# Online Electronics and Communication Engineering Test - Previous Exam Papers Test 2

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.

In a radar system, the range of R1 is achieved at a frequency f1. Then the range R2 at frequency R2 = 8f1 would be __________ [Neglect effect of 1 on the Beam width.]

A.
 R2 = R1
B.
 R2 = 4R1
C.
 R2 = 2R1
D.
 R2 =

Explanation:

The range of the radar is directly proportional to the square root of the frequency.

R ∝

R1

and R2

.

2.

Find Y- parameters

A.
B.
C.
D.
 None of these

Explanation:

Apply Nodal Analysis

At node V

...(i)

At node V2

...(ii)

At node V3

Put V3 in equation (i)

Put V3 in equation (ii)

.

3.

Power gain of antenna equals directive gain in VHF and UHF range if and only if efficiency of the antenna is __________ .

A.
 0.25
B.
 0.5
C.
 0.75
D.
 1

Explanation:

Directive gain and power gain are identical except that power gain takes into account the antenna losses. It may be written as

Gp = ηGd η => efficiency

If η = 1 , GP = Gd .

4.

For the given phase lead network, the maximum possible phase lead is

A.
 sin-1
B.
 30°
C.
 45°
D.
 60°

Explanation:

The maximum phase lead is given by,

sin φm =

Where

Hence sin φm =

Hence φm = 30°.

5.

The region between a pin of parallel perfectly conducting planes of infinite extent is y and z directions is partially filled with a dielectric as shown below.

A 30 GHz TE10 wave is incident on the air-dielectric interface. The VSWR at the interface is

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

Explanation:

.

6.

Time domain equivalent circuit of the figure is

A.
B.
C.
D.
 None of the above

Explanation:

In the left hand loop (- i1) enters the dot end while for the right handed loop i2 enters the dot end.

This will make both the M terms at first of + ve sign but as i1 = - ve hence ultimately the M term of right hand loop involving i1 = - ve.

V1 = - L1 + M

V2 = L2 - M .

7.

A transmitted using AM has in modulated carrier output power of 10 KW and can be modulated to a maximum depth of 90% by a sinusoidal modulating voltage without causing overloading. Find the value to which an modulated carrier power can be increased without resulting in overloading if the maximum permitted modulating index is 40%

A.
 14 KW
B.
 12.96 KW
C.
 26.96 KW
D.
 2.96 KW

Explanation:

Now PT is fixed, μ = 0.4

Then PC is PC =

8.

A signal with ± 10 V ranged and 1 KHz band width is being digitized using a sample and hold circuit and a 10 bit quantizer. The quantization step is :

A.
 1 x 10-9 V
B.
 5 x 10-9 V
C.
 2.5 x 10-9 V
D.
 0.5 x 10-9 V

Explanation:

Quantization step = .

9.

The circuit I in figure is

A.
 1 mA
B.
 4 mA
C.
 8 mA
D.
 10 mA

Explanation:

Current in the circuit is

[2 v at '+' terminal and '-' terminal will be same].

10.

The equivalent form of the logical expression (ABC + ABC + ABC + ABC + ABC) is:

A.
 C + (A ⊕ B)
B.
 (A + B + C)(A + B + C)
C.
 (A + B + C)(A + B + C)(A + B + C)
D.
 (A + B + C)(A + B + C)(A + B + C)

Explanation:

K-map for the expression:

11.

For a binary symmetric channel, the error probability Pc(0) = Pc(1) = and errors are statistically independent. The channel capacity for a signalling speed 2 bits/second.

A.
 2 bits/sec
B.
 1.69 bits/sec
C.
 4 bits/sec
D.
 1 bit/sec

Explanation:

C = r . H

r = 2 bits/second

C = 2 bits/second.

12.

Which of the following statements about the matched filter in a communication receiver are correct?

1. Its impulse response depends on the signed shape
2. It maximizes the SNR at the detection shape.
3. It produces ISI.
4. It may produce phase error if synchronization is improper.
Select the correct answer from the codes given below:

A.
 1 and 4 only
B.
 1 and 2 only
C.
 2, 3 and 4
D.
 1, 2 and 4

13.

The output of a Mealy system is 1 if there has been a pattern of 11000, otherwise 0. The minimum state for this system is :

A.
 4
B.
 5
C.
 6
D.
 7

14.

Consider the following circuit using an ideal OP-AMP. The I-V characteristics of the diode is described by the relation where VT = 25mV, I0 = 1mA and V is the voltage across the diode (taken as positive for forward bias). For an input voltage V1 = - 1 V, the output voltage V0 is

A.
 0 V
B.
 0.1 V
C.
 0.7 V
D.
 1.1 V

15.

What is the purpose of DMA facility in microprocessor based system?

A.
 To increase the speed of data transfer between the mP and the I/O devices
B.
 To increase the speed of data transfer between the mP and the memory
C.
 To increase the speed of data transfer between the memory and the I/O devices
D.
 To improve the reliability of the system

16.

An 8085 executes the following instructions`2710 LXI H, 30A0H2713 DAD H2714 PCHL`
All addresses and constants are in Hex. Let PC be the contents of the program counter and HL be the contents of the HL register pair just after executing PCHL.
Which of the following statements is correct?

A.
 PC = 2715 H HL = 30A0 H
B.
 PC = 30A0H HL = 2715H
C.
 PC = 6104 H HL = 6140 H
D.
 PC = 6140H HL = 2715H

17.

The spectral range of a band pass signal extends from 10 MHz to 10.4 MHz. What is the minimum sampling frequency required for reconstruction?

A.
 20 MHz
B.
 20.8 MHz
C.
 20.4 MHz
D.
 0.8 MHz

18.

The maximum positive and negative numbers which can be represented in 2's complement form using n bits are respectively

A.
 +(2n + 1 - 1), - (2n - 1 - 1)
B.
 +(2n + 1 - 1), - 2n - 1
C.
 +2n - 1, - 2n - 1
D.
 +2n + 1, - (2n - 1 + 1)

19.

Which of the following are universal gates?

1. NAND
2. NOR
3. XOR
Select the correct answer from the codes given below:

A.
 1 and 2 only
B.
 1 and 3 only
C.
 2 and 3 only
D.
 1, 2 and 3

20.

The Nyquist plot of a stable, transfer function G(s) is shown in the figure. We are interested in the stability of the closed loop system in the feedback configuration shown.

Which of the following statements is true?

A.
 G(s) is an all-pass filter
B.
 G(s) has a zero in the right-half plane
C.
 G(s) is the impedance of a passive network
D.
 G(s) is marginally stable