# Avionics Questions and Answers – Transmission Line Basics – 3

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This set of Avionics Quiz focuses on “Transmission Line Basics – 3”.

1. What the model of transmission line that appears as a distributed low-pass filter consisting of series inductors and resistors and shunt capacitors and resistors called?
a) Impedance model of transmission line
b) Lumped model of distributed line
c) Capacitative model of transmission line
d) Complex resistive model of transmission line

Explanation: The sum of the complex impedance by the parallel wires, resistance of the wires and the shunt capacitance results in a transmission line that appears as a distributed low-pass filter consisting of series inductors and resistors and shunt capacitors and resistors. This is called a lumped model of a distributed line.

2. What is the surge impedance if a capacitance of 0.0022 μF (2200 pF) is measured for 100 ft and the inductance of each conductor is measured separately and then added, for a total of 5.5 μH?
a) 48Ω
b) 25Ω
c) 50Ω
d) 74Ω

2. The characteristic impedance of a cable of length 1m is 50Ω. What is the characteristic impedance of the same cable of length 100m?
a) 100Ω
b) 50Ω
c) 25Ω
d) 0.1Ω

Explanation: The characteristic impedance of a cable is independent of length. Thus for 1m or 100m the characteristic impedance is 50Ω.

4. Speed of signal in transmission line is equal to the speed of light.
a) True
b) False

Explanation: The velocity of propagation of a signal in a cable is less than the velocity of propagation of light in free space by a fraction called the velocity factor (VF), which is the ratio of the velocity in the transmission line Vp to the velocity in free space Vc.

5. The velocity factor of a coaxial cable is typically 0.8. What is the speed of transmission?
a) 0.8 x 108 m/s
b) 2.4 x 108 m/s
c) 1.7 x 108 m/s
d) 0.2 x 108 m/s

Explanation:
Velocity of transmission = Velocity factor x Velocity in free space = 0.8 x (3 x 108) = 2.4 x 108 m/s.

6. What is the velocity factor of a coaxial cable having an insulator with dielectric constant 2.1?
a) 0.69
b) 0.54
c) 0.32
d) 0.45

Explanation: The velocity factor in a line can be computed with the expression Where ε is the dielectric constant of the insulating material.

7. Calculate the velocity factor if the transmission speed is 2.04 x 108.
a) 0.43
b) 0.25
c) 0.74
d) 0.68

8. What type of transmission line is used to intentionally delay the signal?
a) Parallel lines
b) Serial lines
c) Delay lines
d) Transit lines

Explanation: A signal applied at one end of a line appears some time later at the other end of the line. This is called the time delay or transit time for the line. A transmission line used specifically for the purpose of achieving delay is called a delay line.

9. if the capacitance of a particular line is 30 pF/ft and its inductance is 0.075 μH/ft,What is the delay time?
a) 0.05 ns/ft
b) 1.62 ns/ft
c) 2.5 ns/ft
d) 1.5 ns/ft

10. What is the phase shift for a transmission line which carries a signal of time period 250ns and has a delay of 75 ns?
a) 108°
b) 147°
c) 154°
d) 96°

11. What is the time delay in a coaxial cable is the dielectric constant is 2.3?
a) 1.36 ns/ft
b) 1.54 ns/ft
c) 5.21 ns/ft
d) 0.21 ns/ft

Sanfoundry Global Education & Learning Series – Avionics.

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