 Hello friends, myself Mr. Elia Arsandane, Assistant Professor from Department of Electronics, Walchen Institute of Technology, Solapur. Today, we are going to see the topic Frequency Generation Part 1, here this is from the subject Analog Communication. So, basically what are the learning outcomes from this topic? At the end of this topic, you can recall the concept of frequency modulation and its mathematical representation. Secondly, discuss the concept of narrow band and wide band frequency modulation. Next, why there is a need of preemphasis and deemphasis circuit and its design. So, basically there are different types of modulation. Here, the frequency modulation is divided into two types, first one is the narrow band where modulation index is small and second one is the wide band where modulation index is large. So, how a narrow band is generated? Here, this is the block diagram which will give you an idea of how a narrow band is generated in FM generator. So, firstly these are the blocks by which the narrow band FM is generated. Here first the integrator is used, this integrator has a input of modulating wave which is known as main information signal. The integrator then integrates all the waves and it then gives the output to the product modulator, where the product modulator has another input from a 90 degree phase shifter which is nothing but it provides a carrier by a phase shifting of minus 90 degrees and this signal is given to the product modulator, where the product modulator adds a product modulator where it multiplies these both signals and then it passes to the adder and subtractor where the adder and subtractor performs the process of addition and subtraction for the narrow band FM generation and then at the output we get a narrow band FM wave. So, basically this is used for the low distance type of communication. Next indirect method of wide band FM generator. So, here the different blocks which are used are the integrator as well as narrow band phase modulator and the frequency multiplier. The integrator again integrates the base band signal and gives it to the narrow band phase modulator where it has another input from the crystal controlled oscillator which provides the carrier signal. The narrow band phase modulator then converts the modulating signal and the carrier signal and provides a narrow band phase modulated signal which is given to the frequency multiplier where the frequency multiplier increases the width of the signal and then at the output we generally get a wide band signal which is a frequency modulated. So, the comparison between narrow band and wide band FM generation are so basically this table will give you an idea for narrow band and wide band frequency modulation. So, the basic parameter first here it is the modulation index, here it is slightly less than 1 and for wide band it is greater than 1. Maximum deviation is of 5 kilohertz for narrow band for wide band it comes up to be 75 kilohertz. Range of modulating frequency it ranges from 20 hertz to 3 kilohertz whereas for wide band it ranges from 20 hertz to 15 kilohertz. Maximum modulation index here the modulation index for narrow band is slightly greater than 1 whereas for the wide band it ranges from 5 to 250. Bandwidth here in narrow band it is slightly less than but it is approximately equal to that of AM which is given by bandwidth is equal to twice of FM where FM is the maximum frequency. Similarly, for wide band it is greater than narrow band which is up to 15 times greater than narrow band of frequency modulated wave and hence it is given by bandwidth is equal to twice del plus FM where del is the deviation which is nothing but the frequency deviation. Variations for narrow band FM are FM mobile communication like police, wireless, ambulance, short range ship to shore communication and other things. Wide band generally this is used in broadcasting of entertainment purpose and it is generally used for high quality of music transmission. Preemphasis and deemphasis basically these are two different processes which are generally used at two different sites preemphasis is generally used at the transmitter side whereas deemphasis is used at the receiver side and as we know that in communication noise affects any type of modulation similarly in FM noise affects more to the higher frequencies hence this noise can be reduced by increasing the value of modulation index for higher frequency this can be done by increasing the frequency deviation. So how a frequency deviation parameter can be increased for that we have to increase the value of amplitude of modulating frequency or the main information signal. So basically the preemphasis circuit this is the preemphasis circuit which is a transistorized circuit here the base of the transistor is given as input to the audio frequency that is the modulating signal and the carrier is provided by the RC oscillator. Here generally we are using this circuit at the transmission side hence at the output we are going to use a high pass filter that means at the output of the preemphasis circuit we are generally getting the high frequency waves which are used for transmission of the signal. The preemphasis curve is shown as such here as modulating frequency increases the capacitive reactance decreases and the modulating voltage goes on increasing hence that provides a high frequency signal at the output. Preemphasis at the transmitter side here for the preemphasis we are using different blocks first preemphasis circuit is used then the FM modulator frequency up converter and the power amplifier. The modulating signal is first given to the preemphasis circuit as we know that the preemphasis circuit will provide a high frequency output which is given to the FM modulator the FM modulator also has a input of carrier signal hence the frequency modulation takes place of the higher frequencies and the carriers signals which are coming from crystal oscillator these FM modulated signal are then given to the frequency up converter for increasing the frequency and then these are given to the power amplifier for the amplification of the power as we are transmitting this these signal the power of this signal needs to be high before the transmission hence a power amplifier is used the power amplifier will amplify the power of these FM modulated signal and then it is transmitted. Deemphasis circuit generally deemphasis circuit uses such type of a circuit where it uses FM demodulator and RC low pass filter as we know that this circuit is generally used at the receiving side hence the FM modulator demodulator has input of FM modulated wave where demodulation takes place and the original signal is passed through this RC low pass filter and at the output we are getting a low frequency signals which is nothing but a deemphasized output here the frequency curve as you know that here the frequency will go on increasing and at a certain point it gets dropped and hence at the output we are getting a low frequency signal which is nothing but our main information signal deemphasis block diagram generally it utilizes FM detector deemphasis block and AF and power amplifier where AF is nothing but audio frequency and power amplifier similarly FM is given as input to the FM detector the demodulated output is given to the deemphasis circuit and then for the amplification of the low frequency signal AF and power amplifier is used and then given to the loudspeaker for the output purpose so comparison between preemphasis and deemphasis circuit is as such first the basic parameter are circuit used it uses high pass filter that is the preemphasis circuit deemphasis uses the low pass filter similarly the circuit diagram and response curve are the two major differentiating points which can be written for the comparison similarly the time constant for the preemphasis is t is equal to rc which is of 50 microseconds and for deemphasis is also the same so basic definition for preemphasis is that it is used for boosting of high frequency signals and at the deemphasis it is generally used for removal of high frequency signals similarly as we have seen these are used at FM transmitter and the deemphasis circuit is generally used at FM receiver so basically these are the references which are used for the making this PPT thank you for watching the video.