What is Ham Radio?
Ham radio is an amateur radio community that mixes elements of being a hobby and a network. Ham radio operators engage in one-way broadcasts and two-way communications with a potentially worldwide audience. "Amateur" in this sense means non-profit, in the same way that "amateur athletes" at the Olympics are not "professional." The technical skills of many ham radio operators are actually very well-developed.
Frequency Governance
Frequency band allocation for amateur radio is regulated by the International Telecommunications Union (ITU). The ITU is a venerable international organization, founded in 1865 and standing as the second-oldest international organization still operating. Its main tasks are international standardization and the international allocation of the radio spectrum. It operates under the aegis of the United Nations.
MF Use
Medium Frequency (MF) operates between 1,800 and 2,000 kHz. Using this band usually requires two separate antennas--one for receiving and one for transmitting--and even then it works well only at night. It's still noisy, even with all of these requirements. However, perhaps because of its difficulties, the MF range is not very popular, less crowded and considered something of a "gentleman's band."
General HF Use
Most ham radio operators work in the 3,500 to 4,000 kHz range, which makes this band something like the international ham radio community's equivalent of the CB radio. In the United States, UK, Norway, Iceland and a small number of other countries, frequencies around 5,000 kHz are also available, but these are regulated by channel format.
Specialized HF Use
Frequencies between 7,000 and 29,700 kHz are also sometimes available to ham radio operators in certain areas, but these bands are shared with non-amateur operators and subject to special restrictions--if they are available at all. For example, 7,000 to 7,300 kHz is very popular because of its excellent night radio wave propogation, and is even capable of medium-range broadcasting during the day. For that reason, that band is usually dominated by commercial broadcasters, and only the bottom of the band is usually available for ham radio. 10,100 to 10,150 kHz is principally used for Morse Code and data transmissions, with voice use illegal in many countries.