2. OBJECTIVES
After studying Chapter 27, the reader should be able to:
Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “H” (Accessories Diagnosis and Repair).
Describe how AM and FM radio works.
Explain how to test speaker polarity.
Explain how to match speaker impedance.
Explain how crossovers work.
List causes and corrections of radio noise and interference.

3. AUDIO FUNDAMENTALS
There are two types of energy that affect audio systems.
Electromagnetic energy or radio waves.
Acoustical energy, usually called sound.
FIGURE 27-1 Audio systems use both electromagnetic radio waves and sound waves to reproduce sound inside the vehicle.

4. AUDIO FUNDAMENTALS
Radio frequencies are measured in kilohertz, thousands of wavelengths per second, and megahertz, millions of wavelengths per second.
FIGURE 27-2 The relationship among wavelength, frequency, and amplitude.

5. AUDIO FUNDAMENTALS Modulation
Modulation is the term used to describe when information is added to a constant frequency.
The two types of modulation are:
Amplitude Modulation (AM)
Frequency Modulation (FM)

6. AUDIO FUNDAMENTALS Modulation
AM waves are radio waves that have amplitude that can be varied, transmitted, and detected by a receiver.
Amplitude is the height of the wave as graphed on an oscilloscope.
FIGURE 27-3 The amplitude changes in AM broadcasting.

7. AUDIO FUNDAMENTALS Modulation
FM waves are radio waves that have a frequency that can be varied, transmitted, and detected by a receiver.
This type of modulation changes the number of cycles per second, or frequency, to carry the information.
FIGURE 27-4 The frequency changes in FM broadcasting and the amplitude remains constant.

8. AUDIO FUNDAMENTALS Radio Wave Transmission
More than one signal can be carried by a radio wave.
When the signal is decoded by the radio, these two signals become the right and left channels.
FIGURE 27-5 Using upper and lower sidebands allows stereo to be broadcast. The receiver separates the signals to provide left and right channels.

9. AUDIO FUNDAMENTALS Noise
Because radio waves are a form of electromagnetic energy, other forms of energy can impact them.
For example, a bolt of lightning generates broad radio frequency bandwidths.

10. AUDIO FUNDAMENTALS FM Characteristics
Because FM waves have a high RF and a short wavelength, they travel only a short distance.
The waves cannot follow the shape of the earth but instead travel in a straight line from the transmitter to receiver.

11. RADIOS AND RECEIVERS
Most late-model General Motors radios and receivers use five inputs:
1. Power—usually a constant 12-volt feed to keep the internal clock alive
2. Ground
3. Serial data—used to turn the unit on and off and provide other functions such as steering wheel control operation
4. Antenna input
5. Speaker outputs

12. RADIOS AND RECEIVERS Types of Antennas
There are five types of antennas currently used on General Motors vehicles. They include:
Slot antenna
Rear-window defogger grid antenna
Powered mast antenna
Fixed-mast antenna
Integrated antenna

13. RADIOS AND RECEIVERS Types of Antennas
FIGURE 27-6 The five types of antennas used on General Motors vehicles include the slot antenna, fixed-mast antenna, rear window
defogger grid antenna, a powered mast antenna, and an integrated antenna.

14. WHAT IS A GROUND PLANE?
Antennas designed to pick up the electromagnetic energy that is broadcast through the air to the transmitting antenna are usually one-half wavelength high, and the other half of the wavelength is the ground plane.
This one-half wavelength in the ground plane is literally underground.

15. WHAT IS A GROUND PLANE?
A design compromise uses the length of the antenna as one-fourth of the wavelength; in addition, the body of the vehicle itself is one-fourth of the wavelength.
FIGURE 27-7 The ground plane is actually one-half of the antenna.

16. ANTENNA DIAGNOSIS The antenna collects all radio-frequency signals.
An AM radio operates best with as long an antenna as possible, but FM reception is best when the antenna height is exactly 31 inches (79 centimeters).

17. ANTENNA DIAGNOSIS Antenna Testing
For proper reception and lack of noise, the case of the antenna must be properly grounded to the vehicle body.
FIGURE 27-8 If all ohmmeter readings are satisfactory, the antenna is good.

18. THE HOLE IN THE FENDER COVER TRICK
A common repair is to replace the mast of a power antenna.
To help prevent the possibility of causing damage to the body or paint of the vehicle, cut a hole in a fender cover and place it over the antenna
FIGURE 27-9 Cutting a small hole in a fender cover helps to protect the vehicle when replacing or servicing an antenna.

19. ANTENNA DIAGNOSIS Power Antenna Testing and Service
Except in the case of cleaning or mast replacement, most power antennas are either replaced as a unit or repaired by specialty shops.
FIGURE A typical power antenna assembly. Note the braided ground wire used to make sure that the antenna has a good ground plane.

