question_answer 1)
Which mode of communication is not employed for the transmission of T.V. signals?
A)
Ground wave propagation done
clear
B)
sky wave propagation done
clear
C)
space wave propagation done
clear
D)
None of these done
clear
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question_answer 2)
Audio signal cannot be transmitted because
A)
the signal has more noise f Thinking done
clear
B)
the signal cannot be amplified for distance communication done
clear
C)
the transmitting antenna length is very small to design done
clear
D)
the transmitting antenna length is very large and impracticable done
clear
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question_answer 3)
An antenna is a device
A)
that converts electromagnetic energy into radio frequency signal done
clear
B)
that converts radio frequency signal into electromagnetic energy done
clear
C)
that converts guided electromagnetic waves into free space electromagnetic waves and vice-versa done
clear
D)
None of these done
clear
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question_answer 4)
Modulation is the process of superposing
A)
low frequency audio signal on high frequency waves done
clear
B)
low frequency radio signal on low frequency audio waves done
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C)
high frequency audio signal on low frequency radio waves done
clear
D)
low frequency audio signal on low frequency radio waves done
clear
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question_answer 5)
The maximum peak to peak voltage of an AM wire is \[24\text{ }mV\] and the minimum peak to peak voltage is \[8\text{ }mV\]. The modulation factor in percentage is
A)
\[10%\] done
clear
B)
\[20%\] done
clear
C)
\[25%\] done
clear
D)
\[50%\] done
clear
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question_answer 6)
A laser beam is used for carrying out surgery because it
A)
is highly monochromatic done
clear
B)
is highly coherent done
clear
C)
is highly directional done
clear
D)
can be sharply focused done
clear
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question_answer 7)
Which of the following frequencies will be suitable for beyond-the horizon communication using sky waves?
A)
\[10\text{ }kHz\] done
clear
B)
\[10\text{ M}Hz\] done
clear
C)
\[\text{1 G}Hz\] done
clear
D)
\[\text{1000 G}Hz\] done
clear
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question_answer 8)
The sky wave propagation is suitable for radio- waves of frequency
A)
upto \[2\,MHz\] done
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B)
from \[2\,MHz\] to \[20\,MHz\] done
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C)
from \[2\,MHz\] to \[30\,MHz\] done
clear
D)
from \[2\,MHz\] to \[50\,MHz\] done
clear
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question_answer 9)
The maximum range \[{{d}_{\max }},\] of radar is
A)
proportional to the cube root of the peak transmitted power done
clear
B)
proportional to the fourth root of the peak transmitted power done
clear
C)
proportional to the square root of the peak transmitted power done
clear
D)
Not related to the peak transmitted power at all done
clear
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question_answer 10)
Frequencies in the UHF range normally propagate by means of-
A)
Ground waves done
clear
B)
Sky waves. done
clear
C)
Surface waves done
clear
D)
Space waves done
clear
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question_answer 11)
A T.V. tower has a height 150 m. What is the population density around the T.V. tower if the total population covered is 50 lakh? The radius of earth is \[6.4\times {{10}^{6}}m\].
A)
\[800\,k{{m}^{-2}}\] done
clear
B)
\[829\,k{{m}^{-2}}\] done
clear
C)
\[82.6\,k{{m}^{-2}}\] done
clear
D)
\[826.6\,k{{m}^{-2}}\] done
clear
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question_answer 12)
What will be the image frequency of an FM radio receiver that is tuned to \[98.6\text{ }MHz\] broadcast station?
