Question

In a communication system, what is meant by modulation? State any two types of modulation.

Answer 1

Hint: When the signal with a specific frequency has to travel very long distances, it needs to be modulated. This modulation means altering any of the properties of a signal wave such as amplitude, frequency, and phase.

Complete step by step answer:
(i) A signal wave can be a sound wave or anything. When the sound wave is produced, it can be heard within a certain distance. But if that same sound has to reach very long distances, it needs to be modulated.
(ii) If the properties of the signal wave are modulated, the message can also get altered. So we have to take care of the signal wave. For that cause, we use a high-frequency wave as a carrier to carry our signal wave. This high-frequency carrier wave has more energy; hence it can travel long distances against external disturbances. We call this high-frequency wave as “carrier wave”
(iii) The process of changing the parameters of a carrier wave in accordance with the signal wave is called modulation.
(iv) The signal which contains the message is called the modulating signal. And the resultant signal after modulation is called a modulated signal. Hence,
Modulating signal + carrier signal = Modulated signal
(v) There are three types of modulations based on the parameters we modulate. They are:
1. Frequency modulation (FM)
2. Amplitude modulation (AM)
3. Phase modulation (PM)

(vi) After we modulate the signal, the antennae radiates the modulated signal out, and then the receiver receives it. That antenna needs to be in order to the wavelength of the modulated signal.
Length of the antennae = wavelength of the modulated signal.
$L = \lambda = \dfrac{c}{\nu }$
$L = \dfrac{{3 \times {{10}^8}}}{\nu }$
If the modulated signal is in the audible frequency \[20Hz - 20KHz\]. Then,
\[L = \dfrac{{3 \times {{10}^8}}}{{20 \times {{10}^3}}}\]
\[L = 15000m\].
We cannot build the antennae of this much longer. So we choose the very high-frequency carrier wave which is more than the audible frequency. Suppose, if we choose the carrier wave of frequency \[3000KHz\]. Then the length would be
\[L = \dfrac{{3 \times {{10}^8}}}{{1000 \times {{10}^3}}}\]
\[L = 100m\]. It is possible to build the antennae of this length. Hence, we should use a very high-frequency carrier wave.
(vii) There are more chances in mixing up of signals while transmitting. The high-frequency carrier wave can avoid this problem. And setting the specific frequencies of each signal can avoid this issue.
(viii) This process of modulation also paves the way for wireless communication.

Note:
The modulation has many applications in the modern world. This helps in larger signal to noise ratio, broadcasting of FM radio, RADAR, telemetry, seismic prospecting, EEG monitoring for new-borns, music synthesis etc.