mcqs in Telecommunication
Q1. Mark Cross against the correct answer:
1. Type of modulation used in visual section of a transmitter. 1. Positive A.M. 2. Negative A.M. 3. F.M. 4. None of the above.
2. The Difference between video I.F. & audio I. F in TV transmitter is 1. 4.43 MHz 2. 3.50 MHz 3. 5.50 MHz 4. None of the above.
3.Duration of vertical blanking is 1. 4.7
second
2. 0.2 milli second 3. 1.6 milli second 4. None of the above.
4. Duration of horizontal sync pulse is 1. 64 second 2. 1.6 milli second 3. 4.7
second
4. None of the above.
5. I.F. at output of TV Receiver tuner for video is 1. 38.9 MHz 2. 33.4 MHz
3. 40.5 MHz 4. None of the above.
6. slotted antenna is used for 1. VHF 2. UHF 3. Both VHF & UHF 4. None of the above.
7. The PDA used for TVRO is used for 1. Receiving signals 2. Transmitting signals 3. Both as (a) & (b) simultaneously 4. None of the above.
8. Three Primary Colours in TV Transmission are 1. Red, Green, Blue. 2. Red, Yellow, Blue 3. Red, Cyan, Magenta 4. None of the above.
9. Colour Temperature of average day light is 1. 3200 K 2. 5600 K 3. 6500 K 4. None of the above.
10. Eye is more sensitive to 1. Red 2. Green 3. Blue
4. Violet
Q2. Fill in the blanks:
1. To receive satellite signal feed is kept at ________________ of PDA. 2. Parking slot of Satellite PAS-4 is ______________________. 3. The valve used in ATRPA stage of Mark-II TV Transmitter is ______. 4. Cooling system used in High Power TV Transmitter (Mark-III) is____________________. 5. Number of picture frames per second in CCIR PAL-B system is _____________. 6. The frequency of colour sub-carrier in CCIR PAL-B system is _____________. 7. TRACT stands for _______________________________________. 8. The binary equivalent of decimal number 13 is _________________. 9. One ton of refrigeration equals ________________ kcal/hr. 10. Two stroke engine is _________efficient as compared to four stroke engine. 11. FET is a ________________________ device. 12. The maximum value of power factor in a. c. circuit is_____________________. 13. Peak
to peak value of an a.c. voltage can be measured with the help of
____________________. 14. High VSWR at TV transmitter will cause ____________________ in picture. 15. Series LC circuit tuned at second harmonic will have ______________ reactance at
fundamental. Answers
Telecommunication
Q1 1 (b) 2 (c) 3 (c) 4 ( c ) 5 (a)
6 (b) 7 (a) 8 (a) 9 (c) 10 (b).
Q2 1. Focal point 2. 68.5 o E 3. 5 F 64 R
4. Forced air 5. 25 6. 4.43 MHz
1. Transportable Remote Area communication terminal
8. 1101 9. 3000 kcal/hr 10. Less efficient
11. Unipolar 12. Unity
13. Cathode ray oscilloscope
14. Ghost 15. Capacitive.
Wave propagation 1. A 'skip zone' is: 1. the distance between the antenna and where the refracted wave first returns to earth 2. the distance between the far end of the ground wave and where the refracted wave first returns to earth 3. the distance between any two refracted waves 4. a zone caused by lost sky waves 2. The medium which reflects high frequency radio waves back to the earth's surface is called the: 1. biosphere 2. stratosphere 3. ionosphere 4. troposphere 3. The highest frequency that will be reflected back to the earth at any given time is known as the: 1. UHF 2. MUF 3. OWF 4. LUF 4. All communications frequencies throughout the spectrum are affected in varying degrees by the: 1. atmospheric conditions 2. ionosphere 3. aurora borealis
4. sun 5. Solar cycles have an average length of: 1. 1 year 2. 3 years 3. 6 years 4. 11 years 6. The 'skywave' is another name for the: 1. ionospheric wave 2. tropospheric wave 3. ground wave 4. inverted wave 7. The polarisation of an electromagnetic wave is defined by the direction of: 1. the H field 2. propagation 3. the E field 4. the receiving antenna 8. That portion of HF radiation which is directly affected by the surface of the earth is called: 1. ionospheric wave 2. local field wave 3. ground wave 4. inverted wave 9. Radio wave energy on frequencies below 4 MHz during daylight hours is almost completely absorbed by this ionospheric layer: 1. C 2. D 3. E 4. F 10. Because of high absorption levels at frequencies below 4 MHz during daylight hours, only high angle signals are normally reflected back by this layer:
