This set of Avionics Multiple Choice Questions & Answers (MCQs) focuses on “Point Source Radio Systems”.
1. Which type of direction finders takes bearings on airborne transmitters and advice the aircraft of its bearing from the ground station?
a) Ground based
b) Airborne direction finders
c) Homing adapters
d) Homing beacon
View Answer
Explanation: Ground based direction finders take bearings on airborne transmitters and advice the aircraft of its bearing from the ground station. Such stations can afford the necessary complex equipment, but the operation is cumbersome and time consuming, and requires airborne transmitter and communication link.
2. 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
View Answer
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.
3. Which of the following type of direction finder has a system that rotates the loop, using a servo system until a null is found?
a) Fixed loop
b) Rotatable loop
c) Rotating loop
d) Fixed, crossed loop
View Answer
Explanation: The rotating loop is driven by a motor and forming part of a servo system that rotates the loop until a null is found and then stops. They are sometimes referred to as the radio compass and are housed inside plastic structures that do not reflect radio waves.
4. Which of the following is not true with respect to loop antennas?
a) Horizontal polarization is assumed
b) Resonance is achieved by a variable capacitor
c) The horizontal antenna pattern is a figure of eight
d) The currents are equal in amplitude and phase when the antenna is 90° with the transmitted signal
View Answer
Explanation: The loop antenna is a rectangular loop of wire whose inductance is resonated by a variable capacitor. The signal is assumed to be vertically polarized and the horizontal antenna pattern is a figure of eight. When the loop is 90° with respect to the transmitted signal the currents induced are of same amplitude and phase.
5. What can be added to reduce signal ambiguity in a loop antenna?
a) Low noise amplifier
b) Amplifiers
c) Sense antenna
d) Increase the antenna size
View Answer
Explanation: The horizontal pattern of the loop antenna is a figure of eight which has two null positions 180° apart. This ambiguity will cause the system to give the same indication whether it is pointing toward a station or away from it. A sense antenna can be added when the signal ambiguity must be resolved.
6. What is used to combine the output of the two fixed loop antenna that are placed at right angles to each other?
a) Oscilloscope
b) Spectrum analyzer
c) Mixer
d) Goniometer
View Answer
Explanation: The goniometer has two sets of fixed windings at right angles to each other, each set connected to one loop. It combines the output from the loop antenna into miniature a magnetic field in which a rotor can operate.
7. The area of reduced signal strength in a non directional beacon is called as ______
a) Cone of silence
b) Zero reception zone
c) Zone of silence
d) Non radio zone
View Answer
Explanation: The NDB works on an omnidirectional antenna which has the radio pattern of a donut. The zone on the middle which is directly above the antenna is called as the cone of silence. In this region, no signal is transmitted.
8. Which of the following is not an advantage of NDB?
a) Inexpensive
b) Omnidirectional
c) Accuracy depends on airborne equipment
d) No mountain and night effect
View Answer
Explanation: NDB uses ground waves which follow the curvature of earth. They are inexpensive and independent of accuracy issues but suffer from night effect and mountain effect. Mountain effect is the distortion of ground wave in terrain of nonuniform character.
9. What frequency does the marker beacon use for fixes along the airways?
a) 50MHz
b) 25MHz
c) 500MHz
d) 75MHz
View Answer
Explanation: Marker beacons were developed for better fixes along the airways in addition to directional information. They operate at 75MHz and radiate a narrow pattern upward from the ground.
10. Which of the following can be used to reinforce the upward beam in a marker beacon?
a) Reflector
b) Amplifier
c) Counterpoise
d) Vertical polarization
View Answer
Explanation: The marker beacons use an array of half wave radiators that are aligned in line with the airway. A wire mesh counterpoise below this array can be used to reinforce the upward beam by increasing the signal strength in a particular direction.
11. What is the frequency of rotation of the directional beam in a VOR?
a) 20rps
b) 15rps
c) 30rps
d) 50rps
View Answer
Explanation: The VOR sends out two signals. One is a highly directional signal that rotates at a frequency of 30 rps and an omnidirectional signal. The omnidirectional signal is pulsed every time the directional signal coincides with north.
12. Which of the following generates the same field pattern as a vertical dipole antenna?
a) Yagi antenna
b) Helix antenna
c) Alford loop
d) Microstrip antenna
View Answer
Explanation: Each radiator in the ground station transmitter is an Alford loop. The Alford loop generates a horizontal polarized signal having the same field pattern as a vertical dipole.
13. What is the time gap between each pulse in an interrogation pulse pair for a DME?
a) 12μsec
b) 5μsec
c) 15μsec
d) 10μsec
View Answer
Explanation: The interrogation pulses are in pairs. Each pulse is placed 12μsec apart with each pulse lasting 3.5μsec. The pulse pair repetition rate ranges between 5 pulse pairs per sec to a maximum of 150 pulse pairs per sec.
14. Why are pulse pairs used in DME instead of single pulses?
a) Reduce interference
b) Better range
c) Reduced noise
d) Redundancy
View Answer
Explanation: Pulse systems can easily interfere with each other even if they are of different frequencies. Paired pulses are used in DME to reduce interference with other pulsed systems.
15. What is the frequency in which the DME transmits?
a) 50Mhz above or below the received frequency
b) 20Mhz above the received frequency
c) 40Mhz below the received frequency
d) 63Mhz above or below the received frequency
View Answer
Explanation: The Ground beacon in the DME receives the airborne pulses, and after a 50μs delay, retransmits them back to the aircraft on a frequency 63Mhz above or below the airborne transmitting frequency. Here the frequency received by the DME is the Airborne transmitting frequency.
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