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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.
| 151. |
Which frequency band is used for connecting the satellite system with the public switched telephone network?(a) L band(b) Ku band(c) C band(d) Ka band |
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Answer» The correct answer is (d) Ka band To explain: The satellites communicate with ground stations called gateways that connect the system to the public switched telephone network. The satellites also communicate among themselves. Both gateway and intersatellite communication takes place over Ka band frequencies. |
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| 152. |
Which type of navigation measure the state vector without regard to the path travelled by the vehicle in the past?(a) Dead reckoning(b) Positioning(c) Direct reckoning(d) AHRS |
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Answer» The correct answer is (b) Positioning Easiest explanation: Navigation systems can be categorized as positioning or dead reckoning. Positioning systems measure the state vector without regard to the path travelled by the vehicle in the past. |
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| 153. |
What is the process called when the state vector is calculated on board the vehicle?(a) Navigation(b) Guidance(c) Surveillance(d) Position location |
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Answer» Right answer is (a) Navigation For explanation: When the state vector is measured and calculated on board, the process is called navigation. When it is calculated outside the vehicle, the process is called surveillance or position location. |
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| 154. |
What provides the sufficient drive to the final power amplifier?(a) Intermediate-power amplifier(b) Operational amplifier(c) Power driver circuit(d) Up converter |
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Answer» Correct choice is (a) Intermediate-power amplifier Explanation: The power amplifier usually begins with an initial stage called the intermediate-power amplifier (IPA). This provides sufficient drive to the final high-power amplifier (HPA). |
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| 155. |
What is the number of components of the vector that describes the translational motion of the vehicle?(a) 6(b) 3(c) 2(d) 1 |
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Answer» Right option is (a) 6 The explanation: The three components of position and the three components of velocity make up a six component state vector that fully describes the translational motion of the vehicle. |
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| 156. |
Which of the following is not true?(a) Right circular polarized antennas can pick up left circular polarized waves due to propagation effects(b) Circular polarization has lesser attenuation in free space(c) Circular polarized wave can follow the curvature of earth(d) In circular polarization the electric and magnetic fields rotate as they leave the antenna |
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Answer» Correct option is (c) Circular polarized wave can follow the curvature of earth Easiest explanation: In circular polarized wave the polarization angle of the electric field and the earth is continuously changing. This does not affect the transmission direction and hence circular polarized waves cannot bend with the curvature of earth, like any other EM wave. |
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| 157. |
Which of the following devices assist in using the same antenna for transmission and receiving?(a) Monoplexer(b) Multiplexer(c) Duplexer(d) Switch |
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Answer» Correct answer is (c) Duplexer The explanation is: An antenna can transmit and receive at the same time as long as some means is provided for keeping the transmitter energy out of the front end of the receiver. A device called a duplexer is used for this purpose. |
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| 158. |
An Em wave is said to be vertically polarized when the angle between the electrical field and earth is _______(a) 50°(b) 20°(c) 90°(d) 180° |
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Answer» The correct choice is (c) 90° Easy explanation: Polarization refers to the orientation of magnetic and electric fields with respect to the earth. If an electric field is parallel to the earth, the electromagnetic wave is said to be horizontally polarized; if the electric field is perpendicular to the earth, the wave is vertically polarized. |
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| 159. |
A fiber optic gyro measures rotation using the _______ of the two beams?(a) Intensity difference(b) Resonance(c) Interference intensity(d) Wavelength difference |
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Answer» Right choice is (c) Interference intensity To elaborate: In a fiber optic gyro, The counterpropagating beams are launched into an optical path and are recombined as they exit. The interference generated by the recombination depends on the optical phase difference between the two beams and therefore provides a measure of rotation. |
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| 160. |
The impedance at the center of the antenna is known as?(a) Characteristic impedance(b) Radiation resistance(c) Transmission impedance(d) Recovery resistance |
