Model Class Test Paper for Student’s...

Model Class Test Paper for Student’s Reference

Government of Rajasthan

GOVERNMENT POLYTECHNIC COLLEGE, PALI

Year: 3rd

yr Branch: Electronics Session: 2017-18

EL-203: Electronic Measurement & Instrumentation

Duration: 1 Hr. Max. Marks: 15

Note: Attempt any THREE questions.

Q.1 Classify transducers. Differentiate between active and passive

transducers with example.

�ां�दसुस का वगकरण क�िजये ! एि�टव एवं पै�सव �ां�दसुस

म� उदहारण क� सहयता से अतंर �प"ठ क�िजये

Classification: 2 Marks

Comparison: 2 Marks

Example: 1 Marks

Q.2 What is Seebeck effect. Explain the measurement of

temperature using thermocouple.

सीबैक इफ़े�ट �या है! थम)कापल क� सहायता से ताप मापन

को समझाइये!

Seebeck effect:2 Marks

Explanation: 2 Marks

Diagram: 1 Marks

Q.3 Draw the block diagram of AC signal conditioning & explain it.

AC �स.नल conditioning का खडं आरेख बनाईए एवं इसको

समझाइये!

Block diagram:2 Marks


Q.4 Write short note on ANY ONE of the following:

3न4न म� से 5कसी एक पर लघु 7टप8णी �ल9खए:

(a) Photo cell

फोटो सेल

Diagram: 2 Marks


(b) LVDT

एल. वी. डी. ट=.

Diagram: 2 Marks





Year: 3rd


EL-206: Wave Propagation & Communication Engineering



Q.1 Derive the expression for the Amplitude modulated waveform

and plot its frequency spectrum.

AM वेवेफोम� के लए expression �ात क�िजये एवं उसका

आव�ृत �पे��म बनाईए !

Waveform: 1 Marks

Derivation: 2 Marks

Spectrum: 2 Marks

Q.2 Explain external types of noises in brief.

!वभ#न $कार क� बाह'रये नॉइज़ को संशपे म, समझाइये !

Definition: 1 Marks


Q.3 A 400 watts carrier is modulated to a depth of 75 percent.

Calculate the total power in the modulated wave.

400 वाट के carrier को 75% तक modulate 7कया गया है!

modulated वेव म, कुल पॉवर �ात क�िजये!

Formula: 2 Marks

Power calculation:3 Marks


�न;न म, से 7कसी एक पर लघु >टप?णी लAखए:

(a) Total power in AM wave

AM वेव म, कुल पॉवर

Power Derivation:5 Marks

(b) Need of modulation

Modulation क� आवेHय�ता


Govt. Polytechnic College, Jalore(Camp-Pali)

Model Test Paper 2017-18

Subject: Audio and Video system

Code: EL-208 Time: 1 Hour

Maximum marks: 15

Answer any three

Q1:Briefly explain modulation techniques used for picture and sound signal ?

Q2: Explain positive and negative modulation ?

Q3: Explain block diagram of TV Transmitter ?

Q4: Explain TV channel bandwidth with suitable diagram?

Q5:Explain different types of TV transmitting antennas ?

Marking Scheme:

Q1: Picture Modulation = 2.5

Sound Modulation = 2.5

Q2: Positive Modulation = 2.5

Negative Modulation = 2.5

Q3:Explanation = 2

Block Diagram = 3

Q4: Diagram = 3

Explanation = 2

Q5:Explanation = 5

CHANDANI SANKHALA

LECTURER ELECTRONICS

GPC JALORE(CAMP-PALI)

MODEL ANSWERS:

Ans1:In TV Transmission the use of FM is made for Audio transmission and AM for

Video transmission.

Amplitude Modulation:In amplitude modulation, the amplitude (signal strength) of the

carrier wave is varied in proportion to the amplitude the message signal being

transmitted.

Let m(t)=message signal

C(t)=Accos2πfct= carrier signal

General expression of AM signal

SAM(t)=Ac[1+kam(t)]cos2πfct

ka= amplitude sensitivity of AM modulator

Frequency Modulation:In Frequency modulation, frequencyof the carrier wave is

varied in proportion to the amplitude the message signal being transmitted.

Ans2:Positive modulation:The amplitude of the carrier increases with increase in

amplitude of the signal and vice versa. This is called “positive modulation”.

Negative modulation: The instantaneous amplitude of the carrier decreases with

increase in instantaneous amplitude of the signal. This is called “negative modulation”.

