Showing papers on "Radio wave published in 1986"

Tools of Radio Astronomy

Abstract: Radio Astronomical Fundamentals.- Electromagnetic Wave Propagation Fundamentals.- Wave Polarization.- Signal Processing and Receivers.- Fundamentals of Antenna Theory.- Filled Aperture Antennas.- Observational Methods.- Interferometers and Aperture Synthesis.- Emission Mechanisms of Continuous Radiation.- Some Examples of Thermal and Nonthermal Radio Sources.- Spectral Line Fundamentals.- Line Radiation of Neutral Hydrogen.- Recombination Lines.- Molecules in Interstellar Space.

Attenuation by Atmospheric Gases

Abstract: A radiowave propagating through the Earth’s atmosphere will experience a reduction in signal level due to the gaseous components present in the transmission path. Signal degradation can be minor or severe, depending on frequency, temperature, pressure, and water vapor concentration. In this chapter the effects of atmospheric gases, primarily oxygen and water vapor at space communications frequencies, are discussed, and methods for calculating the expected attenuation for a radiowave link are presented. Examples are given for atmospheric attenuation at several of the frequencies of interest for space communications systems. Atmospheric gases also affect radio communications by adding atmospheric noise (i.e., radio noise) to the link. This problem is described fully in Chapter 7.

Time delay spread and signal level measurements of 850 MHz radio waves in building environments

Abstract: Time delay spread and signal level measurements of 850 MHz radio signals were made over inside-to-outside radio paths at two residential locations and an office building. Root mean square time delay spreads of up to 420 ns were encountered in residential environments. However, when a direct path was present, this improved to less than 325 ns overall, and even to 100 ns at one residence. Received power levels were around -40 dB, with respect to levels received at 0.3 m antenna separation, Under favorable conditions. In other cases, these relative levels varied from - 40 to - 80 dB. Median signal levels agreed well with continuous wave measurements made earlier at one site. No significant polarization dependence or floor level dependence were seen in these data.

Transmitting and receiving apparatus

Abstract: PURPOSE:To perform the simultaneous use and change-over use of a radio wave and a light wave without lowering the functions of both radio wave and light wave systems, by providing an optical system to the peripheral space part of a radio wave array antenna arranged in a planar state. CONSTITUTION:The radio wave signal from a transmitter 3 is supplied to an array antenna 1 by a duplexer 2 to be emitted to a space. The reflected signal from a target passes through the route reverse to that at the time of transmission to be sent to a receiver 4 by the duplexer 2 and the detection of a target signal is performed by a signal processor 5. The light wave allowed to radiate from the target is converted to an electric signal by a light wave detector 7 through the optical system 6 provided to the space part 10 of the peripheral part of the antenna 1. The light signal from the target converted to the electric signal is sent to a signal processor 9 through an amplifier 8 to perform the detection of a target signal. As mentioned above, by allowing the radio wave system and the light wave system to function independently each other, the effect exerted on the capacity of the radio wave system such as the lowering in the gain of the antenna 1 or the deterioration of side robe capacity becomes min. and, even when both radio wave and light wave systems are arranged in parallel, the lowering in the functions of both systems can be prevented.

New techniques in ground‐based ionospheric sounding and studies

Abstract: Rapid progress in the integrated circuit market has led to new advanced techniques in the remote probing of the ionosphere with HF radio waves. The classical ionosonde which measured virtual height as a function of frequency expanded into a geophysical research tool by measuring all the observables contained in the electromagnetic signals reflected from the ionosphere: amplitude, phase, Doppler, incidence angle, and polarization. A receiving antenna array and high speed digital processing provide the desired spatial and temporal resolution. The current emphasis is on both the on-line and off-line postprocessing of the multiparameter ionogram data to extract the geophysically important ionospheric characteristics: the vertical electron density profiles, horizontal gradients (tilts and waves), plasma drift, the mid-latitude F region trough, and auroral and equatorial spread F. Digital ionosonds deployed in the polar cap and the auroral zone have helped to obtain a better understanding of some of the high-latitude features, and measurements of the equatorial spread F have shown the development and motion of the F region bubbles. HF coherent radar techniques for studying ionospheric irregularity structures measure the velocity of irregularities with scale sizes of one half the radio wavelength. They have mainly been used in the northern auroral zone.

