Everything about Uhf totally explained
Ultra high frequency (UHF) designates a range (
band) of
electromagnetic waves with
frequencies between 300
MHz and 3
GHz (3,000 MHz). Also known as the
decimeter band or
decimeter wave as the wavelengths range from ten to one
decimeters. Radio waves with frequencies above the UHF band fall into the SHF (
Super high frequency) and EHF (
Extremely high frequency) bands; all of which fall into the
Microwave frequency range. Lower frequency signals fall into the VHF (
Very high frequency) or lower bands. See
electromagnetic spectrum for a full listing of frequency bands.
Uses
UHF and VHF are the most commonly used frequency bands for transmission of
television signals. Modern
mobile phones also
transmit and receive within the UHF spectrum. UHF is widely used by public service agencies for two-way radio communication, usually using narrowband
frequency modulation, but digital services are on the rise. There has traditionally been very little radio broadcasting in this band until recently; see
digital audio broadcasting for details. The
Global Positioning System also uses UHF.
One uncommon use of UHF waves is for the detection of
partial discharges. Partial
discharges occur because of the sharp geometries created in high
voltage insulated equipment. The advantage of UHF detection is that this method can be used to localize the source of the discharge. A drawback to UHF detection is the extreme sensitivity to external noise. UHF detection methods are used in the field, especially for large distribution
transformers.
2.45 GHz, now mainly used for
WiFi,
Bluetooth and US
cordless phones has been proposed for
Wireless energy transfer. Some pilot experiments have been performed, but it isn't used on a large scale.
Amateur radio operators also operate in several UHF bands.
Characteristics and advantages
The point to point transmission of radio waves is affected by many variables. Atmospheric moisture, the stream of particles from the sun called
solar wind, and time of day will all have an effect on the signal transmission. All radio waves are partially absorbed by atmospheric moisture. Atmospheric absorption reduces, or
attenuates, the strength of radio signals over long distances. The effects of attenuation increases according to the frequency. UHF signals are generally more degraded by moisture than lower bands such as VHF. The layer of the Earth's atmosphere called the
ionosphere is filled with charged particles that can reflect radio waves. The reflection of radio waves can be helpful in transmitting a radio signal over long distances as the wave repeatedly bounces from the sky to the ground. UHF benefits less from the effects of reflection than lower (VHF, etc.) frequencies. UHF transmissions may be enhanced by
tropospheric ducting as the atmosphere warms and cools throughout the day.
The main advantage of UHF transmission is the physically short wave that's produced by the high frequency. The size of transmission and reception equipment, (particularly
antennas), is related to the size of the radio wave. Smaller and less conspicuous antennas can be used with higher frequency bands.
UHF is widely used in two-way radio systems and
cordless telephones. UHF signals travel over line-of-sight distances. Transmissions generated by two-way radios and cordless telephones don't travel far enough to interfere with local transmissions. A number of public safety and business communications are handled on UHF. Civilian applications such as
GMRS,
PMR446,
UHF CB, and
802.11b ("WiFi") are popular uses of UHF frequencies. A
repeater is used to propagate UHF signals when a distance that's greater than the line-of-sight is required.
History
Australia
In
Australia, UHF was first anticipated in the mid
1970s with TV channels 28 to 69. The first UHF TV broadcasts in Australia were operated by
Special Broadcasting Service (SBS) on channel 28 in
Sydney and
Melbourne starting in 1980, and translator stations for the
Australian Broadcasting Corporation (ABC). The UHF band is now used extensively as
ABC, SBS, commercial and community (
public access) television services have expanded particularly through regional areas.
Australia also provides the
UHF CB service for general-purpose two-way communications.
Ireland
In the
Republic of Ireland, UHF was introduced in 1978 to augment the existing
RTÉ One VHF 625-line transmissions and to provide extra frequencies for the new
RTÉ Two channel. The first UHF transmitter site was
Cairn Hill in
Co. Longford, followed by
Three Rock Mountain in South
Co. Dublin. These sites were followed by
Clermont Carn in
Co. Louth and
Holywell Hill in
Co. Donegal in 1981. Elsewhere in Ireland, both the RTÉ channels are available on VHF. Since then RTÉ have migrated nearly all their low-power relay sites to UHF. TV3 and TG4 are transmitted entirely in UHF only. When
Digital Terrestrial TV is introduced, it's intended to broadcast this on UHF only initially, although VHF allocations exist. VHF TV is likely to cease whenever the existing
analogue broadcasts are switched off. The UHF band is also used in parts of Ireland for Television deflector systems bringing British television signals to towns and rural areas which can't receive these signals directly
Malaysia
UHF broadcasting was used outside
Kuala Lumpur and the
Klang Valley by private TV station
TV3 in the late 80s, with the government stations only transmitting in VHF (Bands 1 and 3) and the 450 MHz range being occupied by the ATUR cellular phone service operated by
Telekom Malaysia. The ATUR service ceased operation in the late 90s, freeing up the frequency for other uses. UHF wasn't commonly used in the Klang Valley until 1994 (despite TV3's signal also being available over UHF Channel 29, as TV3 transmitted over VHF Channel 12 in the Klang Valley). 1994 saw the introduction of the channel MetroVision (which ceased transmission in 1999, got bought over by TV3's parent company - System Televisyen Malaysia Berhad - and relaunched as
8TV in 2004). This was followed by
Ntv7 in 1998 (also acquired by TV3's parent company in 2005) and recently
Channel 9 (which started in 2003, ceased transmission in 2005, was also acquired by TV3's parent company shortly after, and came back as TV9 in early 2006). At current count, there are 4 distinct UHF signals receivable by an analog TV set in the Klang Valley: Channel 25 (8TV), Channel 29 (TV3 UHF transmission), Channel 37 (NTV7) and Channel 39 (TV9). Channel 35 is usually allocated for VCRs, decoder units (for example the ASTRO and MiTV
set top boxes) and other devices that have an RF signal generator (for example game consoles).
