Communication Systems Questions

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Communication Systems Questions

List of communication systems Questions

Question NoQuestionsClass
121. In which of the following remote sensing technique is not
(a) Forest density (b) Pollution
(c) Wetland mapping (d) Medical treatment
212. In a radio receiver, the short wave and medium wave
stations are tuned by using the same capacitor but coils
of different inductance L, and Lm, respectively, then
(a) L > Lm
(6) Is < Lm
(c) L, = Lm
(d) None of these
3(AIEEE 2003)
2. This question has Statement-1 and Statement-2. Of the
four choices given after the statements, choose the one
that best describes the two statements.
Statement 1: Sky wave signals are used for long distance
radio communication. These signals are in general, less
table than ground wave signals.
Statement 2: The state of ionosphere varies from hour to
hour, day to day and season to season.
(a) Statement 1 is true, Statement 2 is false.
(b) Statement 1 is true, Statement 2 is true, Statement 2
is the correct explanation of Statement 1
(c) Statement 1 is true, Statement 2 is true, Statement 2
is not the correct explanation of Statement 1
(d) Statement 1 is false, Statement 2 is true
424. The audio signal used to modulate 60 sin (211 X 106
15 sin 300 nt. The depth of modulation is
(a) 50%
(b) 40%
(c) 25%
(d) 15%
55. The antenna current of an AM transmitter is 8 A when only
carrier is sent but increases to 8.96 A when the carrier is
sinusoidally modulated. The percentage modulation is
(a) 50%
(b) 60%
(c) 65%
(d) 71%
613. Which of the following is the disadvantage of FM over AM?
(a) Larger band width requirement
(b) Larger noise
(c) Higher modulation power
(d) Low efficiency
717. The phenomenon by which light travels in an optical fibres
(a) Reflection
(b) Refraction
(c) Total internal reflection
(d) Transmission
84. In amplitude modulation, sinusoidal carrier frequency
used is denoted by w, and the signal frequency is denoted
by . The bandwidth (Awm) of the signal is such that
Awm «<w. Which of the following frequencies is not
contained in the modulated wave?
(a) Om +
(b) w. – Om
(c) Om
(d) a. (JEE Main 2017)
920. Audio signal cannot be transmitted because
(a) The signal has more noise
(b) The signal cannot be amplified for distance
(c) The transmitting antenna length is very small to design
(d) The transmitting antenna length is very large and
1016. In an FM system, a 7 kHz signal modulates 108 MHz
carrier so that frequency deviation is 50 kHz. The carrier
swing is
(a) 7.143
(b) 8
(c) 0.71
(d) 350
118. The modulation index of an FM carrier having a carrier
swing of 200 kHz and a modulating signal 10 kHz is
(a) 5
(b) 10
(c) 20
(d) 25
1211. The maximum peak to peak voltage of an AM wire is
24 mV and the minimum peak to peak voltage is 8 mV.
The modulation factor is
(a) 10%
(b) 20%
(c) 25%
(d) 50%
1331. A transmitter transmits a power of 10 kW when modulation
is 50%. Power of carrier wave is
(a) 5 kW
(b) 8.89 kW
(c) 14 kW
(d) 5.7 kW
143. A radar has a power of 1 kW and is operating at a frequency
of 10 GHz. It is located on a mountain top of height 500 m.
The maximum distance upto which it can detect object
located on the surface of the earth (Radius of earth =
6.4 x 10 m) is
(a) 80 km
(b) 16 km
(c) 40 km
(d) 64 km (AIEEE 2012)
1523. What should be the maximum acceptance angle at
the aircore interface of an optical fibre if n, and n
are the refractive indices of the core and the cladding
(a) sin-‘(nz/n) (b) sin ‘ Vní – n?
24 The odia cicneluced to modulate 60 sin (2 Ty 1062)
164. A transmitter supplies 9 kW to the aerial when
unmodulated. The power radiated when modulated to
40% is
(a) 5kW
(b) 9.72 kW
(c) 10 kW
(d) 12 kW
17ILLUSTRATION 32.2 A TV tower has a height of 100 m. How
much population is covered by the TV broadcast if the average
population density around the tower is 1000 km (radius of earth
= 6.4 x 100 m).
18ILLUSTRATION 32.1 A TV transmitter has a range of 50 km.
What is the height of the TV transmission tower? Radius of
earth R. = 6.4 x 100 m.
197. The total power content of an AM wave is 900 W. For
100% modulation, the power transmitted by each side
band is
(a) 50 W
(b) 100 W
(c) 150 W
(d) 200 W