20. SPEAKERS
The human ear is capable of hearing sounds from a very low frequency of 20 Hz (cycles per seconds) to as high as 20,000 Hz.
No one speaker is capable of reproducing sound over such a wide frequency range.
FIGURE Between 6 and 7 volts is applied to each speaker terminal and the audio amplifier then increases the voltage on one terminal and at the same time decreases the voltage on the other terminal causing the speaker cone to move. The moving cone then moves the air causing sound.

21. SPEAKERS
Good-quality speakers are the key to a proper sounding radio or sound system.
Replacement speakers should be securely mounted and wired according to the correct polarity.

22. SPEAKERS
FIGURE A speaker polarity tester can be easily constructed using a 1 1/2-volt battery. To test a speaker, connect the positive (+) lead of the battery to one speaker terminal and the negative (-) lead to the other speaker terminal for just a second and observe the direction the speaker cone moves. The positive (+) terminal of the speaker is the terminal that causes the speaker cone to move away from the magnet when touched with the positive (=) battery lead.
FIGURE A typical automotive speaker with two terminals. The polarity of the speakers can be identified by looking at the wiring diagram in the service manual or by using a 1 1/2-volt battery to check.

23. SPEAKERS
If unequal-impedance speakers are used, sound quality may be reduced and serious damage to the radio may result.
FIGURE (a) Two 4-ohm speakers connected in series result in a total impedance of 8 ohms. (b) Two 4-ohm speakers connected in parallel result in total impedance of 2 ohms.

24. SPEAKERS Impedance Matching
All speakers should have the same impedance.
For example, if two 4-ohm speakers are being used for the rear and they are connected in parallel, the total impedance is 2 ohms.

25. SPEAKERS Speaker Wiring
The wire used for speakers should be as large a wire (as low an AWG number) as is practical in order to be assured that full power is reaching the speakers.
All wiring connections should be soldered after making certain that all speaker connections have the correct polarity.

26. SPEAKER TYPES Tweeter
A tweeter is a speaker designed to reproduce high-frequency sounds, usually between 4,000 Hz (4 kHz) and 20,000 Hz (20 kHz).
Tweeters are usually mounted on the inside door near the top, windshield “A” pillar, or similar locations.

27. SPEAKER TYPES Midrange
A midrange speaker is designed and manufactured to be able to best reproduce sounds in the middle of the human hearing range from 400 Hz to 5,000 Hz.
Most people are sensitive to the sound produced by these midrange speakers.

28. SPEAKER TYPES Subwoofer
A subwoofer, sometimes called a woofer, produces the lowest frequency of sounds, usually 125 Hz and lower.
Most subwoofers are mounted in the rear of the vehicle where there is more room for the larger subwoofer speakers.

29. SPEAKER TYPES Speaker Frequency Response
Frequency response is how a speaker responds to a range of frequencies.
A decibel is a measure of sound power, and it is the faintest sound a human can hear in the midband frequencies.
The dB scale is not linear (straight line) but rather logarithmic, meaning that a small change in the dB reading results in a large change in volume of noise.

30. CROSSOVERS
A crossover is designed to separate the frequency of a sound and send a certain frequency range, such as low bass sounds, to a woofer designed to reproduce these low-frequency sounds.
There are two types of crossovers: passive and active.

31. CROSSOVERS Passive Crossover
A passive crossover does not use an external power source.
Rather it uses a coil and a capacitor to block certain frequencies that a particular type of speaker cannot handle and allow those frequencies that can be handled to be applied to the speaker.

32. CROSSOVERS Active Crossover
Active crossovers use an external power source and produce superior performance.
These units include many powered filters and are considerably more expensive than passive crossovers.
FIGURE Crossovers are used in audio systems to send high frequency sounds to the small (tweeter) speakers and the low-frequency
sounds to larger (woofer) speakers.

33. USE A POWERLINE CAPACITOR IF UPGRADING A SOUND SYSTEM
The purpose and function of this capacitor is to provide the electrical reserve energy needed by the amplifier to provide deep bass notes.
FIGURE Two capacitors connected in parallel provide the necessary current flow to power large subwoofer speakers.

34. CROSSOVERS Capacitor Installation
A powerline capacitor connects to the power leads between the inline fuse and the amplifier.
To safely connect a large capacitor, it must be precharged.
FIGURE A powerline capacitor should be connected through the power wire to the amplifier as shown. When the amplifier requires more electrical power (watts) than the battery can supply, the capacitor will discharge
into the amplifier and supply the necessary current for the fraction of a second it is needed by the amplifier. At other times when the capacitor is not needed, it draws current from the battery to keep it charged.

35. VOICE RECOGNITION Parts and Operation
Voice recognition allows the driver of a vehicle to perform tasks, such as locate an address in a navigation system by using voice commands rather than buttons.
Newer systems recognize speech patterns and take action based on learned patterns.

