Showing papers on "Radio wave published in 1987"

Radio position determination method and apparatus

Abstract: A method and apparatus for radio position determination is provided including an unknown position transmitter for transmitting a radio wave having compensation for multipath, a plurality of base repeaters having a synchronized pulse for time reference, for receiving the radio wave emitted by the unknown position transmitter and for determining the relative times-of-arrival of the radio wave with respect to the synchronized pulse, and a central monitoring station coupled to the base repeaters for computing from the locations of the base repeaters and from the measured times-of-arrival, a coarse-position fix of the unknown-position transmitter. The system may include a mobile reference transceiver located within the coarse-position fix, for transmitting a reference signal, wherein the central monitoring station generates a differential position from the reference signal and the radio wave for guiding the mobile reference transceiver to the unknown position transmitter.

Radio propagation experiments in the outer solar system with Voyager

Abstract: Microwave telecommunications transmissions from the two Voyager spacecraft are being used to make detailed studies of planetary atmospheres, ionospheres, rings, and magnetic fields in the outer solar system. Coherently related sinusoidal signals, at wavelengths of 3.6 and 13 cm, transmitted from Voyager but received and analyzed on Earth serve as an active probe of planetary environs. Such studies have been carried out during the spacecraft encounters of Jupiter, Saturn, and Uranus; observations of Neptune's system are planned for August, 1989. The required occultation geometries are obtained either as by-products of the gravity-assist trajectories employed to travel among the planets or, in some cases, by design. Both spacecraft and ground systems are specifically modified and improved to support radio investigations. In particular, the use of hydrogen maser frequency standards on the ground in conjunction with thermally controlled, radiation-hardened quartz oscillators on the spacecraft guarantees long coherence intervals and allows application of new signal processing techniques. These advances lead to spatial resolutions in the media of interest well below the Fresnel zone scale, to current limits of a few tens of meters in the rings of Uranus. The present theory and data reduction methods permit detailed studies of atmospheric structure and scintillation parameters, the radial structure and particle size distribution of planetary rings, and the magnetic control of small-scale ionospheric irregularities. Atmospheric measurements are made at pressures from a few tenths of a millibar to a few bars, extinction profiles of planetary rings have been made to slant optical depths of 8 to 10, and alignments of magnetic fields within ionized regions have been determined to within a few degrees. Fundamental information concerning planetary composition, evolution, and dynamics is obtained from these measurements. Future improvements in radio systems through the use of powerful (> 100 000-W) ground transmitters in conjunction with high-performance receiving and digital signal processing units aboard spacecraft would permit improvements in dynamic range and sensitivity of such propagation experiments of 20 to 40 dB.

Large F‐region electron‐temperature enhancements generated by high‐power HF radio waves

Abstract: During recent experiments at Arecibo, Puerto Rico, large (1000-2000 K) enhancements in electron temperature have been observed when high-power radio waves reflect near the nighttime F region peak. The electron temperature enhancements are accompanied by significant (50-300 K) increases in ion temperature, large (10-15%) reductions in electron density, and strong HF-induced spread F. When large electron temperature enhancements develop, the ionosphere appears to become dynamically unstable resulting in the production of geomagnetic field-aligned striations having elevated electron temperatures and depleted electron densities.

Long‐period dynamic spectrograms of low‐frequency interplanetary radio emissions

Abstract: Dynamic spectrograms of the low-frequency interplanetary radio emissions as observed by Voyagers 1 and 2 from 1983 through mid-1986 are reported. The radio emissions were observed to be most intense in the latter portion of 1983 at 3 kHz but have also been detected at 2 kHz. The emission has been present almost continuously at either 2 or 3 kHz since late 1983. The spectrograms presented herein show that the phenomenon appears almost identically as observed by the two spacecraft separated by more than 10 AU, at least at the higher frequency. One feature revealed by the dynamic spectrograms which had not been noticed previously is a gradual rise in frequency of the 3-kHz component following the onset of the late 1983 event. These new observations reinforce the conclusion that the low-frequency emissions are freely propagating radio waves, but the two-component spectral structure implies that the previous model of emission at twice the plasma frequency at the inner heliosphere shock is inadequate to fully account for the observations. Either an additional source region or an additional source mechanism is suggested.

A 6 × 320-MHz 1024-channel FFT cross-spectrum analyzer for radio astronomy

Abstract: A wide-band FFT spectrum analyzer, which we call FX, has been in operation since 1983 at the Nobeyama Radio Observatory for spectroscopy of radio waves from interstellar molecules. It processes an input of six 320-MHz-bandwidth data streams to produce the output of fifteen cross-power spectra of 1024 frequency channels each. Its highly parallel pipeline architecture made it possible to achieve the above speed, 1010butterfly operations per second, which is 105times that of usual mainframe computers. The FX incorporates about 4500 newly developed CMOS LSI chips. They are designed using CAD (computer-aided design) and have 3900 or 2000 gates/chip, operate at a clock rate of 10 MHz, and consume 100 mW/chip or less. For 80-MHz bandwidth signal at an optimum input level, the SNR (signal-power to noise-power ratio) of the FX is better than 10 dB, which is adequate for astronomical use.

