UHF & VHF Signal in Brazil

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Frederico Custodio

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167,000

Published on May 13, 2017 12:01:09 AM ● Video Link: https://www.youtube.com/watch?v=z5VJJAXPCxQ

Game:

Frequency (2001)

Duration: 3:02

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Ultra high frequency (UHF) is the ITU designation for radio frequencies in the range between 300 MHz and 3 GHz, also known as the decimetre band as the wavelengths range from one meter to one decimeter. Radio waves with frequencies above the UHF band fall into the SHF (super-high frequency) or microwave frequency range. Lower frequency signals fall into the VHF (very high frequency) or lower bands. 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. 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.
The IEEE defines the UHF radar band as frequencies between 300 MHz and 1 GHz. 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.
Radio waves in the UHF band travel almost entirely by line-of-sight propagation (LOS) and ground reflection; there is very little reflection from the ionosphere (skywave propagation), or ground wave. They are blocked by hills and cannot travel far beyond the horizon, but can penetrate foliage and buildings for indoor reception. 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 multipath propagation, especially in built-up urban areas. Atmospheric moisture reduces, or attenuates, the strength of UHF signals over long distances, and the attenuation increases with frequency. UHF TV signals are generally more degraded by moisture than lower bands, such as VHF TV signals.
Occasionally when conditions are right, UHF radio waves can travel long distances by tropospheric ducting as the atmosphere warms and cools throughout the day.
The length of an antenna is related to the length of the radio waves used. The UHF antenna is stubby and short; at UHF frequencies a quarter-wave monopole, the most common omnidirectional antenna is between 2.5 and 25 cm long for example. The short wavelengths make the VHF and UHF bands the first bands at which practical transmitting antennas are small enough to mount on handheld devices, thus these frequencies are used for portable wireless devices. UHF is widely used in cordless telephones, cell phones, walkie-talkies and other two-way radio systems from short range up to the visual horizon, about 40 miles (64 km). Their transmissions do not travel far, allowing frequency reuse. Public safety, business communications and personal radio services such as GMRS, PMR446, and UHF CB are often found on UHF frequencies as well as IEEE 802.11 wireless LANs ("Wi-Fi"). The widely adapted GSM and UMTS cellular networks use UHF cellular frequencies. Radio repeaters are used to retransmit UHF signals when a distance greater than the line of sight is required.
Very high frequency (VHF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) from 30 MHz to 300 MHz, with corresponding wavelengths of ten to one meters. Frequencies immediately below VHF are denoted high frequency (HF), and the next higher frequencies are known as ultra high frequency (UHF).
Common uses for VHF are FM radio broadcasting, television broadcasting, two way land mobile radio systems (emergency, business, private use and military), long range data communication up to several tens of kilometres with radio modems, amateur radio, and marine communications. Air traffic control communications and air navigation systems (e.g. VOR & ILS) work at distances of 100 kilometres or more to aircraft at cruising altitude.
VHF was used for analog television stations in the US, and continues to be used for digital television as well as in Europe but in the latter only Band III is used even though originally Band I was planned to be used. Some older DVB-T receivers included channels E2 to E4 but newer ones only go down to channel E5.
VHF propagation characteristics are suited for short-distance terrestrial communication, with a range generally somewhat farther than line-of-sight from the transmitter (see formula below).
VHF waves are restricted to the local radio horizon less than 100 miles.
VHF is less affected by atmospheric noise and interference from electrical equipment than lower frequencies.
While it is blocked by land features such as hills and mountains, it is less affected by buildings and can be received indoors, although multipath television reception due to reflection from buildings can be a problem in urban areas.
Unlike high frequencies (HF), the ionosphere does not usually reflect VHF waves (called skywave propagation).
VHF waves can be aided by tropospheric ducting.

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