ISRO Electronics & Communication (ECE) 2018 Question Paper & Solutions

Question 1

The circuit shown in the fig. below is a: (A1 & A2 are ideal op-amps)

Accepted Answer

Antilog Amplifier

Answer

Logarithmic Multiplier

Answer

Logarithmic Amplifier

Answer

None of the above

Question 2

Determine the change in collector current, $\Delta I_c$ due to change in base emitter voltage VBE from $25^{\circ}C$ to $100^{\circ}C$ for a Silicon Transistor in Fixed Bias Configuration having $\beta=100$. (Consider following variation in Silicon transistor parameters with temperature- At $T=25^{\circ}C$ $V_{BE}=0.65$ V and At $T=100^{\circ}C$ $V_{BE}=0.5~V)$ $R_B=250k\Omega$ $V_{cc}=10V$ $R_c=1 k\Omega$

Accepted Answer

$60~\mu A$

Answer

$30~\mu A$

Answer

$15~\mu A$

Answer

$120~\mu A$

Question 3

An antenna is fed with 200 W power. The efficiency of the antenna is 75%. If the radiation pattern of the antenna is $P(	heta,\phi)=\sin^2	heta	imes \sin^2\phi$ for $0\le	heta\le\pi$ (azimuth angle) and $0\le\phi\le\pi$ (elevation angle). $=0$ elsewhere. Find the radiation intensity in the direction of maximum radiation

Accepted Answer

225 W/steradian

Answer

150 $\pi$ W/steradian

Answer

200 W/steradian

Answer

250 W/steradian

Question 4

A reflex klystron is oscillating at 10GHz when operated in $2\frac{3}{4}$ mode, find the transit time of the electron in repeller space in nano seconds (ns).

Accepted Answer

0.275

Answer

0.25

Answer

0.036

Answer

0.55

Question 5

Identify A and B current limiting techniques in a.c. to d.c. power supplies respectively, in the graph below. (Graph shows curve A bending back towards origin, curve B dropping vertically at Rated Current)

Accepted Answer

Re-entrant limiting Mode, Current limiting Mode

Answer

Current limiting Mode, Constant Current Mode

Answer

Current limiting Mode, Fold back limiting Mode

Answer

Fold back limiting Mode, Re-entrant limiting Mode

Question 6

A Gold cavity resonator resonating at 10 GHz is fully coated using $2~\mu m$ YBCO (Yttrium Barium Copper Oxide) material and operating at boiling temperature of liquid nitrogen. What is the Skin Depth of RF at this frequency? Assume $\sigma_{Au}=4e7~	ext{Siemens/meter}$ at cavity operating temperature.

Accepted Answer

$(2.5/\pi)\mu m$

Answer

$2~\mu m$

Answer

$0~\mu m$

Answer

None of the above

Question 7

A steady state is achieved in following Network at $t=0$, find the time when $Vc(t)$ will be maximum

Accepted Answer

$ln(9)^{0.125}$ sec

Answer

$ln(9)$ sec

Answer

$ln(9)^{0.25}$ sec

Answer

9 sec

Question 8

Y-parameter for following network is given as

Accepted Answer

$\begin{bmatrix}\frac{9(2s+1)}{8}&\frac{-3(2s+1)}{8}\ \frac{9(2s+1)}{8}&\frac{9(2s+1)}{8}\end{bmatrix}$

Answer

$\begin{bmatrix}\frac{9(s+1)}{8}&\frac{-3(2s+2)}{8}\ \frac{-3(2s+2)}{8}&\frac{9(s+1)}{8}\end{bmatrix}$

Answer

$\begin{bmatrix}\frac{9(2s+1)}{8}&\frac{-3(2s+1)}{16}\ \frac{9(2s+1)}{16}&\frac{9(2s+1)}{8}\end{bmatrix}$

Answer

$\begin{bmatrix}\frac{9(s+1)}{8}&\frac{-3(2s+1)}{8}\ \frac{-3(2s+1)}{8}&\frac{9(s+1)}{8}\end{bmatrix}$

