InterviewSolution
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InterviewSolution
This section includes InterviewSolutions, each offering curated multiple-choice questions to sharpen your knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
What is the spectral separation between each satellite L1 signal in the GLONASS?(a) 50kHz(b) 2MHz(c) 1240MHz(d) 562.5kHz |
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Answer» 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. |
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| 2. |
What are the frequency channels that GLONASS use for normal operation?(a) i=-7 to +4(b) i=+5 to +12(c) i=-7 to +12(d) i=-2 to +7 |
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Answer» Correct answer is (a) i=-7 to +4 The explanation is: The GLONASS use i= -7 to +4 frequency channels for normal operation. This was done so that the signal does not interfere with the radio astronomy ground station which uses the same frequency band. |
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| 3. |
Sculling errors occur when rotation and acceleration are combined.(a) True(b) FalseI have been asked this question by my school teacher while I was bunking the class.The origin of the question is Strap Down and Gimballed Inertial Navigation Systems topic in portion Satellite Radio Navigation & Inertial Navigation of Avionics |
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Answer» Right choice is (a) True The explanation is: In the presence of rotation and acceleration know as sculling, this approximation leads to errors referred to as sculling errors. It can be avoided by executing the velocity transformation at least four times faster than the anticipated frequency of vibration. |
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| 4. |
The input, output and spin axes of a gyro are always perpendicular to each other.(a) True(b) FalseThis question was addressed to me in exam.This interesting question is from Gyroscopes topic in portion Satellite Radio Navigation & Inertial Navigation of Avionics |
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Answer» Right option is (a) True Best explanation: The input, output and spin axes of a gyro are always perpendicular to each other regardless of the motion of the gyro or the platform in which it is fixed. If a gyro is used for heading reference, then the gyro’s spin axes are mounted perpendicular horizontally to the platform. |
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| 5. |
What is the basic principle under which MEMS gyro work?(a) Sagnag effect(b) Coriolis effect(c) Angular momentum conservation(d) Mass conservation |
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Answer» Correct answer is (b) Coriolis effect Best explanation: MEMS Micro Electro Mechanical System gyro exploit the effects of Coriolis force. Coriolis force is experienced when a vibrating mass is subjected to a rate of rotation about an axis in the plane of vibration. |
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| 6. |
Which of the following is false with respect to gimballed platform?(a) Orients the accelerometers into a coordinate frame relative to Earth(b) Euler angles are not easily readable from the gimbals(c) Protect the instruments from large angular motion(d) Protection from vibration, temperature and magnetic effects. |
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Answer» Correct answer is (b) Euler angles are not easily readable from the gimbals Explanation: One of the main purposes of gimballed system is to provide a convenient readout of vehicle attitude by reading each of the gimbals angles separately, thereby yielding convenient Euler angle outputs. |
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| 7. |
Which of the following factors affect the ability of a stable element to remain non-rotating relative to space?(a) Drift rate of the reference gyro(b) Accuracy of gyro torquer(c) Linear motion of the vehicle(d) Orthogonality of the components on the platform |
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Answer» Right choice is (c) Linear motion of the vehicle For explanation I would say: The ability of stable element to remain non-rotating relative to a space or Earth coordinate frame depends on drift rate of the reference gyros, accuracy of gyro torquers, linear motion of the vehicle, orthogonality of the components on the platform. |
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| 8. |
Which of the following antennas produce a vertical radiation pattern?(a) Dipole antenna(b) Yagi antenna(c) Marconi antenna(d) Hertz antenna |
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Answer» Right answer is (c) Marconi antenna Explanation: The same effect as dipole antenna can be achieved with a one-quarter wavelength antenna or Marconi antenna. A vertical dipole with the doughnut-shaped radiation pattern, in which one-half of the pattern is below the surface of the earth. This is called a vertical radiation pattern. |
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| 9. |
Which of the following cause multi path signals?(a) Low transmission power(b) Ground reflection(c) Low frequency transmission(d) High frequency transmission |
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Answer» The correct option is (b) Ground reflection The explanation is: Mulit path Signals are created when a part of the original signal take a different path than LOS to reach the receiver. Thus a signal with same information reaches the receiver at multiple times. Multi path signals are created when the actual signal gets reflected from the ground and reaches the receiver. |
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| 10. |
What is the number of beams that a Doppler radar uses?(a) 4(b) 2(c) 1(d) 3 |
