Name of the College : Noorul Islam College of Engineering
University : Anna University
Degree : B.E
Department : Electronics and Communication Engineering
Subject Code/Name : EC 1301 – Communication Theory
Year : III
Semester : V
Document Type : Question Bank
Website : niceindia.com
Download :https://www.pdfquestion.in/uploads/ni…ion_Theory.pdf
NICE Communication Theory Question Bank
1. Define modulation? :
Modulation is a process by which some characteristics of high frequency carrier signal is varied in accordance with the instantaneous value of the modulating signal.
Related : Noorul Islam College of Engineering EC1403 Microwave Engineering B.E Question Bank : www.pdfquestion.in/2970.html
2.What are the types of analog modulation? :
Amplitude modulation.
Angle Modulation
1. Frequency modulation
2. Phase modulation.
3.Define depth of modulation.
It is defined as the ratio between message amplitude to that of carrier amplitude. m=Em/Ec
4. What are the degrees of modulation? :
** Under modulation. m<1
** Critical modulation m=1
** Over modulation m>1
5.What is the need for modulation? :
Needs for modulation :
** Ease of transmission
** Multiplexing
** Reduced noise
** Narrow bandwidth
** Frequency assignment
** Reduce the equipments limitations.
6.What are the types of AM modulators? :
There are two types of AM modulators. They are :
** Linear modulators
** Non-linear modulators
Linear modulators are classified as follows :
Transistor modulator
There are three types of transistor modulator :
** Collector modulator
** Emitter modulator
** Base modulator
** Switching modulators
Non-linear modulators are classified as follows :
** Square law modulator
** Product modulator
** Balanced modulator
7.Give the classification of modulation :
There are two types of modulation. They are :
** Analog modulation
** Digital modulation
Analog modulation is classified as follows :
** Continuous wave modulation
** Pulse modulation
Continuous wave modulation is classified as follows :
Amplitude modulation :
** Double side band suppressed carrier
** Single side band suppressed carrier
** Vestigial side band suppressed carrier
Angle modulation :
** Frequency modulation
** Phase modulation
Pulse modulation is classified as follows :
** Pulse amplitude modulation
** Pulse position modulation
** Pulse duration modulation
** Pulse code modulation
Digital modulation is classified as follows :
** Amplitude shift keying
** Phase shift keying
** Frequency shift keying
8.What is single tone and multi tone modulation? :
If modulation is performed for a message signal with more than one frequency component then the modulation is called multi tone modulation.
If modulation is performed for a message signal with one frequency component then the modulation is called single tone modulation.
9 .The antenna current of an AM transmitter is 8A when only carrier is sent. It increases to 8.93A when the carrier is modulated by a single sine wave. Find the percentage modulation :
10.Compare AM with DSB-SC and SSB-SC :
AM signal DSB-SC SSB-SC
Bandwidth=2fm
Bandwidth=2fm Bandwidth=fm
Contains USB, LSB, carrier Contains USB,LSB Contains LSB or USB
More power is required for transmission
Power required is less than that of AM.
Power required is less than AM &DSB-SC
11 What are the advantages of VSB-AM?
1.It has bandwidth greater than SSB but less than DSB system.
2.Power transmission greater than DSB but less than SSB system.
3.No low frequency component lost. Hence it avoids phase distortion.
12 Compare linear and non-linear modulators.
Linear modulators Non-linear modulators
1.Heavy filtering is not 1.Heavy filterng is required required.
2.These modulators are used in 2.These modulators are used in low level high level modulation. Modulation.
3.The carrier voltage is very much 3.The modulating signal voltage is very much greater than modulating signal greater than the carrier signal voltage. voltage.
13.How will you generating DSBSC-AM ?
There are two ways of generating DSBSC-AM such as
1.balanced modulator 2.ring modulators
14. What are advantages of ring modulator?
1.Its output is stable.
2. It requires no external power source to activate the diodes.
3.Virtually no maintenance.
4. Long life.
15. Define demodulation.
Demodulation or detection is the process by which modulating voltage is recovered from the modulated signal. It is the reverse process of modulation.