Although your rooftop digital antenna is capable of receiving and sending high definition images to your tuner or television, sometimes that signal needs amplification. Antenna preamplifiers and distribution amplifiers serve to eliminate or reduce the reduction in signal caused by long cable runs and multiple splits. In many installations, both are used to ensure a strong digital television signal from start to finish. Identifying both devices helps you choose the right tool for your needs and install it correctly.
Coaxial cable, like any electrical line, causes a reduction in signal as distance increases. Known as attenuation, this reduction in signal may be enough to create a blocky or intermittent picture once it reaches the tuner depending on the age and condition of the coaxial cable. It isn't uncommon for a coaxial feed from an antenna to the tuner, splitter or distribution amplifier to reach 50 or 100 feet. To combat this loss, preamplifiers are mounted at or very near the antenna mast to boost the feed from the antenna. Preamplifiers also serve to help in fringe reception areas, or when you are trying to receive a channel with comparatively low broadcast strength.
Coaxial Cable Quality
You cannot discuss signal loss preventing solutions like preamplifiers and distribution amplifiers without considering the cabling linking the two. Coaxial cables should be 75 Ohm, RG-6 quad-shielded coaxial cables. The 75 Ohm impedance, or resistance to signal is required to match that found at the antenna and tuner to prevent loss. An apt analogy is connecting a garden hose the same diameter as the spigot. If you connect a hose that is too small and and of a certain length, the water is a trickle at the other end. RG-59 is a cheaper alternative, but does not have the same shielding and signal-carrying capacity as RG-6.
Distribution Amplifiers versus Splitters
A passive splitter is acceptable if you are dividing the incoming coaxial feed up to four times. Remember, however, that each split results in a 3-decibel signal reduction at the output. Combining this loss with an additional 50-plus foot run may result in signal loss. Distribution amplifiers counter this loss by boosting the feed from the incoming coaxial cable. These amplifiers are common in larger homes and businesses where the feed may be split many times without impact to signal.
It may seem logical on the surface to apply as much signal to the cable as possible in every circumstance. This is not the right approach. Preamplifiers and distribution amplifiers may overload tuners, which presents their own set of picture quality problems. A classic over-driven signal appears too white, as though the contrast setting on your television is turned up to maximum. The same is true with distribution amplifiers. Most of these amplifiers are adjustable to prevent overloading of tuners, allowing you to dial in the correct amount of boost. In every case, if the coaxial cable runs are long it is important to boost the signal before it traverses the line, not after. If you know you are within 40 miles of local broadcasters and your coaxial cable runs are not split multiple times and remain under 50 feet, it is unlikely you will need either solution. Adding one or both in these circumstances typically cause more problems than they solve.
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