In addition to stock antennas, several different aftermarket manufacturers also produce antenna products. These can range from an exact OEM replica to something that is fairly exotic. Usually, the consumer has the option of purchasing these aftermarket antennas either with or without a built in pre-amplifier. In simplest terms, an antenna pre-amplifier takes the current variations in the antenna and amplifies them prior to the tuner. The effect of this pre-amplification process can produce results ranging from good to bad.
Weak signals become stronger and thus are of a higher quality.
On the bad side, a pre-amplifier amplifies everything. This includes broadcast stations, natural noise, man-made noise, everything. In addition, a pre-amplified antenna can have a detrimental effect on reception by reducing the tuner's selectivity or ability to single out a specific station. Another form of antenna pre-amplifier is the antenna booster. As a general rule, a booster doesn't work as well as an antenna preamplifier since the actual antenna and booster circuitry are not optimized for each other.