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The CORRECT answer is (a) True

To elaborate: In GLONASS, both the satellite broadcast signals L1 and L2 are bi-phase modulated with PRN codes and navigational DATA. These are necessary for COMPUTING velocity and position of the user in 3D space.

Right choice is (d) 562.5kHz

The best explanation: The unique FREQUENCY for L1 signal in the GLONASS system is GIVEN by the formula f= 1602.0 +0.5625i MHz where I=0,1,2,….,24. The separation between each of these SATELLITES is 562.5 kHz.

The CORRECT ANSWER is (b) BEAM antenna

To EXPLAIN: A uniform power density is required for using GLONASS. A shaped beam antenna is used to PRODUCE uniform power spectral density on the ground.

Right ANSWER is (a) FDMA

To elaborate: GLONASS satellites are distinguished and differentiated by radio frequency channel rather than spread spectrum code as in GPS. They use FDMA whereas GPS USES CDMA.

Correct answer is (d) Binary phase shift KEYING

For 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.

Right option is (d) IIF

Best 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.

Right choice is (b) Helical array antenna

The BEST 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.

The correct answer is (d) 24

Best 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.

Correct answer is (a) True

Easiest 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.

Correct option is (b) IONOSPHERE refraction CORRECTIONS

The 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.

The correct CHOICE is (a) Precise position service

To explain I would say: 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.

Right answer is (b) Selective availability

To elaborate: 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.

The correct option is (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.

The correct answer is (a) Frequency

The explanation is: Unlike the refractivity of the IONOSPHERE, the refractivity of the troposphere is not the function of carrier frequency. At a given altitude it is DETERMINED FROMWHERE P is total pressure, T is the absolute temperature, and e is the partial pressure of WATER VAPOUR.

Correct option is (a) Active 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.

Right ANSWER is (c) Occurs mostly at day

Best EXPLANATION: Ionospheric scintillation causes signal fading and effects in the equatorial and the Polar Regions. Strong scintillation effects are rare LOCALIZED at certain times during the NIGHT, and usually occurs during periods of high SOLAR activity.

Correct choice is (a) True

The best explanation: TEC or the TOTAL ELECTRON content in the ionosphere is a function of SOLAR radiation. As more radiation falls on EARTH, more number of molecules are ionized and HENCE TEC is more in the daytime than at the night.

Correct option is (c) Phase advance

For explanation I would say: The result of satellite SIGNAL travelling through ionosphere is that a particular phase of the signal ARRIVES at the RECEIVER earlier than it would have had if the signal travelled in a complete vacuum. This early arrival is termed as phase advance.

Right option is (a) Velocity increases

Best explanation: The velocity of the carrier, the PURE sinusoidal wave, is increased in the PRESENCE of electrons. THUS the greater the DENSITY of electrons in the ionosphere greater the velocity of the signal.

The correct choice is (b) False

To explain I WOULD SAY: Below 30MHz frequency the ionosphere ALMOST acts like a mirror REFLECTING the signal back to Earth. At higher FREQUENCIES, such as those used in satellite communication, radio waves pass through the atmosphere.

Right ANSWER is (a) True

Easy explanation: Satellite clock errors, including those caused by SA dithering, are completely ELIMINATED by DGPS, EXCEPT for the SA dithering effects DUE to DELAYS in estimating, broadcasting, and making the DGPS corrections.

The correct OPTION is (a) Reduces velocity

Explanation: The major sources of errors are when the SIGNAL pass through the atmosphere. The TROPOSPHERE causes the propagation velocity of the signal to be slowed, compressing the signal wavelength.

Correct option is (a) True

To ELABORATE: The navigational MESSAGES from a satellite INCLUDE parameters describing the satellite’s clock offset and drift, which are PREDICTED by the control segment. Any instability in the satellite’s clock CAUSES this prediction to be in error, thus resulting in range and range rate errors in the user’s navigation solution.

Correct answer is (d) Motion of a PASSING comet

The explanation is: Perturbations cause the ORBITAL plane to oscillate and rotate and VARY the SATELLITE from its elliptical orbital path. These forces include spherical asymmetrical components of Earth’s gravitational field, Lunisolar perturbations, air drag, magnetic and STATIC electric forces.

Right answer is (b) LINE of apsides

The EXPLANATION is: The points where the satellite is closest and FARTHEST from the Earth is CALLED the perigee and apogee respectively. The line connecting the apogee and the perigee is called the line of apsides.

Right choice is (B) False

Easiest explanation: The ascending node is the POINT where the satellite CROSSES the Earth’s EQUATORIAL plane from the southerly latitude to the northerly.

Right OPTION is (c) Line of nodes

The best EXPLANATION: The line of nodes is the INTERSECTION of the orbital PLANE with the Earth’s EQUATORIAL plane. The ascending node and the descending node are the points where the satellite crosses the equatorial plane.

Correct choice is (b) Position and acceleration of satellite

The best I can EXPLAIN: All of the satellite navigation EQUATIONS have either satellite position or velocity as a VARIABLE. The linear independence of the equations, which dictate the observability of the navigation solution, is a function of the relative position of the satellites in orbit. Thus the position and the velocity of satellites is of PRIMARY importance.