Question 9

A satellite transmits signals at a frequency of 6 GHz to a user 40000 km away. The free space path loss incurred by the signal is nearly:

Accepted Answer

200 dB

Answer

100 dB

Answer

150 dB

Answer

300 dB

Question 10

The satellite communication link between two point is established with uplink carrier-to-noise ratio of 20 dB and downlink carrier to noise ratio of 14 dB. The overall C/N is close to:

Accepted Answer

13 dB

Answer

34 dB

Answer

6 dB

Answer

13.5 dB

Question 11

A system generates data at a rate of 5 Mbps. In order to provide resistance to bit errors, a rate $1/2$ error correcting code is applied. Further, the data is mapped to a 16-QAM constellation. What is the resulting symbol rate?

Accepted Answer

2.5 Msps

Answer

1.25 Msps

Answer

5 Msps

Answer

10 Msps

Question 12

Consider a binary linear code with parity check matrix H given below.
$H=\begin{bmatrix}0&1&1&1&0&0\ 1&0&1&0&1&0\ 1&1&0&0&0&1\end{bmatrix}$
Which of the following is a valid codeword?

Accepted Answer

[110110]

Answer

[100101]

Answer

[111101]

Answer

[010010]

Question 13

The minimum distance of a (n,k)=(7,4) linear block code is upper bounded by:

Accepted Answer

4

Answer

1

Answer

2

Answer

3

Question 14

Consider a 4-PSK constellation with points $\{\sqrt{2}, j\sqrt{2}, -\sqrt{2}, -j\sqrt{2}\}$ and a 4-PAM constellation $\{-3, -1, 1, 3\}$. If all the points in the constellation occur with equal probability, the ratio of average energy of 4-PAM signal to that of 4-PSK signal is:

Accepted Answer

2.5

Answer

1

Answer

1.25

Answer

5

Question 15

Difference in number of complex multiplier required for 16 point DFT and 16-point radix-2 FFT is

Accepted Answer

224

Answer

30

Answer

63

Answer

256

Question 16

No of stages(S) in direct form FIR filter is given as $S=$ integer $(K*F_s/\Delta f)$ Where Fs = Sampling Frequency, $\Delta f=$ Filter transition band, $K=3$ (assume). If $x(n)$ is signal with frequency range 0-2.4 MHz and sampled at $F_s=400$ MHz and it is filtered by ... $x(n) \rightarrow LPF(1) \rightarrow$ Decimation by 50 $\rightarrow LPF(2) \rightarrow$ Decimation by 2 $\rightarrow Y_{Filter}(n)$. Assumptions: Both filters are having flat passbands and stopbands. Passband Frequency LPF(1): 1.8 MHz, Stopband Frequency LPF(1): 4 MHz. Passband Frequency LPF(2): 1.8 MHz, Stopband Frequency LPF(2): 2 MHz. Passband attenuation of both filters = 0 dB and stop band attenuation of both filters is infinity. Calculate total no. of stages $S_{LPF1}+S_{LPF2}$

Accepted Answer

665

Answer

120

Answer

545

Answer

555

Question 17

Difference in dynamic range of 32-bit binary number(B) and floating point number(F) is? Standard Format for B and F as given below:
$B=$ Bit 31 Sign Bit, Bit 30-Bit0 Magnitude
$F=$ Bit 31 Sign Bit, Bit 30-Bit23 Exponent, Bit 22-Bit0 fraction

Accepted Answer

$6.02(2^7-31)$ dB

Answer

$6.02(2^7-30)$ dB

Answer

$6.02 (2^8-31)$ dB

Answer

$6.02(2^8-30)$ dB

Question 18

If Sys clock frequency is > 4 * clk_ext frequency. What is the functionality of above circuit? (Circuit shows D1 clocking clk_ext on Sys Clock, passing to D2, then D3. Output $Q_{out}$ is AND of Q2 and NOT(Q3))

