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television antenna
A television antenna, or TV aerial, is an antenna specifically designed for the reception of over-the-air broadcast television signals, which are transmitted at frequencies from about 41 to 250 MHz in the VHF band, and 470 to 960 MHz in the UHF band in different countries. Television antennas are manufactured in two different types: "indoor" antennas, to be located on top of or next to the television set, and "outdoor" antennas, mounted on a mast on top of the owner's house. The most common types of antennas used are the dipole ("rabbit ears") and loop antennas, and for outdoor antennas the yagi〔 and log periodic.〔
==Description==
To cover this range, antennas generally consist of multiple conductors of different lengths which correspond to the wavelength range the antenna is intended to receive. The length of the elements of a TV antenna are usually half the wavelength of the signal they are intended to receive. The wavelength of a signal equals the speed of light (c) divided by the frequency. The design of a television broadcast receiving antenna is the same for the older analog transmissions and the digital television (DTV) transmissions which are replacing them. Sellers often claim to supply a special "digital" or "high-definition television" (HDTV) antenna advised as a replacement for an existing analog television antenna; at best this is misinformation to generate sales of unneeded equipment,〔(TV Antenna Range )〕〔(BBC: Digital switch advice 'shocking' ) 9 of 14 installers gave bad or misleading advice, suggesting that people are likely to need a new aerial for digital switchover ... 5 told the mystery shopper they would need a "digital aerial", when in fact there is no such thing.〕 at worst it may leave the viewer with a UHF-only antenna in a local market (particularly in North America) where some digital stations remain on their original high VHF frequencies.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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