Advantages and disadvantages of pre emphasis and de emphasis in fm
Answers
High frequency noise leads to frequency distortion when its amplitude is higher than the components present in the modulating signal. In order to overcome this, FM circuits use techniques like Pre-emphasis at the transmitter and De-emphasis at the receiver.
Pre-emphasis
Advantages
1. It helps to amplify high frequency signal components so that they have a higher magnitude than the noise components. It improves the Signal to Noise Ratio or SNR.
2. It has a upper cutoff frequency from where the signal enhancement is flattened.
3. It is a simple High Pass Filter with amplification.
Disadvantage
If it is done beyond a limit there can be over modulation.
De-emphasis
1. It helps to bring the pre-amplified signal back to the normal amplitude level.
2. It has a cutoff frequency of about 2123 Hz.
3. It is a simple Low Pass Filter with time constant of around 75 µs.
Disadvantage
Risk of over modulation.