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Shortwave bandsShortwave bands are frequency allocations for use within the high frequency radio spectrum. They are the primary medium for applications such as marine communication, international broadcasting, and worldwide amateur radio activity because they take advantage of ionospheric skip propagation to send data around the world. The bands are conventionally stated in wavelength as measured by meters. Many bands, most notably the VHF 6 meters band, are notable for their behavior that depends on the season and the level of solar activity. The "11-meter" (27 MHz) band is the most significant location allocated by most countries for Citizen's Band service (as well as some early cordless phones), though due to the band's propagation characteristics, which allow long-distance interference with local signals, most land mobile radio activity has moved to VHF or UHF, and most cordless phone activity is also in UHF or higher. Additional recommended knowledge
International broadcasting bandsThe band frequencies below are derived from multiple sources, and different radios can have different numbers. Most international broadcasters use amplitude modulation with a stepping of 5 kHz between channels; a few use single sideband modulation. Different radios may define the bands differently.
Amateur HF bandsMarine and land mobile allocationsThe international maritime distress frequency is 2182 kHz; formerly 500 kHz was reserved for Morse Code distress signals, but this frequency allocation has been discarded in favor of systems such as GMDSS and Inmarsat. As mentioned above, most countries that have HF Citizen's Band allocations allocate 40 channels between 26.965 MHz to 27.405 MHz, in 10 kHz steps. Military HF allocationIn the US and Canada, as well as the Americas (ITU Region 2) as a whole, there are no pre-designated HF allocations for military use. Similar rules exist in Western and Eastern Europe, where it has become necessary for European amateurs to police the bands due to overcrowding. Most military HF band incursions into the HF Ham bands occur in Europe or Africa. Since the end of the Cold War, specific military HF allocations have gradually disappeared from the HF bands -- except for Africa and some parts of Asia. In Australia, the military shares the HF bands with civilian users -- this is mainly due to low population density and relative underuse of the HF bands. The military in the Americas (as well as in Australia) has tended to use the civilian fixed, maritime mobile, and aeronautical mobile allocations on an ad-hoc (non-interference) basis. Industrial/Scientific/Medical (ISM) and other HF allocationsAbove 10 MHz there are numerous frequencies set aside for Radio Astronomy, Space Research (FCC terminology), and standard frequency and time services. RF diathermy equipment uses 27.12MHz to effect heating of bulk materials or adhesives for the purpose of drying or increasing the cure rate. The industrial use of the frequency was one of the motivations to permit widespread use by the citizenry of the 11m band for CB Radio. About a dozen narrow or "sliver" allocations for ISM exist throughout the radio spectrum. See ISM band for more information. These allocations are perhaps the smallest in the HF band, with respect to national HF allocations. See also
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Shortwave_bands". A list of authors is available in Wikipedia. |