1.2 GHz band wave propagation measurements in concrete building for indoor radio communications

Abstract: For the design of indoor radio communication or a portable radio telephone system, 1.2 GHz band radio wave propagation characteristics are investigated in a concrete building. Penetration loss through a window, local median variations, and cumulative distributions of received signal levels in a room, reflection coefficient or equivalent dielectric constant and transmission loss of a wall/floor are discussed.

Antenna system incorporated in the air spoiler of an automobile

Abstract: An antenna system for use in an automotive vehicle comprises a housing mounted on a body of the automotive vehicle and having at least a portion of an upper surface thereof made of a dielectric material which transmits radio waves, at least one planar antenna disposed rotatably within the housing to receive radio waves transmitted through the portion of the upper surface of the housing made of the dielectric material, and driving means for driving the planar antenna to effect scanning of a radio wave receiving direction to search for the radio wave receiving direction of higher sensitivity. The housing protects the antenna system and maintains the fine appearance of the automotive vehicle. Further, the housing has a shape like that of an air spoiler, which makes it possible to maintain the satisfactory aerodynamic characteristic of the automotive vehicle.

Ionospheric radio propagation models and predictions--A mini-review

Abstract: The ionosphere affects radio waves that are propagated within and through it. The magnitude of the effects depends upon the structure of the ionosphere and the frequency of the radio wave. Ionospheric models have been developed over the years to aid in predicting the impact of the ionosphere on ionospheric-dependent telecommunication systems. The status of ionospheric modeling and prediction efforts that are geared toward radio wave propagation system assessment is reviewed.

Radiation from lightning return strokes over a finitely conducting Earth

Abstract: The effects of the conductivity of the earth on radiation from lightning return strokes are examined theoretically using a piecewise linear transmission line model for the return stroke. First, calculations are made of the electric field radiated during the return stroke, and then this electric field is used to compute the response of conventional AM radio receivers and electric field change systems during the return stroke. The calculations apply to the entire transient waveform (they are not restricted to the initial portions of the return stroke) and yield fast field changes and RF radiation in agreement with measurements made during real lightning. This research was motivated by measurements indicating that a time delay exists between the time of arrival of the fast electric field change and the RF radiation from first return strokes. The time delay is on the order of 20 microsec for frequencies in the HF-UHF range for lightning in Florida. The time delay is obtained theoretically in this paper. It occurs when both the effects of attenuation due to conductivity of the earth, and the finite velocity of propagation of the current pulse up the return stroke channel, are taken into account in the model.

Parallel electric fields in extragalactic jets: double layers and anomalous resistivity in symbiotic relationships

Abstract: After examining the properties of Coulomb-collision resistivity, anomalous (collective) resistivity, and double layers, a hybrid anomalous-resistivity/double-layer model is introduced. In this model, beam-driven waves on both sides of a double layer provide electrostatic plasma-wave turbulence that greatly reduces the mobility of charged particles. These regions then act to hold open a density cavity within which the double layer resides. In the double layer, electrical energy is dissipated with 100 percent efficiency into high-energy particles, creating conditions optimal for the collective emission of polarized radio waves.

Improved algorithms for the determination of specific attenuation at sea level by dry air and water vapor, in the frequency range 1–350 GHz

Abstract: This paper presents new algorithms for the determination of specific attenuation by dry air and water vapor, at sea level, in the frequency range from 1 to 350 GHz. The algorithms are shown to be an improvement on those recommended by the International Radio Consultative Committee (CCIR), by including the effects of high-frequency rotational transitions in oxygen, pressure-induced nitrogen absorption (important for ƒ > 150 GHz) and a quadratic dependence of attenuation on water-vapor density. Simple scaling factors are given to include the effects of temperature dependence of attenuation, over the range −20°C to 40°C.

