Television antenna
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A television antenna (TV aerial) is an
Description
The purpose of the antenna is to intercept
In most countries, television broadcasting is allowed in the very high frequency (VHF) band from 47 to 68 MHz, called VHF low band or band I in Europe; 174 to 216 MHz, called VHF high band or band III in Europe, and in the ultra high frequency (UHF) band from 470 to 698 MHz, called band IV and V in Europe.[5] The boundaries of each band vary somewhat in different countries. Radio waves in these bands travel by line-of-sight; hills block them and the visual horizon, limiting a television station's reception area to 65–95 km (40–60 miles), depending on terrain.
Analog vs. digital
In the previous standard
Starting in 2006, many countries in the world switched from broadcasting using an older analog television standard to newer digital television[6] (DTV). However, the same broadcast frequencies are generally used, so the antennas used for the older analog television will also receive the new DTV broadcasts. 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,[7][8] 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 or low VHF frequencies.
Reception issues
Places unable to be reached by television broadcast transmitters are known as "black spots" in Australia.[9] In East Germany, the areas that could not receive western TV signals were referred to as the Tal der Ahnungslosen, or "Valley of the Clueless".
Indoor
Indoor antennas may be mounted on the television itself or stand on a table next to it, connected to the television by a short
Rabbit ears
The oldest and most widely used indoor antenna is the rabbit ears or bunny ears, which are often provided with new television sets.
The measured
Whip antenna
Some portable televisions use a
Loop antenna
The UHF channels are often received by a single turn loop antenna.[4] Since a "rabbit ears" antenna only covers the VHF bands, it is often combined with a UHF loop mounted on the same base to cover all the TV channels.
Flat antenna
Soon after television broadcasting switched from analog to digital broadcasting, indoor antenna marketing evolved beyond the traditional "rabbit ears." Flat antennas are lightweight, thin, and usually square-shaped with the claim of having more omnidirectional reception.[citation needed] They connect to televisions only with a coaxial cable; they may also be sold with a signal amplifier requiring a power source. Internally, the thin, flat square is a loop antenna with its circular metallic wiring embedded into conductive plastic.[citation needed]
Outdoor
When a
Outdoor antenna designs are often based on the
The television broadcast bands are too wide in frequency to be covered by a single antenna, so the two options are separate antennas used for the VHF and UHF bands or a combination (combo) VHF/UHF antenna.
Since directional antennas must be pointed at the transmitting antenna, this is a problem when the television stations to be received are located in different directions. In this case, two or more directional rooftop antennas, each pointed at a different transmitter, are often mounted on the same mast and connected to one receiver for best performance
Sometimes television transmitters are deliberately located such that receivers in a given region need only receive transmissions in a relatively narrow band of the full UHF television spectrum and from the same direction, hence allowing the use of a higher gain grouped aerial.[12]
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A UHF television antenna
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A rabbit ear indoor antenna weatherproofed and installed outdoors
Installation
Antennas are commonly placed on rooftops and sometimes in attics. Placing an antenna indoors significantly attenuates the level of the available signal.[13][14] Directional antennas must be pointed at the transmitter they are receiving; in most cases great accuracy is not needed. In a given region, it is sometimes arranged that all television transmitters are located in roughly the same direction and use frequencies spaced closely enough that a single antenna suffices for all. A single transmitter location may transmit signals for several channels.[15] CABD (communal antenna broadcast distribution) is a system installed inside a building to receive free-to-air TV/FM signals transmitted via radio frequencies and distribute them to the audience.[16]
Analog television signals are susceptible to ghosting in the image, multiple closely spaced images giving the impression of blurred and repeated images of edges in the picture. This is due to the signal being reflected from nearby objects (buildings, trees, mountains); several copies of the signal, of different strengths and subject to different delays, are picked up. This is different for other transmissions. Careful positioning of the antenna can produce a compromise position, which minimizes the ghosts on different channels. Ghosting is also possible if multiple antennas connected to the same receiver pick up the same station, especially if the lengths of the cables connecting them to the splitter/merger are different lengths or the antennas are too close together.[17] Analog television is being replaced by digital, which is not subject to ghosting; the same reflected signal that causes ghosting in an analog signal would produce no viewable content at all in digital. However, in this case, interference causes significantly more significant image quality degradation.
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 guyed mast or mast. The wire connecting the antenna indoors is referred to as the downlead or drop, and the longer the downlead is, the greater the signal degradation in the wire. Certain cables may help reduce this tendency.
