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, slightly similar to a sine wave. It does not carry much information that we can relate to data or speech. The concepts of Amplitude Modulation, Modulation, and Demodulation, along with their differences are explained below.

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 on carrying. Modulation is similar to hiding code in the carrier wave.

Types of Modulation

Types of Modulation And Demodulation

There are three types of modulation, namely:

  • Frequency Modulation
  • Amplitude Modulation
  • Phase Modulation

Amplitude Modulation

It is 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

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

Frequency Modulation

In this modulation the frequency of the carrier signal is altered in proportion to the message signal while the phase and amplitude are kept constant is called frequency modulation.

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 is a bit more complicated when it comes to digital. The voice sample is considered at some rate and then compressed into a bit (the 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 a 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.
  • A modem is an equipment that performs both modulation and demodulation.
  • Both processes aim to achieve transfer information with the minimum distortion, minimum loss, and efficient utilisation 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.

Frequently Asked Questions

What is the effect of distortion in modulation?

Distortion takes place when the amplitude of the modulating signal is greater than the amplitude of the carrier. This results in the transmission of incorrect information.

What is the reference line for the modulating signal?

The reference line for the modulating signal is the carrier peak line.

The reference line for the modulating signal is the carrier peak line.

State if the given statement is true or false: In amplitude modulation, the instantaneous values of carrier changes along with a change in amplitude and frequency of the modulating signal.

The given statement is true. The carrier frequency remains unchanged while the amplitude varies in the modulating signal.

Name the term used for explaining the line connecting the positive and negative peaks of the carrier waveform.

An envelope is defined as an imaginary line that connects the positive and negative peaks of the carrier waveform.

What is measuring wave?

Measuring waves is also known as the modulating wave. It is the wave that is superimposed on a carrier wave with high frequency.


  1. pratyush kumar prabhakar

    nice notes i am impressed

  2. what is the frequency and modulation index of AM Modulation and AM demodulation

    1. The modulation index of AM modulation is defined as the extent of amplitude variation to which the carrier signal can vary from its static level.
      The frequency of the AM modulation is usually restricted to 20 kHz when the carrier signal is at full range. However, most of the signals have the upper modulating frequency limit of 5 kHz.

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