# Draw and explain PLL as an FM demodulator.

Draw and explain PLL as an FM demodulator.

Explanation:- FM signal which is to be demodulated is applied to input of PLL.VCO output must be identical to input signal if PLL is to remain locked. As PLL is locked, VCO starts tracking the instantaneous frequency in the FM input signal The error voltage produced at the output of the amplifier is proportional to the deviation of the input frequency from the centre frequency FM. Thus AC component of the error voltage represents the modulating signal. Thus at the error amplifier output we get demodulated FM output.

## Related questions

Description : Draw block diagram of PLL as a FM demodulator. Explain function of each block.

Answer : Operation:  The FM signal which is to be demodulated is applied at the input of the PLL.  the PLL is locked to the FM  The error voltage produced at ... using PLL ensures a high Linearity, between the instantaneous input frequency and VCO control voltage (error amplifier output)

Description : Draw block diagram of FM receiver and explain the use of limiter circuit.

Answer : Diagram Explanation Amplitude limiter: The function of amplitude limiter is to remove all amplitude variation of FM carrier voltage that may occur due to atmospheric disturbances. Use of amplitude limiter makes the system less noisy.

Description : Draw the circuit diagram of varactor diode FM modulator and explain its working.

Answer : Varactor diode modulator is the direct method of FM generation wherein the carrier frequency is directly varied by the modulating signal. A varactor diode is a semiconductor diode whose ... the magnitude of frequency change is proportional to the amplitude of the modulating signal voltage.

Description : In a FM system, the maximum deviation is 75KHz. Find bandwidth for modulating frequency i. fm=500Hz ii. fm=5KHz iii. fm=10KHz Draw conclusion for bandwidth of FM from answer.

Answer : Given deviation∆=75kHz i) fm=500Hz bandwidth B.W=2(∆+fm)  =2(75k+500)=151kHz  ii). fm=5KHz bandwidth B.W=2(∆+fm)  =2(75k+5k)=160KHz iii) fm=10KHz bandwidth B.W=2(∆+fm)  =2(75k+10k)=170KHz As the modulating frequency increases bandwidth also increases.

Description : Draw the block diagram of FM super heterodyne radio receiver with waveforms.

Description : Explain pre-emphasis and de-emphasis concept in FM.

Answer : Pre-emphasis:- In an FM system the higher frequencies contribute more to the noise than the lower frequencies. Because of this all FM systems adopt a system of pre-emphasis where the higher frequencies are ... at receiver to improve the noise immunity Pre-emphasis/ De-emphasis graph:

Description : Explain the working of amplitude limiter in FM receiver with circuit diagram.

Answer : Amplitude limiter: The function of amplitude limiter is to remove all amplitude variation of FM carrier voltage that may occur due to atmospheric disturbances. Use of amplitude limiter makes the system less noisy  Circuit Diagram:

Description : Explain with block diagram of Armstrong method of FM generation.

Answer : Explanation:- The crystal oscillator generates the carrier at low frequency typically at 1 MHz this is applied to the combining network and a 90o phase shifter. The modulating signal is passed through an ... power amplifier to raise the power level of the FM signal.  Phasor Diagram:-

Description : Explain reactance modulator for FM generation.

Answer : Explanation :- Audio modulating signal is applied to Q1 which varies the base voltage and current of Q1 according to the input information to be transmitted. The collector current ... lower the frequency & decrease capacitance increase the frequency and thus produce direct FM at output.

Description : List the types of FM detector. Explain any one of them.

Answer : Types of FM detector:- 1. Simple slope detector 2. Balanced slope detector 3. Phase discriminator(Foster seely discriminator) 4. Ratio detector 5. PLL detector Simple ... . If the IF amplitude is sufficiently limited prior to reaching the PLL and the loop is properly compensated

Description : Draw and label PLL based FM detector.

Answer : Draw and label PLL based FM detector.

Description : State the IF frequency and bandwidth of FM receiver.

Description : Give the expression for modulation index for AM and FM.

Answer : 1.Modulation index for AM ma=Vm / Vc Where Vm is modulating voltage Vc is the carrier voltage 2.Modulation index for FM mf=δ /fm where δ is the deviation fm is the modulating frequency

Description : Differentiate between AM and FM on the basis of: (i) Definition (ii) Bandwidth (iii) Modulation Index (iv) Application

Answer : Compare AM and FM on the basis of i)Definition ii)Bandwidth iii) Wave propogation iv)Number of sidebands

Description : Compare between FM and PM

Answer : PARAMETERS FM PM 1. Variable parameter of carrier. Frequency Phase 2. Variable parameter proportional to modulating voltage.  Frequency deviation Phase deviation.  3. Amplitude ... for transmitted power More Moderate 6. Signal to noise ratio Best Better

Description : For AM, fc =500kHz , fm = 5 kHz Determine: (i) Upper and lower sideband frequencies (ii) Bandwidth

Answer : Given data fc = 500KHz , fm = 5KHz USB =fc+fm USB = 500+5  =505 KHz. LSB =fc – fm LSB = 500 – 5  =495 KHz Bandwidth = 2fm .  = 2* 5 =10 KHz

Description : State the process FM detection? State it‟s any two types.

