Microwave Communication problems
- 1. In a three cavity klystron amplifier, the oscillations are excited in
Options- A. input cavity
- B. output cavity
- C. intermediate cavity
- D. both (a) and (b) Discuss
Correct Answer: intermediate cavity
Explanation:
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.
- 2. Which of the following lines is non-radiating?
Options- A. Open two wire
- B. Coaxial
- C. Both
- D. None of the above Discuss
Correct Answer: Coaxial
Explanation:
- 3. As the frequency is increased, the charging MVAR in a cable
Options- A. decreases
- B. increases
- C. remain the same
- D. decreases or remains the scheme Discuss
Correct Answer: increases
Explanation:
- 4. A line has Z0 = 300 ? 0° ?. If ZL = 150 ? 0° ?, reflection coefficient is
Options- A. 0.5
- B. 0.3333
- C. -0.3333
- D. -0.5 Discuss
Correct Answer: -0.3333
Explanation:
- 5. A 10 km long line has a characteristic impedance of 400 ohms. If line length is 100 km, the characteristic impedance is
Options- A. 4000 ?
- B. 400 ?
- C. 40 ?
- D. 4 ? Discuss
Correct Answer: 400 ?
Explanation:
and is independent of line length.
- 6. Microwave resonators are used in
Options- A. microwave oscillators
- B. microwave narrow band amplifier
- C. microwave frequency metres
- D. all of the above Discuss
Correct Answer: all of the above
Explanation:
- 7. In a klystron amplifier the input cavity is called
Options- A. buncher
- B. catcher
- C. Pierce gun
- D. collector Discuss
Correct Answer: buncher
Explanation:
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.
- 8. Assertion (A): TWT uses a focussing mechanism to prevent the electron beam from spreading.
Reason (R): In a TWT the electron beam has to travel a much longer distance than in klystron.
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 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.
- 9. For a 50 ? resistor for 3 GHz application, the stray capacitance should be less than
Options- A. 1 ?F
- B. 1 nF
- C. 1 pF
- D. 0.1 pF Discuss
Correct Answer: 0.1 pF
Explanation:
- 10. Which of the following devices uses a slow wave structure?
Options- A. Klystron two cavity amplifier
- B. Klystron multicavity amplifier
- C. Reflex klystron oscillator
- D. TWT Discuss
Correct Answer: TWT
Explanation:
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.
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