Radar type underground searching apparatus

Abstract: This radar type underground searching apparatus is a system for detecting the presence and location of buried objects such as gas pipes buried in the ground. This apparatus includes a pulse generating unit which periodically generates pulse, and a transmitting antenna through which the pulse is sent into the ground. Pulses reflected from an object in the ground and reaching the ground surface are detected by a receiving antenna, and a reflected wave corresponding to each pulse wave received by the receiving antenna is amplified in a radio-frequency amplifier where in the amplification is increasing each time a group of pulses are transmitted. By sampling the output of the radio-frequency amplifier with a sampler at a series of reflex time, each being succeedingly delayed by a fixed period from the transmitting timing of each pulse wave, as the reference, a low-frequency signal which is formed by extending one reflected wave in time base is obtained, and the waveform thereof is displayed on a waveform display unit. On the screen of the display unit, the presence of objects will be detected by the presence of peaks in the low-frequency signal caused by the reflection from the objects and the depths of the objects will be detected by the time at which the peaks appear on the screen. By this construction, the attenuation of radio waves in the ground can be compensated without arising waveform distortion.

Ionospheric heater beam scanning: A mobile source of ELF radiation

Abstract: The heating facility at Ramfjordmoen near Tromso, Norway, is used to modulate the auroral electrojet at extremely low frequencies (ELF) and the radiation of low-frequency waves by the system is now well documented. In most reports the heater has been operated with a stationary heating beam, modulated at ELF, directed toward the zenith. This paper describes the signals recorded at Lycksele, 500 km from the heating site, when the HF heating beam was modulated at an ELF frequency and simultaneously scanned up to 37° from the zenith in the north-south direction. ELF phase measurements at Lycksele confirm that the moving heated patch of ionosphere acts as a mobile source of ELF radio waves in the Earth-ionosphere-waveguide and that this mobile source may be used to determine the propagation parameters of the waveguide. Using square wave modulation of the beam position, of a constant amplitude HF beam, two simultaneous sources of ELF radiation have been produced in the ionosphere and a directional ionospheric ELF radio source synthesized.

The main source of radio emission from the magnetosphere of Uranus.

Abstract: Observations of kilometric radiation from Uranus made with the planetary radio astronomy experiment on the Voyager 2 spacecraft are presented and discussed. Similarities between the auroral kilometric radiation from Earth and the observed Uranus emission are pointed out. A geometrical beaming model is developed in which a single distributed source is located above the darkside auroral region and emits in the extraordinary mode by the cyclotron maser process. The model can account for nearly all the Uranian kilometric radiation from the high-frequency limit near 850 kHz down to about 150 kHz and for much of it down to the lower limit of 20 kHz.

Stochastic model for pulsed radio transmission through stratified forests

Abstract: The paper describes a stochastic radiowave propagation model useful for assessing the effects of forests and other vegetation on communications signals in the UHF band. The stochastic electromagnetic theory employed as the basis of this model considers the forest as a planar, stratified, anisotropic, discrete, random medium, bounded above by air and below by ground, of randomly positioned and oriented canonical scatterers representing the principal forest constituents (tree trunks are represented as infinitely long, parallel, circular, dielectric cylinders; branches as short ones; and leaves as flat, circular, dielectric discs). A physically appealing representation for the mean (coherent) field component of the propagating radio wave has been obtained by recognising that the ensemble of discrete scatterers can be replaced by an equivalent continuous medium described by an effective dyadic permittivity e. The associated electromagnetic boundary-value problem is solved to identify the principal contributions to the mean field: the direct wave, the reflected wave and the lateral wave. Because the equivalent continuous medium characterised by the effective dyadic permittivity e is linear, Fourier-transform techniques have been employed to generalise the model so that it accommodates arbitrarily modulated waveforms.

Observation of ionospheric cavitons.

Abstract: The observation of the change in the ionospheric density profile and the creation of a density cavity at the critical height by high-power radio waves is made by the time-of-flight radar scattering technique. Small-scale cavitons imbedded inside a large caviton are inferred from the suppression of the photoelectron-enhanced plasma lines near the critical height.