202. In a diode AM-detector, the output circuit consist of
R = I KS2 and C= 10 pF. A carrier signal of 100 kHz is to
be detected. Is it good?
(a) Yes
(b) No
(c) Information is not sufficient
(d) None of these
2128. The electron density of E, F1, F2 layers of ionosphere is
2 x 10’1,5 x 101 and 8 x 10″ m respectively. What is
the ratio of critical frequency for reflection of radiowaves
(a) 2:4:3
(b) 4:3:2
(c) 2:3:4
(d) 3:2:4
2213. A ground receiver station is receiving a signal at 5 MHz
and transmitted from a ground transmitter at a height of
300 m, located at a distance of 100 km from the receiver
station. The signal is coming via. [Radius of earth
= 6.4 x 100 m. Nmax of isosphere = 102m’]
(a) Space wave (b) Sky wave propagation
(c) Satellite transponder (d) All of these
2330. A antenna current of an AM broadcast transmitter
modulated by 50% is 11 A. The carrier current is
(a) 10.35 A
(b) 9.25 A
(c) 10 A
(d) 5.5 A
2415. An antenna is a device
(a) That converts electromagnetic energy into radio
frequency signal
(b) That converts radio frequency signal into electromag-
netic energy
(C) That converts guided electromagnetic waves into free
space electromagnetic waves and vice-versa
(d) None of these
16 In an EM System 27 kHz signal modulates 108 MHZ
259. A 500-Hz modulating voltage fed into an FM generator
produces a frequency deviation of 2.25 kHz. If amplitude
of the voltage is kept constant but frequency is raised to
6 kHz, then the new deviation will be
(a) 4.5 kHz
(b) 54 kHz
(c) 27 kHz
(d) 15 kHz
s 250
27. In an FM system a 7 kHz signal modulates 108 MH,
carrier so that frequency deviation is 50 kHz. The carrier
swing is
(a) 7.143
(b) 8
(c) 0.71
(d) 350
2711. An amplitude modulated wave is modulated to 50%. What
is the saving in power if carrier as well as one of the side
bands are suppressed?
(a) 70%
(b) 65.4%
(c) 94.4%
(d) 25.5%
28(a) 50%
12. Sinusoidal carrier voltage of frequency 1.5 MHz and
amplitude 50 V is amplitude modulated by sinusoidal
voltage of frequency 10 kHz producing 50% modulation.
The lower and upper side-band frequencies in kHz are
(a) 1490, 1510 (b) 1510, 1490
(c) 1 1
(c) 1490’1510
29in its inductance is
25. The impedance of coaxial cable, when its induc
0.40 uH and capacitance is 1 x 10- F, can be
(a) 2 x 1022
(b) 1002
(c) 3 x 1032
(d) 3 x 10-22
301. In short wave communication waves, which of the
following frequencies will be reflected back by the
ionospheric layer, having electron density 10″ per mº
(a) 2 MHz
(b) 10 MHz
(c) 12 MHz
(d) 18 MHz
Range of frequencies allotted for commercial FM radio
315. A telephonic communication service is working at
carrier frequency of 10 GHz. Only 10% of it is utilized
for transmission. How many telephonic channels can be
transmitted simultaneously if each channel requires a
bandwidth of 5 kHz?
(a) 2×10
(b) 2×10
(c) 2×104
(d) 2×10
(JEE Main 2018)
3214. An AM wave has 1800 W of total power content, For
100% modulation, the carrier should have power content
equal to
(a) 1000 watt
(b) 1200 watt
(c) 1500 watt
(d) 1600 watt
331. A sky wave with a frequency 55 MHz is incident
on D-region of earth’s atmosphere at 45°. The angle
of refraction is (electron density for D-region is
400 electron/cm)
(a) 60°
(b) 45°
(c) 30°
(d) 15°
3422. For sky wave propagation of a 10 MHz signal, what should
be the minimum electron density in ionosphere?
(a) ~1.2 x 1012 m-3 (b) 106 m-3
(C) -1014 m-
(d) ~1022 m-3
35ILLUSTRATION 32.3 On a particular day, the maximum
frequency reflected from the ionosphere is 10 MHz. On another
day, it was found to increase to 11 MHz. Calculate the ratio of
maximum electron density of the ionosphere on the two days
Point out a plausible explanation for this.
3610. The bit rate for a signal, which has a sampling rate of
8 kHz and where 16 quantisation levels have been used in
(a) 32000 bits/sec (b) 16000 bits/sec
(c) 64000 bits/sec (d) 72000 bits/sec
Sal al If n is the number of hita nar camni 1
37(a) 18 MHZ
2. Range of frequencies allotted for commercial FM radio
broadcast is
(a) 88 to 108 MHz (b) 88 to 108 kHz
(c) 8 to 88 MHz (d) 88 to 108 GHz
3810. An oscillator is producing FM waves of frequency 2 kHz
with a variation of 10 kHz. What is the modulating index?
(a) 0.20
(b) 5.0
(c) 0.67
(d) 1.5

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