 Hello friends, Myself Ilya Arsandhani, Assistant Professor from Department of Electronics, Valchan Institute of Technology, Solapur. Today we are going to see the topic Frequency Detectors Part 1 from the subject Analog Communication. So at the end of this topic, you will come to know or discuss the term FM Detectors in detail, similarly design the different FM Detectors and its types. What are the advantages and disadvantages of FM Detectors? So, first we will see how FM signal is generated. The FM generation of FM signal can be done by using two different methods. First include the direct method which has two sub processes that is first is reactance method and second one is directed diode method whereas the second one for FM generation method is indirect method which includes Armstrong's indirect method of FM generation. So detection of FM this process is generally or this process generally takes place at the receiving side. Here this is also divided into four basic types. The first includes slope detector, the second one includes the balanced detector. The third one includes foster sleeve method and the fourth one includes the ratio detector. So first we are going to see the slope detector. So this is the circuit for the slope detector and this is the particular frequency response for the same. Here the slope detector is nothing but as you can see if we take out these two tuning capacitors from the primary winding and secondary winding it is basic circuit of the half wave rectifier and here this is the response of the slope detector. Here initially at the receiving side the capacitors C1 and C2 these are tuned properly so that they can receive the required signals only and the signals generally lie between FC and FC plus Del F where Del F is nothing but the frequency deviation and this basically depends upon the modulation index of the FM signal. The FM frequency deviation generally is shown over here. This is the frequency deviation and you can see that it generally lies between FC and plus FC and minus FC and the most useful range generally lies or the circuit works properly in the range of FC and FC plus Del F. This generally shows the AM change that is the amplitude variations whenever the signal passes through the circuit and the output is taken across the RC filter. So slope detector here an FM signal is first fed to the input of the tuned circuit which is tuned equivalently to the carrier frequency of FM signal. The output of the signal is taken across the tuned circuit which generally depends upon the frequency deviation of the input FM signal. So as you can see the input of the tuned circuit generally depends upon the carrier frequency of FM signal and the output of the tuned circuit generally depends upon the frequency deviation. Hence we are considering the both cases that is FC and FC plus Del F where Del F is the frequency deviation. The circuit gets detuned at Del F so that to bring the point A back on the curve of the selectivity the curve or the response which we had seen is basically the selectivity curve and the point A generally denotes that at this point the circuit works very efficiently. The frequency variation produces output voltages which is generally proportional to the frequency division that means the output voltage generally depends upon the frequency deviation of FM signal. The output voltage is then applied to the diode circuit with an RC load to provide the same time constant that is the time constant is maintained by the resistor and the capacitor circuit which is connected across the output side of the circuit. What are the advantages of slope detector? Firstly it is simple that is it can be used to provide FM demodulation when only AM detector is present. Secondly it enables frequency modulation to be detected without any additional circuitry and the circuitry is easy to design. What are the disadvantages of slope detector? As it is a simple circuit hence it does not satisfy any conditions which are firstly it is inefficient for the variations in the frequency with respect to the carrier secondly it is linear only along very limited frequency range that means here it works properly for limited range of frequency thirdly it reacts to all amplitude changes hence amplitude limiter circuit is needed fourthly it is relatively difficult to tune the two capacitors that is the primary one and the secondary one for the same frequencies than the carrier frequency. So second one is the balance slope detector this is the circuit for the balance slope detector and this is the frequency response for the same. So as you can see if we remove the three capacitors which is firstly which is connected to the primary and these two which are connected to the secondary windings then this circuit basically will look like a full wave rectifier. Here these three capacitors which are connected to the primary and secondary these are generally used for the tuning of the circuit so that they receive the required signal only and the frequency response as you can see it is linear between fc minus del f and fc plus del f hence again here we are considering the two major points that is the carrier frequency when the circuit or when the signal is at input side and the del f that is the frequency deviation when the signal is considered at the output side. Similarly r1c1 and r2c2 these provide the two outputs which are later summed and given at the output side which is the total output voltage which is given as v0. So balance slope detector working can be explained by using or by the three different cases. First in the first case we are considering the frequency input to be equal to the carrier signal then at this point the primary and the secondary are out of phase by 90 degree hence the input at diode D1 and the input at diode D2 is same. Therefore the input at v hence the output at the rc r1c1 that is v01 and the output at r2c2 which is v02 it is also equal hence these get cancelled out and hence we get output voltage as 0. For case two here we are considering that the f in that is the input frequency generally lies between carrier frequency and fc plus del f. At this point the primary and secondary are less out of phase that is the signal at primary and the signal at secondary is less out of phase by 90 degree. Hence the input at D1 increase is greater than the input at D2 hence the output of the r1c1 is greater than the output of r2c2 which is given by this equation. Hence the output voltage increases positively towards fc plus del f. For the case three here we are considering that the input frequency generally lies between fc minus del f and fc here the primary signal and secondary signal are more out of phase by 90 degree hence the reverse process takes place which is with respect to the case two that is the output voltage of r2c2 is greater than the output voltage of r1c1 which is given by v02 is greater than v01 hence the output voltage increases more to the negative side and hence it increases towards fc minus del f where we are getting the where we are getting a linear signal which lies from fc minus del f to fc plus del f. So, what are the advantages and disadvantages of balanced slope detector the basic advantage is that it is very efficient and linear than the slope detector the disadvantage is that it is very difficult to tune three circuits for three different frequencies that is two capacitors two capacitors c2 and c3 which can be tuned for the input signal and the c1 can be tuned for the carrier and there are amplitude limitations. So, think on this question that give comparison between slope detector and balance slope modulator or balanced slope detector write down the points. So, these are the references for the further study. Thank you for watching the video.