Inspection Procedure 4: Noise is Present while Moving (FM).




DIAGNOSIS PROCEDURE


note FM waves have the same properties as lamp, and can be deflected and blocked. FM signal reception is severely degraded in the shadow of obstructions such as buildings or mountains. An FM receiver will then only receive a reflected signal.
1.The signal becomes weak as the distance from the station’s transmission antenna increases. The signal strength received depends on the signal strength of the transmitting station and intervening obstructions such as buildings and hills. Generally speaking, the area of good reception is approximately 20 - 25 km for stereo reception, and 30 - 40 km for monaural reception.
2.The signal will becomes weak when an area of shadow from the transmitting antenna (places where there are obstructions such as mountains or buildings between the station transmitter and the vehicle), and noise will appear. <This is called first fading, and gives a steady buzzing noise.>
3.If a direct signal hits the antenna at the same time as a signal reflected by obstructions such as mountains or buildings, interference of the two signals will generate noise. When moving, noise will appear each time the vehicle’s antenna passes through this kind of obstructed area. The strength and interval of the noise varies according to the signal strength and the conditions of deflection. <This is called multipath noise, and is a repetitive buzzing.>
4.Since FM stereo transmission and reception has a weaker field than monaural, it is often accompanied by a hissing noise.
After taking measures to prevent the noise, check that no noise occurs.
5.Change to a different station with a stronger wave to boost resistance to interference.
6.Suppress high tones to reduce noise.
7.Extend antenna completely.
If there is noise, the following causes can be considered.
8.If due to vehicle noise: It may not be possible to prevent noise if the signal is weak.
9.If due to external noise: In almost all cases, prevention on the receiver side is not possible. Weak signals especially are susceptible to interference.
If there is more noise than on radios in other vehicles, find out the noise condition and the name and frequency of the receiving stations from the owner, and consult with the radio manufacturer’s service centre.