Accepted Answer

Rising Edge detector with Pulse width of $Q_{out}=$ one cycle of Sys clk

Answer

Falling Edge detector with Pulse width of $Q_{out}=$ one cycle of Sys clk

Answer

Falling Edge detector with Pulse width of $Q_{out}=$ one cycle of clk_ext

Answer

Rising Edge detector with Pulse width of $Q_{out}=$ one cycle of clk_ext

Question 19

Simplify the Boolean expression: $F(w,x,y,z)=\Sigma(0,1,2,4,5,6,8,9,12,13,14)$

Accepted Answer

$y'+w'z'+xz'$

Answer

$w+x+y+z$

Answer

$y+w'z'+xz$

Answer

$x+z'w'y+x'$

Question 20

High State noise margin of standard TTL and 5V CMOS logic gate are

Accepted Answer

0.4V, 1V

Answer

0.4V, 0.4V

Answer

1V, 0.4V

Answer

1V, 1V

Question 21

Determine the Voltage transfer characteristics of the following circuit comprising of Zener diodes having identical characteristics with Zener Breakdown voltage $V_z$ and Diode cut-in voltage $V_T$. (Circuit shows two Zener diodes connected back-to-back in series with a resistor R)

Accepted Answer

Graph showing clipping at $(V_z+V_T)$ and $-(V_z+V_T)$

Answer

Graph showing clipping at $(V_z-V_T)$ and $-(V_z-V_T)$

Answer

Graph showing clipping at $V_z$ and $-V_z$

Answer

Graph showing clipping at $(V_z-V_T)$ and $-(V_z-V_T)$ but asymmetrical

Question 22

Two resistances of values 20Ω and 40Ω made of different materials with temperature coefficients of resistance $3~ppm/^{\circ}C$ and $6~ppm/^{\circ}C$ respectively are connected in series. What is the temperature coefficient of resistance of the net resistance?

Accepted Answer

$5~ppm/^{\circ}C$

Answer

$\sqrt{18}ppm/^{\circ}C$

Answer

$9ppm/^{\circ}C$

Answer

$4.5~ppm/^{\circ}C$

Question 23

Which of the following semiconductor compound is not used in the construction of Light Emitting Diodes?

Accepted Answer

GaSe

Answer

GaAs

Answer

GaP

Answer

GaN

Question 24

An LC tank circuit resonates at a frequency 'fr'. If the temperature coefficient of permittivity of the dielectric material used in the Capacitance is $6ppm/^{\circ}C$, then what is the temperature coefficient of frequency

Accepted Answer

$-3~ppm/^{\circ}C$

Answer

$-6~ppm/^{\circ}C$

Answer

$3~ppm/^{\circ}C$

Answer

$6ppm/^{\circ}C$

Question 25

To avoid difficulties with strapping at high frequencies, the type of cavity structure used in the magnetron is,

Accepted Answer

Rising-Sun

Answer

Hole and Slot

Answer

Slot only

Answer

Vane

Question 26

The transmit time in the repeller space of a reflex klystron must be $(n+3/4)$ cycles to ensure that,

Accepted Answer

Returning electrons give energy to the gap oscillations

Answer

Electrons are accelerated by the gap voltage on their return

Answer

It is equal to the period of the cavity oscillations

Answer

The repeller is not damaged by striking electrons

Question 27

For a circuit given in figure, switch K is closed to position 1 at $t=0$. After $t=1 TC$ (Time Constant), switch is moved to position 2. Find The Current I at $1TC(-)$ (just before one-time constant time) and $1TC(+)$ (just after one-time constant time) respectively (assume $1/e\approx0.37$)
(Position 1 connects 20V, Position 2 connects 40V, R = $500\Omega$, C = $0.5\mu F$)

