Modulation And Demodulation

The frequency of a Radio frequency channel can be explained best as the frequency of a carrier wave. A carrier wave is purely made up of constant frequency, bit similar to sine wave. It doesn’t carry much information that we can relate to data or speech. The concepts of Amplitude Modulation, Modulation and Demodulation, along with their difference is explained below.

Modulation And Demodulation

Modulation And Demodulation

To involve data information or speech information, another wave has to be imposed known as input signal above the carrier wave. This process of imposing an input signal on a carrier wave is known as modulation. Put differently; modulation modifies the shape of a carrier wave to encode the data information that we intended in carrying. Modulation is similar to hiding a code in the carrier wave.

Types of Modulation

Modulation And Demodulation

There are three types of modulation namely:

  • Frequency modulation
  • Amplitude modulation
  • Phase modulation.

Amplitude modulation

A kind of modulation where the amplitude of the carrier signal is changed in proportion to the message signal while the phase and frequency are kept constant.

 Phase modulation

A kind of modulation where the phase of the carrier signal is altered according to the low frequency of the message signal is called as phase modulation.

Frequency modulation

A kind of modulation where the frequency of the carrier signal is altered in proportion to the message signal while the phase and amplitude are kept constant.

Modulation mechanisms can also be digital or analog. An analog modulation scheme has an input wave that changes like a sine wave continuously, but it’s a bit more complicated when it comes to digital. The voice sample is considered at some rate and then compressed into a bit (stream of zeros and ones). This, in turn, is made into a specific type of wave that is superimposed on the carrier.

What is Demodulation?

Demodulation is defined as extracting the original information carrying signal from a modulated carrier wave. A demodulator is an electronic circuit that is mainly used to recover the information content from the modulated carrier wave. There are different types of modulation and so are demodulators. The output signal via demodulator may describe the sound, images or binary data.

Difference between Modulation and Demodulation

  • Modulation is the process of influencing data information on the carrier, while demodulation is the recovery of original information at the distant end from the carrier.
  • Modem is the equipment that performs both modulation and demodulation.
  • Both processes aim to achieve transfer information with the minimum distortion, minimum loss and efficient utilization of spectrum.

Even though there are different methods for modulation and demodulation processes, each has its own advantages and disadvantages. For example, AM is used in shortwave and radio wave broadcasting; FM is mostly used in high-frequency radio broadcasting, and pulse modulation is known for digital signal modulation.


Practise This Question

The magnetic flux linked with a coil at any instant ‘t’ is given by ϕ=5t3100t+300, the e.m.f. induced in the coil at t = 2 second is