 Hello friends, Myself Ilya Arsandhani, Assistant Professor from Department of Electronics, Walsh and Institute of Technology, Solopur. Today, we are going to see the topic frequency generation part 2 from the subject analog communication. So this in this, the learning outcomes are at the end of this topics you will come to know or you can design FM and PM modulator by different methods. Also you can describe the different applications of FM and PM as well as you can discuss the limitations of FM generation system. So generation of FM is done in two ways. First one is the direct method, second one is the indirect method. The direct method includes reactance modulator and vector diode method, whereas the indirect method includes Armstrong's generation method. The reactance modulator generally includes this circuit. So this circuit basically it is a two stage amplifier circuit. This is the first stage and this is the second stage. Here the audio input is given to the first stage amplifier and the carrier is generated in this circuit by itself and the output is generally taken across the RECB configuration. Here the CC generally acts as a coupling capacitor which then is connected to the second stage, here the RFC, here the two RFCs are used. These are generally the inductors which are used for the tuning of the first stage and the second stage transistorized amplifier. Here the CC which provides the coupling output to the second stage, here in this second stage there are variations in the frequency with respect to the carrier which is being generated and the output is generally given to the LC tank circuit where C1 and C2 and a variable capacitor is used. This generally provides a tuning circuit at which the output is taken that is the FM generated output is taken across the secondary windings. The capacitors C and C1 and C2 are tuned to a particular frequency at which we get or we want the particular output. Here this circuit is majorly used in the communication type of the application. Here a diode modulator here this circuit majorly consists of a virector diode which is shown here at D1. The modulating input is given through the coupling capacitor C3 and which then passes through the RFC coil or the inductor which is tuned for a particular frequency. The R1 and R2 generally provides the biasing for the total circuit. Then the positive peak of the signal goes to the virector or passes through the virector diode and through the capacitor C2 the C2 starts charging and then at a particular point that is at the negative stage of the signal it discharges. The virector diode generally maintains the current that is ID for a period and then the output is taken across the L1 and C1 capacitor. The generally the L1 C1 acts as a tank circuit where the output is taken and it is then given to the carrier oscillator. So this is the working of the virector diode modulator. Similarly FM transmitter generally includes the Armstrong method. This method is generally known as the indirect method. In this first the signal is converted into the first the signal is converted into the AM signal and then it is converted into the frequency modulated wave. Here the carrier is provided by the crystal oscillator. This is then given to the buffer which then gives to the combining network. Here basically the combining network has a second input through the audio equalizer which is nothing but a modulating signal which is then given to the balanced modulator. Here balanced modulator gives an output of a single sideband only because here it has another input of 90 degree phase shift due to which only a single sideband is passed to the combining network. Thus the combining network combines the single stage single sideband and the carrier and according to the AF or the sideband the carrier is varied in accordance with the frequency of the single sideband. Then it is given to the first group of multiplier where the carrier frequency and the modulation index is maintained in this first group and then it is again given to the mixer. Here the mixer has another input from the carrier oscillator because here the signal in the mixer has a very low carrier frequency and hence it becomes necessary to give the carrier signal by which the frequency of the carrier will vary in accordance with the sideband of the modulating signal. Here it is then again given to the second group of multiplier so that we get a high carrier frequency and modulation index. Hence the output is taken across the class C power amplifier where the power of the signal which is a FM generated signal is increased before transmitting and hence it is transmitted by using a transmitting antenna. So what are the limitations of direct method? First in this method it is very difficult to get high order stability in carrier frequency. Secondly as a basic oscillator is used the circuit is not stable and hence it is controlled by using a modulating signal. Thirdly in this method we get distorted FM due to non-linearity of the varactor diode which is in terms of the current and the discharging of the capacitor. Next what are the advantages, disadvantages and applications of FM? Basically the advantages of FM are transmitted power remains constant in this type of generation technique. FM receivers are immune to the noise that means noise can get easily affected when the signal passes through the channel and gets received at the receiver. It has a good capture effect, no mixing of signals can be done in the FM. What are the disadvantages of FM? The greatest disadvantage of FM are it uses much of the spectrum space, the bandwidth here required is more that is the bandwidth is wider. Modulation index can be kept low to minimize the bandwidth which can be used. That reduction in modulation index reduces the noise immunity. It is used only for the very high frequencies that is VHF and UHF. Applications of FM here FM can be used in radio broadcasting, secondly sound transmission in TV or police wireless and FM can also be generated by using the IC566. So this is the circuit diagram. So you have to tell the operation of FM that is discuss the operation in which FM can be generated by using IC566 for this you can refer the previous slide. And next you have to discuss the advantages, disadvantages and limitations of direct and indirect FM method FM generation method. So these are the references for you people for the further study. Thank you for watching the video.