Question

In Phase Modulation:
(A) Only the phase of the carrier wave varies
(B) Only the frequency of the carrier wave varies
(C) Both the phase and the frequency of the carrier wave varies
(D)There is no change in the frequency or the phase of the carrier wave

Answer 1

We will first understand what a phase modulation is and then try to answer our question, as to what parameters this type of modulation has an effect. It is a modulation pattern used for enhancing communication signals for transmission. In this modulation, a certain specific message is encrypted as variations in the phase of a carrier wave.

Complete answer:
Let us first understand the basic principle on how Phase Modulation works for a transmission signal. For that purpose, we will first assign some useful terms that we are going to use in our solution.
Let the message signal that is to be transmitted from one place to another be denoted by $m(t)$.
Now, let the carrier wave on to which this message signal is to be modulated be given by $c(t)$, where $c(t)$is given by the following equation:
$\Rightarrow c(t)={{A}_{C}}\sin ({{\omega }_{C}}t+{{\phi }_{C}})$
Now, the phase modulated signal can be given by:
$\Rightarrow y(t)={{A}_{c}}\sin ({{\omega }_{C}}t+{{\phi }_{C}}+m(t))$
Thus, from the final wave equation, we can conclude that frequency and phase vary from moment to moment. Also, the peak amplitude and frequency remains constant, but as we change the amplitude of the message signal, the phase and frequency of the carrier wave changes accordingly.
Hence, from our observation, in Phase Modulation, both the phase and the frequency of the carrier wave changes.

So, the correct answer is “Option C”.

Note: Phase modulation of a transmission signal is generally used in transmission of radio waves and is used in many modern technologies like Wi-fi, Global System of Mobile communication, satellite televisions, etc. Apart from Phase Modulation, there are two other types of modulation. These are Amplitude Modulation and Frequency Modulation and their name suggests to us their working principle.