TV signal boosters come in two varieties: inline or powered. In-line boosters have a single input and a single output. Some powered boosters also function as splitters. They accept one coaxial input and have several output jacks.
As TV signals are transmitted through coaxial cables, they lose strength. Boosters increase the strength of the signal by taking in a weak signal and increasing its power. This is commonly done through a step-up transformer. Powered boosters are much more efficient at increasing the strength of a signal, since they can introduce power from a source outside the coaxial line.
Inline boosters are useful when coupling together long runs of coaxial cables. Each time a cable is coupled together, it loses a bit of signal integrity. By using an inline booster in place of a coupler, the signal integrity is largely maintained, and minor power losses can be reversed. Inline boosters should only be used for boosting signals that are lost in the home. They are not appropriate for boosting poor antenna or cable signals.
Powered boosters, however, can be used to boost signals that are weak from an antenna or cable box, but they will not substitute for antenna boosters. Powered boosters that also serve as splitters must be used with care. All coaxial connectors on the booster must be covered, either by an in-use coaxial cable or a special cap, as exposed connectors can cause signal loss.
Because boosters amplify the signal the cable receives, boosters cannot repair poor signals. If the only signal coming through is static, a booster will output amplified static. They are also ineffective on lower frequency channels, such as 2 and 5, as they do not carry as much power as higher frequency channels.