AM/FM Reception through Controlling the Radio
RADIO/AUDIO SYSTEM DESCRIPTION AND OPERATIONBattery positive voltage is provided to the radio from the RDO/INTLP/ONSTAR fuse in the fuse block-I/P. The radio is grounded to G302 and G303. The radio is enabled/disabled by class 2 messages from the body control module (BCM).
The Entertainment System on this vehicle is configured with a base and uplevel system. The base and uplevel systems contain a radio, antenna, speakers, and on some vehicle lines an audio amplifier.
The uplevel system differs from the base system by providing the customer with enhanced audio system features. Some of those features may include the radio data system (RDS), an audio amplifier and programmable equalizer (EQ). Satellite digital radio (U2K) is available with uplevel systems.
The following list shows the radios available for this vehicle:
- Base Radio (UM7) - AM/FM Stereo
- Base Radio (UM6) - AM/FM Stereo and Cassette
- Base Radio (U1C) - AM/FM Stereo and CD
- Uplevel Radio (UP0 ) - AM/FM Stereo, Cassette, CD, and RDS
- Uplevel Radio (U1P) - AM/FM Stereo, CD, EQ and RDS
- Uplevel Radio (U1Q) - AM/FM Stereo, Cassette, CD, EQ and RDS
- Uplevel Radio (US8) - AM/FM Stereo, CD, MP3, EQ, and RDS
Radio Features Part 1:
Radio Features Part 2:
RADIO FEATURES
Cassette Features:
CASSETTE FEATURES
Compact Disc Features:
COMPACT DISC FEATURES
MP3 Features:
MP3 FEATURES
Each item in the list below represents topics covered in detail below:
- AM/FM Reception
- XM Reception
- Antenna
- Audio Amplifier
- Theft Deterrent
- Remote Playback Device
- Radio Data System (RDS)
- XM Satellite Radio
- XM Advisory Messages
- Radio Chime Level Adjustment
- Tape/CD Player Error Messages
- Technical Information for MP3 Player (US8)
AM/FM RECEPTION
Radio Signal
The radio signal is sent from a broadcast station and is then received by an antenna. The strength of the signal received depends on the following:
- The power output, or wattage, of the broadcasting station
- The location of the vehicle, or receiver, relative to the broadcast tower.
- Obstacles between the tower and the receiver
- Atmospheric conditions
- Which band, AM or FM, the station is broadcasting
- Type of antenna and the ground plane
AM Reception
The AM band has a lower frequency range than the FM band. These longer wavelengths:
- Bend around obstacles
- Follow the curvature of the earth
- May reflect, or skip, off of the ionosphere
The AM frequencies have longer range due to the ground wave. The ground wave follows the curvature of the earth and is affected by its conductivity. Greater conductivity equates to less signal loss, thus transmission over water is better than over land. The AM band has a range of 80-320 km (50-200 mi).
FM Reception
The shorter wavelengths of the higher frequency FM band:
- Reflect off obstacles
- Are absorbed by the ground
- Penetrate the ionosphere
Broadcasts in the FM band are limited to "line of sight" reception which is typically 40 km (25 mi). Even when out of a direct line of sight, the signal may be reflected into areas that would be in a "shadow" otherwise. Factors which affect the line of sight include:
- Height of the broadcast antenna
- Height of the receiving antenna
- Terrain and buildings in the broadcast path
XM RECEPTION
XM satellite radio provides digital radio reception. The XM signal is broadcast from two satellites and, where necessary, terrestrial repeaters. The high power satellites allow the antenna to receive the XM signal even when foliage and other partial obstructions block the antennas view of the satellite. Terrestrial repeaters are used in dense urban areas. These repeaters will receive the satellite signal and re-broadcast them at much higher power levels in order to ensure reception in areas with densely packed tall buildings.
ANTENNA
The antenna is comprised of a fixed mast which is mounted on the body of the vehicle. Mast antennas are located typically on the fender or rear quarter panel of the vehicle.
