Radio Reception
Sirius consists of three satellites that travel in such a way that there are always two satellites over North America. One of these two satellites is in such a position that it can transmit and when one satellite disappears from the transmission area the other one comes in. In order to transmit for 24-hours three satellites are therefore necessary.
There may be times when the transmitting satellite is low on the horizon which means that the sound may disappear for about 30 minutes due to mountains etc. that cover the signal.
The images above show how a satellite moves over eight hours. Note how low over the horizon the satellite is at its lowest, which could reduce the transmission area.
In the event of poor reception, the sound disappears completely and a warning message appears in the Infotainment Control Module (ICM). If the sound disappears for a very short time, no warning message appears.
Other factors that can affect radio reception:
- Tall buildings or mountains
- Branches and leaves on trees
- Bridges
- Power lines
During radio reception the digital radio signals are received by the antenna system and transmitted to the Remote Digital Audio Receiver (RDAR) where they are decoded. Then the Remote Digital Audio Receiver (RDAR) transmits the signals onwards via the MOST network to the infotainment control module (ICM) and the integrated audio module (IAM) or the audio module (AUD) depending on the vehicle configuration.
Remote Digital Audio Receiver (RDAR) uses the signal, satellite or terrestrial, which is strongest at the time.