Circuit Simulation Integrated Laboratory (CSIL Lab) Viva Question Answers

1.What is amplifier?

Amplifier is a device which is used to amplification purpose.

2.What is amplification?

A low strength signal is converted into strengthen signal ie) boost up process

3. List the disadvantages of Rc phase shift Oscillator. (or)

What are the merits of Rc phase shift Oscillator.

i. It is ideal for frequency adjustment over a wide range.

ii. It requires a high β transistor to overcome losses in the network.

4.What is the difference between amplifier and oscillator/

Amplifier is working in the negative feedback while oscillator working in the positive feedback.

5.What is an Oscillator?

An Oscillator is a Circuit, which generates an alternating voltage of any desired

frequency. It can generate an a.c output signal without requiring any externally

applied input  signal.

6.What is a beat frequency oscillator?

Beat frequency Oscillator (BFO) is an Oscillator in which a deserved signal frequency such as the beat frequency produced by combining the different signal frequencies such as on different radio frequencies.

7.What is sustained Oscillation?

The electrical oscillations in which amplitude does not change with time are called as sustained oscillations.It is also called as Undamped Oscillation.

8.What is meant by resonant Circuit Oscillators?

LC Oscillators are known as resonant circuit oscillator because the frequency of operation of LC Oscillator is nothing but a resonant frequency of tank circuit or LC tank circuit produces sustained Oscillation at the resonant circuit oscillator

9.What is piezo electric effect?

The piezo electric Crystals exhibit a property that if a mechanical stress is applied across one face the electric potential is developed across opposite face.The inverse is also live. This phenomenon is called piezo electric effect.

10.List the disadvantages of crystal Oscillator.

It is suitable for only low power circuits  Large amplitude of vibrations may crack the crystal.It large in frequency is only possible replacing the crystal with another one by different frequency.

PLL Demodulator For 4M

INTERNAL 1 QUESTION FOR ELECTROMAGNETIC FIELDS (EMF)

SRI SUBRAMANYA COLLEGE OF ENGINEERING AND TECHNOLOGY

Internal Test –I (2014-15)

              Department of Electronics and Communication Engineering 

Date                     : 12.02.2015                                                     Duration: 1 hr 30 min

Subject     : EC 6403- Electromagnetic fields        Name of the Staff: S.N. Lalitha Parameswari

Year/Sem : II / IV                                                 Marks: 50 marks

               

Part - A                                   Answer all the question                                               (7*2=14)

1. State Biot-Savart’law?

2. State Ampere’s law?

3. What do you mean by magnetic moment?

4. Define Magnetic field intensity and magnetic flux density?

5. Define Magnetic vector potential?

6. Determine the gradient of the scalar field F=5r²+rsinӨ.

7. Calculate the divergence of the field at (1, 2, 3) for D=4xya_x+3xyza_y+2xya_z.

Part –B                                               Compulsory Question                                                 (1*4=4)

8. State and prove Ampere’s circuital law?

Part – C                                              Answer any 2Questions                                  (2*16=32)

9.    (i) Obtain the scalar and vector magnetic potential?                                     (6)       

      (ii) Discuss in detail the applications of Ampere’s circuital law?                   (10)

10. (i) Derive the expression for Curl H=J?                                                          (4)

(ii) Derive the expression for magnetic field intensity H on the axis of a

       Circular loop of radius’a’ carrying the current I?                                     (12)

11. Derive the magnetic field intensity and magnetic flux density at a point due to an                         

              (i) Finite line (8)           and          (ii) infinite line (8)

*** All the Best ***

INTERNAL 1 QUESTION PAPER FOR COMMUNICATION THEORY

SRI SUBRAMANYA COLLEGE OF ENGINEERING AND TECHNOLOGY

Internal Test –I (2014-15)

              Department of Electronics and Communication Engineering 

Date         : 11.02.2015                                                              Duration: 1 hr 30 min

Subject     : EC6402 Communication theory                  Name of the Staff: Mr. M. Marimuthu

Year/Sem : II year / IV Sem                                           Marks: 50 marks

               

 Part - A                                        Answer all the question                          (7*2=14)

1. Why is frequency modulation preferred for voice transmission?

2. If the maximum phase deviation in a PM system is 0.1 radian when a modulating signal  

     is applied is 10V. Determine the value of phase deviation constant.

3. What is the need for pre emphasis?

4. Define frequency discriminators

5. What is meant by amplitude modulation?

6. Why do we need modulation?

7. Determine the range of tuning oscillator of a super heterodyne receiver when f_Lo > f_c.

    The broad cast frequency is 540 Hz to 1600 Hz. Assume: f_if=455 KHz

 Part –B                                  Compulsory Question                                               (1*4=4)

8. Draw the simple schematic of a PLL demodulator     

  Part – C                                Answer any 2Questions                                            (2*16=32)

9    (i) Derive an equation for single tome FM signal                                           (6)

      (ii) Derive an expression for spectrum of FM signal using Bessel function   (10)

10  (i) With neat diagram explain Armstrong method of generating FM signal. (10)

      (ii) Mention any 5 points to differentiate AM from FM wave                       (6)

11.  (i) Explain the working of super-heterodyne receiver with diagram             (8)       

      (ii) Explain in detail about modulation and demodulation of VSB               (8)

*** All The Best ***

COMMUNICATION THEORY Question Bank UNIT WISE

QUESTION BANK

UNIT I – AMPLITUDE MODULATION

PART A

All questions – Two Marks:

1. As related to AM, what is over modulation, under modulation and 100% modulation?

2. Draw the frequency spectrum of VSB, where it is used?

3. Define modulation index of an AM signal

4. Draw the circuit diagram of an envelop detector

5. Draw the spectrum of AM.

6. A transmitter radiates 9 kW without modulation and 10.125 kW

after modulation. Determine depth of modulation.