A)
\[111.8\,MHz\] done
clear
B)
\[108\,MHz\] done
clear
C)
\[121.6\,MHz\] done
clear
D)
\[132\,MHz\] done
clear
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question_answer 13)
The temperature of earth's atmosphere increases with height in
A)
troposphere done
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B)
stratosphere and ionosphere done
clear
C)
mesosphere and tonosphere done
clear
D)
None of these done
clear
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question_answer 14)
Critical frequency \[{{v}_{c}}\] for the ionosphere is -
A)
\[{{v}_{c}}=9.{{N}_{\max }}\] done
clear
B)
\[{{v}_{c}}=9\sqrt{{{N}_{\max }}}\] done
clear
C)
\[{{v}_{c}}=6.IN\max \] done
clear
D)
\[{{v}_{c}}=6.{{N}_{max}}\] done
clear
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question_answer 15)
The phenomenon by which light travels in an optical fibres is
A)
Reflection done
clear
B)
Refraction done
clear
C)
Total internal reflection done
clear
D)
Transmission done
clear
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question_answer 16)
The attenuation in optical fibre is mainly due to
A)
absorption done
clear
B)
scattering done
clear
C)
neither absorption nor scattering done
clear
D)
both (a) and (b) done
clear
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question_answer 17)
The fundamental radio antenna is a metal rod which has a length equal to
A)
\[\lambda \] in free space at the frequency of operation done
clear
B)
\[\lambda /2\] in free space at the frequency of operation done
clear
C)
\[\lambda /4\] in free space at the frequency of operation done
clear
D)
\[3\lambda /4\] in free space at the frequency of operation done
clear
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question_answer 18)
Long range radio transmission is possible when the radio waves are reflected from the ionosphere. For this to happen the frequency of the radio waves must be in the range:
A)
\[80-150\,MHz\] done
clear
B)
\[8-25MHz\] done
clear
C)
\[1-3\,MHz\] done
clear
D)
\[150-1500\,kHz\] done
clear
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question_answer 19)
The TV telecast is to cover a radius of \[120\text{ }km\] (given the radius of the Earth\[=6400\text{ }km\]), the height of the transmitting antenna is
A)
\[1280\,m\] done
clear
B)
\[1125\,m\] done
clear
C)
\[1560\,m\] done
clear
D)
\[79\text{ }m\] done
clear
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question_answer 20)
The radio waves of frequency \[300\text{ }MHz\] to \[3000\text{ }MHz\] belong to
A)
high frequency band done
clear
B)
very high frequency band done
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C)
ultra high frequency band done
clear
D)
super high frequency band done
clear
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question_answer 21)
Electromagnetic waves with frequencies greater than the critical frequency of ionosphere cannot be used for communication using sky wave propagation because:
A)
the refractive index of the ionosphere becomes very high for \[f>{{f}_{c}}\] done
clear
B)
the refractive index of the ionosphere becomes very low for \[f>{{f}_{c}}\] done
clear
C)
the refractive index of the ionosphere very high for \[f<{{f}_{c}}\] done
clear
D)
none of the above done
clear
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question_answer 22)
In an amplitude modulated wave for audio frequency of 500 cycle/second, the appropriate carrier frquency will be
A)
\[50\,cycles/s\] done
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B)
\[100\,cycles/s\] done
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C)
\[500\,cycles/s\] done
clear
D)
\[50,000\,cycles/s\] done
clear
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question_answer 23)
Long distance short-wave radio broadcasting uses
A)
ground wave done
clear
B)
ionospheric wave done
clear
C)
direct wave done
clear
D)
sky wave done
clear
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question_answer 24)
What is the modulation index of an over modulated wave
A)
\[1\] done
clear
B)
Zero done
clear
C)
\[<\,1\] done
clear
D)
\[>\,1\] done
clear
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question_answer 25)
Which of the following statements is correct?
A)
Short waves are completely absorbed by ionosphere. done
clear
B)
Radio waves are unpolarised electromagnetic waves. done
clear
C)
Optical interference between fibres is zero. done
clear
D)
Shorter the wavelength, the smaller is the velocity of wave propagation. done
clear
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question_answer 26)
Broadcasting antennas are generally
A)
omnidirectional type done
clear
B)
vertical type done
clear
C)
horizontal type done
clear
D)
None of these done
clear
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question_answer 27)
Which range of frequencies is suitable for sky wave propagation?
