Q&A: ELECTRONICS and COMMUNICATION

 

ELECTRONICS and COMMUNICATION Engineering Questions and Answers

1. Expand ECE?
Electronics & Communication Engineering.

2. What is Electronic?
The study and use of electrical devices that operate by controlling the flow of electrons or other electrically charged particles.

3. What is communication?
Communication means transferring a signal from the transmitter which passes through a medium then the output is obtained at the receiver. (or)communication says as transferring of a message from one place to another place called communication.

4. Different types of communications? Explain.
Analog and digital communication.

As a technology, analog is the process of taking an audio or video signal (the human voice) and translating it into electronic pulses. Digital on the other hand is breaking the signal into a binary format where the audio or video data is represented by a series of “1”s and “0”s.
Digital signals are immune to noise, the quality of transmission and reception is good, components used in digital communication can be produced with high precision and power consumption is also very less when compared with analog signals.

5. Define What is engineering?
The application of science to the needs of humanity and a profession in which a knowledge of the mathematical and natural sciences gained by study, experience, and practice is applied with judgment to develop ways to use economically the materials and forces of nature for the benefit of mankind.

6. Difference between electronic and electrical.

Electronics work on DC and with a voltage range of -48vDC to +48vDC. If the electronic device is plugged into a standard wall outlet, there will be a transformer inside which will convert the AC voltage you are supplying to the required DC voltage needed by the device. Examples: Computer, radio, T.V, etc…
Electric devices use line voltage (120vAC, 240vAC, etc…). Electric devices can also be designed to operate on DC sources but will be at DC voltages above 48v. Examples: incandescent lights, heaters, fridges, stoves, etc…

7. What is sampling?
The process of obtaining a set of samples from a continuous function of time x(t) is referred to as sampling.

8. State sampling theorem.
It states that, while taking the samples of a continuous signal, it has to be taken care that the sampling rate is equal to or greater than twice the cut-off frequency and the minimum sampling rate is known as the Nyquist rate.

9. What is a pass band?
Passband is the range of frequencies or wavelengths that can pass through a filter without being attenuated.

10. What is a stop band?
A stopband is a band of frequencies, between specified limits, in which a circuit, such as a filter or a telephone circuit, does not let signals through, or the attenuation is above the required stopband attenuation level.

11. Difference between a mobile and a cell phone.

• There is no difference, just language use, which differs from country to country, so in Britain, it is called a mobile, and in the USA and South Africa and other places a cell phone.
• Even in Europe, the name differs. The Germans call it “handy”, which in English has completely another meaning as an adjective, meaning useful.

• In Italy, it is called a Telefonica or “little phone”.

• This difference in British and American English is also evident in many other things we use every day, like lifts and elevators, nappies and diapers, pickups, and trucks. The list goes on and on, any student of English has to decide which he or she will use, as the default setting.

12. Explain RF?
Radiofrequency (RF) is a frequency or rate of oscillation within the range of about 3 Hz to 300 GHz. This range corresponds to the frequency of alternating current electrical signals used to produce and detect radio waves. Since most of this range is beyond the vibration rate that most mechanical systems can respond to, RF usually refers to oscillations in electrical circuits or electromagnetic radiation.

13. What is modulation? And where it is utilized?

• Modulation is the process of varying some characteristics of a periodic wave with an external signal.
• Radio communication superimposes this information-bearing signal onto a carrier signal.
• These high-frequency carrier signals can be transmitted over the air easily and are capable of traveling long distances.
• The characteristics (amplitude, frequency, or phase) of the carrier signal are varied in accordance with the information-bearing signal.
• Modulation is utilized to send an information-bearing signal over long distances.

14. Define what is demodulation?
Demodulation is the act of removing the modulation from an analog signal to get the original baseband signal back. Demodulating is necessary because the receiver system receives a modulated signal with specific characteristics and it needs to turn it into a base-band.