7. Draw the spectrum of DSB-SC.

8. Define the transmission efficiency of AM signal.

9. Draw the phasor diagram of AM signal.

10. Advantages of SSB.

11. Disadvantages of DSB-SC.

12. Draw the spectrum of SSB

13. Advantages of VSB.

14. Distinguish between low level and high level modulator.

15. Define FDM & frequency translation.

16. Give the parameters of receiver.

17. Define multitone modulation.

18. Need for modulation.

19. Application of AM.

20. What is meant by diagonal clipping and negative peak clipping?

21. Define envelope.

22. Distinguish between linear and non linear modulator.

23. What are the limitations of AM.

24. Draw the envelope of AM.

25. Suggest one application for AM, SSB, DSB and VSB modulation techniques and justify your answer.

26. When a signal m(t) = 3 cos (2p x 103t ) modulates a carrier c(t) = 5 cos (p x 106t), find the modulation index and transmission bandwidth if the modulation is AM.

COMMUNICATION THEORY Question Bank For UNIT 1

UNIT -1

1.      Represent an amplitude modulated wave as a function of time with amplitude sensitivity of the modulator as the constant. (AU: Dec 13)

The amplitude sensitivity of the modulator is basically variation in amplitude of the carrier with respect to modulating signal. Refer AM envelope diagram.

2.      For an AM system, the instantaneous values of carrier and modulating signal are 60 sinw_ct and 40 sinw_mt respectively. Determine the modulation index. (AU: May 14)

E_c=60V E_m=40

Modulation index = E_m/E_c = 40/60 =0.6667

3.      State the difference between SSB and VSB. (AU: May 14)

Single side band	Vestigial side band
Only one side is transmitted	One side and part of other side is transmitted
Frequencies near edges are attenuated	Frequencies near edges are not attenuated
Bandwidth requirement is low	Bandwidth requirement is high

4.      What is meant by frequency translation? (AU: Dec 11)

In the single sideband modulation, the message spectrum is shifted by an amount equal to carrier frequency. This is called frequency translation.

5.      A transmitter radiates 10KW without modulation and 11.125 KW after modulation. Determine modulation index m. (AU: May 11)

P _total = P_c ((1+m²⁾/2) using this formula, m=0.474

6.      State the theorem by which average power of the signal is calculated. (AU: Dec 11)

Parseval’s theorem states that if x(t) is the periodic power signal with fourier co-efficient x(k), then average power in the signal is given by

P = ∑|X(k)|²

7.      Mention the important limitations of amplitude modulation system. (AU: May 11)

AM signal has varying amplitude. Hence the transmitter power is not constant. Also, it is very difficult to identify noise, since amplitude level is not constant.

8.      What is meant by amplitude modulation? (AU: Dec 05)

The process of changing the amplitude of the carrier signal with respect to message signal is called amplitude modulation.

9.      Why do we need modulation? (AU: May 11)

·         If the message signal is directly transmitted, it gets attenuated highly

·         The size of antennas needed is huge without modulation

·         The signal cannot be transmitted over longer distance

·         Message signals get interfered and distorted in channel without modulation

·         Multiplexing is not possible without modulation

10.  Determine the range of tuning oscillator of a super heterodyne receiver when f_LO >f_c. The  broadcast frequency is 540 Hz to 1600 Hz. Assume f_IF=455 KHz.

F0 =f_c + f_IF = (455.54 to 456.6) KHz

16 marks

1. Derive the equation of AM wave. Also draw  the modulated wave for various modulation index (AU: May 13) (8 Marks)

A 1000 KHz carrier is simultaneously AM modulated with 300, 800 and 1.5 KHz audio sine waves. What will be the frequencies present in the output? (AU:May 13) (4 marks)

Explain how Am signal is generated using non-linear modulator circuit? (AU: Dec 12) (4 marks)

2. Derive the equation for suppressed carrier system and draw its frequency spectrum. (AU: May 14) (8 marks)

Explain the generation of DSB-SC signal using balanced and ring modulators (AU: Dec 10) (8 marks)

3. Derive the equation for SSB modulation and demodulation (6 marks)

Discuss the generation of SSB with filter method, phase shift method and weaver’s methods. (AU: May 10) (12 marks)

4. Explain the working of super heterodyne receiver with suitable block diagram. (AU: Dec 13) (16 marks)
5. Explain in detail about modulation and demodulation of VSB using various methods. (AU: May 14) (16 marks)

COMMUNICATION THEORY Question Bank For UNIT 2 (2 Mark With Answer)

UNIT  II

Two marks questions

1.    Why is frequency modulation preferred for voice transmission? (AU-MAY14)

Voice signal requires the frequencies upto 10KHz. For such a small range of voice frequencies FM does not have wide bandwidth. Hence FM is preferred.

2.    If the maximum phase deviation in a PM system is 0.1 radian when a modulating signal is applied is 10V. determine the value of phase deviation constant. (AU-MAY14)

K= Ѳ(t)/e(t) = 0.1/10 = 0.01 rad/volts.

3.    What is the need for pre emphasis? (AU-MAY14)

The noise has greater effect on higher modulating frequencies and less effect on lower ones. Hence higher modulating frequencies should be artificially boosted, so that effect of noise can be reduced. This is done by pre emphasis.

4.    Define frequency discriminators. (AU-MAY11)

The frequency discriminator produces the signal whose amplitude is proportional to the deviation in the frequency of FM signal. Thus the discriminator is similar to frequency to voltage convertor. It is used in FM detection. Balanced slope detector is an example of frequency discriminator.