The higher the antenna is placed, the better it will perform. An antenna of higher
Indoor antennas
As discussed previously, antennas may be placed indoors where signals are strong enough to overcome antenna shortcomings. The antenna is simply plugged into the television receiver and placed conveniently, often on the top of the receiver ("set-top"). Sometimes, the position needs to be experimented with to get the best picture. Indoor antennas can also benefit from RF amplification, commonly called a TV booster. Reception from indoor antennas can be problematic in weak signal areas.[citation needed]
Attic installation
Sometimes, it is desirable not to put an antenna on the roof; in these cases, antennas designed for outdoor use are often mounted in the attic or loft, although antennas designed for attic use are also available. Putting an antenna indoors significantly decreases its performance due to lower elevation above ground level and intervening walls; however, in strong signal areas, reception may be satisfactory.
Multiple antennas, rotators
It is sometimes desired to receive signals from transmitters which are not in the same direction. This can be achieved, for one station at a time, by using a
For side-by-side placement of multiple antennas, as is common in a space of limited height such as an attic, they should be separated by at least one full wavelength of the lowest frequency to be received at their closest point.
When multiple antennas are often used, one is for a range of co-located stations, and the other is for a single transmitter in a different direction.
Safety
- TV antennas are good conductors of electricity and attract lightning, acting as a lightning rod. A lightning arrester is usually used to protect against this. A large grounding rod connected to both the antenna and the mast or pole is required.[20]
- Properly installed masts, especially tall ones, are power linesif they fall.
- There is an inherent danger in being on the rooftop of a house, required for installing or adjusting a television antenna.
See also
- Broadcast television systems
- Radio masts and towers, sometimes called Radio and TV antennas
- Satellite dish
- Satellite television
- Terrestrial television
References
- ^ Johnson 1993 Antenna Engineering Handbook, 3rd Ed. Archived 2023-07-01 at the Wayback Machine, p. 29.5-29.6
- ^ ISBN 978-8122416077. Archivedfrom the original on 2023-07-01. Retrieved 2021-10-16.
- ISBN 9780070323810. Archived from the original on 2023-07-01. Retrieved 2022-03-31.)
{{cite book}}
: CS1 maint: multiple names: authors list (link - ^ a b c d e f g h i j Johnson 1993 Antenna Engineering Handbook, 3rd Ed. Archived 2023-07-01 at the Wayback Machine, p. 29.6
- ^ Johnson 1993 Antenna Engineering Handbook, 3rd Ed. Archived 2023-07-01 at the Wayback Machine, p. 29.2
- S2CID 247126109.
- ^ "TV Antenna Range". www.dennysantennaservice.com. Archived from the original on 2021-05-11. Retrieved 2009-11-10.
- ^ BBC: Digital switch advice 'shocking' Archived 2017-09-05 at the Wayback Machine October 13, 2008, 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.
- ^ "Going digital: tracing the transition to digital terrestrial television in Australia digital". Parliament of Australia. 12 June 2011. Archived from the original on 6 August 2021. Retrieved 6 August 2021.
- ^ Johnson 1993 Antenna Engineering Handbook, 3rd Ed. Archived 2023-07-01 at the Wayback Machine, p. 29.16-29.21
- ^ Johnson 1993 Antenna Engineering Handbook, 3rd Ed. Archived 2023-07-01 at the Wayback Machine, p. 29.14-29.16
- ^ UK aerial groups Archived 2019-12-19 at the Wayback Machine In the UK transmitters are grouped into A, B, C, D, E, and K frequency bands and located so that, as far as possible, they are all in the same direction for receivers in a given region. This allows optimal reception of all stations by a single fixed narrow-band (and hence high-gain) antenna pointing in a fixed direction.
- ^ "Rob's TV Digital Aerial installations". Archived from the original on 2011-03-04. Retrieved 2011-03-20.
- ^ a b "Attic Mounted TV Antennas - Stallions Satellite and Antenna". tvantenna.com. Archived from the original on 2009-12-13. Retrieved 2009-12-19.
- ^ "UK TV Transmitters". www.aerialsandtv.com. Archived from the original on 2019-12-19. Retrieved 2019-12-21.
- ^ "Digital TV". www.digitaltv.gov.hk. Archived from the original on 2016-03-04. Retrieved 2015-10-17.
- ^ a b "Combining or Stacking Two TV Antennas - Stallions Satellite and Antenna". tvantenna.com. Archived from the original on 2009-11-24. Retrieved 2009-11-11.
- ^ "Over-the-Air Reception Devices Rule". Federal Communications Commission. December 9, 2015. Archived from the original on January 8, 2017. Retrieved January 7, 2017.
- ^ "Antennas Direct - FAQs About HD Television Antennas". www.terrestrial-digital.com. Archived from the original on 2009-03-29. Retrieved 2009-12-19.
- ^ "Lightning Protection for TV and Radio Antennas". nojolt.com. Archived from the original on 2010-03-30. Retrieved 2009-12-19.