Avionics MCQs – NAVSTAR GPS
1 - Question
Which of the following is false with respect to GPS?
a) Active system
b) All weather system
c) Continuous system
d) Space based system
Explanation: The GPS is an all weather global navigational system. It is passive, survivable, continuous, space based system that provides any suitable equipped user with highly accurate three dimensional position, velocity, and time information anywhere on or near the Earth.
2 - Question
What is the approximate time taken by the GPS for one complete orbit?
a) 11 minutes
b) 45 minutes
c) 5 hours
d) 12 hours
Explanation: The GPS satellites are in approximately 12 hour orbits( 11 hours, 57 minutes, 57.27 seconds) at an altitude of approximately 11,000 nmi. At any point on Earth, 4 satellites are visible at all times.
3 - Question
What is the reason for sending two transmissions in the same band?
b) Ionosphere refraction corrections
d) Reducing traffic
Explanation: Each GPS satellite transmits signals at two frequencies in the L-band to permit ionospheric refraction corrections by properly equipped users. These signals are in sync with the pseudorandom noise that is unique to each satellite to provide instant ranging capabilities.
4 - Question
Which of the following position services provided by the GPS require crypto keys?
a) Precise position service
b) Standard position service
c) Ultimate position service
d) Doppler position service
Explanation: GPS provides two position services, The precise position service and the standard position service. The PPS can be denied to unauthorized users while SPS is free to everyone. Users need crypto keys to access the PPS. These are generally military users.
5 - Question
The intentional degradation of GPS signal in specific areas is called ________
a) Selective degradation
b) Selective availability
c) Distributed GPD
d) Signal jamming
Explanation: The intentional degradation of GPS signal is meant to deny accuracy to unfriendly forces. It is known as selective availability. SA also denies accuracy to unauthorized users who are friendly, which is the entire civil community.
6 - Question
Only L2 signal carries the encrypted precise code.
Explanation: Precise codes are required to correct for the international degradation of signals. Only the L2 signal carries the p code and only authorized users can access them.
7 - Question
What is the number of GPS satellites used?
Explanation: The fully operational GPS satellite constellation comprises 24 satellites, 4 each in six 55° inclined orbit placed 60° apart in longitude. The number of satellites is limited mainly due to budget restrictions.
8 - Question
What type of antenna is used in GPS systems?
a) Yagi antenna
b) Helical array antenna
c) Loop antenna
d) Parabolic antenna
Explanation: The GPS antenna array is formed by an inner quad helices encircled by a ring of eight outer helices that provide near equal power to all terrestrial users. The helical antenna is optimum since circular polarization is least affected by weather and atmosphere.
9 - Question
Which of the following is the latest block of GPS satellites?
Explanation: The IIF block of the GPS is the latest launched till date. The twelfth and final IIF launch was February 5, 2016. The third generation GPS satellites are scheduled to be launched by SpaceX in 2018.
10 - Question
What type of modulation is used in L1 Signal of the GPS?
a) Amplitude modulation
b) Phase modulation
c) Frequency shift keying
d) Binary phase shift keying
Explanation: The L1 consists of two components: a precise and a coarse PRN code. The PRN codes and data are modulated onto the carriers using binary phase shift keying.