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  • Question

  • In a TWT the amplitude of resultant wave travelling down the helix


  • Options
  • A. increases exponentially
  • B. increases linearly
  • C. decreases exponentially
  • D. is almost constant

  • Correct Answer
  • increases exponentially 

    Explanation
    In a klystron the resonant structure limits the bandwidth.

    A TWT is a broadband device. Its main components are electron gun (to produce the electron beam) and a structure supporting the slow electromagnetic wave.

    The velocity of wave propagation along the helix structure is less than velocity of light.

    The beam and wave travel along the structure at the same speed.

    Thus interaction occurs between beam and wave and the beam delivers energy to the RF wave.

    Therefore the signal gets strengthened and amplified output is delivered at the other end of tube.

    The main features of TWT are :

    1. Frequency range - 0.5 GHz to 90 GHz

    2. Power output - 5 mW at low frequencies(less than 20 GHz) 250 kW (continuous wave) at 3 GHz 10 MW (pulsed) at 3 GHz

    3. Efficiency - about 5 to 20%

    4. Noise - about 5 dB for low power TWT 25 dB for high power TWT

    TWT is used as RF amplifier in broadband microwave receivers, repeater amplifier in broad band communication systems, communication satellites etc.

    More questions

    • 1. As compared to dimensions of most feeds, the skin depth at microwave frequencies is

    • Options
    • A. of the same magnitude
    • B. much larger
    • C. much smaller
    • D. either (b) or (c)
      • Discuss
    • 2. For a 1 cm x 2 cm air filled rectangular waveguide the maximum frequency should be less than about

    • Options
    • A. 1000 MHz
    • B. 5000 MHz
    • C. 14000 MHz
    • D. 140000 MHz
      • Discuss
    • 3. In a radio receiver

    • Options
    • A. all stages contribute equally to noise
    • B. RF stage has no effect on S/N ratio
    • C. mixer stage contributes most of the noise generated
      • Discuss
    • 4. As compared to an ordinary semiconductor diode, a Schottky diode

    • Options
    • A. has higher reverse saturation current
    • B. has higher reverse saturation current and higher cut in voltage
    • C. has higher reverse saturation current and lower cut in voltage
    • D. has lower reverse saturation current and lower cut in voltage
      • Discuss
    • 5. A 3 port circulator is in the given figure. Its scattering matrix is

    • Options
    • A.
    • B.
    • C.
    • D.
      • Discuss
    • 6. The total field developed by an antenna array at a distant point is

    • Options
    • A. phasor sum of fields produced by individual antennas of the array
    • B. algebraic sum of fields produced by individual antennas of the array
    • C. either (a) or (b) depending on type of array
    • D. neither (a) nor (b)
      • Discuss
    • 7. A standard cell of 1.0185 V is used with a slide wire potentiometer. The balance was obtained at 60 cm. When an unknown emf was connected, the balance was obtained at 82 cm. The magnitude of unknown emf is

    • Options
    • A. 1.39 V
    • B. 0.75 V
    • C. 13.9 V
    • D. 7.45 V
      • Discuss
    • 8. The number of valence electrons in donor impurity are

    • Options
    • A. 5
    • B. 4
    • C. 3
    • D. 1
      • Discuss
    • 9. Assertion (A): A DIAC has four layers but only two terminals.

      Reason (R): A DIAC can conduct in both directions.


    • Options
    • A. Both A and R are correct and R is correct explanation of A
    • B. Both A and R correct but R is not correct explanation of A
    • C. A is correct but R is wrong
    • D. A is wrong but R is correct
      • Discuss
    • 10. A NAND gate has 3 inputs and one output. The number of thyristors required for this gate are

    • Options
    • A. 1
    • B. 2
    • C. 3
    • D. 3 or 4
      • Discuss

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