Online Encyclopedia
Ultra high frequency
- 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. Modern mobile phones transmit and receive within the UHF spectrum.
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. UHF can experience troposheric refraction like VHF, but this occurs more rarely, and the range is not as great (e.g., 100-200 miles). Sporadic E propagation at UHF frequencies is very rare. 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, parodied this phenomenon.
However, with the emergence of additional broadcast television networks (Fox, UPN, WB, and Pax), the concentration of media ownership, and the proliferation of cable television, digital television, and DSS in the 1990s, the distinction between UHF and VHF stations has virtually disappeared in the United States. Most HDTV stations (those using the ATSC television standard) broadcast their over-the-air signal in the UHF band.
A brief summary of some UHF frequency usage:
- 300 - 420 MHz: government use, including meteorology
- 420 - 450 MHz: radiolocation and Amateur "70 cm" band
- 450 - 470 MHz: UHF business band, GMRS, and FRS 2-way "walkie-talkies"
- 470 - 512 MHz: TV channels 14-20, public safety
- 512 - 806 MHz: TV channels 21-69 (channels 53-69 to be auctioned)
- 806 - 824 MHz: pocket pagers and Nextel SMR band
- 824 - 849 MHz: cellular phones, A & B franchises, mobile phone
- 849 - 869 MHz: public safety 2-way (fire, police, ambulance)
- 869 - 894 MHz: cellular phones, A & B franchises, base station
- 902 - 928 MHz: ISM band: cordless phones and stereo, datalinks
- 928 - 960 MHz: mixed Studio-Transmitter Links, mobile 2-way, other
- 1240 - 1300 MHz: Amateur radio
- 1850 - 1910 MHz: PCS mobile phone - note below
- 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
- 2310 - 2360 MHz: Satellite radio Sirius and XM
- 2390 - 2450 MHz: Amateur radio, shared with below:
- 2400 - 2483.5 MHz: ISM, IEEE 802.11, 802.11b, 802.11g Wireless LAN
- around 2450 MHz: Microwave oven
United Kingdom
In Britain, UHF television began with the launch of BBC2 in 1964, using a 625-line system (which had higher resolution, and therefore required greater bandwidth, than the existing 405-line system). BBC1 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 with 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.
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