The Radio Spectrum

Radio transmissions are regulated in the United States by the Federal Communications Commission (FCC) and the National Telecommunications and Information Administration (NTIA). The FCC is an independent regulatory agency which administers spectrum for non-Federal Government use. The NTIA is an operating unit of the Department of Commerce which administers spectrum for Federal Government use.

The FCC and NTIA arbitrarily define that the radio spectrum in the United States is that part of the natural spectrum of electromagnetic radiation lying between the frequency limits of 9 kilohertz and 300 gigahertz. That is a merely legal definition for regulatory purposes. There is no scientific reason that radio transmissions cannot be made at lower or higher frequencies, although there are serious technical problems associated with using lower or higher frequencies in most practical radio applications at the current state of the art.

The electromagnetic spectrum is divided various ways into many individually-named sub-spectrums. The following names are commonly used to identify some of the lower portions:

3 kHz to 30 kHz Very Low Frequencies (VLF)

30 kHz to 300 kHz Low Frequencies (LF)

300 kHz to 3,000 kHz Medium Frequencies (MF)

3,000 kHz to 30,000 kHz High Frequencies (HF)

30,000 kHz to 300,000 kHz Very High Frequencies (VHF)

300,000 kHz to 3,000,000 kHz Ultra High Frequencies (UHF)

Those named portions are all within the larger portion arbitrarily defined for regulatory purposes as the radio spectrum, except for the small 6 kHz portion from 3 kHz to 9 kHz. Each of the portions above are further subdivided into many other sub-portions or "bands." For example, the American AM Broadcast Band extends from 535 kHz to 1705 kHz, which is within the portion known as Medium Frequencies. AM Broadcast Band stations are therefore Medium Frequency stations, but not all Medium Frequency stations transmit within the AM Broadcast Band.
Examples of other named "bands" are the Amateur Radio Bands, Citizen Band, and International Broadcast Bands. Those bands are named by their approximate wavelengths (although some have more than one name). Band frequency limits vary to some extent in different countries, but many are the same or similar. They also are subject to regulatory changes from time-to-time.

sources http://www.smeter.net/