AUDIO AMPLIFIER
The purpose of an amplifier is to increase the power of a voltage or current signal. The output signal of an amplifier may consist of the same frequencies as the input signal or it may consist of only a portion of the frequencies of the input signal, as in the case of a subwoofer or a mid-range amplifier.
When the radio is turned on, the radio sends a voltage signal to the audio amplifier via the radio on signal circuit. The gain control signal circuit allows the radio to recognize that an amplifier is present. Once the radio detects the amplifier, the radio will output low level audio signals to the amplifier. With the amplifier enabled, the signal that drives the speaker is now amplified.
THEFT DETERRENT
The "Theftlock" theft deterrent system is a feature on all base and uplevel radios. There is no need to program a security code into the radio as in past model years. The theft deterrent system now utilizes class 2 serial data to determine if the radio is in the appropriate vehicle. Each time the radio receives the "run" power mode message, it compares the VIN information it has stored to the VIN information received from a module on the class 2 serial data circuit responsible for transmitting that information. If a mis-match occurs, the radio display will indicate to the user the radio is locked. Once this takes place, a DTC will set, the radio will not respond to any button presses and become inoperative. The two scenarios able to cause this condition are:
- A radio is installed from another vehicle.
- A module which communicates on the class 2 serial data circuit which supplies VIN information to the radio is replaced and not properly setup with the correct VIN information for that vehicle.
The only way to unlock the radio is by using a scan tool. Always refer to the table in this section to diagnose the "Theftlock" DTC for further information.
Personal Choice Radio Controls, If Equipped
With this feature, your vehicle will recall the latest radio settings as adjusted the last time your vehicle was operated. This feature allows 2 different drivers to store and recall their own radio settings for AM and FM presets, last tuned station, volume, tone and audio source -radio, cassette or CD. The settings recalled by the radio are determined by which transmitter was used to enter the vehicle. After the UNLOCK button is pressed on the transmitter and the ignition is in RUN, the radio settings will automatically adjust to where they were last set by the identified driver. All vehicles are shipped with this feature on. This feature can be disabled by your dealer if desired. Refer to Driver Personalization in Personalization.
REMOTE PLAYBACK DEVICE, IF EQUIPPED
The remote playback device is either installed at the factory or in some instances it is dealer installed. There are 3 types of remote playback devices, a multi disc remote CD changer, a single disc CD player and a cassette player. All 3 devices have a wiring harness which plugs into the back of the radio. The radio controls and communicates with the remote playback device through a Entertainment and Comfort (E&C) or Class 2 communication circuit.
Remote CD Changer (CDX)
The remote CD changer allows for multiple compact disks to be played continuously without having to manually change compact discs. Normal size discs may be played using the slots supplied in the magazine. The magazine must first be loaded with discs before it can played. To load CD's, insert the CDs from bottom to top, placing the discs in the magazine label side up. If a disc is loaded label side down, the disc will not play and an error will occur. Care should be used to align and insert the disc into one disc tray only. Repeat this procedure for loading all of the discs in the magazine. Once the discs are loaded into the magazine, push the magazine into the changer in the direction of the arrow marked on the magazine. When the CD magazine is loaded, the changer will begin checking for discs in the magazine. This will continue for up to one and a half minutes, depending on the number of discs loaded. To eject the magazine from the player, push the CD changer door. The door will open. Then press the eject button. Whenever a CD magazine with discs is loaded in the changer, the CD changer symbol will appear on the radio display. If the CD changer is checking the magazine for CDs, the CD symbol will flash on the display until the changer is ready to play.
IMPORTANT: If the CD magazine fails to eject after the EJECT button has been pressed, do not attempt to pry the magazine from the CD changer.
RADIO DATA SYSTEM (RDS)
All uplevel audio systems are equipped with technology known as the Radio Data System (RDS). RDS is a system that sends data along with the audio of the FM station you are currently tuned to. RDS is a standard that defines how a FM broadcast station may send digital data along with the audio program. Think of it as a one way wireless modem, allowing the broadcaster to send information about the program to your receiver.
