PSU EXAM MCQ QUESTIONS ON TOPIC ELECTROMAGNETIC WAVE,COMMUNICATION,RADARS,ANTENNA ETC
THIS IS THE SOLUTION FOR MCQ QUESTIONS THAT ASKED ON AERONAUTICAL SOCIETY OF INDIA-AVIONICS 2 SUBJECT.THESE QUESTIONS ARE ALSO ASKED IN PSU EXAMS FOR ELECTRONICS,ELECTRICAL AND COMMUNICATION ENGINEERING.
1.High frequency waves are:
(a) absorbed by F2 layer
(b) reflected by D layer
(c) absorbed by E layer
(d) affected by the solar cycle
ANSWER:AFFECTED BY THE SOLAR CYCLE
2.The absorption of radio waves by the atmosphere depends on
(a) polarization of atmosphere
(b) polarization of the waves
(c) their frequency
(d) their distance from the transmitter
ANSWER:THEIR FREQUENCY
3. In a rectangular wave guide dominant mode is characterized by
(a) Higher cutoff wavelength
(b) lowest cutoff wavelength
(c) No attenuation
(d) highest cutoff frequency
ANSWER: HIGHEST CUTOFF WAVELENGTH
4. Which of the following antennas is best excited from a wave guide
(a) Biconical
(b) Horn
(c) Helical
(d) Folded dipole
ANSWER : HORN
5. To couple a coaxial line to a parallel wire transmission line,it is best to use a
(a) Balun
(b) slotted line
(c) directional couple
(d) quarter wave section of a line
ANSWER: BALUN
6. Electric length of an antenna is
(a) greater than its physical length
(b) equal to its physical length
(c) smaller than its physical length
(d) always equal to 5/\ (5lamda)
ANSWER: GREATER THAN ITS PHYSICAL LENGTH
7. In a radar system if the antenna diameter is increased by a factor of 4,the minimum range of detection will be increased by a factor of
ANSWER: 4
8.In case of a surface wave,to prevent short circuiting of electric component,the wave should be
(a) Vertically polarized
(b) Horizontally polarized
(c) Circularly polarized
(d) elliptically polarized
ANSWER: VERTICALLY POLARIZED
9. Both End fire and Broadside array are
(a) non linear
(b) non resonant
(c) of wide bandwidth
(d) not suitable for short wave transmission
ANSWER: OT SUITABLE FOR SHORT WAVE TRANSMISSION
10. The main disadvantage of a two hole directional coupler is
(a) Low directional coupling
(b) poor directivity
(c) high attenuation
(d) narrow bandwidth
ANSWER: NARROW BANDWIDTH
11. The maximum effective aperture of a microwave antenna which has a directivity of 900,will be
(a) 71.619 /\^2
(b) 717.79 /\^2
(c) 7171.9 /\^2
(d) 7.1619/\^2
ANSWER: 71.619 /\^2
12. A rectangular wave guide is designed to propagate the dominant mode TE10 at a frequency of 5 GHz. The cut off frequency is 0.8 times the signal frequency. The ratio of the wave guide height to width is 2. The broader dimension of the wave guide is
(a) 3.75 cm
(b) 4.0 cm
(c) 2.25 cm
(d) 4.5 cm
ANSWER: 3.75 cm
13. In a radar system the target cross section is continuously changing.The best system for accurate tracking is
(a) lobe switching
(b) sequential lobing
(c) conical scanning'
