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Avionics - Transmission Lines Quiz(MCQ)
1 .
Which of the following is not a requirement of transmission lines?
A)
Less noise
B)
High power signal
C)
Should not radiate signal
D)
Minimum attenuation of signal

Correct Answer :   High power signal

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 .
What is used between the two lead wires of a parallel transmission line?
A)
Plastic
B)
Metal
C)
Wood
D)
Ceramic

Correct Answer :   Plastic

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 .
What is used as a surrounding for the solid center core in a coaxial cable?
A)
Metal
B)
Wood
C)
Ceramic
D)
Plastic dielectric

Correct Answer :   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 .
For what purpose was twisted pair cable first used?
A)
AM
B)
Wi-Fi
C)
Telephone
D)
Digital data transmission

Correct Answer :   Telephone

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 .
What is the device that converts the balanced line to an unbalanced line called?
A)
Balun
B)
Balancer
C)
Equalizer
D)
Unbalancer

Correct Answer :   Balun

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.”

6 .
Coaxial cables are ________ lines?
A)
LAN
B)
Unbalanced
C)
Balanced
D)
Parallel wire

Correct Answer :   Unbalanced

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.

7 .
What is the type of transmission line in which neither wire is connected to the ground?
A)
LAN lines
B)
Unbalanced line
C)
Balanced line
D)
Twisted pair cable

Correct Answer :   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.

8 .
What is it called when the noise is present in the transmission line but gets canceled at the receiver?
A)
Rectification
B)
Common mode rejection
C)
Cancellation mode
D)
Common mode cancellation

Correct Answer :   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 .
What is the phase difference between the current flowing in the two wires of a balanced line?
A)
90°
B)
100°
C)
150°
D)
180°

Correct Answer :   180°

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.

10 .
Cables that carry RF signal are not ______
A)
Covered
B)
Inductors equivalents
C)
Capacitors equivalents
D)
Simple resistive conductors

Correct Answer :   Simple resistive conductors

Explanation : Cables used to carry RF energy are not simply resistive conductors but are complex equivalents of inductors, capacitors, and resistors. If simple resistive conductors are used then undesirable effects such as noise, power loss occurs.

11 .
For an operating frequency of 450 MHz, what length of a pair of conductors is considered to be a transmission line?
A)
0.219ft
B)
0.35ft
C)
0.542ft
D)
0.754ft

Correct Answer :   0.219ft

Explanation : A pair of conductors does not act as a transmission line unless it is at least 0.1λ long.
λ = 984/450 = 2.19 ft
0.1λ = 2.19 x (0.1) = 0.219 ft.

12 .
Which of the following is not a type of coaxial cable connector?
A)
BNC
B)
SMA
C)
PL-259
D)
Banana pin connector

Correct Answer :   Banana pin connector

Explanation : The most common types of coaxial cable connectors are the PL-259 or UHF, BNC, F, SMA, and N-type connectors. Banana pin connectors are used in power cables.

13 .
Which is the best type of coaxial cable connector in terms of performance?
A)
PL-259
B)
N-type connector
C)
BNC
D)
SMA

Correct Answer :   N-type connector

Explanation : The best-performing coaxial connector is the N-type connector, which is used mainly on large coaxial cable at the higher frequencies, both UHF and microwave. N-type connectors are complex and expensive, but do a better job than other connectors in maintaining the electrical characteristics of the cable through the interconnections.

14 .
Which of the following is called as UHF connector?
A)
PL-259
B)
N-type connector
C)
BNC
D)
SMA

Correct Answer :   PL-259

Explanation : The PL-259 is also referred to as a UHF connector, can be used up to low UHF values (less than 500 MHz), although it is more widely used at HF and VHF. It can accommodate both large (up to 0.5-in) and small (0.25-in) coaxial cable.

15 .
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)
Capacitative model of transmission line
C)
Lumped model of distributed line
D)
Complex resistive model of transmission line

Correct Answer :   Lumped model of distributed line

Explaination : 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.

16 .
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)
25Ω
B)
48Ω
C)
50Ω
D)
74Ω

Correct Answer :   50Ω

Explaination : avionics

17 .
What type of transmission line is used to intentionally delay the signal?
A)
Serial lines
B)
Transit lines
C)
Delay lines
D)
Parallel lines

Correct Answer :   Delay 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.

18 .
What is the time delay in a coaxial cable is the dielectric constant is 2.3?
A)
0.21 ns/ft
B)
1.36 ns/ft
C)
1.54 ns/ft
D)
5.21 ns/ft

Correct Answer :   1.54 ns/ft

Explanation : avionics

19 .
Which of the following does not cause standing waves?
A)
Open circuit
B)
Short circuit
C)
Impedance is not matched
D)
High frequency high power signal

Correct Answer :   High frequency high power signal

Explanation : If the load at the end of a line is an open circuit or a short circuit or has an impedance other than the characteristic impedance of the line, the signal is not fully absorbed by the load. This causes the signal to get reflected back the line and cause a standing wave.

20 .
Which of the following is not true regarding standing wave?
A)
Standing waves are not desirable
B)
Standing waves do not affect signal strength
C)
In a standing wave power loss occurs
D)
In a standing wave the energy moves towards the power source

Correct Answer :   Standing waves do not affect signal strength

Explanation : Standing waves are not desirable. Some of the energy is reflected from the end of the line and actually moves back up the line. This reflection indicates that the power produced by the generator is not totally absorbed by the load. When there is a power loss naturally the strength of the signal goes down.

21 .
What is the load on a transmission line?
A)
0 ?
B)
Infinity
C)
Some value between 0 and 1
D)
Some value between 0 and infinity

Correct Answer :   Some value between 0 and infinity

Explanation : In practice, however, the load on a transmission line is neither infinite nor 0Ω; rather, it is typically some value in between. The load may be resistive or may have a reactive component.