15. Name the modulation techniques.
For Analog modulation–AM, SSB, FM, PM, and SM
Digital modulation–OOK, FSK, ASK, Psk, QAM, MSK, CPM, PPM, TCM, OFDM

16. Explain AM and FM.

1. AM-Amplitude modulation is a type of modulation where the amplitude of the carrier signal is varied in accordance with the information-bearing signal.
2. FM-Frequency modulation is a type of modulation where the frequency of the carrier signal is varied in accordance with the information-bearing signal.

17. where do we use AM and FM?

1. AM is used for video signals for example TV. Ranges from 535 to 1705 kHz.
2. FM is used for audio signals for example Radio. Ranges from 88 to 108 MHz.

18. How does a mobile work?

When you talk into a mobile telephone it converts the sound of your voice to radiofrequency energy (radio waves). The radio waves are transmitted through the air to a nearby base station. The base station then sends the call through the telephone network until it reaches the person you are calling. When you receive a call on your mobile phone the message travels through the telephone network until it reaches a base station near you. The base station sends out radio waves, which are detected by your telephone and converted back to speech. Depending on the equipment and the operator, the frequency that each operator utilizes is 900MHz, 1800MHz, or 2100MHz.
The mobile phone network operates on the basis of a series of cells. Each cell requires a radio base station to enable it to function.

• There are three types of base stations and each has a particular purpose:
• The Macrocell is the largest type and provides the main coverage for mobile phone networks.
• The Microcell is used to improve capacity in areas where demand to make calls is high, such as shopping centers.
• The Picocell only has a range of a few hundred meters and may be used to boost weak signals within large buildings.
• Each base station can only cope with a certain number of calls at any one time. So if demand exceeds the capacity of a base station an additional base station is needed.

19. What is a base station?

The base station is a radio receiver/transmitter that serves as the hub of the local wireless network, and may also be the gateway between a wired network and the wireless network.

20. How many satellites are required to cover the earth?
3 satellites are required to cover the entire earth, which is placed at 120 degrees from each other. The life span of the satellite is about 15 years.

21. What is a repeater?
A repeater is an electronic device that receives a signal and retransmits it at a higher level and/or higher power, or onto the other side of an obstruction so that the signal can cover longer distances without degradation.

22. What is attenuation?

Attenuation is the reduction in amplitude and intensity of a signal. Signals may attenuate exponentially by transmission through a medium, or by increments calculated in electronic circuitry or set by variable controls. Attenuation is an important property in telecommunications and ultrasound applications because of its importance in determining signal strength as a function of distance. Attenuation is usually measured in units of decibels per unit length of medium (dB/cm, dB/km, etc) and is represented by the attenuation coefficient of the medium in question.

23. What is multiplexing?
Multiplexing (known as muxing) is a term used to refer to a process where multiple analog message signals or digital data streams are combined into one signal over a shared medium. The aim is to share an expensive resource. For example, in telecommunications, several phone calls may be transferred using one wire.

24. What is CDMA, TDMA, FDMA?
Code division multiple access (CDMA) is a channel access method utilized by various radio communication technologies. CDMA employs spread-spectrum technology and a special coding scheme (where each transmitter is assigned a code) to allow multiple users to be multiplexed over the same physical channel. By contrast, time-division multiple access (TDMA) divides access by time, while frequency-division multiple access (FDMA) divides it by frequency.
An analogy to the problem of multiple access is a room (channel) in which people wish to communicate with each other. To avoid confusion, people could take turns speaking (time division), speaking at different pitches (frequency division), or speaking in different directions (spatial division). In CDMA, they would speak different languages. People speaking the same language can understand each other, but not other people. Similarly, in radio CDMA, each group of users is given a shared code. Many codes occupy the same channel, but only users associated with a particular code can understand each other.

25. Difference between CDMA and GSM.
These are the two different means of mobile communication being presently used worldwide. The basic difference lies in the Multiplexing method used in aerial communication i.e. from Mobile Tower to your mobile and vice versa.

CDMA uses Code Division Multiple Access as the name itself indicates, for example, you are in a hall occupied with a number of people speaking a different language. You will find that the one language you know will be heard by you and the others will be treated like noise. In the same manner, each CDMA mobile communication takes place with a “code” communicating between them and the other end if one is knowing that code then only it can listen to the data being transmitted i.e. the communication is in the coded form.