1. C 2. D 3. E 4. F 11. Scattered patches of high ionisation developed seasonally at the height of one of the layers is called: 1. sporadic-E 2. patchy 3. random reflectors 4. trans-equatorial ionisation 12. For long distance propagation, the radiation angle of energy from the antenna should be: 1. less than 30 degrees 2. more than 30 degrees but less than forty-five 3. more than 45 degrees but less than ninety 4. 90 degrees 13. The path radio waves normally follow from a transmitting antenna to a receiving antenna at VHF and higher frequencies is a: 1. circular path going north or south from the transmitter 2. great circle path 3. straight line 4. bent path via the ionosphere 14. A radio wave may follow two or more different paths during propagation and produce slowlychanging phase differences between signals at the receiver resulting in a phenomenon called: 1. absorption 2. baffling 3. fading 4. skip 15. The distance from the far end of the ground wave to the nearest point where the sky wave returns to the earth is called the: 1. skip distance
2. radiation distance 3. skip angle 4. skip zone 16. High Frequency long-distance propagation is most dependent on: 1. ionospheric reflection 2. tropospheric reflection 3. ground reflection 4. inverted reflection 17. The layer of the ionosphere mainly responsible for long distance communication is: 1. C 2. D 3. E 4. F 18. The ionisation level of the ionosphere reaches its minimum: 1. just after sunset 2. just before sunrise 3. at noon 4. at midnight 19. One of the ionospheric layers splits into two parts during the day called: 1. A & B 2. D1 & D2 3. E1 & E2 4. F1 & F2 20. Signal fadeouts resulting from an 'ionospheric storm' or 'sudden ionospheric disturbance' are usually attributed to: 1. heating of the ionised layers 2. over-use of the signal path 3. insufficient transmitted power 4. solar flare activity 21. The 80 metre band is useful for working:
1. in the summer at midday during high sunspot activity 2. long distance during daylight hours when absorption is not significant 3. all points on the earth's surface 4. up to several thousand kilometres in darkness but atmospheric and man-made noises tend to be high 22. The skip distance of radio signals is determined by the: 1. type of transmitting antenna used 2. power fed to the final amplifier of the transmitter 3. only the angle of radiation from the antenna 4. both the height of the ionosphere and the angle of radiation from the antenna 23. Three recognised layers of the ionosphere that affect radio propagation are: 1. A, E, F 2. B, D, E 3. C, E, F 4. D, E, F 24. Propagation on 80 metres during the summer daylight hours is limited to relatively short distances because of 1. high absorption in the D layer 2. the disappearance of the E layer 3. poor refraction by the F layer 4. pollution in the T layer 25. The distance from the transmitter to the nearest point where the sky wave returns to the earth is called the: 1. angle of radiation 2. maximum usable frequency 3. skip distance 4. skip zone 26. A variation in received signal strength caused by slowly changing differences in path lengths is called: 1. absorption
2. fading 3. fluctuation 4. path loss 27. VHF and UHF bands are frequently used for satellite communication because: 1. waves at these frequencies travel to and from the satellite relatively unaffected by the ionosphere 2. the Doppler frequency change caused by satellite motion is much less than at HF 3. satellites move too fast for HF waves to follow 4. the Doppler effect would cause HF waves to be shifted into the VHF and UHF bands. 28. The 'critical frequency' is defined as the: 1. highest frequency to which your transmitter can be tuned 2. lowest frequency which is reflected back to earth at vertical incidence 3. minimum usable frequency 4. highest frequency which will be reflected back to earth at vertical incidence 29. The speed of a radio wave: 1. varies indirectly to the frequency 2. is the same as the speed of light 3. is infinite in space 4. is always less than half the speed of light 30. The MUF for a given radio path is the: 1. mean of the maximum and minimum usable frequencies 2. maximum usable frequency 3. minimum usable frequency 4. mandatory usable frequency 31. The position of the E layer in the ionosphere is: 1. above the F layer 2. below the F layer 3. below the D layer 4. sporadic