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Answer» The correct option is (a) 4 The explanation is: Although only three beams are required to provide the three components of velocity, most modern Doppler radars employ four beams, because of the planar array antennas generally four such beams. The fourth beam shift can be combined with that of the third to obtain a more accurate component of velocity. |
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| 11. |
The configuration in which the Doppler radar beams are both forward and backward looking is called as?(a) Janus(b) Dual(c) Redundant(d) Wide beam |
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Answer» Right option is (a) Janus To elaborate: Since the three orthogonal components of velocity are of interest, a minimum of three noncoplanar beams are required to measure the three components. Since such a beam configuration has both forward and rearward looking beams it is called Janus configuration, named after the roman god who has the ability to look backward as well as forward. |
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| 12. |
In any order of gimbal, the innermost gimbal has unlimited freedom.(a) True(b) FalseI got this question in a job interview.Question is taken from Strap Down and Gimballed Inertial Navigation Systems in portion Satellite Radio Navigation & Inertial Navigation of Avionics |
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Answer» Correct choice is (a) True Best explanation: Any gimbal order can be chosen, subject to mission limitations. The innermost and the outermost gimbal axes have potentially unlimited freedom, whereas the middle axis is limited to approximately 70° on either side. |
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| 13. |
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(d) Radome |
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Answer» The correct option is (c) Receiver low noise amplifier To elaborate: 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. |
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| 14. |
Which of the following is false with respect to spinning rotor gyros?(a) Mechanically complex(b) High probability of failure(c) Low run up time(d) High power consumption |
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Answer» The correct option is (c) Low run up time The best explanation: The major disadvantage of spinning wheel or spinning rotor gyros is that they are mechanically complex and have a high probability of failure due to the moving components. They also require high powers and have high run up time. Run up time is the time taken for the gyro to start spinning at the required RPM after engine start. |
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| 15. |
GLONASS time and GPS time follows leap the second correction.(a) True(b) FalseThe question was posed to me in a job interview.My question is from Global Orbiting Navigational Satellite System in section Satellite Radio Navigation & Inertial Navigation of Avionics |
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Answer» Right choice is (b) False The explanation is: GPS time does not follow the leap second correction that UTC occasionally makes. GLONASS time does. |
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| 16. |
What technique does DSP use to double the number of channels by using helical antennas?(a) Spatial isolation(b) Frequency reuse(c) Multiplexing(d) Modulation |
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Answer» Correct option is (b) Frequency reuse The explanation is: The digital signal is transmitted from the satellite to the receivers using circular polarization. The DBS satellites have right-hand and left-hand circularly polarized (RHCP and LHCP) helical antennas. By transmitting both polarities of signal, frequency reuse can be incorporated to double the channel capacity. |
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| 17. |
Which technique, in Loran, allows the use of single transmitter station in two chains?(a) Blinking(b) Blanking(c) Pulsing(d) Continuous wave transmission |
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Answer» The correct answer is (b) Blanking Explanation: The Loran signal format can be modified to accommodate a single transmitter station in two chains. This is accomplished by permitting transmission for one of the chains to take precedence over the other when the signal format calls for simultaneous transmission in both chains. This function is called blanking. |
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| 18. |
What is the technique of calculating position from measurements of velocity called?(a) Dead reckoning(b) Doppler radar(c) Secondary surveillance(d) Celestial navigation |
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Answer» Right answer is (a) Dead reckoning To explain: Dead reckoning is the technique of calculating position from the measurements of velocity. It is the means of navigation in the absence of position fixes and consists in calculating the position by extrapolating measured ground speed. |
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| 19. |
When does a gimbal lock occur on a three axis platform?(a) Inner gimbal approaches 90°(b) Inner gimbal approaches 0°(c) Outer gimbal approaches 90°(d) Middle gimbal approaches 90° |
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Answer» The correct answer is (d) Middle gimbal approaches 90° To elaborate: The condition in which the middle gimbal angle approaches 90° is called gimbal lock. In this condition, the innermost and outermost axis coincide, thus depriving the platform one of its degrees of freedom. |
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| 20. |
What type of waveform must be transmitted to reduce Doppler shit errors?(a) Square(b) Triangular(c) Sine(d) Cosine |
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Answer» The correct choice is (b) Triangular Best 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. |
