Editing Shortwave radio (section)

===Amateur use of shortwave propagation===
[[File:Tuning dial, Hallicrafters SX-28.png|thumb|right|[[Hallicrafters SX-28]] shortwave receiver analog tuning dial, {{circa}} 1944]]
[[Amateur radio|Amateur radio operators]] also discovered that long-distance communication was possible on shortwave bands. Early long-distance services used [[surface wave]] propagation at [[Very low frequency|very low frequencies]],<ref>{{cite web |website=Stormfax.com |title=Marconi wireless on Cape Cod |url=http://www.stormfax.com/wireless.htm |access-date=2009-05-24 |archive-date=2008-10-24 |archive-url=https://web.archive.org/web/20081024192918/http://www.stormfax.com/wireless.htm |url-status=live}}</ref> which are attenuated along the path at wavelengths shorter than 1,000&nbsp;meters. Longer distances and higher frequencies using this method meant more signal loss. This, and the difficulties of generating and detecting higher frequencies, made discovery of shortwave propagation difficult for commercial services.

Radio amateurs may have conducted the first successful transatlantic tests in December&nbsp;1921,<ref name=RCA1921/> operating in the 200&nbsp;meter [[mediumwave]] band (near 1,500&nbsp;kHz, inside the modern AM broadcast band), which at that time was the shortest wavelength / highest frequency available to amateur radio. In 1922 hundreds of North American amateurs were heard in Europe on 200&nbsp;meters and at least 20&nbsp;North American amateurs heard amateur signals from Europe. The first two-way communications between North American and Hawaiian amateurs began in 1922 at 200&nbsp;meters. Although operation on wavelengths shorter than 200&nbsp;meters was technically illegal (but tolerated at the time as the authorities mistakenly believed that such frequencies were useless for commercial or military use), amateurs began to experiment with those wavelengths using newly available [[vacuum tube]]s shortly after World War&nbsp;I.

Extreme interference at the longer edge of the 150–200&nbsp;meter band – the official wavelengths allocated to [[amateur radio operators|amateurs]] by the Second National Radio Conference<ref name=RadSvcBlt_1923/> in 1923 – forced amateurs to shift to shorter and shorter wavelengths; however, amateurs were limited by regulation to wavelengths longer than 150&nbsp;meters (2&nbsp;MHz). A few fortunate amateurs who obtained special permission for experimental communications at wavelengths shorter than 150&nbsp;meters completed hundreds of long-distance two-way contacts on 100&nbsp;meters (3&nbsp;MHz) in 1923 including the first transatlantic two-way contacts.<ref name=Raide_1998/>

By 1924 many additional specially licensed amateurs were routinely making transoceanic contacts at distances of 6,000&nbsp;miles (9,600&nbsp;km) and more. On 21&nbsp;September 1924 several amateurs in California completed two-way contacts with an amateur in [[New Zealand]]. On 19&nbsp;October amateurs in New Zealand and England completed a 90&nbsp;minute two-way contact nearly halfway around the world. On 10&nbsp;October the Third National Radio Conference made three shortwave bands available to U.S. amateurs<ref name=ThirdNRC_1924/> at [[80-meter band|80&nbsp;meters]] (3.75&nbsp;MHz), [[40-meter band|40&nbsp;meters]] (7&nbsp;MHz) and [[20-meter band|20&nbsp;meters]] (14&nbsp;MHz). These were allocated worldwide, while the [[10-meter band|10&nbsp;meter band]] (28&nbsp;MHz) was created by the Washington International Radiotelegraph Conference<ref name=Continelli_1996/> on 25&nbsp;November 1927. The [[15-meter band|15&nbsp;meter band]] (21&nbsp;MHz) was opened to amateurs in the United States on 1&nbsp;May 1952.