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Communication Systems
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Question
In FM signal with a modulation index
m
f
is passed through a frequency tripler. The wave in the output of the tripler will have a modulation index of
Options
A.
m
f
B. 3
m
f
C.
m
f
/3
D.
m
f
/9
Correct Answer
3
m
f
Explanation
Frequency multiplier increase the deviation,
.
More questions
1. A certain sound has 10000 times more energy than another sound. The number of times it would sound stronger to a listener is
Options
A. 40
B. 10000
C. 100
D. 10
Show Answer
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Discuss
Correct Answer: 40
2. A single phase half wave rectifier circuit has a free wheeling diode. The free wheeling diode will conduct only if
Options
A. load is purely resistive
B. load is purely inductive
C. load is combination of R and L
D. load is purely inductive or combination of R and L
Show Answer
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Correct Answer: load is purely inductive or combination of R and L
3. In thermal ohm's law, temperature and power loss are analogous to
Options
A. V and I respectively of ohm's law
B. I and V respectively of ohm's law
C. R and V respectively of ohm's law
D. I and R respectively of ohm's law
Show Answer
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Correct Answer: I and V respectively of ohm's law
4. In a 3 phase bridge inverter with 180° mode of operation the numbers of thyristors conducting at one time are
Options
A. 1
B. 2
C. 3
D. 4
Show Answer
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Discuss
Correct Answer: 3
5. In integral cycle control of ac regulators, the period of integral cycle control,
i
.
e
., (
m
+
n
) T should be
Options
A. less than mechanical or thermal time constant of the system
B. more than the mechanical or thermal time constant of the system
C. more or less than the mechanical or thermal time constant
D. very high
Show Answer
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Discuss
Correct Answer: less than mechanical or thermal time constant of the system
6. The electric dipole moment of a neutral system of point charges Q
1
, Q
2
.... is
Q
i
r
i
. The charges Q
i
Options
A. must be all positive
B. must be all negative
C. must be such that
Q
i
= 0
D. either (a) or (b)
Show Answer
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Discuss
Correct Answer: must be such that
Q
i
= 0
Explanation:
The system is neutral and hence sum is zero.
7. An n pulse rectifier is fed by a source having an inductance L. If load current is I
0
, the voltage drop due to overlap is
Options
A.
B.
C.
D.
Show Answer
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Correct Answer:
8. In a 3 phase full converter, the instantaneous output voltage can have negative part if
Options
A. firing angle is less than 60°
B. firing angle is less than 90°
C. firing angle is more than 60°
D. firing angle is more than 90°
Show Answer
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Correct Answer: firing angle is more than 60°
9. In a 3 phase full converter, the firing angle is less than 60°. The instantaneous output voltage
Options
A. will have positive part only
B. will have both positive and negative parts
C. may have both positive and negative parts
D. will have negative part if load is inductive
Show Answer
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Correct Answer: will have positive part only
10. At present, the radio-frequency band mainly used by most satellites is
Options
A. EHF
B. UHF
C. VHF
D. SHF
Show Answer
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Discuss
Correct Answer: SHF
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