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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 1
11.
A 400 W carrier is amplitude modulated with m = 0.75. The total power in AM is
400 W
512 W
588 W
650 W
Answer: Option
Explanation:

.

12.
c(t) and m(t) are used to generate an FM signal. If the peak frequency deviation of the generated FM signal is three times the transmission bandwidth of the AM signal, then the coefficient of the term cos [2p(1008 x 103t)] in the FM signal (in terms of the Bessel Coefficients) is
5 J4(3)
J8(3)
J8(4)
5 J4(6)
Answer: Option
Explanation:

As, we known FM, s(t)

Frequency deviation = 3 . (AM Bandwidth) = 6 fm

and β= 6 is given in (d) only.

ωc + n ωm = (1008 x 103)2p

2p x 106 + n. 4p x 103 = (1008 x 103).2p

n = 4

So, β = 6, n = 4 hence answer is 5j4(6).

13.
Non-coherently detection is not possible for
PSK
ASK
FSK
both (a) and (c)
Answer: Option
Explanation:
No answer description is available. Let's discuss.
14.
Tracking of extra terrestrial objects requires
high transmitting power
very sensitive receiver
fully steerable antenna
all of the above
Answer: Option
Explanation:

All the three are required.

15.

Assertion (A): Free space does not interfere with normal radiation and propagation of radio waves

Reason (R): Free space has no magnetic or gravitational fields.

Both A and R are correct and R is correct explanation of A
Both A and R are correct but R is not correct explanation of A
A is correct but R is wrong
A is wrong but R is correct
Answer: Option
Explanation:

Since free space does not have magnetic and other fields, waves can propagate without any interference.

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