Accepted Answer

0.0148 A and 0.055 A

Answer

0.0148 A and -0.055 A

Answer

0.0296 A and 0.11 A

Answer

0.0296 A and -0.11 A

Question 28

For a network shown in figure, which of the following statement is true. (Circuit has dependent current source $\beta I_1$)

Accepted Answer

Neither symmetric nor reciprocal

Answer

Reciprocal and symmetric

Answer

Reciprocal but not-symmetric

Answer

Symmetric but non-reciprocal

Question 29

Pair of differential equations that describes motion of planet about sun using first two laws of Kepler is given as:

Accepted Answer

$2\dot{r}\dot{	heta}+r\dot{	heta}=0$ and $\dot{r}+r\dot{	heta}^2(r\frac{a}{b^2}-1)=0$

Answer

$2\dot{r}\dot{	heta}+r\dot{	heta}=0$ and $\dot{r}+r\dot{	heta}^2(r\frac{a}{b^2}+1)=0$

Answer

$2\dot{r}\dot{	heta}-r\dot{	heta}=0$ and $\dot{r}-r\dot{	heta}^2(r\frac{a}{b^2}-1)=0$

Answer

$2\dot{r}\dot{	heta}-r\dot{	heta}=0$ and $\dot{r}-r\dot{	heta}^2(r\frac{a}{b^2}+1)=0$

Question 30

Two communication antennas A and B, one operating at 300 MHz and other at 3 GHz respectively and having same gain, are illuminated with identical flux density of $-100~dBW/m^2$. What is the relation between the received powers $(P_A:P_B)$?

Accepted Answer

100:1

Answer

1:10

Answer

10:1

Answer

1:100

Question 31

Consider identical four, 3-faced dice. When the dice are rolled, the faces of the dice appear with probabilities given below. Which distribution has the maximum entropy?

Accepted Answer

(1/3, 1/3, 1/3)

Answer

(1/2, 1/4, 1/4)

Answer

(1/6, 2/3, 1/6)

Answer

(1/4, 1/6, 7/12)

Question 32

If System 1 and 2 are Linear Time Invariant systems and same input $x(n)$ is provided both configuration.
Statement 1: $y_1(n)=y_2(n)$
Statement 2: $f(n)=g(n)$

Accepted Answer

Statement 1 is always true

Answer

Statement 2 is always true

Answer

Both Statement 1 and Statement 2 are always true

Answer

Both Statement 1 and statement 2 are not true

Question 33

Benefit(s) of Bandpass sampling over low pass sampling

Accepted Answer

It reduces speed requirement of A/D convertor

Answer

Increase the amount of digital memory necessary to capture a given interval of signal

Answer

Both (a) and (b) are correct

Answer

Both (a) and (b) are incorrect

Question 34

For a signal with $F_c$ (Centre Frequency) = 1200 MHz and BW = 100 MHz which of the following Sampling frequency ($F_s$) will cause spectrum inversion:

Accepted Answer

1600 MHz

Answer

287.5 MHz

Answer

575 MHz

Answer

1150 MHz

Question 35

If $x_{in}(t)=\sin(2*\pi*4000*t)+0.75*\sin(2*\pi*5000*t+\pi/4)$ is sampled with $F_s=16000Hz$ calculate $X(0)$ if $X(m)=\sum_{n=0}^{N-1}x(n)e^{-j2\pi mn/N}$ When N=8, where $x(n)=x_{in}(nT_s)$

Accepted Answer

0.0 - j 0.0

Answer

0.0 - j 4.0

Answer

1.414 + j 1.414

Answer

0.0 + j 4.0

Question 36

The Above Verilog/ VHDL module depicts which sequential element:

Accepted Answer

Rising edge Flip-flop with synchronous Reset

Answer

Falling edge Flip-Flop with synchronous Reset

Answer

Rising edge Flip-flop with asynchronous Reset

Answer

Falling edge Flip-Flop with asynchronous Reset

Question 37

An ideal p-n junction diode in series with a 100 $\Omega$ resistance is forward biased such that the forward current flowing through the diode is 100 mA. If voltage across this circuit is instantaneously reversed to 20 V at time instant $t=t_0$, then the reverse current flowing through the diode at time instant $t=t_0$ is approximately given by

