A clandestine radio station usually sounds like any other broadcasting station. However "legitimate" a clandestine station might sound, however, it is "extralegal" and deceptive in its operation. Here are some key elements that distinguish a clandestine broadcaster from "ordinary" broadcasters:

Clandestine broadcasters are deceptive. They often lie about their location, sponsoring government or organization, and their intentions. Programming is essentially propaganda, and may largely be half-truths or outright lies.

Clandestine broadcasters aim to bring about political changes or actions in a target country. They may want to incite revolution in another country or simply to influence the populace of the target country to be more sympathetic toward the country or organization operating the clandestine.

Clandestine broadcasters are temporary. Since the purpose of a clandestine is political, clandestine stations usually leave the air quickly when political situations change. Numerous clandestines were active in and around Vietnam during the late 1960s, but all went off the air when North Vietnam conquered South Vietnam in 1975.

Clandestine broadcasting began in World War II, with the Allied and Axis nations directing broadcasts toward each other. In fact, the longest-running clandestine station in history started in 1941. After Franco’s victory in the Spanish Civil War, the Spanish Communist Party set up a station called Radio España Independiente. This station at first broadcast from the USSR, and after World War II used transmitters in Eastern Bloc nations as well. It remained on the air until 1977, when it left the air following Franco’s death.

The busiest era for clandestine broadcasting was the 1960s. In addition to the stations active during the Vietnam War, China and the USSR operated clandestine broadcasters against each other as their ideological conflict worsened. For most SWLs in North America, however, the real excitement involved clandestine broadcasters directed against Cuba. The most famous of these was Radio Swan/Radio Americas.

Radio Swan first appeared on 1160 and 6000 kHz in May, 1960. The station claimed to be a commercial station broadcasting from Swan Island, an island in the Gulf of Mexico that was claimed both by the United States and Honduras. It broadcast entirely in Spanish, and its programs had a strong anti-Castro slant. Despite being on what the United States claimed as its territory, the FCC claimed it had no knowledge of Radio Swan.

Radio Americas solicited reception reports to a post office box in Miami, and replied with this colorful QSL card. The location of Swan Island is indicated by the station's name in the middle of the card. This card was received by Harry Helms for reception on 1160 kHz on May 18, 1966. In 1966, the only station on 1160 at night was KSL in Salt Lake City, and Radio Americas could be well heard east of the Rockies.

During the ill-fated May, 1961 Bay of Pigs invasion, Radio Swan transmitted coded messages to the invading forces. This resulted in widespread speculation that the station was actually a CIA operation. Later in 1961, Radio Swan changed its name to Radio Americas and remained on the air until it abruptly left the air in May, 1968.

As of 1997, the hot spot for clandestine radio activity is the Middle East, with Iraq being both the main target of, and the main instigator of, clandestine activity. Main stations operated against Iraq tried to stir up rebellion among Iraq’s Kurdish population. Iraq does the same with clandestines targeting Iran and Saudi Arabia. In Asia, both North Korea and South Korea operate clandestine stations directed against each other.

Colombia is home to two currently active clandestines, Radio Patria Libre and La Voz de la Resistencia. These are interesting because both apparently operate within Colombia itself from rebel-controlled areas. The frequencies of these two stations vary, but they are currently active from 6250 to 6260 kHz around 2200 to 2300 UTC.

Most clandestine stations are operated by governments, but a few are operated by private organizations with the tolerance of a host country. An example is the last remaining anti-Castro clandestine, La Voz del Cuba Independiente y Democrática (CID). Currently, this station is still heard sporadically during the evening and night hours in North America around 6305 kHz. It is rumored to be operating from Guatemala.

The last anti-Castro clandestine still active is La Voz del Cuba Independiente y Democrática, funded by Cuban exile groups and believed to be broadcasting from Guatemala.

Clandestine radio is an exciting specialty within the SWLing hobby. Political intrigue, stations that suddenly appear and disappear from the air, and the challenge of pulling a weak signal out of the noise—what more could a dedicated SWL want?