High-power Radio Research Articles

Exposure to electromagnetic fields and the risk of childhood leukaemia: a review

Extremely low-frequency magnetic fields have been classified as possibly carcinogenic to humans, mainly based on epidemiological studies consistently showing an association between long-term average exposures to magnetic fields above 0.3/0.4 microT and the risk of childhood leukaemia. No mechanism to explain this finding has been established and no support for a causal link emerged from experimental studies. Chance or bias cannot be ruled out with reasonable confidence as an explanation for the observed association. If the association is causal, it explains only a small fraction of childhood leukaemia cases. There were some reports of childhood leukaemia clusters in the vicinity of high-power radio and television broadcast transmitters in studies in Australia and Italy. However, recent large-scale systematic studies in Korea and Germany show no association between exposure to radio frequency electromagnetic fields emitted from broadcast towers and childhood leukaemia risk. Studies on mobile phone use and leukaemia risk in adolescents and young adults may be indicated.

Childhood Leukemia in Relation to Radio Frequency Electromagnetic Fields in the Vicinity of TV and Radio Broadcast Transmitters

A case-control study of radio frequency electromagnetic fields (RF-EMFs) and childhood leukemia was conducted in West Germany. The study region included municipalities near high-power radio and TV broadcast towers, including 16 amplitude-modulated and 8 frequency-modulated transmitters. Cases were aged 0-14 years, were diagnosed with leukemia between 1984 and 2003, and were registered at the German Childhood Cancer Registry. Three age-, gender-, and transmitter-area-matched controls per case were drawn randomly from population registries. The analysis included 1,959 cases and 5,848 controls. Individual exposure to RF-EMFs 1 year before diagnosis was estimated with a field strength prediction program. Considering total RF-EMFs, the odds ratio derived from conditional logistic regression analysis for all types of leukemia was 0.86 (95% confidence interval: 0.67, 1.11) when upper (>or=95%/0.701 V/m) and lower (<90%/0.504 V/m) quantiles of the RF-EMF distribution were compared. An analysis of amplitude-modulated and frequency-modulated transmitters separately did not show increased risks of leukemia. The odds ratio for all types of leukemia was 1.04 (95% confidence interval: 0.65, 1.67) among children living within 2 km of the nearest broadcast transmitter compared with those living at a distance of 10-<15 km. The data did not show any elevated risks of childhood leukemia associated with RF-EMFs.

On the feasibility of high-power radios in sensor networks

Wireless sensor nodes are constrained by limited energy resources. A significant portion of this limited energy is spent in communication, making energy efficiency of the radio a very important factor in increasing the overall lifetime of a sensor node. An ideal radio, in terms of energy efficiency (ignoring issues of transmission range and delay), should satisfy two requirements. First, it should minimize the energy used per bit when transmitting or receiving. Second, its idle time energy consumption should be minimal. Unfortunately, no such "ideal" radio exists. Current sensor radios (e.g., CC2420) meet the second requirement - the energy consumption in the inactive states is very low in comparison to IEEE 802.11 radios, which are comparatively energy-inefficient due to high switching-on cost and idle state energy consumption. On the other hand, IEEE 802.11 radios perform much better when it comes to energy consumption per bit. So the natural question to ask is whether there exists a way to combine the positive features of these two types of radios leading to increased energy conservation. We argue that this objective can indeed be achieved by adding a high-power IEEE 802.11 radio to the mote platform alongside the already existing sensor radio and managing them by an energy-efficient scheme as proposed in this work.

Modification of the earth’s ionosphere by high-power HF radio emission: Artificial periodic inhomogeneities and the sporadic E layer

We present the results of new studies of the sporadic E layer in the case of heating of the ionosphere by high-power HF radio emission. The measurements were performed at the “Sura” heating facility. Ionosphere was modified by high-power radio emission from the “Sura” facility and was sounded by the probing radio waves of the same frequency and mode. The heating of the ionosphere resulted in the formation of artificial periodic inhomogeneities, and an increase in the intensity of all signals scattered by the D, E, and F regions and the sporadic E layer by 5–20 dB was observed. The increase was observed during heating of the ionosphere by each magnetoionic component, but was smaller for heating by an ordinary-mode wave. This effect was resonant and disappeared as a result of the frequency detuning down to 85 kHz. During the ionospheric modification, the signal-intensity increased due to modulation of the natural profile of the electron number density by the artificial periodic structure.