36. VOICE RECOGNITION Parts and Operation
Voice recognition can be used for the following functions:
1. Navigation system operation
2. Sound system operation
FIGURE Voice commands can be used to control many functions, including navigation systems, climate control, telephone, and radio.

37. VOICE RECOGNITION Parts and Operation
3. Climate control system operation
4. Telephone dialing and other related functions
FIGURE The voice command icon on the steering wheel of a Cadillac.

38. VOICE RECOGNITION Diagnosis and Service
If a problem occurs with the system, perform the following steps:
1. Verify the customer complaint (concern).
2. Check for any aftermarket accessories that may interfere or were converted to components used by the voice recognition system,
3. Check for stored diagnostic trouble codes (DTCs) using a TECH 2 scan tool.
4. Follow the recommended troubleshooting procedures as stated in service information.

39. BLUETOOTH Operation
Bluetooth is a wireless standard that works on two levels:
It provides physical communication using low power, requiring only about one milliwatt (1/1,000 of a watt) of electrical power making it suitable for use with small handheld or portable devices, such as an ear-mounted speaker/microphone.
It provides a standard protocol for how bits of data are sent and received.

40. BLUETOOTH Operation
Many cell phones are equipped with Bluetooth, which may allow the user to use an ear-mounted microphone and speaker.
FIGURE Bluetooth earpiece that contains a microphone and speaker unit that is paired to a cellular phone. The telephone has to be within
33 feet of the earpiece.

41. SATELLITE RADIO Parts and Operation
Satellite radio, also called Satellite Digital Audio Radio Services or SDARS uses satellites to broadcast high-quality radio.
SDARS broadcasts on the S-band of 2.l320 GHz to GHz.

42. SATELLITE RADIO XM Radio
XM radio is standard equipment or optional in most General Motors vehicles.
XM radio uses two satellites launched in 2001 called Rock (XM-2) and Roll (XM-1) in a geosynchronous orbit above North America.

43. SATELLITE RADIO Reception
To help ensure consistent reception, both SDARS providers do the following:
Include in the radio itself a buffer circuit that can store several seconds of broadcasts to provide service when traveling out of a service area.
Provide land-based repeater stations in most cities.

44. SATELLITE RADIO Reception
FIGURE SDARS uses satellites and repeater stations to broadcast radio.

45. SATELLITE RADIO Antenna
To be able to receive satellite radio, the antenna needs to be able to receive signals from both the satellite, as well as repeater stations located in many large cities.
FIGURE An aftermarket XM radio antenna mounted on the rear deck lid. The deck lid acts as the ground plane for the antenna.
FIGURE A shark-fin-type factory antenna used for both XM and OnStar.

46. SATELLITE RADIO Diagnosis and Service
If no satellite service is being received, first check with the customer to verify that the monthly service fee has been paid and the account is up to date.
If poor reception is the cause, carefully check the antenna for damage or faults with the lead-in wire.

47. RADIO INTERFERENCE
A “whine” that increases in frequency with increasing engine speed is usually referred to as alternator whine and is eliminated by installing a radio choke or a filter capacitor in the power feed wire to the radio.
FIGURE A radio choke and/or a capacitor can be installed in the power feed lead to any radio, amplifier, or equalizer.

48. RADIO INTERFERENCE
Ignition noise is usually a raspy sound that varies with the speed of the engine.
This noise is usually eliminated by the installation of a capacitor on the positive side of the ignition coil.
FIGURE Many automobile manufacturers install a coaxial capacitor, like this one, in the power feed wire to the blower motor to eliminate interference caused by the blower motor.

49. RADIO INTERFERENCE
A “sniffer” can be used to locate the source of the radio noise.
FIGURE A “sniffer” can be made from an old antenna lead in cable by removing about 3 inches of the outer shielding from the end. Plug the lead-in cable into the antenna input of the radio and tune the radio to a weak station. Move the end of the antenna wire around the vehicle dash area. The sniffer is used to locate components that may not be properly shielded or grounded and can cause radio interference through the case (housing) of the
radio itself.

50. LIGHTNING DAMAGE
A radio failed to work in a vehicle that was outside during a thunderstorm.
Both the radio and the antenna were replaced to correct the problem.
FIGURE The tip of an antenna that was struck by lightning.

51. SUMMARY
Radios receive AM (amplitude modulation) and FM (frequency modulation) signals that are broadcast through the air.
The radio antenna is used to induce a very small voltage signal as an input into the radio from the electromagnetic energy from the broadcast station.
AM requires an antenna whereas FM may be heard from a radio without an antenna.
Speakers reproduce the original sound, and the impedance of all speakers should be equally matched.