On the other hand, GSM (Global System for Mobile Communications)uses narrowband TDMA, which allows eight simultaneous calls on the same radio frequency. TDMA works by dividing a radio frequency into time slots and then allocating slots to multiple calls. In this way, a single frequency can support multiple, simultaneous data channels.

26. What is an Amplifier?
An electronic device or electrical circuit that is used to boost (amplify) the power, voltage or current of an applied signal.

27. What are Barkhausen's criteria?

Barkhausen criteria, without which you will not know which conditions, are to be satisfied for oscillations.
“Oscillations will not be sustained if, at the oscillator frequency, the magnitude of the product of the transfer gain of the amplifier and the magnitude of the feedback factor of the feedback network ( the magnitude of the loop gain ) are less than unity”.
The condition of unity loop gain -Aβ = 1 is called the Barkhausencriterion. This condition implies that | Aβ|= 1 and that the phase of – Aβ is zero.

28. Explain Full duplex and half duplex.

• Full duplex refers to the transmission of data in two directions simultaneously. For example, a telephone is a full-duplex devicebecause both parties can talk at once. In contrast, a walkie-talkie is ahalf-duplex device because only one party can transmit at a time.
• Most modems have a switch that lets you choose between full-duplex and half-duplex modes. The choice depends on whichcommunications program you are running.
• In full-duplex mode, data you transmit does not appear on yourscreen until it has been received and sent back by the other party. This enables you to validate that the data has been accurately transmitted. If your display screen shows two of each character, it probably means that your modem is set to half-duplex mode when it should be in full-duplex mode.

29. What is a feedback? And explain different types of feedback.
Feedback is a process whereby some proportion of the output signal of a system is passed (fed back) to the input. This is often used to control the dynamic behaviour of the system.
Types of feedback:

1. Negative feedback: This tends to reduce output (but in amplifiers, stabilizes and linearizes operation). Negative feedback feeds part of a system’s output, inverted, into the system’s input; generally with the result that fluctuations are attenuated.
2. Positive feedback: This tends to increase output. Positive feedback, sometimes referred to as “cumulative causation”, is a feedback loop system in which the system responds to perturbation (Aperturbation means a system, is an alteration of function, induced by external or internal mechanisms) in the same direction as the perturbation. In contrast, a system that responds to the perturbation in the opposite direction is called a negative feedback system.
3. Bipolar feedback: which can either increase or decrease output.

30. Advantages of negative feedback over positive feedback.
Much attention has been given by researchers to negative feedback processes, because negative feedback processes lead systems towards equilibrium states. Positive feedback reinforces a given tendency of a system and can lead a system away from equilibrium states, possibly causing quite unexpected results.

31. Example for negative feedback and positive feedback.
Example for –ve feedback is —Amplifiers
And for +ve feedback is – Oscillators

32. What is Oscillator?
An oscillator is a circuit that creates a waveform output from a direct current input. The two main types of oscillator are harmonic and relaxation. The harmonic oscillators have smooth curved waveforms, while relaxation oscillators have waveforms with sharp changes.

33. What is a transducer and transponder?
A transducer is a device, usually electrical, electronic, electro-mechanical, electromagnetic, photonic, or photovoltaic that converts one type of energy or physical attribute to another for various purposes including measurement or information transfer.
In telecommunication, the term transponder (short-forTransmitter-responder and sometimes abbreviated to XPDR, XPNDR, TPDR or TP) has the following meanings:
An automatic device that receives, amplifies, andretransmits a signal on a different frequency (see alsobroadcast translator).
An automatic device that transmits a predetermined messagein response to a predefined received signal.
A receiver-transmitter that will generate a reply signal upon proper electronic interrogation.
A communications satellite’s channels are called transponders, because each is a separate transceiver or repeater.

34. What is an Integrated Circuit?
An integrated circuit (IC), also called a microchip, is an electronic circuit etched onto a silicon chip. Their main advantages are low cost, low power, high performance, and very small size.

