What Is the Bandwidth of VHF?
VHF (Very High Frequency) is a radio frequency that ranges between 30 MHz and 300 MHz. VHF is commonly used in a number of consumer and civilian communication methods: television, FM radio, amateur radio, air traffic control and mobile stations all operate on different frequencies of the VHF bandwidth.
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Frequency and Bandwidth Range
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VHF occupies the radio bandwidth (or frequency) of 30 MHz to 300 MHz. VHF's frequency is situated between HF (High Frequency) and UHF (Ultra High Frequency). The wavelength range of VHF is from 1m - 10m.
Uses of VHF
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VHF is ideal for short-distance communication; its range typically extends past line-of-sight from the transmitting tower or station. VHF transmissions generally do not reflect off of the ionosphere (a layer of the earth's atmosphere), which restricts how far VHF signals may be transmitted.
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Tropospheric Ducting
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VHF is less susceptible to atmospheric noise caused by cloud cover and solar behavior. Interference from electrical equipment (operating on lower frequencies) is, is general, not disruptive to VHF signals. VHF, because it is point-to-point (and doesn't use the ionosphere to bounce radio signals) is only moderately affected by physical land features. VHF signals aren't blocked as easily as higher-frequency signals (like UHF) by buildings and landscapes.
Using VHF
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Tropospheric ducting is one of two phenomenon that allow unusually long transmission ranges of VHF. Tropospheric ducting occurs in front of and parallel to cold weather fronts and can create environmental and atmospheric conditions that allow VHF signals to be carried farther than normal. VHF frequencies travel inside of the duct and will bend and refract for hundreds of miles.
Sporadic E and VHF
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The second high-range phenomenon, sporadic E, refers to VHF's interaction with the E-layer of the ionosphere. The mechanism of action behind sporadic E is not fully understood, but is believed to occur as the result of randomly ionized spots in the ionosphere. These ionized spots are dense enough to reflect VHF frequencies and will bounce VHF signals hundreds of miles.
VHF Bands in the United States
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VHF bands in the United States and Canada must be established in conjunction, to prevent unnecessary interference. The U.S. uses a range of bands for VHF broadcasting and assignments, ranging from 30 MHz to 225 MHz. A large portion of the VHF spectrum has been allocated to television broadcasts.
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References
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