Accepted Answer

200 mA

Answer

0 mA

Answer

100 mA

Answer

2 mA

Question 38

Determine output voltage 'Vo' for below circuit where $V_{in}=	ext{Sin}(100\pi t)$

Accepted Answer

2 Cos (100\pi t) (as visually deduced from standard pairs, text partially obscured)

Answer

2 Sin (100\pi t)

Answer

Sin (200\pi t)

Answer

0.5 Sin (100\pi t)

Question 39

Determine the channel half-width for an n-channel silicon FET having Gate-to-Source voltage, $V_{GS}=V_P/4$, where $V_P$ is the Pinch-off voltage and drain current, $I_d=0$. (Consider Donor Concentration $N_D=10^{15}	ext{ electrons}/cm^3$ and Channel half-width for $V_{GS}=0	ext{ V is } 3\mu m$).

Accepted Answer

$1.5\mu m$

Answer

$2.25\mu m$

Answer

$3 \mu m$

Answer

$0.75 \mu m$

Question 40

Design a single section, quarter wave impedance transformer at 5 GHz from $3.75~cm	imes 2$ cm guide to $3.75~cm	imes 1$ cm guide. Assume air filled wave guide with transformer section having same width as that of the input and output sections.

Accepted Answer

Height = 1.414 cm, Length=2.5 cm

Answer

Height=1.414 cm, Length=3 cm

Answer

Height=1.5 cm, Length=2.5 cm

Answer

Height=1.5 cm, Length=3 cm

Question 41

A four port directional coupler has 4:1 power splitting ratio and has dissipation loss of 3dB. The coupler directivity is 40dB. What fraction of input power P1 will go to ports P2 and P3?

Accepted Answer

$P2=0.4	imes P1$, $P3=0.1	imes P1$

Answer

$P2=0.8	imes P1$, $P3=0.2	imes P1$

Answer

$P2=0.6	imes P1$, $P3=0.15	imes P1$

Answer

$P2=0.1	imes P1$, $P3=0.4	imes P1$

Question 42

A cell phone transmits at a power level of 800 mW with an antenna gain of 3.0 dB. The cell tower has an antenna gain of 10.0 dB and is at a distance of 5 km away. Transmission frequency is 600 MHz. Noise level at Receiver Input is -95 dBm and required Signal to Noise ratio to close the link is 5 dB. Find the link margin in dB. (assume $\pi^2=10)$

Accepted Answer

30 dB

Answer

150 dB

Answer

60 dB

Answer

35 dB

Question 43

What is the value of magnetic flux in Weber, if it is 2000 in Maxwell?

Accepted Answer

$2	imes 10^{-5}$

Answer

$2	imes 10^{-3}$

Answer

$2	imes 10^5$

Answer

$2	imes 10^3$

Question 44

How resistance of Eureka varies with temperature?

Accepted Answer

Remains Constant

Answer

Decreases

Answer

Linearly Increases

Answer

Exponentially increases

Question 45

A resistor $R1=4	ext{ k}\Omega$ is connected across the secondary of transformer for which $L1=0.2H, L2=10H$ and flux coupling coefficient $k=0.5$ Find the peak voltage across resistor R1 when 250V peak voltage at $400	ext{ rad/sec}$ is applied to primary winding of transformer.

Accepted Answer

707 V

Answer

353.55 V

Answer

500 V

Answer

1000 V

Question 46

For a network shown in figure, Calculate current i2.

