Sideband Modulation


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In the process of Amplitude Modulation or Phase Modulation, the modulated wave consists of the carrier wave and two sidebands. The modulated signal has the information in the whole band except at the carrier frequency.

Sideband

A Sideband is a band of frequencies, containing power, which are the lower and higher frequencies of the carrier frequency. Both the sidebands contain the same information. The representation of amplitude modulated wave in the frequency domain is as shown in the following figure.

Sideband

Both the sidebands in the image contain the same information. The transmission of such a signal which contains a carrier along with two sidebands, can be termed as Double Sideband Full Carrier system, or simply DSB-FC. It is plotted as shown in the following figure.

DSBFC System

However, such a transmission is inefficient. Two-thirds of the power is being wasted in the carrier, which carries no information.

If this carrier is suppressed and the power saved is distributed to the two sidebands, such a process is called as Double Sideband Suppressed Carrier system, or simply DSBSC. It is plotted as shown in the following figure.

DSBSC System

Now, we get an idea that, as the two sidebands carry the same information twice, why can’t we suppress one sideband. Yes, this is possible.

The process of suppressing one of the sidebands, along with the carrier and transmitting a single sideband is called as Single Sideband Suppressed Carrier system, or simply SSB-SC or SSB. It is plotted as shown in the following figure.

SSBSC System

This SSB-SC or SSB system, which transmits a single sideband has high power, as the power allotted for both the carrier and the other sideband is utilized in transmitting this Single Sideband (SSB).

Hence, the modulation done using this SSB technique is called as SSB Modulation.

Sideband Modulation − Advantages

The advantages of SSB modulation are −

  • Bandwidth or spectrum space occupied is lesser than AM and DSB signals.

  • Transmission of more number of signals is allowed.

  • Power is saved.

  • High power signal can be transmitted.

  • Less amount of noise is present.

  • Signal fading is less likely to occur.

Sideband Modulation − Disadvantages

The disadvantages of SSB modulation are −

  • The generation and detection of SSB signal is a complex process.

  • Quality of the signal gets affected unless the SSB transmitter and receiver have an excellent frequency stability.

Sideband Modulation − Applications

The applications of SSB modulation are −

  • For power saving requirements and low bandwidth requirements.

  • In land, air, and maritime mobile communications.

  • In point-to-point communications.

  • In radio communications.

  • In television, telemetry, and radar communications.

  • In military communications, such as amateur radio, etc.

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