Technical Ability - SPLessons
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Radio Communication and Radar System

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Radio Communication and Radar System

shape Introduction

RADAR, an acronym that stands for Radio Detection and Ranging was developed around 1940s. RADAR System uses the principle of echo. RADAR system is an electromagnetic system which is used to detect the location and distance of an object from the point where the RADAR is placed. RADAR System works by radiating energy into space and monitoring the echo or reflected signal from the objects.
How does RADAR work? The RADAR system generally consists of a transmitter which produces an electromagnetic signal which is radiated into space by an antenna. When this signal strikes any object, it gets reflected or re-radiated in many directions. This reflected or echo signal is received by the radar antenna which delivers it to the receiver, where it is processed to determine the geographical statistics of the object. The range is determined by the calculating the time taken by the signal to travel from the RADAR to the target and back. The target’s location is measured in angle, from the direction of maximum amplitude echo signal, the antenna points to. To measure range and location of moving objects, Doppler Effect is used.

shape Quiz

Q1. Virtual height of an ionosphere layer is........... the beat height
    A. less than B. equal to C. more than D. none of these Answer: C

Q2. In ground wave propagation the absorption of waves
    A. decreases with frequency B. increases with frequency C. both (a) and (b) D. none of these Answer: B

Q3. The ionosphere consists of
    A. positively charged layer B. negatively charged layer C. both (a) and (b) D. none of these Answer: B

Q4. In radio receiver's tube EM84 is used as
    A. audio amplifier B. magic eye C. both (a) and (b) D. none of these Answer: A

Q5. In a radio receiver the noise is generally increased by
    A. power supply B. mixer C. local oscillator D. none of these Answer: B

Q6. The value of a resistor creating thermal noise is doubled. The noise power generated will be
    A. halved B. doubled C. unchanged D. none of these Answer: C

Q7. Which of the following noise is of great importance at high frequencies?
    A. Flicker noise B. Transit-time noise C. Short noise D. None of these Answer: B

Q8. Neper is
    A. equal to decibel B. smaller than decibel C. both (a) and (b) D. none of these Answer: D

Q9. Which of the following crystal filter is used only at the higher frequencies?
    A. Half lattice B. Ladder C. Crystal gale D. None of these Answer: B

Q10. The frequency at which the reactance of the two arms in a crystal gate are equal is
    A. zero B. maximum attenuation frequency C. both (a) and (b) D. none of the above Answer: B
Q11. The effect of transit-time noise is significant in
    A. HF B. LF C. both (a) and (b) D. none of these Answer: A

Q12. A beat frequency between 1500 kHz and 1955 kHz is
    A. 455 kHz B. 350 kHz C. 665 kHz D. 750 kHz Answer: A

Q13. In troposcatter which of the following antenna is preferred?
    A. Parabolic antenna B. Lens antenna C. Both (a) and (b) D. None of these Answer: A

Q14. In a radio receiver padders are provided
    A. to improve tracking B. to improve sensibility C. both (a) and (b) D. none of these Answer: A

Q15. Diversity reception system is used to minimize the troubles due to
    A. synchronous fading B. general fading only C. both (a) and (b) D. none of the above Answer: C

Q16. The output of a diode detector does not contain
    A. output signal B. modulating signal C. both (a) and (b) D. none of these Answer: A

Q17. When power ratios are expressed in dB m, the reference power is
    A. 1 mW B. 3 mW C. 2 mW D. 5 mW Answer: A

Q18. Which stage contains the primary of the first IF transformer?
    A. Oscillator B. Detector C. Both (a) and (b) D. None of these Answer: D

Q19. During heterodyne process in a receiver the modulation of the signal
    A. increases B. decreases C. remains constant D. both (a) and (b) Answer: C

Q20. Channel capacity is equal to
    A. parabolic antenna B. lens antenna C. both (a) and (b) D. none of these Answer: A
Q21. If the image frequency is 2010 kHz, the frequency hf station must be
    A. 1350 kHz B. 1500 kHz C. 1700 kHz D. none of these Answer: D

