AMATEUR RADIO

            Amateurradio

                                                  

RADIO

amateur radio, also called ham radio, noncommercial two-way radio communications. Messages are sent either by voice or in International Morse Code.

Interest in amateur radio arose around the turn of the 20th century, shortly after Italian inventor Guglielmo Marconi successfully sent the first transatlantic wireless signal in 1901. The interference of amateur broadcasts with commercial and military transmissions led to the institution of government control in 1911. After World War I, amateurs became active in radio experimentation, contributing to developments in long-distance broadcasting and becoming the first radio operators successfully to exploit the upper medium-frequency and lower high-frequency radio bands. Over the years, amateur radio operators have also provided emergency communications during forest fires, floods, hurricanes, and other disasters. They serve as an important link between stricken communities and the outside world until normal communications are reestablished.

Amateur radio operators in the United States are subject to international and federal regulations. There are three classes of licenses; all require a knowledge of radio theory and regulation. Amateur radio is allocated frequency bands across the radio spectrum, from medium frequency (e.g., 1.8–2 megahertz) to ultrahigh frequency (up to 1300 megahertz). There are restrictions on the power of the transmitters, and certain frequencies must be shared with due regard for the needs of other users.

     Satellite radio

satellite radio, type of digital broadcast, which transmits audio signals over large areas with greater clarity and consistency than conventional radio.

A satellite radio service works by transmitting its signal from a ground-based station to one or more satellites orbiting Earth. The satellite bounces the signal back to specialized receivers on the ground, commonly located in automobiles and home stereo systems. Because the signal is broadcast from outer space, it can reach across an entire continent. Ground-based repeaters augment the signal in urban areas where tall buildings might cause interference. In the United States, satellite radio operates on the 2.3 gigahertz (GHz) S band of the electromagnetic spectrum; elsewhere, it often uses the 1.4 GHz L band.

                                              

SATELLITE RECEIVER

Most satellite radio services operate on a subscription model. A consumer buys a proprietary receiver, which is activated with the purchase of a subscription. Once activated, a receiver can decode the satellite’s encrypted digital signals. Satellite radio typically offers a much clearer signal and greater dynamic range than conventional radio, often approaching the sound quality of compact discs (CDs). Services typically offer a hundred or more channels, including music, news, talk, and sports. Many channels are free of advertising.

              

In the United States, rivals XM Satellite Radio and Sirius Satellite Radio, launched in 2001 and 2002, respectively, competed to attract exclusive talent, such as television host Oprah Winfrey and radio star Howard Stern. However, the splitting of marquee stars between the two services, along with a similar split in sports programming, hampered both companies. Laden by debt, the two companies merged in 2008, and the newly formed company, named Sirius XM Radio, became the sole American satellite radio provider (they remained separate entities in Canada).

satellite station