Placement Papers: Indian Airforce Oct 2008

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Indian Airforce

Branch: Electronics and Communications Time: 20min

  1. In a communication system, noise is most likely to get into the system

    1. At the transmitter

    2. In the channel

    3. In the information source

    4. At the destination

  2. When modulation frequency is doubled, the modulation index is halved, and the modulating voltage remains constant, the modulation system is

    1. Amplitude modulation

    2. Phase modulation

    3. Frequency modulation

    4. Angle modulation

  3. Impedance inversion may be obtained with

    1. A short circuited stub

    2. An open circuited stub

    3. A quarter wave line

    4. A half wave line

  4. HIGH frequency waves are

    1. Observed by the F2 layer

    2. Reflected by D layer

    3. Capable of use for long-distance communication on the moon

    4. Affected by the solar cycle

  5. Which one of the following terms does not apply to the Yagi-uda array?

    1. Good band width

    2. Parasitic elements

    3. Folded dipole

    4. High gain

  6. A duplexer is used

    1. To couple two different antennae to a transmitter without mutual interference

    2. To allow one antenna to be used for reception or transmission without mutual interference

    3. To prevent interference between two antennae when they are connected to receiver

    4. To increase the speed of the pulses in the pulsed radar

  7. Indicate which of the following system is digital

    1. Pulse Position modulation

    2. Pulse Code modulation

    3. Pulse Width modulation

    4. Pulse Frequency modulation

  8. A forward error correcting code corrects errors only

    1. Requiring partial retransmission of the signal

    2. Requiring retransmission of entire signal

    3. Using parity to correct to errors in all cases

    4. Requiring no part of the signal to be transmitted

  9. A typical signal strength received from a geosynchronous communication satellite is of the order of

    1. A few milli watts

    2. Kilo watts

    3. Watts

    4. Few pico watts

  10. Telephone traffic is measured

    1. With echo cancellers

    2. By the relative congestion

    3. In terms of the grade of service

    4. In erlangs

  11. Positive logic in a logic circuit is one in which

    1. Logic 0 and 1 are represented by 0 and positive voltage respectively

    2. Logic 0 and 1 are represented by negative and positive voltages respectively

    3. Logic 0 voltage level in higher than logic 1 voltage level

    4. Logic 0 voltage level is lower than logic 1 voltage level

  12. A half-adder can be made from

    1. Two NAND gates

    2. A NOT gate and an OR gate

    3. An AND gate and an OR gate

    4. An AND gate and an X-OR gate

  13. Which of the following devices has its characteristics very close to that of an ideal current source?

    1. Field effect transistor

    2. Transistor in common bas mode

    3. Zener diode

    4. MOSFET

  14. The main use of a common base transistor amplifier is

    1. As voltage amplifier

    2. Current amplifier

    3. For matching a high source impedance to a low load impedance

    4. For rectification of a. c. Signal

  15. A class-B amplifier is biased

    1. Just at cut-off

    2. Nearly twice cut-off

    3. At mid point of load line

    4. so that IB equals jut IC

  16. If the peak transmitted power in a radar system is increased by a factor of 16, the maximum range will be increased by a factor of

    1. 2

    2. 4

    3. 8

    4. 16

  17. A high PRF will (indicate the false statement)

    1. Make the returned echoes easier to distinguish from noise

    2. Make target tracking easier with conical scanning

    3. Increase the maximum range

    4. Have no effect of the range resolution

  18. A solution to the blind speed problem in a radar system is to

    1. Change the Doppler frequency

    2. Vary the PRF

    3. Use mono pulse

    4. Use MTI

  19. The number of active picture elements in a television image depends on

    1. Fly back time

    2. CRT screen size

    3. Received band width

    4. FB ratio of receiver antenna

  20. In a color TV, the three primary colors are

    1. Red, orange and blue

    2. Red, blue and green

    3. Red, green and yellow

    4. Red, orange and green