Modulation

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Introduction - 

Hi guys,

Have you heard about modulation, what is mean by modulation, what are different types of modulation? I am sure you have if you are Engineering student. So, in this blog we will discuss basics of modulation.

So, our human voice signal contains the frequency up to 3 kHz and entire audible spectrum is between 20 Hz to 20 kHz. These low frequency signal called Baseband signal.

Baseband signal can not be transmitted over long distance, we need to convert into high frequency signal to transmit over long distance. This high frequency signal is called Carrier signal.

What is Modulation? 

Modulation is a process of converting baseband signal into a signal that varies with one of its properties like amplitude, frequency, phase.

We obtain modulated signal by adding carrier signal to baseband signal.












Why we need Modulation?

Reduce the antenna size –

So, how we can reduce the size of the antenna, we will understand this point with the help of some basic calculation. Length is directly proportional to wavelength, below equation will help you to understand the concept.

Equation –

L α λ

L = λ/4

C = λ x f

(C = speed of light i.e., 3 x 108 m/s, f = frequency of the transmitted signal, λ = wavelength of the transmitted signal)

So, if transmitted signal is of low frequency, then wavelength value will increase, and length is directly proportional to wavelength so length of antenna will also increase.

Reduce the interference –

If we transmit carrier signals without modulation then frequencies will be mixed it will cause interference, hence, to reduce interference carrier signals are transmitted with different frequencies.

Allow multiplexing of the signals –

When we transmit the signals with frequency modulation technic then multiple signals can be transmitted at the same time.

Moving next, we will see different types of modulation.

Types of Modulation –

1. Analog Modulation

2. Digital Modulation

1. Analog Modulation –

If signal in analog or sine wave form, then we called it as analog modulation.

There are two types of analog modulation,

i) Continuous wave Modulation

ii) Pulse Modulation

Continuous wave Modulation –

If signal is in continuous wave form, then we called it Continuous wave Modulation.

          Carrier signal



Continuous wave modulation further divided into three categories,

Amplitude Modulation (AM) –

The amplitude of the carrier signal changes according to the massage signal or audio signal.

Frequency Modulation (FM) -  

The frequency of the carrier signal changes according to the massage signal or audio signal.

Phase Modulation (PM) –

The phase of the carrier signal changes according to the massage signal or audio signal.


Pulse Modulation –

If signal is in pulse form, then we called it Pulse Modulation.


                                                                                Carrier signal

Pulse modulation further divided into four categories,

Pulse Amplitude Modulation (PAM) –

The amplitude of the carrier signal changes according to the massage signal or audio signal, width will remain same.


Pulse Width Modulation (PWM) –

The width of the carrier signal changes according to the massage signal or audio signal, amplitude will remain same.



Pulse Position Modulation (PPM) –

The position of the modulated pulse changes with respect to carrier signal with the change in the massage signal, width and amplitude will remain same.



Pulse Code Modulation (PCM) –

The massage signal samples and quantized at regular time interval and then with the help of analog to digital convertor signal is encoded.



2. Digital Modulation –

If signal is in square wave form, then we called it as digital modulation.

Digital Modulation further divided into three types,

Amplitude Shift Keying (ASK) –

Amplitude of the carrier signal changes according to digital bit stream.



Phase shift Keying (PSK) –

Phase of the carrier signal changes according to digital bit stream.


Frequency Shift Keying (FSK) –

Frequency of the carrier signal changes according to digital bit stream.


So I have covered the basics of Modulation in this blog, thank you for your time. If any query let me know in comment section.







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