Boosters amplify cable signals by multiplying and retransmitting the signals at one or more points along a cable. Passive and powered boosters both work the same way, but powered boosters can produce a stronger amplified signal, transmit the signal over longer distances and provide quality signals even through multiple splits.
Boosters are necessary because, as a cable television signal travels along a coaxial cable, it begins to lose some of its original quality. The longer the length of the cable, the more the original signal becomes degraded. The ideal location for a booster is around the midpoint of the cable. When the original signal arrives at the booster, the device multiplies the signal and sends it down the remaining length of cable. The signal begins to degrade again as soon as it leaves the booster, so multiple boosters are necessary for extremely long cables.
Powered signal boosters require connection to wall outlets or some other sources of external electricity. Passive boosters use only the very small electrical current in the cable itself to amplify cable television signals. These boosters are small and convenient, but they lack the range and amplification of powered boosters. Both types of boosters can only amplify the existing signal they receive; they cannot improve its original quality.