Friday, August 30, 2013

Tv Aerials for outdoors
Tv Aerials for outdoors
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.

Rooftop and other outdoor antennas
Aerials are attached to roofs in various ways, usually on a pole to elevate it above the roof. This is generally sufficient in most areas. In some places however, such as a deep valley or near taller structures, the antenna may need to be placed significantly higher, using a lattice tower or mast. The wire connecting the antenna to indoors is referred to as the downlead or drop, and the longer the down lead is, the greater the signal degradation in the wire.
The higher the antenna is placed, the better it will perform. An antenna of higher gain will be able to receive weaker signals from its preferred direction. Intervening buildings, topographical features (mountains), and dense forest will weaken the signal in many cases the signal will be reflected such that a usable signal is still available. There are physical dangers inherent to high or complex antennas, such as the structure falling or being destroyed by the weather. There are also varying local ordinanceswhich restrict and limit such things as the height of a structure without obtaining permits. For example, in the Usa, the Telecommunications Act of 1996 allows any homeowner to install "An antenna that is designed to receive local television broadcast signals", but that "masts higher than 12 feet above the roof-line may be subject to local permitting requirements.

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