 Today we are going to see amplitude modulation in this unit. So in this unit the learning outcomes will be first the students can be able to derive an equation for AM that is amplitude wave equation. Next we can compare different levels of modulation. Here we are going to see what are the different levels of modulation and thirdly we can compute the power current and modulation index of an AM signal that is amplitude modulated signal. So these are the learning outcomes which we are going to go through in this unit. So basically what is amplitude modulation? It is defined as it is generally a process of it is a process in which amplitude of carrier signal is varied in accordance with the instantaneous values of amplitude of the information signal or it is also known as the modulating signal. This is the basic definition of amplitude modulation. Next in this as a carrier is used here the carrier is having a high frequency then that of the modulating signal or the main information signal. Here in other words here the modulating signal is superimposed on the carrier signal then it is transmitted. So what are the amplitude modulation basic definitions? We are going to see these basic definitions in terms of the equation. So as you can see here this is the modulating signal, this is the carrier signal and here it is the amplitude modulated wave. Here you will see the envelope and here is the later part. Here generally this acts as the Vmax and here it is the V minimum. So what are the respective equations for these waveforms? So these are the respective equations for these waveforms. The AM wave that is amplitude modulated wave is given by this equation AC1 plus K MT cos omega CT where AC cos omega CT is nothing but it is the equation of a carrier wave. MT is the equation or it is generally the representation of a modulating signal in time domain and whereas the K generally this denotes the modulation index of that particular amplitude modulated wave. So these are the equations and the respective waveforms. Next we are going to see what is the envelope and how a AM signal is represented. So basically now here as you can see the envelope. This part is the envelope part where it is nothing but AC1 plus KM of T. Here the envelope generally means the Vmax of that particular AM modulated signal or here this equation generally represents the side bands of the two side bands of the AM modulated signal and the total AM signal as we have seen in the previous slide it is given by this equation. Next the AM spectrum generally we are going to see the AM spectrum that is amplitude modulated wave spectrum in time domain and frequency domain. First we are going to see it in terms of time domain. So this is the waveform which generally shows the AM spectrum in time domain. Here as you can see this is the upper envelope this is the lower envelope. This generally denotes the Vmax and it is given by AC plus AM cos 2 pi FM T and here as it is the negative going envelope it is just represented in terms of a negative sign whereas the equation remains the same. Here as you can see the highest part of the envelope is denoted by AM or Vmax and the lowest part is denoted by AM or Vmin. As we know that the amplitude corresponds to the respective voltage of that particular frequency or that particular signal. Now we are going to see the AM spectrum in terms of frequency domain. Here M of T generally represents the modulating signal and S of T is the modulated signal. As you can see the M of T here it is represented by a single frequency band and the S of T that is the modulated signal is represented in terms of the two side bands and a carrier signal. So this one is the carrier signal and these two are the two side bands. Similarly now we are going to see what is meant by modulation index. So modulation index it is generally the measure of the extent to which carrier voltage is varied by the modulating signal. That means the carrier voltage is varied in accordance with the voltage of the modulating signal. Hence it is denoted by generally the modulation index is denoted by small M. It is given by the equation as M is equal to EM upon EC where EM is the maximum voltage of the modulating signal and EC is the maximum voltage of the carrier signal. Similarly it is given in terms of E max and E minimum also. So now we are going to see the cases the three different cases of the modulation index. First is the perfect one, second one is the over and third one is the under. So these are the three cases where the modulation index here we are considering the modulation index to be less than or equal to zero. In the second case we are considering the modulation index to be one where the percentage of modulation index is a hundred percent and in case three where the modulation index is greater than one. As we all know that modulation for getting a perfect modulation the modulation index should be of a value unity that is one. We are going to see the respective waveforms for such three cases. So here first as you can see we are getting such kind of the waveforms for the modulation index where modulation index is one or unity. Next when the value is greater than one here we are taking the value as two and the maximum amplitude of this waveform is two volt and one volt is added. This case is generally known as over modulation and you are seeing the respective waveforms in this. Next the modulation index here the modulation index value lies below one. Here we are taking the value as 0.05 where only 40 volt is added into the main waveform. Here we are seeing the respective waveform for the modulation index less than one such is called as the under modulation. So friends discuss the modulation index as we have studied in the later or the previous parts or the previous slides. Next we are going to see the different levels of the AM modulation or AM modulator transmitters. These are basically divided into low level and high level transmitters. So this is the basic block diagram for the low level AM transmitter which generally consists of RF carrier, buffer amplifier, modulator, RF power amplifier and then antenna. Voltage amplifier is also shown which gives whose output is given to the modulator. Here generally the RF carrier gives the output in these are the oscillations which are given to the buffer amplifier for the amplification purpose. The modulator will receive the two inputs that is carrier and the modulating signal through the mic and then the modulation takes place and then it is given to the power amplifier for the antenna coupling and then it is transmitted. Here in the high level as you can see here the RF carrier are there same blocks are used but here AF voltage amplifier and AF power amplifier used are used in the first stage and then later the modulation takes place. So what is the basic difference between low level and high level transmitters? So in the low level as you can see here the low in low level amplification takes place at the first stage and then modulation and in the high level initially the modulation takes place and then the amplification. So we will see the summary for this the lower level transmitter this can produce any kind of modulation that is AM, FM and PM. What is the disadvantage? It requires a linear RF power amplifier which reduces DC efficiency and the production cost due to this the production cost increases. The high level transmitter generally this have better DC efficiency than the lower transmitter and these are operated by using the battery. Next these high level transmitters are having some restrictions to generate AM modulation only. So students discuss types of AM modulation transmitters. So these are the references. Thank you for