A)
\[1\,kHz\] to \[500\,kHz\] done
clear
B)
\[1\,MHz\] to \[2\,MHz\] done
clear
C)
\[2\,MHz\] to \[20\,MHz\] done
clear
D)
Above \[30\,MHz\] done
clear
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question_answer 28)
In earth's atmosphere, for \[{{F}_{2}}\] -layer, the virtual height and critical frequency in night time are
A)
\[210\,km\] and \[5\text{ }MHz\] done
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B)
\[250\,km\] and \[6\,MHz\] done
clear
C)
\[280\text{ }km\] and \[7\text{ }MHz\] done
clear
D)
\[350\,km\] and \[6\,MHz\] done
clear
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question_answer 29)
In ground or surface wave propagation, the loss of power in a signal wave is due to
A)
induced charges in earth which travel in ground along with the wave, resulting the alternating currents in the earth's surface done
clear
B)
interference of waves done
clear
C)
superposition of waves done
clear
D)
high frequency of signal wave. done
clear
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question_answer 30)
A transducer used at the transmitting end, serves the purpose of converting
A)
electrical signal to sound form done
clear
B)
sound signal to electrical form done
clear
C)
electrical signal to magnetic form done
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D)
sound signal to magnetic form done
clear
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question_answer 31)
In which frequency range, space waves are normally propagated
A)
HF done
clear
B)
VHF done
clear
C)
UHF done
clear
D)
SHF done
clear
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question_answer 32)
In an optical fibre, the diameter of the core is nearly
A)
\[{{10}^{-2}}m\] done
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B)
\[{{10}^{-4}}m\] done
clear
C)
\[{{10}^{-8}}m\] done
clear
D)
\[{{10}^{-10}}m\] done
clear
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question_answer 33)
Communication satellite is used when the distance of transmission is greater than -
A)
\[100\,km\] done
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B)
\[500\,km\] done
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C)
\[10\,km\] done
clear
D)
\[1000\,km\] done
clear
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question_answer 34)
The electron density of a layer of ionosphere at a height \[150\text{ }km\] from the earth's surface is \[9\times {{10}^{9}}\,per\,{{m}^{3}}.\]For the sky transmission from this layer up to a range of \[250\text{ }km,\]The critical frequency of the layer is
A)
\[2\,Hz\] done
clear
B)
\[2.7\,Hz\] done
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C)
\[2.78\,Hz\] done
clear
D)
\[2.7\,MHz\] done
clear
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question_answer 35)
What should be the maximum acceptance angle at the aircore interface of an optical fibre if \[{{n}_{1}}\]and \[{{n}_{2}}\] are the refractive indices of the core and the cladding, respectively?
A)
\[{{\sin }^{-1}}({{n}_{2}}/{{n}_{1}})\] done
clear
B)
\[{{\sin }^{-1}}\sqrt{n_{1}^{2}-n_{2}^{2}}\] done
clear
C)
\[\left[ {{\tan }^{-1}}\frac{{{n}_{2}}}{{{n}_{1}}} \right]\] done
clear
D)
\[\left[ {{\tan }^{-1}}\frac{{{n}_{1}}}{{{n}_{2}}} \right]\] done
clear
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question_answer 36)
Space wave propagation is useful for -
A)
low frequency waves and large distances done
clear
B)
low frequency waves and small distances done
clear
C)
high frequency waves done
clear
D)
ultra-high frequency waves done
clear
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question_answer 37)
Which one of the following is used in line-transmission -
A)
coaxial cable done
clear
B)
optical fibre cable done
clear
C)
twisted pair done
clear
D)
all the above done
clear
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question_answer 38)
A TV tower has a height of\[100m\]. By how much the height of tower be increased to triple its coverage range?
A)
\[800\text{ }m\] done
clear
B)
\[700\text{ }m\] done
clear
C)
\[600\text{ }m\] done
clear
D)
\[500\text{ }m\] done
clear
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question_answer 39)
In a radio receiver, noise is generally developed at-
A)
IF stage done
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B)
audio stage done
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C)
RF stage done
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D)
receiving antenna done
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question_answer 40)
Range of frequencies allotted for commercial FM radio broadcast is -
A)
\[88\]to\[108\text{ }MHz\] done
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B)
\[88\] to \[108\text{ }kHz\] done
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C)
\[8\]to\[88\text{ }MHz\] done
clear
D)
\[88\] to \[108\text{ }GHz\] done
clear
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question_answer 41)
