ag捕鱼王程序揭秘Selecting the right TV antenna for your particular television and location requires a number of things to be considered.
The type of antenna - is it to be used for satellite or terrestrial, along with decisions about an internal or external antenna, antenna gain, format and many other things.
ag捕鱼王程序揭秘When selecting an antenna there is a huge variety of antennas from which to make a selection.
Satellite or terrestrial
The first decision to be made is whether the antenna is to be used for terrestrial or satellite (DBS) broadcasts.
ag捕鱼王程序揭秘Satellite antennas typically require the use of a parabolic reflector or dish antenna. These need to be accurately aligned on the antenna and receive signals from the satellite, often at frequencies typically between 10.95 and 12.75GHz.
ag捕鱼王程序揭秘Terrestrial transmissions typically operate on frequencies in the UHF portion of the radio spectrum, although there are still some operating in the VHF portion of the spectrum in some countries.
ag捕鱼王程序揭秘A variety of antennas can be used from external antennas on rooftops to internal ones that may take one of a variety of forms.
It is essential that a specific satellite antenna is used for satellite transmissions and a terrestrial antenna for terrestrial TV transmissions.
Indoor / outdoor
One major consideration to think about when buying a TV antenna is whether the antenna should be internal or external. Internal antennas typically do not perform as well - the walls of the building reduce the signal and there are also reflections caused by objects on the building. Interference levels are also higher from fluorescent lights, electrical equipment and many other items. External antennas are able to pick up a much better signal, but they cost more to erect and the cables are longer.
If you live in a high signal area then an internal antenna may work well for you, but if the signal is not too strong, then an external antenna will always be better.
When buying a TV antenna, the frequency coverage is a key point to note. In countries where there is VHF TV then a VHF antenna will be required. However most TV is broadcast on UHF. Even when UHF is used, there are many bands, so be aware that the right TV antenna for your area will be needed. Alternatively very wide band antennas may be required - these are often called log periodic antennas.
ag捕鱼王程序揭秘Sometimes antennas will be sold as “Digital Antennas”. This refers more to the section of the TV band used rather than receiving analogue or digital transmissions.
ag捕鱼王程序揭秘Be aware that in some countries, different areas of the country may use TV channels in different sections of the band. Normally they are grouped together so that the antenna bandwidth can code. But check on the Internet or with your local dealer to find out whether antennas need to be bought to match your particular area.
Gain / directivity
ag捕鱼王程序揭秘One of the key parameters of any antenna is its gain. This is the increase in what may be termed its sensitivity in a particular direction. The higher the gain, the greater its ability to pick up weak signals.
When the gain is increased the antenna also becomes more directive, meaning that it must be more accurately directed towards the TV transmitter, but also this has the effect of reducing the level of interference that might be received from other directions.
The gain is specified in dB, or decibels. The higher the number of decibels the higher the gain. It should be noted that decibels are based on logarithms and therefore 10dB is an increase in gain of 10 fold, and 20dB is an increase in gain of 100 fold.
ag捕鱼王程序揭秘As decibels are only a ratio, it means that the ratio must compare the gain of the TV antenna to a standard. Two may be used. The first is a dipole and the second is what is termed an isotropic source - this is one that radiates equally well in all directions. As the dipole itself has some gain, 2.1 dB over an isotropic source, it is necessary to know what the TV antenna gain is compared to. 10dB gain when referred to a dipole is the same as 12 dB when referred to an isotropic source . . so beware when comparing different antennas that the gain is referenced to the same type of reference antenna.
Antenna type or style
There are very many different styles of antenna used for terrestrial TV. The most popular form is the Yagi or Yagi-Uda, but many other types are available. Parabolic reflectors for satellite television; log periodic antennas where the television stations may be widely spaced in frequency and a wide bandwidth is required, etc . . The log periodic should be considered when TV reception is needed for a wide range of frequencies, but it will offer a lower gain than other types.
ag捕鱼王程序揭秘The main thing is to look at the size and the gain. If it is physically too large then it may be more difficult to mount. It will also be more susceptible to damage from the wind, and more robust fixing arrangements will be needed and this will cost more.
In some areas a TV antenna amplifier may be needed to boost the signal. There are many different types of TV antenna booster amplifiers that are available, often enabling a single antenna to feed more than one television.
. . . Read more about TV antenna amplifiers / boosters
ag捕鱼王程序揭秘These are some of the main features of TV antennas. Buying an antenna is normally a relatively straightforward process and they can be bought from the Internet or a local dealer. Make sure that when an antenna is bought that good quality cable is used - old cable, especially if it has been used outside can have moisture in it and this will increase the level of loss it introduces - it is always best to use new cable with a new antenna, and seal the external end to prevent moisture getting inside it.
More Antenna & Propagation Topics:
EM waves Radio propagation Ionospheric propagation Ground wave Meteor scatter Tropospheric propagation Cubical quad Dipole Discone Ferrite rod Log periodic antenna Parabolic reflector antenna Vertical antennas Yagi Antenna grounding Coax cable Waveguide VSWR MIMO
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