Hint: Modulation is the process by which some characteristic usually amplitude, frequency or phase angle of a high frequency carrier wave is varied in accordance with the instantaneous value of the low frequency audio signal, called the modulating signal.
Complete step by step answer:
Let us see what is frequency modulation: It is the process of changing the frequency of the carrier voltage according to the instantaneous value of the modulating voltage. The original frequency is called centre frequency. Frequency deviation is the amount by which the frequency of the carrier wave changes or shifts above or below the resting frequency.
It is the process in which the amplitude of the high frequency carrier wave changes in accordance with the instantaneous value of modulating signal. In amplitude modulation voltage proportional to the amplitude of the modulating signal gets added to the carrier wave.
In order to transmit the audio signal each signal is translated to a low frequency signal range. So that it is easily recoverable and distinguishable from other signals at the receiving stations.
For T.V broadcasting we use frequency modulation for audio signal and amplitude modulation for video transmission. As different modulations have different advantages.
Hence, the correct answer is option A.
Need of modulation:
(I)Message signals are also called baseband signals. In fact the term base band refers to the band of frequencies of the original signal , as produced by the source of information. Audio signals have a bandwidth of about 20 KHz such low frequencies cannot be transmitted directly to long distances and hence need to be modulated.
(II)Amplitude of the carrier wave changes according to the modulated signal. Also the frequency of amplitude modulated waves is equal to the frequency of the unmodulated carrier wave.