Analog Communciation Interview Question

8/19/2019 Analog Communciation Interview Question

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ANALOG COMMUNCIATION

1. What are the main components needed for a

communication?

• Sender, Transmission line and ecei!er"

1. What is Sampling? What is Sampling Theorem?

Sampling is defined as the process in which an analog signals are converted into digital signals. It means that a

continuous time signal is converted into a discrete time signal.

Sampling Theorem is defined as : ’The continuous time signal that can be represented in its samples and

recovered back if the sampling frequency (fs) is greater than the maimum frequency of the signal (fm) that is fs

>2fm’.

2. Define PAM and write down its drawa!"s?

Pulse !mplitude "odulation is the process by which the amplitude of the regularly spaced pulses varies according

to the the amplitude of the modulating signal.

The drawa!"s are:

a. Since the amplitude of the pulses varies therefore the peak power of the modulating s#g is much greater.

. The bandwidth required for transmitting is greater since the amplitude varies.

#. What is Mod$lation? What happens in o%er mod$lation?

!ns$ Modulation is defined as the process in which some characteristics of the signal called carrier is varied

according to the modulating or baseband signal. %or eample & !mplitude "odulation' hase "odulation'

%requency "odulation.

In case of over modulation' the modulation inde is greater than one and envelope distortion occurs.

&. What do 'o$ mean ' (')$ist rate?

!ns$ In case of yquist rate' the sampling frequency is equal to the maimum frequency of the signal and

therefore the successive cycles of the spectrum does not overlap.

*. What do 'o$ mean ' +M and !lassif' +M?

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Ans: Frequency Modulation can be defined as the frequency of the carrier (wc) is varied acc. to the modulating

signal about an unmodulated frequency.

+M are of 2 t'pes:

a. arrowband %"

. *ideband %"

,. What is $nder sampling?

Ans: +nder sampling is also known as aliasing effect in which the the sampling frequency is less than the

maimum frequency of the signal and therefore the successive cycles of the spectrum overlap.

-. State the ad%antages of s$perheterod'ning?

Ans: The advantages are$

a. ,igh selectivity and sensitivity.

. o change in -andwidth that is bandwidth remains same all over the operating range.

!. ,igh adacent channel reection.

To heterodyne means to mix to frequencies together so as to produce a beat frequency, namely

the difference between the two. Amplitude modulation is a heterodyne process: the information

signal is mixed with the carrier to produce the side-bands. The side-bands occur at precisely the

sum and difference frequencies of the carrier and information. These are beat frequencies

(normally the beat frequency is associated with the lower side-band, the difference between the

two).

superheterodyne refers to creating a beat frequency that is lower than the original

signal

the superheterod#ne recei!er always reduces to the same valueof IF. we have discussed that superheterodyning is simply reducingthe incoming signal is frequency by mixing. In a radio application weare reducing the AM or FM signal which is centered on the carrier

http://blog.oureducation.in/frequency-modulation/http://blog.oureducation.in/description-of-composite-video-signal-construction/http://blog.oureducation.in/frequency-modulation/http://blog.oureducation.in/description-of-composite-video-signal-construction/


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frequency to some intermediate value, called the IF intermediatefrequency!.

. What is m$ltiple/ing? (ame the t'pes of m$ltiple/ing?

Ans: Multiplexing is defined as the process in which a number of message signals are combined together to form

composite signals so that they can be transmitted through the common channel.

The two types of multipleing are$

a. +re)$en!' Di%ision M$ltiple/ing: In this technique' fied frequency bands are allotted to every user in the

complete channel bandwidth. Such frequency is allotted to user on a continuous basis.

. Time Di%ision M$ltiple/ing: *hen the pulse is present for the short time duration and most of the time their

is no signal present in/between them than this free space between the two pulses can occupied by the pulses from

other channels. This is known as Time 0ivision "ultipleing.

0. What is Amplit$de Mod$lation?

Ans: Amplitude Modulation is defined as the process in which the instantaneous value of the amplitude of the

carrier is varied according to the amplitude of the modulating or base band signal.

1. ow !an e aliasing e a%oided?

Ans: !liasing can be avoided if$

a. Sampling frequency must be greater than the frequency of the modulating signal.

. The frequency should be band limited to maimum frequency of the signal(fm) ,t1.

$estion32: Draw the 4asi! 4lo!" Diagram of 5omm$ni!ation S'stem.

Answer: The block diagram of communication system is given as follow$

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6$estion #: 7/plain different modes $sed for !omm$ni!ation.

Answer: !ccording to the mode of communication' it is divided into

18 9ine 5omm$ni!ation: In this mode of communication' the medium of transmission is a pair of conductors

called transmission lines. -oth the T and 2 are connected via a wire or line.

28 Wireless or adio 5omm$ni!ation: In this mode' a message is transmitted through a open medium as in

space by electromagnetic wave which are known as radio waves.

6$estion &: What are different t'pes of !omm$ni!ation s'stem.

Answer: Their are three basic types of communication system' which are/

18 Simple/ 5omm$ni!ation S'stem:

Simple 3ommunication System

,ere' the communication system that is capable of transmitting information through' called simple transmission

system. In simple type' one unit is equipped with a transmitter and the other side is equipped with only one

receiver but communication is done only one way by transmitter.

+or 7/ample: T.4. broadcast system.

28 alf3D$ple/ 5omm$ni!ation S'stem:

,alf/0uple 3ommunication System

,ere' the communication system that is capable of transmitting information in both directions but the flow is only

one way at a given time that why it is known as half/duple. In ,05 type' one unit is equipped with transmitter as

well receiver at one end and a transmitter/receiver at the other end but information can’t flow simultaneously in

both the directions.

+or 7/ample: *alkie/Talkie6

#8 +$ll D$ple/ 5omm$ni!ation S'stem:

%ull 0uple 3ommunication System

http://blog.oureducation.in/wireless-communication-concepts/http://blog.oureducation.in/wireless-communication-concepts/


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,ere the flow of communication takes place in both the direction simultaneously. %ull/duple 7thernet connections

work on the principles of full/duple where data packets are received and sent simultaneously at a given time.

+or 7/ample: hone6$estion -: What is the differen!e etween analog mod$lation and digital mod$lation.

Answer: In analog modulation bandwidth required is low while in digital modulation due to higher bit rate' heigherchannel bandwidth are required.

6$estion 1: 7/plain the term !ompanding.Answer: 3ompanding is the term derived from the combination of two terms5;MPA(D


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• A signal5to5noise ratio is the ratio of the magnitude of the signal to

that of noise often expressed in decibels*"

6. "hat is phase5loc#ed loop 788!%

•

7hase5loc#ed loop 788! is a circuit that loc#s onto a phaserelationship between an input signal and a 92: signal, and

produces an error signal. ;he error signal is fed bac# to control the

92: frequency so that it equals the input frequency.


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Analog Communciation Interview Question