Radio frequency
2008/9 Schools Wikipedia Selection. Related subjects: Physics
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 or electromagnetic radiation.
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 it can ionize air to create a conductive path through air. This property is exploited by 'high frequency' units used in electric arc welding. 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.
Frequencies
| Name | Symbol | Frequency | Wavelength | Applications |
|---|---|---|---|---|
| Extremely low frequency | ELF | 3 to 30 Hz | 10,000 km to 100,000 km | directly audible when converted to sound, communication with submarines |
| Super low frequency | SLF | 30 to 300 Hz | 1,000 km to 10,000 km | directly audible when converted to sound, AC power grids (50 hertz and 60 hertz) |
| Ultra low frequency | ULF | 300 to 3000 Hz | 100 km to 1,000 km | directly audible when converted to sound, communication with mines |
| Very low frequency | VLF | 3 to 30 kHz | 10 km to 100 km | directly audible when converted to sound |
| Low frequency | LF | 30 to 300 kHz | 1 km to 10 km | international broadcasting, navigational beacons, lowFER |
| Medium frequency | MF | 300 to 3000 kHz | 10 m to 1 km | navigational beacons, AM broadcasting, maritime and aviation communication |
| High frequency | HF | 3 to 30 MHz | 10 m to 100 m | shortwave, citizens' band radio |
| Very high frequency | VHF | 30 to 300 MHz | 1 m to 10 m | FM broadcasting, broadcast television, aviation, GPR |
| Ultra high frequency | UHF | 300 to 3000 MHz | 10 cm to 100 cm | broadcast television, mobile telephones, wireless networking, remote keyless entry for automobiles, microwave ovens, GPR |
| Super high frequency | SHF | 3 to 30 GHz | 1 cm to 10 cm | wireless networking, satellite links, microwave links, Satellite television, door openers. |
| Extremely high frequency | EHF | 30 to 300 GHz | 1 mm to 10 mm | microwave data links, radio astronomy, remote sensing, advanced weapons systems, advanced security scanning |