Ultra high frequency
Ultra high frequency (UHF) designates a range (
band) of
electromagnetic waves whose
frequency is between 300
MHz and 3.0
GHz. Waves whose frequency is above the UHF band fall into the
microwave or higher bands, while lower frequency signals fall into the
VHF or lower bands. See
electromagnetic spectrum for a full listing of frequency bands.
UHF and VHF are the most common frequency bands for
television. Modern
mobile phones also
transmit and receive within the UHF spectrum, and UHF is widely used for two-way radio communication (usually using narrowband
frequency modulation, but digital services are on the rise) by both public service agencies and the general public. Though television broadcasting is common on UHF, there has traditionally been very little radio broadcasting in this band until fairly recently; see
digital audio broadcasting for details.
One uncommon use of UHF waves is in the detection of
partial discharges. These
discharges occur due to the sharp geometries created in high
voltage insulated equipment. The advantage is that this method can be used to localize the source of the discharge, but it is extremely sensitive to external noise. Nonetheless, such detection methods are used in the field especially for large distribution
transformers.
The transmission of radio waves from one point to another is affected by many variables such as
atmospheric moisture, the stream of particles from the sun called
solar wind, and time of day. All radio waves are somewhat absorbed by atmospheric moisture. This reduces, or
attenuates, the strength of radio signals over long distances. However, this effect increases according to the frequency: UHF signals are generally more degraded by moisture than lower bands such as VHF. As well, the layer of the Earth's atmosphere called the
ionosphere is filled with charged particles that can reflect radio waves. This can be helpful in transmitting a radio signal, since the wave bounces from the sky to the ground over and over, covering long distances. However, UHF benefits less from this effect than lower (VHF, etc.) frequencies. As the atmosphere warms and cools throughout the day, UHF transmissions may be enhanced by
tropospheric ducting.
The main advantage of UHF transmission is that its high frequency means it has a physically short wave. Since the size of transmission and reception equipment (particularly
antennas) is related to the size of the wave, smaller, less conspicuous antennas can be used than with VHF or lower bands.
UHF is also widely used in two-way radio systems and
cordless phones due to the fact that since UHF signals essentially travel over line-of-sight distances, distant transmissions cannot travel far enough to interfere with local transmissions. A great number of public safety and business communications are handled on UHF, and civilian applications such as
GMRS,
PMR446, and
UHF CB are extremely popular. Where communications greater than line-of-sight are required, a
repeater is used to propagate signals that otherwise would not reach their destinations.
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 true commercially licensed UHF television station on the air was
KPTV/Channel 27 (now VHF Channel 12) in
Portland, Oregon on
September 18,
1952.
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 weaker signal propagation than their VHF counterparts (channels 2–13). The movie
UHF, starring
"Weird Al" Yankovic and
Michael Richards (of
Seinfeld fame), parodied this phenomenon. In the late 1940s/early 1950s, the four major TV networks (
NBC,
CBS,
ABC and
DuMont) transmitted their programs mainly through VHF and the independent stations mainly through UHF (Although ABC and particularly Dumont had a large number of UHF affiliates).
However, with the emergence of additional broadcast television networks (
Fox,
UPN,
WB, and
i), the
concentration of media ownership, and the proliferation of
cable television,
digital television, and
DBS in the
1990s, the distinction between UHF and VHF stations has virtually disappeared in the United States. Most
HDTV stations broadcast their over-the-air signal 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 also a great amount of unlicensed activity (cordless phones, wireless networking, and the like) clustered around 800 MHz and 2.4 GHz.
United Kingdom
In
Britain, UHF television began with the launch of
BBC2 in
1964.
BBC1 and
ITV soon added their own services on UHF (British channels 21 to 69) on
November 15 1969, and
PAL colour was introduced on UHF only in
1967 (for BBC2) &
1969 (for BBC1 & ITV). VHF only carried BBC1 & ITV and was only ever in 405 line Black & White. VHF television was closed in February
1985. Today all British terrestrial (non-satellite) television channels (
analogue 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.
Australia also provides the
UHF CB service for general-purpose two-way communications.
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 VLF and VHF and the 450MHz 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 was not commonly used in the Klang Valley (Dispite TV3's signal being also available over UHF Channel 29, as TV3 also transmitted over VHF Channel 12 in the Klang Valley) until 1994, with 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
Channel 9 recently (which started in 2003, ceased transmission in 2005, got also acquired by TV3's parent company shortly after and came back as TV9 in early 2006). At corrent count there are currently 4 distinct UHF signal 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 (i.e. the ASTRO and MiTV set top boxes) and other devices that has an RF signal generator (i.e game consoles).
A brief summary of some UHF frequency usage:
*300–420 MHz: government use, including
meteorology*420–450 MHz: 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"
*470–512 MHz: TV channels 14–20, public safety
*512–698 MHz: TV channels 21–51 (channel 34 used for
radar, channel 37 used for
radio astronomy)
*698–806 MHz: TV channels 52–69 (to be auctioned for other uses once conversion to digital TV has been accomplished)
*806–824 MHz: pocket pagers and Nextel SMR band (formerly TV channels 70–72)
*824–849 MHz:
Cellular phones, A & B franchises, 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: cellular phones, A & B franchises, base station (formerly TV channels 80–83)
*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, other
*1240–1300 MHz: Amateur radio (ham -
23 cm band)
*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 (ham -
13 cm band)
*2400–2483.5 MHz: ISM,
IEEE 802.11, 802.11b, 802.11g Wireless
LAN, IEEE 802.15.4
*around 2450 MHz:
Microwave oven*430–440 MHz: Amateur radio (ham -
70 cm band)
*470–862 MHz: TV channels 21â€"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 auctioned for other uses)
*1240–1316 MHz: Amateur radio (ham -
23 cm band)
*2310–2450 MHz: Amateur radio (ham -
13 cm band)
*
Channel 37* Tomislav Stimac,
"Definition of frequency bands (VLF, ELF... etc.)". IK1QFK Home Page (vlf.it).
