Discussion
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- Question
A quarter wave line open circuited at far end behaves as
Options- A. inductance
- B. L and C in parallel
- C. capacitance
- D. L and C in series
- Correct Answer
- L and C in series
ExplanationA quarter wave line o.c. at far end behaves as a series tuned circuit.
Microwave Communication problems
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- 1. In a backward wave oscillator the wave travelling along the line winds itself back and forth
Options- A. True
- B. False Discuss
Correct Answer: True
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.
- 2. Skin effect is more pronounced at high frequencies.
Options- A. True
- B. False Discuss
Correct Answer: True
Explanation:
Skin effect increases as frequency increases.- 3. The reflection coefficient on a line is 0.2 ?45°. The SWR is
Options- A. 0.8
- B. 1.1
- C. 1.2
- D. 1.5 Discuss
Correct Answer: 1.5
Explanation:
- 4. A waveguide section in a microwave circuit acts as
Options- A. LP filter
- B. Bandpass filter
- C. HP filter
- D. Band stop filter Discuss
Correct Answer: HP filter
Explanation:
It allows high frequencies.- 5. In the given figure the time taken by the wave to make one round trip is
Options- A. 10 ns
- B. 20 ns
- C. 30 ns
- D. 40 ns Discuss
Correct Answer: 40 ns
Explanation:
- 6. Assertion (A): Artificial transmission lines are frequently used in laboratories.
Reason (R): An artificial transmission line can be used to represent an actual line and can also be used as a delay circuit, as attenuator, as filter network etc.
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:
Artificial transmission lines have many applications. One of the applications is to simulate an actual line in the laboratory.- 7. In a TWT the amplitude of resultant wave travelling down the helix
Options- A. increases exponentially
- B. increases linearly
- C. decreases exponentially
- D. is almost constant Discuss
Correct Answer: increases exponentially
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.
- 8. In a turnstile antenna two-half wave resonant wire radiators are placed at 90° to each other in the same plane and are excited
Options- A. in phase
- B. in phase opposition
- C. 90° out of phase with each other
- D. 45° out of phase with each other Discuss
Correct Answer: 90° out of phase with each other
Explanation:
Since the two wire radiators are at 90° to each other, they have to be excited 90° out of phase with each other.- 9. 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 Discuss
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.
- 10. Assertion (A): The impedance of a matched load is equal to characteristic impedance of line.
Reason (R): A matched termination absorbs all the power incident on it.
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:
Matched load means no reflections.
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