  # ISRO Scientist or Engineer Electronics 2018

Instructions

For the following questions answer them individually

Question 1

# The circuit shown in the fig. below is a: ($$A_1 \& A_2$$ are ideal op-amps) Question 2

# Determine the change in collector current, $$\triangle I_c$$ due to change in base emitter voltage $$V_{BE}$$ 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 $$T = 100^\circ C. V_{BE} = 0.5 V)$$  Question 3

# An antenna is fed with $$200 \pi W$$ power. The efficiency of the antenna is 75%. If the radiation pattern of the antenna is$$P(\theta, \phi) = \sin^2 \theta \times \sin^2 \phi$$ for $$0 \leq \phi \leq \pi$$ (elevation angle). = 0 elsewhereFind the radiation intensity in the direction of maximum radiation 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). Question 5

# Identify A and B current limiting techniques in a.c. to d.c. power supplies respectively, in the graph below.  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 $$\sigma_{A \mu} = 4e 7$$ Siemens/meter at cavity operating temperature. Question 7

# A steady state is achieved in following Network at t = 0, find the time when $$V_{c(t)}$$ will be maximum  Question 8

# Y-parameter for following network is given as  Question 9

# A satellite transmits signals at a frequency of 6 GHz to a user 40000 km away. The free space pathloss incurredby the signal is nearly : Question 10

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