Accepted Answer

2/3 A

Answer

3/2 A

Answer

1/3 A

Answer

None of the above

Question 47

For a network shown in figure, a steady state is reached with switch k is open. Switch is closed at time t=0, Calculate $(di_1/dt)$ and $(di_2/dt)$ at $t=0+$

Accepted Answer

16.67 A/sec and $-4.16	imes10^4 A/sec$

Answer

16.67 A/sec and $-3.33	imes10^4 A/sec$

Answer

25 A/sec and $-4.16	imes10^4 A/sec$

Answer

25 A/sec and $-3.33	imes10^4 A/sec$

Question 48

Signal flow diagram of following analog computer circuit is

Accepted Answer

Graph with nodes A, s^2y, sy, y and input -7

Answer

Graph with nodes A, s^2y, sy, y and feedbacks 2, 3, 4

Answer

Graph with nodes A, s^2y, sy, y and feedbacks -2, 3, 4

Answer

Graph with nodes A, -s^2y, -sy, y

Question 49

Find the variance of the distribution shown in the figure.

Accepted Answer

$\frac{\Delta^2}{12}$

Answer

$\frac{\Delta^2}{2}$

Answer

$\frac{\Delta^2}{8}$

Answer

$\frac{\Delta^2}{4}$

Question 50

Fourier transform of $te^{-\alpha t}u(t)$, (where, $\alpha>0$, $u(t)$ is the Unit step function) is:

Accepted Answer

$\frac{1}{(\alpha+j2\pi f)^2}$

Answer

$\frac{\alpha}{(\alpha+j2\pi f)^2}$

Answer

$j\frac{dX(\omega)}{d\omega}$

Answer

$\frac{\alpha}{(\alpha+j2\pi f)}$

Question 51

Consider waveforms $\cos(2\pi f_1t+	heta)$ and $\cos(2\pi f_2t)$, $(f_1>f_2)$, to be used for non-coherent binary FSK signalling. If the symbol duration is T seconds, and $	heta$ is constant arbitrary angle from 0 to $2\pi$, what is the minimum separation required between $f_1$ and $f_2$ for non-coherent, orthogonal FSK?

Accepted Answer

$f_1-f_2=\frac{1}{T}$

Answer

$f_1-f_2=\frac{2}{T}$

Answer

$f_1-f_2=\frac{1}{4T}$

Answer

$f_1-f_2=\frac{1}{3T}$

Question 52

Let $X(e^{j\omega})=\sum_{n=-\infty}^{\infty}x[n]e^{-j\omega n}$ and $x[n]=\frac{1}{2\pi}\int_{-\pi}^{\pi}X(e^{j\omega})e^{j\omega n}d\omega$. If $X(e^{j\omega})=\frac{1}{(1-0.2e^{-j\omega})(1-0.1e^{-j\omega})}$, what is $x[n]$ in terms of unit discrete step function $u(n)$?

Accepted Answer

$2(0.2)^nu(n)-(0.1)^nu(n)$

Answer

$2(0.1)^nu(n)-(0.2)^nu(n)$

Answer

$(0.2)^nu(n)-(0.1)^nu(n)$

Answer

$(0.1)^nu(n)-(0.2)^nu(n)$

Question 53

What is the content of Accumulator in binary after execution of following 8051 Assembly code:
MOV A, #27H
MOV R1, A
SWAP A
ANL A, # 0FH
MOV B, #10
MUL AB
MOV R2, A
MOV A, R1
ANL A, #0FH
ADD A, R2

Accepted Answer

00100111

Answer

01110010

Answer

01010101

Answer

11001011

Question 54

In a 16-Bit micro-controller if a two-dimensional integer array A[5,7] is stored at base location 0x8000, What is the address of A[4,2]?

Accepted Answer

0x803E

Answer

0x800C

Answer

0x801F

Answer

0x8400

Question 55

Content of variable flag after following 'C' code execution:
Unsigned char flag = 0x7C;
flag = flag | 0x80;
flag = flag | (1<<4);
flag &= ~(1<<7);
flag ^= (1<<6);

Accepted Answer

0x3C

Answer

0x1C

Answer

0x20

Answer

0x24

Question 56

Process P1, P2 and P3 with execution time of 6 ms, 4 ms and 2 ms respectively enter in ready state together in order P1, P2, P3. Calculate the waiting and turnaround time of Process P1. Assuming no wait time due to I/O and round robin scheduling with time slot of 2 ms.

