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shortwave bands
Shortwave bands are frequency allocations for use within the shortwave radio spectrum (the upper MF band and all of the HF band). They are the primary medium for applications such as maritime communications, 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, measured in metres. Propagation behavior on the shortwave bands depends on the time of day, the season and the level of solar activity.
==International broadcast bands==
The bands and frequencies below are derived from multiple sources, and different radios may have different frequency numbers. Most international broadcasters use amplitude modulation with 5 kHz steps between channels; a few use single sideband modulation.〔http://www.monitoringtimes.com/html/swb.html Short wave broadcast bands, retrieved 2010 Nov 19〕
The World Radiocommunication Conference (WRC), organized under the auspices of the International Telecommunication Union, allocates bands for various services in periodic conferences. The most recent WRC took place in 2012.
At WRC-97 in 1997, the following bands were allocated for international broadcasting:
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