From Wikipedia, the free encyclopedia
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 |
a 3–30 Hz |
k 10,000–100,000 km |
Directly audible when converted to sound, communication with submarines |
| Super low frequency |
SLF |
b 30–300 Hz |
j 1,000–10,000 km |
Directly audible when converted to sound, AC power grids (50–60 Hz) |
| Ultra low frequency |
ULF |
c 300–3000 Hz |
i 100–1,000 km |
Directly audible when converted to sound, communication with mines |
| Very low frequency |
VLF |
d 3–30 kHz |
h 10–100 km |
Directly audible when converted to sound (below ca. 20 kHz; or ultrasound otherwise) |
| Low frequency |
LF |
e 30–300 kHz |
g 1–10 km |
AM broadcasting, navigational beacons, lowFER, amateur radio |
| Medium frequency |
MF |
f 300–3000 kHz |
f 100–1000 m |
Navigational beacons, AM broadcasting, amateur radio, maritime and aviation communication |
| High frequency |
HF |
g 3–30 MHz |
e 10–100 m |
Shortwave, amateur radio, citizens' band radio, skywave propagation |
| Very high frequency |
VHF |
h 30–300 MHz |
d 1–10 m |
FM broadcasting, amateur radio, broadcast television, aviation, GPR, MRI |
| Ultra high frequency |
UHF |
i 300–3000 MHz |
c 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 |
j 3–30 GHz |
b 1–10 cm |
Wireless networking, satellite links, amateur radio, microwave links, satellite television, door openers |
| Extremely high frequency |
EHF |
k 30–300 GHz |
a 1–10 mm |
Microwave data links, radio astronomy, amateur radio, remote sensing, advanced weapons systems, advanced security scanning |
[edit] See also
[edit] External links
