Shortwave radio is a type of long-range radio transmission that bounces signals off a layer of the atmosphere to be received in another part of the world. The shortwave spectrum is made of groups of frequencies between about 3 and 30 megahertz (mHz).
Shortwave radio depends largely on special layer of the Earth's atmosphere called the ionosphere. The ionosphere, located about 100 miles (160 km) over the earth's surface, has the unique ability of being able to reflect certain radio frequencies. Unlike AM and FM radio, shortwave frequencies can bounce off of the ionosphere and be heard many thousands of miles away. This allows users to be able to hear shortwave broadcasters from other countries throughout the world. The ionosphere typically bounces the widest variety of shortwave frequencies at night, especially within a few hours of sunset and sunrise.
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The unique ability of these radio transmissions to travel large distances have led to many uses. Radio broadcasters in almost every country worldwide transmit on shortwave frequencies. Some famous broadcasters, such as the Voice of America in the US and the BBC in the UK, broadcast news in many languages, allowing listeners to hear news that might not be broadcast at home. Other listeners prefer to learn more about certain countries or pick up a new language through classes broadcast on some stations. Shortwave radio has also attracted a number of hobbyists who listen to it for fun. Many of them will attempt to listen to stations in as many countries as possible.
Another use of the shortwave radio spectrum is amateur, or "ham" radio. Amateur radio hobbyists transmit and receive messages from hobbyists in other countries. Unlike shortwave listeners, who only listen to stations, amateur radio operators must typically pass a government-run licensing examination and follow certain rules to ensure safety and orderly use of the radio spectrum. In addition to being a hobby, amateur radio operators regularly assist in disasters when other forms of communication are unavailable.
A wide variety of shortwave radios are on the market today for almost any budget. Radios range from battery-powered portable models to desktop versions. Costs vary as well, ranging from under $100 to more than $1000. More expensive models tend to have more features, including electronic displays and preset memory settings. While a typical telescopic antenna on a portable model is sufficient to receive many of the popular shortwave stations, some hobbyists construct more elaborate antenna systems to receive weaker transmissions from areas farther away.