1. 24 telephone channels, each band limited to 3.
4 kHz are to be time division multiplexed using
PCM. If sampling frequency is 10 kHz and number of quantization levels is 128, the required
bandwidth of PCM is
A. 1.68 MHz
B. 240 kHz
C. 81.6 kHz
D. 3.072 MHz
Answer: Option A
Explanation:
Bandwidth 24 (ln2 128) 10 kHz = 1.68 MHz.
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2. Resonant circuits are used in
A. audio amplifiers
B. RF amplifiers
C. both audio and RF amplifiers
D. none of the above
Answer: Option B
Explanation:
RF amplifiers use resonant loads (L and C in parallel).
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3. The bandwidth of DSB suppressed carrier modulation system when the modulating frequency
varies between 500 Hz and 5 kHz is
A. 555 kHz
B. 505 kHz
C. 500 kHz
D. 9 kHz
Answer: Option D
Explanation:
fm = 5 kHz - 500 Hz 4.5 kHz
Bandwidth = 2 fm 2 x 4.5 kHz = 9 kHz.
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4. Linear diode detector utilizes
A. linear portion of static characteristics of diode
B. linear portion of dynamic characteristic of diode
C. square law portion of dynamic characteristics of diode
D. rectification property of diode
Answer: Option D
Explanation:
Detection (also called demodulation) is due to rectification property of diode.
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5. In the equivalent circuit of a moving coil cone type loudspeaker, the mass of the moving system
is represented by
A. a resistance
B. a capacitance
C. an inductance
D. a conductance
Answer: Option C
Explanation:
Mass has inertia and is analogous to inductance.
6. Assertion (A): In India we use CCIR-B standard
Reason (R): Video signals are frequency modulated.
A. Both A and R are correct and R is correct explanation of A
B. Both A and R are correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
Answer: Option C
Explanation:
Video signals are amplitude modulated.
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7. CATV stands for
A. Common Antenna Television
B. Community Antenna Television
C. Cable Antenna Television
D. Channel Antenna Television
Answer: Option B
Explanation:
In USA the first cable service was called community antenna television.
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8. Household tape recorders use
A. separate motor for each operation
B. only one motor for all operations
C. one motor for capstan and another for take up reel
D. a total of 3 motors
Answer: Option B
Explanation:
For reasons of economy only one motor is used.
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9. A 400 W carrier is modulated to a depth of 75 percent. The total power in modulated wave will
be
A. 38.5 W
B. 400 W
C. 512.5 W
D. 615.5 W
Answer: Option C
Explanation:
Sideband frequencies will be fc fm.
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10. A geostationary satellite
A. is located at a height of 358, 00 km
B. appears stationary over earth's magnetic pole
C. is motionless in space but keeps spinning
D. orbits the earth within a 24 hour period
Answer: Option D
Explanation:
It orbits the earth in a 24 hour period. Thus it appears to be stationed over one spot of the globe.
11. A line has L = 0.8 H/m and C = 32 pF/m. Z0 =
A. 6000
B. 600
C. 158
D. 15.8
Answer: Option C
Explanation:
.
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12. A line has standing waves with a voltage maximum of 35 mV and minimum of 17.5 mV VSWR is
A. 2
B. 4
C. 0.5
D. 0.25
Answer: Option A
Explanation:
.
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13. For a bit rate of 8 kbps, the best possible values of the transmitted frequencies in a coherent
binary FSK system are
A. 16 kHz and 20 kHz
B. 20 kHz and 32 kHz
C. 20 kHz and 40 kHz
D. 32 kHz and 40 kHz
Answer: Option D
Explanation:
where i is integer, and nc is fixed integer.
fi = Rb(nc + i) (3 + 1) x 8 32 kHz
(4 + 1)0.8 40 kHz.
