# Online Electronics and Communication Engineering Test - Previous Exam Papers Test 6

Instruction:

• This is a FREE online test. DO NOT pay money to anyone to attend this test.
• Total number of questions : 20.
• Time alloted : 30 minutes.
• Each question carry 1 mark, no negative marks.
• DO NOT refresh the page.
• All the best :-).

1.

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 .

2.

The ratio of the diffusion coefficient in a semiconductor has the units

A.
 V-1
B.
 em.V-1
C.
 V.cm-1
D.
 V.s

Explanation:

.

3.

(2)3 + (3)4 = (?)5

A.
 4
B.
 11
C.
 none of these
D.
 not possible

Explanation:

(2)3 + (3)4 = 2 + 3 = 5 and (10)5 = 51 + 0 = 5

(2)3 + (3)4 = (10)5 .

4.

In the following network, the switch is closed at t = 0- and the sampling starts from t = 0. The sampling frequency is 10Hz.

The expression and the region of convergence of the z-transform of the sampled signal are

A.
 |z| < e-5
B.
 |z| < e-0.05
C.
 |z| < e-0.05
D.
 |z| > e-5

Explanation:

X(Z) = 5.e-0.05n.Z-n

.

5.

In the circuit shown below current through the resistor is shown. Voltage across 4 Ω resistor is:

A.
 8 volt
B.
 ≈ 5.87 V
C.
 ≈ 6.87 V
D.
 None of these

Explanation:

Voltage across 5 Ω = 10 V

Thus voltage across 7 Ω = 10 V (5 Ω || 7 Ω)

6.

The energy of constant-amplitude complex valued exponential sequence is __________ (where A is the constant amplitude)

A.
 0
B.
 1
C.
 ∞
D.
 A2

Explanation:

Let the constant amplitude complex valued exponential sequence.

x(n) = Ae-jωn

Energy = |x(n)|2 = |Ae-jωn|2

A2 |(e-jωn)|2 = A2(∞) = ∞

Hence energy in infinite.

7.

Find Z11,

A.
 2 Ω
B.
 4 Ω
C.
 1 Ω
D.
 Ω

Explanation:

Z11(s) = Z1(s) + Z2(s) = 1 Ω.

8.

Consider the pulse shape s(t) as shown. The impulse response h(t) of the filter matched to this pulse is

A.
B.
C.
D.

Explanation:

h(t) = s(T - t).

9.

If the closed-loop transfer function T(s) of a unity negative feedback system is given by then the steady state error for a unit ramp input is :

A.
B.
C.
D.
 ∞

Explanation:

.

10.

For each of the positive edge-triggered J-K flip flop used in the following figure, the propagation delay is ΔT

Which of the following waveforms correctly represents the output at Q1?

A.
B.
C.
D.

Explanation:

Two JK flip flop. Thus propagation delay will be 2ΔT

Frequency is getting reduced by a factor e.

11.

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

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.

12.

The system shown in figure remains stable when :

A.
 k £ - 1
B.
 -1 < k < 1
C.
 l < k < 3
D.
 k > 3

Explanation:

Pi = 1 x k x s-1 x 1 ⇒

, L2 = k x s-1

System will be stable when k - 3 > 0 or k > 3.

13.

Find Leq if each L is 1 H

A.
 4/3 H
B.
 1/3 H
C.
 2/3 H
D.
 3/2 D

14.

Which of the following transducers requires a high input impedance preamplifier for proper measurements?

A.
 Thermocouple
B.
 Piezoelectric
C.
 Thermistor
D.
 L.V.D.T

15.

Given the transfer function

Polar plot will be of shape.

A.
B.
C.
D.

16.

Which one of the following statements is correct?

A.
 AGC in radio receivers will keep the total signal output fairly constant but the noise component will be reduced; with the result the ratio will improve.
B.
 AGC in radio receivers is a linear operation w.r.t. both signals and noise
C.
 Sudden changes in the output while tuning, which may cause damage to the components, is an unavoidable feature of AGC
D.
 AGC operation is independent of the filter components used in AGC circuit.

17.

A 4 bit shift register is initialized to value 1000 for (Q3, Q2, Q1, Q0). The D input is derived from Q0, Q2 and Q3 through two XOR gates as shown in figure. The pattern 1000 will appear at

A.
 3rd pulse
B.
 7th pulse
C.
 6th pulse
D.
 4th pulse

18.

Transfer function of a certain system is

Which one of the following will be the A, B matrix pair of state variable representation of this system?

A.
B.
C.
D.

19.

Consider the following circuits. Assume all gates to have finite propagation delay

Which of these circuits generate a periodic square wave at the output Vo?

A.
 (1) only
B.
 (1) and (2) only
C.
 (2) (3) and (4) only
D.
 All (1) (2) (3) and (4)

20.

Which of the following is a microwave power amplifier?

A.
 Gunn diode
B.
 Reflex klystron
C.
 Magnetron
D.
 Travelling wave tube