chap47 pps Automotive technology at University of Cambridge
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Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
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OBJECTIVES:
After studying Chapter 47, 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.
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
Hall- -Upper
UpperSaddle
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OBJECTIVES:
After studying Chapter 47, the reader should
be able to:
•
•
Explain how crossovers work.
List causes and corrections of radio noise and
interference.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
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PrenticeHall
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KEY TERMS:
active crossover • alternator whine • amplitude
modulation (AM)
bluetooth
carrier wave • crossover
decibels (dB)
electronically tuned receiver (ETR)
floating ground system • flutter • frequency • frequency
modulation (FM)
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
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KEY TERMS:
ground plane
hertz • high-pass filter • impedance
low-pass filter
modulation
picket fencing • powerline capacitor
radio choke • radio frequency (RF) • root-mean-square (RMS)
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
PearsonEducation,
Education,Inc.
Inc.
Pearson
PearsonPrentice
PrenticeHall
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KEY TERMS:
satellite digital audio radio services (SDARS) • sideband
operation • speakers • stiffening capacitor • subwoofer
total harmonic distortion (THD) • tweeter
voice recognition
wavelength
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
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Inc.
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The audio system of today’s vehicles is a complex
combination of antenna system, receiver, amplifier,
and speakers all designed to provide living room-type
music reproduction while the vehicle is traveling in city
traffic or at highway speed.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
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Inc.
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AUDIO FUNDAMENTALS
There are two types of energy that affect audio systems.
Electromagnetic energy or radio waves Antennas capture
the radio waves which are then sent to the radio or receiver to
be amplified.
Acoustical energy, usually called sound Radios and
receivers amplify the radio wave signals and drive speakers
which reproduce the original sound that was transmitted by
radio waves.
See Figure 471.
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
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Figure 47–1 Audio systems use both electromagnetic radio waves and sound waves to
reproduce sound inside the vehicle.
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
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Electromagnetic energy moves through the air while acoustical
energy moves air. Radio waves are measured in two ways:
wavelength and frequency. A radio wave has a series of high points
and low points.
A wavelength is the time and distance between two consecutive
points, either high or low, measured in meters. Frequency, also
known as radio frequency, or RF, is the number of times a
particular waveform repeats itself in a given amount of time and is
measured in hertz.
A signal with a frequency of one hertz is one radio wavelength per
second. Radio frequencies are measured in kilohertz, thousands of
wavelengths per second, and megahertz, millions of wavelengths
per second. See Figure 47–2 and examples following.
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
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The higher the frequency,
the shorter the wavelength.
The lower the frequency,
the longer the wavelength.
Figure 47–2 The relationship among
wavelength, frequency, and amplitude.
Longer wavelengths travel
farther than shorter ones.
Lower frequencies provide
better reception at longer
distances.
AM radio frequencies range
from 530, to 1,710 kilohertz.
FM radio frequencies range
from 87.9 to 107.9 MHz.
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
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Modulation The term used to describe when information is added to
a constant frequency is modulation. The base radio frequency used
for RF is called the carrier wave. A carrier is a radio wave that is
changed to carry information. The two types of modulation are:
Amplitude Modulation (AM)
Frequency Modulation (FM)
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
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Figure 47–3 The amplitude changes in AM broadcasting.
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.
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
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Figure 47–4 The frequency changes in FM broadcasting and the amplitude remains constant.
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.
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
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Radio Wave Transmission More than one signal can be carried by
a radio wave. This process is called sideband operation. Sideband
frequencies are measured in kilohertz.
The amount of the signal above the assigned frequency is referred to
as the upper sideband. The amount of the signal below the assigned
frequency is called the lower sideband.
This capability allows radio signals to carry stereo broadcasts.
Stereo broadcasts use the upper sideband to carry one channel of the
stereo signal, and the lower to carry the other channel.
When the signal is decoded by the radio, these two signals become
the right and left channels.
See Figure 47–5.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
Continued
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Figure 47–5 Using upper and lower sidebands allows stereo to be broadcast. The receiver
separates the signals to provide left and right channels.
