ISRO Placement Paper Contributed by Nithi updated on Mar 2019

                                    ISRO Scientist Engineer Model Paper

Electronics & Communication Engineering

1. A unit step voltage travels from left to right along an infinite transmission line. It hits an inductive discontinuity at t=0. What will be the waveform immediately to the left of the discontinuity?
a) Positive spike on a unit step 
b) Unit step with reduced rise time
c) Attenuated unit step 
d) Magnified unit step

2. A lossy open stub having a length of 1/32 wavelength, is approximately equivalent to
a) A small capacitor in shunt with a small resistor
b) A small capacitor in shunt with a large resistor
c) A small inductor in shunt with a small resistor
d) A large inductor in shunt with a large resistor

3. Ampere's law relates
a) Electric field and Charge 
b) Electric field and Current
c) Magnetic field and Current 
d) Magnetic field and Charge

4. Across which type of boundary does the electric field have a continuous tangential component?
a) Charge free boundary 
b) Current free boundary
c) Any boundary 
d) Charged boundary

5. A CMOS digital circuit consumes P watts of dynamic power while operating at 20 MHz clock frequency and 5V supply. What will be its dynamic power consumption if the clock frequency is increased to 40 MHz and supply voltage is decreased to 2.5V?
a) P/4 
b) P/2 
c) P 
d) 2P

6. A communication channel with Additive White Gaussian Noise, has a bandwidth of 4 kHz and SNR of 31dB. Its channel capacity is
a) 1.6 kbps 
b)20 kbps 
c) 32 kbps 
d) 256 kbps

7. If the total power of an amplitude modulated signal is 600W and the carrier power is 400W, the modulation index is
a) 0.75 
b) 0.5 
c) 0.25 
d) 1

8. What is the advantage of Offset QPSK (OQPSK) compared to conventional QPSK?
a) Constant envelope 
b) Bandwidth efficiency
c) Simple demodulator 
d) All of above

9. An angle modulated signal with carrier frequency co = 2ir x 10' is described by the equation s(t) = 10 cos (o)pt + 5 sin(3000nt) + 10 sin(20007tt) ). What is the frequency deviation of ?
a) 12387.32 Hz 
b) 17500 Hz 
c) 20000 Hz 
d) 15000 Hz

10. The Fourier transform of a signal x(t) = e 41tl is
a) 8/(16 + cot) 
b) -8I(16 - cot)
c) 4 /(16 + (ot) 
d) -4/(16 + (02)

11. For a particular toroidal inductor core, the inductance value obtained for 50 Turns is 200µH. If two such inductors are wired in parallel, the resulting inductance is
a) 200µH 
b) 50µH 
c) 400µH 
d) 100µH

12. The magnetic equivalent of Ohm's Law is
a) Lenz's Law 
b) Faraday's Law
c) Rowland's Law 
d) Maxwell's Law

13. A coaxial transmission line carrying an RF signal is perfectly matched to the load. Consider the cross-section of the line, at a plane where the instantaneous voltage is at its maximum value. How will the curl of the E-field vary over this cross-section? 
a) Increases from the center to the outer conductor 
b) Decreases from the center to the outer conductor 
c) Zero everywhere 
d) Constant value proportional to the RF voltage 

14. Which mode of a circular waveguide will have the lowest attenuation?
a) TE11 Mode 
b) TM01 Mode 
c) TE21 Mode 
d) TE01 Mode

15. A signal with two frequency components at 6 kHz and 12 kHz, is sampled at the rate of 16 kHz and then passed through a Low Pass filter having a cut-off frequency of 16 kHz. The output signal of the filter 
a) is an undistorted version of the original signal 
b) contains the 6 kHz component and a spurious component of 4 kHz c) contains only the 6 kHz components 
d) contains both the components of the original signal and two spurious components 
of 4 kHz and 6 kHz 

16. What is the greatest allowable PRF for unambiguous reception in a radar having a maximum range of 120 km?
a) 1250 pps 
b) 2500 pps 
c) 1200 pps 
d) 5000 pps

17. A microprocessor has a cache memory with access time of 2 ns and a main memory with access time of 10 ns. If the cache miss ratio is 0.6, what is the average memory access time?
a)6.8ns 
b)6ns 
c)5.2ns 
d)12ns