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| 21. |
What is the cause of lock-in phenomena in RLG?(a) Backscatter(b) Low intensity(c) High intensity(d) Low standing wave ratio |
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Answer» Correct option is (a) Backscatter To explain: Lock-in phenomenon leads makes the RLG insensitive to low angular rates. The cause of the lock-in phenomenon is backscatter within the cavity, usually resulting from imperfections in or particulates in the mirror surfaces. |
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| 22. |
Which technique uses two different antennas to reduce traffic on the same frequency?(a) Spatial isolation(b) Frequency reuse(c) Multiplexing(d) Modulation |
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Answer» Correct answer is (b) Frequency reuse Easy explanation: In the frequency reuse technique two systems use the same frequency, although operating on exactly the same frequencies, they are isolated from each other by the use of special antenna techniques. For example, a vertically polarized antenna will not respond to a horizontally polarized signal and vice versa. Or a left-hand circularly polarized (LHCP) antenna will not respond to a right-hand circularly polarized (RHCP) signal and vice versa. |
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| 23. |
What is it called when the position is determined by angles between a star and an accurate time reference?(a) Position fix(b) Celestial fix(c) Sun fix(d) Horizontal fix |
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Answer» The correct option is (b) Celestial fix Best explanation: Navigators on early transoceanic flights used sextants to manually measure star angle with respect to their local vertical. Using the line of sights form two or more stars, along with a star catalog and accurate time reference, the position in Earth latitude and longitude can be deduced. This was known as celestial fix. |
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| 24. |
The sensors that maintain a centered star image for celestial navigation is called as _________(a) Star fixer(b) Celestial fixer(c) Star tracker(d) Star searcher |
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Answer» Right answer is (c) Star tracker To explain I would say: The star sensors have a narrow field of view and maintain a centered star image through the gimbal drive commands and are called star trackers. They have day and night tracking capability, given reasonable cloud cover conditions. |
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| 25. |
Which type of rebalancing technique use voltage applied to pendulum and electrode for correction?(a) Charge forcing(b) Voltage forcing(c) Current forcing(d) Potential forcing |
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Answer» Right answer is (b) Voltage forcing Best explanation: In potential forcing, a potential is applied to the pendulum and to one or both the electrodes. The voltage establishes electric fields that induce the charge of the nonconducting pendulum. This causes a net force to act on the proof mass. |
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| 26. |
What is the range of an order of angular rate magnitude that gyros used in military planes need?(a) 8(b) 8.5(c) 7.1(d) 3 |
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Answer» The correct answer is (b) 8.5 To explain I would say: A gyroscope on a military aircraft must sense angular rates as low as 0.005 deg/hr and as high as 400deg/sec, a range of 8.5 orders of magnitude. Strapdown gyros in civil aircraft need only sense an 8 order of magnitude range of angular rates. |
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| 27. |
Which one of the following is not a purpose of strapdown calculations?(a) Calculate vehicle’s attitude(b) Transform accelerometer measurements into navigational coordinates(c) Perform dead-reckoning computations(d) Provide inputs to air data computer |
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Answer» Right choice is (d) Provide inputs to air data computer Easiest explanation: The purpose of strapdown computations are to calculate the vehicle’s attitude relative to the navigational coordinates using the gyro measurements, to transform the accelerometer measurements from vehicle axes into navigational coordinates, and to perform the dead-reckoning computations. Air data computer is independent of inertial navigation system. |
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| 28. |
Which method uses a turntable in RLG to reduce lock-in errors?(a) Intensity control(b) Rate biasing(c) Using mechanical dither(d) Random rate fixing |
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Answer» Right answer is (b) Rate biasing Explanation: The method of rate biasing employs a turntable that applies a constant rotation to the gyro. An angular encoder measures the relative angle between the instrument and its base. |
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| 29. |
Which of the following is required to integrate stellar navigation and inertial navigation to get the best estimate navigation solution?(a) Kalman filter(b) Star fix(c) Celestial fix(d) Multisensor processing |
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Answer» Right option is (a) Kalman filter Easiest explanation: Navigational systems use Kalman filtering techniques to integrate all the sensed navigational data to obtain the best estimate navigation solution. The use of Kalman filter to integrate stellar measurements requires that star observations and errors be correctly modeled. |
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| 30. |
Why is the inertial navigation system combined with celestial navigation system?(a) Correction of drift error(b) Deriving true north(c) Deriving magnetic north(d) Correction for weather effects |
