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- Question
High speed logic circuits use
Options- A. pulses with very small width
- B. pulses with very large width
- C. pulses whose width is neither small nor large
- D. either (b) or (c)
- Correct Answer
- pulses with very small width
ExplanationHigh speed means time period is small. Therefore pulses should also have small width.
Microwave Communication problems
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- 1. A magnetron requires an external magnetic field with flux lines parallel to axis of cathode
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. The directive gain of a transmitting antenna is proportional to
Options- A. its cross-sectional area
- B. square of cross-sectional area
- C. square root of cross-sectional area
- D. cube root of cross-sectional area Discuss
Correct Answer: its cross-sectional area
Explanation:
and is thus proportional to cross sectional area.
- 3. Which one of the following is transferred locking electron device C antenna?
Options- A. BARITT diode
- B. IMPATT diode
- C. Gunn diode
- D. Step recovery diode Discuss
Correct Answer: Gunn diode
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.
- 4. If a line having Z0 = 300 ? 0 W is open circuited at far end, VSWR is
Options- A. 0
- B. 1
- C. ?
- D. 2 Discuss
Correct Answer: ?
Explanation:
If line is o.c. |rv| = 1 and VSWR
= ?.
- 5. The main feature of a parametric amplifier is
Options- A. low noise
- B. very high gain
- C. broad bandwidth
- D. both (b) and (c) Discuss
Correct Answer: broad bandwidth
Explanation:
Since reactance does not contribute thermal noise to the circuit, it is a low noise device.- 6. The total field developed by an antenna array at a distant point is
Options- A. phasor sum of fields produced by individual antennas of the array
- B. algebraic sum of fields produced by individual antennas of the array
- C. either (a) or (b) depending on type of array
- D. neither (a) nor (b) Discuss
Correct Answer: phasor sum of fields produced by individual antennas of the array
Explanation:
Since field is a phasor quantity we have to take phasor sum.- 7. A (75 - J50) ohm load is connected to a coaxial of Z0 = 75 ohm at 10 GHz. The best method of matching is to connect
Options- A. an inductance at load
- B. a short circuited stub at load
- C. a short circuited stub at specific distance from load
- D. a capacitance at specific distance from load Discuss
Correct Answer: a short circuited stub at specific distance from load
Explanation:
A short-circuited stub is a suitable method of matching.- 8. Assertion (A): The condition of minimum distortion in a transmission line is L = RC/G.
Reason (R): Line loading means addition of inductance to satisfy the condition L = RC/G.
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:
Oscillator circuits using vacuum tubes (triodes, pentodes) have the following limitations at very high frequencies (microwave region).The stray capacitances and inductances become important and affect the operation of the circuit.
At low frequencies the transit time between cathode and anode is a small fraction of period of oscillation.
However, at microwave frequencies this transit time becomes comparable to time period of oscillations.
- 9. To couple a coaxial line to a parallel wire line it is best to use
Options- A. slotted line
- B. balun
- C. directional coupler
- D. ?/4 transformer Discuss
Correct Answer: balun
Explanation:
A balun gives 4 : 1 impedance transformation.- 10. Assertion (A): Magnetron is generally used in n mode.
Reason (R): Frequency for p mode can be easily separated from adjacent modes.
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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