Jkp Constable Telecommunication Telecommunication Mcqs Jkp Constable (1089 MCQs) | JKSSB & SSC Quiz

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Practice Questions

1089 Total
Question 101 Discuss
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A carrier wave of 500 W is subjected to 100% amplitude modulation. What is the power in each sideband?

A
125 W
B
250 W
C
500 W
D
750 W

Answer & Explanation

Correct Option: A

Total power Pt = Pc(1 + m^2/2) = 500(1 + 1/2) = 750 W. Power in both sidebands = 750 - 500 = 250 W. Each sideband = 125 W.
Question 102 Discuss
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Which modulation scheme is characterized by a constant envelope, making it highly resistant to non-linear distortion in power amplifiers?

A
Amplitude Modulation
B
Frequency Modulation
C
Quadrature Amplitude Modulation
D
Single Sideband Suppressed Carrier

Answer & Explanation

Correct Option: B

FM has a constant amplitude envelope, so non-linearities in Class C amplifiers do not distort the information, which is encoded in frequency variations.
Question 103 Discuss
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In an FM system, the frequency deviation is 60 kHz and the maximum modulating frequency is 12 kHz. What is the modulation index?

A
0.2
B
5.0
C
72.0
D
120.0

Answer & Explanation

Correct Option: B

Modulation index (mf) for FM is the ratio of frequency deviation to modulating frequency: 60 kHz / 12 kHz = 5.0.
Question 104 Discuss
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A superheterodyne receiver with an IF of 455 kHz is tuned to receive a 1200 kHz signal. What must be the local oscillator frequency if high-side injection is used?

A
745 kHz
B
1655 kHz
C
2110 kHz
D
2400 kHz

Answer & Explanation

Correct Option: B

In high-side injection, Local Oscillator freq (fLO) = Signal freq (fs) + IF = 1200 + 455 = 1655 kHz.
Question 105 Discuss
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The process of recovering the original modulating signal from a DSB-SC wave requires:

A
An envelope detector
B
A ratio detector
C
A synchronous or coherent detector
D
A Foster-Seeley discriminator

Answer & Explanation

Correct Option: C

DSB-SC has no carrier, so envelope detection fails. It requires coherent detection using a locally generated carrier with exact phase and frequency.
Question 106 Discuss
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What happens to the skip distance of a sky wave if the transmission frequency is increased?

A
It decreases
B
It remains constant
C
It increases
D
It drops to zero

Answer & Explanation

Correct Option: C

Higher frequencies penetrate deeper into the ionosphere before reflecting, resulting in a longer skip distance.
Question 107 Discuss
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Which frequency band is most susceptible to atmospheric absorption caused by water vapor and oxygen?

A
MF
B
VHF
C
UHF
D
EHF (Microwave)

Answer & Explanation

Correct Option: D

Extremely High Frequencies (EHF), especially around 22 GHz and 60 GHz, experience severe attenuation due to water vapor and oxygen molecules.
Question 108 Discuss
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Calculate the critical frequency of an ionospheric layer if its maximum electron density is 10^12 electrons/m^3.

A
3 MHz
B
9 MHz
C
12 MHz
D
81 MHz

Answer & Explanation

Correct Option: B

Critical frequency fc = 9 * sqrt(Nmax). fc = 9 * sqrt(10^12) = 9 * 10^6 Hz = 9 MHz.
Question 109 Discuss
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In a television transmitter, audio is typically modulated using which technique?

A
Amplitude Modulation (AM)
B
Frequency Modulation (FM)
C
Vestigial Sideband (VSB)
D
Phase Modulation (PM)

Answer & Explanation

Correct Option: B

In standard analog TV broadcasting, video is transmitted using VSB (a form of AM) while audio is transmitted using FM for better noise immunity.
Question 110 Discuss
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The 'front porch' and 'back porch' in a composite video signal are parts of the:

A
Vertical synchronizing pulse
B
Horizontal blanking pedestal
C
Color burst signal
D
Active video line

Answer & Explanation

Correct Option: B

The front and back porches sit at the blanking level before and after the horizontal sync pulse, ensuring the electron beam is fully suppressed during retrace.
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