# Electronics and Communication Engineering - Communication Systems

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

 A. 16 B. 256 C. 2 D. 4

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

 A. 1000 Ω B. 1/1000 Ω C. 36 x 103 Ω D. x 103 Ω

Explanation:

.

3.

Audio cassettes used in household tape recorders have a width of

 A. 1" B. 1/2" C. 1/4" D. 1/8"

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

 A. 1 W B. 0.1 W C. 10-5 W D. 10-12 W

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

 A. 100 W B. 66 W C. 50 W D. 25 W

Explanation:

Modulation index = 100% 1

Pc = 100 W