Communication Systems Practice Questions - DPP for JEE

 Page 1


PART-I (Single Correct MCQs)
1. 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)
(b)
(c)
(d)
2. Given the electric field of a complete amplitude modulated wave as
.
Where the subscript c stands for the carrier wave and m for the modulating
signal. The frequencies present in the modulated wave are
(a)
(b) ?
c
, ?
c
 + ?
m
 and ?
c
 – ?
m
Page 2


PART-I (Single Correct MCQs)
1. 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)
(b)
(c)
(d)
2. Given the electric field of a complete amplitude modulated wave as
.
Where the subscript c stands for the carrier wave and m for the modulating
signal. The frequencies present in the modulated wave are
(a)
(b) ?
c
, ?
c
 + ?
m
 and ?
c
 – ?
m
(c) ?
c
 and ?
m
(d) and 
3. The power radiated from antenna of length l is proportional to
(a)
(b)
(c)
(d)
4. The mobile telephones operate typically in the range of
(a) 1–100 MHz
(b) 100–200 MHz
(c) 1000–2000 MHz
(d) 800–950 MHz
5. Depth of modulation (m
a
) in terms of E
max
 and E
min
 is
(a) m
a
 = E
max
 + E
min
/E
min
(b) m
a
 = E
max
 – E
min
/E
max
(c) m
a
 = E
max
 – E
min
/E
max 
+ E
min
(d) m
a
 = E
max
 + E
min
/E
max 
– E
min
6. 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
(b) the TV programme consists of both audio and video signals
Page 3


PART-I (Single Correct MCQs)
1. 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)
(b)
(c)
(d)
2. Given the electric field of a complete amplitude modulated wave as
.
Where the subscript c stands for the carrier wave and m for the modulating
signal. The frequencies present in the modulated wave are
(a)
(b) ?
c
, ?
c
 + ?
m
 and ?
c
 – ?
m
(c) ?
c
 and ?
m
(d) and 
3. The power radiated from antenna of length l is proportional to
(a)
(b)
(c)
(d)
4. The mobile telephones operate typically in the range of
(a) 1–100 MHz
(b) 100–200 MHz
(c) 1000–2000 MHz
(d) 800–950 MHz
5. Depth of modulation (m
a
) in terms of E
max
 and E
min
 is
(a) m
a
 = E
max
 + E
min
/E
min
(b) m
a
 = E
max
 – E
min
/E
max
(c) m
a
 = E
max
 – E
min
/E
max 
+ E
min
(d) m
a
 = E
max
 + E
min
/E
max 
– E
min
6. 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
(b) the TV programme consists of both audio and video signals
(c) the TV signals are less powerful than radio signals
(d) the surface of earth is curved like a sphere
7. The frequency deviation in a FM transmission is 18.75 KHz. If it
broadcasts in 88-108 MHz band, then the percentage modulation is
(a) 10%
(b) 25%
(c) 50%
(d) 75%
8. An AM- signal is given as
x
AM
 (t) = 100 [p(t) + 0.5g(t)] cos ?
c
t in interval 0 = t = 1. One set of possible
values of the modulating signal and modulation index would be
(a) t, 0.5
(b) t, 1.0
(c) t, 1.5
(d) t
2
, 2.0
9. In earth’s atmosphere, for F
2
-layer, the virtual height and critical
frequency in night time are
(a) 210 km and 5 MHz
(b) 250 km and 6 MHz
(c) 280 km and 7 MHz
(d) 350 km and 6 MHz
10. For good demodulation of AM signal of carrier frequency f, the value of
RC should be
(a)
(b)
Page 4


PART-I (Single Correct MCQs)
1. 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)
(b)
(c)
(d)
2. Given the electric field of a complete amplitude modulated wave as
.
Where the subscript c stands for the carrier wave and m for the modulating
signal. The frequencies present in the modulated wave are
(a)
(b) ?
c
, ?
c
 + ?
m
 and ?
c
 – ?
m
(c) ?
c
 and ?
m
(d) and 
3. The power radiated from antenna of length l is proportional to
(a)
(b)
(c)
(d)
4. The mobile telephones operate typically in the range of
(a) 1–100 MHz
(b) 100–200 MHz
(c) 1000–2000 MHz
(d) 800–950 MHz
5. Depth of modulation (m
a
) in terms of E
max
 and E
min
 is
(a) m
a
 = E
max
 + E
min
/E
min
(b) m
a
 = E
max
 – E
min
/E
max
(c) m
a
 = E
max
 – E
min
/E
max 
+ E
min
(d) m
a
 = E
max
 + E
min
/E
max 
– E
min
6. 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
(b) the TV programme consists of both audio and video signals
(c) the TV signals are less powerful than radio signals
(d) the surface of earth is curved like a sphere
7. The frequency deviation in a FM transmission is 18.75 KHz. If it
broadcasts in 88-108 MHz band, then the percentage modulation is
(a) 10%
(b) 25%
(c) 50%
(d) 75%
8. An AM- signal is given as
x
AM
 (t) = 100 [p(t) + 0.5g(t)] cos ?
c
t in interval 0 = t = 1. One set of possible
values of the modulating signal and modulation index would be
(a) t, 0.5
(b) t, 1.0
(c) t, 1.5
(d) t
2
, 2.0
9. In earth’s atmosphere, for F
2
-layer, the virtual height and critical
frequency in night time are
(a) 210 km and 5 MHz
(b) 250 km and 6 MHz
(c) 280 km and 7 MHz
(d) 350 km and 6 MHz
10. For good demodulation of AM signal of carrier frequency f, the value of
RC should be
(a)
(b)
(c)
(d)
11. An audio signal represented as 25 sin 2p(2000 t) amplitude modulated
by a carrier wave : 60 sin 2p(100, 000)t. The modulation index of the
modulated signal is
(a) 25%
(b) 41.6 %
(c) 50 %
(d) 75 %
12. A radio transmitter transmits at 830 kHz. At a certain distance from the
transmitter magnetic field has amplitude 4.82 × 10
–11
T. The electric
field and the wavelength are respectively
(a) 0.014 N/C, 36 m
(b) 0.14 N/C, 36 m
(c) 0.14 N/C, 360 m
(d) 0.014 N/C, 360 m
13. A carrier frequency of 1.5 MHz and peak value of 50 V is amplitude
modulated with a signal frequency of 10 kHz producing 50%
modulation. The lower and upper side-band frequencies in kHz are
(a) 1490, 1510
(b) 1510, 1490
(c)
(d)
Page 5


