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Query Abt FM & AM

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konarkk

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I need help for below que.

Why FM is preffered over AM for sound signal transmission?

do reply early
 

vicky

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HI DEAR,
FM broadcasting is a broadcast technology invented by Edwin Howard Armstrong that uses frequency modulation (FM) to provide high-fidelity sound over broadcast radio.

Random noise has a 'triangular' spectral distribution in an FM system, with the effect that noise occurs predominantly at the highest frequencies within the baseband. This can be offset, to a limited extent, by boosting the high frequencies before transmission and reducing them by a corresponding amount in the receiver. Reducing the high frequencies in the receiver also reduces the high-frequency noise. These processes of boosting and then reducing certain frequencies are known as pre-emphasis and de-emphasis respectively.

The amount of pre-emphasis and de-emphasis used is defined by the time constant of a simple RC filter circuit. In most of the world a 50 µs time constant is used. In North America, 75 µs is used. This applies to both mono and stereo transmissions and to baseband audio (not the subcarriers).

The amount of pre-emphasis that can be applied is limited by the fact that many forms of contemporary music contain more high-frequency energy than the musical styles which prevailed at the birth of FM broadcasting. They cannot be pre-emphasized as much because it would cause excessive deviation of the FM carrier. (Systems more modern than FM broadcasting tend to use either program-dependent variable pre-emphasis; e.g. dbx in the BTSC TV sound system or none at all.)
 

cameo_2007

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Both signals are prone to slight changes in amplitude. In an AM , these changes result in static. In an FM, slight changes in amplitude doest matter,since the audio signal is conveyed through changes in frequency, the FM receiver can just ignore changes in amplitude.
 

rkodaira

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Commercial FM transmissions have 15kHz audio bandwidth. AM transmissions have bandwidth narrower than FM (if i remember well, around 5kHz), so its translates to much better quality for audio signals over FM transmission. Commercial FM has two audio channels (stereo) and AM is monoaural (one channel). Last: FM channels have larger separation than AM channels.
 

jinal patel

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The biggest advantage of FM over AM is the sound quality. It really porivde a high quality sound with excelent effect of each High frequency components.More over the effect of noise is very small since the information is contain in frequency vatiations rather then amplitude variations. Also further reduction of noise can be obtained by using pre-emphasis circuit in transmitting side and De-emphasis circuit in receiving side.
Further more we can use Class C power amplifier for successiding stage to increase the over all eficiency. Also due to using Amplitude limiter circuits in receiving side, any unwanted amplitude variation can be minimized in receiver.
So do to all above it mainly provide superier sound quality than AM
 

grittinjames

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external nose will never chage frequency of another signal .it can disturb amplitude.

in fm change in frequency is used to modulate sound singnal . so if we are able to retrive the signal with disturbanse in aplitude also be able to demodulate with out disturbanse in signal
 

Electronica

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an AM signal is more susceptible to noise than FM because of infinetly large bandwidth of FM.
 

Mansour_M

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Hi Dear konarkk!

The answer is simple! Sound is sensetive and some noise can damage it completely and this effect is easily reflected when you are listening to a sound. The noise is usually adding to the amplitude of sound singnal and as you know AM is based on modulatin amplitude of the carrier, so the noise adds itself to the amplitude of modulated signal. In order to omit this problem we can use FM method. Because in FM method the informmation signal is embeded in the carrier frequency and noise seldom interfere with frequency of signals. On the other hand you can transmit a stereo sound signal with FM.

Thanks!
 

saubhik

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Because FM is more immune to noise than AM , and in ca of transmitting the sound signal to a far place ther comes the chance of amplitude power loss of signal .

these are the main reasons why FM is preferred wrt Am in Sound signal transmission
 

anwer_sbh

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FM cost more B.W , since vedio has high frequencies thus FM will require more B.W than AM.
 

spikeyang

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an AM signal is more susceptible to noise than FM because of infinetly large bandwidth of FM

Mm, this is what spectrum spreading means. thinking...
 

IBO

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am is more prone to noise than fm.
fm larger bw better quality.
 

ibeanjacob

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FM is preffered over AM because

1. FM is frequency modulation and AM is amplitude modulation.
Noise generally distorts amplitude,so FM is less prone to noise.

2.In FM there is less inter-channel interference.

3.In FM your can transmit CD quality sound(that is upto 15khz frequency which covers almost the whole audio range of humans),which is not possible in AM.

4.Higher frequecy so smaller antenneas.

5.More channels.
 

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