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very high frequency
- Definição1
- The VHF (very high frequency) range of the radio spectrum is the band extending from 30 MHz to 300 MHz. The wavelengths corresponding to these limit frequencies are 10 meters and 1 meter. In the VHF band, electromagnetic fields are affected by the earth's ionosphere and troposphere. Ionospheric propagation occurs regularly in the lower part of the VHF spectrum, mostly at frequencies below 70 MHz. In this mode, the communication range can sometimes extend over the entire surface of the earth. The troposphere can cause bending, ducting, and scattering, extending the range of communication significantly beyond the visual horizon. Auroral, meteor-scatter, and EME (earth-moon-earth, also called moonbounce) propagation take place on occasion, but these modes do not offer reliable communication and are of interest primarily to amateur radio operators. The VHF band is popular for mobile two-way radio communication. A great deal of satellite communication and broadcasting is done at VHF. Wideband modulation is used by some services; the most common example is fast-scan television broadcasting. Channels and subbands within the VHF portion of the radio spectrum are allocated by the International Telecommunication Union (ITU).
- Fonte1
- SEARCHNETWORKING.COM. What is VHF (very high frequency)?. [S. l.], 2000. Disponível em: http://searchnetworking.techtarget.com/definition/VHF. Acesso em 25 maio 2011.
- Fonte2
- INTERNATIONAL MARITIME ORGANIZATION; INTERNATIONAL CIVIL AVIATION ORGANIZATION. IAMSAR manual: international aeronautical and maritime search and rescue manual. Montréal, 2005. (Doc. 9731)
- Nota adicional1
- Acronym in English: VHF.
- Contexto
- Frequency bands allocated by ITU for the aeronautical mobile service include some in the high frequency (HF) spectrum (3,000 to 30,000 kHz), others in the very-high frequency (VHF) spectrum (30 to 300 MHz) and ultra-high frequency (UHF) (300 MHz to 3,000 MHz).
- Subárea1
- Aeronautical Telecommunications
- Related Term
- frequency
- medium frequency
- radio-frequency
- Português
- frequência muito alta