52. SUMMARY
Crossovers are used to block certain frequencies to allow each type of speaker to perform its job better. A low-pass filter is used to block high-frequency sounds being sent to large woofer speakers, and a high-pass filter blocks low frequency sounds being sent to tweeters.
Radio interference can be caused by many different things, such as a defective generator (alternator), a fault in the ignition system, or a fault in a relay or solenoid.

53. REVIEW QUESTIONS
Explain why AM signals travel farther than FM signals.
Explain the purpose and function of the ground plane.
Describe how to match the impedance of speakers.
List two items that may need to be added to the wiring of a vehicle to control or reduce radio noise.

54. CHAPTER QUIZ
Technician A says that a radio can receive AM signals, but not FM signals, if the antenna is defective. Technician B says that a good antenna should give a reading of about 500 ohms when tested with an ohmmeter between the center antenna wire and ground. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

55. CHAPTER QUIZ
Technician A says that a radio can receive AM signals, but not FM signals, if the antenna is defective. Technician B says that a good antenna should give a reading of about 500 ohms when tested with an ohmmeter between the center antenna wire and ground. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

56. CHAPTER QUIZ
2. An antenna lead-in wire should have how man ohms of resistance between the center terminal and the grounded outer covering?
Less than 5 ohms
5 to 50 ohms
300 to 500 ohms
Infinity (OL)

57. CHAPTER QUIZ
2. An antenna lead-in wire should have how man ohms of resistance between the center terminal and the grounded outer covering?
Less than 5 ohms
5 to 50 ohms
300 to 500 ohms
Infinity (OL)

58. CHAPTER QUIZ
3. Technician A says that a braided ground wire is best to use for audio equipment to help reduce interference. Technician B says to use insulated 14-gauge or larger ground wire to reduce interference. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

59. CHAPTER QUIZ
3. Technician A says that a braided ground wire is best to use for audio equipment to help reduce interference. Technician B says to use insulated 14-gauge or larger ground wire to reduce interference. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

60. CHAPTER QUIZ
4. What maintenance should be performed to a power antenna to help keep it working correctly?
Remove it from the vehicle and lubricate the gears and cable
Clean the mast with a soft cloth
Disassemble the mast and pack the mast with silicone grease (or equal)
Loosen and then retighten the retaining nut

61. CHAPTER QUIZ
4. What maintenance should be performed to a power antenna to help keep it working correctly?
Remove it from the vehicle and lubricate the gears and cable
Clean the mast with a soft cloth
Disassemble the mast and pack the mast with silicone grease (or equal)
Loosen and then retighten the retaining nut

62. CHAPTER QUIZ
5. If two 4-ohm speakers are connected in parallel (positive [+] to positive [+] and negative [-] to negative [-]), the total impedance will be _________.
8 ohms
4 ohms
2 ohms
1 ohm

63. CHAPTER QUIZ
5. If two 4-ohm speakers are connected in parallel (positive [+] to positive [+] and negative [-] to negative [-]), the total impedance will be _________.
8 ohms
4 ohms
2 ohms
1 ohm

64. CHAPTER QUIZ
6. If two 4-ohm speakers are connected in series (positive [+] of one speaker connected to the negative [-] of the other speaker), the total impedance will be _________.
8 ohms
4 ohms
2 ohms
1 ohm

65. CHAPTER QUIZ
6. If two 4-ohm speakers are connected in series (positive [+] of one speaker connected to the negative [-] of the other speaker), the total impedance will be _________.
8 ohms
4 ohms
2 ohms
1 ohm

66. CHAPTER QUIZ
7. An aftermarket satellite radio has poor reception. Technician A says that a lack of a proper ground plane on the antenna could be the cause. Technician B says that mountains or tall buildings can interfere with reception. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

67. CHAPTER QUIZ
7. An aftermarket satellite radio has poor reception. Technician A says that a lack of a proper ground plane on the antenna could be the cause. Technician B says that mountains or tall buildings can interfere with reception. Which technician is correct?
Technician A only
Technician B only
Both Technicians A and B
Neither Technician A nor B

68. CHAPTER QUIZ 8. 100,000 μF means _________. 0.10 farad 0.01 farad

69. CHAPTER QUIZ 8. 100,000 μF means _________. 0.10 farad 0.01 farad

70. 9. A radio choke is actually a _________.
CHAPTER QUIZ
9. A radio choke is actually a _________.
Resistor
Capacitor
Coil (inductor)
Transistor

71. 9. A radio choke is actually a _________.
CHAPTER QUIZ
9. A radio choke is actually a _________.
Resistor
Capacitor
Coil (inductor)
Transistor

72. CHAPTER QUIZ
10.What device passes AC interference to ground and blocks DC voltage and is used to control radio interference?
Resistor
Capacitor
Coil (inductor)
Transistor

73. CHAPTER QUIZ
10.What device passes AC interference to ground and blocks DC voltage and is used to control radio interference?
Resistor
Capacitor
Coil (inductor)
Transistor

74. END