35. What is crosstalk?
Crosstalk is a form of interference caused by signals in nearby conductors. The most common example is hearing an unwanted conversation on the telephone. Crosstalk can also occur in radios, televisions, networking equipment, and even electric guitars.

36. What is a rectifier?

• A rectifier changes alternating current into direct current. This process is called rectification. The three main types of rectifier are the half-wave, full-wave, and bridge. A rectifier is the opposite of an inverter, which changes direct current into alternating current.
• HWR- The simplest type is the half-wave rectifier, which can be made with just one diode. When the voltage of the alternating current is positive, the diode becomes forward-biased and current flows through it. When the voltage is negative, the diode is reverse-biased and the current stops. The result is a clipped copy of the alternating current waveform with only positive voltage, and an average voltage that is one third of the peak input voltage. This pulsating direct current is adequate for some components, but others require a more steady current. This requires a full-wave rectifier that can convert both parts of the cycle to positive voltage.
• FWR- The full-wave rectifier is essentially two half-wave rectifiers, and can be made with two diodes and an earthed centre tap on the transformer. The positive voltage half of the cycle flows through one diode, and the negative half flows through the other. The centre tap allows the circuit to be completed because current cannot flow through the other diode. The result is still a pulsating direct current but with just over half the input peak voltage, and double the frequency.

37. What is resistor?
A resistor is a two-terminal electronic component that opposes anelectric current by producing a voltage drop between its terminals in proportion to the current, that is, in accordance with Ohm’s law: V= IR.

38. What is capacitor?

• A capacitor is an electrical/electronic device that can store energyin the electric field between a pair of conductors (called “plates”). The process of storing energy in the capacitor is known as “charging”, and involves electric charges of equal magnitude, but opposite polarity, building up on each plate.
• Capacitors are often used in electric and electronic circuits asenergy-storage devices. They can also be used to differentiate between high-frequency and low-frequency signals. This property makes them useful in electronic filters.
• Capacitors are occasionally referred to as condensers. This term is considered archaic in English, but most other languages use acognate of condenser to refer to a capacitor.

39. What is inductor?
An inductor is a passive electrical device employed in electrical circuits for its property of inductance. An inductor can take many forms.

40. What is conductor?
A substance, body, or device that readily conducts heat, electricity, sound, etc. Copper is a good conductor of electricity.

41. What is a semi conductor?
A semiconductor is a solid material that has electrical conductivityin between that of a conductor and that of an insulator(AnInsulator is a material that resists the flow of electric current. It is an object intended to support or separate electrical conductorswithout passing current through itself); it can vary over that wide range either permanently or dynamically.

42. What is diode?
In electronics, a diode is a two-terminal device. Diodes have two active electrodes between which the signal of interest may flow, and most are used for their unidirectional current property.

43. What is transistor?
In electronics, a transistor is a semiconductor device commonly used to amplify or switch electronic signals. The transistor is the fundamental building block of computers, and all other modernelectronic devices. Some transistors are packaged individually but most are found in integrated circuits.

44. What is op-amp?
An operational amplifier, often called an op-amp , is a DC-coupledhigh-gain electronic voltage amplifier with differential inputs[1] and, usually, a single output. Typically the output of the op-amp is controlled either by negative feedback, which largely determines the magnitude of its output voltage gain, or by positive feedback, which facilitates regenerative gain and oscillation.

45. What is cut-off frequency?
The frequency at which the response is -3dB with respect to the maximum response.

ECE Interview Questions ::

1.The impedance curve of an R-L-C network cuts the frequency axis only when the frequency is such that
(a) XL=XC (b) XL=XC=0
(c) R=0 and XL=XC (d) none of these

2.In a semiconductor diode, P-side is grounded and N-side is applied a potential of -5V through a resistance of 100 ohms. the diode shall
(a) conduct fully (b) not conduct
(c) conduct partially (d) none of these

3. the junction diode’s capacitance that is made use of in varactors is known as
(a) transition capacitance (b) diffusion capacitance
(c) space charge capacitance (d) inter-electrode capacitance.