PART-I (Single Correct MCQs)
1. 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)
(b)
(c)
(d)
2. Given the electric field of a complete amplitude modulated wave as
.
Where the subscript c stands for the carrier wave and m for the modulating
signal. The frequencies present in the modulated wave are
(a)
(b) ?
c
, ?
c
 + ?
m
 and ?
c
 – ?
m
(c) ?
c
 and ?
m
(d) and 
3. The power radiated from antenna of length l is proportional to
(a)
(b)
(c)
(d)
4. The mobile telephones operate typically in the range of
(a) 1–100 MHz
(b) 100–200 MHz
(c) 1000–2000 MHz
(d) 800–950 MHz
5. Depth of modulation (m
a
) in terms of E
max
 and E
min
 is
(a) m
a
 = E
max
 + E
min
/E
min
(b) m
a
 = E
max
 – E
min
/E
max
(c) m
a
 = E
max
 – E
min
/E
max 
+ E
min
(d) m
a
 = E
max
 + E
min
/E
max 
– E
min
6. 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
(b) the TV programme consists of both audio and video signals
(c) the TV signals are less powerful than radio signals
(d) the surface of earth is curved like a sphere
7. The frequency deviation in a FM transmission is 18.75 KHz. If it
broadcasts in 88-108 MHz band, then the percentage modulation is
(a) 10%
(b) 25%
(c) 50%
(d) 75%
8. An AM- signal is given as
x
AM
 (t) = 100 [p(t) + 0.5g(t)] cos ?
c
t in interval 0 = t = 1. One set of possible
values of the modulating signal and modulation index would be
(a) t, 0.5
(b) t, 1.0
(c) t, 1.5
(d) t
2
, 2.0
9. In earth’s atmosphere, for F
2
-layer, the virtual height and critical
frequency in night time are
(a) 210 km and 5 MHz
(b) 250 km and 6 MHz
(c) 280 km and 7 MHz
(d) 350 km and 6 MHz
10. For good demodulation of AM signal of carrier frequency f, the value of
RC should be
(a)
(b)
(c)
(d)
11. An audio signal represented as 25 sin 2p(2000 t) amplitude modulated
by a carrier wave : 60 sin 2p(100, 000)t. The modulation index of the
modulated signal is
(a) 25%
(b) 41.6 %
(c) 50 %
(d) 75 %
12. A radio transmitter transmits at 830 kHz. At a certain distance from the
transmitter magnetic field has amplitude 4.82 × 10
–11
T. The electric
field and the wavelength are respectively
(a) 0.014 N/C, 36 m
(b) 0.14 N/C, 36 m
(c) 0.14 N/C, 360 m
(d) 0.014 N/C, 360 m
13. A carrier frequency of 1.5 MHz and peak value of 50 V is amplitude
modulated with a signal frequency of 10 kHz producing 50%
modulation. The lower and upper side-band frequencies in kHz are
(a) 1490, 1510
(b) 1510, 1490
(c)
(d)
14. A radio station has two channels. One is AM at 1020 kHz and the other
FM at 89.5 MHz. For good results you will use
(a) longer antenna for the AM channel and shorter for the FM
(b) shorter antenna for the AM channel and longer for the FM
(c) same length antenna will work for both
(d) information given is not enough
15. For sky wave propagation of a 10 MHz signal, what should be the
minimum electron density in ionosphere
(a) ~ 1.2 × 10
12
 m
–3
(b) ~ 10
6
 m
–3
(c) ~ 10
14
 m
–3
(d) ~ 10
22
 m
–3
16. Which of the following statement is NOT correct?
(a) Ground wave signals are more stable than the sky wave signals.
(b) The critical frequency of an ionospheric layer is the highest frequency
that will be reflected back by the layer when it is vertically
incident.
(c) Electromagnetic waves of frequencies higher than about 30 MHz cannot
penetrate the ionosphere.
(d) Sky wave signals in the broadcast frequency range are stronger at night
than in the day time.
17. If a carrier wave c(t) = A sin ?
c
t is amplitude modulated by a modulator
signal m(t) = A sin ?
m
t then the equation of modulated signal [C
m
(t)]
and its modulation index are respectively
(a) C
m 
(t) = A (1 + sin ?
m 
t) sin ?
c 
t and 2
(b) C
m
 (t) = A (1 + sin ?
m 
t) sin ?
m 
t and 1
(c) C
m
 (t) = A (1 + sin ?
m 
t) sin ?
c 
t and 1