UHF
The spectrum 300 MHz through to 3 Gllz. Terrestrial broadcast television occupies 470 to 890 Mhz. The 620 to 790 MHz band is allocated for community DBS dowiiiinks in developing countries and remote areas and is used by the Soviet Union.
Ultra high frequency (UHF) designates a range (band) of electromagnetic waves whose frequency is between 300 MHz (Wavelength 1 meter) and 3.0 GHz (Wavelength 10 centimetres) . 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.
VHF
30 to 300 megahertz
Very high frequency (VHF) is the radio frequency range from 30 MHz (wavelength 10 m) to 300 MHz (wavelength 1 m). Frequencies immediately below VHF is HF, and the next higher frequencies are known as Ultra high frequency (UHF).
Common uses for VHF are FM radio broadcast at 88–108 MHz and television broadcast (together with UHF). VHF is also commonly used for terrestrial navigation systems (VOR in particular) and aircraft communications.
VHF frequencies' propagation characteristics are ideal for short-distance terrestrial communication, with a range generally somewhat farther than line-of-sight from the transmitter (see formula below). Unlike high frequencies (HF), the ionosphere does not usually reflect VHF radio and thus transmissions are restricted to the local area (and don't interfere with transmissions thousands of kilometres away). VHF is also less affected by atmospheric noise and interference from electrical equipment than low frequencies. Whilst it is more easily blocked by land features than HF and lower frequencies, it is less bothered by buildings and other less substantial objects than higher frequencies.
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.
Frequency Allocation - United States
A brief summary of some UHF frequency usage:
* 300–420 MHz: government use, including meteorology
* 420–450 MHz: radiolocation and Amateur radio (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
* 512–698 MHz: TV channels 21–51 (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
* 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, RFID, datalinks, Amateur radio (33 cm band)
* 928–960 MHz: mixed Studio-Transmitter Links, mobile 2-way, other
* 1240–1300 MHz: Amateur radio (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 (13 cm band)
* 2400–2483.5 MHz: ISM, IEEE 802.11, 802.11b, 802.11g Wireless LAN
* around 2450 MHz: Microwave oven
Also;
VHF (viral hemorrhagic fever) is a group of illnesses caused by a viral infection (usually restricted to a specific geographic area); fever and gastrointestinal symptoms are followed by capillary hemorrhage.