Quezi

This modern shortwave radio comes complete with an emergency light and crank charger. Thomas Rockstar photo. CC-BY.

If you’ve ever tuned across the AM radio band late at night, chances are you’ve heard radio stations from far away that you can’t hear during the daytime. What’s happening is that the radio signals are bouncing off the ionosphere, an area in the upper reaches of the atmosphere where ultraviolet light from the sun affects subatomic particles in such a way that radio signals can bounce off them. The principle behind shortwave radio is the same — radio broadcasters use frequencies that readily bounce off the ionosphere in order to reach audiences hundreds or even thousands of miles away.

The shortwave radio bands extend from a frequency of about 1.7 megahertz (the top of the AM broadcasting band in many areas) to around 30 megahertz (the lower level of what is considered VHF broadcasting). At the lower and of the shortwave band, signals bounce off the ionosphere at night, while at the upper end, they tend to bounce off the ionosphere during daylight hours. At much higher frequencies, such those used by FM and TV broadcasters, signals don’t bounce off the ionosphere at all except under unusual circumstances.

Shortwave radio isn’t used as much as it used to be, partly because satellites and the Internet have reduced the cost of international communications and made it more reliable than shortwave can be. But shortwave radio still has its uses. Many governments of the world still use shortwave radio — two of the biggest shortwave broadcasters are the Voice of America and the BBC Radio World Service — to provide news or propaganda to areas where local broadcasting is sparse or restricted by local governments. Many religious organizations use shortwave broadcasts to reach a broad international audience that can’t be reached by conventional broadcasting. Some governments and organizations broadcast to geographically dispersed audiences in languages such as Swahili. And amateur radio operators use shortwave radio as a hobby, seeing how many foreign countries they can contact or seeing how well they can communicate with only a few watts of power, sometimes using Morse Code.

The technology needed for picking up most shortwave broadcasts isn’t particularly sophisticated — AM receivers made to pick up the shortwave bands can be purchased in the U.S. for under $50, but of course it is possible to spend hundreds for ones that are designed to pick up weak signals or separate the signals of stations that are broadcasting on about the same frequency. There is also a move toward the use of digital shortwave, which traditional receivers can’t decipher. People who listen to shortwave radio as a hobby are known as SWLers (for shortwave listeners), and they often collect postcards (known as QSLs) from shortwave stations they have heard.

Even with an inexpensive shortwave radio it’s possible to pick up stations from throughout the world. While walking home at night in the Northwestern U.S. carrying a handheld shortwave receiver, I’ve listened to many broadcasts in Spanish, sometimes from Cuba, and have heard Radio Vatican and various Protestant missionary broadcasts. There are even a few stations, some of them of a right-wing political nature, that target U.S. audiences. Most interestingly, I’ve run across one of the mysterious Spanish-language “numbers stations,” stations that broadcast nothing but a series of numbers. Supposedly, these broadcasts are used to send messages to spies in a way that is untraceable to the recipient.

One good source of information for those getting started at shortwave listening is Prime Time Shortwave, which offers an up-to-date list of English-language program schedules for a variety of stations.