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Answer» Correct answer is (a) Correction of drift error Easy explanation: Inertial navigational suffer from drift after long hours of using. Since the position error growth of these free inertial navigation systems was excessive on long flights, it was natural to periodically update their position with position updates from manual star fixing. |
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| 31. |
What is the purpose of a gyro in an inertial navigation system?(a) Space-stabilize the accelerometer(b) Angle of rotation(c) Measure rotation rate(d) Calculate velocity |
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Answer» Right answer is (a) Space-stabilize the accelerometer The explanation is: The purpose of gyroscope or gyro in an inertial navigation system is to space stabilize the accelerometers. In gimballed platforms, the gyros measure the rotation of the platform, which is angularly isolated from the vehicle’s motion. |
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| 32. |
What the gyro act as in a strapdown system?(a) Angular rate sensors(b) Null sensors(c) Angle indicators(d) Orientation indicators |
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Answer» The correct option is (a) Angular rate sensors Easy explanation: In a strapdown system, the gyros do not act as null sensors as in a gimballed system but act as inertial angular rate sensors. Angle and orientation are computed from the measured angular rates by the algorithms that calculate heading and orientation. |
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| 33. |
In which type of inertial navigation system are the gyro and accelerometer rigidly mounted to the body?(a) Gimballed system(b) Fixed system(c) Strapdown system(d) Void system |
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Answer» The correct option is (c) Strapdown system The best explanation: In a strapdown navigator, Gyroscopes and accelerometers are rigidly mounted to a sensor assembly that is usually mounted to the vehicle on a set of strap mounts. The gyroscopes track the rotation of the body and compute the orientation of the body. |
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| 34. |
Which of the following is true with respect to flexure pivot accelerometers?(a) Flexure must provide maximum resistance in the direction of input axis(b) Flexure must provide maximum resistance in the direction other than input axis(c) Torquer coil current measures the acceleration(d) Unbalanced accelerometer type |
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Answer» The correct choice is (a) Flexure must provide maximum resistance in the direction of input axis Best explanation: The pivot or flexure supporting the pendulum must provide minimal restraint for the pendulum in the direction of the input axis while exhibiting high stiffness in the other two directions. The spring constant of the flexure or pivot generates a restoring force that reduces the gain of the electronic restoring loop. |
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| 35. |
What is the output given by an accelerometer if the instrument is accelerated upward with an acceleration of 7g?(a) 5g(b) 8g(c) 6g(d) 6.5g |
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Answer» Right answer is (b) 8g Easy explanation: Accelerometer is used to measure acceleration of the vehicle and thus must be corrected for the Earth’s gravitational effect. If the accelerometer is being accelerated upward with an acceleration of 7g, then (a-G) = 7g – (-1g), and the instrument reads 8g. |
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| 36. |
What does the accelerometer measure?(a) Mass(b) Acceleration(c) Velocity(d) Distance |
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Answer» Right answer is (b) Acceleration Best explanation: The accelerometer is a type of inertial instrument that measures the acceleration in any given axes. The measured acceleration can be integrated over time to obtain velocity and distance. |
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| 37. |
Which accelerometer uses torquer coil and pick off supported by a flexure to measure acceleration?(a) MEMS accelerometer(b) Flexure pivot accelerometer(c) Vibrating beam accelerometer(d) Mechanical accelerometer |
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Answer» The correct option is (b) Flexure pivot accelerometer To explain: The flexure pivot accelerometer is the most commonly used in aircraft systems. The sensitive element consists of a pendulum with a torquer coil and a pick off supported by torsional spring or flexure. |
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| 38. |
What is the angle between the normal to the reference ellipsoid and the equatorial plane at a point called?(a) Geodetic angle(b) Correction factor(c) Geodetic latitude(d) Earth angle |
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Answer» The correct choice is (c) Geodetic latitude For explanation I would say: Geodetic latitude of a point is the angle between the normal to the reference ellipsoid and the equatorial plane. Geodetic latitude is our usual understanding of map latitude. |
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| 39. |
A special PCM system uses 16 channels of data, one whose purpose is an identification (ID) and synchronization. The sampling rate is 3.5 kHz. The word length is 6 bits. Find the serial data rate.(a) 451kHz(b) 326kHz(c) 152kHz(d) 336kHz |
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Answer» Correct choice is (d) 336kHz The explanation is: Serial data rate = sampling rate x no. bits/frame = 3.5 kHz x 96 = 336 kHz. |
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| 40. |
