Avionics MCQs – Atmospheric Effects on Satellite Signals
1 - Question
How does troposphere affect the satellite signals?
a) Reduces velocity
b) Reflects the signals
c) Refracts the signal
d) Bit inversion occurs
View Answer
Explanation: The major sources of errors are when the signal pass through the atmosphere. The troposphere causes the propagation velocity of the signal to be slowed, compressing the signal wavelength.
2 - Question
Which of the following makes the existence of ionosphere possible?
a) Rotation of the Earth
b) Ultraviolet radiation from sun
c) Solar flares
d) Radiation from distant stars
View Answer
Explanation: The ionosphere owes its existence to the ultraviolet radiation from the sun. The photons possess a certain amount of energy which is enough to break down electrons from their parent atom. The result is a large number of free, negatively charged, electrons and positively charged atoms and molecules called ions.
3 - Question
Satellite signals are refracted by the ionosphere.
a) True
b) False
View Answer
Explanation: Below 30MHz frequency the ionosphere almost acts like a mirror reflecting the signal back to Earth. At higher frequencies, such as those used in satellite communication, radio waves pass through the atmosphere.
4 - Question
What happens to the satellite signals as the density of the ionosphere is high?
a) Velocity increases
b) Velocity decreases
c) Signal strength increases
d) Frequency reduces
View Answer
Explanation: The velocity of the carrier, the pure sinusoidal wave, is increased in the presence of electrons. Thus the greater the density of electrons in the ionosphere greater the velocity of the signal.
5 - Question
What is the increase in velocity of the signal by the ionosphere termed as?
a) Differential velocity
b) Velocity advance
c) Phase advance
d) Signal advance
View Answer
Explanation: The result of satellite signal travelling through ionosphere is that a particular phase of the signal arrives at the receiver earlier than it would have had if the signal travelled in a complete vacuum. This early arrival is termed as phase advance.
6 - Question
TEC in the ionosphere is a function of solar radiation.
a) True
b) False
View Answer
Explanation: TEC or the total electron content in the ionosphere is a function of solar radiation. As more radiation falls on Earth, more number of molecules are ionized and hence TEC is more in the daytime than at the night.
7 - Question
Which of the following is true with respect to ionospheric scintillation effects?
a) It causes signal fading
b) Occurs at the equatorial and polar regions
c) Occurs mostly at day
d) Occurs when high solar activity is present
View Answer
Explanation: Ionospheric scintillation causes signal fading and effects in the equatorial and the Polar Regions. Strong scintillation effects are rare localized at certain times during the night, and usually occurs during periods of high solar activity.
8 - Question
The refractivity of the troposphere is not a function of ________
a) Frequency b) Temperature c) Pressure d) Partial pressure of water vapour
View Answer
Answer: a
Explanation: Unlike the refractivity of the ionosphere, the refractivity of the troposphere is not the function of carrier frequency. At agiven altitude it is determined from 
where P is total pressure, T is the absolute temperature, and e is the partial pressure of water vapour.