ultra high frequency

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Ultra high frequency (UHF) is the
ITU 260px, ITU Monument, Bern The International Telecommunication Union is a specialized agency of the United Nations responsible for all matters related to information and communication technologies Information and communications technology ...
designation for
radio frequencies Radio frequency (RF) is the oscillation Oscillation is the repetitive variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. The term '' vibration'' is prec ...
in the range between 300
megahertz The hertz (symbol: Hz) is the unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a discrete piece of action (or beat) in a theatric ...
(MHz) and 3
gigahertz The hertz (symbol: Hz) is the SI derived unit, derived unit of frequency in the International System of Units (SI) and is defined as one cycle (geometry), cycle per second. It is named after Heinrich Hertz, Heinrich Rudolf Hertz, the first per ...
(GHz), also known as the decimetre band as the wavelengths range from one meter to one tenth of a meter (one
decimeter The decimetre (SI symbol dm) or decimeter ( American spelling) is a unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a discrete p ...
). Radio waves with frequencies above the UHF band fall into the
super-high frequency Super high frequency (SHF) is the ITU designation for radio frequencies (RF) in the range between 3 and 30 gigahertz The hertz (symbol: Hz) is the SI derived unit, derived unit of frequency in the International System of Units (SI) an ...
(SHF) or
microwave Microwave is a form of electromagnetic radiation In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies mat ...

frequency range. Lower frequency signals fall into the VHF (
very high frequency Very high frequency (VHF) is the International Telecommunication Union, ITU designation for the range of radio frequency electromagnetic waves (radio waves) from 30 to 300 megahertz (MHz), with corresponding wavelengths of ten meters to one mete ...
) or lower bands. UHF radio waves propagate mainly by
line of sight Line of sight (adjectival form line-of-sight) may refer to: Common meanings * Sightline, an unobstructed line-of-sight between a subject and object * Line of sight (gaming), visibility on a gaming field, ''i.e.'' who can see what Arts and enterta ...
; they are blocked by hills and large buildings although the transmission through building walls is strong enough for indoor reception. They are used for
television broadcasting A television network or broadcaster is a telecommunications network for distribution of television program content, where a central operation provides programming to many television stations or pay television providers. Until the mid-1980s, te ...
,
cell phones A mobile phone, cellular phone, cell phone, cellphone, handphone, or hand phone, sometimes shortened to simply mobile, cell or just phone, is a portable telephone that can make and receive telephone call, calls over a radio frequency link wh ...

, satellite communication including
GPS The Global Positioning System (GPS), originally Navstar GPS, is a satellite-based radionavigation system owned by the United States government The federal government of the United States (U.S. federal government) is the national ...

,
personal radio service A personal radio service is any system that allows individual to operate radio transmitters and receivers for personal purposes with minimal or no special license or individual authorization. Personal radio services exist around the world and typica ...
s including Wi-Fi and Bluetooth, walkie-talkies, cordless phones, and numerous other applications. The Institute of Electrical and Electronics Engineers, IEEE defines the UHF Radio spectrum#IEEE, radar band as frequencies between 300 MHz and 1 GHz. Two other IEEE radar bands overlap the ITU UHF band: the L band between 1 and 2 GHz and the S band between 2 and 4 GHz.

# Propagation characteristics

Radio waves in the UHF band travel almost entirely by line-of-sight propagation (LOS) and ground reflection; unlike in the High frequency, HF band there is little to no reflection from the ionosphere (skywave propagation), or ground wave. UHF radio waves are blocked by hills and cannot travel beyond the horizon, but can penetrate foliage and buildings for indoor reception. Since the wavelengths of UHF waves are comparable to the size of buildings, trees, vehicles and other common objects, reflection and Knife-edge effect, diffraction from these objects can cause fading due to multipath propagation, especially in built-up urban areas. Atmospheric moisture reduces, or Attenuation, attenuates, the strength of UHF signals over long distances, and the attenuation increases with frequency. UHF TV signals are generally more degraded by moisture than lower bands, such as Very high frequency, VHF TV signals. Since UHF transmission is limited by the visual horizon to 30–40 miles (48–64 km) and usually to shorter distances by local terrain, it allows the same frequency channels to be reused by other users in neighboring geographic areas (frequency reuse). Radio repeaters are used to retransmit UHF signals when a distance greater than the line of sight is required. Occasionally when conditions are right, UHF radio waves can travel long distances by tropospheric ducting as the atmosphere warms and cools throughout the day.

# Antennas

The length of an antenna (radio), antenna is related to the length of the radio waves used. Due to the short wavelengths, UHF antennas are conveniently stubby and short; at UHF frequencies a monopole antenna, quarter-wave monopole, the most common omnidirectional antenna is between 2.5 and 25 cm long. UHF wavelengths are short enough that efficient transmitting antennas are small enough to mount on handheld and mobile devices, so these frequencies are used for two-way radio, two-way land mobile radio systems, such as walkie-talkies, two way radios in vehicles, and for portable wireless devices; cordless phones and cell phones. Omnidirectional UHF antennas used on mobile devices are usually short whip antenna, whips, sleeve dipole antenna, dipoles, rubber ducky antennas or the planar inverted F antenna (PIFA) used in cellphones. Higher gain omnidirectional UHF antennas can be made of collinear antenna array, collinear arrays of dipole antenna, dipoles and are used for mobile base stations and sector antenna, cellular base station antennas. The short wavelengths also allow directional antenna, high gain antennas to be conveniently small. High gain antennas for point-to-point (telecommunications), point-to-point communication links and UHF television reception are usually Yagi-Uda antenna, Yagi, log periodic antenna, log periodic, corner reflector antenna, corner reflectors, or reflective array antennas. At the top end of the band, slot antennas and parabolic antenna, parabolic dishes become practical. For satellite communication, helical antenna, helical, and turnstile antennas are used since satellites typically employ circular polarization which is not sensitive to the relative orientation of the transmitting and receiving antennas. For television broadcasting specialized vertical radiators that are mostly modifications of the slot antenna or reflective array antenna are used: the slotted cylinder, zig-zag, and panel antennas.

# Examples of UHF frequency allocations

## Australia

* UHF CB, UHF citizens band (Land mobile service): 476–477 MHz * Television broadcasting uses Australian and New Zealand television frequencies, UHF channels between 503 and 694 MHz * Fixed point-to-point Link 450.4875 - 451.5125 MHz * Land mobile service 457.50625 - 459.9875 MHz * Mobile satellite service: 406.0000 - 406.1000 MHz * Segment and Service examples: Land mobile for private, Australian, State and Territory Government, Rail industry and Mobile-Satellite

* 430–450 MHz: Amateur radio (70 cm band) * 470–806 MHz: Terrestrial television (with select channels in the 600 & 700 MHz bands left vacant) * 1452–1492 MHz: Digital Audio Broadcasting (L band) * Many other frequency assignments for Canada and Mexico are similar to their US counterparts

## United States

*Digital Audio Broadcasting and its regional implementations of DAB, regional implementations *Digital terrestrial television *The Thing (listening device)

# References

U.S. cable television channel frequencies
*Tomislav Stimac, "