32. A distant amplitude-modulated station is heard quite loudly but the modulation is at times severely distorted. A similar local station is not affected. The probable cause of this is: 1. transmitter malfunction 2. selective fading 3. a sudden ionospheric disturbance 4. front end overload 33. Skip distance is a term associated with signals through the ionosphere. Skip effects are due to: 1. reflection and refraction from the ionosphere 2. selective fading of local signals 3. high gain antennas being used 4. local cloud cover 34. The type of atmospheric layers which will best return signals to earth are: 1. oxidised layers 2. heavy cloud layers 3. ionised layers 4. sun spot layers 35. The ionosphere: 1. is a magnetised belt around the earth 2. consists of magnetised particles around the earth 3. is formed from layers of ionised gases around the earth 4. is a spherical belt of solar radiation around the earth 36. The skip distance of a sky wave will be greatest when the: 1. ionosphere is most densely ionised 2. signal given out is strongest 3. angle of radiation is smallest 4. polarisation is vertical 37. If the height of the reflecting layer of the ionosphere increases, the skip distance of a high frequency transmission: 1. stays the same
2. decreases 3. varies regularly 4. becomes greater 38. If the frequency of a transmitted signal is so high that we no longer receive a reflection from the ionosphere, the signal frequency is above the: 1. speed of light 2. sun spot frequency 3. skip distance 4. maximum usable frequency 39. A 'line of sight' transmission between two stations uses mainly the: 1. ionosphere 2. troposphere 3. sky wave 4. ground wave 40. The distance travelled by ground waves in air: 1. is the same for all frequencies 2. is less at higher frequencies 3. is more at higher frequencies 4. depends on the maximum usable frequency 41. The radio wave from the transmitter to the ionosphere and back to earth is correctly known as the: 1. sky wave 2. skip wave 3. surface wave 4. F layer 42. Reception of high frequency radio waves beyond 4000 km normally occurs by the: 1. ground wave 2. skip wave 3. surface wave 4. sky wave
43. A 28 MHz radio signal is more likely to be heard over great distances: 1. if the transmitter power is reduced 2. during daylight hours 3. only during the night 4. at full moon 44. The number of high frequency bands open to long distance communication at any time depends on: 1. the highest frequency at which ionospheric reflection can occur 2. the number of frequencies the receiver can tune 3. the power being radiated by the transmitting station 4. the height of the transmitting antenna 45. Regular changes in the ionosphere occur approximately every 11: 1. days 2. months 3. years 4. centuries 46. When a HF transmitted radio signal reaches a receiver, small changes in the ionosphere can cause: 1. consistently stronger signals 2. a change in the ground wave signal 3. variations in signal strength 4. consistently weaker signals 47. The usual effect of ionospheric storms is to: 1. increase the maximum usable frequency 2. cause a fade-out of sky-wave signals 3. produce extreme weather changes 4. prevent communications by ground wave 48. Changes in received signal strength when sky wave propagation is used are called: 1. ground wave losses
2. modulation losses 3. fading 4. sunspots 49. Although high frequency signals may be received from a distant station by a sky wave at a certain time, it may not be possible to hear them an hour later. This may be due to: 1. changes in the ionosphere 2. shading of the earth by clouds 3. changes in atmospheric temperature 4. absorption of the ground wave signal 50. VHF or UHF signals transmitted towards a tall building are often received at a more distant point in another direction because: 1. these waves are easily bent by the ionosphere 2. these waves are easily reflected by objects in their path 3. you can never tell in which direction a wave is travelling 4. tall buildings have elevators Answer 1
2
3
4
5
6
7
8
9
10
b
c
b
d
d
a
c
c
b
c
11
12
13
14
15
16
17
18
19
20
a
a
c
c
d
a
d
b
d
d
21
22
23
24
25
26
27
28
29
30
d
d
d
a
c
b
a
d
b
b
31
32
33
34
35
36
37
38
39
40
b
b
a
c
c
c
d
d
d
b
41
42
43
44
45
46
47
48
49
50
a
d
b
a
c
c
b
c
a
b
Electronics and Communication Engineering Test Paper
Choose the correct answer
1. Output power of 10 kW FM transmitter modulated with 1 Khz sinusoidal tone with deviation of + 75 kHz shall be
10 kW
15 kW
7.5 kW
2. Adaptive pre-emphasis in FM limiter is
Independent of frequency.
Dependent on frequency.
Independent of level.
Dependent on level.
3. The feeder used to connect the FM Transmitter to the antenna is
Co-axial cable.
2-wire shielded cable.
Twin flat cable.
None of the above.
4. The maximum permissible frequency shift in mW transmitter is
+ 10 Hz
+ 12 Hz
+ 5 Hz
None of the above.
5. Second harmonic trap in MW Transmitter is connected in
Output of modulator
Output of final power amplifier
Input of final power amplifier
Output of A.T.U.
6. The power supply is required for one of the following microphone
Dynamic
Cardioid
Ribon
Condenser
7. The polar diagram of a cardiod microphone is
Omni-directional
Bi-directional
Heart-shaped
None of the above.