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
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Inc.
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Noise Because radio waves are a form of electromagnetic energy,
other forms of energy can impact them.
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 travel in a straight line
from transmitter to receiver. FM waves travel the ionosphere into
space and don’t reflect back to earth like AM waves.
This causes an echo effect in the speakers. Flutter, or picket
fencing as it is sometimes called, is caused by the blocking of part
of the FM signal. This blocking causes a weakening of the signal
resulting in only part of the signal getting to the antenna causing
an onagain offagain radio sound. Flutter also occurs when the
transmitter and the receiving antenna are far apart.
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
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RADIOS AND RECEIVERS
The antenna receives the radio wave where it is converted into very
weak, fluctuating electrical current. This current travels along the
antenna leadin to the radio, which amplifies the signal and sends
the new signal to the speakers where it is converted into acoustical
energy.
Most latemodel GM radios and receivers use five inputs:
1.
2.
3.
4.
5.
Power—constant 12volt feed to keep the clock alive
Ground
Serial data—used to turn the unit on and off and provide
other functions such as steering wheel control operation
Antenna input
Speaker outputs
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
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Types of Antennas The typical radio electromagnetic energy from
the broadcast antenna induces a signal in the antenna that is very
small—only about 25 micro volts AC (0.000025 VAC) in strength.
Slot antenna—The slot antenna is concealed in the roof of some
plasticbody vehicles such as the U van. This antenna is
surrounded by metal on a Mylar sheet.
Rearwindow defogger grid antenna—This type of system uses
the heating wires to receive the signals and special circuitry to
separate the RF from the DC heater circuit.
Powered mast antenna—Powered mast antennas are controlled
by the radio. When the radio is turned on, the antenna is raised,
when the radio is shut off, the antenna is retracted. The antenna
system consists of an antenna mast and a drive motor.
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
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Fixedmast antenna—The fixedmast antenna offers the best overall
performance currently available. The mast is simply a vertical rod. Mast
antennas are typically located on the fender or rear quarter panel of the
vehicle
Integrated antenna—This type of antenna is sandwiched in the
windshield and an appliqué on the rear window glass. The antenna in the
rear window is the primary antenna and receives both AM and FM
signals. The secondary antenna is located in the front windshield typically
on the passenger side of the vehicle. This antenna receives only FM
signals.
See Figure 476.
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
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Figure 47–6 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.
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
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What is a Ground Plane?
Antennas designed to pick up electromagnetic energy 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.
For ideal reception, the receiving antenna should be the same wavelength
as the signal. Because this is not practical, a design compromise uses the
length of the antenna as one-fourth of the wavelength and the body of the
vehicle as one-fourth of the wavelength. The body of the vehicle becomes
the ground plane. Any faulty condition in the ground plane circuit will cause
the ground plane to lose effectiveness, such as:
•
•
•
•
•
Loose or corroded battery cable terminals
Acid buildup on battery cables
Engine grounds with high resistance
Loss of antenna or audio system grounds
A defective generator causes an AC ripple exceeding 50 millivolts
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
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Figure 47–7 The ground plane is actually one-half of the antenna.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
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ANTENNA DIAGNOSIS
The antenna collects all radiofrequency signals. AM radio
operates best with as long an antenna as possible. FM reception is
best when the antenna height is exactly 31 inches (79 cm).
Most fixedlength antennas are exactly this height. The horizontal
section of a windshield antenna is 31 inches (79 cm) long.
A defective antenna will be most noticeable with AM radio
reception.
Continued
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
©©2008
2009Pearson
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Antenna Testing If the antenna or leadin cable is broken (open),
FM reception will be heard but may be weak, and there will be no
AM reception. An ohmmeter should read infinity between the center
antenna lead and the antenna case.
For proper reception and
lack of noise, the case of
the antenna needs to be
properly grounded to the
vehicle body.
Figure 47–8 If all ohmmeter readings are
satisfactory, the antenna is good.
Automotive Technology: Principles, Diagnosis, and Service, 3rd Edition
By James D. Halderman
Continued
©©2008
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