Io plasma torus and the source of jovian kilometric radiation (bKOM)

Abstract: One of the many discoveries by Voyagers 1 and 2 during their flyby of Jupiter was the detection of radio emission at kilometric wavelengths1,2 in the frequency range 20–500 kHz. Broadband jovian kilometric radiation bKOM was observed to be beamed away from the zenomagnetic equatorial plane, the beaming angle increasing with increasing frequency1–3. It was suggested that bKOM is created by the linear conversion of electrostatic upper hybrid waves to electromagnetic waves in the density gradients at the lo torus4. The beaming is inherent to the conversion mechanism and depends on the characteristic frequencies of the source plasma. Here I present results, based on this theory, of remote sensing of the lo torus using bKOM observed by Voyager 2 when inbound towards Jupiter. The density profiles obtained are in remarkable agreement with measurements of the torus densities obtained in situ by Voyager 1. This seems to provide very strong evidence that bKOM is produced at the lo torus by the linear mode-conversion mechanism and indicates that the technique used for remote sensing could be a powerful method of determining the torus characteristics when no in situ measurements are available.

Structure of HF pump in ionospheric modification experiments. Linear treatment

Abstract: In order to demonstrate the versatility and flexibility of the uniform approximation technique, introduced by the authors for solving the problem of propagation of radio waves in an inhomogeneous, collisional and magnetised plasma, the standing wave pattern of a radio wave reflected from an ionospheric Chapman layer is calculated. Comparisons with results obtained from standard formulas in the literature show the superiority of the uniform approximation method. The derivation of the accurate analytic uniform approximation formulas is motivated by the need for a detailed analysis of non-linear wave phenomena induced by the electromagnetic pump in ionospheric modification experiments.

Battery saving system

Abstract: PURPOSE: To reduce power consumption of a battery by making the operating period of a radio terminal equipment longer when the result of detection of the strength of a radio wave at the radio terminal equipment indicates that the strength is a reference value or below. CONSTITUTION: In monitoring whether or not information addressed to a radio terminal equipment is sent by operating a receiver by the transmission time of a frame synchronously with the period of the frame assigned to a group belonging to the radio terminal equipment, the strength of the radio wave sent from a radio base station is detected by providing an electric field strength detection section 4 to the radio terminal equipment. If the state of the strength of a detected radio wave less than the reference value of the strength of the radio wave required for the transmission of information set to the radio terminal equipment is consecutive for a prescribed period or over, a radio wave terminal control section 6 controls a battery control section 5 to extend the period to operate the radio terminal equipment. Thus, the power consumption of the battery is reduced and the consecutive operating time of the radio terminal equipment is increased. COPYRIGHT: (C)1988,JPO&Japio

Backup system by radio equipment at important line is at fault

Abstract: PURPOSE:To transmit stably command talking to a terminal device at a fault of an important wired line by providing a switching function to a radio equipment to a master and terminal equipments at both ends of the important line. CONSTITUTION:If even one line is faulty among important lines 9, command line sections 21-23 of the master equipment detect it to activate internal relays L1-Ln of a wire/radio connector 3, contacts L connect the line 9 to a radio control equipment 5 and a signal is transmitted to the terminal device. On the other hand, when a line supervisory circuit 41 in a loudspeaker controller 4 at the terminal device detect a line fault, a relay 42 is activated to receive information from a radio receiver 6. When a radio wave transmitted from the control equipment 5 of the master equipment reaches the receiver 6, a switch in the receiver 6 is turned on, a relay 43 in the controller 4 is activated and a contact 431 switches the talking line to a loudspeaker amplifier 7 from the wired side to the radio receiver 6 and a contact 432 starts the amplifier 7 to give command information.

Thermoelectric thermometer of radio transmission type

Abstract: A thermoelectric thermometer of the radio transmission type incorporating a thermocouple for measuring the temperature of an object having a relatively high temperature, such as metal in a molten state or being heat-treated. A signal representing the temperature measured is transmitted by radio waves and received at a desired location away from the hot object to remotely detect the temperature of the object.