Time division multiplex mobile communication system

Abstract: PURPOSE:To attain channel changeover without hit by allowing a mobile equipment to switch a frequency of a local oscillator at a high speed for each time slot, to monitor sequentially radio waves from an adjacent radio base station except its communication to keep the decision of quality and deciding a transferred radio zone by the mobile equipment itself. CONSTITUTION:The mobile equipment 5 switches a transmission/reception channel (frequency and time slot) at a high speed, monitors sequentially radio waves from plural adjacent base station 2-4 except the time assigned to the communication to estimate the present position and decides the moving direction and the radio zone by itself. When the frequency of the mobile destination zone and time slot are assigned to a mobile equipment MSS, the mobile station communicates the base station 2 before the changeover into the transfer destination channel during the communication, an equalizer or the like is set to improve the characteristic in a new propagation line and the radio continuity test is conducted. In the signal transmission from the MSS to the radio base station MBS, so-called in the outgoing direction, even when no voice is sent during the communication, predetermined information is kept for the transmission, through an idle time slot. Thus, the channel is switched without hit.

Radio paging communication system

Abstract: PURPOSE:To attain the expansion of a service area and the effective utilization of a frequency by forming a fixed radio network by a small power radio equipment and plural weak radio wave radio equipments, and sending a signal from a portable radio equipment to one of the weak radio wave radio equipments after a communication channel is set. CONSTITUTION:A radio base station 8 sending a radio wave received in a prescribed area R including plural service areas R1-R5 and the weak radio wave radio stations R11-R15 coupled with the base station 8 through a transmission line and using one of the service areas R1-R5 constitute the fixed radio network. A radio wave sent from the radio base station 8 is used for the transmission to the portable radio equipments 9-16 using plural weak radio waves existing in the area R, and as to the transmission from each portable radio equipment, in order to set or release a communication channel prior to the transmission, the communication channel is set or released by sending/receiving a control signal through the use of a weak radio wave between each portable radio equipment and the weak radio wave radio station corresponding thereto, and after the communication channel is set, the transmission from each portable radio equipment is applied to one weak radio wave radio station in the plural service areas.

The Propagation of Radio Waves: The Theory of Radio Waves of Low Power in the Ionosphere and Magnetosphere

Abstract: This is a most welcome addition to the library of books on radio waves in the ionosphere. The standard references in the western world are all quite old, although they are still remarkably useful: S.K. Mitra's The Upper Atmosphere (Asiatic Society, Calcutta, India, 1952), K.G. Budden's Radio Waves in the Ionosphere (Cambridge University Press, London, 1961), and K. Davies' Ionospheric Radio Waves (Blaisdell, Waltham, Mass., 1969). In the eastern world, Y.L. Alpert and V.L. Ginzburg are the authorities, and both now have volumes in English: Alpert's The Near Earth and Interplanetary Plasmas (volumes 1 and 2, Cambridge University Press, London, 1983) and Ginzburg's The Propagation of Electromagnetic Waves in Plasmas (Pergamon, New York, 1970).

A new interpretation of plasma‐line overshoot phenomena

Abstract: The temporal evolution of Langmuir waves excited by high-power, high-frequency (HF) radio waves in the ionosphere is studied theoretically. This study is motivated by past observations made with the 450 MHz radar at Arecibo Observatory in Puerto Rico. Two kinds of nonlinear damping to the parametric decay instability are considered in the derivation of the rate equation for the spectral intensity of enhanced Langmuir waves. They are Langmuir wave cascading caused by nonlinear Landau damping and cross-field electron diffusion. The first damping process leads to the saturation of individual unstable Langmuir wave. The second process, which results from the incoherent scattering of electron orbits by the total excited Langmuir waves, yields anomalous damping that applies to each Langmuir wave. Consequently, Langmuir waves with smaller growth rates will be suppressed by those with larger growth rates. Such a mode competition process may cause the overshoot of the HF-enhanced plasma line observed with the Arecibo 430 MHz radar. Favorable agreement is obtained between theory and the Arecibo observations.

Ionospheric demodulation of powerful pulsed radio waves: A potential new diagnostic for radars suggested by Tromsø heater results

Abstract: Pulses of radio waves in the ELF and VLF range can be generated in the auroral ionosphere by the transient conductivity perturbation (in the presence of an ambient electric field) caused by artificial heating using pulsed high-power HF radio waves. Examples of such waves generated by the Max-Planck heating facility near Tromso are briefly reviewed. The waves generated can be used to provide information on the horizontal ionospheric electric field. A model which has successfully explained these results quantitatively is used to predict the amplitudes produced by lower power HF radars (partial reflection experiments) in auroral regions. The model results show ELF/VLF amplitudes which are typically an order of magnitude below those obtained for the Tromso heater but may nevertheless provide useful ionospheric information as a byproduct of the radar's normal operation.

