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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 3
36.
In a tape recorder the output from RF oscillator is given to
only erase head coil
only record head coil
coils of both erase head and record head
none of the above
Answer: Option
Explanation:

RF waves (about 75 kHz frequency) are fed to erase head for erasing.

37.
A + 1.9 lens has a focal length of 25 mm. The diameter of lens is about
13 mm
1.3 mm
130 mm
none of the above
Answer: Option
Explanation:

.

38.
Which of the following terms are applicable to troposcatter propagation?
Faradays rotation
SIOs
Fading
Atmospheric storms
Answer: Option
Explanation:

Tropospheric scatter propagation is subject to two types of fading called Rayleigh fading (due to multipath propagation) and fading due to variations in atmospheric conditions along the propagation path.

39.
If the amplitude of the voltage is kept constant, but its frequency is raised to 6 kHz, the new deviation will be for the modulation index is, if fm = 500 Hz, Δf = 2.25
6 kHz
12 kHz
27 kHz
54 kHz
Answer: Option
Explanation:

Δf = β x fm 4.5 x 6 kHz 27 kHz.

40.
In TV scanning sequence of lines is
left to right
right to left
left to right for odd fields and right to left for even field
left to right for even fields and right to left for odd field
Answer: Option
Explanation:

Scanning is always from left to right.

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