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Modulation

What is it?

  • Modulation is a process of mixing a signal with a sinusoid to produce a new signal. 

  • The sinusoidal signal that is used in the modulation is known as the carrier signal.

  • Such a higher frequency carrier wave is able to travel much farther than the baseband signal.

  • In other words, we can say that modulation is used because some data signals are not always suitable for direct transmission, but the modulated signal may be more suitable.

​​​MODULATOR

Message signal

Carrier signal

Modulated

Signal

This modulated signal is to be transmitted to the receiver. 

  • A radio frequency modulator (or RF modulator) takes a baseband input signal and then outputs a radio frequency modulated signal. This is often a preliminary step in signal transmission, either by an antenna or to another device such as a television.

  • A demodulator is a circuit that is used in amplitude modulation and frequency modulation receivers in order to separate the information that was modulated onto the carrier from the carrier itself.

Types of Modulation

There are 3 basic types of modulation.

Modulation

Amplitude Modulation (AM)

Frequency Modulation (FM)

Phase Modulation

(PM)

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

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

A type of modulation where the phase of the carrier signal is varied according to the low frequency of the message signal is known as phase modulation.

Differences between AM & FM

AM

Amplitude Modulation

VS

  • Works by varying the Amplitude of the signal while frequency remains constant.

+

Message signal

 

Carrier signal

 

Modulated signal

 

FM

Frequency Modulation

  • Works by varying the Frequency of the signal while frequency remains constant.

+

Message signal

 

Carrier signal

 

Modulated signal

 

  • Has poorer sound quality.

  • Has better sound quality.

FM RADIO

  • AM can be used for transmission over long distance.

  • MF can be used for transmission over short distances.

  • AM is cheaper.

  • Simple circuitry.

  • FM is costly.

  • Complicated circuitry for transmission and reception.

  • Ranges from 535 to 1705 KHz.

  • Ranges in a higher spectrum from 88 to 108 MHz.

  • suitable is aviation communications.

  • With an AM broadcast, it susceptible to noise.These changes result in static.

  • Used in aerospace and defense, wireless, and broadband communications applications.

  • With an FM broadcast, slight changes in amplitude don't matter.

Need of Modulation

  • The height of the Antenna can be reduced.

  • Reduce wire over an analog communication line.

  • Can eradicate interference of multiple signals.

  • To reduce the noise & distortions.

  • To multiplex the number of signals.

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