Identification Of Noise Source

Radio Description

Radio frequency band
1. Radio broadcasts use the radio frequency bands shown in the table below
  
  Fig 1: Radio Frequency Bands Reference Chart
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
Service area
1. The service areas of AM and FM broadcasts are vastly different Sometimes an AM broadcast can be received very clearly but an FM stereo cannot The FM stereo has the smallest service area, and is prone to pick up static and other types of interference such as noise.
Fig 2: Identifying AM And FM Broadcasts Service Area
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
Radio reception problems
HINT.

In addition to static, other problems such as "phasing", "multipath", and "fade out" exist These problems are not caused by electrical noise, but by the radio signal propagation method itself
1. Phasing
  AM broadcasts are susceptible to electrical interference and another kind of interference called phasing Occurring only at night, phasing is the interference created when a vehicle receives 2 radio wave signals from the same transmitter One signal is reflected off the ionosphere and the other signal is received directly from the transmitter.
  
  Fig 3: Identifying Radio Frequency Area (Phasing)
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
2. Multipath
  Multipath is a type of interference created when a vehicle receives 2 radio wave signals from the same transmitter One signal is reflected off buildings or mountains and the other signal is received directly from the transmitter
  
  Fig 4: Identifying Radio Frequency Area (Multipath)
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
3. Fade out
  Fade out is caused by objects (buildings, mountains, and other such large obstacles) that deflect away part of a signal, resulting in a weaker signal when the object is between the transmitter and vehicle High frequency radio waves, such as FM broadcasts, are easily deflected by obstructions. Low frequency radio waves, such as AM broadcasts, are less likely to deflect
  
  Fig 5: Identifying Radio Frequency Area (Fade Out)
  Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002

Noise problem

Technicians must have a clear understanding about each customer's noise complaint Use the following table to diagnose noise problems

DIAGNOSIS CHART (NOISE PROBLEM)

Radio Frequency	Noise Occurrence Condition	Presumable Cause
AM	Noise occurs in a specified area	Foreign noise
AM	Noise occurs when listening to an intermittent broadcast	An identical program transmitted from multiple towers can cause noise where the signals overlap
AM	Noise occurs only at night	Music beat from a distant broadcast
FM	Noise occurs while driving in a specified area	Multipath or phasing noise resulting from a change in FM frequency

HINT

If the noise does not match the examples above, refer to the descriptions about phasing and multipath.