Types of radio spectrum and their well explain frequency range

1. Extremely Low Frequencies: Extremely low frequencies (ELFs) are those in the 30- to 300-Hz range. These include ac power line frequencies (50 and 60 Hz are com¬mon) as well as those frequencies in the low end of the human hearing range.

2. Voice Frequencies: Voice frequencies (VFs) are those in the range of 300 to 3000 Hz. This is the normal range of human speech. Although human hearing extends from approximately 20 to 20,000 Hz, most intelligible sound occurs in the VF range. Very low frequencies (VLFs): include the higher end of the human hearing range up to about 15 to 20 kilohertz (kHz). Many musical instru¬ments also make sounds in this range as well as in the ELF and VF ranges. The VLF range is also used in some government and military communications. For example, VLF radio transmission is used by the navy to communicate with submarines.

3. Low Frequencies: Low frequencies (LFs) are those in the 30¬to 300-kHz range. The primary communications services in this range are those used in aeronautical and marine navigation. Frequencies in this range are also used as subcarriers. Subcarriers are signals that carry the baseband modulating information but which, in turn, modulate another higher-frequency carrier.

4. Medium Frequencies: Medium frequencies (MFs) are in the 300¬to 3000-kHz [3-megahertz (MHz)] range. The major application of frequencies in this range is AM radio broadcasting (535 to 1605 kHz). Other services in this range include variousmarine and aeronautical communications applications.

5. High Frequencies: High frequencies (HFs) are those in the 3- to 30-MHz range. These are the frequencies generally known as short waves (SWs). All kinds of twoway radio communications take place in this range as well as some shortwave radio broadcasting. Voice of America and British Broadcasting Corporation (BBC) broadcasts occur in this range. Government and military services use these frequencies for two-way communications. Amateur radio and CB communications also occur in this part of the spectrum.

6. Very High Frequencies: Very high frequencies (VHFs) cover the 30- to 300-MHz range. This is an extremely popular frequency range and is used by many services including mobile radio, marine and aeronautical communications, FM radio broadcasting (88 to 108 MHz), and television channels 2 through 13. Radio amateurs also have numerous bands in this frequency range.

7. Ultrahigh Frequencies: Ultrahigh frequencies (UHF) cover the 300--to 3000-MHz range. This too is an extremely widely used portion of the frequency spectrum. It includes the UHF television chan¬nels 14 through 67. It is also widely used for land mobile communications and services such as cellular telephones. The military services widely use these frequencies for com¬munications. In addition, some radar and navigation services occupy this portion of the frequency spectrum. Radio amateurs also have bands in this part of the spectrum. Incidentally, frequencies above the 1000pMHz [1 gigahertz (GHz)] range are called microwaves.

8. Superhigh Frequencies: The superhigh frequencies (SHFs) are those in the 3- to 30-GHz range. These are microwave frequencies that are widely used for satellite communications and radar. Some specialized forms of two-way radio communications also occupy this region.

9. Extremely High Frequencies: Extremely high frequencies (EHFs) extend from 30 to 300 GHz. Equipment used to generate and receive signals in this range is extremely complex and expensive. Presently there is only a limited amount of activity in this range, but it does include satellite communications and some specialized radar. As technological developments permit equipment advances, this frequency range will be more widely used. Signals directly above this range are generally referred to as millimeter waves.

10. Infrared: Those electromagnetic signals whose frequen¬cies are higher than 300 GHz are not referred to as radio waves. Special names are given to the various bands in the spectrum beyond that point. The infrared region is sandwiched between the highest radio frequencies and the visible portion of the electromagnetic spectrum. It occupies the range between approximately 0.01 millimeter (mm) and 700 nanometers (nm) or 0.7 to 10 mi¬crons (µm). Infrared frequencies are often given in microns, where a micron is one millionth of a meter (m), or in nanometers or one billionth of a meter (10-9 m). Infrared is divided into two areas, long infrared (0.01 mm to 1000 nm) and short infrared (1000 to 700 nm).