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  • Question

  • The frequency of oscillation in a backward wave oscillator can be changed by


  • Options
  • A. varying the voltage which controls beam velocity
  • B. varying the beam current
  • C. both by varying the beam current and by light varying the voltage which controls beam velocity
  • D. changing the rate of thermionic emission

  • Correct Answer
  • varying the voltage which controls beam velocity 

    Explanation
    It is somewhat similar to TWT and can deliver microwave power over a wide frequency band.

    It has an electron gun and a helix structure. However the interaction between electron beam and RF wave is different than in TWT.

    The growing RF wave travels in opposite direction to the electron beam.

    The frequency of wave can be changed by changing the voltage which controls the beam velocity.

    Moreover the amplitude of oscillations can be decreased continuously to zero by changing the beam current.

    It features are:

    1. Frequency range - 1 GHz to 1000 GHz.

    2. Power output - 10 mV to 150 mW (continuous wave) 250kW (pulsed).

    It is used as signal source in transmitters and instruments.

    More questions

    • 1. In pulse width modulation of chopper

    • Options
    • A. T is kept constant and Ton is varied
    • B. Ton is kept constant T is varied
    • C. both T and Ton are varied
    • D. either T or Ton is varied
      • Discuss
    • 2. The colour code on a carbon resistor is green-blue-yellow. The tolerance is

    • Options
    • A. ± 5%
    • B. ± 10%
    • C. ± 20%
    • D. ± 30%
      • Discuss
    • 3. Wave guides are pressurised above normal atmospheric pressure for

    • Options
    • A. increasing the power handling capacity
    • B. improving conductivity of walls
    • C. preventing higher modes from propagation
    • D. varying the wave impedance
      • Discuss
    • 4. A transmission line discontinuity is defined as any interruption in the uniformity of the line.

    • Options
    • A. True
    • B. False
      • Discuss
    • 5. Which of the following is not a valid variable name in C?

    • Options
    • A. 1 a
    • B. a 1 2
    • C. a b 123
    • D. a b c 123
      • Discuss
    • 6. If an amplifier with gain of - 1000 and feedback factor ? = - 0.1 had a gain change of 20% due to temperature, the change in gain of the feedback amplifier would be

    • Options
    • A. 10%
    • B. 5%
    • C. 0.2%
    • D. 0.01%
      • Discuss
    • 7. Permeability is analogous to

    • Options
    • A. resistivity
    • B. retentivity
    • C. conductivity
    • D. coercivity
      • Discuss
    • 8. In a Gunn diode oscillator drift velocity of electron is 107 cm/s and active region length is 10 x 10-4 cm. The natural frequency of oscillation is

    • Options
    • A. 1 MHz
    • B. 10 MHz
    • C. 1 GHz
    • D. 10 GHz
      • Discuss
    • 9. A cycloconverter is a group of controlled rectifiers.

    • Options
    • A. True
    • B. False
      • Discuss
    • 10. If the valence electron is separated from a copper atom, the remaining part of atom has a net charge of

    • Options
    • A. 1
    • B. - 1
    • C. 0
    • D. + 3
      • Discuss

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