4. when current through a zener diode increases by a factor of 2, voltage across its terminals
(a) is halved (b) is doubled too
(c) is practically unchanged (d) none of these

5. SCRs are connected in series to enchance
(a) their overall dv/dt rating (b) their voltage ratings
(c) their current handling capabilities (d) none of these

6. the condition that decides the oscillator’s out put frequency is :
(a) loop gain should at least be unity
(b) loop phase-shift should be zero or integral multiple of 2p radians
(c) loop gain should be precisely unity
(d) loop phase-shift should be precisely zero radian.

7. most popular oscillator configuration for audio applications is :
(a) Hartley oscillator (b) colpitt’s oscillator
(c) wein-bridge oscillator (d) R-C phase shift oscillator.

8. pick the odd-one out :
(a) Hartley oscillator (b) collpitt oscillator
(c) clap oscillator (d) wein bridge oscillator

9.the output voltage at no load in an unregulated power supply is the same as its output voltage at rated load current. its internal resistance is therefore
(a) extremely small (b) zero
(c) infinite (d) extremely large.

10. mark the rectifier circuit that produces the least ripple
(a) single rectifier,half wave, single phase (b) four rectifiers,full wave,single phase
(c) two rectifiers,full wave,single phase (d) six rectifiers,full wave,three phase.

11. indicate the false statement
(a) closed loop gain is always less than the open loop gain.
(b) input impedance is always greater than the out put impedance
(c) the open loop gain falls to zero decibel at a frequency equal to unity gain crossover frequency
(d) closed loop bandwidth is always greater than the open loop babdwidth.

12. one of the following statements in reference to a unity gain noninverting buffer using an opamp is in correct. identify this statement
(a) it has extremely high input impedance,much higher than even its open loop input impedance
(b) its input impedance is very high almost approaching its open loop input impedance magnitude
(c) the voltage gain is unity. (d) the inputis applied to the non-inverting input
(e) the feed back magnitude is 100 per cent.

13.the SLEW RATE specification of an opamp is usually measured in
(a) microvolts per second (b) volts per microsecond
(c) decibels (d) volts per microvolt

14. a given opamp has an open loop gain of 110dB and a CMRR rating of 106dB. what should be the open loop common mode gain of this op-amp?
(a) it cannot be determined from the given data (b)4dB
(c) 216 dB (d) 110Db

15. in a 555 astable multivibrator operating from Vcc of 15V, the output wave from duty cycle is 0.4 (duty cycle = ON-time/total time period.) the circuit is slightly modified with the capacitor now charging from a voltage of 30V rather than Vcc. the duty cycle of the output waveform in the modified circuit will
(a) remain unchanged (b) become about 0.6
(c) be approximately 0.2 (d) none of these

16. the pulse width in a 555 monostable multivibrator is given by
(a)t = 0.69 RC (b)t = 1.1 RC
(c)t = RC (d) none of these

17. in the astable mode of operation of IC 555, the timing capacitor always charges between
(a) 0 and 1/3 Vcc (b) 1/3 Vcc and 2/3Vcc
(c) 0 and 2/3 Vcc (d) 0 and Vcc

18.when a PLL is being used as an FM demodulator,the demodulated signal appears at
(a) the output of phase comparator (b) the output of low pass filter
(c) the VCO output (d) none of these.

19.”A NOR gate is equivalent to a bubbled AND gate”. this statement is an outcome of
(a) demorgan’s theorems (b) involution law
(c) absorption law (d) idempotent law

20.for one of the following conditions, clocked j-k flip flop can be used as DIVIDE BY 2 circuit where the pulse train to be divided is applied at clock input.
(a) J=1, K=1 and the flip flop should have active HIGH inputs
(b) J=1, K=1 and the flip flop should have active LOW inputs
(c) J=0, K=0 and the flip flop should have active high inputs
(d) J=1, K=1 and the flip flop should be a negative edge triggered one.

