radio wavephysics

Assorted References

• major reference ( in electromagnetic radiation: Radio waves )

  Radio waves are used for wireless transmission of sound messages, or information, for communication, as well as for maritime and aircraft navigation. The information is imposed on the electromagnetic carrier wave as amplitude modulation (AM) or as frequency modulation (FM) or in digital form (pulse modulation). Transmission therefore involves not a single-frequency electromagnetic wave but...

• Cygnus A ( in Cygnus A )

  most powerful cosmic source of radio waves known, lying in the northern constellation Cygnus about 500,000,000 light-years (4.8 × 10²¹ km) from Earth. It has the appearance of a double galaxy. For a time it was thought to be two galaxies in collision, but the energy output is too large to be accounted for in that way. Radio energy is emitted from Cygnus A at an estimated...

• eclipses ( in eclipse: Lunar research )

  ...eclipses can yield information about the cooling of the Moon’s soil when the Sun’s radiation is suddenly removed and therefore about the soil’s conductivity of heat and its structure. Infrared and radio-wavelength radiation from the Moon declines in intensity more slowly than does visible light emission during an eclipse because they are emitted from below the surface, and measurements...

• emission by radio sources ( in radio source )

  in astronomy, any of various objects in the universe that emit relatively large amounts of radio waves. Nearly all types of astronomical objects give off some radio radiation, but the strongest sources of such emissions include pulsars, certain nebulas, quasars, and radio galaxies.

• ionosphere ( in plasma: The ionosphere and upper atmosphere )

  ...chart the vertical structure of this region of the atmosphere, and numerous satellites have provided latitudinal and longitudinal information. The ionosphere was discovered in the early 1900s when radio waves were found to propagate “over the horizon.” If radio waves have frequencies near or below the plasma frequency, they cannot propagate throughout the plasma of the ionosphere...

• ionosphere and magnetosphere ( in ionosphere and magnetosphere )

  regions of Earth’s atmosphere in which the number of electrically charged particles—ions and electrons—are large enough to affect the propagation of radio waves. The charged particles are created by the action of extraterrestrial radiation (mainly from the Sun) on neutral atoms and molecules of air. The ionosphere begins at a height of about 50 km (30 miles) above the surface, but...

  in ionosphere and magnetosphere: Discovery of the ionosphere )

  ...1950 by a committee of the Institute of Radio Engineers as “the part of the earth’s upper atmosphere where ions and electrons are present in quantities sufficient to affect the propagation of radio waves.” Much of the early research on the ionosphere was carried out by radio engineers and was stimulated by the need to define the factors influencing long-range radio communication....

  in ionosphere and magnetosphere: D region )

  ...from the E and F regions in that its free electrons almost totally disappear during the night, because they recombine with oxygen ions to form electrically neutral oxygen molecules. At this time, radio waves pass through to the strongly reflecting E and F layers above. During the day some reflection can be obtained from the D region, but the strength of radio waves is reduced; this is the...

  in ionosphere and magnetosphere: Ionospheric variations )

  ...produced at high altitudes during the day maintain a sizable density of electrons at the F2 peak throughout the day and then diffuse downward at night. This accounts for the fact that radio reception (both in the broadcast and shortwave bands) is generally best at night. Ionization at lower altitudes—primarily those corresponding to the D region—tends to interfere with...

• Jupiter ( in Jupiter: Radio emission )

  Jupiter was the first planet found (in 1955) to be a source of radiation at radio wavelengths (see radio and radar astronomy). The radiation was recorded at a frequency of 22 megahertz (corresponding to a wavelength of 13.6 metres, or 1.36 decametres) in the form of noise bursts with peak intensities sometimes great enough to make Jupiter the brightest source in the sky at this wavelength,...

• radio-frequency heating ( in radio-frequency heating )

  process of heating materials through the application of radio waves of high frequency—i.e., above 70,000 hertz (cycles per second). Two methods of radio-frequency heating have been developed. One of these, induction heating, has proved highly effective for heating metals and other materials that are relatively good electric conductors. The other method, called dielectric heating,...

• shortwave radio signals ( in shortwave radio )

  ...by means of electromagnetic waves about 10 to 80 m (33 to 262 feet) in length having frequencies of approximately 29.7 to 3.5 megahertz. During the early 1920s attempts were made to transmit radio signals over long distances by bouncing them off the layers of charged particles in the Earth’s ionosphere. The success of these experiments prompted the establishment of worldwide shortwave...

• telecommunication systems ( in telecommunications media: Radio transmission )

  Radio wave propagation is not constrained by any physical conductor or waveguide. This makes radio ideal for mobile communications, satellite and deep-space communications, broadcast communications, and other applications in which the laying of physical connections may be impossible or very costly. On the other hand, unlike guided channels such as wire or optical fibre, the medium through which...