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14. If luminance signal Y = 0.3 R + 0.59 G + 0.11 B, the hue of R - Y colour is
A. 0.7 R - 0.59 G - 0.11 B
B. - 0.7 R + 0.59 G + 0.11 B
C. 1.3 R - 0.59 G - 0.11 B
D. none of the above
Answer: Option A
Explanation:
R - Y = R - 0.3R - 0.59C - 0.11B = 0.7R - 0.59G - 0.11B.
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15. Trap circuits used in video IF amplifier of colour TV are
A. High Q, LC resonant circuit
B. Low Q, LC resonant circuit
C. High Q, RLC resonant circuit
D. Low Q, RLC resonant circuit
Answer: Option A
Explanation:
High Q LC resonant circuit provides high selectivity.
16. A 1000 kHz carrier is simultaneously modulated with 300 Hz, 800 Hz and 2 kHz audio sine
waves. Which of the following frequency is least likely to be present in the output?
A. 1002 kHz
B. 1000 kHz
C. 999.2 kHz
D. 998.0 kHz
Answer: Option B
Explanation:
Frequency present in the sidebands is equal to = fc fm, fc 2fm, fc 3fm .
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17. A 300 Hz sound wave of intensity 20 dB is transmitted by a 1500 kHz radio wave by frequency
modulation. It is seen that instantaneous frequency varies between 1500.2 kHz and 1499.8 kHz,
300 times a second. If the intensity of sound wave is 100 dB.
The instantaneous frequency variations will be between 1500.2 and 1499.8 kHz, 1500
A.
times a second
The instantaneous frequency variations will be between 1501 and 1499 kHz, 1500 times
B.
a second
The instantaneous frequency variations will be between 1501 and 1499 kHz, 300 times a
C.
second
The instantaneous frequency variations will be between 1501 and 1499 kHz, 60 times a
D.
second
Answer: Option C
Explanation:
Since, the intensity of audio wave has been increased five times, the instantaneous frequency
variation is also increased five times.
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18. If the average power of radar transmitters is 2 kW and the peak power of the transmitter is 1000
kW, what will be the duty cycle?
A. 0.002
B. 0.02
C. 0.001
D. 0.01
Answer: Option A
Explanation:
.
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19. An analog signal is band limited to B Hz sampled at Nyquist rate and samples are quantized into
4 levels each with probability . The information rate is
A. 4 bits/s
B. B bits/s
C. 4 B bits/s
D. 0.25 B bits/s
Answer: Option C
Explanation:
.
Signal should be sampled at frequency 2B Hz.
Hence, information rate = 2 (2B) = 4B bits/s.
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20. The HV supply to a TV receiver is 25 kV and the total beam current for the three electron guns is
2000 A. The power handled by IHVT is
A. 5W
B. 0.5 W
C. 50 W
D. 500 W
Answer: Option C
Explanation:
25 x 103 x 2000 x 10-6 = 50 W.
21. Some advantages of optical fibre cables are
1. small diameter
2. Immunity to cross talk and EM interference
3. Laser and LED modulation methods lend themselves ideally to digital operation
Which of the above are correct?
A. 1 only
B. 1 and 2
C. 1, 2, 3
D. 2, 3
Answer: Option C
Explanation:
Fibre optic cables have all these advantages.
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22. The contrast control in colour TV receiver is done by
A. chroma amplifier
B. SAW filter
C. video detector
D. luminance amplifier
Answer: Option D
Explanation:
Luminance amplifier changes the luminance levels and provides contrast control.
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23. The requirements of carrier frequency are
A. precise frequency value
B. low frequency drift
C. both (a) and (b)
D. neither (a) nor (b)
Answer: Option C
Explanation:
Both should have a precise value and low drift.
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24. If N bits are lumped together to get an N-bit symbol, the possible number of symbols is
A. 2N
B. 2N - 1
C. 2N - 2
D. 2N - 4
Answer: Option A
Explanation:
Each bit can have two levels. Hence 2N.
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25. The received signal frequency at any time of a super-heterodyne receiver having IF = 456 kHz is
1 MHz. The corresponding image signal is
A. within the medium band
B. outside the medium band
C. depend upon modulation index
D. depends on Modulating frequency
Answer: Option A
Explanation:
Image signal frequency = Received signal frequency - 2 x Intermediate frequency.
