Which one is the right option: A) Ground waves. B) Sky waves. C) Surface waves. D) Space waves.

Digital signals
(i)    do not provide a continuous set of values,
(ii)    represent values as discrete steps,
(iii)    can utilize binary system, and
(iv)    can utilize decimal as well as binary systems.
Which of the above statements are true?

(i) and (ii) only
(ii) and (iii) only
(i), (ii) and (iii) but not (iv)
All of (i), (ii), (iii) and (iv).

C.

(i), (ii) and (iii) but not (iv)

(c) Reason: Digital signals connot utilise decimal system which represents a continuous set of values.

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A carrier wave of peak voltage 12V is used to transmit a message signal. What should be the peak voltage of the modulating signal in order to have a modulation index of 75%?

Peak voltage, A_c = 12 V

Modulation index = 75 % = 0.75

μ = 0.75 = \frac{A_{m}}{A_{c}}

Hence,

A_{m} = 0.75 A_{c}

\Rightarrow

A_{m} = 0.75 \times 12 V = 9 V is the peak voltage .

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Which of the following frequencies will be suitable for beyond-the-horizon communication using sky waves?

10 kHZ
10 MHz
1 GHz
1000 GHz

A.

10 kHZ

10 kHz cannot be radiated because the size of antenna is large. 1 GHz and 1000 GHz will penetrate.

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Frequencies in the UHF range normally propagate by means of
Ground waves.
Sky waves.
Surface waves.
Space waves.

D.

Space waves.

Reason: Propagation of waves in ultra high frequency range 0.3 - 3 GHz is possible by space waves. Because these waves can reflect from ionosphere.

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Is it necessary for a transmitting antenna to be at the same height as that of the receiving antenna for line-of-sight communication? A TV transmitting antenna is 81 m tall. How much service area can it cover if the receiving antenna is at the ground level?

No. Height of receiving antenna should be LOS of transmitting antenna.