Question

Pre-emphasis in FM system is done to

• A. compress modulating signal.
• B. expand modulating signal.
• C. amplify lower frequency component of the modulating signal.
• D. amplify higher frequency component of the modulating signal.

Answer 1

Answer: (D)

amplify higher frequency component of the modulating signal.

Pre-emphasis of higher frequency component is required in FM-system because high frequency terms of modulating signal have small amplitude and therefore small power relative to those of low frequency term.
In the reproduced program at the o/p, these high frequency terms have poor SIN ratio and at time noise may completely mask the signal at these high frequencies, so it is necessary to provide pre-emphasis of high frequencies.