Answer : FM detection: In any radio that is designed to receive frequency modulated signals there is some form of FM demodulator or detector. This circuit takes in frequency modulated RF signals and takes the ... 3. Ratio Detector 4. Phase Discriminator 5. FM Detector using Phase Locked Loop (PLL)

Description : Describe the block diagram of FM superhetrodyne receiver

Answer : RF amplifier:- There are two important functions of RF amplifier: 1) To increase the strength of weak RF signal. 2) To reject image frequency signal. In FM broadcast the ... FM broadcast, the maximum modulating frequency is 15 kHz. Hence the audio amplifier must have large bandwidth.

Description : What are the different types of FM detector?

Answer : The different types of FM Detectors are: 1. Simple Slope Detector 2. Balanced Slope Detector 3. Ratio Detector 4. Phase Discriminator 5. FM Detector using Phase Locked Loop (PLL)

Description : Define modulation index in FM. What is maximum value of deviation ratio.

Answer : Modulation Index of FM: It is defined as the ratio of Frequency Deviation (δ) to the modulating signal frequency (fm). (OR)

Description : Draw practical set-up and explain the procedure to measure selectivity of radio receiver.

Answer : Procedure to measure selectivity of radio receiver: Throughout the measurement the receiver is kept tuned to desired frequency 950 Khz. Now the generator output frequency is deviated below ... the generator output voltage is adjusted to get a standard 50 miliwatt receiver output power.

Description : Draw construction of Yagi-Uda antenna and explain.

Answer : Explanation A Yagi-Uda antenna, commonly known as a Yagi antenna, is a directional antenna consisting of multiple parallel elements in a line, usually half-wave dipoles made of ... receiver with a transmission line and additional parasitic elements called reflector and one or more directors.

Description : Draw and explain block diagram of electronic communication system.

Answer : Block diagram of electronic communication system. Explanation Transducer: A transducer is usually required to convert the output of a source into an electrical signal that is suitable for ... etc. Output Transducer: The output transducer converts electrical signal in to sound signal.

Description : Explain loop antenna with neat sketch. Draw radiation pattern. State its advantages and applications.

Answer : Loop antenna:-The single turn coil carrying RF current through it having length less than the wavelength.   Advantages:- 1. highly directive 2. Small size Applications:- 1. For direction finding 2. In portable receivers 3. In navigation

Description : Draw the circuit diagram of practical diode detector and explain its working.

Answer : Circuit diagram of practical diode detector:  Explanation- The circuit operates in the following manner- The diode has been reversed so that now the negative envelope is demodulated. Due to this ... to produce AGC voltage. The DC AGC voltage is proportional to the amplitude of AM signal.

Description : Draw the circuit diagram of limiter and explain its working.

Answer : Circuit diagram of amplitude limiter:- Explanation:- 1. In frequency modulation, the signal amplitude is held constant while the carrier frequency is varied. 2. Any noise that contaminates ... V p-p instead of the alternately driven into saturation and cutoff, it limits the signal amplitude

Description : Draw the TRF receiver block diagram and explain its working.

Answer : Explanation:- 1. TRF receivers are simple and having high sensitivity. The AM transmission takes place in MW band and SW band. MW frequency range is 540KHz to 1640KHz. 2. ... power level to drive the loudspeaker. 7. The loudspeaker converts electrical signal into original sound information.

Description : Draw circuit diagram of transistor reactance modulator. Explain its working.

Answer : Explanation- A reactance modulator is illustrated in figure. It is basically a standard commonemitter class A amplifier. Resistors R1 and R2 from a voltage divider to bias ... frequency, whereas a lower capacitance increases the frequency. The circuit produces direct frequency modulations.

Description : Draw the diagram for PAM generation using transistors. Explain its working.

Answer : Explanation:-1. Transistor Q1 is used in the active region so it has been provided with DC biasing to its base. 2. Modulating signal is applied to the base of transistor Q1 3. In the emitter of ... . 7. In the time interval between sampling pulses output is zero. Thus we get the output as PAM.

Description : Draw the block diagram of AM transmitter, explain its operation.

Answer : AM transmitter is of two types i)High Level AM Transmitter ii)Low Level AM Transmitter i) RF crystal oscillator: It is a source of carrier signal of desired frequency. The circuit is ... AM signal is then applied to the transmitting antenna which radiates this AM signal into air or space.

Description : Draw waveform for standing waves on an open and shorted line. Prove that impedance is inverted at every quarter wavelength interval.