United Kingdom
In the
UK, UHF television began in 1964 following a plan by the
GPO to allocate sets of frequencies for 625-lined television to regions across the country, so as to accommodate four national networks with regional variations (the VHF allocations only allowed for only two such networks using 405 lines). The UK UHF channels would range from 21 to 68 (later extended to 69) and regional allocations were generally grouped close together to allow for the use of aerials designed to receive a specific sub-band with greater efficiency than wider-band aerials could. Aerial manufacturers would therefore divide the band into over-lapping groups; A (channels 21-34), B (39-53), C/D (48-68) and E (39-68). The first service to use UHF was
BBC2 in
1964 followed by
BBC1 and
ITV (already broadcast on VHF) in
1969 and
Channel 4/
S4C in 1982.
PAL colour was introduced on UHF only in
1967 (for BBC2) and
1969 (for BBC1 & ITV).
As a consequence of achieving maximum national coverage, signals from one region would typically over-lap with that of another, which was accommodated for by allocating a different set of channels in each adjacent area, often resulting in greater choice for viewers when a network in one region aired different programmes to the neighbouring region.
Initial uptake of UHF television was very slow: Differing propagation characteristics between VHF and UHF meant new additional transmitters needed to be built, often at different locations to the then-established VHF sites, and generally with a larger number of relay stations to fill the greater number of gaps in coverage that came with the new band. This led to poor picture quality in bad coverage areas, and many years before the service achieved full national coverage. In addition to this, the only exclusively UHF service, BBC2, would run for only a few hours a day and comprised of alternative programming for minority audiences in contrast to the more
popularist schedules of BBC1 and ITV. However the 1970s saw a large increase in UHF TV viewing, and VHF take a significant decline: The appeal of colour, which was never introduced to VHF (despite preliminary plans to do so in the late 1950s and early 1960s) and the fall in television prices saw most households use a UHF set by the end of that decade. With the second and last VHF television service having launched in
1955, VHF TV was finally decommissioned for good in
1985 with no plans for it to return to use.
The launch of
Channel 5 in
1997 added a fifth national television network to UHF, requiring deviation from the original frequency allocation plan of the early 1960s and the allocation of UHF frequencies previously not used for television (such as UK Channels 35 and 37 which was previously reserved for domestic
VCRs requiring an expensive VCR re-tuning programme funded by the new network). A lack of capacity within the band to accommodate a fifth service with the complex over-lapping led to the fifth and final network having a significantly reduced national coverage compared to the other networks, with reduced picture quality in many areas and the use of wide-band aerials often required.
The launch of
digital terrestrial television in 1998 saw the continued use of UHF for television, with six
multiplexes allocated for the service, all within the UHF band. However
analogue transmissions have been planned to cease completely by
2012 after which time it's uncertain as to whether the vacated capacity will be used for additional digital television services or put into alternative use, such as mobile telecommunications or internet services.
United States
On
December 29,
1949,
KC2XAK of
Bridgeport, Connecticut, became the first UHF television station to operate on a regular daily schedule. The first commercially licensed UHF television station on the air was
KPTV/Channel 27 (now VHF Channel 12) in
Portland, Oregon, on
September 18,
1952. The station even used much of the equipment, including the transmitter, from KC2XAK, which was delivered by high-speed freight train.