A super heterodyne receiver is designed to receive transmitted signals between 5 and\[10\text{ }MHz\]. The tuning range of the local oscillate for IF frequency \[600\text{ }kHz\] for high-side tuning would be
A)
\[4.6\] to\[9.6\text{ }MHz\] done
clear
B)
\[5.6\] to \[10.6\text{ }MHz\] done
clear
C)
\[4.6\] to\[10.6\text{ }MHz\] done
clear
D)
\[5.6\] to \[9.6\text{ }MHz\] done
clear
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question_answer 42)
For television broadcasting, the frequency employed is normally -
A)
\[30-300\text{ }MHz\] done
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B)
\[3-30\text{ }MHz\] done
clear
C)
\[30-300\text{ }KHz\] done
clear
D)
\[30-300\text{ }Hz\] done
clear
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question_answer 43)
If the heights of transmitting and the receiving antennas are each equal to h, the maximum line- of-sight distance between them is (R is the radius of earth)
A)
\[\sqrt{2Rh}\] done
clear
B)
\[\sqrt{4Rh}\] done
clear
C)
\[\sqrt{6Rh}\] done
clear
D)
\[\sqrt{8Rh}\] done
clear
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question_answer 44)
A signal of peak voltage \[5\text{ }V\] at \[10\text{ }kHz\] is modulated using a carrier wave of peak voltage \[10\text{ }V\] at\[2\text{ }MHz\]. The side band frequencies are
A)
\[2010kHz,1990kHz\] done
clear
B)
\[2000kHz,\text{ }1990kHz\] done
clear
C)
\[2010kHz,\text{ }2000\text{ }kHz\] done
clear
D)
\[2100kHz,\text{ }1900kHz\] done
clear
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question_answer 45)
If the maximum amplitude of an amplitude modulated wave is \[25\text{ }V\] and the minimum amplitude is \[5\text{ }V,\] the modulation index is:
A)
\[\frac{1}{5}\] done
clear
B)
\[\frac{1}{3}\] done
clear
C)
\[\frac{3}{2}\] done
clear
D)
\[\frac{2}{3}\] done
clear
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question_answer 46)
The electromagnetic waves of frequency \[2\text{ }MHz\] to \[30\text{ }MHz\] are used
A)
in ground wave propagation done
clear
B)
in sky wave propagation done
clear
C)
in microwave propagation done
clear
D)
in satellite communication done
clear
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question_answer 47)
100% modulation in FM means ,
A)
actual frequency deviation > maximum allowed frequency deviation done
clear
B)
actual frequency deviation = maximum allowed frequency deviation done
clear
C)
actual frequency deviation > maximum allowed frequency deviation done
clear
D)
actual frequency deviation < maximum allowed frequency deviation done
clear
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question_answer 48)
The antenna current of an AM transmitter is 8 A when only the carrier is sent, but it increases to 893 A when the carrier is sent, but it increases to 893 A when the carrier is modulated by a single sine wave. Find the percentage modulation.
A)
\[60.1%\] done
clear
B)
\[70.1%\] done
clear
C)
\[80.1%\] done
clear
D)
\[50.1%\] done
clear
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question_answer 49)
When radio waves passes through ionosphere, phase difference between space current and capacitive displacement current is
A)
0 rad done
clear
B)
\[(3\pi /2)\]rad done
clear
C)
\[(\pi /2)\]rad done
clear
D)
\[\pi \,rad\] done
clear
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question_answer 50)
The rms value of a carrier voltage is 100 volts. Compute its rms value when it has been amplitude modulated by a sinusoidal audio voltage to a depth of 30%.
A)
\[94\,V\] done
clear
B)
\[104.5\,V\] done
clear
C)
\[114.4\,V\] done
clear
D)
\[124\,V\] done
clear
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question_answer 51)
A carrier frequency of \[1\text{ }MHz\] and peak value of \[10\text{ }V\] is amplitude modulated with a signal frequency of \[10\text{ }kHz\] with peak value of\[0.5\text{ }V\]. Then, the modulation index and the side band frequencies respectively are
A)
\[0.05\]and\[1\pm 0.010\text{ }MHz\] done
clear
B)
\[0.5\]and \[1\pm 0.010\text{ }MHz\] done
clear
C)
\[0.5\]and \[1\pm 0.005\text{ }MHz\] done
clear
D)
\[0.05\]and \[1\pm 0.005\text{ }MHz\] done
clear
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question_answer 52)
The wrong statement is
A)
Electromagnetic waves with frequencies more than the critical frequency of ionosphere cannot be used for communication using sky wave propagation. done
clear
B)
The refractive index of the ionosphere becomes very high for frequencies higher than the critical frequency. done
clear
C)
Diode lasers are used as optical sources in optical communication. done
clear
D)
Diode lasers consume more energy. done
clear
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question_answer 53)
A sinusoidal carrier voltage of frequency \[10\text{ }MHz\] and amplitude 200 volts is amplitude modulated by a sinusoidal voltage of frequency \[10\text{ }kHz\]producing \[40%\]modulation. Calculate the frequency of upper and lower sidebands.
