Where does selective fading occur? - Avionics MCQ

Aeronautical & Aerospace Engineering : Avionics - Quiz(MCQ)

Where does selective fading occur?

A)

Antenna

B)

Amplifier

C)

Atmosphere

D)

Attenuator

Correct Answer : Atmosphere

Explanation : Since an AM signal is a combination of waves of different frequencies when it is passed through the atmosphere, they get affected by the ionosphere and the upper atmosphere which attenuate signals below the frequency of 50Hz. If one sideband is above 50Hz and the other one is below 50Hz the atmosphere attenuates one sideband alone. This is known as selective fading.

Recently Updated in Avionics Questions

Which of the following is true with respect to the bandwidth of a 2kHz audio signal and a 2kHz binary data?

A)

Bandwidth is higher for binary data than audio signals

B)

Bandwidth is higher for audio signals than binary data

C)

Bandwidth remains the same for both

D)

Bandwidth keeps increasing with time for the binary data

Correct Answer : Option (A) : Bandwidth is higher for binary data than audio signals

Explanation : Since binary data is transmitted in square waves or pulses, they are generally made up of numerous fundamental sine waves. This occupies a huge bandwidth as compared to audio signals which are analog in nature and usually comprise of a lesser number of sine waves.

What is the signal to noise ratio if the maximum allowable frequency deviation is 4kHz and the frequency deviation by noise is 156.42Hz?

A)

0.0364

B)

0.0391

C)

20.45

D)

25.75

Correct Answer : Option (D) : 25.75

Explaination : N/S = Frequency deviation by noise / maximum deviation = 156.42/4000 =0.0391
S/N = (N/S)^-1=25.57.

Calculate the phase difference by noise if the Signal to noise ratio is 7:2.

A)

8.21°

B)

13.65°

C)

15.366°

D)

17.5°

Correct Answer : Option (C) : 15.366°

Explanation : ?=sin^-1(N/S)=sin^-1(2/7)=sin^-1(0.265)=15.366°.

Advertisement