SIDDHARTH INSTITUTE OF ENGINEERING & TECHNOLOGY: PUTTUR

(AUTONOMOUS)
Siddharth Nagar, Narayanavanam Road – 517583
QUESTION BANK WITH ANSWERS (DESCRIPTIVE)

Subject with Code: Analog Communications(19EC0408) Course & Branch: B.Tech – ECE
Year &Sem: II-B.Tech & II-Sem Regulation: R19

1 a) Draw the Basic block diagram of communication system.

Communication means sending, receiving and processing of information between two or more devices. A
collection of elements (devices) which works together to establish a communication between the sender and
receiver is called a communication system. Some examples of communication system include radio
broadcasting, television broadcasting, radio telegraphy, mobile communication, computer communication
etc. Two or more people communicating with each other by using sound signals is also known as the
communication system.
1 b) Explain the function of each block of communication system.
Information Source:
As we know that the communication system establishes the communication bridge between the sender
(transmitter) and receiver. To establish this communication bridge between the sender and receiver, first, we
need an information to send. This information originates in the information source.
The information generated by the source may be in the form of sound (human speech), picture (image source),
words (plain text in some particular language such as English, French, German etc.)
For example, if you are talking with your friend on a phone, you are considered as the information source who
generates information in the form of sound.

Input Transducer:
The device which is used to convert this sound signal into another form of signal is called transducer.
A transducer is a device which converts one form of energy or signal into another form of energy or signal.
The transducer is present at the input side and output side of the communication system. The transducer that
is present at the input side of the communication system is called input transducer. Generally, the input
transducer converts the non-electrical signal (sound signal or light signal) into an electrical signal. The best
example of an input transducer is the microphone which is placed between the information source and the
transmitter section. A microphone is a device which converts your voice signals (sound signals) into electrical
signals.

Transmitter:
The transmitter is a device which converts the signal produced by the source into a form that is suitable for
transmission over a given channel or medium. Transmitters use a technique called modulation to convert the
electrical signal into a form that is suitable for transmission over a given channel or medium. Modulation is
the main function of a transmitter.
When we send the signal to larger distances, it undergoes various circumstances which makes the signal weak.
In order to send the signals to larger distances, without the effect of any external interferences or noise addition
and without getting faded away, it has to undergo a process called modulation. Modulation increases the
strength of a signal without changing the parameters of the original signal. Thus, the resulted signal overcomes
the various effects which make it to become weak.

Communication Channel:
The communication channel is a medium through which the signal travels.
or
The communication channel is a wired or wireless medium through which the signal (information) travels
from source (transmitter) to destination (receiver).
or
The communication channel is a wired or wireless medium that is used to send the signal from the
source (transmitter) to the destination (receiver).
The communication channel is a wired or wireless medium that connects the transmitter and receiver for
sending the signal.
Communication channels are divided into two categories: wired and wireless. Some examples of wired
channels include co-axial cables, fiber optic cables, and twisted pair telephone lines. Examples of wireless
channels are air, water, and vacuum.

Noise:
Noise is an unwanted signal that enters the communication system via the communication channel and
interferes with the transmitted signal. The noise signal (unwanted signal) degrades the transmitted signal
(signal containing information).
Receiver
The receiver is a device that receives the signal (electrical signal) from the channel and converts the signal
(electrical signal) back to its original form (light and sound) which is understandable by humans at the
destination. TV set is a good example of a receiver. TV set receives the signals sent by the TV transmitting
stations and converts the signal into a form which is easily understandable by the humans who are watching
TV.

Output Transducer:
The transducer that is present at the output side of the communication system is called output transducer.
Generally, the output transducer converts the electrical signal into a non-electrical signal (sound signal, light
signal, or both sound and light signal). The best example of an output transducer is the loudspeaker which is
placed between the receiver section and the destination. The loudspeaker converts the electrical signals into
sound signals which are easily understandable by the humans at the destination.

Destination:
The destination is the final stage in the communication system. Generally, humans at some place are
considered as the destination. A destination is a place where humans consume the information. For example,
if you are watching TV, you are considered as the destination.
2 a) Define modulation? Explain different types of modulation.

MODULATION
2 b) Explain the NEED for Modulation.

NEED FOR MODULATION

3 a) Define Amplitude Modulation. Derive the expression on AM by both Time domain and
Frequency domain representation with necessary waveforms.
3 b) Define Modulation index and percentage of modulation index.

4 a) Obtain the expression for total transmitted power of AM wave.

4 b) An AM transmitter radiates 9kW of power when the carrier is unmodulated and 10.125kW of power
when the carrier is sinusoidal modulated. Find the modulation index & Percentage modulation. Now if
another sine wave corresponding to 40% modulation is transmitted Simultaneously. Calculate total radiated
power.
5 a) Derive an expression for transmission efficiency of AM.
5 b) A given AM broadcast station transmits a total power of 5kW when the carrier is modulated by
sinusoidal signal with a modulation index of 0.7071. Determine Carrier power and Transmission Efficiency.

Sol:

The total Power Pt=5KW

Modulation Index(µ)=0.7071

Carrier Power Pc=Pt / [1+ µ2/2] = 5KW/[1+(0.7071)2/2] = 4kw

Transmission Efficiency η = [µ2/ µ2+2] = [(0.7071)2/ (0.7071)2+2] = 0.7498

interms of % η= 74.98%
6 a) Explain Amplitude modulation for single tone information.
6 b) A modulating signal 10sin(2π×103t) is used to modulate a carrier signal 20sin(2π×104t). Determine the
modulation index, % of modulation index, frequency of sideband components and their amplitudes. What
will be the bandwidth of modulated signal?
bandwidth of modulated signal =2fm=2*1KHz=2KHz

7 a) Explain the generation of AM wave using SQUARE-LAW modulator along with relevant diagram and
analysis.

SQUARE LAW MODULATOR:

7 b) What are the advantages and Disadvantages of AM wave?
8 a) With a neat diagram and relevant equations explain the generation of AM wave using SWITCHING
modulator.

SWITHING MODULATOR:
8 b) Define demodulation? Mention different types of AM demodulators.

Note: Here Just give brief explanation from 9 a) & 9 b)

9 a) Show that a SQUARE-LAW device can be used for the detection of an AM wave.

SQUARE LAW DETECTOR:

9 b) What are the other AM Modulators?

10 a) How a modulating signal can be detected using ENVELOP DETECTOR and explain.

ENVELOP DETECTOR:
10 b) Mention the Applications of AM wave.