8. Pre-emphasis employed in FM transmitter in AIR is
50 m Sec.
75 m Sec.
100 m Sec.
None of the above.
9.-70 dBu output of microphone equals
245.08 mV
0.0775 mV
0.775 mV
None of the above.
10. The voltage level for 0 dBm in 50 ohms equals
0.224 Volt
0.775 Volt
7.75 Volt
None of the above.
Answers
1 (a) 2 (b) 3 (a) 4 (a) 5 (b) 6 (d) 7 (c) 8 (a) 9 (a) 10 (a).
Electronics and Communication Engineering Test Paper
Choose the correct answer
1. The output power of an audio power amplifier is 12 W, which is approximately
a) 20 dBm b) 41 dBm c) 62 dBm d) 86 dBm
2. The bandwidth of a wide-band amplifier to reproduce a pulse faithfully depends on
a) Width of the pulse b) Rise time of the pulse c) Frequency of the pulse d) All of these
3. When the peak power is 10 kW and average power is 800 W, then duty cycle is
a) 0.008% b) 0.08% c) 0.8% d) 8%
4. The primary purpose of helix in a travelling wave tube is to
a) Reduce the axial velocity of RF field
b) Ensure broadband operation
c) Reduce the noise figure
d) Prevent the electron beam from spreading in the long tube
5. A parabolic antenna is commonly used at
a) 38 kHz b) 19 kHz c) 455 kHz d) None of these
6. If the input signal to noise ratio of a system is 30, and the output signal to noise ratio is 3, then the noise figure F of the system is
a) 90 b) 10 c) 900 d) 33
7. The unit of loudness is: a) phon d) sone c) decibel d) mel
8. Soundproof door in studios generally provides attenuation of the order of: a) 60 dB b) 50 dB c) 30 dB d) 15 dB
9. An FM signal with a deviation d is passed through a mixer and has its frequency reduced five fold. The deviation in the output of mixer will be: a) 5d b) d c) d/5 d) indeterminate
10. Top loading is used with an antenna in order to increase its a) effective height b) bandwidth c) Beamwidth d) input capacitance
11. What is the aspect ratio of HDTV application?
a) 4:3 b) 3:4 c) 9:16 d) 16:9
12. Why are radiators stacked vertically on a TV tower?
a) for wideband matching b) To obtain desired gain c) For omni-directional pattern d) None of these
13. What is the minimum field strength required for UHF TV transmission?
a) 110 dBmV/m b) 65 dBmV/m c) 55 dBmV/m d) 45 dBmV/m
14.What is the tape speed in Beta-cam VTR?
a) 90 mm/sec b) 101.5 mm/sec c)65 mm/sec d)110 mm/sec
15. What is the duration of active period of a line in CVS (Composite Video Signal)?
a) 62 msec b) 27 msec c) 108 msec d) 52 msec
16. In a 3-wire circuit, the loads on the Y and B phases draw 1 A each from the line and the R phase is open circulated. What is the current flowing through the neutral conductor?
a) 0 A b) 1 A c) 2 A d) 3 A
17. A PERT chart helps in:
Identifying the critical activities of a Project.
Knowing the earliest possible completion date of each activity.
Knowing the lag permissible for each activity
All the above.
18.The interior of an air-conditioning duct is lined with:
a) Mineral wool b) Common straw c) Cotton d) Thin concrete slabs.
19. The horse power of a Diesel Engine is decided by:
a) the bore b) no. of cylinders c) the rpm d) all of these
Answers: 2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
b
d
b
d
b
c
c
b
a
d
b
c
b
d
b
d
a
d
1 b
Electronics and Communication Engineering Test Paper
Choose the correct answer
1. Medium wave broadcast band is from
a) 530 kHz to 1600 kHz b) 3 MHz to 10 MHz c) 10 MHz to 30 MHz
2.Spark gap at the mast base is for the purpose of impedance matching
(True/False)
3. Multiple pads are made up of
a) Resistances b) Resistances & capacitors c) Capacitors and Inductance
4. We take frequency response of studio chain by using
a) Audio frequency generator b) Multi- frequency test record c) Standard test tape
5. The three grids G1, G2, G3 in a pentode value are respectively called.
a) Suppressor, Screen, Control b) Screen, Control, Suppressor c) Control, Screen, suppressor
6. The main advantage of crystal oscillator is :
a) Its frequency is stable b) It is easily tunable c) It gives greater output.
