9 Jun 2018

Conventional AM Vs DSB-SC Vs SSB-SC Vs VSB - Comparison of AM Techniques - Types of Amplitude Modulation

Here we will discuss, What is Amplitude Modulation and various Amplitude Modulation Techniques.
The amplitude modulation systems may be of different types. Here the comparison of a Amplitude Modulation Systems (AM systems) has been discussed.

What is Amplitude Modulation (AM)

Amplitude Modulation may be defined as a system, where the maximum amplitude of the carrier wave varies, according to the instantaneous value (amplitude) of the modulating (message or baseband) signal.

Types of Amplitude Modulation

1- Conventional Amplitude Modulation (Conventional AM)
2- Double SideBand - Suppressed Carrier (DSB-SC)
3- Single SideBand - Suppressed Carrier (SSB-SC) and
4- Vestigial SideBand (VSB)

Amplitude Modulation Techniques Video


 

So let's understand the basic concept of all these various Amplitude Modulation systems and their comparison. Here we will also discuss where these Amplitude Modulation systems are used i.e. their applications in various fields.

So let's starts 
Let me first tell you, what these various Amplitude Modulation Techniques mean-

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Conventional Amplitude Modulation (Conventional AM)


In this modulation system the amplitude modulated signal contains carrier wave and 2 sidebands (upper side band and lower side band)

Double Sideband Suppressed Carrier (DSB-SC)


As clear by the name itself, the double sideband suppressed carrier contains only 2 sidebands and the carrier is suppressed (not present).

Single Sideband Suppressed Carrier (SSB-SC) 


The single sideband suppressed carrier contains only one sideband and no carrier is present. In this one sideband is suppressed.

Vestigial Sideband (VSB) 

In Vestigial sideband modulation, instead of rejecting one sideband completely (like SSB), a gradual cutoff of one side band is allowed.

Comparison of AM Modulation Techniques (Conventional AM vs DSBSC vs SSBSC vs VSB


1.Demodulation (detection) of conventional AM is easier than that of double sideband suppressed carrier and single sideband amplitude modulated systems. We can use rectifier or envelope detector to demodulate conventional amplitude modulation. Not only the demodulation of conventional AM is easy but also it is less expensive in comparison to other amplitude modulated systems.

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2. Conventional AM can be used for broadcasting services, because it is possible to produce conventional AM signals at high power levels.

3- Double sideband suppressed carrier and single sideband systems require lesser power to transmit the same information in comparison to conventional amplitude modulation (AM).
As we know that conventional AM contains two sidebands along with the carrier wave. Nearly 2/3rd of power is required to transmit this carrier wave and rest 1/3rd for the transmission of two sidebands. But it is important to note here that, the information is present only in the sidebands, the carrier contains no information. Although one sideband contains the full information and the other sideband is just the replica of it. So from this power point of view, conventional Amplitude Modulation is least efficient in comparison to other amplitude modulation techniques (schemes/systems)
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4- DSB-SC and SSB modulation systems are used in point-to-point communication while conventional AM finds application in public broadcasting systems. The double sideband - suppressed carrier and single sideband - suppressed carrier are but are much more Complex and expensive techniques. And it is always desirable for a broadcasting system to be very simple and less expensive. Because a broadcasting system contains 1 transmitter and serves millions of people while in point-to-point communication, we have 1 transmitter and few receivers.

5- following is the order of bandwidth required in various Amplitude Modulation systems-
Conventional AM > DSB-SC > VSB > SSB
It is clear from this order of bandwidth required that the single sideband is the most efficient modulation scheme.
It should also be noted here that, the bandwidth required for single sideband is only half of the bandwidth required for double sideband suppressed carrier and the bandwidth of vestigial sideband is nearly 25% higher than that of the single sideband but much lesser than double sideband - suppressed carrier.

6- Vestigial SideBand (VSB) signal generation is easiest in comparison to other techniques like conventional AM, double sideband - suppressed carrier and single sideband.

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7- VSB modulation scheme is used for the transmission of television signals while SSB is used for long distance transmission of voice signals, because it allows large spacing between the repeaters. The conventional Amplitude Modulation finds application mostly in public broadcasting services as it can be produced at higher power levels in comparison to other amplitude modulation techniques.


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