Ultra high frequency facts for kids
Ultra High Frequency (UHF) is a type of electromagnetic radiation. Think of it as a kind of invisible wave, like radio waves or light. These waves have a frequency between 300 MHz (megahertz) and 3 GHz (gigahertz), which is 3,000 MHz.
Because UHF waves have a short wavelength, they are very focused. This means they travel in a more direct line and don't spread out much. UHF is often used for television signals. It's strong enough to avoid interference from other signals. However, because it's so focused, obstacles like buildings can block the signal more easily. This is why you sometimes need sensitive sensors or antennas to pick up UHF signals.
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How UHF Waves Are Used
UHF frequencies are affected more by moisture in the air. They also don't "bounce" off the ionosphere (a part of Earth's atmosphere) as well as lower frequencies like VHF (Very High Frequency) waves do. This means UHF signals are not great for very long-distance communication that relies on bouncing signals around the globe.
However, the short wavelengths of UHF waves have a big advantage: they allow for smaller and more compact antennas. Many people find these smaller antennas look better than the larger ones needed for VHF signals.
UHF in the United States
The first UHF television station to broadcast regularly in the United States was KC2XAK in Bridgeport, Connecticut, on December 29, 1949.
For a long time, UHF stations (channels above 13) were seen as different from VHF stations (channels 2–13). UHF stations were often smaller, more local, and sometimes had a weaker signal. The movie UHF, starring Weird Al Yankovic, even made fun of this idea.
But things changed in the 1990s with new TV networks like Fox and the growth of cable television. Also, digital television (DTV) became popular. Today, most high-definition TV (HDTV) signals broadcast over the air use the UHF band. This means the old differences between UHF and VHF stations have mostly disappeared in the U.S.
UHF in the United Kingdom
In Britain, UHF television started in 1964 with the launch of BBC2. This new system used 625 lines for a clearer picture, which needed more bandwidth. Soon after, BBC1 and ITV also started broadcasting their 625-line services on UHF (British channels 21 to 69).
Color TV was introduced on UHF only between 1967 and 1969. By 1986, VHF broadcasting was completely stopped. Today, all British terrestrial TV channels, both analog and digital, use UHF. One challenge with UHF in the UK is that many small relay transmitters are needed to fill in gaps where the main transmitters don't reach. This wouldn't have been as necessary with a VHF system.
Other Pages to Explore
Images for kids
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A UHF television antenna on a house. This type of antenna is called a Yagi-Uda antenna.
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Walkie-talkies that use the 446 MHz PMR (Professional Mobile Radio) band. Their short wavelength allows them to use very small "Rubber Ducky" antennas.
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A corner reflector UHF-TV antenna from the 1950s.
See also
In Spanish: UHF para niños
