Question

Pre emphasis in FM mode is done to
A) compress modulating signal
B) expand modulating signal
C) amplify lower frequency component of modulating signal
D) amplify higher frequency component of modulating signal

Answer 1

The high frequency waves will have a poor SIN ratio usually at the output and this leads to more noise production which results in masking of the signal at high frequencies. Therefore, we need to check the high frequency signals and make certain changes in it before producing the output.

Complete answer:

We need pre-emphasis on higher frequency components in FM systems because high frequency terms of modulating signals have small amplitudes and they need small power relative to those of low frequency terms. Also, the higher frequency will have poor sin ratio and more noise is produced at the output which masks the signal at the output.
Therefore, to overcome this issue, we need to pre-emphasis the higher frequency component of modulating signal in the FM mode.

So, the correct answer is “Option D”.

Additional Information:
In transmissions such as phonograph record tape, the input signal whose frequency close to noise frequency is boosted. This procedure is pre-emphasis. Later, when signal is retrieved, de-emphasis is applied so that any noise added during the time of pre-emphasis or noise present in frequency range previously boosted signal will get attenuated. Attenuation is the process of reducing some force or value of something. In physics, we use this term when we reduce the amplitude of signals or electric current for some purposes.

Note:
The pre-emphasis procedure is always done at the transmitter and the de-emphasis is done at the receiver. De-emphasis is attenuating the frequencies that are boosted at the transmitter. We use these two procedures so that the signal output is free form noise and the signal-to-noise ratio will also get improved.