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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 7
26.
Compact discs use
magnetic recording and retrieval
optical recording and retrieval
optical recording but magnetic retrieval
magnetic recording but optical retrieval
Answer: Option
Explanation:

CD uses optical recording and retrieval.

27.
A carrier is phase modulated (PM) with frequency deviation of 10 kHz by a single tone frequency of 1 kHz. If the single tone frequency is increased to 2 kHz, assuming that phase deviation remains unchanged, the bandwidth of the PM signal is
21 kHz
22 kHz
42 kHz
44 kHz
Answer: Option
Explanation:

Frequency deviation = 10 kHz, fm = 1 kHz

2(fm + Df)

Bandwidth = 22 kHz

2(10 + 1) 22 kHz

fm is doubled

Hence 22 x 2 44 kHz bandwidth.

28.
In a communication receiver, a squelch circuit is normally inserted
before detector
after detector
before mixer
after power amplifier
Answer: Option
Explanation:

Squelch, i.e., muting is added after detector to suppress noise when no carrier is present at input.

29.
In PCM, the information lies
in one or two properties of the pulse
in absence of pulse
in presence of pulse
in presence or absence of pulse
Answer: Option
Explanation:

Depending on which logic is used.

30.
A carrier is simultaneously modulated by two sine waves having modulation indices of 0.4 and 0.3. The total modulation index will be
0.1
0.7
0.5
0.35
Answer: Option
Explanation:

m1= 0.4, m2 = 0.3 .

.

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