# Analog Communications Important Questions unit 2 (FAQ)

UNIT 2:

1. What is meant by Carson’s rule? Problem on calculation of Bandwidth of FM signal using Carson’s rule.(imp)
2. Distinguish between NBFM and WBFM.(imp)
3. Problems on instantaneous phase and frequency.
4. What is the basic principle involved in Phase discriminator?
5. Define capture range and lock range of a PLL.
6. Problem on Armstrong method of generation of a WBFM signal?(imp)
7. Capture effect and threshold effects in FM (very very imp).
8. Problems on carrier swing, frequency deviation, BW, modulation index etc.
9. Phasor diagrams of NBFM and AM.
10. What is the need for limiter in FM receivers? (Very very imp).
11. Find the maximum Frequency deviation of Frequency Modulated signal given by  S(t) = 10 cos(1000000 *pi*t + 5 sin(2000*pi*t)).
12. A carrier signal 10 cos(8x 106πt) is modulated by a modulating signal               5 cos(30x 103πt)  then i. Find the Band width of Frequency Modulated signal assuming  kf  =15KHz.   ii.     Calculate Highest Frequency and lowest Frequency of FM signal.  iii. Find  Modulation index of FM signal.
13. Compare Frequency Modulation with Phase Modulation.

1. Explain the operation of balanced slope detector in detail.
2. Explain in detail about frequency spectrum of WBFM signal using Bessel functions.
3. write in detail about generation methods of FM signal
4. Direct method of generation
5. Indirect method of generation (Armstrong method).(very very imp)
6. What is ratio detector? Explain its working in detail with neat circuit diagram. Explain how ratio detector provides amplitude limiting?
7. What is amplitude limiter? Draw its circuit diagram explain its working. Why amplitude limiter is needed in FM receivers justify.(very very imp)
8. Compare and contrast foster seeley discriminator with ratio detector.
9. What is PLL? What are the applications of PLL? Explain the working of PLL with neat block diagram.(imp)
10. How audio frequency signal is demodulated by using PLL? Explain in detail.
11. Write about pre-emphasis and de-emphasis circuits in detail. Give the significance of pre-emphasis and de-emphasis.(imp)
12. In an FM system if the AF is 500 Hz and its amplitude is 2.4V with a frequency deviation of 4.8 KHz. If the AF voltage is increased to 7.2V then find the modified frequency deviation calculate BW in above two cases.
13. Design Armstrong FM generator for the generation of WBFM signal with frequency deviation=75 KHz and using the NB carrier as 100 KHz and second carrier as 10 MHz Find the suitable multiplying factors. Assume the message signal is defined in the range 100Hz-15 KHz.
14. Draw the block diagram of single-tone NBFM signal if message signal is.
15. Derive an expression for an FM signal with carrier frequency fc and a modulating signal Obtain an expression for its spectrum.
16. Why an FM system is preferred over an AM system?

Unit 2

Assignment 2

1. Explain the generation techniques of FM signal using Direct and Indirect methods in detail.
2. Explain the working of the following demodulator circuits of FM                        i. Balanced slope Detector for FM modulation.                                                            ii. Foster-Seeley discriminator.                                                                                         iii. Ratio-detector.
3. Explain the detection of FM signal using PLL.
4. Explain in detail about pre-emphasis and De-emphasis circuits in FM.

Unit 2

Assignment 2

1. Illustrate the working of PLL using a Block Diagram. Define capture range and Lock range in PLL.                                                                                                                 5M.
2. Sketch the circuit diagram of Ratio-detector and explain working of it in detail. 5M.
3. Sketch the frequency response curves & compare the working of pre-emphasis and De-emphasis circuits in FM communication System.

TUTORIAL TEST 2

Answer any three of the following

1. In an FM system if the AF is 500 Hz and its amplitude is 2.4V with a frequency deviation of 4.8 KHz. If the AF voltage is increased to 7.2V then find the modified frequency deviation calculate BW in above two cases.
2. Explain in detail about frequency spectrum of WBFM signal.
3. Draw the block diagram of single-tone NBFM signal if message signal is
4. Write any four differences between NBFM and WBFM.

## Author: Lakshmi Prasanna Ponnala

Completed M.Tech in Digital Electronics and Communication Systems.

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