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- Question
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
- Correct Answer
- 0.1 pF
ExplanationXC should be at least ten times greater than R. Therefore for 50 ? resistor at 3 GHz, C should be less than 0.1 pF.
Microwave Communication problems
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- 1. 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:
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.
- 2. In a klystron amplifier the input cavity is called
Options- A. buncher
- B. catcher
- C. Pierce gun
- D. collector Discuss
Correct Answer: buncher
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.
- 3. 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:
They are used in all the devices.- 4. 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.
- 5. 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:
Reflection coefficient
- 6. 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:
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.
- 7. Which of the following can be accessed only sequentially?
Options- A. Floppy disk
- B. Hard disk
- C. Magnetic tape
- D. ROM Discuss
Correct Answer: Magnetic tape
Explanation:
Magnetic tape can be accessed only sequentially.- 8. In
ALU 1C 74181 the addition and subtraction is in
Options- A. 2's complement
- B. 1's complement
- C. binary
- D. none of the above Discuss
Correct Answer: 2's complement
Explanation:
2's complement is universally used in computers.- 9. Which of the following is a computer language?
Options- A. MS WORD
- B. Page maker
- C. MS EXCEL
- D. LISP Discuss
Correct Answer: LISP
Explanation:
LISP is a computer language. The remaining are software packages.- 10. During processing the instructions, data, intermediate results and final results in a computer are held in
Options- A. CPU
- B. ALU
- C. Primary memory
- D. Secondary memory Discuss
Correct Answer: Primary memory
Explanation:
Primary memory holds these during processing of instructions.
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- 1. Assertion (A): TWT uses a focussing mechanism to prevent the electron beam from spreading.