Avionics MCQs – Primary and Secondary Radar
1 - Question
Which of the following cannot be measured in primary radar?
a) Height of the aircraft
b) Speed of the aircraft
c) Direction of the aircraft
d) Position of the aircraft
Explanation: One of the major disadvantages of the primary radar is that it cannot provide a three dimensional fix, that is position and altitude. They are radars that can find the height of the aircraft but can only be used for short distances.
2 - Question
Which of the following is false with respect to primary radar?
a) Friend or foe identification is possible
b) Height of the aircraft cannot be determined
c) Has a wide range
d) Requires high power
Explanation: Friend or foe identification is not possible in primary radar and hence it is hard to determine if the aircraft is an enemy or friend. It has a wide range and requires high transmitting power due to the two way travel of the radar signal.
3 - Question
What type of radar is the primary radar?
b) Continuous wave
c) Low frequency
Explanation: The primary radar uses pulse techniques. It sends out short bursts of pulse and the aircraft surface reflects the radio energy back to the radar antenna. It is possible to measure the elapsed time and determine the range or distance of the aircraft.
4 - Question
What is the full form of RADAR?
a) Radio and ranging
b) Radio range
c) Range detection radio
d) Radio Detection and Ranging
Explanation: The term Radar was coined by the U.S. navy for as the acronym for Radio Detection and Ranging. The term has entered several languages and is used so extensively that it lost capitalization and is used as a common noun.
5 - Question
How well a target backscatters radar depends on ________
a) The objects RCS
b) Power of radar
c) Speed of the object
d) Heat signature of the object
Explanation: When radar pulse strikes the aircraft some radio pass through the object whereas some get reflected back. The amount of radio energy that gets reflected back depends upon the Radar cross section of the aircraft. RCS depends on size, material on the surface of the aircraft and many more parameters.
6 - Question
The transmitted and received power is the same in a primary radar.
Explanation: The radio energy has to travel two way: to the aircraft and back to the receiver, this caused attenuation by the atmosphere. In addition to this, only a part of the actual transmission radio energy is reflected back to the receiver.
7 - Question
What is one of the main objectives of a military aircraft design?
a) High heat signature
b) Low RCS
c) High RCS
d) Highly stable configuration
Explanation: Military aircraft usually wish to have a very low RCS or radar cross section so that they are stealthy and undetectable on the enemy’s primary radar. RCS can be reduced by various methods like using radar energy absorbing materials on the surface of the aircraft and not having sharp corners on the aircraft which are more likely to reflect radio energy back to the radar antenna.
8 - Question
Which of the following is false with respect to secondary radar?
a) Requires more power than primary radar
b) Needs a transponder device on the aircraft
d) Better range
Explanation: Secondary radar requires less power than primary radar for the same amount of coverage area. This is because in secondary radar the pulse is one way; it triggers a reply pulse in the transponder of the aircraft which replies with some of the important flight parameters of the aircraft.
9 - Question
The ability of the antenna to turn radiated energy into conducted energy is called ____________
a) Return ratio
b) Power ratio
c) Capture area
Explanation: The ability of the antenna to turn radiated energy into conducted energy is called a capture area. As an example, if a power density of mw/m2 illuminates an antenna with 1 m2 capture area, then the antenna provides 1 mw power at the output connector.
10 - Question
What is the reflected pulse in primary radar called?
d) Radio reply
Explanation: The reflected or backscattered radio energy that reaches the radar antenna is called an echo. In secondary radar it is called a reply since the transponder replies for the interrogation signal.
11 - Question
Secondary radar can identify an aircraft flying in its range.
Explanation: In secondary radar the transponder present in the aircraft reply for the interrogation pulse with information of the aircraft such as flight name and some of the important flight parameters like airspeed and altitude.
12 - Question
The strength of a secondary radar varies inversely with distance to the ______ power.
Explanation: In the secondary radar, the strength of the communication system varies inversely with distance to the second power, compared with primary radar which reduced with the fourth power.
13 - Question
Which mode of the secondary radar gives only altitude?
a) Mode A
b) Mode B
c) Mode C
d) Mode S
Explanation: There are two types of interrogations in the ATCRBS: mode A and mode C. Mode A provides identity only and mode C provides identity and altitude of the aircraft.
14 - Question
The undesirable responses from buildings and clouds for the radar pulse are called as __________
d) Radio error
Explanation: The primary radar pulse is reflected by buildings and clouds and cause undesirable effects in the actual identification. These are called as clutter and can be eliminated by combing primary radar with secondary radar.
15 - Question
What is the time separation for P1 and P3 for mode A secondary radar?
a) 8 μs
b) 21 μs
c) 6 μs
d) 4 μs
Explanation: The time delay between P1 and P3 determines the type of interrogation. When the Time lag is 8μs, it corresponds to mode A whereas a separation of 21 μs corresponds to mode C.