SWL - Shortwave Listening
Material extracted from wikipedia SWL
Shortwave listening (abbreviated as SWLing) is the hobby of listening to shortwave radio broadcasts located on frequencies between 1700 kHz and 30 MHz.  Listeners range from casual users seeking international news and entertainment programming to hobbyists immersed in the technical aspects of radio reception and DXing. In some developing countries, shortwave listening enables remote communities to obtain regional programming traditionally provided by local medium wave broadcasters. Some estimates have placed the number of shortwave listeners worldwide in the millions.
The practice of long distance radio listening began in the 1920s when shortwave broadcasters were first established in the US and Europe. Audiences discovered that international programming was available on the shortwave bands of many consumer radio receivers, and a number of magazines and listener clubs catering to the practice arose as a result. Shortwave listening was especially popular during times of international conflict such as World War II, the Korean War and the Persian Gulf War.
Listeners use inexpensive portable "world band" radio receivers to access the shortwave bands, and some advanced hobbyists employ specialized communications receivers featuring digital technology designed for optimum reception of shortwave signals, along with outdoor antennas to enhance performance.
With the advent of the internet, many international broadcasters have scaled back or terminated their shortwave transmissions in favor of web-based program distribution, while others transition to digital broadcasting modes such as Digital Radio Mondiale that allow more efficient delivery of shortwave programming. The number of organized shortwave listening clubs has diminished along with printed magazines devoted to the hobby, however many enthusiasts continue to exchange information and news on the web.