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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 6
41.
In the television system in India, the aspect ratio is
4 : 3
3 : 4
5 : 4
4 : 5
Answer: Option
Explanation:

Aspect ratio is the width/height ratio of TV receiver. It is .

42.
In high power radars, which of the following are used for switching?
Power diode
Power BJT
Power MOSFET
Thyristor
Answer: Option
Explanation:

For high power switching thyristor is the most suitable device.

43.
A remote control for TV uses
LED in receiver and photodiode in transmitter
LED in transmitter and photodiode in receiver
LED in both transmitter and receiver
Photodiode in both transmitter and receiver
Answer: Option
Explanation:

Infrared LED transmits the pulse. At receiver photo diode converts infrared signals into electrical signals.

44.
In the FM wave described by equation v = 15 sin (4 x 108 t + 3 sin 1100 t), the carrier frequency and signal frequency respectively are
63.66 MHz and 175 Hz
4 x 108 Hz and 1100 Hz
175 Hz and 63.66 MHz
1100 Hz and 4 x 108 Hz
Answer: Option
Explanation:

.

45.
A sequence x(n) with the z transform X(z) = z4 + z2 - 2z + 2 - 3z - 4 is applied as an input to a linear, time invariant system with the impulse response h(n) = 2δ(n - 3) where

The output at n = 4 is
- 6
zero
2
- 4
Answer: Option
Explanation:

Y(Z) = X(Z) x H(Z)

= 2 x (Z4 + Z2 - 2Z + 2) x Z-3

Y(n) = 2[δ(n + 1) - δ(n - 1) - 2(n - 2) + 2δ(n - 3) - 3δ(n - 7)]

at n = 4, Y(4) = 0.

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