(d) monopulse
ANSWER: MONOPULSE
14. The dominant modes in rectangular and cylindrical wave guides, are respectively
(a) TE10 & TE11
(b) TE10 & TM10
(c) TE11 & TE10
(d) TE10 & TM11
ANSWER: TE10 & TE11
15. Microwave links are generally preferred to coaxial cable for TV transmission because
(a) they have less overall phase distortion
(b) they are cheaper
(c) of their greater bandwidths
(d) of their relative immune noise
ANSWER:THEY HAVE LESS OVERALL PHASE DISTORTION
16. A parametric amplifier sometimes uses a circular to
(a) provide a greater gain
(b) avoid the need for cooling
(c) provide greater bandwidth
(d) reduce circuit complexity
ANSWER: PROVIDE GREATER BANDWIDTH
17. A TWT (Traveling wave tube) is sometimes preferred to the magnetron as a radar transmitter output tube because it is
(a) capable of longer duty cycle
(b) more broadband
(c) a more efficient amplifier
(d) less noisy
ANSWER: CAPABLE OF LONGER DUTY CYCLE
18. Which one of the following terms does not apply to the Yagi Uda array?
(a) Good bandwidth
(b) folded dipole
(c) parasitic elements
(d) high gain
ANSWER: HIGH GAIN
19. One of the following is unlikely to be used as a pulsed device
(a) Klystron
(b) BWO
(c) CFA
(d) TWT
ANSWER: BWO
20. A parametric amplifier has input and output frequency of 2.25 GHz and is pumped at 4.75 GHz.It is a
(a) DegeneratE amplifier
(b) traveling amplifier
(c) lower side band up converter
(d) upper side band up converter
ANSWER:DEGENERATE AMPLIFIER
21. For a parabolic reflector antenna,the beam width is given by
(a) 70 /\ /D
(b) 170 D/ /\
(c) 30 D. /\
(d) D/ (30 /\)
ANSWER:70 /\ /D
WHERE /\=FREE SPACE WAVE LENGTH,D=DIAMETER OF ANTENNA
22. A microwave tube amplifier uses an axial magnetic field and a radial electric field.This tube represents
(a) Reflex Klystron
(b) TWT
(c) Magnetron
(d) CFA
ANSWER: CFA
23. A Parametric amplifier must be cooled
(a) because parametric amplification generates a lot of heat
(b) to increase bandwidth
(c) because it cannot operate at room temperature
(d) to improve the noise performance
ANSWER: TO IMPROVE THE NOISE PERFORMANCE
24. The glass tube of a TWT may be coated with aquadag to
(a) help focusing
(b)provide attenuation
(c) improve bunching
(d) increase gain
ANSWER: PROVIDE ATTENUATION
25. One of the following is very useful as a multi band HF receiving antenna. This represents
(a) conical horn
(b) folded dipole
(c) log periodic
(d) square loop
ANSWER:LOG PERIODIC
26. If the length of an antenna is increased,the directive gain
(a) increases
(b) decreases
(c) remains same
(d) infinite
ANSWER:INCREASES
27. The antenna commonly used for microwave links are
(a) Loop antennas
(b) Log periodic antennas
(c) Parabolic dishes
(d) Rhombic antennas
ANSWER:PARABOLIC DISHES
ANSWER: HALF WAVELENGTHS OF E AND H FIELDS
29. In the end fire array,maximum radiation occurs
(a) perpendicular to the array
(b) at 30 degree to the array
(c) along the array
(d) at 45 degree to the array
ANSWER:ALONG THE ARRAY
30. A hollow wave guide act as
(a) LPF
(b) BPF
(c) HPF
(d) BSF
ANSWER: HPF
31. The dominnt modes in cylindrical and rectangular wave guides are respectively
(a) TE10 & TE11
(b) TE10 & TM11
(c) TM10 & TE10
(d) TE11 & TE10
ANSWER: TE11 AND TE10
32. The average and peak power of a radar transmitter are respectively 2 KW and 1 MW .T he duty cycle is given by
(a) 0.002
(b) 0.01
(c) 0.02
(d) 0.001
ANSWER:0.002
33. In order to couple two generators to a wave guide system without coupling them to each other,one could not use a
(a) Rat race
(b) E plane Tee
(c) Magic Tee
(d) Hybrid ring
ANSWER: E plane Tee
1.High frequency waves are:
(a) absorbed by F2 layer
(b) reflected by D layer
(c) absorbed by E layer
(d) affected by the solar cycle
ANSWER:AFFECTED BY THE SOLAR CYCLE
2.The absorption of radio waves by the atmosphere depends on
(a) polarization of atmosphere
(b) polarization of the waves
(c) their frequency
(d) their distance from the transmitter
ANSWER:THEIR FREQUENCY
3. In a rectangular wave guide dominant mode is characterized by
(a) Higher cutoff wavelength
(b) lowest cutoff wavelength
(c) No attenuation
(d) highest cutoff frequency
ANSWER: HIGHEST CUTOFF WAVELENGTH
4. Which of the following antennas is best excited from a wave guide
(a) Biconical
(b) Horn
(c) Helical
(d) Folded dipole
ANSWER : HORN
5. To couple a coaxial line to a parallel wire transmission line,it is best to use a
(a) Balun
(b) slotted line
(c) directional couple
(d) quarter wave section of a line
ANSWER: BALUN
6. Electric length of an antenna is
(a) greater than its physical length
(b) equal to its physical length
(c) smaller than its physical length
(d) always equal to 5/\ (5lamda)
ANSWER: GREATER THAN ITS PHYSICAL LENGTH
7. In a radar system if the antenna diameter is increased by a factor of 4,the minimum range of detection will be increased by a factor of
ANSWER: 4
8.In case of a surface wave,to prevent short circuiting of electric component,the wave should be
(a) Vertically polarized
(b) Horizontally polarized
