Avionics - Terrestrial Radio Navigation System Quiz(MCQ)

1 .

The ratio of terminating impedance to the power density of the incident wave is called as?

A)

Gain

B)

Directivity

C)

Maximum allowable power

D)

Maximum effective aperture

Correct Answer : Maximum effective aperture

Explanation : Maximum effective aperture is defined as the ratio of terminating impedance to the power density of the incident wave. It is also called the effective area of an antenna and is given by Dλ/4π.

2 .

The factor by which a receiver fails to reach the theoretical internal noise limit is known as ________

A)

Noise

B)

Noise factor

C)

Noise figure

D)

Coefficient of noise

Correct Answer : Noise figure

Explanation : The factor by which a receiver fails to reach the theoretical internal noise limit is often expressed as a ratio, in decibels, and is known as the noise figure. It can also be described as the ratio between the noise power output of a practical receiver and the noise power output of an ideal receiver.

3 .

What is the maximum limit on the frequency that can be used for ground wave communication?

A)

3MHz

B)

5MHz

C)

6MHz

D)

7MHz

Correct Answer : 3MHz

Explanation : 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.

4 .

What type of polarization is used for ground waves?

A)

Vertical polarization

B)

Horizontal polarization

C)

Left circular polarization

D)

Right circular polarization

Correct Answer : Vertical polarization

Explanation : At lower frequencies, along the surface of the earth, vertical polarization is universally used. This way minimum signal is radiated into the ground.

5 .

Why can we not use sky waves for navigation?

A)

Low power

B)

More noise

C)

Not economical

D)

Unpredictable path

Correct Answer : Unpredictable path

Explanation : The sky waves makes some types of long range communication possible, but is of less value to navigation system because it’s transmission path is unpredictable. A rough location where the sky waves might get reflected can be determined by Snell’s law.

6 .

Ground waves are not adversely affected by which of the following factors?

A)

Lightning strikes

B)

Day/night changes

C)

Dielectric of earth

D)

Conductivity of earth

Correct Answer : Day/night changes

Explanation : Propagation of ground waves depends on several additional factors. Some of which are conductivity and dielectric constant of earth. Weather changes like thunderstorms and lightning strikes also create extra atmospheric noise and degrade signal.

7 .

The method in which the user’s receiver and the reference station are assumed not to be synchronized in time is called as _______

A)

Integrity method

B)

Differential method

C)

Pseudoranging

D)

Redundancy method

Correct Answer : Pseudoranging

Explanation : In this method, the user’s receiver and the reference station are assumed not to be synchronized in time. By measuring several such pseudoranges, the user’s three dimensional position and its time offset can be determined.

8 .

_____ is the error in determining position relative to an earth referenced coordinate system?

A)

Relative error

B)

Repeatable error

C)

Absolute error

D)

Differential error

Correct Answer : Absolute error

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.

9 .

The effect of signal simultaneously taking different paths to reach the receiver is called as _______

A)

Multipath effects

B)

Propagation noise

C)

Atmospheric distortion

D)

Differential path effects

Correct Answer : Multipath effects

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.

10 .

Which type of direction finders takes bearings on airborne transmitters and advice the aircraft of its bearing from the ground station?

A)

Homing beacon

B)

Ground based

C)

Homing adapters

D)

Airborne direction finders

Correct Answer : Ground based

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.

11 .

Which of the following is not true with respect to airborne direction finder?

A)

Very low error

B)

Uses the simplest of systems

C)

They are also called homing adapters

D)

Take bearings on the ground transmitter

Correct Answer : Very low error

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.

12 .

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

Correct Answer : Rotating loop

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.

13 .

Which of the following is not true with respect to loop antennas?

A)

Resonance is achieved by a variable capacitor

B)

The horizontal antenna pattern is a figure of eight

C)

The currents are equal in amplitude and phase when the antenna is 90° with the transmitted signal

D)

Horizontal polarization is assumed

Correct Answer : Horizontal polarization is assumed

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.

14 .

What is the frequency in which the DME transmits?

A)

20Mhz above the received frequency

B)

40Mhz below the received frequency

C)

50Mhz above or below the received frequency

D)

63Mhz above or below the received frequency

Correct Answer : 63Mhz above or below the received frequency

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.

15 .

Why are pulse pairs used in DME instead of single pulses?