Hopes that UHF would allow dozens of television stations in every
media market were thwarted by poor
image frequency rejection in
superheterodyne tuners with 45.75 MHz
intermediate frequency. This shortcoming led to "UHF taboos," which limited each area to only modestly more UHF than VHF stations, despite the much larger number of channels. See
(External Link
)
In the United States, UHF stations (broadcast channels above 13) originally gained a reputation for being locally owned, less polished and professional, not as popular, and having weaker signal propagation than their VHF counterparts (channels 2 through 13). The movie
UHF, starring
"Weird Al" Yankovic and
Michael Richards, parodied the phenomenon. In the late 1940s/early 1950s, affiliates of the four major US
television networks (
NBC,
CBS,
ABC and
DuMont) transmitted their programs primarily through VHF. Most UHF stations that operated in major population centers of the USA were unable to obtain network affiliation and thus were independent stations. ABC and DuMont, being smaller and less prosperous networks, did have a number of UHF affiliates, and the later
PBS had even more. Conversely, many mid-sized and small television markets within the United States were too close to the outer fringe of the broadcast range of VHF stations from major population centers to qualify for their own VHF licenses from the
FCC, because of interference from would-be overlapping broadcast ranges. Instead, the FCC granted many mid- and small-sized cities only UHF licenses (even for the big three networks), because of the vastly greater number of available channels (56 total UHF channels vs. only 12 total VHF).
A minority of UHF TV transmitters have no programming or commercial identity of their own, and merely retransmit the signal of a VHF station that owns it, to a smaller area poorly covered by the VHF signal. Such transmitters are called "
translators" rather than “stations”.
The distinction between UHF and VHF characteristics has declined in importance with the emergence of additional broadcast television networks (
Fox,
The CW,
MyNetworkTV,
Univision,
Telemundo and
ION), and the decline of direct
OTA reception. The
concentration of media ownership, the proliferation of
cable television,
digital television and
DBS have contributed to the quality equalization of VHF and UHF broadcasts. Most
HDTV stations broadcast over-the-air signals in the UHF band.
The
Family Radio Service and
General Mobile Radio Service use the 462 and 467 MHz areas of the UHF spectrum. There is a considerable amount of (legal) unlicensed activity (cordless phones, wireless networking) clustered around 900 MHz and 2.4 GHz.
In February 2009, as part of the
transition from analog to digital over-the-air broadcast of television, the spectrum from 698 MHz to 806 MHz (UHF channels 52-69) will no longer be used for TV broadcasting. The
FCC's scheduled
auction for this newly-available spectrum was completed in March 2008.
(External Link)
Frequency allocation
Australia
UHF Citizens Band: 476.425–477.400 MHz
United Kingdom
380–395 MHz: Terrestrial Trunked Radio (TETRA) service for emergency use
430–440 MHz: Amateur radio (ham - 70 cm band)
606–614 MHz: Protected for radio-astronomy
470–862 MHz: TV channels 21–69 (channel 36 used for radar, channel 38 used for radio astronomy, channel 69 used for licenced and licence exempt wireless microphones, channels 31-40 and 63-68 to be released and may be made available for other uses by Ofcom. Public consultation due December 2006)
1240–1316 MHz: Amateur radio (ham - 23 cm band)
1880–1900 MHz: DECT Cordless telephone
2310–2450 MHz: Amateur radio (ham - 13 cm band)
United States
A brief summary of some UHF frequency use:
300–420 MHz: Government use, including meteorology and federal two-way use
420–450 MHz: Government radiolocation and amateur radio (ham - 70 cm band)
450–470 MHz: UHF business band, General Mobile Radio Service, and Family Radio Service 2-way "walkie-talkies", public safety
470–512 MHz: TV channels 14–20
512–698 MHz: TV channels 21–51 (channel 34 used sometimes for radar, channel 37 used for radio astronomy)
698–806 MHz: TV channels 52–69 (was auctioned in March 2008; bidders will get full use once conversion to digital TV has been accomplished which is scheduled for February 2009)
806–824 MHz: Pagers (formerly TV channels 70–72)
824–849 MHz: AMPS A & B franchises, terminal (mobile phone) (formerly TV channels 73–77)
849–869 MHz: Public safety 2-way (fire, police, ambulance — formerly TV channels 77–80)
869–894 MHz: AMPS A & B franchises, base station (formerly TV channels 80–83) (one translator is still in use on channel 83)
902–928 MHz: ISM band: cordless phones and stereo, radio frequency identification, datalinks, amateur radio (33 cm band)
928–960 MHz: Mixed studio-transmitter links, mobile 2-way, paging, other.
1240–1300 MHz: Amateur radio (ham - 23 cm band)
1850–1910 MHz: PCS mobile phone—note below
1920–1930 MHz: DECT Cordless telephone
1930–1990 MHz: PCS base stations—note below
note: order is A, D, B, E, F, C blocks. A, B, C = 15 MHz; D, E, F = 5 MHz
2300–2310 MHz: Amateur radio (ham - 13 cm band, lower segment)
2310–2360 MHz: Satellite radio (Sirius and XM)
2390–2450 MHz: Amateur radio (ham - 13 cm band, upper segment)
2400–2483.5 MHz: ISM, IEEE 802.11, 802.11b, 802.11g Wireless LAN, IEEE 802.15.4, Bluetooth
around 2450 MHz: Microwave ovenFurther Information
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