Modulation and demodulation play a very important role in communication.
Without Modulation and demodulation it will be very difficult to communicate on mobile phones, serve internet, watch TV, listen FM radio etc.



There are 3 basic types of modulation:
  • Amplitude modulation (AM).
  • Frequency modulation (FM).
  • Phase modulation (PM).


For ex-

If we produce an electric signal of voice using microphone then it will contain many frequencies within 20Hz – 20KHz. By transmitting this signal, it can interference (mixing of signals) with other signal in space produced by other devices. Also, for these low frequencies we need very large antenna to transmit the signal i.e. maximum of 3750 km. So, we must give particular device a particular bandwidth (frequency range) in which that channel can broadcast. This is done by modulating the voice signal.

Modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal (High frequency signal), with a modulating signal that typically contains information to be transmitted.
Advantages of Modulation
  • Antenna size gets reduced.
  • No signal mixing occurs (i.e. interference).
  • Communication range increases.
  • Multiplexing of signals occur.
  • Adjustments in the bandwidth is allowed.
  • Reception quality improves.
Here is the simple circuit diagram for Amplitude modulated wave.



It used n-p-n transistor in common emitter mode to increase the amplitude of the signal so that is can travel a large distance without much attenuation(signal given below).

Before demodulation we filter out the extra frequencies which we don’t want by using and LC oscillator circuit. It is the circuit which resonates at particular frequency given by-


Demodulation is extracting the original information-bearing signal from a carrier wave. A demodulator is an electronic circuit (or computer program in a software-defined radio) that is used to recover the information content from the modulated carrier wave.





In above picture capacitor and resistance can be of different values.

After demodulation we get our original signal through speaker.
This was the basic part of communication.