A)

Redundancy

B)

Better range

C)

Reduce interference

D)

Reduced noise

Correct Answer : Reduce interference

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.

16 .

What is the time gap between each pulse in an interrogation pulse pair for a DME?

A)

10?sec

B)

12?sec

C)

15?sec

D)

25?sec

Correct Answer : 12?sec

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.

17 .

Which of the following generates the same field pattern as a vertical dipole antenna?

A)

Alford loop

B)

Yagi antenna

C)

Helix antenna

D)

Microstrip antenna

Correct Answer : Alford loop

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.

18 .

What can be added to reduce signal ambiguity in a loop antenna?

A)

Amplifiers

B)

Sense antenna

C)

Low noise amplifier

D)

Increase the antenna size

Correct Answer : Sense antenna

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.

19 .

What is the frequency of rotation of the directional beam in a VOR?

A)

30rps

B)

50rps

C)

65rps

D)

90rps

Correct Answer : 30rps

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.

20 .

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

Correct Answer : Counterpoise

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.

21 .

What is used to combine the output of the two fixed loop antenna that are placed at right angles to each other?

A)

Mixer

B)

Oscilloscope

C)

Spectrum analyzer

D)

Goniometer

Correct Answer : Goniometer

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.

22 .

The area of reduced signal strength in a non directional beacon is called as ______

A)

Zone of silence

B)

Cone of silence

C)

Zero reception zone

D)

Non radio zone

Correct Answer : Cone of silence

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.

23 .

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

Correct Answer : No mountain and night effect

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.

24 .

What frequency does the marker beacon use for fixes along the airways?

A)

25MHz

B)

50MHz

C)

75MHz

D)

500MHz

Correct Answer : 75MHz

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.

25 .

Which one of the following is not a hyperbolic radio system?

A)

VOR

B)

Chayka

C)

Omega

D)

Loran-C

Correct Answer : VOR

Explanation : Loran-C, Omega, Decca, and Chayka are the hyperbolic navigational systems whereas the VOR, DME falls under the point source navigational systems.

26 .

What does Omega and Decca have in common?

A)

Both measure the time difference

B)

Both measure the phase difference

C)

Both measure the power difference

D)

Both operate in the same frequency range

Correct Answer : Both measure the phase difference

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.

27 .

Which of the following is not true with respect to Loran-C?

A)

Subjected to site errors

B)

Uses ground waves

C)

Uses pulse techniques

D)

Loran stands for Long range navigation

Correct Answer : 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.

28 .

What is the minimum number of transmitter stations required for a Loran system?

A)

0

B)

1

C)

2

D)

3

Correct Answer : 3

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.

29 .

What is the region in which Omega signals are confined according to VLF wave guide model known as?

A)

Earth-Sea wave guide

B)

Sea-Ionosphere wave guide

C)

Earth-Atmosphere wave guide

D)

Earth-Ionosphere wave guide

Correct Answer : 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.

30 .

Which of the following is false with respect to Omega systems?

A)

One unique frequency for each station

B)

Four common transmitted signal frequencies

C)

Constant length transmission periods

D)

0.2 sec separation between each of eight transmissions

Correct Answer : 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.

31 .

Which of the following is not a function of the monitoring facility in Omega systems?

A)

Acts as relays

B)

Monitor performance

C)

Detect solar terrestrial events

D)

Provide data to phase synchronize the stations

Correct Answer : Acts as relays

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.

32 .

What is the process of ensuring that the receiver works on ground waves?

A)

ECD

B)

HCG

C)

TOPCO

D)

PGTR identification

Correct Answer : 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.

33 .

Which technique, in Loran, allows the use of single transmitter station in two chains?

A)

Pulsing

B)

Blanking

C)

Blinking

D)

Continuous wave transmission

Correct Answer : 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.

34 .

What is the pulse frequency used in Loran?

A)

100kHz

B)

120MHz

C)

150MHz

D)

1000MHz

Correct Answer : 100kHz

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.

35 .

The short term propagation effects caused by local weather changes are called as __________

A)

Noise

B)

Diurnal

C)

Seasonal

D)

Temporal

Correct Answer : 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.

36 .

What is used to indicate that a baseline is not usable?

A)

Pulse

B)

Blank

C)

Blink

D)

Continuous wave

Correct Answer : Blink

Explanation : 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.

37 .