= 1 MHz - 2 x 456kHz
1 MHz - 912 kHz 88 kHz
which lies in medium bond.
26. For an ideal 3000 Hz channel, Nyquist rate is
A. 3000 bps
B. 6000 bps
C. 9000 bps
D. 12000 bps
Answer: Option B
Explanation:
For 3000 Hz.
Nyquist rate is twice, i.e., 6000 bps.
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27. Assertion (A): Electromagnetic waves in free space spread uniformly in all directions from a
point source
Reason (R): Free space has no interference or obstacles.
A. Both A and R are correct and R is correct explanation of A
B. Both A and R are correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
Answer: Option A
Explanation:
Since free space has no interference or obstacles, EM waves spread uniformly.
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28. In the FM wave described by equation v = 15 sin (4 x 108 t + 3 sin 1100 t), the maximum
frequency deviation is
A. 175 Hz
B. 525 Hz
C. 3 Hz
D. 58.33 Hz
Answer: Option B
Explanation:
.
Maximum frequency deviation = 3 x 175 = 525 Hz.
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29. The radar cross-section of a target depends an
A. frequency
B. polarization of incident wave
C. aspect of target
D. all of the above
Answer: Option D
Explanation:
Effective area of target is called radar cross-section.
It depends on frequency polarization of incident wave and aspect of target.
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30. The Nyquist sampling interval, for the signal sin c (700t) + sin c (5000 t) is
A.
B.
C.
D.
Answer: Option C
Explanation:
g(t) = sin c (700 t) + sin c (500 t)
[sin ( 700 t) + sin ( 500 t)]
fm = 350 Hz
fs = 700 Hz, Nyquist rate = .
31. A directional microphone gives an output of 0.5 mV whereas an omnidirectional one gives an
output of 0.5 V in the same position for the same sound pressure. The directivity of the
directional microphone is
A. 120 dB
B. 90 dB
C. 60 dB
D. 30 dB
Answer: Option C
Explanation:
Directivity =
= 60 dB.
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32. If Eb, the energy per bit of a binary digital signal is 10-6 watt sec. and the one sided power
spectral density of the white noise N0 = 10-5 W/Hz, then the output SNR of the matched filter is
A. 26 dB
B. 10 dB
C. 20 dB
D. 13 dB
Answer: Option D
Explanation:
O/P SNR = 10 log10 [2 x 10-6 x 10-5].
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33. Consider the following statements about Rhombic antenna
1. It is non resonant
2. It is a broad band antenna
3. It is ideally suited for HF transmission
Which of the above are correct?
A. 1, 2, 3
B. 1, 3 only
C. 2, 3 only
D. 1 only
Answer: Option A
Explanation:
All the three features are correct.
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34. Assertion (A): A composite video signal has synchronising pulses.
Reason (R): It is necessary to synchronise the scanning process in the transmitter and receiver.
A. Both A and R are correct and R is correct explanation of A
B. Both A and R are correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
Answer: Option A
Explanation:
Synchronisation of scanning process at transmitter and receiver is necessary for proper
reproduction at TV receiver.
For this purpose synchronising pulses are sent as a part of video signal.
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35. Noise with uniform power spectral density of N0/Hz is passed through a filter H() = 2 exp (-J
ty) followed by an ideal low pass filter of bandwidth B Hz. The output noise power in watts is
A. 2 N0B
B. 4 N0B
C. 8 N0B
D. 16 N0B
Answer: Option B
Explanation:
Output spectral power density
= | H() | x I/P spectral power density
= 2 x 2N0 4N0
Output power = 4 N0B.
36. Assertion (A): In standing wave pattern, the nodes and anti nodes are separated by half wave-
length
Reason (R): When line is terminated in resistance RL, the standing wave ratio is SWR = Z0/RL or
RL/Z0
A. Both A and R are correct and R is correct explanation of A
B. Both A and R are correct but R is not correct explanation of A
C. A is correct but R is wrong
D. A is wrong but R is correct
Answer: Option B
Explanation:
.