A)
\[10010kHz,9990\text{ }kHz\] done
clear
B)
\[1010kHz,990kHz\] done
clear
C)
\[10100\text{ }Hz,9990\text{ }Hz\] done
clear
D)
\[1010MHz,990MHz\] done
clear
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question_answer 54)
The most useful transmission for low frequency and small distance is through -
A)
sky waves done
clear
B)
ground waves done
clear
C)
surface waves done
clear
D)
space waves done
clear
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question_answer 55)
A \[1000\text{ }kHz\] carrier is simultaneously modulated with \[300\text{ }Hz,\] \[800\text{ }Hz\] and \[2\text{ }kHz\] audio waves. The frequencies present in the output is
A)
\[999.7\text{ }kHz,\text{ }100.3\text{ }kHz,\text{ }999.2\text{ }kHz\] done
clear
B)
\[1000.8\text{ }kHz,\text{ }998\text{ }kHz,\text{ }1002\text{ }kHz\] done
clear
C)
\[1002.8\text{ }kHz,\text{ }996\text{ }kHz,\text{ }1106\text{ }kHz\] done
clear
D)
both (a) and (b) done
clear
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question_answer 56)
The maximum distance upto which TV transmission from a TV tower of height h can be received is proportional to -
A)
\[{{h}^{1/2}}\] done
clear
B)
h done
clear
C)
\[{{h}^{3/2}}\] done
clear
D)
\[{{h}^{2}}\] done
clear
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question_answer 57)
For good demodulation of AM signal of carrier frequency/, the value of RC should be
A)
\[RC=\frac{1}{f}\] done
clear
B)
\[RC<\frac{1}{f}\] done
clear
C)
\[RC\ge \frac{1}{f}\] done
clear
D)
\[RC>>\frac{1}{f}\] done
clear
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question_answer 58)
An audio frequency of \[10\text{ }kHz\] is transmitted by SSB after AM with carrier waves of frequency\[1\,MHz\]. The frequency of current in output load is
A)
\[1010\,kHz\] or \[990\,kHz\] done
clear
B)
\[1010\,MHz\] or \[1010\,MHz\] done
clear
C)
\[110\text{ }kHz\] or \[990\text{ }kHz\] done
clear
D)
\[110\text{ }MHz\] or \[990\text{ }MHz\] done
clear
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question_answer 59)
At maximum modulation (i.e. \[m=1\]), the power in each sideband is......... of that of carrier.
A)
\[25%\] done
clear
B)
\[50%\] done
clear
C)
\[40%\] done
clear
D)
\[60%\] done
clear
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question_answer 60)
In an FM system a \[7\text{ }kHz\] signal modulates \[108\,MHz\]carrier so that frequency deviation is\[50\,kHz\]. The carrier swing is
A)
\[7.1\] done
clear
B)
\[2.8\] done
clear
C)
\[5.8\] done
clear
D)
\[3.2\] done
clear
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question_answer 61)
An FM signal has a resting frequency of \[105\text{ }MHz\] and highest frequency of \[105.03\text{ }MHz\] when modulated by a signal of frequency \[5\text{ }kHz.\]The carrier swing is
A)
\[25\,kHz\] done
clear
B)
\[54\,kHz\] done
clear
C)
\[60\,kHz\] done
clear
D)
\[75\,kHz\] done
clear
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question_answer 62)
A detector circuit must -
A)
rectify the signal done
clear
B)
deliver an audio output signal done
clear
C)
perform the above two functions done
clear
D)
None of the above done
clear
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question_answer 63)
An oscillator is producing FM waves of frequency \[2\text{ }kHz\] with a variation of\[10\text{ }kHz\]. What is the modulating index?
A)
5 done
clear
B)
4 done
clear
C)
3 done
clear
D)
2 done
clear
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question_answer 64)
An AM- signal is given as \[{{x}_{AM}}(t)=100\,[p(t)+0.5\,g(t)]\,\,\cos \,{{\omega }_{c}}t\] in interval \[0\le t\le 1.\]. One set of possible values of the modulating signal and modulation index would be
A)
\[t,\,\,0.5\] done
clear
B)
\[t,\,\,1.0\] done
clear
C)
\[t,\,\,1.5\] done
clear
D)
\[{{t}^{2}},\,\,2.0\] done
clear
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question_answer 65)
In frequency modulated wave:
A)
frequency varies with time done
clear
B)
amplitude varies with time done
clear
C)
both frequency and amplitude vary with time done
clear
D)
both frequency and amplitude are constant done
clear
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question_answer 66)
In light modulation, which characteristic of the carrier light wave is varied?
A)
Amplitude done
clear
B)
Frequency done
clear
C)
Phase done
clear
D)
Intensity done
clear
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question_answer 67)
An FM radio station operating at \[630\text{ }kHz\] is permitted to broadcast audio frequencies up to\[\text{6 }kHz\]. The band pass filter in its modulation circuit can retain the frequencies
A)
\[636\,kHz,\text{ }630\,kHz\] done
clear
B)
\[12\,kHz,\text{ }6\,kHz\] done
clear
C)
\[1260\,kHz,6\,kHz\] done
clear
D)
\[1260kHz,\text{ }630kHz\] done
clear
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question_answer 68)
What is the band width in amplitude modulation?
