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What is a primary advantage of using shorted sections of transmission lines in circuit design?
What is a primary advantage of using shorted sections of transmission lines in circuit design?
When a load is purely inductive or purely capacitive, what is its effect on energy absorption and the reflection coefficient?
When a load is purely inductive or purely capacitive, what is its effect on energy absorption and the reflection coefficient?
What is the primary purpose of using transmission-line stubs in impedance matching?
What is the primary purpose of using transmission-line stubs in impedance matching?
What is a significant benefit offered by using the Smith chart?
What is a significant benefit offered by using the Smith chart?
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Who developed the Smith chart and when was it published?
Who developed the Smith chart and when was it published?
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What primary electrical constant is associated with the insulation between conductors in a transmission line?
What primary electrical constant is associated with the insulation between conductors in a transmission line?
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Which of the following is NOT a distributed parameter that characterizes a transmission line?
Which of the following is NOT a distributed parameter that characterizes a transmission line?
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What impact does the length of a transmission line have on its perceived impedance at a high signal frequency?
What impact does the length of a transmission line have on its perceived impedance at a high signal frequency?
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In a transmission line, what contributes to series resistance besides the inherent resistance of the conductor?
In a transmission line, what contributes to series resistance besides the inherent resistance of the conductor?
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In the lumped model of a transmission line, what combination of components forms the equivalent circuit?
In the lumped model of a transmission line, what combination of components forms the equivalent circuit?
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Why is the shunt leakage resistance often considered negligible in a simplified transmission line model?
Why is the shunt leakage resistance often considered negligible in a simplified transmission line model?
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What is the primary reason distributed parameters of a transmission line are 'lumped' into units per length?
What is the primary reason distributed parameters of a transmission line are 'lumped' into units per length?
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If the series resistance of a transmission line segment is found to be very low, what can be inferred?
If the series resistance of a transmission line segment is found to be very low, what can be inferred?
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What term describes electromagnetic waves traveling from the source towards the load along a transmission line?
What term describes electromagnetic waves traveling from the source towards the load along a transmission line?
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In free space, what is the approximate speed of a TEM wave?
In free space, what is the approximate speed of a TEM wave?
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What parameter describes the spatial distance of one complete cycle of an electromagnetic wave?
What parameter describes the spatial distance of one complete cycle of an electromagnetic wave?
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A pair of conductors begins to act as a transmission line when its length reaches what fraction of the signal's wavelength?
A pair of conductors begins to act as a transmission line when its length reaches what fraction of the signal's wavelength?
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In a balanced transmission line, how are the currents in the two conductors related?
In a balanced transmission line, how are the currents in the two conductors related?
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What type of currents flow in opposite directions in a balanced wire pair?
What type of currents flow in opposite directions in a balanced wire pair?
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In a balanced line, what is the primary advantage regarding noise interference?
In a balanced line, what is the primary advantage regarding noise interference?
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In a balanced transmission line, how is the signal referenced?
In a balanced transmission line, how is the signal referenced?
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If a transmission line has a distributed capacitance of 100 pF/m and a distributed inductance of 250 nH/m, what is the approximate velocity of propagation?
If a transmission line has a distributed capacitance of 100 pF/m and a distributed inductance of 250 nH/m, what is the approximate velocity of propagation?
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A 200-ft length of transmission line has a 3 dB loss at 50 MHz. Assuming the loss is proportional to length, What is the approximate loss if the line is cut to 100 ft?
A 200-ft length of transmission line has a 3 dB loss at 50 MHz. Assuming the loss is proportional to length, What is the approximate loss if the line is cut to 100 ft?
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Which of the following is NOT a common type of loss in transmission lines?
Which of the following is NOT a common type of loss in transmission lines?
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What effect does increasing the frequency have on the ac resistance of a conductor?
What effect does increasing the frequency have on the ac resistance of a conductor?
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What is the primary reason for conductor loss in transmission lines?
What is the primary reason for conductor loss in transmission lines?
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Which type of transmission line typically exhibits the lowest conductor loss?
Which type of transmission line typically exhibits the lowest conductor loss?
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What happens to the characteristic impedance of a transmission line if you increase the diameter of the wire?
What happens to the characteristic impedance of a transmission line if you increase the diameter of the wire?
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What primary factor determines the extent of radiation loss in a transmission line?
What primary factor determines the extent of radiation loss in a transmission line?
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What factor can be useful to determine the relationship between the dielectric constant and the velocity of propagation?
What factor can be useful to determine the relationship between the dielectric constant and the velocity of propagation?
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How does frequency affect radiation loss in transmission lines?
How does frequency affect radiation loss in transmission lines?
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Above approximately what frequency does the center of a conductor have no effect on conductor loss?
Above approximately what frequency does the center of a conductor have no effect on conductor loss?
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What is the primary cause of dielectric heating loss in transmission lines?
What is the primary cause of dielectric heating loss in transmission lines?
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Which type of transmission line typically experiences negligible dielectric heating loss?
Which type of transmission line typically experiences negligible dielectric heating loss?
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What causes coupling loss in transmission lines?
What causes coupling loss in transmission lines?
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What is the phenomenon known as 'corona' in the context of transmission lines?
What is the phenomenon known as 'corona' in the context of transmission lines?
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What does SWR measure in a transmission line?
What does SWR measure in a transmission line?
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In a transmission line, what is the voltage that propagates from the source towards the load called?
In a transmission line, what is the voltage that propagates from the source towards the load called?
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What is the effect of a matched impedance condition in a transmission line?