An Introduction to Radar Absorbent Materials (RAM)

Abstract: : The purpose of this Introduction is to present, in a straightforward way, the electromagnetic principles of Radar Absorbent Materials (RAM) for the benefit of the non-electromagnetic-specialist who finds himself involved in this field. The fundamental theory of electromagnetic wave propagation in media and at the interfaces between different media is reviewed and the various approaches to absorber design are described in the light of this. The types of materials required and the techniques for measuring both their electromagnetic properties and the performance of the finished absorber are outlined. Finally, a means of designing absorbers from a knowledge of the properties of its constituent materials is described.

Solar radio signatures suggestive of proton beams

Abstract: Electron beams propagating in the solar corona excite the ambient plasma to emit radio waves at the local plasma frequency and/or its harmonic. This general interpretation of type III radio bursts is well confirmed by in situ measurements. The rate at which peak flux drifts in frequency and time is a measure of the velocity of the exciter. Here we report a class of radio bursts with a significantly lower drift than normal; consequently, we show that they defy the usual interpretation. Possible exciters are slowly moving beams of protons.

A Compact Magnetometer Data Acquisition System with Accurate Chronometer

Abstract: A compact data acquisition system in use for a geomagnetic pulsation study has been constructed. The system is composed of a data processing system controlled by a microprocessor, cassette tape recorder, chronometer and short wave radio receiver. The system is programmed to calibrate the chronometer every five minutes by receiving a standard time signal, such as JJY (Japan), WWV (USA) and so on. The system improves a signal to noise ratio of the radio waves by signal stacking processes to minimize errors in the chronometer calibration. Even in a very weak signal, the system can discriminate a second pulse. The calibration accuracy is 10msec, including circuit signal delay when a radio propagation delay is neglected. The system is programmed to sample three component magnetometer signals at intervals of 3 sec and can store 1.3 Mbytes of data in a C-90 cassette tape which is equivalent to ten-day data. The system is suited for an unmanned operation at a station remote from the standard signal station.

Absorption of radio waves during a solar eclipse

Abstract: In this paper, the results of our observations on Al-method ionospheric absorption of radio waves on 1.8 and 2.2 MHz during the solar eclipse of 16 February 1980 are presented. The absorption decreased by about 41% and 46% of the normal value respectively at the above two frequencies at Ahmedabad following the maximum phase of the eclipse (about 77% of full disc) with a delay of 18 minutes. The quantityAT(f) which is a measure of eN vdh is now examined for better clarity of the influence of the changes in theE-layer. The results are discussed in relation to the observations of the ionizing radiations from the sun, changes in the electron density, recombination rate and absorption in the underlyingD andE regions.

Periodic amplitude variations in Jovian continuum radiation

Abstract: An analysis of periodic variations in the amplitude of continuum radiation near 3 kHz trapped in the Jovian magnetosphere shows structure with periods near both five and ten hours. Contrary to a plausible initial idea, the continuum amplitudes are not organized by position of the observer relative to the dense plasma sheet. Instead, there seem to be preferred orientations of system III longitude with respect to the direction to the sun which account for the peaks. This implies a clock-like modulation of the continuum radiation intensity as opposed to a searchlight effect. The importance of the dipole longitude-solar wind alignment to the amplitude of the continuum radiation implies the source region of the radiation is near the magnetopause and may indirectly tie the generation of the radio waves to the clocklike modulation of energetic electron fluxes from Jupiter.

The effect of small amplitude wave irregularities on radio wave observations of the ionosphere

Abstract: Variational theory is used to derive the effects of wavelike ionospheric irregularities on group path, phase path, Doppler shift and angle of arrival of radio waves when the earth's magnetic field is neglected. General results are obtained showing the relationship between these quantities for perturbations to vertical incidence rays. In the case of irregularities with relatively large vertical wave numbers, asymptotic results are obtained for different model ionospheric layers. In the case of an exponential layer, the accuracies of the first-order and asymptotic results have been checked and found to be very acceptable. Examples of observations of topside and bottomside irregularities which can be analyzed by using the results are discussed.

