Avionics MCQs – Transmission Line Basics – 1
1 - Question
Which of the following is not a requirement of transmission lines?
a) Minimum attenuation of signal
b) Should not radiate signal
c) High power signal
d) Less noise
Explanation: The primary requirements of a transmission line are that the line introduces minimum attenuation, less noise to the signal and the line did not radiate any of the signals as radio energy. All transmission lines and connectors are designed with these requirements in mind.
2 - Question
What is used between the two lead wires of a parallel transmission line?
Explanation: A parallel transmission line is a two-wire balanced line in which insulating spacers have been used to keep the wires separated. Such lines are rarely used today. The spacing between the wires is maintained by a continuous plastic insulator.
3 - Question
What is used as a surrounding for the solid center core in a coaxial cable?
a) Plastic dielectric
Explanation: The coaxial cable consists of a solid center conductor surrounded by a dielectric material, usually a plastic insulator such as Teflon. Outside the insulation, there is a second conductor made of fine wires.
4 - Question
For what purpose was twisted pair cable first used?
d) Digital data transmission
Explanation: Twisted-pair cable uses two insulated solid copper wires covered with insulation and loosely twisted together. This type of cable was first used in telephone wiring and is still used for that today. But it is also used for security system wiring of sensors and other equipment.
5 - Question
What is the type of transmission line in which neither wire is connected to the ground?
a) Unbalanced line
b) Twisted pair cable
c) LAN lines
d) Balanced line
Explanation: A balanced line is one in which neither wire is connected to ground. Instead, the signal on each wire is referenced to ground.
6 - Question
What is the phase difference between the current flowing in the two wires of a balanced line?
Explanation: In a balanced line, the same current flows in each wire with respect to ground, although the direction of current in one wire is 180° out of phase with the current in the other wire.
7 - Question
In a balanced line, noise is present in the transmission line but cancels at the receiver.
Explanation: Balanced-line wires offer significant protection from noise pickup and crosstalk. Because of the identical polarities of the signals on balanced lines, any external signal induced into the cable (noise) appears on both wires simultaneously but cancels at the receiver.
8 - Question
What is it called when the noise is present in the transmission line but gets canceled at the receiver?
a) Cancellation mode
b) Common mode cancellation
c) Common mode rejection
Explanation: When the noise affects the transmission, its effect is on both the wires but since they are 180° out of phase when the signal reaches the receiver the noise gets cancelled out. This is called common-mode rejection, and noise reduction can be as great as 60 to 70 dB.
9 - Question
Coaxial cables are ________ lines?
d) Parallel wire
Explanation: Coaxial cables are unbalanced lines; the current in the center conductor is referenced to the braid, which is connected to ground. Coaxial cable and shielded twisted-pair cable provide significant but not complete protection from noise pickup or cross talk from inductive or capacitive coupling due to external signals.
10 - Question
What is the device that converts the balanced line to an unbalanced line called?
Explanation: It is sometimes necessary or desirable to convert from balanced to unbalanced operation or vice versa. This is done with a device called a balun, from “balanced-unbalanced.”