Circular-linear polarized wave converter

Abstract: PURPOSE: To attain miniaturization by selecting the length of a 1st transmission line longer than a 2nd transmission line by λg/4 (λg is the wavelength). CONSTITUTION: The 1st transmission line 21 is selected longer than the 2nd transmission line 22 by λg/4 (λg is the wavelength) so that the phase of a radio wave sent through the transmission line 21 is delayed substantially by 90° than the phase of the radio wave sent through the 2nd transmission line 22. Since a phase difference on one and same plane formed by strip lines is given to two components constituting a circularly polarized wave, the wavelength is reduced to a value D 2 (=λg'/4λg, is the guide wavelength). Thus, the converter is remarkably decreased in size. COPYRIGHT: (C)1989,JPO&Japio

Ionospheric Refraction Effects on Radio Interferometer Phase

Abstract: The refraction of radio waves as they traverse through the terrestrial ionosphere and troposphere introduces a differential phase path which results for a radio interferometer in variations of the visibility phase. Though refraction due to troposphere is significant for synthesis radio telescopes operating at 1.0 GHz and above, ionospheric refraction is dominant at lower frequencies. This problem is important in the case of Ooty Synthesis Radio Telescope (OSRT) operating at 326.5 MHz, due to its proximity to the magnetic equator. This paper deals with the nature of phase variations suffered by OSRT due to refraction and explains the methodology evolved to alleviate them.

A galactic gravitational lens as the ultimate astronomical telescope

Abstract: When a galaxy acts as a gravitational lens it behaves more like a raindrop deflecting sunlight than like a true lens. The images formed by a galaxy exist as directions of incidence of rays on the observer and the best a galaxy can do is to generate complex surfaces called caustics1–4. Here we point out that the caustic surfaces of galactic lenses are powerful telescopes, with point-source intensifications varying with frequency from 105 for radio waves to 108 for X rays. The diffraction limit to the angular resolution varies from 10–11 to 10–17 arcs from radio waves to X rays and exceeds the resolution of man-made telescopes by many orders of magnitude. The signature of a point source crossing the caustic is a burst of radiation modulated in time by a characteristic diffraction pattern. The microcaustic surfaces generated by stars in the lensing galaxy are also powerful telescopes that yield large intensifications of small sources crossing the microcaustic. Decaying cosmic strings could be an important source of cosmic rays with energies above 1010 GeV.

Hybrid integrated circuit

Abstract: PURPOSE:To obtain a hybrid IC having high reliability by sealing a printed circuit board with one or more layers of radio wave absorbing resin to prevent noises between lines and circuit parts in the IC from rounding about. CONSTITUTION:A semiconductor element 4 and a driven element 5 are placed on an epoxy substrate 2, coated with an Si resin 6 and the first radio wave absorbing resin 7 to prevent noises from rounding about, and contained in a housing 1. Then, resins 8-12 are sequentially packed in the housing, cured, and the substrate 2 and lead pins 3 are secured. Since at least one of the resin layers is disposed as the innermost layer as the radio wave absorbing layer, it is extremely effective. When carbon or metal piece is mixed in the resin, a high frequency current flows to the surface layer to attenuate the radio wave. When a ferrite is mixed, it prevents lines of magnetic force to interrupt the radio wave. The surfaces of the lead pins are coated with insulating films to prevent them from short-circuiting with conductive resin, various radio wave absorbing materials are used together to obtain a hybrid IC which interrupts the all radio waves.

Scintillation of a radio source observed through the tail of comet Halley

Abstract: On 29 March 1986 between 16:00 and 23:00 UT we observed the strong compact radio source 1827-360 as the plasma tail of comet Halley swept across the source. We noted the appearance of weak intensity fluctuations during the interval 17:00 to 19:00 UT when the Sun, the comet's nucleus and the radio source were accurately aligned. We interpret this behaviour as the result of diffraction of radio waves by electron-density irregularities in the plasma tail. At a distance 5.4 × 106 km downstream from the cometary nucleus the central part of the plasma tail contained electron density irregularities about 14 times as strong as those in the undisturbed solar wind.

Satellite reception antenna system

Abstract: PURPOSE:To use a single reflection mirror in common for the reception from two kinds of satellites by placing a primary radiator used for higher frequency waves among radio waves from the two kinds of the satellites to a focus of the reflection mirror and placing other primary radiator to a deviation point. CONSTITUTION:The reflection mirror 3 is positioned so that a transmission wave from the 1st satellite 1 is in parallel with an axis 3b of the reflection mirror 3, the primary radiator 10 for the satellite 1 is arranged to a focus 3b of the reflection mirror 3 and the 1st satellite reception antenna is set to obtain the maximum sensitivity. The primary radiator 20 receiving the transmission wave from the 2nd satellite 2 is arranged at a position deviated from a focus so as to be made coincident with the reflected wave from the reflection mirror. Since the radiator is fed with a deviation, the deterioration of the gain is caused, but it is negligible because the frequency of the irradiated wave of the satellite 2 is low in the frequency in comparison with that of the satellite 1 and the gain reduction is remarkably low. Thus, the single reflection mirror can receive the radio waves from the two satellites having a different transmission frequency.