This set of Avionics Multiple Choice Questions & Answers (MCQs) focuses on “Hyperbolic Radio Systems – 1”.
1. Hyperbolic navigational systems are called so because of their hyperbolic lines of position.
Explanation: Hyperbolic navigational systems are called so because of the hyperbolic lines of the position they produce rather than the circles and radial lines associated with the system that measures distance and bearing.
2. Which one of the following is not a hyperbolic radio system?
Explanation: Loran-C, Omega, Decca, and Chayka are the hyperbolic navigational systems whereas the VOR, DME falls under the point source navigational systems.
3. What does Omega and Decca have in common?
a) Both measure the phase difference
b) Both measure the time difference
c) Both measure the power difference
d) Both operate in the same frequency range
Explanation: Omega and Decca measure the phase differences between the signals transmitted from pairs of stations while the Loran-C and Chayka measure the time difference between the signal from two or more transmitting stations.
4. Loran-C is a line of sight navigational system.
Explanation: Loran is a hyperbolic navigational system that came into usage right before the outbreak of world war II. The Loran-C uses ground waves at low frequencies, thereby securing an operating range of over 1000miles, independent of line of sight.
5. Which of the following is not true with respect to Loran-C?
a) Loran stands for Long range navigation
b) Uses ground waves
c) Uses pulse techniques
d) Subjected to site errors
Explanation: The Loran stands for Long range navigation and uses ground waves with pulsed technique to avoid sky wave contamination. Being a hyperbolic system, it is not subjected to the site errors of point source systems.
6. What is the minimum number of transmitter stations required for a Loran system?
Explanation: Loran consists of transmitter stations in groups forming chains. At least three transmitter stations make up a chain. One station is designated as the master while the other is called secondaries.
7. Which technique, in Loran, allows the use of single transmitter station in two chains?
d) Continuous wave transmission
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.
8. What is the pulse frequency used in Loran?
Explanation: Each station transmits signals that have standard pulse leading edge characteristics. Each pulse consists of a 100kHz that rapidly increases in amplitude in a prescribed manner and then decays at a rate that depends on the particular transmitter.
9. _____ is defined as the portion of pules after 65μsec?
a) Pulse trailing edge
b) Final pulse
c) Decay zone
Explanation: 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.
10. The short term propagation effects caused by local weather changes are called as ______________
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.
11. What is the process of ensuring that the receiver works on ground waves?
a) PGTR identification
Explanation: PGTR or Pulse group time reference identification is the process of ensuring that the receiver is operating on the ground wave of the signal. The basic principle behind it is that ground waves travel faster than sky ways.
12. Which of the following is not a function of the monitoring facility in Omega systems?
a) Monitor performance
b) Acts as relays
c) Provide data to phase synchronize the stations
d) Detect solar terrestrial events
Explanation: Each station has a signal monitoring facility that is situated 20 to 50km away from the antenna. These stations perform functions such as monitor signal performance, provide the required data to phase synchronize the stations, and detecting solar terrestrial events that cause shifts in the propagated signal phase.
13. Which of the following is false with respect to Omega systems?
a) Four common transmitted signal frequencies
b) One unique frequency for each station
c) 0.2 sec separation between each of eight transmissions
d) Constant length transmission periods
Explanation: The Omega system has variable length transmission periods. This makes it possible for users to synchronize an Omega receiver to the signal format with no additional extra information.
14. Which of the following techniques reduces the diurnal variation but does little effect on the phase behaviour of signal of equal path length over different environments?
a) Composite Omega
b) Propagation corrections
d) Subtracting the signal phases at two of the frequencies
Explanation: The composite Omega technique reduces the diurnal variation but does little to reduce the wide variation in phase behaviour exhibited by paths of equal length over substantially electromagnetic/geophysical environments.
15. What is the region in which Omega signals are confined according to VLF wave guide model known as?
a) Earth-Atmosphere wave guide
b) Sea-Ionosphere wave guide
c) Earth-Sea wave guide
d) Earth-Ionosphere wave guide
Explanation: In the wave guide model of VLF wave propagation the region in which the Omega signals are confined is known as the Earth-Ionosphere wave guide.
Sanfoundry Global Education & Learning Series – Avionics.
To practice all areas of Avionics, here is complete set of 1000+ Multiple Choice Questions and Answers.