Ans3: Block diagram of TV Transmitter:

The block diagram can be broadly divided into two separate section, viz., one that -

Generates an electronic signal (called video signal) corresponding to the actual picture

and then uses this video signal to modulate an R-F carrier so as to be applied to the

transmitting antenna for transmission, other that generates an electronic signal (called

audio signal) containing sound information and then uses this signal to modulate

another RF carrier and then applied to the transmitting antenna for

transmission.However only one antenna is used for transmission of the video as well as

audio signals. Thus these modulated signals have to be combined together in some

appropriate network. Video as well as audio signals have to be amplified to the desired

degree before they modulate their respective RF carriers.This function is performed by

video and audio amplifiers. Video signal transmitter employs an AM transmitter as

amplitude-modulation is used for video signals whereas audio signal transmitter

employs FM modulator as frequency modulation is used for sound information.

Ans4:TV Channel Bandwidth:

The sound carrier is always positioned at extremity of the fully radiated upper

sideband and hence is 5.5MHz away from the picture carrier .The FM sound signal

occupies a frequency spectrum of about +/-75KHz around the sound carrier.A guard

band of 0.25MHz is allowed on the sound carrier side of the television channel to allow

for adequate inter channel separation. The total channel bandwidththus occupies 7 MHz.

Ans5:Television Transmitting antenna:

Turnstile Array: To obtain an omnidirectional radiation pattern in the horizontal plane,

for equal television signal radiation in all direction, an arrangement known as ‘Turnstile

array’ is used. In this type of antenna two crossed dipoles are used in a

Turnstilearrangement. These are fed in quadrature from the same source by means of an

extra λ/4 line. Each dipole has a figure of eight pattern in the horizontal plane, but

crossed with each other. Thus the resultant pattern is as shown in the figure.

Dipole Panel Antenna System:This antenna system consists of dipole panels mounted

on the four sides at the top of the antanna tower. Each panel consists of an array of full

wave dipoles mounted in front of reflectors.For obtaining unidirectional pattern the four

panels mounted on the four sides of the tower are so fed that the current in each lags

behind the previous by 90 degree.

Govt. Polytechnic College ,Jalore(Camp-Pali)


Code: EL 209 Time: 1 Hour

Maximum marks: 15

Answer any three

Q1: What is Megger ? Explain its working with suitable diagram ?

Q2: What is Spectrum Analyser ? Explain its working with suitable diagram?

Q3: Explain Harmonic Distortion Analyser ?

Q4: What is working principle of Q meter ? Explain its working with diagram ?

Marking Scheme:

Q1: Definition = 1

Working = 3

Diagram = 1

Q2:Definition = 1

Working = 3

Diagram = 1

Q3:Explanation = 3

Diagram = 2

Q4: Working principal = 2

Working = 2

Diagram = 1

CHANDANI SANKHALA



MODEL ANSWERS:

Ans1: Megger:Megger is a portable instrument which is used to measure insulation

resistance of the electrical machinery or system. It can be battery operated or mechanically

operated (hand crank dc generator) and gives direct reading in ohms.

Working of Megger:

The testing voltage is usually 500, 1000 or 2500 V which is generated by the hand driven

generator. The generator has centrifugal clutch due to which the generator supplied the

constant for the insulation test. The constant voltage is used for testing the insulation having

low resistance.The Megger has three coils two pressure coils and one current coil. The

pressure coil rotates the moving coil in the anticlockwise direction, whereas the current coil

rotates it in the clockwise direction.When the unknown resistance is connected in the

circuit, the pointer of the moving coil becomes stable. The pressure coil and the current coil

balance the pointer and set it in the middle of the scale.The deflection of the pointer is

directly proportional to the voltage applied to the external circuit. When the testing circuit is

applied across the Megger, and if there is no shorting throughout the insulation then the

pointer deflects towards the infinity. Which shows that the resistance has high insulation.

For low resistance, the pointer moves towards zero.

Ans2:SpectrumAnalyser:A Spectrum Analyzer provides a calibrated graphical display on

its CRT, with frequency on the horizontal axis and amplitude (voltage) on the vertical axis.

Working:

Basic Spectrum Analyzer Using Swept Receiver Design

Referring to the block diagram of Figure the sawtooth generator provides the sawtooth

voltage which drives the horizontal axis element of the scope and this sawtooth voltage is

frequency controlled element of the voltage tuned oscillator. As the oscillator sweeps from

fmin to fmax of its frequency band at a linear recurring rate, it beats with the frequency

component of the input signal and produce an IF, whenever a frequency component is met

during its sweep. The frequency component and voltage tuned oscillator frequency beats

together to produce a difference frequency, i.e. IF. The IF corresponding to the component

is amplified and detected if necessary, and then applied to the vertical plates of the CRO,

producing a display of amplitude versus frequency.

Ans3:Harmonic Distortion Analyser:

A Harmonic Distortion Analyzer measures the total harmonic power present in the test

wave rather than the distortion caused by each component. The simplest method is to

suppress the fundamental frequency by means of a high pass filter whose cut off frequency

is a little above the fundamental frequency. This high pass allows only the harmonics to

pass and the total harmonic distortion can then be measured.

