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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 2
36.
If k is dielectric constant of a medium, the velocity factor in that medium is
3
(k)1/3
Answer: Option
Explanation:

.

37.
An AM signal and a narrowband FM signal with identical carriers, modulating signals and modulation index of 0.1 are added together. The resultant signal can be closely approximated by
Broadband FM
SSB with carrier
DSB-SC
SSB without carrier
Answer: Option
Explanation:

s(t)AM + s(t)NBFM = A1 sin ωct + A2 cos ωct + (A - B) m

m(t) sin ωct

it will not be NBFM because μ = 0.1, and SSB with carrier.

38.
The equation v(t) = A cos [ωct + φ(t)] where A and ωc are constant and φ(t) is a function of base signal represents
  1. Phase modulation
  2. Amplitude modulation
  3. Angle modulation
  4. Frequency modulation
Which of the above are true?
3 only
1, 3 and 4
1, 2, 3, 4
3 and 4 only
Answer: Option
Explanation:

This equation can represent frequency, angle and phase modulation.

39.
An FM signal with deviation δ is passed through mixer. Its frequency is reduced five fold. The deviation in output of mixer is
0.28
δ
5 δ
very very high
Answer: Option
Explanation:

Deviation is not affected by mixer.

40.
The total number of channels allotted for cellular telephone is
666
333
221
111
Answer: Option
Explanation:

Cellular telephones have been assigned 666 channels (826 to 845 MHz and 870 to 890 MHz). Each channel has width of 30 kHz.

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