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- Question
Figure shows a chopper feeding RLE load, The free wheeling diode conducts when
Options- A. thyristor is on
- B. thyristor is off
- C. both when thyristor is on and thyristor is off
- D. partly when thyristor is off and partly when thyristor is on
- Correct Answer
- thyristor is off
ExplanationFD is forward biased only when thyristor is off.
More questions
- 1. India's first three-axis stabilised geostationary communication satellite is
Options- A. Rohini
- B. Aryabhatta
- C. Apple
- D. Bhaskara Discuss
Correct Answer: Apple
- 2. Match the following:
List I List II A. RF amplifier 1. Amplifier received carrier and sidebands B. Loudspeaker 2. Gives acoustic output C. Demodulator 3. Has IF input and AF output D. IF amplifier 4. Fixed-tuned to intermediate frequency
Options- A. A-1, B-2, C-3, D-4
- B. A-2, B-1, C-3, D-4
- C. A-3, B-4, C-1, D-2
- D. A-1, B-4, C-3, D-2 Discuss
Correct Answer: A-1, B-2, C-3, D-4
- 3. A line of characteristic impedance 400 ? is terminated by a resistance of 400 ?. The reflected quantities are
Options- A. zero
- B. equal to incident quantities
- C. half the incident quantities
- D. double the incident quantities Discuss
Correct Answer: zero
- 4. In a degenerate n type semiconductor material, the Fermi level,
Options- A. is in valence band
- B. is in conduction band
- C. is at the centre in between valence and conduction bands
- D. is very near valence band Discuss
Correct Answer: is in conduction band
Explanation:
This is due to high level of doping.- 5. Assertion (A): A backward wave oscillator can be used as a sweep generator.
Reason (R): The frequency of oscillation of a backward wave oscillator can be changed by varying the voltage which controls the beam velocity.
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
Correct Answer: Both A and R are correct and R is correct explanation of A
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.
- 6. Assertion (A): A backward wave oscillator has an internal positive feedback.
Reason (R): A positive feedback is necessary for sustained oscillations.
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
Correct Answer: Both A and R are correct but R is not correct explanation of A
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.
- 7. VSWR = Emax/Emin.
Options- A. True
- B. False Discuss
Correct Answer: True
- 8. Assertion (A): Klystron amplifiers use one or more intermediate cavities in addition to buncher and catcher cavity.
Reason (R): When one or more intermediate cavities are used the bandwidth can be increased.
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
Correct Answer: Both A and R are correct and R is correct explanation of A
Explanation:
A Klystron is a vacuum tube used for generation/amplification of microwaves.An electron beam is produced by oxide coated indirectly heated cathode and is focussed and accelerated by focussing electrode.
This beam is transmitted through a glass tube. The input cavity where the beam enters the glass tube is called buncher.
As electrons move ahead they see an accelerating field for half cycle and retarding field for the other half cycle.
Therefore, some electrons are accelerated and some are retarded. This process is called velocity modulation.
The velocity modulation causes bunching of electrons. This bunching effect converts velocity modulation into density modulation of beam.
The input is fed at buncher cavity and output is taken at catcher cavity.
In a two cavity klystron only buncher and catcher cavity are used. In multi cavity klystron one or more intermediate cavities are also used.
The features of a multicavity klystron are :
1. Frequency range - 0.25 GHz to 100 GHz
2. Power output - 10 kW to several hundred kW
3. Power gain - 60 dB (nominal value)
4. Efficiency - about 40%.
A multicavity klystron is used in UHF TV transmitters, Radar transmitter and satellite communication.
- 9. Assertion (A): Impatt diode can be used in both amplifiers and oscillators.
Reason (R): Impatt diode has a low resistance.
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
Correct Answer: Both A and R are correct but R is not correct explanation of A
Explanation:
An Impatt diode has n+ - p - i - p + structure and is used with reverse bias.It exhibits negative resistance and operates on the principle of avalanche breakdown.
Impatt diode circuits are classified as broadly tunable circuit, low Q circuit and high Q circuit.
The impedance of Impatt diode is a few ohms. The word Impatt stands for Impact Avalanche Transit Time diode.
The features of Impatt diode oscillator are : frequency 1 to 300 GHz, Power output (0.5 W to 5 W for single diode circuit and upto 40 W for combination of several diodes), efficiency about 20%.
Its applications include police radar systems, low power microwave transmitter etc.
- 10. Match the following:
List I (Roots in s plane) List II (Impulse response) A. Two imaginary roots 1. 
B. Two complex roots in right half plane 2. 
C. A single root on negative real axis 3. 
D. A single root at origin 4. 
Options- A. A-2, B-3, C-1, D-4
- B. A-1, B-2, C-3, D-4
- C. A-4, B-3, C-2, D-1
- D. A-3, B-2, C-4, D-1 Discuss
Correct Answer: A-2, B-3, C-1, D-4
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