18. A zero memory source emits six messages with probabilities 0.3, 0.25, 0.15, 0.12, 0.1and 0.08. If binary Huffman coding is used, what will be the average code length?
a) 2.45 bits 
b) 3.45 bits 
c) 2.54 bits 
d) 3.54 bits

19. A sample and hold amplifier is connected to an ADC. The acquisition time of the sample and hold amplifier is 10 µsec and the conversion time of the ADC is 15 µsec.What is the highest possible data rate?
a) 100 ksamples 
b) 400 ksamples 
c) 40 ksamples 
d) 66 ksamples

20. In an inverting OP-AMP, the input bias current is -1µA, and the input and the feedback resistances are both 1MG. What will be the output voltage for an input voltage of 2.5V?
a)-2.5V 
b) -3.OV 
c) -3.5V 
d) 4.O V

21. Which of the following devices can be used for generating a PWM signal?
a) Comparator 
b) 555 timer
c) Counter and magnitude comparator 
d) All the above

22. A microwave receiving antenna on a satellite is pointing towards the earth. The antenna beamwidth is 50 degrees. The earth subtends 5 degrees at the satellite. What will be the noise temperature of the antenna?
a) 30 degrees Kelvin 
b) 5 degrees Kelvin
c) 300 degrees Kelvin 
d) 1000 degrees Kelvin

23. The electric field measured in the far field of an antenna at a distance of 50m is 1V/m. The average power density at a distance of 500m from the antenna is
a) 26.6µW/m2 
b) 0.1µW/m2 
c) 10µW/m2 
d) 13.3µW/m2

24. A quarter wave monopole antenna is situated above a perfectly conducting ground plane. It is driven by a 50V source at 500MHz through an internal impedance of 63.512. The average power radiated by the antenna is
a) 39.37W/m2 
b) 4.56W/m2 
c) 68.49W/m2 
d) 45.6W/m2

25. Directional derivative of U=2x3y-3y2z at P(1,2,-1) in a direction towards Q(3,-1,5) is
a) -90/7 
b) 30/7 
c) 90/49 
d) None of the above

26. Consider the equation Re(1/z)=c, where z is a complex number, c is a nonzero constant and Re() represents the real part. The equation describes a
a) Straight line 
b) Parabola 
c) Circle 
d) None of the above

27. How many adders are required to realize a 256 point radix-2 FFT using decimation-in-time?
a) 256 
b) 1024 
c) 4096 
d) 2048

28. A sine wave is applied to a balanced modulator. The peak output envelope power is 1000 times the minimum output envelope power. Estimate the carrier suppression in dBc.
a) 24 dBc 
b) 30 dBc 
c) 36 dBc 
d) 40 dBc

29. Consider a single error correcting (7, 4) cyclic code with generator matrix g(x) = x3 +x2+1. What will be the transmitted data if received vector r is 1101101?
a) 1100 
b) 1010 
c) 0001 
d) 1110

30. Consider a Golay's (23,12) code with t bits of error correction capability. For what value oft will the code exactly satisfy the Hamming bound ?
a)2 
b)3 
c)4 
d)5

31. The maximum range of a monostatic Radar is R. If a target having a Radar cross-section of 10m2 exists at R/2, what should be the target cross-section at 3R/2 to result in an equal signal strength at the Radar?
a) 90m2 
b) 270W/m2 
c) 810m2 
d) 30W/m2

32. The electric field intensity at a distance of 10km from an antenna having a directive gain of 10dB and radiating a total power of 60kW is
a) 0.6V/m 
b) 1.2V/m 
c) 0.36V/m 
d) 13.3µW/m2

33. What is the characteristic impedance of a coaxial transmission line having inner conductor radius of 1mm, outer conductor radius of 2mm and dielectric constant of 4.0?
a) 50 ohm 
b) 60 ohm 
c) 20.62 ohm 
d) none

34. An impedance of -10 - j2 ohms is connected to another impedance of 45 + j5 ohms through a transmission line having a characteristic impedance of 50 ohms. Assess the stability of this circuit.
a) Highly stable
b) Stability cannot be determined from the given information
c) Highly unstable
d) Marginally unstable

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