Q22. Three-point tracking is achieved by
    A. the padder capacitor B. variable selectivity C. both (a) and (b) D. none of these Answer: A

Q23. The input of the mixer stage is
    A. RF signals only B. local oscillator signals only C. signals only D. both (a) and (b) Answer: D

Q24. The disadvantage of tuned radio frequency receiver is
    A. bandwidth variation B. instability C. both (a) and (b) D. none of these Answer: C

Q25. Radar is
    A. a mechanical device B. an electrical device C. a pneumatic device D. an electromagnetic device Answer: D

Q26. The Chain Home Low System is effective within the range of ....... from the target.
    A. 5 km B. 7 km C. 10 km D. 15 km Answer: A

Q27. Radars can be used under
    A. bad weather conditions B. good weather conditions C. all weather conditions D. none of these Answer: C

Q28. Chain Home System was designed for the location and detection of
    A. enemy B. approaching aircraft bombers C. both (a) and (b) D. none of these Answer: B

Q29. Air-traffic control radar monitors are installed
    A. in vicinity of airports B. enroute between air terminals C. both (a) and (b) D. none of these Answer: C

Q30. In communication receivers the fidelity is provided by
    A. audio stage B. mixer stage C. both (a) and (b) D. None of these Answer: A
Q31. Surveillance raders detect and locate hostile targets for the purpose of
    A. military action B. proper military action C. war D. none of these Answer: B

Q32. Radars are used in
    A. detection B. tracking of weather C. both (a) and (c) D. none of these Answer: C

Q33. Radar can be used to guide
    A. vehicles B. space vehicles C. the science D. none of these Answer: B

Q34. In Chain Home Low System, same aexial was used for
    A. transmission and modulation B. reception and modulation C. transmission and reception D. none of these Answer: C

Q35. The performance of radar is unaffected by
    A. darkness B. fog C. rain D. (a), (b) and (c) Answer: D

Q36. Chain Home Low System was first introduced in
    A. 1952 B. 1959 C. 1964 D. 1972 Answer: B

Q37. In foul weather, radar is used with Ground Controlled Approach (GCA) System to guide aircrafts
    A. to a safe landing B. in any direction C. to fly in the sky D. none of the above Answer: A

Q38. Distance Early Warning (DEW) radar/radars is/are used to detect the
    A. aircrafts B. enemies C. both (a) and (b) D. none of these Answer: A

Q39. The techiques developed for radar have paved the way of more advanced research in
    A. solar system B. microwave C. spectroscopy D. none of these Answer: C

Q40. Radar has vastly increased out knowledge of meteorology, aurora, meteors, and other objects of the
    A. sciences B. world C. solar system D. none of these Answer: C
Q41. In Chain Home Low System, the target ranges were more than
    A. 100 km B. 85 km C. 65 km D. 75 km Answer: A

Q42. When installed in ships or high flying aeroplanes, radars can be used under all weather conditions to find the positions of mountains and
    A. icebergs in the sea B. shore lines C. lakes etc. D. (a), (b) and (c) Answer: D

Q43. Hartley law states that
    A. the maximum rate of information transmission depends on the depth of modulation B. the maximum rate of information transmission depends on the channel bandwidth. C. redundancy is essential D. only binary codes may be used. Answer: B

Q44. The Ballistic Missile Early Warning Systems radar is used to detect the track of
    A. missiles B. ballistic missiles C. intercontinental ballistic missiles D. both (a) and (b) Answer: C

Q45. Radar is used by military for
    A. surveillance B. safety C. weapons D. none of these Answer: A

Q46. Radar can be used for the exploration of
    A. solar system B. interplanetary space C. both (a) and (b) D. none of these Answer: B

Q47. Radar is used by ships, large and small, for navigation especially in
    A. bad weather B. with poor visibility C. (a) and (b) D. none of these Answer: C

Q48. Chief civilian application of radar has been for ....... navigation.
    A. marine B. air C. both (a) and (b) D. none of these Answer: C

Q49. Radar can be used in
    A. satellites B. space research C. solar system D. none of these Answer: A

Q50. Radar gives target's
    A. Range B. Size C. Vepocity and range D. Color Answer: C
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