What is the effect of a matched impedance condition in a transmission line?
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What is the return loss (RL) in a transmission line parameter?
What is the return loss (RL) in a transmission line parameter?
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What is the main consequence of a mismatched transmission line?
What is the main consequence of a mismatched transmission line?
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What happens to a forward wave in an infinite transmission line?
What happens to a forward wave in an infinite transmission line?
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What is the implication of a high voltage standing-wave ratio?
What is the implication of a high voltage standing-wave ratio?
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What is the transmitted power (PT) in the context of transmission lines?
What is the transmitted power (PT) in the context of transmission lines?
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A transmission line with a characteristic impedance of $50 \Omega$ is connected to a $20 \Omega$ load. Which statement is true?
A transmission line with a characteristic impedance of $50 \Omega$ is connected to a $20 \Omega$ load. Which statement is true?
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Study Notes
Transmission Lines
- Transmission lines are metallic conductor systems used to transfer electrical energy from one point to another
- They consist of two or more conductors separated by an insulator
- Transmission lines can be short (a few inches) or long (thousands of miles)
- They are used to propagate DC, low-frequency AC signals (like 60Hz power, audio), and high-frequency signals (like intermediate and radio frequencies)
- The primary requirements for a transmission line are minimizing signal attenuation and preventing signal radiation as radio energy
Transverse Electromagnetic Waves
- Electrical power propagation along a transmission line occurs in the form of transverse electromagnetic (TEM) waves
- TEM waves are characterized by oscillatory motion, where vibration of one particle excites similar vibrations in nearby particles.
- TEM waves propagate primarily through the non-conducting (dielectric) material separating the two conductors of the transmission line
- Transverse waves are characterized by displacement perpendicular to the direction of propagation
Types of Transmission Lines
- Transmission lines can be classified as balanced or unbalanced based on how the conductors carry current
- A balanced transmission line features conductors carrying current that are 180° out of phase with each other
- In an unbalanced transmission line, one conductor is grounded, while the other carries the current
- Currents flowing in opposite directions in a balanced line are called metallic circuit currents, while those flowing in the same direction are called longitudinal currents
Parallel-Conductor Transmission Lines
- Open-wire transmission lines consist of two parallel wires separated by air, with non-conductive spacers
- Twin-lead is a similar design, but with the spacers being replaced by solid dielectric
- Twisted-pair cables consist of insulated conductors twisted together, for example, Cat-5e Ethernet cables
- Shielded cable pairs use a braid to reduce radiation losses and interference; the braid is connected to ground
Concentric or Coaxial Transmission Lines
- Concentric or coaxial transmission lines feature a center conductor surrounded by a concentric outer conductor
- This design effectively shields against external interference, especially at higher frequencies, though it is less effective at lower frequencies.
- The outer conductor is usually grounded.
Connectors
- Most transmission lines end with connectors—devices used to connect the cable to equipment or another cable
- Common connectors include power plugs and outlets as well as more specialized connectors for coaxial and parallel lines
- Special connectors are needed in coaxial cables to preserve the relevant characteristics of the cable
- Different connector types include PL259 (UHF), BNC, F, SMA, N, and RCA connectors
Transmission-Line Equivalent Circuit
- Transmission line characteristics are determined by electrical properties (like wire diameter and conductor spacing) and physical properties (like wire diameter and conductor spacing)
- The primary electrical constants are series DC resistance (R), series inductance (L), shunt capacitance (C) and shunt conductance (G)
- Resistance and inductance reside along the line, whilst capacitance and conductance reside between the two conductors, meaning they are often called distributed parameters (throughout the line)
Characteristic Impedance
- The characteristic impedance (Z₀) of a transmission line is an AC quantity that is independent of frequency and length
- In a purely resistive load (and in the case of an infinitely long transmission line), Z₀ fully reflects incident power.
- Z₀ can be determined from the primary electrical constants (R, L, C)
Transmission Line Losses
- Transmission lines have inherent losses due to conductor resistance, radiation loss, dielectric heating loss, coupling loss and corona
Incident and Reflected Waves
- In bidirectional transmission lines, voltage/current that propagates from the source toward the load is called incident voltage/current, while the voltage/current that propagates from the load toward the source is called reflected (and vice-versa).
- Power is incident toward the load and reflected toward the source
- For an infinitely long transmission line and purely resistive load, incident power is entirely absorbed
Resonant and Nonresonant Lines
- Nonresonant lines have no reflected power and the voltage and current remain constant
- Resonant transmission lines experience continuous transfer of energy between magnetic and electric fields
Propagation Constant
- Propagation constant (γ) expresses attenuation (signal loss) and phase shift per unit length in transmission lines
- Calculated via the equation: γ = (\sqrt{(R + jωL)(G + jωC)})
- The current and voltage distribution along a transmission line with a matched load line is given by: I = Ise^(-γl), V = Vse^(-γl)
Velocity Factor
- Velocity Factor (Vp/c) is defined as the ratio of the actual propagation velocity through a given medium to the speed of light in a vacuum.
- Vp/c = (1/√(ε_r)) where εr is the relative permittivity of the dielectric
Electrical Length
- The electrical length is the length of a line relative to the length of a propagating wavelength
- Calculated using the equation: βl° = 360°L/λ (in degrees) and β_rad = 2πL/λ (in radians), with L representing the physical length and λ the wavelength
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Description
Test your knowledge on transmission line concepts, including impedance matching, the Smith chart, and electrical constants. This quiz covers key principles and applications relevant to circuit design and transmission line parameters.