Bridging the gap between ground- and space-based investigations of magnetosphere–ionosphere coupling processes

Until recently spacecraft investigations of dynamic magnetospheric processes have occurred independently from those undertaken using ground-based active radar observations of the ionospheric signatures associated with these phenomena. This paper will review recent experiments combining these data sets in order to study magnetosphere–ionosphere coupling. The techniques discussed will include: (i) the investigation of ULF waves generated by wave–particle interactions in the inner magnetosphere and subsequent ring current energy dissipation in the ionosphere; (ii) studies of the high latitude acceleration region responsible for the formation of aurora and (iii) the tagging of flux tubes in order to increase the confidence that ground and space observations are truly conjugate. In each case the satellite observations will be discussed in the context of coherent HF and incoherent UHF radar measurements as well as high power radio heating experiments that can be employed to simulate naturally occurring processes.

Features of Excitation of Stimulated Electromagnetic Emission of the Ionosphere Modified by an Oblique High-Power Radio Wave

We present the results of measuring the characteristics of the stimulated electromagnetic emission (SEE) of the ionosphere with variation in the zenith angle of a pump beam of high-power O-mode radio waves in the geomagnetic-meridian plane. The experiments were performed at the midlatitude heating facility “Sura.” It is established that the maximum intensity of the DM and BC components of SEE is observed for southward inclination angles θ ≈ 8°--12° of the antenna beam, for which the most intense generation of artificial small-scale ionospheric irregularities also takes place. Based on the results of measurements near the fourth and fifth harmonics of the electron gyrofrequency, it is found that the first component of the BUM (BUM-1) is generated only when the pump wave reaches the plasma-resonance region. This allows one to assume that, unlike the second component of the BUM (BUM-2), whose generation is determined by development of instability in the upper-hybrid resonance region, the BUM-1 generation mechanism should be related to processes of interaction between a high-power radio wave and the plasma in the plasma-resonance region.

Prediction of the timing of the 2–3 kHz radio emission within the solar cycle

High power radio emissions near 2–3 kHz originating in the outer heliosphere have been observed by the Voyager spacecraft. Recent theories for these emissions combine acceleration of nonthermal electrons at global merged interaction region shocks with formation of a superthermal electron tail by lower‐hybrid drive associated with pick‐up ions, beyond the heliopause. This paper examines the efficiency of this process during the solar cycle, based on variations of the availability of pick‐up ions in the source region associated with periodic solar cycle variations in the solar wind ram pressure. It is predicted that high levels of pick‐up ions are present in the source region approximately 2–3 years after solar maximum, leading to strong emissions, in close agreement with the observed timing of events: the 1983–84, 1992–93 and 2003 events were preceded by solar maxima in 1980, 1990 and 2000, respectively. These results provide further evidence for the proposed model.

Experimental Studies of the Effects Observed During the Nonlinear Interaction of Two High-Power Radio Waves in a Magnetoplasma

We present the results of experiments on modification of the ionospheric F region by two high-power (Peff ≈ 20 MW) O-mode electromagnetic waves. The experiments were performed at the “Sura” heating facility of the Radiophysical Research Institute (Nizhny Novgorod, Russia) in May 23–27, 1993 at the pump frequencies near the 4th, 5th, or 6th harmonics of the electron gyrofrequency. Ionospheric perturbations were diagnosed by measuring the stationary spectral characteristics of the stimulated electromagnetic emission (SEE) of the ionospheric plasma. We determine the features of variation in the spectral characteristics of particular SEE components during the simultaneous heating of the ionospheric plasma by two radio waves in comparison with the case of a monochromatic pump wave. We observed the effect of enhanced generation of the broad up-shifted maximum (BUM) by the higher-frequency pump wave. This is accompanied by strong suppression of the BUM induced by the lower-frequency pump wave. It is shown that the effects observed during the two-frequency heating of the ionosphere have well pronounced gyroharmonic properties, i.e., depend on both the electron-gyroharmonic number and the frequency detuning of the pump waves from a harmonic of the electron gyrofrequency. We also pointed out that a change in the properties of artificial small-scale ionospheric irregularities (striations) excited by high-power radio waves is not the cause of a change in the properties of the down-shifted maximum and the BUM during the two-frequency modification of the ionospheric plasma. Ways for the further development of these studies are discussed.

Adult and childhood leukemia near a high-power radio station in Rome, Italy.

