UHF wavelengths are short enough that efficient transmitting antennas are small enough to mount on handheld and mobile devices, so these frequencies are used for two-way land mobile radio systems, such as walkie-talkies, two way radios in vehicles, and for portable wireless devices cordless phones and cell phones. Due to the short wavelengths, UHF antennas are conveniently stubby and short at UHF frequencies a quarter-wave monopole, the most common omnidirectional antenna is between 2.5 and 25 cm long. The length of an antenna is related to the length of the radio waves used. Occasionally when conditions are right, UHF radio waves can travel long distances by tropospheric ducting as the atmosphere warms and cools throughout the day.Ĭorner reflector UHF-TV antenna from 1950s Radio repeaters are used to retransmit UHF signals when a distance greater than the line of sight is required. Since UHF transmission is limited by the visual horizon to 30–40 miles (48–64 km) and usually to shorter distances by local terrain, it allows the same frequency channels to be reused by other users in neighboring geographic areas ( frequency reuse).
UHF TV signals are generally more degraded by moisture than lower bands, such as VHF TV signals. Atmospheric moisture reduces, or attenuates, the strength of UHF signals over long distances, and the attenuation increases with frequency. Since the wavelengths of UHF waves are comparable to the size of buildings, trees, vehicles and other common objects, reflection and diffraction from these objects can cause fading due to multipath propagation, especially in built-up urban areas. UHF radio waves are blocked by hills and cannot travel beyond the horizon, but can penetrate foliage and buildings for indoor reception. Radio waves in the UHF band travel almost entirely by line-of-sight propagation (LOS) and ground reflection unlike in the HF band there is little to no reflection from the ionosphere ( skywave propagation), or ground wave. Two other IEEE radar bands overlap the ITU UHF band: the L band between 1 and 2 GHz and the S band between 2 and 4 GHz. The IEEE defines the UHF radar band as frequencies between 300 MHz and 1 GHz. They are used for television broadcasting, cell phones, satellite communication including GPS, personal radio services including Wi-Fi and Bluetooth, walkie-talkies, cordless phones, and numerous other applications.
UHF radio waves propagate mainly by line of sight they are blocked by hills and large buildings although the transmission through building walls is strong enough for indoor reception.
Lower frequency signals fall into the VHF ( very high frequency) or lower bands. Radio waves with frequencies above the UHF band fall into the super-high frequency (SHF) or microwave frequency range. Ultra high frequency ( UHF) is the ITU designation for radio frequencies in the range between 300 megahertz (MHz) and 3 gigahertz (GHz), also known as the decimetre band as the wavelengths range from one meter to one tenth of a meter (one decimeter).