7.In a MW transmitter, the modulator stage is
a) Audio frequency amplifier b) Radio frequency amplifier c) A combined audio and Radio frequency amplifier
8. A receiver which is able to receive weak signal is called
a) Sensitive b) Selective c) High quality
9. Efficiency of class A amplifier is about
a) 30% b) 50% c) 70% d) 90%
10. In class C amplifier, the valve conducts for
a) 360o b) 180o c) 120o
11. When P1 is input power and P2 is output power, the gain of an amplifier expressed in dB is
12. The signal to noise ratio of an amplifier should be
a) 70 db b) -70 dB c) 30 dB d) -30 dB
13. Equalisers are used to provide attenuation to the signal (True/False)
14. Which antenna is most commonly used with TV receiver.
a) Folded dipole b) Inverted 'L' c) Rhombic
15. In Indian TV system, the total RF channel width in VHF band
a) 6 MHz b) 7 MHz c) 8 MHz
16. In the tape recorder which magnetic head has the widest air gap
a) Erase head b) Record head c) Replay Head
17. The three primary colour beams in TV picture tube are
a) Red, Green, Blue b) Yellow, Magneta, Green c) Cyan, Pink, Blue
18. Ribbon microphone is
a) Uni-directional b) Bi-directional c) Omni-directional
19. For the level measurement in dBm, the reference level choosen is
a) 1 Watt b) 1 micro watt c) 1 milliwatt
20. a) AND gate b) OR gate c) NOR gate
21. When all the inputs of AND gate are '1', the output of AND gate will be
a) 1 b) 0
22. The class of amplifier which provide maximum efficiency is
a) A b) B c) C
23. In a circuit, diode is used for
a) Matching b) Rectification c) Amplification
24. VU meter is used for indicating
a) Level of programme b) Distortion of programme c) Quality of programme
25. Double dipole aerial is used for
a) Medium wave b) Shortwave c) FM wave
26. 0 dBm is same as
a) 10 milliwatt b) 1 milliwatt
c) 1 watt d) 10 watt
27. Electrical signal is converted into sound by
a) Loudspeaker b) Microphone c) Monitoring amplifier
28. Dirty record and replay heads cause
a) Wow and Flutter b) LF loss c) HF l oss
29. Austin transformer is used at
a) Switch gear room b) HT room c) Mast base
30. For transmitting the signal to satellite, the frequency is in the range of
a) 30 MHz to 60 MHz b) 100 MHz to 200 MHz c) 4 GHz to 6 GHz
31. Dish antenna is used to receive signals from
a) ground waves b) Satellite c) Ionosphere
32. In a TV studio chain, video signal passes through
a) Camera amplifier, Video Switcher and White limiter b) Video switcher, White limiter and Camera amplifier
c) Camera amplifier, White limiter and Video switcher
33. Immediately after microphone ___________ is connected.
a) Programme amplifier b) Pre amplifier c) Cue amplifier
34. Time delay relay is used at the transmitter to give sufficient time before the bias i s put ON.
a) To heat the crystal oven b) To heat the filament c) To close the doors
35. AVR is used to
a) Heat the crystal oven b) Supply a low voltage c) Supply a constant voltage
36. Value of capacitance between A & B is
37. Write the name against each of the following symbols
38. Write the full form of the following
a) SMPS b) LNBC c) dB d) PDA e) mH
39. Self radiating towers are used in TV transmitter stations (True/False)
40. Positive feed back in amplifier will result in oscillation (True/False)
41. The word "micro" prefixed before a scientific unit makes it to change to
a) One millionth b) One thousandth c) Million times
42. Oscillator crystals are made up of
a) Silicon b) Germanium c) Quartz
43. In frequency modulation
Amplitude of carrier remains constant
Frequency of the carrier remains constant
Both frequency & amplitude of the carrier remain constant
44. Heat sinks are provided to power transistor to dissipate heat. (True/False)
45. The expected value of earth pit resistance should be about
a) 0.5 ohm b) 10 ohm c) 30 ohm d) 50 ohm
46. For a good transistor, the emitter to collector resistance should be about
a) 0 ohm b) 250 ohm c) 25000 ohm
47. For a NPN transistor, the collector supply should be
a) Positive b) Negative c) Grounded
48. For a feeder of 230 ohm impedance, the number of wires used in the feeder of 10 kW medium wave transmitter is normally,
a) 4 wires b) 6 wires c) 2 wires d) 16 wires
49. Transformer oil is used in
a) Filament transformer b) Austin transformer c) HT transformer d) All the above
50. For joining the feeder wire with another feeder wire you will use
a) Line tap b) Soldering c) Threading