Answer : Waveform- Explanation When the transmission line is short circuited voltage is zero and current is maximum.The variation is according to the wavelength. When the ... The pattern repeats for every half wavelength. Thus impedance is inverted at every quarter wavelength interval.

Description : Draw and label the circuit diagram of ratio detector

Answer : Draw and label the circuit diagram of ratio detector

Description : Draw the structure and state applications of: i) Ferrite loop (rod) antenna ii) Horn antenna

Answer : Horn antenna: Application:- i) Used at microwave frequency. ii) Used in satellite tracking.  Ferrite loop antenna: Application:- In Am radio receiver to receive MW and SW band signals. In FM radio receiver

Description : Define PAM, PWM, and PPM. Draw waveforms.

Answer : Pulse amplitude modulation is defined as a process of varying the amplitude of the carrier pulse in accordance to the modulating signal variations. Pulse width modulation is defined as a ... of varying the position of the carrier pulse, in accordance to the modulating signal variations.

Description : Draw block diagram of basic electronic communication system and state the function of each block.

Answer : i) Input signal: - The information can be in the form of sound, picture or data coming from computer. ii) Input transducer: - it converts original information into equivalent electrical ... back to suitable form. vii) Output transducer: - It converts electrical signal into original form.

Description : Draw amplitude modulated waveform in time domain and frequency domain with proper labeling.

Answer : AM in Time domain  AM in frequency domain

Description : Draw the structure of horn antenna and its radiation pattern. List its any two applications.

Answer : The structure of horn antenna Radiation pattern of Horn Antenna Application:- i) Used at microwave frequency. ii) Used in satellite tracking

Description : Define the transmission line? Draw it‟s general equivalent circuit.

Answer : Transmission line: A conductor or conductors designed to carry electricity or an electrical signal over large distances with minimum losses and distortion.  Equivalent circuit:

Description : Draw radiation pattern for following antenna i) Yagi-Uda antenna ii) Loop antenna iii) Dish antenna iv) Horn antenna

Answer : Type of antenna Radiation Patteren  Yagi-Uda antenna Loop antenna Dish antenna Horn antenna

Description : Define pre-emphasis. State its need. Draw the circuit of pre-emphasis.

Answer : Definition- The artificial boosting of higher modulating frequencies to reduce the effect of noise is called as pre-emphasis. Need:- The artificial boosting of higher audio modulating ... by increasing the amplitude of modulating signal at higher frequencies. Circuit diagram

Description : Draw the circuit diagram of PWM using IC555. State its operation.

Answer : Operation: i. The timer IC555 is operated in monostable mode. ii. The negative going carrier pulses are to the differentiator formed by R1 & C1. The differentiator produces sharp negative ... . Thus PWM signal is generated at the output pin (3) of IC555 as monostablemultivibrator.

Description : Draw Yagiuda antenna with its radiation pattern.

Description : Draw general equivalent circuit of transmission line.

Answer : Fig. General Equivalent circuit of transmission line

Description : Draw the block diagram of PWM. List its advantages

Answer : Block diagram of PWM:- Advantages of PWM:- 1. More immune to noise. 2. Synchronization between transmitter and receiver is not required. 3. Possible to separate out signal from noise.

Description : Draw the radiation pattern for Dipole antenna: (i) Half wave dipole (ii) Folded dipole.

Answer : The radiation pattern for Half wave dipole antenna The radiation pattern for Folded dipole antenna.

Description : State the need of stub. Explain single stub and double stub matching.

Answer : Stub:- Stub is the piece of short circuited transmission line which is used to tune out the reactance of the load when connected across the transmission line as close as possible. ... but lengths are independently adjustable. The double stub matching provides wide range of impedance matching.

Description : Define and explain the term beam width related to antenna with a sketch.

Answer : Definition: The beam width of an antenna is described as the angles created by comparing the half power point (3dB) on the main radiation lobe to its maximum power point. As an example the beam width ... max voltage at center of lobe (these point are known as half power points.) Sketch-

Description : State and explain the concept of transmission bandwidth.

Answer : Bandwidth is defined as the portion of the electromagnetic spectrum occupied by a signal We may also define the bandwidth as the frequency range over which as information signal is transmitted. Bandwidth is the ... to 15 KHZ. Therefore the bandwidth is(f2-f1) BW= f2 - f1= 15000-20=14980Hz

Description : Explain working of envelope detector with suitable diagram and waveform.

Answer : Envelope Detector: An Envelope Detector is an electronic circuit that takes a high frequency signal as input and provides an output which is as envelopes of the original signal. The capacitor ... decreases the responsiveness thus, real-world designs must be optimized for the application.

Description : Explain how modulation reduces height of antenna and avoid mixing of signals.

Answer : Modulation reduces antenna height: For the transmission of radio signals, the antenna height must be multiple of λ/4 ,where λ is the wavelength . λ = c /f where c : is the ... will occupy different slots in the frequency domain (different channels). Thus, modulation avoids mixing of signals.

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