Electronics and Communication Engineering - Exam Questions Papers

26. 

Figure shows four D type FFs are connected as a shift register using an XOR gate. The initial state and 3 subsequent states for 3 clock pulses are also given


The state QA QB QC QD after the 4th clock pulse is

A. 0000
B. 1111
C. 1001
D. 1000

Answer: Option D

Explanation:

After the 3rd pulse FF3 is 0 and FF4 is 1, so that XOR output is 1 which is fed to DA.

So, QA = 1, QA to QB → 0

AB to AC → 0, QC → QD → 0.


27. 

A rectangular wave guide is designed to propagate at the dominant mode TE10 at a frequency of 5 GHz. The cut-off frequency is 0.8 of signal frequency. The ratio of the guide width to height is 2. The dimensions of the guide are

A. 3.75 cm, 1.875 cm
B. 4 cm, 2 cm
C. 8 cm, 4 cm
D. 2.54 cm, 1.27 cm

Answer: Option A

Explanation:

λc = 2a or

a = 3.75 cm

Also,

.


28. 

In the Taylor series expansion of exp(x) + sin(x) about the point x = p, the coefficient of (x - p)2 is

A. exp (p)
B. 0.5 exp (p)
C. exp (p) + 1
D. exp (p) - 1

Answer: Option B

Explanation:

f(x) = ex + sin x

Coefficient of (x - p)2 = 1 / 2! f''(x)

f'(x) = ex + cos x

f'(x) = ex - sin x

f''(x)|x=p = ep

Thus coefficient of (x - p)2 = 0.5 .


29. 

The Z transform of a particular signal is given as

The practical implementation of the system will be

A. non causal and stable
B. causal and stable
C. unstable and noncausal
D. can't say

Answer: Option B

Explanation:

When get high value at ω = 0, and low value at ω = p, hence we get a low pass filter.

So the system is min-phase causal system. For practical implementation of the system, the system has to be stable.


30. 

If g(t) = e-pt2 then G(1/p) is __________ where g(t) G(f)

A. e-2/p
B. e-1/p
C. e-p
D. e2p

Answer: Option B

Explanation:

The signal g(t) given above is a gaussian pulse and it satisfies the relation

g(t) = - 2pt g(t)

Its fourier transform is same as the signal itself in frequency domain

G(f) = e-pf2

G(1/p) = e-p(1/p)2 = e-1/p.