Before we start off writing the directions on how to hook up an HD radio to your car, we must know the meaning of the HD radio. It is a service that delivers digital audio by the radio stations especially FM radio. Generally the HD radio has two parts in the installation. One is its head unit. This head unit is generally fixed in the car by the factory and has all the necessary controls to control the audio. The second part is the radio. This is connected to head unit for controls. This HD radio is not available with all factory cars and is optional. The interested people have to buy it separately. There are other types of radios like satellite radio. This radio need to be fees for use. Unlike this, the HD radio is does not require fee.