Excitation of upper hybrid resonance in the ionospheric plasma by an intense radio wave

Abstract: An effective displacement of ionospheric plasma from a localized region in the vicinity of the upper hybrid resonance of an intense radio wave has been observed. A plasma reflector which focuses test waves has been observed to appear in this region. The observed effects are evidence of the local excitation of plasma turbulence. 9 references.

Plasma waves and continuum radiation in planetary magnetospheres

Abstract: Voyager data on whistler mode waves and electron cyclotron harmonic emissions are analyzed to understand the interaction of the waves with the dynamics of the electrons. The occurrence and characteristics of Jovian whistler mode chorus and the interactions with the plasma in and near the Io torus are emphasized. Bernstein waves, especially those near the upper hybrid or plasma frequency are discussed to provide insight into an important plasma diagnostic tool and to compare the relevant portions of the electron distribution function at Earth, Jupiter, and Saturn. The nonthermal continuum radiation common to the magnetospheres of Earth, Jupiter, and Saturn is considered. Because of the very low frequency of these radio waves and their close association with upper hybrid resonance emissions, continuum radiation is often associated more closely with the plasma wave spectrum of a planetary magnetosphere than with the planet's radio spectrum.

Stimulated radio emission of the ionospheric plasma at the second harmonic of the pump wave frequency

Abstract: Observations of emission from regions of the ionosphere acted upon by an intense radio wave are made at the second harmonic of the pump wave (PW), and the emission characteristics are analyzed. Calculations are made for the energy density at the second harmonic which arises because of the merging of plasma waves excited by the PW. Experimental and calculation results are compared. It is shown that the emission observed at the second harmonic is caused by plasma waves excited in the reflection region of the PW due to parametric instability.

Receiving system of wireless transmission data

Abstract: PURPOSE:To select an antenna of the strongest receiving level at all times by performing measurement of the intensity of electric field of radio waves received by each antenna at the receiving level of non-modulated radio waves of fixed amplitude in the transmitting side. CONSTITUTION:Radio waves transmitted from a remote station are made to waves of frame structure and a time slot of only carrier that does not contain data is provided in a part of it. Signals received by any one of antennas pass through a switching section 1 and the level detecting section 21 of a receiving section 2, and demodulated by the demodulating circuit 31 of a receiving section 3. When a signal of carrier only arrives, a switching circuit 41 of a controlling section 4 is turned off by outputs of a no-data detecting section 32. An AGC circuit 22 is separated and the response speed of the detecting section is made quicker. The carrier level detected by the level detecting section 21 is stored in a storing circuit 42, and compared with the already stored level of other antennas, and a receiving antenna of the largest level is determined.

Ocean waves and turbulence as observed with an adaptive coherent multifrequency radar

Abstract: An adaptive coherent multifrequency radar system has been developed for several applications. By means of this the velocity distribution (Doppler spectrum) and spectral intensity of 15 different irregularity scales (waves and turbulence) can be measured simultaneously. Changing the azimuth angle of the antennas at regular intervals, the direction of the wave/turbulence pattern on the sea surface can also be studied. Using this radar system, series of measurements for different air/sea conditions have been carried out from a coast-based platform in southern Norway. Experiments in the Atlantic were also performed with the same equipment, making use of the NASA Electra aircraft. There are many air/sea phenomena that play a role in relation to backscattering of radio waves in the microwave region: gravity waves “modulate” the capillary wave structure, overturning wave crests produce focusing effects and also periodic regions of strong turbulence, and the boundary layer wind field with strong turbulence amplified by the ocean waves will conceivably leave a patchy and even periodic footprint on the sea surface. Internal waves originating from density gradients in this ocean further complicates the sea surface irregularity pattern. By virtue of the fact that the multifrequency radar allows one to measure the velocity distribution (“coherent and incoherent component”) associated with 15 different ocean irregularity scales simultaneously for several azimuth directions, it is possible to study the different air/sea mechanisms in some degree of detail.