Bridged T-Network Method

The switch S is first connected to point A so that the attenuator is excluded and the bridge

T-network is adjusted for full suppression of the fundamental frequency, i.e. minimum

output. Minimum output indicates that the bridged T-network is tuned to the fundamental

frequency and that the fundamental frequency is fully suppressed.The switch is next

connected to terminal B, i.e. the bridged T-network is excluded. Attenuation is adjusted

until the same reading is obtained on the meter. The attenuator reading indicates the total

rms distortion. Distortion measurement can also be obtained by means of a wave analyzer,

knowing the amplitude and the frequency of each component, the Harmonic Distortion

Analyzer can be calculated. However, distortion meters based on fundamental suppression

are simpler to design and less expensive than wave analyzers. The disadvantage is that they

give only the total distortion and not the amplitude of individual distortion components.

Ans4: Working principal of Q-meter:

The Q-meter is an instrument designed for the measurement of Q-factor of the coil as well

as for the measurement of electrical properties of coils and capacitors. -This instru-ment

operates on the principle of series resonance i.e. at resonate condition of an ac series circuit

voltage across the capacitor is equal to the applied voltage times of Q of the circuit. If the

voltage applied across the circuit is kept-constant then voltmeter connected across the

capacitor can be calibrated to indicate Q directly.

Working:

A wide-range os-cillator with frequency range from 50 kHz to 50 MHz is used as a power

supply to the circuit. The output of the oscillator is shorted by a low-value resistance, Rsh

usually of the or-der of 0.02 ohm. So it introduces almost no resistance into the oscillatory

circuit and represents a voltage source with a very small or of almost negligible internal

resistance. The voltage across the low-value shunt resistance Rsh, is measured by a thermo-

couple meter and the voltage across the capacitor, Vc is measured by an electronic

voltmeter.For carrying out the measurement, the unknown coil is connected to the test

terminals of the instrument, and the circuit is tuned to resonance either by varying the

frequency of the oscillator or by varying the resonating capacitor C. Readings of voltages

across capacitor C and shunt resistance Rsh are obtained and Q-factor of the coil is

deter-mined as follows :

By definition Q-factor of the coil

Q = XL / R

And when the circuit is under resonance condition

XL = XC

Or

IXL = IXC = VC

And the voltage applied to the circuit.

V = IR

So, Q = XL / R = IXL / R = VC / V




Year: 3rd


EL-307: Linear Integrated Circuit & Design



Q.1 Explain the application of Phase Locked Loop (PLL) as frequency

translator.

PLL का आव�ृत ांसलेटर के �प म� अनु�योग �ल�खए!

. Diagram: 2 Marks


Equations: 1 Marks

Q.2 Design differentiator circuit using Op-Amp and draw the output

waveforms for the different input signals.

Op-Amp क सहयता से Differentiator प"रपथ $डजाईन क"रये एवं

(व�भ*न इनपुट �स,नल के �लए आउटपुट �स,नल भी �द�श1त क"रये!

Diagram: 1 Marks

Design Equations :2 Marks

Waveforms: 2 Marks

Q.3 Compare Ideal and practical Op-Amp.

आदश1 एवं �ैि4टकल Op-Amp क तुलना क िजये!

Comparison: 5 Marks


�न5न म� से 6कसी एक पर लघु 8टप9णी �ल�खए:

(a) AMV using 555 IC

555 IC क सहायता से AMV

Diagram: 2 Marks


Waveforms: 1 Marks

(b) Block diagram of Op-Amp

Op-Amp का खडं आरेख

Block Diagram:2 Marks


Govt. Polytechnic College ,Jalore(Camp-Pali)


Code: EL 308 Time: 1 Hour

Maximum marks: 15

Answer any three

Q1: Briefly explain about the centralized SPC ?

Q2:Explain a two stage network with multiple switching matrices in each stage with suitable

diagram ?

Q3: Differentiate single stage and multiple stage network ?

Q4: Explain enhanced services in telecommunication ?

Q5: Explain different level of processing in “distributed SPC” ?

Marking Scheme:

Q1: Explanation = 3

Diagram = 2

Q2: Explanation = 3

Diagram = 2

Q3: Comparision = 5

Q4: Explanation = 5

Q5: Explanation = 4

Diagram = 1

CHANDANI SANKHALA



MODEL ANSWERS:

Ans.1: .Centralized SPC: In this control, all the control equipment is replaced by a single

processor which must be quite powerful.

FIG - Typically Centralized SPC Organization

In centralized SPC, dual processor architecture may be configured to operate in

one of three modes:

1. Standby mode: In this mode, one processor is active and the other is onstandby, both

hardware and software wise. The standby processor broughtonline when active processor fails.

