Identification Of Noise Source

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

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2. 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. FM stereo has the smallest service area, and is prone to pick up static and other types of interference such as noise.
3. 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.

   Fig 2: Identifying Service Areas Of AM And FM Broadcasts

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   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: Radio Reception Problems (Phasing)

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   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: Radio Reception Problems (Multipath)

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   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 much more difficult to deflect.

   Fig 5: Radio Reception Problems (Fade Out)

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4. Noise problem

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

HINT:

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