Avionics MCQs – Radar Altimeter
1 - Question
Why is the radio altimeter placed in the tail of aircraft?
a) Can be placed anywhere
b) When landing tail is closer to the ground
c) When landing nose is closer to the ground
d) Weight balance
Explanation: When an aircraft lands it has to do the flare maneuver where the pilot pitches the aircraft’s nose up to slow down the plane. Radio altimeter measures precise distance from the ground and since the tail is closer to the ground than the nose, to measure the minimum distance it is placed in the tail.
2 - Question
What is the maximum altitude that can be measured using a radio altimeter?
c) 50 ft
Explanation: Radio altimeters are generally used for measuring altitude during landing or take off. A radio altimeter gives the distance between the aircraft and the ground and not the pressure altitude. Maximum range of a radio altimeter is 5000ft but is usually switched to at 2500ft.
3 - Question
Altimeters that are specifically designed to provide mark signals at specific altitudes for automatic operations are called as _________
a) Radar altimeter
b) Pressure altimeter
c) Altitude marking radar
d) Mark altimeter
Explanation: Altitude marking radar are generally low altitude altimeter designed specifically to provide mark signals at specific altitudes for initiation of an automatic operation such as fuze triggering on submunitions or chute opening on lunar landing systems.
4 - Question
What is the function leading edge range tracker servo loop?
a) Provide range to the nearest return
b) Speed measurements
c) Vertical speed measurement
d) Automatic ground navigation
Explanation: To provide a range to the nearest return within the bounds of the antenna beam, many modern radar altimeters incorporate the gate in a pulse modulated radar or a filter in a frequency modulated radar over the leading edge of the return.
5 - Question
What is the frequency designated to radar altimeters?
a) 4.2 to 4.4 GHz
b) 2.4 to 4.2 GHz
c) 500 to 1 GHz
d) 13 to 14 GHz
Explanation: The frequency band of 4.2 to 4.4 GHz is assigned to radar altimeters. This frequency band is high enough to result in a reasonable small sized antenna to produce 40° to 50° beam but significantly low so that attenuation by rain is minimum.
6 - Question
Which of the following is true with respect with solid state transmitters in pulsed radar altimeters?
a) Input power is around 100W
b) Use receiver pre-amplifiers
c) High reliability
d) Small size
Explanation: The early pulsed radars were evolved to 5W solid state transmitters incorporating receiver pre-amplifiers. They also provided a high degree of reliability, low probability of intercept, small size, and high accuracy.
7 - Question
Which of the following is responsible for the reduced use of transmitter power in radar altimeter?
a) Low range
b) Interference with other bands
c) Receiver low noise amplifier
Explanation: The transmitter power depends on the sensitivity of the receiver. The receiver low noise amplifier typically has a 2 to 3 dB noise figure, resulting in a sensitivity level that allows relatively low transmitter power.
8 - Question
What type of waveform must be transmitted to reduce Doppler shit errors?
Explanation: To reduce the errors due to the Doppler shift of the return, a triangular waveform is usually used to modulate the transmitter. Thus a positive Doppler shift will produce a negative frequency error on the rising modulation slope. By averaging the frequency count the error can be minimized.