Definition

radio frequency (RF, rf, orr.f.)

See also audio frequency (AF).

Radio frequency (abbreviated RF, rf, orr.f.) is a term that refers to alternating current (AC) havingcharacteristics such that, if the current is input to an antenna, an electromagnetic (EM) field is generated suitable for wireless broadcastingand/or communications. These frequencies cover asignificant portion of the electromagnetic radiation spectrum, extending from nine kilohertz (9 kHz),the lowest allocated wireless communications frequency (it's within the range of human hearing), to thousands of gigahertz(GHz).

When an RF current is supplied to an antenna, itgives rise to an electromagneticfield that propagates through space. This field is sometimescalled an RF field; in less technical jargon it is a "radiowave." Any RF field has a wavelength that is inverselyproportional to the frequency. In the atmosphere or in outerspace, if f is the frequency in megahertz and sis the wavelength in meters, then

s = 300/f

The frequencyof an RF signal is inversely proportional to the wavelengthof the EM field to which it corresponds. At 9 kHz, the free-spacewavelength is approximately 33 kilometers (km) or 21 miles (mi). At the highestradio frequencies, the EM wavelengths measure approximately one millimeter (1 mm). As the frequency isincreased beyond that of the RF spectrum, EM energy takes the form ofinfrared (IR), visible, ultraviolet (UV), X rays, and gamma rays.

Many types of wireless devices makeuse of RF fields. Cordless and cellular telephone, radio andtelevision broadcast stations, satellite communications systems,and two-way radio services all operate in the RF spectrum. Somewireless devices operate at IR or visible-light frequencies,whose electromagnetic wavelengths are shorter than those of RFfields. Examples include most television-set remote-controlboxes, some cordless computer keyboards and mice, and a fewwireless hi-fi stereo headsets.

The RF spectrum is divided into several ranges, orbands. With theexception of the lowest-frequency segment, each band represents an increaseoffrequencycorresponding to an order of magnitude (power of 10). The tabledepictsthe eightbands in the RF spectrum, showing frequency and bandwidth ranges. TheSHF and EHFbands are often referred to as the microwave spectrum.

Designation

Abbreviation

Frequencies

Free-space Wavelengths

Very Low Frequency

VLF

9 kHz - 30 kHz

33 km - 10 km

Low Frequency

LF

30 kHz - 300 kHz

10 km - 1 km

Medium Frequency

MF

300 kHz - 3 MHz

1 km - 100 m

High Frequency

HF

3 MHz - 30 MHz

100 m - 10 m

Very High Frequency

VHF

30 MHz - 300 MHz

10 m - 1 m

Ultra High Frequency

UHF

300 MHz - 3 GHz

1 m - 100 mm

Super High Frequency

SHF

3 GHz - 30 GHz

100 mm - 10 mm

Extremely High Frequency

EHF

30 GHz - 300 GHz

10 mm - 1 mm

This was last updated in May 2008
Posted by: Margaret Rouse

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