EC1311 Communicating Engineering B.E Question Bank : niceindia.com

Name of the College : Noorul Islam College of Engineering
University : Anna University
Degree : B.E
Department : Electrical & Electronic Engineering
Subject Code/Name : EC 1311 – Communicating Engineering
Year : III
Semester : V
Document Type : Question Bank
Website : niceindia.com

Download :https://www.pdfquestion.in/uploads/ni…ngineering.pdf

NICE Communicating Engineering Question Paper

Unit I

Modulation Systems :
1. Define amplitude Modulation :
Amplitude Modulation is the process of changing the amplitude of a relatively high frequency carrier signal in proportion with the instantaneous value of the modulating signal.

Related : Noorul Islam College of Engineering XCS355 Design of Analysis M.Sc Question Bank : www.pdfquestion.in/3140.html

2. Define Modulation index and percent modulation for an AM wave :
Modulation index is a term used to describe the amount of amplitude change present in an AM waveform .It is also called as coefficient of modulation.
Mathematically modulation index is m = Em/ Ec
Where m = Modulation coefficient
Em = Peak change in the amplitude of the output waveform voltage.
Ec = Peak amplitude of the unmodulated carrier voltage.
Percent modulation gives the percentage change in the amplitude of the output wave when the carrier is acted on by a modulating signal.

3. Define Low level Modulation :
In low level modulation, modulation takes place prior to the output element of the final stage of the transmitter. For low level AM modulator class A amplifier is used.

4. Define High level Modulation :
In high level modulators, the modulation takes place in the final element of the final stage where the carrier signal is at its maximum amplitude. For high level modulator class C amplifier is used.

5. What is the advantage of low level modulation? :
An advantage of low level modulation is that less modulating signal power is required to achieve a high percentage of modulation.

6. Distinguish between low level and high level modulation :
In low level modulation, modulation takes place prior to the output element of the final stage of the transmitter.It requires less power to achieve a high percentage of modulation.

In high level modulators, the modulation takes place in the final element of the final stage where the carrier signal is at its maximum amplitude and thus,requires a much higher amplitude modulating signal to achieve a reasonable percent modulation.

7. Define image frequency :
An image frequency is any frequency other than the selected radio frequency carrier that ,if allowed to enter a receiver and mix with the local oscillator ,will produce a cross product frequency that is equal to the intermediate frequency.

8. Define Local Oscillator tracking :
Tracking is the ability of the local oscillator in a receiver to oscillate either above or below the selected radio frequency carrier by an amount equal to the intermediate frequency throughout the entire radio frequency band.

9. Define High side injection tracking :
In high side injection tracking , the local oscillator should track above the incoming RF carrier by a fixed frequency equal to fRF +fIF .

10. Define Low side injection tracking :
In low side injection tracking ,the local oscillator should track below the RF carrier by a fixed frequency equal to fRF -fIF .

11. Define tracking error.How it is reduced :
The difference between the actual local oscillator frequency and the desired frequency is called tracking error.It is reduced by a technique called three point tracking.

12. Define image frequency rejection ratio :
The image frequency rejection ratio is the measure of the ability of preselector to reject the image frequency.
Mathematically ,IFRR is IFRR =(1+Q2r2)1/2
Where r= (fim/fRF)-(fRF/fim)

13. Define Heterodyning :
Heterodyne means to mix two frequencies together in a nonlinear device or to translate one frequency to another using nonlinear mixing.

14. What are the disadvantages of conventional (or) double side band full carrier system? :
In conventional AM ,carrier power constitutes two thirds or more of the total transmotted power.This is a major drawback because the carrier contains no information ;the sidebands contain the information .

Second ,conventional AM systems utilize twice as much bandwidth as needed with single sideband systems.

15. Define Single sideband suppressed carrier AM :
AM Single sideband suppressed carrier is a form of amplitude modulation in which the carrier is totally suppressed and one of the sidebands removed.

UNIT II

Transmission Medium
31. Define transmission line.
A transmission line is a metallic conductor system that is used to transfer electrical energy from one point to another. A transmission line is two or more conductors separated by an insulator, such as a pair of wires or a system of wire pairs.

32. Define balanced transmission line.
In balanced transmission line, both conductors carry current; one conductor carries the signal and the other is the return. This type of transmission is called differential or balanced signal transmission. 33. Define unbalanced transmission line.
In unbalanced transmission line, one wire is at ground potential where as the other wire is at signal potential. This type of transmission is called single ended or unbalanced signal transmission.

34. Define Open wire transmission line.
An open wire transmission line is a two wire parallel conductor. It consists simply of two parallel wires, closely spaced and separated by air. Nonconductive spacers are placed at periodic intervals for support and to keep the dielectric between the conductors constant. The dielectric is simply the air between and around the two conductors in which the TEM wave propagates.

35. What are the advantages of open wire transmission line?
a. Simple in construction
b. Radiation losses are high
c. It is susceptible to noise pickups.