RDS data is carried in what is known as a "subcarrier". A subcarrier is a frequency that the FM broadcaster is authorized to use to send data or other audio programs that are not audible in the main audio program. RDS information can be used to display program information and to control the radio.
To receive the RDS signal, all that is needed is an FM receiver with an RDS circuit. A special integrated circuit capable of dealing with the RDS signal is in the RDS circuit and passes it along to the receiver's microprocessor where it is decoded and acted upon.
RDS Basic Information
- RDS functions are provided in the FM broadcast band only.
- RDS functions will only work with FM broadcast stations that are broadcasting RDS data.
- Not all FM Broadcast stations broadcast RDS data or offer all of the RDS services.
- RDS functions may not work properly when reception is weak, reception is of poor quality, or RDS is not implemented properly by the FM Broadcaster.
In some cases, a radio station broadcasting incorrect information may cause the RDS features of the radio to appear to work improperly.
Displaying RDS Information
The RDS feature is always on. When tuned to a non-RDS station, the radio will display frequency information as you would normally expect. When tuned to an RDS station, the radio can operate as follows:
- The radio will change from displaying the frequency of the FM station to displaying the call letters of the station or display the nickname of the station.
- Display the type of program.
- Display general information such as artist and song title, call in phone numbers, etc.
Viewing and Selecting RDS Information for Display
Press the TUNE knob once for less than 2 seconds when the radio displays the program service (PS) name and the frequency of the station will be displayed. Press the knob again, and the program type (P-Type) will be displayed. Pressed again, and the program type (PTY) name will be displayed, if the broadcaster is broadcasting one. The PTY name is an eight-character name that the broadcaster may use to further identify the type of programming currently being broadcast. Should you decide that Frequency, P-Type or PTY name is more desirable to display when tuned to an RDS station than the PS name, press the TUNE knob until the desired information is displayed, then press and hold for more than 2 seconds. A beep should be heard and the radio will now display the selected information whenever tuned to an RDS broadcaster. The radio will display frequency for all non-RDS broadcast stations.
Using RDS Program Types to Tune Radio
Listed are several ways on how to tune your radio using RDS program types.
The radio will now be configured to tune based on RDS data rather than frequency.
A Fast Way to Find a RDS Station In Your Listening Area
1. Press the PROG TYPE or P-TYPE button, the radio displays the current P-Type to search for.
2. Rotate the TUNE SELECT RCL knob until the radio displays "ANY TYPE". Press the SEEK SCAN button again and the radio will now seek the first RDS Broadcaster of any kind that it can find in the FM band.
Finding a RDS Station By Specific Program Type
1. Press the PROG TYPE or P-TYPE button, the radio will display the current P-Type to search for.
2. Rotate the TUNE SELECT RCL knob until the desired program type is shown in the display.
3. Press the SEEK SCAN button and the radio will now seek the first RDS Broadcaster of the selected P-Type.
If the radio cannot find the desired P-Type, the radio displays "NOT FOUND" and will return to the last station you were listening to.
Using the INFO Feature
When the INFO icon appears in the radio display, a new text message is available for viewing. These text messages are from the RDS broadcaster to the listening public and may be general information such as artist and song title, call in phone numbers, etc.
How to View the INFO Message
- To view the message when the INFO icon appears, press the INFO button to display the text message. If you do not press the INFO button again, the text message will automatically be displayed 8 characters at a time, 3 seconds between updates.
- To view the text message faster, press the INFO button for less than 1 second to scroll through the message at your own speed.
- The INFO icon disappears as soon as you press the INFO button. The INFO icon will appear when a new different message is received.
- To view the most recent received message, press the INFO icon at any time, even if the icon does not appear in the display.
Controlling the Radio
RDS can control the radio when data the receiver can use responds to timely information performing the following:
- Interrupt the playback of your cassette or CD for traffic or emergency bulletins.
- Search for stations by type of program.
- Automatically follow networked programming from transmitter to transmitter as you travel from one listening area to another.
- Set your clock to the time that the RDS broadcast station broadcasts.