There are a few things to consider when purchasing a car antenna amplifier. The first is the type of amplifier. Some car antennas are designed to be amplified, while others are not. Amplification can make a big difference in the strength of the signal received from a car antenna. Another thing to consider is the size of the amplifier. Some amplifiers are small enough to fit into a small space, while others are larger and require a dedicated space. Finally, the type of antenna that is being used should be considered. Some antennas are designed to be used with a car's audio system, while others are not. If the antenna is not designed to be used with a car's audio system, it may not be able to receive a strong signal.