22 .
The transmission line in which the resistive impedance is equal to the characteristic impedance is called _____
A)
Matched lines
B)
Balanced lines
C)
Paralleled lines
D)
Unbalanced lines

Correct Answer :   Matched lines

Explanation : Ideally, a transmission line should be terminated in a load that has a resistive impedance equal to the characteristic impedance of the line. This is called a matched line.

23 .
How would the graph of wavelength vs voltage look like if the transmission line is matched (neglect resistive loss)?
A)
Constant
B)
Linearly increasing
C)
Linearly decreasing
D)
Exponentially decreasing

Correct Answer :   Constant

Explanation : If a voltmeter is moved down a matched line from the generator to load and the rms voltage values are plotted, the resulting wavelength versus voltage line will be flat.

24 .
In an unmatched line the actual signal on the line is ___________
A)
The modulus of forward signal
B)
The product of forward and reflected signals
C)
The sum of forward and reflected signals
D)
The difference of forward and reflected signals

Correct Answer :   The sum of forward and reflected signals

Explanation : In an unmatched line, standing waves are formed which is a combination of forward and reflected signal. The signal actually on a line is simply the algebraic sum of the forward and reflected signals.

25 .
What percentage of power is reflected if the reflection coefficient is 0.5?
A)
12%
B)
25%
C)
50%
D)
75%

Correct Answer :   25%

Explanation : Reflected power= Γ2= 0.52=0.25 = 25% of initial power.

26 .
What is the reflection coefficient If a line is terminated in its characteristic impedance?
A)
0
B)
0.5
C)
2
D)
Infinity

Correct Answer :   0

Explanation : The reflection coefficient of a line that is fully terminated in its characteristic impedance is 0. This is because there is no reflected voltage on the line.

27 .
How does a shorted transmission line appear to a generator whose length is a quarter of the wavelength?
A)
RC tuned circuit
B)
Short circuited line
C)
Very low impedance
D)
Very high impedance

Correct Answer :   Very high impedance

Explanation : At the load end of the shorted one quarter wavelength line, voltage is zero and current is maximum. But one-quarter wavelength back, at the generator, the voltage is maximum and the current is zero. To the generator, the line appears as an open circuit, or at least very high impedance.

28 .
When does a shorted transmission line look like an inductor to the generator?
A)
Length is more the one half of the wavelength
B)
Length is one quarter wavelength
C)
Length is between one quarter and one half of wavelength
D)
At all times

Correct Answer :   Length is one quarter wavelength

Explanation : If the line length is less than one-quarter wavelength at the operating frequency, the shorted line looks like an inductor to the generator. If the shorted line is between one quarter and one-half wavelength, it looks like a capacitor to the generator.

29 .
Microstrip and striplines can be made by using monolithic, thin-film, and hybrid IC techniques to produce ________
A)
Nano circuits
B)
Micro circuits
C)
Embedded circuits
D)
Microwave integrated circuits

Correct Answer :   Microwave integrated circuits

Explanation : Even tinier microstrip and striplines can be made by using monolithic, thin-film, and hybrid IC techniques. When these are combined with diodes, transistors, and other components, microwave integrated circuits (MICs) are formed.

30 .
What is the transmission line in which a flat conductor is sandwiched between two ground planes?
A)
Microstrip
B)
Coaxial line
C)
Stripline
D)
Balanced line

Correct Answer :   Stripline

Explanation : Stripline is a conductor sandwiched between two ground planes. It is more difficult to make than microstrip; however, it does not radiate as microstrip does.

31 .
Which of the following is not true with respect to microstrip?
A)
Microstrip is ever onequarter or one-half wavelength long.
B)
Copper is etched on an insulating base material
C)
Used for transmission in UHF and microwave region
D)
Point to point communications with wire are eliminated

Correct Answer :   Microstrip is ever onequarter or one-half wavelength long.

Explanation : Microstrip is a flat conductor separated by an insulating dielectric from a large conducting ground plane. The microstrip is usually onequarter or one-half wavelength long and is used for transmission in the UHF and microwave region.

32 .
When does an open transmission line look like an inductor to the generator?
A)
Length is one quarter wavelength
B)
Length is more the one half of the wavelength
C)
Length is between one quarter and one half of wavelength
D)
At all times

Correct Answer :   Length is between one quarter and one half of wavelength

Explanation : If the open transmission line is less than one-quarter wavelength, the generator sees a capacitance. If the line is between one-quarter and one-half wavelength, the generator sees an inductance. These characteristics repeat for lines that are some multiple of one-quarter or one-half wavelengths.

33 .
The impedance of a line is zero when ________
A)
It acts as inductor
B)
It acts as capacitor
C)
It acts as a resistor
D)
Series resonant circuit

Correct Answer :   Series resonant circuit

Explanation : If the line acts as a series resonant circuit, its impedance is zero. If the line is of such a length that it acts as a parallel resonant circuit, its impedance is near infinity. If the line is some intermediate length, it is reactive.

34 .
The special transmission lines constructed on PCBs to act as tuned circuits is called as?
A)
Loop lines
B)
Stripline
C)
Printed lines
D)
Transmission lines

Correct Answer :   Stripline

Explanation : At UHF and microwave frequencies the values of inductance and capacitance become so small that it is difficult to realize them physically with standard coils and capacitors. Special transmission lines constructed with copper patterns on a printed circuit board (PCB), called microstrip or stripline, can be used as tuned circuits, filters, phase shifters, reactive components, and impedance-matching circuits at these high frequencies.