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21.

A point-to-point communication mode is seen in

satellite cable communication

television transmission

fax transmission

FM radio transmission

22.

If the heights of transmitting and the receiving antennas are each equal to h, the maximum line-of-sight distance between them is (R is the radius of the earth)

$\sqrt{2\mathrm{Rh}}$

$\sqrt{4\mathrm{Rh}}$

$\sqrt{6\mathrm{Rh}}$

$\sqrt{8\mathrm{RH}}$

23.

A repeater is a combination of

receiver and modulator

receiver and transducer

receiver and transmitter

receiver and amplifier

24.

Find the mismatch

Sky wave communication : Frequency upto 30 MHz

Line of sight communication : Frequency greater than 40 MHz

Mobile telephony : Frequency range 800 – 950 kHz

Facsimile : Static document

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25.

A television tower of height 140 m can broadcast its signal upto a maximum area of (Radius of earth = 6.4 x 10^{6} m)

1.56 × 10

^{6}km^{2}5.6 × 10

^{3}km^{2}5.6 × 10

^{10}km^{2}1.56 × 10

^{9}km^{2}

26.

The waves that are bent down by the ionosphere are

ground waves

surface waves

sky waves

space waves

27.

A ground receiver in line-of-sight communication cannot receive direct waves due to

its low frequency

curvature of earth

its high intensity

smaller antenna

28.

In an amplitude modulation with modulation index 0.5, the ratio of the amplitude of the carrier wave to that of the side band in the modulated wave is

4 : 1

1 : 1

1 : 2

2 : 1

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29.

The distance of coverage of a transmitting antenna is 12.8 km. Then, the height of the antenna is (Given that radius of earth = 6400 km)

6.4 m

12.8 m

3.2 m

16 m

30.

If E_{c} = 20 sin 10^{5 }πt and E_{m} = 10 sin 400 πt are carrier and modulating signals, the modulation index is

56 %

30 %

50 %

48 %

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