A)
Equal to signal frequency done
clear
B)
Two times the signal frequency done
clear
C)
Half the signal frequency done
clear
D)
One fourth the signal frequency done
clear
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question_answer 69)
A \[10\text{ }kW\] carrier is sinusoidally modulated by two carriers corresponding to a modulation index of 30% and 40% respectively then total power radiated by the modulator is
A)
\[10.25\,kW\] done
clear
B)
\[11.25\,kW\] done
clear
C)
\[12.75\,kW\] done
clear
D)
\[17\,kW\] done
clear
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question_answer 70)
As the modulation level is increased, the carrier power -
A)
is increased done
clear
B)
is decreased done
clear
C)
remains the same done
clear
D)
None of the above done
clear
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question_answer 71)
A device with input \[x(t)\] and output \[y(t)\] is characterized by: \[y(t)={{x}^{2}}(t)\]. An FM signal with frequency deviation of \[90\text{ }kHz\] and modulating signal bandwidth of \[5\text{ }kHz\] is applied to this device. The bandwidth of the output signal is
A)
\[370\,kHz\] done
clear
B)
\[190\,kHz\] done
clear
C)
\[380\,kHz\] done
clear
D)
\[95\,kHz\] done
clear
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question_answer 72)
12 signals each band limited to \[5\text{ }kHz\] are to be transmitted by frequency-division multiplexer. If AM-SSB modulation guard band of \[\text{1 }kHz\] is used then the bandwidth of multiplexed signal is
A)
\[\text{101 }kHz\] done
clear
B)
\[\text{99 }kHz\] done
clear
C)
\[\text{84 }kHz\] done
clear
D)
\[\text{71 }kHz\] done
clear
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question_answer 73)
If level of modulation is increased........power is increased.
A)
carrier done
clear
B)
sideband done
clear
C)
carrier as well as sideband done
clear
D)
none of the above done
clear
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question_answer 74)
Determine the modulation index and carrier swing of an FM carrier having a frequency deviation of \[25\text{ }kHz\] and a modulating signal of\[5\text{ }kHz\].
A)
\[7,\,\,70\,kHz\] done
clear
B)
\[8,\,\,80\,kHz\] done
clear
C)
\[5,\,\,50\,kHz\] done
clear
D)
\[10,\,\,100\,kHz\] done
clear
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question_answer 75)
A radio station has two channels. One is AM at \[1020\text{ }kHz\] and the other FM at\[89.5\text{ }MHz\]. For good results you will use
A)
longer antenna for the AM channel and shorter for the FM done
clear
B)
shorter antenna for the AM channel and longer for the FM done
clear
C)
same length antenna will work for both done
clear
D)
information given is not enough to say which one to use for which done
clear
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question_answer 76)
Band width is dependent on -
A)
the frequency of carrier done
clear
B)
the frequency of modulated signal done
clear
C)
the thickness of the cable done
clear
D)
the resistance of the circuit. done
clear
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question_answer 77)
An audio signal represented as \[25\,\sin \,2\pi (2000\,t)\]amplitude modulated by a carrier wave: \[60\,\sin \,2\pi (100\,,\,000)t\]. The modulation index of the modulated signal is
A)
\[25%\] done
clear
B)
\[41.6%\] done
clear
C)
\[50%\] done
clear
D)
\[75%\] done
clear
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question_answer 78)
If a carrier wave c(t) = A \[\sin {{\omega }_{c}}t\] is amplitude modulated by a modulator signal \[m(t)=A\,\sin {{\omega }_{m}}t\]then the equation of modulated signal \[[{{C}_{m}}(t)]\]and its modulation index are respectively
A)
\[{{C}_{m}}(t)=A(1+\sin {{\omega }_{m}}t)\,\sin {{\omega }_{c}}t\] and 2 done
clear
B)
\[{{C}_{m}}(t)=A(1+\sin {{\omega }_{m}}t)\,\sin {{\omega }_{m}}t\] and 1 done
clear
C)
\[{{C}_{m}}(t)=A(1+\sin {{\omega }_{m}}t)\,\sin {{\omega }_{c}}t\] and 1 done
clear
D)
\[{{C}_{m}}(t)=A(1+\sin {{\omega }_{c}}t)\,\sin {{\omega }_{m}}t\] and 2 done
clear
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question_answer 79)
When the modulating frequency is doubled, the modulation index is halved and the modulating voltage remains constant. The modulation system is
A)
Amplitude modulation done
clear
B)
Phase modulation done
clear
C)
Frequency modulation done
clear
D)
All of the above done
clear
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question_answer 80)
Pre-emphasis in FM system is done to
A)
compress modulating signal done
clear
B)
expand modulating signal done
clear
C)