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Answer» Right option is (b) Radiation resistance Explanation: The transmission line is connected at the center. The dipole has an impedance of 73 V at its center, which is the radiation resistance. At the resonant frequency, the antenna appears to be a pure resistance of 73 V. |
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| 161. |
The type of dipole antenna that has a higher band width is called as?(a) Conical antenna(b) Yagi antenna(c) Helical antenna(d) Marconi antenna |
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Answer» The correct choice is (a) Conical antenna The explanation: A common way to increase bandwidth in the antenna is to use a version of the dipole antenna known as the conical antenna. The overall length of the antenna is 0.73λ or 0.73(984)/f = 718.32/f. This is longer than the traditional one-half wavelength of a dipole antenna, but the physical shape changes the necessary dimensions for resonance. |
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| 162. |
What happens when the radiation resistance of the antenna matches the characteristic impedance of the transmission line?(a) No transmission occurs(b) No reception occurs(c) SWR is maximum(d) SWR is minimum |
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Answer» Right answer is (d) SWR is minimum To explain I would say: When the radiation resistance of the antenna matches the characteristic impedance of the transmission line, the SWR is minimum and maximum power reaches the antenna. This allows maximum power to be transmitted. |
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| 163. |
The transmission line in which the resistive impedance is equal to the characteristic impedance is called _____(a) Matched lines(b) Paralleled lines(c) Balanced lines(d) Unbalanced lines |
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Answer» The correct choice is (a) Matched lines Easy explanation: Ideally, a transmission line should be terminated in a load that has a resistive impedance equal to the characteristic impedance of the line. This is called a matched line. |
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| 164. |
When does a shorted transmission line look like an inductor to the generator?(a) Length is one quarter wavelength(b) Length is between one quarter and one half of wavelength(c) Length is more the one half of the wavelength(d) At all times |
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Answer» Correct answer is (a) Length is one quarter wavelength Explanation: If the line length is less than one-quarter wavelength at the operating frequency, the shorted line looks like an inductor to the generator. If the shorted line is between one quarter and one-half wavelength, it looks like a capacitor to the generator. |
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| 165. |
How does a shorted transmission line appear to a generator whose length is a quarter of the wavelength?(a) Very high impedance(b) Very low impedance(c) Short circuited line(d) RC tuned circuit |
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Answer» Right answer is (c) Short circuited line For explanation I would say: At the end of a shorted one half wavelength line, the generator sees the same conditions as at the end of the line, i.e., zero voltage and maximum current. This represents a short, or very low impedance. |
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| 166. |
In a parasitic array antenna, the conductors that are not connected to the transmission line is called as?(a) Driven element(b) Parasitic elements(c) Extra elements(d) Array elements |
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Answer» The correct option is (b) Parasitic elements The best I can explain: A parasitic array consists of a basic antenna connected to a transmission line plus one or more additional conductors that are not connected to the transmission line. These extra conductors are referred to as parasitic elements, and the antenna itself is referred to as the driven element. |
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| 167. |
What percentage of power is reflected if the reflection coefficient is 0.5?(a) 50%(b) 75%(c) 25%(d) 12% |
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Answer» Correct answer is (c) 25% For explanation I would say: Reflected power= Γ^2= 0.5^2=0.25 = 25% of initial power. |
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| 168. |
Parasitic element that is typically about 5 percent longer than the half-wave dipole-driven element is called _______(a) Array element(b) Director element(c) Reflector element(d) Driven element |
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Answer» Right option is (c) Reflector element To elaborate: The reflector, a parasitic element that is typically about 5 percent longer than the half-wave dipole-driven element, is spaced from the driven element by a distance of 0.15λ to 0.25λ. When the signal radiated from the dipole reaches the reflector, it induces a voltage into the reflector and the reflector produces some radiation of its own creating a highly focused beam in the direction of the driven element. |
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| 169. |
What is the reflection coefficient If a line is terminated in its characteristic impedance?(a) 0(b) Infinity(c) 2(d) 0.5 |
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Answer» The correct answer is (a) 0 The explanation is: The reflection coefficient of a line that is fully terminated in its characteristic impedance is 0. This is because there is no reflected voltage on the line. |
