# Electronics and Communication Engineering - Exam Questions Papers

11.

Radiation resistance of an antenna is 54 Ω and loss resistance is 6 Ω. If antenna has power gain of 10, then directivity is:

 A. 9 B. 11.11 C. data not sufficient D. 10

Explanation:

Efficiency of antenna Power gain = 10

Thus directivity .

12.

If the power spectral density of stationary random process is a sine-squared function of frequency, the shape of its autocorrelation is

 A. B. C. D. Explanation:

Since autocorrelation function and power spectral density bears a Fourier transform relation, then since required in frequency domain will five rectangular convolutions in time domain thus it is triangular function.

13.

The inverse of given Laplace transform is  A. sin t B. cos t C. et D. e2t

Explanation: s = x2 - ex x(t) = cos t.

14.

Consider the amplitude modulated (AM) signal Ac cos ωct + 2 cos ωmt cos ωct For demodulating the signal using envelope detector, the minimum value of Ac should be

 A. 2 B. 1 C. 0.5 D. 0

Explanation:

AC cos ωct + 2 cos ωmt cos ωct

AC cosωct for envelope detection μ < 1 ⇒ < 1 ⇒ Ac should be at least-2.

15.

In a 4 bit weighted resistor D/A converter, the resistor value corresponding to LSB is 32 kΩ. The resistor value corresponding to MSB will be

 A. 32 KΩ B. 16 KΩ C. 8 KΩ D. 4 KΩ

Explanation:

2n - 1 R = 32 K&Omeg;

n = 4

⇒ 8R = 32

R = 4 KΩ.