21. in a presettable, clearable positive edge triggered J-K flip flop, the Q output when the flip flop is clocked for J=1,K=0,preset=1 and clear = 0 will be
(a) 1 (b) 0
(c) indeterminate (d) complement of what it was at the time of clocking
(assume all the inputs to be active LOW inputs).

22. A 4-bit circulating register is initially set to 0001(1 is the true output of the first flip flop and represents LSB).
4-bit number preset in the register at the end of 16 clock pulses is
(a) 0001 (b) 0010
(c) 0100 (d) 1000

23. a shift counter comprising of 5 flip flops with an inverse feedback from the output of the MSB flip flop to the input of the LSB flip flop is a
(a) divide by 32 counter (b) divide by 10 counter
(c) 5-bit shift register (d) modulus-5 counter

24. number of comparators needed to build a 6-bit simultaneous A/D converter is
(a) 63 (b) 64
(c) 7 (d) 6

25. the average conversion time in a 4-bit counter type A/D converter run by a 10 MHZ clock shall be
(a) 8ms (b) 400ns
(c) 800ns (d) none of these

26. out of the following,the fastest A/D converter type is
(a) counter type A/D converter
(b) successive approximation type A/D converter
(c) dual slope integrating type A/D converter

27. if the received carrier frequency in an AM communications broadcast receiver is changed from 560kHz to 1120kHz the resonant frequency of the IF tuned circuits
(a) would have to be changed from 455Khz to 910kHz.
(b) would remain unchanged at 455kHz
(c) would also change in the same proportion but in the opposite direction.

28. in a broadcast communication receiver,most of the receiver selectivity is achieved in
(a) RF Section (b) IF Section (c) Mixer

29. antenna reciprocity is put to use in :
(a) television broadcast systems (b) commercial radio broadcast
(c) radar systems (d) none of these

30. an antenna behaves as a resonant circuit only when its length is :
(a) l/2 (b) l/4
(c) l/2 or its integral multiple (d) none of these

31. an antenna should have :
(a) a very high SWR (b) a very small SWR
(c) a moderate value of SWR (d) none of these

32. the input impedance of a centre-fed half-wave dipole is :
(a) 300 W (b) 288 W
(c) 75 W (d) none of these

33. an antenna is radiating 100 watts and is drawing 2A from the transmitter, its radiation resistance is :
(a) 100 W (b) 50 W
(c) 25 W (d) none of these

34.smaller the beamwidth angle :
(a) smaller the directivity (b) higher the directivity
(c) higher the power gain (d) none of these

35. in a broadside array :
(a) maximum reception is in a direction perpendicular axis
(b) maximum reception is along the axis
(c) the directional pattern is undirectional
(d) none of these

36. in an end-fire array:
(a) maximum reception is along the axis
(b) maximum reception is perpendicular to the axis
(c) directional pattern is bi-directional
(d) none of these

37.the simplest parasitic array comprises of :
(a) two elements (b) three elements
(c) five elements (d) none of these

38. a yagi-antenna in horizontal plane :
(a) produces an end-fire pattern (b) produces a broadside pattern
(c) produces a figure eight pattern (d) none of these

39. a television transmitting antenna should have :
(a) an omnidirectional pattern (b) an end-fire pattern
(c) a broadside pattern (d) none of these

40. by increasing the height of the TV receiving antenna :
(a) the range of TV broadcast decreases (b) signal pick up is less
(c) antenna may fail to receive the signal (d) the range of TV broadcast increases
(e) none of these

41. a transmission line is having a reflection coefficient of 1/3 when terminated in a certain load. it is SWR is :
(a) 2 (b) ½
(c) 3 (d) none of these

42. medium wave travel as :
(a) space waves (b) surface waves
(c) sky waves (d) none of these

43. high frequency waves follow :
(a) the ground wave propagation (b) the line of sight direction
(c) the ionosphere propagation (d) the bend along the curvature of earth.

44. VHF waves travel as :
(a) space waves (b) sky waves
(c) ground waves (d) surface waves

45. UHF waves travel as :
(a) space waves (b) surface waves
(c) ground waves (d) sky waves

46. during night- time the ionosphere consists of :
(a) D,E,F1,F2 layers (b) D,E,F1, layers
(c) E,F1,F2 layers (d) E and F2 layers.