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| 170. |
In an unmatched line the actual signal on the line is ___________(a) The sum of forward and reflected signals(b) The difference of forward and reflected signals(c) The product of forward and reflected signals(d) The modulus of forward signal |
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Answer» The correct choice is (a) The sum of forward and reflected signals Easiest explanation: In an unmatched line, standing waves are formed which is a combination of forward and reflected signal. The signal actually on a line is simply the algebraic sum of the forward and reflected signals. |
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| 171. |
What is the Standing wave ratio if a 75Ω antenna load is connected to a 50Ω transmission line?(a) 1(b) 2(c) 1.5(d) 1.43 |
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Answer» Right choice is (c) 1.5 Best explanation: Standing wave ratio = SWR = Load impedance/ Characteristic impedance = 75/50 = 1.5. |
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| 172. |
What is the resistive load if SWR= 3.05 and Zo =75Ω?(a) 1.23Ω(b) 51.23Ω(c) 254.2Ω(d) 24.59Ω |
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Answer» Correct answer is (d) 24.59Ω To elaborate: Zl = Zo/SWR = 75/3.05 = 24.59Ω. |
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| 173. |
The characteristic impedance of a cable of length 1m is 50Ω. What is the characteristic impedance of the same cable of length 100m?(a) 100Ω(b) 50Ω(c) 25Ω(d) 0.1Ω |
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Answer» The correct option is (b) 50Ω To explain I would say: The characteristic impedance of a cable is independent of length. Thus for 1m or 100m the characteristic impedance is 50Ω. |
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| 174. |
How would the graph of wavelength vs voltage look like if the transmission line is matched (neglect resistive loss)?(a) Linearly increasing(b) Linearly decreasing(c) Exponentially decreasing(d) Constant |
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Answer» The correct option is (d) Constant Easiest explanation: If a voltmeter is moved down a matched line from the generator to load and the rms voltage values are plotted, the resulting wavelength versus voltage line will be flat. |
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| 175. |
What is the maximum limit on the frequency that can be used for ground wave communication?(a) 6MHz(b) 2MHz(c) 5MHz(d) 3MHz |
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Answer» Correct option is (d) 3MHz The explanation is: Up to 3MHz, an appreciable amount of energy follows the curvature of the earth and are called as the ground wave. Above 3MHz, the radio waves do not follow the curvature of the earth and are used for a line of sight communication. |
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| 176. |
______ is the error in determining position relative to an earth referenced coordinate system?(a) Absolute error(b) Repeatable error(c) Relative error(d) Differential error |
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Answer» Right answer is (a) Absolute error Easy explanation: The absolute or predictable error is the error in determining position relative to an earth referenced coordinate system. The earth frame is one such coordinate system that has its origin at the Earth’s center of mass and its axes fixed on Earth. |
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| 177. |
The effect of signal simultaneously taking different paths to reach the receiver is called as _______(a) Multipath effects(b) Differential path effects(c) Propagation noise(d) Atmospheric distortion |
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Answer» The correct answer is (a) Multipath effects Best explanation: Serious distortion of signal modulation may occur due to different paths simultaneously travelled by the signal between transmitter and receiver. These are called multipath effects. |
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| 178. |
Which of the following bands cannot be used for satellite communication?(a) MF(b) Ku(c) X(d) C |
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Answer» The correct answer is (a) MF To explain: MF is a lower frequency band than Ku, C and X bands and does not lie in the microwave spectrum. Microwaves are used for satellite communication since the lower bands get reflected by the ionosphere. |
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| 179. |
What is the maximum theoretical data rate if a transponder is used for binary transmission and has a bandwidth of 36MHz?(a) 32Mpbs(b) 72Mpbs(c) 36Mpbs(d) 12Mpbs |
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Answer» Correct choice is (b) 72Mpbs For explanation: For binary transmission, the maximum theoretical data rate or channel capacity C for a given bandwidth B is C = 2B = 2(36) =72Mpbs. |
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| 180. |
Coaxial cables are ________ lines?(a) Balanced(b) Unbalanced(c) LAN(d) Parallel wire |
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Answer» Correct choice is (b) Unbalanced The explanation: Coaxial cables are unbalanced lines; the current in the center conductor is referenced to the braid, which is connected to ground. Coaxial cable and shielded twisted-pair cable provide significant but not complete protection from noise pickup or cross talk from inductive or capacitive coupling due to external signals. |
