Discussion
Home ‣ Electronics and Communication Engineering ‣ Communication Systems Comments
- Question
Energy content of atmospheric noise
Options- A. does not depend on frequency
- B. decreases as frequency is increased
- C. increases as frequency is increased
- D. either (a) or (c) depending on the temperature
- Correct Answer
- decreases as frequency is increased
ExplanationAtmospheric noise decreases as frequency is increased.
Communication Systems problems
Search Results
- 1. Non-coherently detection is not possible for
Options- A. PSK
- B. ASK
- C. FSK
- D. both (a) and (c) Discuss
Correct Answer: PSK
- 2. Radio broadcasts are generally
Options- A. amplitude modulation
- B. frequency modulation
- C. both amplitude and frequency modulation
- D. neither amplitude nor frequency modulation Discuss
Correct Answer: frequency modulation
Explanation:
Frequency modulation gives noise free reception and is used for radio broadcasts.- 3. Push pull amplifier is
Options- A. voltage amplifier
- B. current amplifier
- C. power amplifier
- D. none of the above Discuss
Correct Answer: power amplifier
Explanation:
Push pull is a power amplifier.- 4. If the frequency of a wave 20 Hz, the time period is
Options- A. 20 secs
- B. 2 secs
- C. 0.2 secs
- D. 0.05 secs Discuss
Correct Answer: 0.05 secs
Explanation:
.
- 5. Assertion (A): Free space does not interfere with normal radiation and propagation of radio waves
Reason (R): Free space has no magnetic or gravitational fields.
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:
Since free space does not have magnetic and other fields, waves can propagate without any interference.- 6. The range of a cordless telephone is about
Options- A. 1000 m
- B. 500 m
- C. 100 m
- D. 10 m Discuss
Correct Answer: 100 m
Explanation:
The range depends on quality of instrument and is about 100 m.- 7. VSB modulation is preferred in TV because
Options- A. it reduces the bandwidth requirement to half
- B. it avoids phase distortion at low frequencies
- C. it results in better reception
- D. none of the above Discuss
Correct Answer: it reduces the bandwidth requirement to half
Explanation:
VSB (vestigial side band) transmission transmits one side band fully and the other side band partially thus, reducing the bandwidth requirement.- 8. Assertion (A): The phenomenon of differential mobility is called transferred electron effect.
Reason (R): GaAs exhibits transferred electron effect.
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:
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.
- 9. A line is excited by a 100 V dc source. If reflection coefficients at both ends are 1 each then
Options- A. there will be no oscillations on line
- B. there will be only 1 or 2 oscillations on line
- C. there will be a finite number of oscillations on line
- D. the oscillations will continue indefinitely Discuss
Correct Answer: the oscillations will continue indefinitely
Explanation:
Because rv = 1 at each end, the line voltage will not reach a steady value and oscillations will continue indefinitely.- 10. Reflex klystron oscillator is essentially a low power device
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.
Comments
There are no comments.
More in Electronics and Communication Engineering:
Programming
Copyright ©CuriousTab. All rights reserved.