47. if the heights of the transmitting and receiving antennas are doubled, the range of TV broadcast:
(a) decrease by a factor of 2 (b) increases by a factor of 2
(c) increases by factor of 1:414 (d) is reduced to one-fourth.

48. in electromagnetic waves, polarisation is :
(a) due to transverse nature of waves (b) always vertical in isotropic medium
(c) due to longitudinal nature of waves (d) caused by reflection of waves

49. the UHF waves are also called as :
(a) millimeter waves (b) centimeter waves
(c) long waves (d) short waves

50. a transmission line has an SWR of 3 when terminated in a certain load. the reflection co-efficient is
(a) 3 (b) ½
(c) 1/3 (d) none of these

51. lines of constant resistance on a smith chart are
(a) parallel to each other (b) all circle tangent to each other on one extreme
(c) arcs of circles (d) none of these

52. electromagnetic wave in which the electric field is entirely transverse to the direction of propogation is known as
(a) TE wave (b) TEM wave
(c) TM wave (d) TE10 wave
(e) TE11 wave

53. one of the following modes does not exist in wave guides
(a) TE10 mode (b) TE11 mode
(c) TEM mode (d) TM01 mode

54. the dominant mode in rectangular waveguides is the
(a) TE10 mode (b) TM01 mode
(c) TE11 mode (d) TM11 mode.

55. for a rectangular wave guide with a=2 cm and b=1 cm, the cut-off wavelength for TE10 mode will be
(a) 2 cm (b) 1 cm
(c) 4 cm (d) none of these.

56. in a radar system, a rotating system is used to
(a) determine the target range (b) determine the target cross-section
(c) determine the target bearing (d) none of these

57. a device that is used to detect objects under water is known as
(a) radar (b) sonar
(c) MTI (d) pulse compression radar

58. a radar system that can determine the range of the target along with the target velocity is
(a) CW radar (b) MTI
(c) pulse radar (d) Doppler radar

59. market the correct expression
(a) Doppler shift = 2vrf/c (b) Doppler shift = 2cf/v4
(c) Doppler shift = 2f/cv4 (d) Doppler shift = vrf/c

60. in a TV picture tube, the deflection of electron beam is achieved by :
(a) electrostatic means
(b) electromagnetic means
(c) electrostatic means for horizontal deflection and electromagnetic means for vertical deflection
(d) electromagnetic means for horizontal deflection and electrostatic means for vertical deflection

61. identify secondary colours
(a) red,green,blue (b) red,cyan,yellow
(c) cyan,yellow,magneta (d) magneta,cyan,green

62. luminance signal is expressed by
(a) Y = R+G+B (b) Y=0.3 R +0.59G+0.11B
(c) Y = 0.5 R + 0.5 G + 0.5 B (d) Y=0.59R + 0.3 G +0.11B

63. one of the following camera tubes is based on photo emissive principle
(a) vidicon (b) saticon
(c) image orthicon (d) newvicon

64. pick the odd one out
(a) vidicon camera (b) plumbicon camera
(c) CCD camera (d) saticon camera

65. transient response of a control system is the one
(a) which approaches zero when the time approaches infinity
(b) which does not depend up on time
(c) which is time dependent
(d) none of these

66. a causal system is the one in which the output depends up on
(a) input as well as output
(b) present and past inputs
(c) present as well as future inputs
(d) present and past inputs and past outputs

67. area under a unit impulse function is
(a) infinity (b) zero (c) unity (d) none of these

68. stability of a control system can be determined from one of the following responses.
(a) impulse response (b) step response
(c) ramp response (d) steady state response

69. a feed back control system has a transfer function given by

P (s) = (s+1)(s+3)/s(s+2)(s+4)
it’s a
(a) type-5 system (b) type -2 system (c) type-3 system (d) type-4 system