Accepted Answer

6 ms, 12 ms

Answer

6 ms, 10 ms

Answer

4 ms, 4 ms

Answer

4 ms, 6 ms

Question 57

A. HDL Coding/RTL Design
B. Synthesis
C. Static Timing Analysis
D. Place and Route
E. Programming file generation
What is the correct order of FPGA design flow?

Accepted Answer

A,B,D,C,E

Answer

A,B,C,D,E

Answer

B,D,C,E,A

Answer

C,A,D,E,B

Question 58

Electric Field of 1 V/m is applied to a Boron doped Silicon semiconductor slab having doping density of $10^{16}atoms/cm^3$ at 300K temperature. Determine the approximate resistivity of the slab. (Consider intrinsic carrier concentration of Silicon at 300 $K = 1.5	imes10^{10}/cm^3$; Hole Mobility $= 500~cm^2/Vs$ at 300 K; Electron Mobility $= 1300~cm^2/Vs$ at 300 K).

Accepted Answer

1.25 $\Omega$-cm

Answer

0.48 $\Omega$-cm

Answer

0.35 $\Omega$-cm

Answer

0.16 $\Omega$-cm

Question 59

What will be the voltage reading of DC Voltmeter placed across the terminals of the Diode in the circuit below, having the following periodical input signal $V_i(t)$? (Assume cut-in voltage of the Diode = 0 V Forward resistance of the Diode = 2 $\Omega$)

Accepted Answer

2.5 V

Answer

1.25 V

Answer

0 V

Answer

0.1 V

Question 60

A monostatic pulsed radar operating at 30GHz has a transmitter with 2KW O/P power and an antenna with 30dB gain. Minimum detectable signal in the receiver is -100dBm. Determine the maximum range of the radar, if it is required to detect a target having radar cross section of 10sq.m (consider $log_{10}4\pi=1.1$). Assume EM wave propagate under ideal conditions.

Accepted Answer

10 km

Answer

21.5 km

Answer

56 km

Answer

100 km

Question 61

Which of the following statement is not true about delay line cancellers?

Accepted Answer

Time delay in one channel of the delay line canceller is one half of the pulse repetition period

Answer

It eliminates DC components of fixed targets and passes AC components of moving targets

Answer

It is used in moving target indicator radar

Answer

It rejects any moving target whose Doppler frequency happens to be the same as the PRF or a multiple thereof

Question 62

An air filled rectangular waveguide with dimensions $a=75$ mm, $b=37.5$ mm has same guide wavelength at frequencies $f_1$ and $f_2$ when operated at TE10 and TE20 modes respectively. If the frequency $f_1$ is $\sqrt{13}$ GHz, what is frequency $f_2$ in GHz?

Accepted Answer

5

Answer

10

Answer

$\sqrt{13}/2$

Answer

$2\sqrt{13}$

Question 63

A waveguide of dimensions a = 15 mm and $b=7.5$ mm is used as a high-pass filter. If the stop band attenuation required at 8 GHz is ~109.2 dB, what is the length of the filter? (assume conductor losses to be zero, approximate $\pi=3.14$ and 1 Np ~8.69 dB) $(\log_{10}e=0.4343)$

Accepted Answer

100 mm

Answer

869 mm

Answer

86.9 mm

Answer

54.6 mm

Question 64

An RF signal is applied to a $50\Omega$ lossless transmission line which is terminated in a load with impedance, $Z_L=j50\Omega$. The wavelength is 8 cm. Find the position of voltage and current maximum respectively nearest to the load measured from load end?

Accepted Answer

1 cm, 3 cm

Answer

3 cm, 1 cm

Answer

3 cm, 5 cm

Answer

5 cm, 3 cm

ISRO Electronics & Communication (ECE) 2018 Question Paper & Solutions

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