Discussion
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- Question
If a line having Z0 = 300 ? 0 W is short circuited at far end, VSWR is
Options- A. 0
- B. 1
- C. ?
- D. 2
- Correct Answer
- ?
ExplanationIf line is s.c |rv| = 1 and VSWR = ?.
Microwave Communication problems
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- 1. When a line is loaded the characteristic impedance is equal to
Options- A. (R + j?L)(G + j?C)
- B.
- C.
- D. LC Discuss
Correct Answer:
Explanation:
or 
.
- 2. Consider the following applications
- TV tuning
- Active filter
- Microwave frequency multiplication
Options- A. 1 2 and 3
- B. l and 2 only
- C. 1 and 3 only
- D. 2 and 3 only Discuss
Correct Answer: 1 2 and 3
Explanation:
Varactor diode is used in all the three applications.- 3. A klystron amplifier generally uses Pierce gun
Options- A. True
- B. False Discuss
Correct Answer: True
Explanation:
It uses a single cavity resonator for generating microwave oscillations.Its parts are electron gun, resonator, repeller and output coupling.
It operates on the principle of positive feed back.
The repeller electrode is at negative potential and sends the partially bunched electron beam back to resonator cavity.
This positive feedback supports oscillations. Its feature are:
1. Frequency range - 2 to 100 GHz
2. Power output - 10 MW to about 2 W
3. Efficiency - 10 - 20 %
Its applications include radar receivers, local oscillator in microwave devices, oscillator for microwave measurements in laboratories etc.
- 4. Assertion (A): Impedance measurement at microwave frequencies is done by finding SWR.
Reason (R): SWR and reflection coefficient depend on the characteristic impedance and load impedance.
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:
- 5. A pulsed radar produces 1 ? sec pulses at a rate of 1000 per second. The duty cycle is
Options- A. 0.001
- B. 0.01
- C. 0.1
- D. 1 Discuss
Correct Answer: 0.001
Explanation:
1 x 10-6 x 1000 = 0.001.- 6. A reflex klystron oscillator uses
Options- A. one cavity resonator
- B. two cavity resonators
- C. three cavity resonators
- D. none of the above Discuss
Correct Answer: one cavity resonator
Explanation:
It uses a single cavity resonator for generating microwave oscillations.Its parts are electron gun, resonator, repeller and output coupling.
It operates on the principle of positive feed back.
The repeller electrode is at negative potential and sends the partially bunched electron beam back to resonator cavity.
This positive feedback supports oscillations. Its feature are:
1. Frequency range - 2 to 100 GHz
2. Power output - 10 MW to about 2 W
3. Efficiency - 10 - 20 %
Its applications include radar receivers, local oscillator in microwave devices, oscillator for microwave measurements in laboratories etc.
- 7. Ga As exhibits negative differential mobility
Options- A. True
- B. False Discuss
Correct Answer: True
Explanation:
A Gunn diode uses GaAs which has a negative differential mobility, i.e., a decrease in carrier velocity with increase in electric field.This effects is called transferred electron effect. The impedance of a Gunn diode is tens of ohms.
A Gunn diode oscillator has a resonant cavity, an arrangement to couple Gunn diode to cavity, biasing arrangement for Gunn diode and arrangement to couple RF power to load.
Applications of Gunn diode oscillator include continuous wave radar, pulsed radar and microwave receivers.
- 8. Microwave links are typically 50 km apart
Options- A. because of atmospheric attenuation
- B. because of output tube power limitation
- C. because of earth's curvature
- D. to ensure that applied dc voltage is not excessive Discuss
Correct Answer: because of earth's curvature
Explanation:
Earth's curvature limits the distance between microwave links.- 9. If antenna diameter is increased four times, the maximum range is increased by a factor of
Options- A. 2
- B. 2
- C. 4
- D. 0.2 Discuss
Correct Answer: 4
Explanation:
Range of radar is proportional to antenna diameter.- 10. Assertion (A): In the interaction region of magnetron an electron is subjected to three forces: force due to electric field, force due to magnetic field and centrifugal force.
Reason (R): The mechanism of generation of microwaves, in a magnetron, involves interaction of electromagnetic fields with electrons moving in static electric and magnetic fields oriented at right angles to each other.
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.
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