# Avionics MCQs – Radio Propagation and Noise Characteristics

1 - Question

Received radio energy is a function of the area of the receiving antenna.
a) True
b) False
Explanation: The received radio energy is a function of the area of the receiving antenna. If the transmission is omnidirectional, the received energy is proportional to the area of the receiving antenna divided by the area of the sphere of radius equal to the distance from the transmitter

2 - Question

The ratio of terminating impedance to the power density of the incident wave is called as?
a) Maximum effective aperture
b) Maximum allowable power
c) Directivity
d) Gain
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.

3 - Question

The factor by which a receiver fails to reach the theoretical internal noise limit is known as ________
a) Noise factor
b) Noise
c) Coefficient of noise
d) 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.

4 - Question

What is the maximum limit on the frequency that can be used for ground wave communication?
a) 6MHz
b) 2MHz
c) 5MHz
d) 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.

5 - Question

What type of polarization is used for ground waves?
a) Vertical polarization
b) Right circular polarization
c) Horizontal polarization
d) Left circular 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.

6 - Question

Why can we not use sky waves for navigation?
a) Low power
b) More noise
c) Unpredictable path
d) Not economical
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.

7 - Question

Ground waves are not adversely affected by which of the following factors?
a) Conductivity of earth
b) Dielectric of earth
c) Lightning strikes
d) 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.

8 - Question

The propagation velocity is not constant in ground waves.
a) True
b) False
Explanation: A characteristic of ground waves is that their propagation velocity is not entirely constant. While the variation is quite small, it is sufficient to limit the ability to obtain fixes at extreme ranges as good as the instrumentation might otherwise permit.

9 - Question

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
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 - Question

______ 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
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.

11 - Question

The method in which the user’s receiver and the reference station are assumed not to be synchronized in time is called as _______
a) Redundancy method
b) Pseudoranging
c) Integrity method
d) Differential method