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| 181. |
_____ is defined as the portion of pules after 65μsec?(a) Pulse trailing edge(b) Final pulse(c) Decay zone(d) Null |
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Answer» The correct answer is (a) Pulse trailing edge To elaborate: The pulse trailing edge is defined as that portion of the Loran-C pulse following the peak of the pulse or 65μsec after the pulse is initiated. The pulse trailing edge is controlled in order to maintain spectrum requirements. |
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| 182. |
Which of the following type of gyro works by counting the nodes of standing waves of laser beams?(a) Ring laser gyro(b) Optical fiber gyro(c) Dry tuned gyro(d) Floated gyro |
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Answer» Correct choice is (a) Ring laser gyro Explanation: In a Ring laser gyro, the counterpropagating beams form resonant nodes within the gyro cavity and create an electromagnetic standing wave that remains fixed with inertial space. When the housing of the gyro rotates, a detector can count nodes of the standing waves, each of which represents an angle. |
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| 183. |
The short term propagation effects caused by local weather changes are called as ______________(a) Seasonal(b) Temporal(c) Diurnal(d) Noise |
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Answer» The correct option is (c) Diurnal Explanation: The diurnal variations are short term propagation effects caused primarily by local weather changes and day/night transitions along the signal path. Variations in a refractive index of the atmosphere versus height from the ground contribute to the short term propagation errors. |
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| 184. |
The satellite that is used as a relay to extend communication distance is called as __________(a) Relay satellites(b) Communication satellites(c) Repeater satellites(d) Geosynchronous satellites |
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Answer» The correct answer is (b) Communication satellites The explanation is: Communication satellites are not originators of information to be transmitted. If a transmitting station cannot communicate directly with one or more receiving stations because of line-of-sight restrictions, a satellite can be used. The transmitting station sends the information to the satellite, which in turn re-transmits it to the receiving stations. |
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| 185. |
Which of the following is not true with respect to airborne direction finder?(a) They are also called homing adapters(b) Uses the simplest of systems(c) Very low error(d) Take bearings on the ground transmitter |
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Answer» The correct answer is (c) Very low error The best explanation: Airborne direction finder or homing adapters take bearing from ground transmitters. These direction finders typically can afford only the simplest of systems and must, therefore, tolerate large errors. |
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| 186. |
Which of the following transponders convert the uplink signal to downlink signal using two mixers(a) Single conversion transponders(b) Dual conversion transponders(c) Regenerative transponders(d) Dual mixer transponder |
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Answer» Correct choice is (b) Dual conversion transponders The best I can explain: A dual-conversion transponder makes the frequency translation in two steps with two mixers. No demodulation occurs. |
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| 187. |
Which of the following is used to detect the failure in an ILS?(a) Fail safe ILS(b) Radiation monitors(c) ILS detector(d) ILS failure system is not used anywhere |
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Answer» The correct answer is (b) Radiation monitors The best explanation: Radiation monitors are used to detect ILS failure. They are placed at a particular distance away from the runway to check for errors in ILS transmission or drift in the frequency of radiation. |
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| 188. |
What is the frequency at which the marker beacons operate?(a) 65 MHZ(b) 50 MHZ(c) 150 MHZ(d) 75 MHz |
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Answer» The correct option is (d) 75 MHz The explanation: All the marker beacons, all around the world, operate on a single frequency of 75MHz. |
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| 189. |
What is the type of polarization is used in ILS systems?(a) Horizontal polarization(b) Vertical polarization(c) Circular polarization(d) No polarization |
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Answer» Correct answer is (a) Horizontal polarization To explain I would say: Every transmitter in the ILS including the glide slope transmitter, localizer and the marker beacons radiate continuous wave, horizontally polarized, radio frequency energy which can be received by the on-board receiver. |
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| 190. |
Which of the following is supplemented with GPS to provide non-precision and Category I approaches?(a) Primary radar(b) WAAS(c) ILS(d) MLS |
