Name the type of waves which are used for line of sight (LOS) communication. What is the range of their frequencies?
A transmitting antenna at the top of a tower has a height of 20 m and the height of the receiving antenna is 45 m. Calculate the maximum distance between them for satisfactory communication in LOS mode. (Radius of the Earth = 6.4 × 106 m)
Types of waves are:
i) space waves
ii) radio waves
iii) microwave
The frequency range for LOS communication is 40 MHz.
Given,
Height of the transmitting antenna, h = 20 m
Height of receiving antenna = 45 m
So, the maximum distance between transmitting antenna and receiving antenna is given by,
The decimal number equivalent to a binary number 1011001 is
13
17
89
178
C.
89
Given, binary number = 1011001
Its equivalent decimal number
= 2° + 0 + 0 + 23 + 24 + 26
= 1 + 8 + 16 + 64
= 89
The decimal equivalent of the binary number (11010.101)2 is
9.625
25.265
26.625
26.265
C.
26.625
The decimal equivalent can be found as follows,
(11010.101)2 = 0 × 20 + 1 × 21 + 0 × 22 + 1 × 23 + 1 × 24 + 1 × 2-1 + 0 × 2-2 + 1 × 2-3
= 0 + 2 + 0 + 8 + 16 + + 0 +
= 26 + = ≈ 26.625
In the block diagram of a simple modulator for obtaining an AM signal, shown in the figure, identify the boxes A and B. Write their functions. 
In the block diagram,
A is the square law device- This is a non-linear device and produces a non-linear output of message and carrier signals.
B is the band pass filter and it rejects high and low frequencies. It allows only a band of frequencies to pass through.
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