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  • Question

  • Which of the following devices uses a helix?


  • Options
  • A. Klystron amplifier
  • B. Klystron oscillator
  • C. TWT
  • D. Both (a) and (b)

  • Correct Answer
  • TWT 

    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. Match the following:

      List I (Digital circuit) List II (Circuit type)
      A. BCD to 7 segment decoder 1. sequential circuit
      B. 4-to-1 MUX 2. combinational circuit
      C. 4 bit shift register 3. neither sequential nor combinational circuit


    • Options
    • A. A-2, B-1, C-2, D-1
    • B. A-3, B-2, C-1, D-3
    • C. A-2, B-2, C-1, D-1
    • D. A-3, B-1, C-2, D-3
      • Discuss
    • 2. Match the following:

      List I List II
      A. PMMC 1. Square law type scale
      B. Moving iron 2. Very good response
      C. Thermo-couple 3. Linear scale
      D. Electrostatic 4. Voltmeter


    • Options
    • A. A-4, B-1, C-2, D-3
    • B. A-3, B-2, C-1, D-4
    • C. A-4, B-2, C-1, D-3
    • D. A-3, B-1, C-2, D-4
      • Discuss
    • 3. Assertion (A): A high dv/dt may cause triggering of a thyristor.

      Reason (R): A high dv/dt results in charging current in the thyristor.


    • 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
    • 4. The factor ? for a UJT is about

    • Options
    • A. 0.1
    • B. 0.2
    • C. 0.6
    • D. 0.9
      • Discuss
    • 5. Assertion (A): In some materials, ?r is independent of temperature while in others, ?r depends on temperature.

      Reason (R): If permanent dipoles are absent, ?r varies with temperature.


    • Options
    • A. Both A and R are true and R is correct explanation of A
    • B. Both A and R are true but R is not correct explanation of A
    • C. A is true but R is false
    • D. A is false but R is true
      • Discuss
    • 6. Assertion (A): CO2 has no resultant dipole moment but CO has a dipole moment.

      Reason (R): The structure of CO2 is O = C = O.


    • Options
    • A. Both A and R are true and R is correct explanation of A
    • B. Both A and R are true but R is not correct explanation of A
    • C. A is true but R is false
    • D. A is false but R is true
      • Discuss
    • 7. Assertion (A): In Figure, the intercept of the line on y-axis is equal to N (ae + ai), where N is number of atoms/m3, ae is electronic polarizability and ai is ionic polarizability.

      Reason (R): ae and ai are independent of temperature.


    • Options
    • A. Both A and R are true and R is correct explanation of A
    • B. Both A and R are true but R is not correct explanation of A
    • C. A is true but R is false
    • D. A is false but R is true
      • Discuss
    • 8. Assertion (A): The circuit of figure thyristor will conduct for 180° during positive half cycle if it is continuously fired.

      Reason (R): A thyristor can conduct only when it is forward biased.


    • 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
    • 9. Assertion (A): In ionic dielectrics, P = Pe + Pi.

      Reason (R): In ionic crystals, permanent electric dipole moment is zero.


    • Options
    • A. Both A and R are true and R is correct explanation of A
    • B. Both A and R are true but R is not correct explanation of A
    • C. A is true but R is false
    • D. A is false but R is true
      • Discuss
    • 10. Assertion (A): The condition of minimum distortion in a transmission line is L = RC/G.

      Reason (R): Line loading means addition of inductance to satisfy the condition L = RC/G.


    • Options
    • A. Both A and R are correct and R is correct explanation of A
    • B. Both A and R are 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

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