amplify lower frequency component of the modulating signal done
clear
D)
amplify higher frequency component of the modulating signal done
clear
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question_answer 81)
A broadcast radio transmitter radiates \[12\text{ }kW\]when percentage of modulation is 50%, then the unmodulated carrier power is
A)
\[5.67\,kW\] done
clear
B)
\[7.15\,kW\] done
clear
C)
\[9.6\text{ }kW\] done
clear
D)
\[12\text{ }kW\] done
clear
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question_answer 82)
AM is used for broadcasting because
A)
it is more noise immune than other modulation systems done
clear
B)
it requires less transmitting power compared with other systems done
clear
C)
its use avoids receiver complexity done
clear
D)
no other modulation system can provide the necessary bandwidth faithful transmission. done
clear
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question_answer 83)
The frequency deviation in a FM transmission is\[18.75\text{ }KHz\]. If it broadcasts in \[88-108\text{ }MHz\] band, then the percent modulation is
A)
\[10%\] done
clear
B)
\[25%\] done
clear
C)
\[50%\] done
clear
D)
\[75%\] done
clear
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question_answer 84)
A transmitter radiates \[10\text{ }kW\] of power with the carrier unmodulated and \[11.8\text{ }kW\] with the carrier sinusoidally modulated. The modulation factor is
A)
\[56%\] done
clear
B)
\[60%\] done
clear
C)
\[72%\] done
clear
D)
\[84%\] done
clear
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question_answer 85)
A modulated signal \[{{C}_{m}}(t)\] has the form \[{{C}_{m}}(t)=30\]\[\sin 300\pi t+10(\cos 200\pi t-\cos 400\pi t)\]. The carrier frequency \[{{f}_{c}},\] the modulating frequency (message frequency) \[{{f}_{\omega }}\] and the modulation index \[\mu \] are respectively given by :
A)
\[{{f}_{c}}=200\,Hz;\,{{f}_{w}}=50\,Hz;\,\,\mu =\frac{1}{2}\] done
clear
B)
\[{{f}_{c}}=150\,Hz;\,{{f}_{w}}=50\,Hz;\,\,\mu =\frac{2}{3}\] done
clear
C)
\[{{f}_{c}}=150\,Hz;\,{{f}_{w}}=30\,Hz;\,\,\mu =\frac{1}{3}\] done
clear
D)
\[{{f}_{c}}=200\,Hz;\,{{f}_{w}}=30\,Hz;\,\,\mu =\frac{1}{2}\] done
clear
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question_answer 86)
The T.V. transmission tower in Delhi has a height of\[240\text{ }m\]. The distance upto which the broadcast can be received. (Radius of earth is \[6.4\times {{10}^{6}}m\])
A)
\[60\,km\] done
clear
B)
\[100\,km\] done
clear
C)
\[50\,km\] done
clear
D)
\[55\,km\] done
clear
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question_answer 87)
An audio signal consists of two distinct sounds: one a human speech signal in the frequency band of \[200\text{ }Hz\] to \[2700\text{ }Hz,\] while the other is a high frequency music signal in the frequency band of \[10200\text{ }Hz\] to \[15200\text{ }Hz\]. The ratio of the AM signal bandwidth required to send both the signals together to the AM signal bandwidth required to send just the human speech is:
A)
\[2\] done
clear
B)
\[5\] done
clear
C)
\[6\] done
clear
D)
\[3\] done
clear
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question_answer 88)
A signal of \[5\text{ }kHz\] frequency modulates a carrier of frequency \[1\text{ }MHz\] and peak voltage \[25\,V\]. If the amplitude at the side bands of the amplitude modulated signal is \[5V,\] then the modulation index is:
A)
\[0.8\] done
clear
B)
\[0.6\] done
clear
C)
\[0.5\] done
clear
D)
\[0.4\] done
clear
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question_answer 89)
Television signals on earth cannot be received at distances greater than 100 km from the transmission station. The reason behind this is that
A)
the receiver antenna is unable to detect the signal at a disance greater than 100 km done
clear
B)
the TV programme consists of both audio and video signals done
clear
C)
the TV signals are less powerful than radio signals done
clear
D)
the surface of earth is curved like a sphere done
clear
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question_answer 90)
A carrier frequency of \[10\,kV\] at \[1\text{ }MHz\] is amplitude modulated by a \[1\text{ }kHz\] signal of \[6\text{ }kV\] peak voltage. When the modulation pattern is observed on a calibrated CRO, the voltage indicated by the CRO will be
A)
\[16\] done
clear
B)
\[32\] done
clear
C)
\[864\] done
clear
D)
\[84\] done
clear
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question_answer 91)
Determine the modulation index and carrier swing of an FM carrier having a frequency deviation of \[56\text{ }kHz\] and a modulating signal of\[8\text{ }kHz\].
