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ECE Objective Questions { Antenna }

36.  Fading in ship to ship communication can be reduced by using which of the following?
A. Space diversity
B. Frequency diversity A more directional antenna
C. A broad band antenna

37.  In a turnstile antenna, the crossed dipoles are excited with voltages
A. in phase with each other
B. 45? out of phase with each other
C. 60? out of phase with each other
D. 90? out of phase with each other

38.  In which of the following short-term fading is commonly observed?
A. Troposcatter communication
B. Ground wave propagation
C. Satellite communication
D. All of the above

39.  For a satellite tracking at VHF, helical antenna is often used because of
A. Faraday effect
B. super refraction
C. ionospheric refraction
D. troposcatter

40.  A range of microwave frequencies more easily passed by the atmosphere than the others is called
A. a window
B. a critical frequency
C. a resonance is the atmosphere
D. a gyro-frequency range

41.  Waveguide feeders are pressurised to
A. detect faults
B. reduce noise
C. reduce loss
D. prevent ingress of moisture

42.  In a wave guide the angle between electric and magnetic fields is
A. 0?
B. 45?
C. 90?
D. 180?

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