Avionics MCQs – Fourier Theory
1 - Question
A sine wave whose frequency is some integer multiple of a fundamental sine wave is called?
a) Complex wave
b) Square wave
c) Harmonic
d) Digital pulses
View Answer
Answer: c
Explanation: A harmonic is a sine wave whose frequency is some integer multiple of a fundamental sine wave. The third harmonic of a 2-kHz sine wave is a sine wave of 6 kHz.
2 - Question
What is the duty cycle of a square wave with equal duration positive and negative alterations?
a) 100%
b) 50%
c) 200%
d) 25%
View Answer
Answer: b
Explanation: Duty cycle is the ratio of the duration of the positive alteration t1 to the period T expressed as percentage. D= t1⁄T*100 = t1⁄2t1 * 100 = 50%.
3 - Question
What is the frequency of 7th harmonic of a 2KHz sine wave?
a) 14Khz
b) 9KHz
c) 5KHz
d) 2KHz
View Answer
Answer: a
Explanation: The frequency of 7th harmonic sine wave = 7 x 2KHz = 14KHz.
4 - Question
An infinite number of odd harmonics are present in a sine wave.
a) True
b) False
View Answer
Answer: a
Explanation: A square wave is made up of a sine wave at the fundamental frequency of the square wave plus an infinite number of odd harmonics. For example, if the fundamental frequency of the square wave is 1 kHz, the square wave can be synthesized by adding the 1-kHz sine wave and harmonic sine waves of 3 kHz, 5 kHz, 7 kHz, 9 kHz, etc.
5 - Question
What is the peak value of 5th harmonic if the square wave has a peak voltage of 3v and a frequency of 48Khz?
a) 0.74
b) 0.52
c) 0.76
d) 1.5
View Answer
Answer: c
Explanation 
6 - Question
Which instrument produces frequency domain information?
a) Oscilloscope
b) Spectrum analyzer
c) Frequency divider
d) Beam analyzer
View Answer
Answer: b
Explanation: The test instrument for producing a frequency-domain display is the spectrum analyzer. Like the oscilloscope, the spectrum analyzer uses a cathode-ray tube for display, but the horizontal sweep axis is calibrated in hertz and the vertical axis is calibrated in volts or power units or decibels.
7 - Question
What is the band width required to pass a signal with t0=75×10-9 without excessive distortions?
a) 14MHz
b) 53.7MHz
c) 13.33MHz
d) 11.56MHz
View Answer
Answer: c
Explanation: 
8 - Question
A pulse train has a rise time of 6 ns. What is the minimum bandwidth to pass this pulse train faithfully?
a) 58.3MHz
b) 42.6MHz
c) 812MHz
d) 41.5MHz
View Answer
Answer: a
Explanation: 
9 - Question
A circuit has a bandwidth of 200 kHz. What is the fastest rise time this circuit will pass?
a) 1.5μs
b) 2.3μs
c) 1.2μs
d) 1.75μs
View Answer
Answer: d
Explanation: 
10 - Question
Fourier analysis helps us to determine how much bandwidth a particular signal occupies.
a) True
b) False
View Answer
Answer: a
Explanation: Fourier analysis allows us to determine not only the sine wave components in any complex signal but also how much bandwidth a particular signal occupies. Although a sine or cosine wave at a single frequency theoretically occupies no bandwidth, complex signals obviously take up more spectrum space.