A)
\[9,\,\,580\,kHz\] done
clear
B)
\[3,\,101\,kHz\] done
clear
C)
\[7,112\,kHz\] done
clear
D)
\[8,\,\,80\,kHz\] done
clear
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question_answer 92)
Given the electric field of a complete amplitude modulated wave as \[\vec{E}=\hat{i}{{E}_{C}}\left( 1+\frac{{{E}_{m}}}{{{E}_{C}}}\cos {{\omega }_{m}}t \right)\,\cos {{\omega }_{C}}t.\] Where the subscript c stands for the carrier wave and m for the modulating signal. The frequencies present in the modulated wave are
A)
\[{{\omega }_{C}}\] and \[\sqrt{\omega _{C}^{2}+\omega _{m}^{2}}\] done
clear
B)
\[{{\omega }_{C}},\,{{\omega }_{C}}+{{\omega }_{m}}\] and \[{{\omega }_{C}}-{{\omega }_{m}}\] done
clear
C)
\[{{\omega }_{C}}\] and \[{{\omega }_{m}}\] done
clear
D)
\[{{\omega }_{C}}\] and \[\sqrt{{{\omega }_{C}}{{\omega }_{m}}}\] done
clear
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question_answer 93)
In optical communication system operating at \[1200\text{ }nm,\] only \[2%\] of the source frequency is available for TV transmission having a bandwidth of \[5\text{ }MHz\]. What is the number of TV channels that can be transmitted?
A)
1 million done
clear
B)
50 million done
clear
C)
1 thousand done
clear
D)
50 thousand done
clear
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question_answer 94)
The velocity of all radio waves in free space is \[3\times {{10}^{8}}m/s.\] What the frequency of a radio wave of wavelength is \[150\,m\].
A)
\[5\,MHz\] done
clear
B)
\[2\,MHz\] done
clear
C)
\[0.5\,MHz\] done
clear
D)
\[0\,MHz\] done
clear
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question_answer 95)
Maximum usable frequency (MUF) in F-region layer is x, when the critical frequency is \[60\text{ }MHz\]and the angle of incidence is \[70{}^\circ \]. Then calculate x.
A)
\[122\,MHz\] done
clear
B)
\[216\,Hz\] done
clear
C)
\[175\,MHz\] done
clear
D)
\[75\text{ }Hz\] done
clear
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question_answer 96)
If \[{{E}_{c}}=20\,\sin \,{{10}^{5}}\pi t\] and \[{{E}_{m}}=10\,\sin \,400\,\pi t\] are carrier and modulating signals, the modulation index is:
A)
\[56\,%\] done
clear
B)
\[30\,%\] done
clear
C)
\[50\,%\] done
clear
D)
\[48\,%\] done
clear
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question_answer 97)
The area of the region covered by the TV broadcast by a TV tower of 100 m height is (Radius of the earth \[=6.4\times {{10}^{6}}m\]).
A)
\[1.28\pi \times {{10}^{3}}k{{m}^{2}}\] done
clear
B)
\[2\pi \times {{10}^{4}}k{{m}^{2}}\] done
clear
C)
\[3.1\times {{10}^{4}}k{{m}^{2}}\] done
clear
D)
\[6\pi \times {{10}^{4}}k{{m}^{2}}\] done
clear
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question_answer 98)
Determine the modulation index \[({{m}_{f}})\] and carrier swing (S) of an FM carrier having a frequency deviation of \[25\text{ }kHz\] and a modulating signal of\[5\text{ }kHz\].
A)
\[{{m}_{f}}=3\] done
clear
B)
\[{{m}_{f}}=5\] done
clear
C)
\[S=80\,kHz\] done
clear
D)
\[S=60\,kHz\] done
clear
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question_answer 99)
Calculate the power developed by an amplitude modulated wave in a load resistance of \[100\,\Omega ,\] if the peak voltage of carrier wave is \[100\text{ }V\] and modulation index is \[0.4\].
A)
50 watt done
clear
B)
54 watt done
clear
C)
104 watt done
clear
D)
4 watt done
clear
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question_answer 100)
The maximum range for the tropospheric transmission of radio wave of wavelength 3m using the transmitting antenna and receiving antenna of heights \[100\,m\] and \[60\,m\] respectively is
A)
\[8\,m\] done
clear
B)
\[800\,m\] done
clear
C)
\[8\,km\] done
clear
D)
\[80\,km\] done
clear
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