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37. An amplifier has an input resistance of 10 k and the noise voltage is 10 V. If two such
resistances of 10 k each are connected in series at the input, the total noise voltage is about
A. 20 V
B. 5V
C. 14.14 V
D. 10 V
Answer: Option C
Explanation:
Noise voltage = 10 = 14.14 V.
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38. A 400 W carrier is modulated to a depth of 75 percent. The total power in modulated wave will
be
A. 38.5 W
B. 400 W
C. 512.5 W
D. 615.5 W
Answer: Option C
Explanation:
Pc = 400 W, m = 0.75
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39. In a colour TV receiver the bandwidth of RF amplifier is
A. exactly equal to channel width
B. a little less than channel width
C. a little more than channel width
D. either (a) or (b)
Answer: Option C
Explanation:
It is kept a little more than channel width so that reception is not restricted.
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40. An FM signal with a deviation is passes through the mixer, and has its frequency reduced five
fold. The deviation in the output of the mixer is
A.
B. 5
C. /5
D. indeterminant
Answer: Option A
Explanation:
f (frequency deviation) is independent of fm , f depends only upon amplitude of message
signal.
f = kf.Am .
41. FSK is a system involving
A. pulse modulation
B. frequency modulation
C. amplitude modulation
D. phase modulation
Answer: Option B
Explanation:
FSK, i.e., frequency shift keying is a system of frequency modulation.
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42. A 200 Hz sound wave is to be transmitted by a 1000 kHz radio wave using frequency
modulation. The instantaneous frequency variation will be
A. 100 times a second
B. 200 times a second
C. 400 times a second
D. 1000 times a second
Answer: Option B
Explanation:
The instantaneous frequency variation is equal to frequency of audio signal.
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43. In a TV studios, flying spot scanner is a device for
A. mixing video and audio signals
B. telecasting feature films
C. live telecast of outdoor programs
D. telecast of indoor music programs
Answer: Option B
Explanation:
It is used to telecast feature films. Flying spot scanner uses a special low persistence high
brightness cathode ray tube.
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44. A broadcast radio transmitter radiates 5 kW when the modulation percentage is 60. How much
of this is carrier power?
A. 6.66 kW
B. 5 kW
C. 4.9 kW
D. 4.23 kW
Answer: Option D
Explanation:
m = 1,
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45. A device has two resistances 300 and 200 respectively. The noise voltages due to these
two resistance calculated separately are 5.38 V and 4.38 V respectively. When both of them
are used together, the noise voltage will be
A. 9.76 V
B. 1 V
C. 23.56 V
D. 6.94 V
Answer: Option D
Explanation:
6. The antenna diameter of a radar system is doubled. The maximum range will
A. be doubled
B. become four times
C. be halved
D. decrease to one fourth
Answer: Option A
Explanation:
Range is proportional to antenna diameter.
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47. Which of the following microphones works on the piezoelectric effect?
A. Carbon
B. Condenser
C. Moving coil
D. Crystal
Answer: Option D
Explanation:
As per piezoelectric effect application of pressure across the faces of a crystal produces an emf
across the faces.
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48. In PAL system weighting of R - Y and B - Y signals is done to
A. prevent over modulation on saturated colours
B. prevent under modulation of saturated colours
C. allow over modulation of saturated colours
D. allow under modulation on saturated colours
Answer: Option A
Explanation:
Weighting reduces the chances of over-modulation of the transmitter carrier in the presence of
highly saturated colours when picture has very light or very dark parts.
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49. In case of probability of the message is 1 to 16 then the information will be
A. 16 bits
B. 8 bits
C. 4 bits
D. 2 bits
Answer: Option C
Explanation:
.
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50. The saving of power in DSB-SC modulated at 80% is
A. NIL
B. 80%
C. 75.76%
D. 50%
Answer: Option C
Explanation:
.
