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Electronics and Communication Engineering - Communication Systems

Exercise : Communication Systems - Section 3
1.
The output resistance of a microphone is 20 ohms. It is to feed a line of impedance 320 ohms. To ensure maximum power transfer, the turn ratio of transformer is
16
256
2
4
Answer: Option
Explanation:

(20)(4)2 = 320 ohms.

2.
In a reactance FET, gm = 9 x 10-3 Siemens, gate to source resistance is one-ninth of reactance of gate to drain capacitor and frequency is 4 MHz. The capacitive-reactance is
1000 Ω
1/1000 Ω
36 x 103 Ω
x 103 Ω
Answer: Option
Explanation:

.

3.
Audio cassettes used in household tape recorders have a width of
1"
1/2"
1/4"
1/8"
Answer: Option
Explanation:

Home tape recorders use in (i.e., 6.3 mm) tape having two tracks of 2.5 mm width each with an in between separation of 1.3 mm.

4.
The receiver of a pulsed RADAR can detect signal power in the order of
1 W
0.1 W
10-5 W
10-12 W
Answer: Option
Explanation:

It can detect very low power signals.

5.
In a 100% amplitude modulated signal, the power in the upper sideband when carrier power is to be 100 W and modulation system SSBSC, is
100 W
66 W
50 W
25 W
Answer: Option
Explanation:

Modulation index = 100% 1

Pc = 100 W

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