Uses of Shortwave Radio

Shortwave radio is radio transmission using shortwave frequencies, generally 1.6–30 MHz, just above the medium wave M broadcast band.

Shortwave radio is used for long distance communication by means of skywave or skip propagation, in which the radio waves are reflected or refracted back to Earth from the ionosphere, allowing communication around the curve of the Earth. Shortwave radio is used for broadcasting of voice and music, and long-distance communication to ships and aircraft, or to remote areas out of reach of wired communication or other radio services. Additionally, it is used for two-way international communication by amateur radio enthusiasts for hobby, educational and emergency purposes.

Development of Shortwave

Early radio telegraphy had used long wave transmissions. The drawbacks to this system included a very limited spectrum available for long distance communication, and the very expensive transmitters, receivers and gigantic antennas that were required. It was also difficult to beam the radio wave directionally with long wave, resulting in a major loss of power over long distances. Prior to the 1920s, the shortwave frequencies above 2 MHz were regarded as useless for long distance communication and were designated in many countries for amateur use.

Shortwave communications began to grow rapidly in the 1920s, similar to the internet in the late 20th century. By 1928, more than half of long distance communications had moved from transoceanic cables and longwave wireless services to shortwave and the overall volume of transoceanic shortwave communications had vastly increased. Shortwave also ended the need for multi-million dollar investments in new transoceanic telegraph cables and massive longwave wireless stations, although some existing transoceanic telegraph cables and commercial longwave communications stations remained in use until the 1960s.

The cable companies began to lose large sums of money in 1927, and a serious financial crisis threatened the viability of cable companies that were vital to strategic British interests. The British government convened the Imperial Wireless and Cable Conference in 1928 "to examine the situation that had arisen as a result of the competition of Beam Wireless with the Cable Services". It recommended and received Government approval for all overseas cable and wireless resources of the Empire to be merged into one system controlled by a newly formed company in 1929, Imperial and International Communications Ltd. The name of the company was changed to Cable and Wireless Ltd. in 1934.

Uses

Some major uses of the shortwave radio band are:

• International broadcasting primarily by government-sponsored propaganda or cultural stations to foreign audiences: the most common use of all.
• Domestic broadcasting: to widely dispersed populations with few longwave, mediumwave and FM stations serving them; or for specialty political, religious and alternative media networks; or of individual commercial and non-commercial paid broadcasts.
• Utility" stations transmitting messages not intended for the general public, such as aircraft flying between continents, encrypted diplomatic messages, weather reporting, or ships at sea.
• Clandestine stations. These are stations that broadcast on behalf of various political movements, including rebel or insurrectionist forces, and are normally unauthorised by the government-in-charge of the country in question. Clandestine broadcasts may emanate from transmitters located in rebel-controlled territory or from outside the country entirely, using another country's transmission facilities. Clandestine stations were used during World War II to transmit news from the Allied point of view into Axis-controlled areas. Although the Nazis confiscated many radios and executed their owners, many people continued to listen.
• Numbers Stations These stations regularly appear and disappear all over the shortwave radio band but are unlicenced and untraceable. It is believed that Numbers Stations are operated by government agencies, and are used to communicate with clandestine operatives working within foreign countries. However, no definitive proof of such use has emerged. Because the vast majority of these broadcasts contain nothing but the recitation of blocks of numbers, in various languages, with occasional bursts of music, they have become known colloquially as "Number Stations". Perhaps the most noted Number Station is the "Lincolnshire Poacher", named after the 18th century English folk song, which is transmitted just before the sequences of numbers.
• Amateur radio operators.
• Time signal and radio clock stations: In North America, WWV radio and WWVH radio transmit at these frequencies: 2500 kHz, 5000 kHz, 10000 kHz, and 15000 kHz; and WWV also transmits on 20000 kHz. The CHU radio station in Canada transmits on the following frequencies: 3330 kHz, 7850 kHz, and 14670 kHz. Other similar radio clock stations transmit on various shortwave and longwave frequencies around the world. The shortwave transmissions are primarily intended for human reception, while the longwave stations are generally used for automatic synchronization of watches and clocks.
• Over-the-horizon radar: From 1976 to 1989, the Soviet Union's Russian Woodpecker over-the-horizon radar system blotted out numerous shortwave broadcasts daily.

The term DXing, in the context of listening to radio signals of any user of the shortwave band, is the activity of monitoring distant stations. In the context of amateur radio operators, the term "DXing" refers to the two-way communications with a distant station, using shortwave radio frequencies.

The Asia-Pacific Telecommunity estimates that there are approximately 600,000,000 shortwave broadcast-radio receivers in use in 2002. WWCR claims that there are 1.5 billion shortwave receivers worldwide.

Advantages

Shortwave does possess a number of advantages over newer technologies, including the following:

• Difficulty of censoring programming by authorities in restrictive countries: unlike their relative ease in monitoring the Internet, government authorities face technical difficulties monitoring which stations (sites) are being listened to (accessed). For example, during the Russian coup against President Mikhail Gorbachev, when his access to communications was limited, Gorbachev was able to stay informed by means of the BBC World Service on shortwave.
• Low-cost shortwave radios are widely available in all but the most repressive countries in the world.
• In many countries (particularly in most third world nations and in the Eastern bloc during the Cold War era) ownership of shortwave receivers has been and continues to be widespread (in many of these countries some domestic stations also used shortwave).
• Many newer shortwave receivers are portable and can be battery-operated, making them useful in difficult circumstances. Newer technology includes hand-cranked radios which provide power without batteries.
• Shortwave radios can be used in situations where Internet or satellite communications service is temporarily or long-term unavailable (or unaffordable).
• Shortwave radio travels much farther than broadcast FM (88-108 MHz). Shortwave broadcasts can be easily transmitted over a distance of several thousands of kilometers, including from one continent to another.
• Particularly in tropical regions, SW is somewhat less prone to interference from thunderstorms than medium wave radio, and is able to cover a large geographic area with relatively low power (and hence cost). Therefore, in many of these countries it is widely used for domestic broadcasting.
• Very little infrastructure is required for long-distance two-way communications using shortwave radio. All one needs is a pair of transceivers, an antenna, and a source of energy (such as a battery, a portable generator, or the electrical grid). This makes shortwave radio one of the most robust means of communications, which can be disrupted only by interference or bad ionospheric conditions. Modern digital transmission modes such as MFSK and Olivia are even more robust, allowing successful reception of signals well below the noise floor of a conventional receiver.

https://en.wikipedia.org/wiki/Shortwave_radio