Some recent epidemiologic studies suggest an association between lymphatic and hematopoietic cancers and residential exposure to high-frequency electromagnetic fields (100 kHz to 300 GHz) generated by radio and television transmitters. Vatican Radio is a very powerful station located in a northern suburb of Rome, Italy. In the 10-km area around the station, with 49,656 residents (in 1991), leukemia mortality among adults (aged >14 years; 40 cases) in 1987-1998 and childhood leukemia incidence (eight cases) in 1987-1999 were evaluated. The risk of childhood leukemia was higher than expected for the distance up to 6 km from the radio station (standardized incidence rate = 2.2, 95% confidence interval: 1.0, 4.1), and there was a significant decline in risk with increasing distance both for male mortality (p = 0.03) and for childhood leukemia (p = 0.036). The study has limitations because of the small number of cases and the lack of exposure data. Although the study adds evidence of an excess of leukemia in a population living near high-power radio transmitters, no causal implication can be drawn. There is still insufficient scientific knowledge, and new epidemiologic studies are needed to clarify a possible leukemogenic effect of residential exposure to radio frequency radiation.

PKS 1117+146: Gravitational Lens or Micro lobes

PKS 1117+146 is a high power radio source (L327MHz=5.4 × 1026 W/Hz) identified with a galaxy of 20.1 red magnitude at z=0.362 (de Vries et al. 1995). At this redshift 1 mas ≃ 2.9 pc (H0 = 100 km/s–1Mpc–1). Based on the properties of the radio spectra, PKS 1117+146 is classified as a GigaHertz Peaked Spectrum source (GPS) (Stanghellini et al. 1990). The GPS are powerful but physically small (sub-galactic sizes) radio sources with turnovers in their radio spectra at v ≃ 1 GHz. They are supposed to be isotropically emitting radio sources confined by exceptional dense circumnuclear gas (O'Dea et al. 1991) or still relatively young (Fanti et al. 1990). PKS 1117+146 is also a low frequency variable (LFV) with no sign of variability at v &gt; 1 GHz (Padrielli et al. 1987, Mitchell et al. 1994). The low frequency variability is caused by propagation effects in the interstellar medium of our Galaxy (Mantovani et al. 1990, Spangler et al. 1993). PKS 1117+146 was observed with VLBI global arrays at 608 MHz (Padrielli et al. 1991), at 327 MHz (Altschuler et al. 1995), and at 1667 MHz (Bondi et al. 1996). All the maps are in agreement showing a compact double structure with components separated by about 70 mas. Flux densities and separation of the two components derived from VLBI and MERLIN (see below) maps are listed in Table 1. The flux ratios of the two components from the VLBI observations are very similar, and the spectral index is relatively flat (α ≃ 0.3–0.4), even if the strong low frequency variability can introduce uncertainties. The similarity of the VLBI morphology and spectral properties of the two components suggested that 1117+146 could be a possible gravitational lens candidate prompting for higher frequency observations. We observed PKS 1117+146 with MERLIN at 22 GHz in March 1993. MERLIN observations reveal for the first time a weak central component with a total flux density of about 20 mJy (Fig.1). From Table 1 we can note that the P.A. between the components is constant at all the frequencies while the separation between the peak flux densities significantly increases at higher frequencies. This is the expected behaviour if the 2 components are 2 lobes with hot-spot at the outer edges. The MERLIN map at 22 GHz seems to rule out the possibility that the morphology of PKS 1117+146 is caused by gravitational lensing.

Linear modulators based on RF synthesis: realization and analysis

A technique for generating a gain and phase modulated high power radio signal is described using RF synthesis. The realization, which uses a unique twin VCO design, can give a theoretical near 100% amplifier efficiency with excellent linearity. A number of architectures are presented supported by both analytical and simulation results. Laboratory tests have verified the predicted performance for /spl pi//4 QPSK modulation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Artificial modification of ionosphericE-layer by high power radio transmitters

Some anomalous TV receptions in India on band I have been interpreted as being propagated viaF-layer artificially modified by high power broadcast transmitters. In this paper, the possibility of VHF communication by artificially modifiedE-layer is discussed. The presented theoretical analysis shows that high-power broadcast trasmitters can produce substantial changes in temperature and ionisation in theE-layer. The rate of energy transfer from the wave to the medium particles has also been computed. Model calculations are made for a transmitter located near Calcutta. The possibility of the extra-ionisation producing field-aligned structures to support VHF communication is discussed.