A special PCM system uses 16 channels of data, one whose purpose is an identification (ID) and synchronization. The word length is 6 bits. Find the number of bits per frame.(a) 94(b) 95(c) 96(d) 125 |
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Answer» Right answer is (c) 96 Easy explanation: Here, Data channels = 16 and word length is 6 bits. Bits per frame = 6 x 16 = 96. |
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| 41. |
The velocity at which yawing motion can be produced by rudder deflection while the aircraft is on the ground is called _______(a) Ground roll speed(b) Ground control speed(c) Minimum control speed on the ground(d) Control speed |
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Answer» The correct option is (c) Minimum control speed on the ground For explanation I would say: Minimum control speed on the ground is the minimum speed at which enough aerodynamic force can be generated in the vertical fin by rudder deflection while the aircraft is still rolling on the ground to produce a yawing moment on the aircraft. |
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| 42. |
Departure and approach are subphases of what?(a) Landing phase(b) Takeoff phase(c) Terminal phase(d) Surface phase |
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Answer» Correct answer is (c) Terminal phase Easiest explanation: The terminal phase consists of the departure and the approach phase. Departure starts when the aircraft is in the ground and ends when it is out of the terminal area. The approach starts when the aircraft enters the terminal control area and ends when the aircraft intercepts the landing aids at approach fix. |
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| 43. |
Which of the following conditions does not lead to missed approaches?(a) Poor visibility(b) Excess fuel(c) Alignment with runway(d) Traffic |
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Answer» Correct answer is (b) Excess fuel Explanation: A missed approach is initiated at the pilot’s option or at the traffic controller’s request, typically because of poor visibility, poor alignment with a runway, equipment failure, or conflicting traffic. A fuel dump is initiated when there is excess fuel in the aircraft. |
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| 44. |
What does the light bar provide to the pilot?(a) Pitch, roll and azimuth cues(b) Roll cues(c) Pitch cues(d) Azimuth cues |
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Answer» Right choice is (a) Pitch, roll and azimuth cues For explanation I would say: The light bars provide azimuth, roll and pitch cues to the pilot. Center line and edge lights provide rollout cues. |
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| 45. |
What is the inclination of the glide slope with respect to the moving flight deck?(a) 3°(b) 5°(c) 3.5°(d) 4° |
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Answer» Right answer is (d) 4° The best I can explain: The approach path, often called the glide slope, is in the vertical plane containing the runway center line and is inclined 3.5° relative to the sea at the touchdown point and 4° relative to the moving flight deck. |
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| 46. |
Wake perturbations are caused by ________(a) High speed landings(b) Low visibility(c) Heaving motion of ship(d) Steady state wake |
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Answer» The correct answer is (c) Heaving motion of ship To explain: Wake perturbations, due to the ship’s angular motions and heave, causing fluctuations with standard deviations of 2 ft/sec(horizontal) and 4 ft/sec (vertical) about the steady state wake. |
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| 47. |
What is the minimum descent altitude for non precision flight?(a) 100 to 1000ft(b) 10 to 100ft(c) 250 to 1000ft(d) 1000 to 2000ft |
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Answer» Right answer is (c) 250 to 1000ft Explanation: For non precision approach, the minimum descent altitude is defined below which the aircraft may not descend without visual contact with the runway. It ranges from 250 to 1000ft depending upon local obstructions, aircraft type, navigational aids and runway lighting. |
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| 48. |
Which of the following is the latest block of GPS satellites?(a) I(b) IA(c) II(d) IIF |
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Answer» 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. |
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| 49. |
Why is the boom of the yagi antenna connected to a metal mast and electrical ground?(a) Better signal directivity(b) Increased bandwidth(c) Lightning protection(d) To avoid short circuiting |
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Answer» Right choice is (c) Lightning protection Explanation: The centers of the parasitic elements are neutral electrically; these elements can be connected directly to the boom. For the best lightning protection, the boom can then be connected to a metal mast and electrical ground. |
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| 50. |
What is the length of the shortest element in the yagi antenna?(a) One quarter the wavelength of the highest frequency(b) One quarter the wavelength of the lowest frequency(c) One half the wavelength of the highest frequency(d) One half the wavelength of the lowest frequency |
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Answer» Right option is (c) One half the wavelength of the highest frequency To explain: The lengths of the driven elements vary from long to short and are related logarithmically. The longest element has a length of one-half wavelength at the lowest frequency to be covered, and the shortest element is one-half wavelength at the higher frequency. The spacing is also variable. |
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