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  • Question

  • In a TWT the axial component of electric field advances along the tube


  • Options
  • A. at a velocity that is almost equal to speed of light
  • B. at a velocity that is a small fraction of speed of light
  • C. at a velocity that is about 50% of speed of light
  • D. at a velocity that may be even more than speed of light

  • Correct Answer
  • at a velocity that is a small fraction of speed of light 

    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. In communication satellites, the up-link normally operates at a higher frequency than the down-link because it

    • Options
    • A. gives a narrow beam shining into space
    • B. results in lesser signal attenuation
    • C. gives better beam-shaping
    • D. is easier to polarize a high frequency beam
      • Discuss
    • 2. The action of backward wave oscillator is similar to that of

    • Options
    • A. klystron amplifier
    • B. reflex klystron oscillator
    • C. TWT
    • D. magnetron
      • Discuss
    • 3. A thyristor has a maximum allowable junction temperature of 120°C and the ambient temperature is 40°C. If thermal resistance is 1.6° C/W, the maximum allowable internal power dissipation is

    • Options
    • A. 20 W
    • B. 50 W
    • C. 92 W
    • D. 128 W
      • Discuss
    • 4. The speed at which axial electric field due to signal advances in a TWT is equal to

    • Options
    • A. speed of light
    • B. (speed of light) (helix pitch helix circumference)
    • C. (speed of light) (helix circumference helix pitch)
    • D. (speed of light) (helix pitch) (helix circumference)
      • Discuss
    • 5. Match the following:

      List I (Transducer) List II (Quantity measured)
      A. LVDT 1. Pressure
      B. Bourden gauge 2. Temperature
      C. Strain gauge 3. Displacement
      D. Thermistor 4. Stress


    • Options
    • A. A-4, B-3, C-2, D-1
    • B. A-3, B-2, C-1, D-4
    • C. A-4, B-1, C-3, D-2
    • D. A-3, B-1, C-4, D-2
      • Discuss
    • 6. Assertion (A): If an electron having charge e is revolving in an orbit of radius R and with angular velocity ?, the magnetic dipole moment of orbit is 0.5 e?R2.

      Reason (R): Orbital angular momentum and magnetic dipole moment are always equal.


    • 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): Resistivity of a perfect single crystal of a metal goes to zero as T approaches zero.

      Reason (R): Scattering of electrons is due to deviations from perfect periodicity of lattice.


    • 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): Hall effect is used to determine whether the semi- conductor is p or n type.

      Reason (R): Under the influence of field, holes and electrons move in opposite direction.


    • 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
    • 9. Match the following:

      List I (Operator) List II (Description)
      A. & & 1. Assignment
      B. | | 2. Logical AND
      C. = 3. Logical OR


    • Options
    • A. A-1, B-2, C-3
    • B. A-2, B-3, C-1
    • C. A-3, B-2, C-1
    • D. A-1, B-3, C-2
      • Discuss
    • 10. Which of the following is a computer language?

    • Options
    • A. MS WORD
    • B. Page maker
    • C. MS EXCEL
    • D. LISP
      • Discuss

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