Lexus ES300 (1997 year). Manual - part 134

The radio wave bands used in radio broadcasting are as follows:

Frequency

Designation

Radio wave

Modulation method

LF: Low frequency MF: Medium Frequency HF: High Frequency VHF: Very High Frequency

Amplitude modulation

Frequency modulation

30 kHz

300 kHz

3 MHz

30 MHz

300 MHz

LF

MF

HF

VHF

AM

FM

BE060–01

BE2818

FM (Stereo)

FM (Monaural)

AM

BE2819

Fading

lonosphere

BE–142

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AUDIO SYSTEM

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AUDIO SYSTEM

DESCRIPTION

1.

RADIO WAVE BAND

2.

SERVICE AREA

There are great differences in the size of the service area for AM
and FM monaural. Sometimes FM stereo broadcasts cannot be
received even through AM can be received in very clearly.
Not only does FM stereo have the smallest service area, but it
also picks up static and other types of interference (”noise”)
easily.

3.

RECEPTION PROBLEMS

Besides the problem of static, there are also the problems
called ”fading”, ”multipath” and ”fade out”. These problems are
caused not by electrical noise but by the nature of the radio
waves themselves.

(a)

Fading
Besides electrical interference, AM broadcasts are also
susceptible to other types of interference, especially at
night. This is because AM radio waves bounce off the ion-
osphere at night. These radio waves then interfere with
the signals from the same transmitter that reach the ve-
hicle’s antenna directly. This type of interference is called
”fading”.

BE2820

Multipath

BE2821

Fade Out

AM

FM

Noise occurs at a specific place.

Strong possibility of foreign noise.

Noise occurs when listening to
faint broadcasting.

Noise occurs only at night.

Noise occurs while driving and
at a specific place.

There is a case that the same program is broadcasted
from each local station and that may be the case you are
listening different station if the program is the same.

Strong possibility of the beat from a distant broadcasting.

Strong possibility of multipath noise and fading noise
caused by the changes of FM waves.

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BODY ELECTRICAL

AUDIO SYSTEM

BE–143

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(b)

Multipath

One type of interference caused by the bounce of radio waves
off of obstructions is called ”multipath”. Multipath occurs when
a signal from the broadcast transmitter antenna bounces off
buildings and mountains and interferes with the signal that is re-
ceived directly.

(c)

Fade Out

Because FM radio waves are of higher frequencies than AM ra-
dio waves, they bounce off buildings, mountains, and other ob-
structions. For this reason, FM signals often seem to gradually
disappear or fade away as the vehicle goes behind a building
or other obstruction. This is called ”fade out”.

4.

NOISE PROBLEMS

(a)

Questionnaire for noise:
It is very important for noise troubleshooting to have good
understanding  of the claims from the customers, so that
make the best use of following questionnaire and diag-
nose the problem accurately.

HINT:
In the case that the noise occurrence condition does not meet
any of the above questionnaire, check based on the ”Trouble
Phenomenon”.
Refer to above descriptions for multipath and fading.

N21545

Glass Printed Antenna

Noise

Signal

Radio

Noise

Noise

Noise

Noise

N21546

to Radio

Battery

Noise

Choke Coil

BE–144

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(b)

Matters that require attention when checking:

Noise coming into the radio usually has no harm for
practical use as the noise protection is taken and it
is hardly thinkable for an extremely loud noise to
come in. When extremely loud noise comes into the
radio, check if the grounding is normal where the
antenna is installed.

Check if all the regular noise prevention parts are
properly installed and if there is any installation of
non–authorized  parts and non–authorized wiring.

If you leave the radio under out of tune (not tuning),
it is easy to diagnose the phenomenon as noise oc-
curs frequently.

(c)

Antenna and noise:
Electronic signal received by the antenna will reach to the
radio transmitting through the core wire of the coaxial
cable. Any noise wave other than radio wave is mixed into
this core wire, that naturally causes noise in the radio and
poor sound quality. In order to prevent these noises from
mixing into the radio, the core wire inside the coaxial cable
is covered with a mesh wire called shield wire. This shield
wire shelters the noise and transmits it to the ground, thus
preventing noise from mixing in.

If this shield wire has grounding failure, that causes noise.
(d)

Choke coil and noise:
The choke coil is connected in the rear window defogger
circuit. This is connected so to prevent noise from mixing
into the radio by making the noise current included in the
power source of the rear window defogger flow to the
ground.

N21547

Plug (Main)

Antenna
Terminal (Main)

Plug (Sub)

Antenna
Terminal (Sub)

1

2

3

4

Z19487

Antenna Code

Choke Coil

Ground Point

Center Brace (RH)

Pillar (LH)

Pillar (RH)

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(e)

Antenna code continuity check and grounding point:

HINT:
During troubleshooting, in case that the antenna code continu-
ity check, grounding check and grounding check of the choke
coil are needed, please check refering to the following illustra-
tion.

Terminal connection

Normal condition

(1) 

↔

 (2)

Continuity

(3) 

↔

 (4)

No continuity

5.

COMPACT DISC PLAYER

Compact Disc (hereafter called ”CD”) Players use a laser beam
pick–up to read the digital signals recorded on the CD and re-
produce analog signals of the music, etc. There are 4.7 in. (12
cm) and 3.2 in. (8 cm) discs in the CD player.
HINT:
Never attempt to disassemble or oil any part of the player unit.
Do not insert any object other than a disc into the magazine.
NOTICE:
CD players use an invisible laser beam which could cause
hazardous radiation exposure. Be sure to operate the play-
er correctly as instructed.