Ultra high frequency
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- This article is about the radio frequency. See also UHF (movie)
Ultra high frequency (UHF) radio frequencies are those between 300
MHz and 3.0
GHz, which is higher than those of
very high frequency (VHF). UHF and VHF are the most common frequency bands for
television.
UHF frequencies have higher
attenuation from atmospheric moisture and benefit less from 'bounce', or the reflection of signals off the
ionosphere back to earth, when compared to VHF frequencies. The frequencies of 300-3000 MHz are always at least an order of magnitude above the
MUF (Maximum Usable Frequency). The MUF for most of the earth is generally between 25-35 MHz. Higher frequencies also benefit less from ground mode transmission. However, the short wavelengths of UHF frequencies allow compact receiving antennas with narrow elements; many people consider them less ugly than VHF-receiving models
United States
On December 29, 1949 KC2XAK of Bridgeport, Connecticut became the first UHF television station to operate on a regular daily schedule.
In the United States, UHF stations (broadcast channels above 13) originally gained a reputation for being more locally owned, less polished, less professional, less popular, and for having a weaker signal than their VHF counterparts (channels 2-13). The movie UHF, starring Weird Al Yankovic, parodies this phenomenon. Recently, with the emergence of eight major broadcast television networks, that notion has changed as bigger and bigger media companies seek a bigger slice of the television pie. Many Fox, UPN, WB, and Pax network affiliates broadcast in the UHF band.
As cable television, digital television, and DSS have penetrated the television market, the distinction between VHF and UHF stations has dissipated.
United Kingdom
In Britain, UHF television began with the launch of BBC TWO in 1964, using a 625-line system (which had higher resolution, and therefore required greater bandwidth, than the existing 405-line system). BBC ONE and ITV soon added their own 625-line services on UHF (British channels 21 to 69), and PAL colour was introduced on UHF only in 1967 - 1969. VHF was phased out by 1986. Today all British terrestrial television channels (analog and digital) are on UHF. A drawback to this is the very large number of small relay transmitters needed to fill in gaps in the main transmitters' coverage, which would not have been necessary wth a VHF system due to its different propagation characteristics.
Australia
In Australia, UHF was first anticipated in the mid 1970s with 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.