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Answer» The correct option is (b) WAAS To explain I would say: For non-precision and Category I precision approaches, the limitations by the GPS is mitigated by the FAA’s Wide Area Augmentation System. It may be supplemented with local differential GPS stations located near runways. |
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| 191. |
Which of the following is not a reason for not using the basic GPS for landing systems?(a) Accuracy(b) Integrity(c) Availability of satellites(d) Number of users |
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Answer» The correct option is (d) Number of users Explanation: The primary reason for not using basic GPS for landing systems is because does not provide the accuracy that is required for landing, it lacks a monitoring system and the availability of a sufficient number of satellites to provide location information. |
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| 192. |
What type of antenna is used in GPS systems?(a) Yagi antenna(b) Helical array antenna(c) Loop antenna(d) Parabolic antenna |
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Answer» 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. |
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| 193. |
Which of the following systems use a collection of radio transmitting stations to guide an aircraft to a particular runway?(a) ILS(b) GPS(c) VOR(d) RADAR |
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Answer» Correct answer is (a) ILS The explanation: The instrument landing system or ILS is a collection of radio transmitting stations used to guide aircraft to a specific airport runway, especially during times of limited visibility. |
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| 194. |
_______ standardized the signal in space for the ILS ground transmitting equipment?(a) ISRO(b) FAA(c) ICAO standards and recommended practices(d) NASA |
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Answer» Right answer is (c) ICAO standards and recommended practices For explanation: The ICAO Standards and Recommended Practices for the ILS, subscribed by the180 member states, standardize the signal in space for the ILS ground transmitting equipment, no matter where they are manufactured to maintain international standards. |
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| 195. |
How many ILS systems does an airport require?(a) 0(b) 1(c) Depends upon aircraft size(d) Depends upon density of traffic on the airspace |
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Answer» The correct option is (d) Depends upon density of traffic on the airspace For explanation: High density airports where a lots of planes land and take off typically have more than one runways with multiple ILS systems. Chicago’s O’Hare airport had an ILS installed on 12 runways in 1996. |
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| 196. |
What is used to indicate that a baseline is not usable?(a) Blank(b) Blink(c) Pulse(d) Continuous wave |
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Answer» The correct answer is (b) Blink The explanation is: The secondary stations blink to notify the user that a master secondary pair is unusable. Blink is repetitive on/off pattern of the first two pulses of the secondary signal. |
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| 197. |
Which mode of Loran-C requires a minimum of 3 transmitters with iterative computation to obtain a fix?(a) Hyperbolic mode(b) Rho-Rho-Rho(c) Rho-Rho-Theta(d) Rho-Theta-Zulu |
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Answer» The correct choice is (b) Rho-Rho-Rho Explanation: There are some Loran-C users who do not employ Loran-C in a hyperbolic mode but rather in the direct range rho-rho-rho mode. The rho-rho-rho process involves a minimum of three transmitter stations and the use of an iterative computation to obtain fix. |
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| 198. |
What is the reason for carrying multiple transponders in a satellite?(a) More number of operating channel(b) Better reception(c) More gain(d) Redundancy |
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Answer» Right choice is (a) More number of operating channel Easy explanation: To be economically feasible, a satellite must be capable of handling several channels. As a result, most satellites contain multiple transponders, each operating at a different frequency. Each transponder represents an individual communication channel. |
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| 199. |
What is the number of transponders if the satellite uses 12 channels of frequency and frequency reuse is implemented?(a) 12(b) 6(c) 24(d) 3 |
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Answer» Correct option is (c) 24 The explanation is: Since in frequency reuse each channel can be used twice the numbers of transponders are also doubled. 12 x 2 = 24 transponders, two for each frequency. |
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| 200. |
Why are VHF, UHF, and microwave signals used in satellite communication?(a) More bandwidth(b) More spectrum space(c) Are not diffracted by the ionosphere(d) Economically viable |
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Answer» Right answer is (c) Are not diffracted by the ionosphere The explanation is: VHF, UHF, and microwave signals penetrate the ionosphere with little or no attenuation and are not refracted to earth. Lower frequencies undergo total internal refraction and get reflected back to earth. |
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