(c) Circularly polarized
(d) elliptically polarized
ANSWER: VERTICALLY POLARIZED
9. Both End fire and Broadside array are
(a) non linear
(b) non resonant
(c) of wide bandwidth
(d) not suitable for short wave transmission
ANSWER: OT SUITABLE FOR SHORT WAVE TRANSMISSION
10. The main disadvantage of a two hole directional coupler is
(a) Low directional coupling
(b) poor directivity
(c) high attenuation
(d) narrow bandwidth
ANSWER: NARROW BANDWIDTH
11. The maximum effective aperture of a microwave antenna which has a directivity of 900,will be
(a) 71.619 /\^2
(b) 717.79 /\^2
(c) 7171.9 /\^2
(d) 7.1619/\^2
ANSWER: 71.619 /\^2
12. A rectangular wave guide is designed to propagate the dominant mode TE10 at a frequency of 5 GHz. The cut off frequency is 0.8 times the signal frequency. The ratio of the wave guide height to width is 2. The broader dimension of the wave guide is
(a) 3.75 cm
(b) 4.0 cm
(c) 2.25 cm
(d) 4.5 cm
ANSWER: 3.75 cm
13. In a radar system the target cross section is continuously changing.The best system for accurate tracking is
(a) lobe switching
(b) sequential lobing
(c) conical scanning'
(d) monopulse
ANSWER: MONOPULSE
14. The dominant modes in rectangular and cylindrical wave guides, are respectively
(a) TE10 & TE11
(b) TE10 & TM10
(c) TE11 & TE10
(d) TE10 & TM11
ANSWER: TE10 & TE11
15. Microwave links are generally preferred to coaxial cable for TV transmission because
(a) they have less overall phase distortion
(b) they are cheaper
(c) of their greater bandwidths
(d) of their relative immune noise
ANSWER:THEY HAVE LESS OVERALL PHASE DISTORTION
16. A parametric amplifier sometimes uses a circular to
(a) provide a greater gain
(b) avoid the need for cooling
(c) provide greater bandwidth
(d) reduce circuit complexity
ANSWER: PROVIDE GREATER BANDWIDTH
17. A TWT (Traveling wave tube) is sometimes preferred to the magnetron as a radar transmitter output tube because it is
(a) capable of longer duty cycle
(b) more broadband
(c) a more efficient amplifier
(d) less noisy
ANSWER: CAPABLE OF LONGER DUTY CYCLE
18. Which one of the following terms does not apply to the Yagi Uda array?
(a) Good bandwidth
(b) folded dipole
(c) parasitic elements
(d) high gain
ANSWER: HIGH GAIN
19. One of the following is unlikely to be used as a pulsed device
(a) Klystron
(b) BWO
(c) CFA
(d) TWT
ANSWER: BWO
20. A parametric amplifier has input and output frequency of 2.25 GHz and is pumped at 4.75 GHz.It is a
(a) DegeneratE amplifier
(b) traveling amplifier
(c) lower side band up converter
(d) upper side band up converter
ANSWER:DEGENERATE AMPLIFIER
21. For a parabolic reflector antenna,the beam width is given by
(a) 70 /\ /D
(b) 170 D/ /\
(c) 30 D. /\
(d) D/ (30 /\)
ANSWER:70 /\ /D
WHERE /\=FREE SPACE WAVE LENGTH,D=DIAMETER OF ANTENNA
22. A microwave tube amplifier uses an axial magnetic field and a radial electric field.This tube represents
(a) Reflex Klystron
(b) TWT
(c) Magnetron
(d) CFA
ANSWER: CFA
23. A Parametric amplifier must be cooled
(a) because parametric amplification generates a lot of heat
(b) to increase bandwidth
(c) because it cannot operate at room temperature
(d) to improve the noise performance
ANSWER: TO IMPROVE THE NOISE PERFORMANCE
24. The glass tube of a TWT may be coated with aquadag to
(a) help focusing
(b)provide attenuation
(c) improve bunching
(d) increase gain
ANSWER: PROVIDE ATTENUATION
25. One of the following is very useful as a multi band HF receiving antenna. This represents
(a) conical horn
(b) folded dipole
(c) log periodic
(d) square loop
ANSWER:LOG PERIODIC
26. If the length of an antenna is increased,the directive gain
(a) increases
(b) decreases
(c) remains same
(d) infinite
ANSWER:INCREASES
27. The antenna commonly used for microwave links are
(a) Loop antennas
(b) Log periodic antennas
(c) Parabolic dishes
(d) Rhombic antennas
ANSWER:PARABOLIC DISHES
28. In a wave guide suffix m and n of the modes TE/TM denote
(a) Half wavelength of E field and full wave length of H field
(b) Half wavelengths of E and H field
(c) Full wavelength of E field and half wavelength of H field
(d) Half wavelengths of E and H fields
ANSWER: HALF WAVELENGTHS OF E AND H FIELDS
29. In the end fire array,maximum radiation occurs
(a) perpendicular to the array
(b) at 30 degree to the array
(c) along the array
(d) at 45 degree to the array
ANSWER:ALONG THE ARRAY
30. A hollow wave guide act as
(a) LPF
(b) BPF
(c) HPF
(d) BSF
ANSWER: HPF
31. The dominnt modes in cylindrical and rectangular wave guides are respectively
(a) TE10 & TE11
(b) TE10 & TM11
(c) TM10 & TE10
(d) TE11 & TE10
ANSWER: TE11 AND TE10
32. The average and peak power of a radar transmitter are respectively 2 KW and 1 MW .T he duty cycle is given by
(a) 0.002
(b) 0.01
(c) 0.02
(d) 0.001
ANSWER:0.002
33. In order to couple two generators to a wave guide system without coupling them to each other,one could not use a
(a) Rat race
(b) E plane Tee
(c) Magic Tee
(d) Hybrid ring
ANSWER: E plane Tee
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