Radio frequency

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Radio frequency (RF) is a frequency or rate of oscillation within the range of about 3 Hz to 300 GHz. This range corresponds to frequency of alternating current electrical signals used to produce and detect radio waves. Since most of this range is beyond the vibration rate that most mechanical systems can respond to, RF usually refers to oscillations in electrical circuits.


[edit] Special properties of RF electrical signals

Electrical currents that oscillate at RF have special properties not shared by direct current signals. One such property is the ease with which they can ionize air to create a conductive path through air. This property is exploited by 'high frequency' units used in electric arc welding, although strictly speaking these machines do not typically employ frequencies within the HF band. Another special property is an electromagnetic force that drives the RF current to the surface of conductors, known as the skin effect. Another property is the ability to appear to flow through paths that contain insulating material, like the dielectric insulator of a capacitor. The degree of effect of these properties depends on the frequency of the signals.

[edit] Frequencies

Name Symbol Frequency Wavelength Applications
Extremely low frequency ELF 3–30 Hz 10,000–100,000 km Directly audible when converted to sound, communication with submarines
Super low frequency SLF 30–300 Hz 1,000–10,000 km Directly audible when converted to sound, AC power grids (50–60 Hz)
Ultra low frequency ULF 300–3000 Hz 100–1,000 km Directly audible when converted to sound, communication with mines
Very low frequency VLF 3–30 kHz 10–100 km Directly audible when converted to sound (below ca. 20 kHz; or ultrasound otherwise)
Low frequency LF 30–300 kHz 1–10 km AM broadcasting, navigational beacons, lowFER, amateur radio
Medium frequency MF 300–3000 kHz 100–1000 m Navigational beacons, AM broadcasting, amateur radio, maritime and aviation communication
High frequency HF 3–30 MHz 10–100 m Shortwave, amateur radio, citizens' band radio, skywave propagation
Very high frequency VHF 30–300 MHz 1–10 m FM broadcasting, amateur radio, broadcast television, aviation, GPR, MRI
Ultra high frequency UHF 300–3000 MHz 10–100 cm Broadcast television, amateur radio, mobile telephones, cordless telephones, wireless networking, remote keyless entry for automobiles, microwave ovens, GPR
Super high frequency SHF 3–30 GHz 1–10 cm Wireless networking, satellite links, amateur radio, microwave links, satellite television, door openers
Extremely high frequency EHF 30–300 GHz 1–10 mm Microwave data links, radio astronomy, amateur radio, remote sensing, advanced weapons systems, advanced security scanning

[edit] See also

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