipath components arrive at the receiver in various directions.

High‐latitude ionospheric phenomena diagnostics by high‐frequency radio wave propagation observations

Abstract: With the help of a system of radio paths in the decameter wave band the problem of diagnostics of high-latitude ionospheric phenomena is solved experimentally. The latter are understood to be auroral substorms, main ionization trough, and daytime polar cusp. On the term “cusp” we suggest cusp/cleft region. As a source of information on a phenomenon, the use is made of either the statistical parameters of radio signals at radio channel output or the radio wave propagation parameter by the data of the oblique sounding of ionosphere. The first approach is taken in diagnostics of auroral substorms and main ionization trough. The oblique sounding is used in daytime polar cusp diagnostics. The experimental observations were carried out by two systems of paths: one is situated north of Eastern Siberia and the other encompasses the area north of the European part of the USSR. The range of corrected geomagnetic latitudes covered is Φ′ = 55°–75°. The main conclusion of the paper is that this system of radio paths allows us to conduct qualitative short-time prediction of the said ionospheric phenomena.