Modulation : -

Transmission of information by communication systems over large distances is quite a feat of human ingenuity. We can talk, video chat and text anyone on this planet! The communication system uses a very clever technique called Modulation to increase the reach of the signals. Two signals are involved in this process.

Types of Modulation -

There are three types of Modulation:

1. Amplitude Modulation
2. Frequency Modulation
3. Phase Modulation

Message signals also known as baseband signals are the band of frequencies representing the original signal. This is the signal to be transmitted to the receiver. Frequency of such a signal is usually low. The other signal involved with this is a high-frequency sinusoidal wave. This signal is called the carrier signal. The frequency of carrier signals is almost always higher than that of the baseband signal. The amplitude of the baseband signal is transferred to the high-frequency carrier. Such a higher frequency carrier is able to travel much farther than the baseband signal.

Need for modulation : -

• Antenna lengths : The transmitting and receiving antenna can have convenient lengths comparable to a quarter of the carrier wavelength λ.

• Transmission range : For smaller λ (or higher frequency), the maximum power that cna be radiated from an anenna of a given length increases. This increases the transmission range.

• Frequency translation : Modulation of baseband signals onto a high frequency carrier confines the signals into a narrow frequency band. With the choice of appropriate carrier frequency and modulation technique, this frequency band can be suitably shifted into the passband of the intended communication channel.

• Multiplexing : Confining a message signal into a narrow frequency band allows sending multiple message signals at the same time over the shared communication channel by a technique called multiplexing.