Identification Of Noise Source

1. Radio frequency band
   1. Radio broadcasts use the radio frequency bands shown in the table below.
      Fig 1: Frequency Reference Table

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1. The broadcast range for AM and FM is very different. Sometimes an AM broadcast can be received very clearly but FM stereo cannot. FM stereo has the smallest service area, and is prone to picking up static and other types of interference (for example, noise).

HINT:

Besides the problem of static, there are other problems, such as "phasing", "multi path" and "fade out". These problems are caused not by electrical noise but by the nature of the radio waves themselves.

Fig 2: Identifying Service Area

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1. AM broadcasts are susceptible to electrical 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 of the ionosphere and the other signal is received directly from the transmitter.
   Fig 3: Identifying Phasing

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2. Multi path is a type of interference created when a vehicle receives 2 radio wave signals from the same transmitter. One signal is reflected off of buildings or mountains and the other signal is received directly from the transmitter.
   Fig 4: Identifying Multi path

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
3. Fade out is caused by objects (buildings, mountains, etc.) 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 much more difficult to deflect.

1. Technicians must have a clear understanding about the customer's noise complaints. Use the following table to diagnose the problems.
   Fig 5: Identifying Fade Out

   Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
   RADIO WAVE PRESUMABLE CAUSE CHART
   
   

   Radio Wave	Condition in Which Noise Occurs	Presumable Cause
   AM	Noise occurs in a specified area	Strong possibility of foreign noise
   AM	Noise occurs when listening to faint broadcasting	The same program may be broadcasted from multiple local stations If the program is the same, one of those may be tuned in
   AM	Noise occurs only at night	Strong possibility of beats from a distant broadcasting
   FM	Noise occurs at a specific location during driving	Strong possibility of multi path noise and fading noise caused by changes in FM frequency

   HINT:

   When the noise that occurs does not match the examples above, refer back to "Reception Problems" (step  3). Refer to the descriptions about phasing and multi path.