Low Level and High Level Modulation Block Diagram (AM Transmitter Block Diagram)

This post is about the generation of amplitude modulation. Here we will see two different ways of generating Amplitude Modulation (AM).
So the generation of amplitude modulation (AM) can be of following two types-

Types of Amplitude Modulation Generation

Low level Amplitude Modulation
High level Amplitude Modulation

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Here we will understand the difference between these two types of techniques of generation of AM, with the help of block diagrams-

Low Level Amplitude Modulation (Block Diagram)

The image given below shows the block diagram of a Low Level Amplitude Modulation

Block Diagram of Low Level Amplitude Modulation 

Now observe the image carefully-
This block diagram shows 3 main blocks-
#Low level AM modulator
#Wideband power amplifier and
#RF carrier oscillator

As you can see in the diagram that low level AM modulator has two inputs. At its first input we apply the modulating signal source (message signal) and it's second input is supplied by the RF carrier oscillator.
Since it is low level amplitude modulation therefore before applying the modulating signal to the low level AM modulator, we do not amplify it. In the same way, RF carrier is also not amplified.
Therefore you observe here that in low level AM modulation, neither the modulating signal nor the RF carrier is amplified before applying to low level AM modulator.

But when we get the amplitude modulated wave at the output of this low level AM modulator, then it is amplified by the wide band power amplifier. 
This wideband power amplifier amplifies the power level of the amplitude modulated wave. The wideband is used to preserve the sidebands of the amplitude modulated wave and then it is transmitted with the help of this antenna.

High Level Amplitude Modulation (Block Diagram)

The image below is the block diagram of high level amplitude modulation.

Block Diagram of High Level Amplitude Modulation

The main building blocks of high level amplitude modulation include-
#Wideband power amplifier
#RF carrier oscillator
#Narrow band power amplifier and
#High level AM modulator

As this is high level amplitude modulation, therefore it uses a high level AM modulator which operates at high level. Before applying the message signal and the carrier wave to the high-level AM modulator, both of these signals are amplified.
The modulating signal is power amplified by the wide band power amplifier to preserve the sidebands of the modulating signal but the RF carrier is amplified by the narrow band power amplifier as the carrier wave has fixed frequency. Therefore narrowband power amplifier is sufficient for its amplification. 
Now after amplification of both the signals, they are applied to the high level AM modulator. Then this amplitude modulated signal is transmitted by the antenna.
The example of high level Amplitude Modulation is the collector modulation method.

So this was all about the generation of amplitude modulation with the help of low level amplitude modulator and high level amplitude modulator.

Read More:

Go to home page
Need and benefits of modulation
Amplitude modulation (time domain equations and waveforms)
Frequency spectrum of amplitude modulation (waveforms and equations derivation)
Amplitude modulation vs frequency modulation (advantages and disadvantages)
Conventional AM vs DSB-SC vs SSB-SC vs VSB (comparison of AM systems)
Low level and high level modulation block diagram (AM transmitter block diagram)
Frequency translation / frequency mixing / frequency conversion / heterodyning (basic concepts and need)