AUDIO AND VISUAL SYSTEM IDENTIFICATION OF NOISE SOURCE


  1. Radio Description


    1. Radio frequency band


      1. Radio broadcasts use the radio frequency bands shown in the table below.

        A003BY9E02
    2. A003DFCE01
      Text in Illustration
      *1 FM (Stereo)
      *2 FM (Monaural)
      *3 AM

      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 broadcast cannot. An FM stereo broadcast has the smallest service area, and is prone to pick up static and other types of interference such as noise.

    3. Radio reception problems

      Tech Tips

      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. A003C50E01
        Text in Illustration
        *1 Phasing
        *2 Ionosphere

        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.

      2. A003EMWE01
        Text in Illustration
        *1 Multipath

        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.

      3. A003DQIE01
        Text in Illustration
        *1 Fade Out

        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.

    4. Noise problem

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

      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

    Tech Tips

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