Tuner Unit
The tuner unit is a separate digital radio tuner interface. Received AM/FM radio waves are processed on the digital signal processor (DSP) and sent to the audio-navigation unit via the dedicated digital audio line (SPDIF1). All of the information about AM/FM reception (includes RBDS information) are sent from the tuner unit via the dedicated serial bus (RS485). This unit holds AM/FM radio frequency presets even when the 12 volt battery is disconnected.
For vehicles with Sirius XM (R) radio, the antenna for receiving the AM/FM radio waves and satellite/terrestrial (XM) signal uses a roof antenna. The AM/FM radio wave is amplified by the AM/FM antenna amplifier. The sensitivity of the FM wave is raised by the auto gain control. The XM antenna receives satellite signal and terrestrial signal by using the high-gain antenna. Signals are sent to the audio-navigation unit via the dedicated single line (SAT/TER).