Which mode of Loran-C requires a minimum of 3 transmitters with iterative computation to obtain a fix?

A)

Rho-Rho-Theta

B)

Rho-Theta-Zulu

C)

Rho-Rho-Rho

D)

Hyperbolic mode

Correct Answer : 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.

38 .

Which of the following is false about Direct ranging in Loran-C?

A)

Cost efficient

B)

Uses Rho-Rho mode

C)

Requires minimum 2 stations

D)

High stable user frequency standard

Correct Answer : Cost efficient

Explanation : Direct ranging Rho-Rho mode requires a minimum of two stations, a highly stable user frequency standard and precise knowledge of the time of transmission of the signal. The use of this mode is limited by the high cost of stable frequency standard.

39 .

Which of the following methods breaks the signal into finite segments to find the ASF?

A)

Bill’s method

B)

Differential method

C)

Table look up process

D)

Millington’s method

Correct Answer : Millington’s method

Explanation : In Millington’s method, the signal between the transmitter and the receiver is broken down into finite segments of different conductivity levels, based on conductivity maps. The incremental phase delay is then computed as a function of range and conductivity for each path segment summed and averaged to provide an estimate of ASF.

40 .

Which of the following advantages does the differential Loran-C provide?

A)

Cost efficient

B)

Stable user frequency

C)

Very high range of 500miles

D)

No seasonal errors

Correct Answer : No seasonal errors

Explanation : The corrections using differential Loran-C are generally valid for the co-relation distance of approximately 100 miles from the reference station. Real time co-relations remove both seasonal and diurnal errors can be broadcast.

41 .

Which of the following derives all the signals needed by the transmitter from the timer?

A)

ECD

B)

PATCO

C)

HCG

D)

TOPCO

Correct Answer : PATCO

Explanation : Dual redundant pulse amplitude and timing controllers or PATCO accept timing signals from the timer and derive from this all the signals needed by the transmitter. Signals generated by the PATCO include start triggers, charging triggers, digital amplitude reference signals, amplitude compensation signals, and megatron reference trigger.

42 .

What is the use of notch filters in Loran-C receivers?

A)

Reduce atmospheric noise

B)

Reduce interference from sky waves

C)

Reduce interference from other frequencies

D)

Reduce interference from other stations

Correct Answer : Reduce interference from other frequencies

Explanation : Loran-C signal reception can be impaired by interference from other signal broadcast on slightly different frequencies. To avoid degradation of S/N associated with these interfering sources, Loran -C sets are equipped with notch filters.

43 .

What is the approximate range of Chayka system?

A)

100mi

B)

200mi

C)

300mi

D)

1000mi

Correct Answer : 1000mi

Explanation : Chayka is a pulse phase radio navigation system similar to the Loran-C system. By using ground waves at low frequencies, the operating range is 1000mi and by using pulse techniques, sky wave contamination can be avoided.

44 .

What type of transmitter is used in a Decca system?

A)

Crystal controlled

B)

Digital

C)

Local oscillator

D)

Frequency synthesizer

Correct Answer : Crystal controlled

Explanation : A typical Decca chain consists of a master station and three slave stations. A station has a 2kW crystal controlled transmitter feeding a 300ft antenna.

45 .

What type of transmission is used in Omega system?

A)

Phase modulated wave

B)

Continuous wave

C)

Amplitude modulated wave

D)

Frequency modulated wave

Correct Answer : Continuous wave

Explanation : At each Omega station, continuous wave signals on four common frequencies and one station unique frequency. The signal frequencies are time shared among the stations so that a given frequency is transmitted by only one station at any given time.

46 .

_____ acts as a coarse tuning device for the antenna?

A)

Loop

B)

Helix

C)

Filters

D)

Amplifiers

Correct Answer : Helix

Explanation : The RF signal that is to be transmitted is transferred to the ‘Helix,’ a large helical coil that acts as a coarse tuning device for the antenna. The helix is equipped with separate taps for each signal frequency transmitted.

47 .

Which of the following type is not used in an Omega system?

A)

Valley span

B)

Insulated tower

C)

Hanging tower

D)

Grounded tower

Correct Answer : Hanging tower

Explanation : Since the Omega stations transmit in very low frequencies, the antennas are the largest physical structures in the stations. Three types of antennas are employed in the Omega system: grounded tower, insulated tower, and the valley span.