Artificial Airglow Excited by High-Power Radio Waves

High-power electromagnetic waves beamed into the ionosphere from ground-based transmitters illuminate the night sky with enhanced airglow. The recent development of a new intensified, charge coupled-device imager made it possible to record optical emissions during ionospheric heating. Clouds of enhanced airglow are associated with large-scale plasma density cavities that are generated by the heater beam. Trapping and focusing of electromagnetic waves in these cavities produces accelerated electrons that collisionally excite oxygen atoms, which emit light at visible wavelengths. Convection of plasma across magnetic field lines is the primary source for horizontal motion of the cavities and the airglow enhancements. During ionospheric heating experiments, quasi-cyclic formation, convection, dissipation and reappearance of the cavites comprise a major source of long-term variability in plasma densities during ionospheric heating experiments.

Observations of ionospheric cavities generated by high-power radio waves.

High-power hf electromagnetic waves have been used to generate large electron-density cavities in the night-time $F$-region ionospheric plasma. Previous modification experiments have described induced density perturbations of only a few percent. Here we report the first observations of density depletions exceeding 50%, extending hundreds of kilometers along the geomagnetic field. These cavities are thermally driven, with electron temperatures in the depletions increased by factors of 3 to 4. The depletion dynamics exhibits many of the characteristics associated with thermal cavitons.

Nonlinear reflectivity of high-power radio waves in the ionosphere

An important result of earlier ionospheric modification experiments performed at Platteville, Colorado, was the discovery that the reflectivity of the ionosphere was greatly reduced in the reflection region of a high-power radio (pump) wave1. Because the reflectivity of low-power diagnostic waves passing through the modified region with frequencies from just below the pump wave frequency up to the F region critical frequency were reduced, the phenomenon was termed wide-band absorption (WBA). Subsequent experimental and theoretical work (for review see ref. 2) has led to the conclusion that WBA is due to the scattering of radio waves from field-aligned irregularities into plasma waves. These irregularities are generated by the interaction of the pump wave and the ionospheric plasma but the mechanism by which this occurs is not completely understood. It is evident, however, that in the process the pump wave itself undergoes WBA. In a recent campaign using the Max-Planck Institute ionospheric modification facility at Ramfjordmoen, near Tromso, Norway, the existence of WBA at high latitudes was confirmed by experiments using low-power diagnostic waves passing through the reflection region of the high-power radio wave3,4. As we report here, during an experiment to measure the effect of WBA on the pump wave itself, the essentially nonlinear nature of the interaction between the high-power radio waves and the ionosphere was demonstrated in a new and striking way.

Nonlinear Effects in the Propagation of High-Power Radio Waves in the Ionosphere

Nonlinear Effects in the Propagation of High-Power Radio Waves in the Ionosphere

VHF and UHF bistatic observations of a region of the ionosphere modified by a high power radio transmitter

VHF and UHF bistatic radar investigation of a region of the ionosphere modified by a high power transmitter has revealed two modes of scatter. The modes are described in association with parameters of the scatter region and of the received signals.

Нелинейные явления при распространении радиоволн высокой мощности в ионосфере

Нелинейные явления при распространении радиоволн высокой мощности в ионосфере

Properties of orbiting dipole belts

view Abstract Citations (13) References (1) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Properties of orbiting dipole belts Morrow, W. E., Jr. ; MacLellan, D. C. Abstract Thin microwave dipoles orbiting in belts about the earth have been proposed for reliable long-range radio communication. This paper examines the possible effects of such microwave dipole belts on radio communi- cations, radar, and measurements by optical and radio astronomers. In addition, a comparison is made of the probabilities of micrometeorite and dipole collisions with space craft. Calculations have been carried out for a proposed experimental belt consisting of 35 kg of 8000 Mc dipoles orbiting at a few thousand kilometers altitude. It is shown that no interference would be caused to radio or radar services, that such a belt produces only a few percent change in the optical brightness of the night sky in the direction of the belt, and that the influence of the belt on radio astronomy observations is not measurable except when viewing the belt where it is illuminated by very high power radio equipment operating at frequencies near the dipole resonance. Investigation also shows that micrometeorite collisions with a space craft located in a dipole belt are an order of magnitude more likely than those caused by the dipoles. Furthermore, the small mass of the dipoles limits the collision effects to little more than surface scratches. Publication: The Astronomical Journal Pub Date: April 1961 DOI: 10.1086/108384 Bibcode: 1961AJ.....66..107M full text sources ADS |

Interference between High-Power Radio Stations

Interference between High-Power Radio Stations