Communication Systems Test

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Communication Systems Test - 1

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Weekly Quiz Competition

Question 1
4 / -1

The characteristic impedance of a coaxial wire line is of order

A
1000 ohm

B
200 ohm

C
30 ohm

D
80 ohm

Solution

For a coaxial cable with air dielectric and a shield of a given inner diameter, the attenuation is minimized by choosing the diameter of the inner conductor to give a characteristic impedance of 76.7 Ω. When more common dielectrics are considered, the best-loss impedance drops down to a value between 52–64 Ω.
Question 2
4 / -1

In which manner does current or voltage vary in an analog signal with time?

A
not a fixed pattern

B
discontinuously

C
sometime continuously and sometime discontinuously

D
continuously

Solution

An analog signal is any continuous signal for which the time-varying feature (variable) of the signal is a representation of some other time-varying quantity, i.e., analogous to another time-varying signal. For example, in an analog audio signal, the instantaneous voltage of the signal varies continuously with the pressure of the sound waves. It differs from a digital signal, in which the continuous quantity is a representation of a sequence of discrete values which can only take on one of a finite number of values.
Question 3
4 / -1

If an antenna radiates electromagnetic waves from a height h, then the range d upto which the signal can be detected is given by (R is the radius of the earth)

A
d = √2RH

B
d = 2Rlh

C
d = 2Rl√h

D
d = 2Rh

Solution

Let O be the centre and R is the radius of the earth. PQ is a T.V. antenna of height h. Two tangents QT and QS are drawn from the top Q of the tower. T.V. signal can reach to the point S and T only not at other area:
∠QTO=90[TO⊥QT]
In ΔQTO,
OQ2=OT2+TQ2
OQ=R+h, QT=d, OT=R,
(R+h)2=R2+d2
R2+h2+2Rh=R2+d2
d2=h2+2Rh h⋘R neglect
d2=2Rh
d= √2Rh
Question 4
4 / -1

Super high frequencies of __________ are used in Radar and Satellite Communication.

A
2000 to 25000 MHz

B
3000 to 30000 MHz

C
1000 to 10000 MHz

D
5000 to 30000 MHz

Solution

Super high frequency (SHF) is the ITU designation for radio frequencies (RF) in the range between 3 and 30 gigahertz (GHz). This band of frequencies is also known as the centimetre band or centimetre wave as the wavelengths range from one to ten centimetres.
Question 5
4 / -1

The bandwidth sufficient for commercial telephonic communication:

A
700 Hz

B
2800 Hz

C
1400 Hz

D
300 Hz

Solution

For speech signals (as in telephone) frequency range 300 Hz- 3100 Hz is adequate i.e., a speech signal requires a bandwidth of 2800 Hz.
Question 6
4 / -1

Optical communication using fibres is performed in the frequency range of

A
few kHz

B
54-72 MHz

C
1THz to 1000 THz

D
30-40 MHz

Solution

Optical communication using fibers is performed in the frequency range of 1 THz to 1000 THz (microwaves to ultraviolet). An optical fiber can offer a transmission bandwidth in excess of 100 GHz.
Question 7
4 / -1

Modes of communication system are classified into :

A
Line communication and space communication

B
Space communication and Digital communication

C
Point to point communication and broadcast communication

D
Line communication and analog communication
Question 8
4 / -1

If the area of a TV telecast is to be doubled, then height of transmitting antenna will have to be

A
doubled

B
halved

C
unchanged

D
quadrupled

Solution

Distance of receiving antenna a from transmitting antenna is d = √(2Rh) i.e. d ∝ √h area covered ∝ d2 that is area covered ∝ h. Hence if the area is double, the height of the antenna will also be doubled.
Question 9
4 / -1

With the increase in frequencies more than 2 MHz, Ground wave propagation

A
Increases

B
Fails

C
Does not depend on the frequency of propagation

D
None of the above

Solution

The ground wave is the preferred propagation type for long distance communication using frequencies below 3 MHz (the earth behaves as a conductor for all frequencies below 5 MHz). The ground wave is also used for short distance communications using frequencies between 3 and 30 MHz.
Question 10
4 / -1

What should be the approximate height of antenna if the TV telecast is to cover a radius of 100 km?

A
128 m

B
78 m

C
781 m

D
1280 m

Solution

Here , d=100km=100×10³m,
R=6.4×10⁶m
d=√2Rh
or h=d²/2R=(100×10³)²/2×6.4×10⁶=781.25m

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Re-Attempt Weekly Quiz Competition

Communication Systems Test - 1

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Communication Systems Test - 1

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SHARING IS CARING

Question 1

1000 ohm

200 ohm

30 ohm

80 ohm

Solution

Question 2

not a fixed pattern

discontinuously

sometime continuously and sometime discontinuously

continuously

Solution

Question 3

d = √2RH

d = 2Rlh

d = 2Rl√h

d = 2Rh

Solution

Question 4

2000 to 25000 MHz

3000 to 30000 MHz

1000 to 10000 MHz

5000 to 30000 MHz

Solution

Question 5

700 Hz

2800 Hz

1400 Hz

300 Hz

Solution

Question 6

few kHz

54-72 MHz

1THz to 1000 THz

30-40 MHz

Solution

Question 7

Line communication and space communication

Space communication and Digital communication

Point to point communication and broadcast communication

Line communication and analog communication

Question 8

doubled

halved

unchanged

quadrupled

Solution

Question 9

Increases

Fails

Does not depend on the frequency of propagation

None of the above

Solution

Question 10

128 m

78 m

781 m

1280 m

Solution

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