70. gain margin can be determined from the root locus plot by
(a) value of gain factor (K) at imaginary crossover/design value of (k)
(b) design value of gain factor (k) / value of gain factor (k) at imaginary crossover
(c) value of gain factor (K) at real axis crossover/design value of (k)
(d) none of these

71. a higher value of gain factor (K) at the imaginary axis crossover of the root locus part of a control system
(a) brings it closer to instability (b) takes it farther from instability
(c) is always undesirable (d) none of these

72. for drawing the root locus plot of a certain closed loop control system, one needs to know
(a) only the open loop transfer function of the system
(b) the closed loop transfer function
(c) the closed loop system pole-zero map
(d) the open loop transfer function, gain and phase margins

73. when the PLL is being used as a frequency multiplier or a frequency divider, the output is taken from
(a) the VCO input (b) the output of phase comparator
(c) the VCO output (d) LPF output

74. the essential building blocks of a phase locked loop are
(a) the VCO , the phase comparator and the error amplifer
(b) the VCO, the phase comparator and the low pass filter
(c)the VCO, the low pass filter and the error amplifer
(d) the phase comparator,the low pass filter and the error amplifier
(e) the phase comparator and the VCO

75. while connecting SCRs in series, the individual SCRs chosen for the purpose should have closely matched
(a) di/dt rating (b) reverse biased characteristics
(c) forward and reverse blocking characteristics (d) forward ON-state characteristics

76. while connecting SCRs in parallel, the SCRs to be connected in parallel should have closely matched
(a) forward ON- state characteristics
(b) forward and reverse OFF- state characteristics
(c) forward OFF-state and ON-state characteristics
(d) SCRs cannot be connected in parallel

77. a UJT relaxation oscillator circuit produces a sawtooth like waveform
(a) at B1 terminal (b) at B2 terminal
(c) across the capacitor (d) none of these

78. in half wave SCR power control circuit, if the firing angle is 300 c, then for one complete cycle of operation,the load gets power for
(a) 600 (b) 1500 (c) 3300 (d) 300

79. most popular oscillator configuration for audio applications is :
(a) Hartley oscillator (b) colpitt’s oscillator
(c) wein-bridge oscillator (d) R-C phase shift oscillator.

80. the multivibrator characterized by one quasi-stable state is:
(a) bistable multivibrator (b) monostable multi vibrator
(c) astable multivibrator (d) Schmitt trigger

81. one of the following can be used to generate a pulse when ever triggered:
(a) flip-flop (b) monostable multivibrator
(c) astable multivibrator (d) Schmitt trigger

82. one of the following opamp type number is a comparator
(a) LM710 (b) LM 741
(c) LM748 (d) LM747

83. the operation of a thermocouple is based on :
(a) seebeck effect (b) peltier effect
(c) Thomson effect (d) faraday’s laws

84. a high Q-factor coil has:
(a) a flat response (b) a response with slightly lower bandwidth
(c) a higher power loss (d) a peaked response

85.lower the thermal resistances (junction-to-case-to-ambient) of a bipolar transistor,
(a) lower is the power dissipation capability for a given ambient temperature
(b) higher is the power dissipation capability for a given ambient temperature
(c) higher is the probability of the device going to thermal runaway
(d) better is its high frequency performance

86. pulse communication system that is inherently highly immune to noise is
(a) PCM (b) PAM (c) PPM (d) PAM

87. the characteristic impedance of a certain transmission line section is 75 ohms. if the length of the line is doubled, the characteristic impedance would
(a) reduce to half (b) double too
(c) increase four times (d) characteristic impedance is independent of length of line.

88. one of the following is a tracking radar
(a) monostatic radar (b) bistatic radar
(c) monopulse radar (d) secondary surveillance radar

89. the radar that has a higher range resolution and that makes use of matched filter design is
(a) pulse compression radar (b) MTI
(c) pulse Doppler radar (d) monopulse radar

90. in the radar guidance of missiles where the missile has its own radar and it extracts the tracking data from the target reflected energy, the technique is known as
(a) command guidance (b) beam rider guidance
(c)homming guidance (d) none of these