Car antennas are rods, typically made of metal or plastic, which are used to receive and transmit radio signals from an external source to the vehicle's audio system. Antennas come in many shapes and sizes and are usually mounted on the car body or roof of the vehicle. The primary role of a car antenna is to amplify radio signals so that they can be heard over longer distances. Additionally, antennas act as an obstacle to outside interference and can help block out frequencies from other radio signals that can interfere with radio reception. Some newer vehicles are equipped with digital antennas that are integrated into the vehicle's audio system and don't require any external mounting.