Discussion
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- Question
Assertion (A): Impedance matching can be done by using stubs.
Reason (R): A double stub is used for impedance matching when frequency of signal varies.
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
- Correct Answer
- Both A and R are correct and R is correct explanation of A
ExplanationHollow metallic enclosures exhibit resonance behaviour when excited by electromagnetic field.These enclosures are called cavity resonators.
Microwave Communication problems
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- 1. Assertion (A): The velocity of electromagnetic waves on overhead lines and coaxial cables is the same.
Reason (R): Free space has an intrinsic impedance of 377 ohms.
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: A is wrong but R is correct
Explanation:
Velocity of em waves on caoxial cables is less than that on overhead lines.- 2. In the given figure the reflected current wave after first reflection is
Options- A. 0.18 A
- B. -0.18 A
- C. 0.3 A
- D. -0.3 A Discuss
Correct Answer: -0.18 A
Explanation:
- 3. Which device has internal positive feedback?
Options- A. Two cavity klystron amplifier
- B. Multi-cavity klystron amplifier
- C. Reflex klystron amplifier
- D. All of the above Discuss
Correct Answer: Reflex klystron amplifier
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.
- 4. In the given figure the E and H lines in a coaxial cable
Options- A. The radial lines are E lines and circular lines are H lines
- B. Radial lines are H lines and circular lines are E lines
- C. The directions of E and H lines are wrong
- D. Radial lines may be E and H lines depending an direction of current Discuss
Correct Answer: The radial lines are E lines and circular lines are H lines
Explanation:
H lines are concentric circles around conductor and E lines are radial.- 5. In a multicavity klystron amplifier the signal to be amplified develops an ac voltage of signal frequency across the gap in buncher cavity
Options- A. True
- B. False Discuss
Correct Answer: True
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.
- 6. Atomic and molecular resonance is observed in many substances
Options- A. at microwave frequencies
- B. at low frequencies
- C. at frequencies used in AM broadcast
- D. at both (b) and (c) Discuss
Correct Answer: at microwave frequencies
Explanation:
Atomic and molecular distances are very small. Therefore resonance can occur only at microwave frequencies.- 7. The expression HZ = C cos(Bx) cos(Ay)yz is for
Options- A. TE wave
- B. TM waves
- C. both TE and TM waves
- D. some TE and some TM waves Discuss
Correct Answer: TE wave
Explanation:
In TM mode Hz = 0.- 8. If the minimum range of a radar is to be doubled, the peak power has to be increased by a factor of
Options- A. 2
- B. 4
- C. 8
- D. 16 Discuss
Correct Answer: 16
Explanation:
Range = (power)025.- 9. 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.
- 10. The semiconductor diode which can be used in switching circuit in microwave range is
Options- A. PIN diode
- B. Varactor diode
- C. Tunnel diode
- D. Gunn diode Discuss
Correct Answer: PIN diode
Explanation:
A PIN diode has an intrinsic (i) layer between p and n layers. When reverse bias is applied depletion layers are formed at p-i and i-n junctions.The effective/width of depletion layer increases by the width of i layer. It can be used as a voltage controlled attenuator.
At high frequencies the rectification effect ceases and impedance of diode is effectively that of i layer.
This impedance varies with the applied bias. It is used in high frequency switching circuits, limiters, modulators etc.
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- 1. Assertion (A): The velocity of electromagnetic waves on overhead lines and coaxial cables is the same.