An important requirement of this configuration is the ability of the standby processor to

reconstitute the state ofthe exchange system when it takes over the control.

2. Synchronous duplex mode: In synchronous duplex mode, hardwarecoupling is provided

between the two processors which execute the same set of instructions and compare the results

continuously. If a mismatch occurs,the faculty processor is identified and taken out of service

immediately.When the system is operating normally, the two processors have the same

data in their memories at all the times and receive all information from theexchange

environment.

3. Load Sharing mode; In load sharing operation, an incoming call is assigned randomly or

in a predetermined order to one of the processors which then handles the call right through

completion. Thus both the processors are activesimultaneously and share the load and the

resources dynamically.

Ans 2: Two stage network: In this architecture M inlets are divided into rblocks of p inlets

each such that M=pr. Similarly N outlets are divided into s blocks of q outlets each

such that N=qs.In order to ensure full availability there must be at least one out let

from each block in the first stage terminatingas inlet on every block of the second

stage.

Number of switching elements

S=psr+qrs=Ms+Nr

Switching Capacity i.e., the number of links between the first and the second stages.

SC=sr

Ans 3:

SINGLE STAGE MULTISTAGE

Inlet to outlet connection is through a single

cross point.

Inlet to outlet connection is through a

multiple cross points.

Better quality link. multiple cross points degrade quality of

link.

If a crosspoint fails, associated connection

cannot be established.

Alternative cross points and paths are

available.

Cross points are inefficiently used. Cross points are efficiently used.

No. of crosspoints is prohibitive. No. of crosspoints is reduced

significantly.

The network is non blocking in character. The network is blocking in character.

Time for establishing a call is less. Time for establishing a call is more.

Ans 4:ENHANCED SERVICES

Categories of enhanced services

1. Services associated with the calling subscriber and designed to reduce the time spent on

dialing and the number of dialing errors.

2. Services associated with the called subscriber and designed to increase the call completion

rate.

3. Services involving more than two parties.

4. Miscellaneous services.

Category 1

• Abbreviated dialing

• Recorded number calls or no dialing calls.

• Call back when free

Category 2

• Call forwarding

• Operator answer

Category 3

• Calling number record

• Call waiting

• Consultation hold

• Conference calls

Category 4

• Automatic alarm

• STD barring

• Malicious call tracing

• STD：subscriber trunk dialing

Ans 5: Distributed SPC:

The distributed SPC offers better availability and reliability than the centralized SPC.

Entire exchange control functions may be decomposed either horizontally or vertically

for distributed processing. In vertical decomposition, the exchange environment is

divided into several blocks and each block is assigned to a processor that performs all

control functions related to that block of equipment. In horizontal decomposition, each

processor performs one or some of the exchange control functions. Figure shows the

distributed control where switching equipment is divided into parts, each of which has

its own processor.

Level 3 Processing:

Level 3 Processing will include the functions like:

• Scanning

• Distribution

• Marking

• Controlling all incoming & Outgoing local calls, STD Calls, ISD

Calls, Fax &Data services

• Control of all functions are carried by specially designed Processors

With“Micro-programmed Control”

Level 2 Processing:

Level 2 Processing or Processor is also called SwitchingProcessor. The architecture of

switching processors is designed to for 99.9% availability.

Switching Occupancy: The traffic handling capacity of the control equipment isusually

limited by the capacity of the switching processor. The load on theswitching processor

is measured by its occupancy “t” estimated by the simpleformula:

t=a+bN

a=fixed overhead depending upon the exchange capacity and configuration

b= average time to process one call

N= no. of calls per unit time

Level 1 Processing:

The Level 1 processor control O & M functionswhich involve following steps:

• Administer the exchange hardware and software

• Add, modify or delete information in translation table

• Put a new line or trunk into operation

• Monitor traffic

• Run diagnostic and test programs.




Year: 3rd


EL-309: Computer Communication



Q.1 Explain ALOHA technique and calculate its throughput.

ALOHA तकनीक को समझाइये एवं इसका throughput �ात

क�िजये!


Throughput Evaluation :2 Marks

Q.2 Explain in detail the Go-Back-N ARQ (Automatic Repeat

Request) retransmission technique.

Go-Back-N ARQ retransmission तकनीक को �व�तार से

समझाइये

Diagram: 2 Marks


Q.3 Explain circuit switching technique in brief.

स क! ट ि�वि#चगं तकनीक को समझाइये !

Diagram: 2 Marks



&न'न म( से कसी एक पर लघु -टप.णी 0ल1खए:

(b) MAN

एम.्ऐ.एन.

Diagram: 2 Marks


c) MODEM

मॉडमे

Diagram: 2 Marks


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