Question

Define modulation. Why is it necessary?

Answer 1

Hint: Transmitting signals is very useful and important for every human these days. Without the transmission of signals, everyone would get non-synchronized. Signals can be transmitted wirelessly or using wires. When we say something, the person nearby us hears our voice and hence the signal gets transmitted. But what if the person to which we need to talk is at a large distance from us? In such cases transmission plays a major role.

Complete step by step answer:
What is modulation? – Modulation is the process in which one of the properties of waves like amplitude, frequency and phase is changed according to the base band signal.
Why is it necessary? –
1. To reduce the size of the antenna for transmission.
2. To reduce interference of signals so as to maintain the uniqueness of each signal.
3. To allow multiplexing of the signals.
Now we’ll see each point one by one.
1. To reduce the size of the antenna – We know that the wavelength ($\lambda$) of the signal transmitted is directly proportional to the length (L) of the antenna. Roughly the relationship is $\lambda = \dfrac L4$.
Suppose we need to transmit the signal of frequency 10kHz:
That means the wavelength should be $\dfrac{3\times 10^8}{10000} = 30km$ [using $\nu \lambda = c$]
So roughly the size of antenna = $\dfrac{30000}{4}=\ 7500m$
Constructing this size of antenna is practically not possible.
But if the signal is of frequency 10MHz:
i.e. we increased the frequency by factor of 1000. In this way the size of the antenna will decrease to 7.5m, which is practically possible.
Varying frequency of the carrier wave is done by the process of modulation.
2. To reduce interference: We know that the favorable condition for interference is that the frequency of the waves must be almost the same. To transmit the waves of nearly the same frequency through the same channel would create disturbance. Hence we’ll not get the required signal at the output end. Hence by varying frequencies, we can prevent interference and signal can be transmitted through the same channel. This is also the advantage for Multiplexing of signals.

Note:
Thus by varying frequency, we get a lot of advantages in communication. Interference can also be prevented by varying the amplitudes of the waves. In some cases, we want desired interference of the waves, which can be achieved by changing the phase of the waves. Hence modulation plays a very important role in communication systems.