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Subelement L14

Transmission Lines.

Section L14

For an antenna tuner of the "Transformer" type, which of the following statements is FALSE?

  • The input is suitable for 50 ohm impedance
  • The output is suitable for impedances from low to high
  • The circuit is known as a transformer-type antenna tuner
  • Correct Answer
    The circuit is known as a Pi-type antenna tuner

A tuning circuit using two inductively-coupled windings can readily effect an impedance transformation like a transformer. The coupling may be fixed or variable. Moving a tap on the output coil changes the turns ratio and permits raising or lowering impedance.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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For an antenna tuner of the "Series" type, which of the following statements is false?

  • The output is suitable for impedances from low to high
  • The input is suitable for impedance of 50 ohms
  • Correct Answer
    The circuit is known as a Pi-type antenna tuner
  • The circuit is known as a Series-type antenna tuner

A simple series L-C network is one of the ways to couple a random-length antenna, whose impedance can be quite unpredictable, directly to a transmitter. Other options include the L and Pi networks.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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For an antenna tuner of the "L" type, which of the following statements is false?

  • The circuit is known as an L-type antenna tuner
  • Correct Answer
    The circuit is suitable for matching to a vertical ground plane antenna
  • The transmitter input is suitable for 50 ohms impedance
  • The antenna output is high impedance

A resonant vertical ground plane antenna offers an impedance in the range 30 to 50 ohms. A low-pass "L" network (series inductor followed by parallel capacitor) is commonly used with a high impedance random wire. With only two variables components, an "L" network has a limited range of impedance transformation. [ In reality, four "L" configurations are possible, two of which can match to a lower impedance. ]

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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For an antenna tuner of the "Pi" type, which of the following statements is false?

  • The circuit is a Pi-type antenna tuner
  • Correct Answer
    The circuit is a series-type antenna tuner
  • The transmitter input is suitable for impedance of 50 ohms
  • The antenna output is suitable for impedances from low to high

The "Pi" configuration, usually an input shunt capacitor, a series inductor and an output shunt capacitor, resembles two L networks back-to-back. The Pi has greater impedance transformation range than the L network.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What is a pi-network?

  • Correct Answer
    A network consisting of one inductor and two capacitors or two inductors and one capacitor
  • An antenna matching network that is isolated from ground
  • A network consisting of four inductors or four capacitors
  • A power incidence network

The "Pi" configuration, usually an input shunt capacitor, a series inductor and an output shunt capacitor, resembles two L networks back-to-back. The Pi has greater impedance transformation range than the L network.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Which type of network offers the greatest transformation ratio?

  • Chebyshev
  • Butterworth
  • L-network
  • Correct Answer
    Pi-network

With only two variables components, an "L" network has a limited range of impedance transformation. The "Pi" configuration, usually an input shunt capacitor, a series inductor and an output shunt capacitor, resembles two L networks back-to-back. The Pi has greater impedance transformation range than the L network. The "Pi-L" network, where the Pi output capacitor doubles as an input capacitor to a subsequent L section, provides even more harmonic suppression and a greater transformation ratio.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Why is an L-network of limited utility in impedance matching?

  • It has limited power handling capability
  • Correct Answer
    It matches only a small impedance range
  • It is thermally unstable
  • It is prone to self-resonance

With only two variables components, an "L" network has a limited range of impedance transformation. The "Pi" configuration, usually an input shunt capacitor, a series inductor and an output shunt capacitor, resembles two L networks back-to-back. The Pi has greater impedance transformation range than the L network. The "Pi-L" network, where the Pi output capacitor doubles as an input capacitor to a subsequent L section, provides even more harmonic suppression and a greater transformation ratio.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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How does a network transform one impedance to another?

  • Correct Answer
    It cancels the reactive part of an impedance and changes the resistive part
  • It produces transconductance to cancel the reactive part of an impedance
  • It introduces negative resistance to cancel the resistive part of an impedance
  • Network resistances substitute for load resistances

Within the context of matching the line to a transmitter, the goal is to present a suitable resistive impedance to the final amplifier. Impedance comprises a reactive value and a resistive value. To achieve matching, reactance must be cancelled and resistance transformed.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What advantage does a pi-L network have over a pi-network for impedance matching between a vacuum tube linear amplifier and a multiband antenna?

  • Greater transformation range
  • Correct Answer
    Greater harmonic suppression
  • Higher efficiency
  • Lower losses

Key words: MULTIBAND ANTENNA. Such an antenna may radiate harmonics more readily. The added harmonic suppression of the "Pi-L" network is advantageous.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Which type of network provides the greatest harmonic suppression?

  • Inverse pi-network
  • Pi-network
  • L-network
  • Correct Answer
    Pi-L network

With only two variables components, an "L" network has a limited range of impedance transformation. The "Pi" configuration, usually an input shunt capacitor, a series inductor and an output shunt capacitor, resembles two L networks back-to-back. The Pi has greater impedance transformation range than the L network. The "Pi-L" network, where the Pi output capacitor doubles as an input capacitor to a subsequent L section, provides even more harmonic suppression and a greater transformation ratio.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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A Smith Chart is useful:

  • to solve problems in direct current circuits
  • because it only works with complex numbers
  • Correct Answer
    because it simplifies mathematical operations
  • only to solve matching and transmission line problems

"The Smith chart, invented by Phillip H. Smith (1905�1987), is a graphical aid or nomogram designed for electrical and electronics engineers specializing in radio frequency (RF) engineering to assist in solving problems with transmission lines and matching circuits. (...) The Smith chart is most frequently used at or within the unity radius region. However, the remainder is still mathematically relevant, being used, for example, in oscillator design and stability analysis". (Wikipedia)

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What kind of impedance does a quarter wavelength transmission line present to the source when the line is shorted at the far end?

  • A very low impedance
  • Correct Answer
    A very high impedance
  • The same as the characteristic impedance of the transmission line
  • The same as the output impedance of the source

Line lengths that are multiples of a half-wavelength replicate the load impedance at the input regardless of the Characteristic Impedance: i.e., the input impedance equals the load impedance. Line lengths that are odd multiples of a quarter-wavelength behave as impedance transformers. Quarter-wavelength line sections are said to invert impedance: an open is reflected as a short and vice-versa. When used for matching right at the antenna, a quarter-wavelength line section is called a "Q Section" or "Quarter-Wave Transformer".

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What kind of impedance does a quarter wavelength transmission line present to the source if the line is open at the far end?

  • A very high impedance
  • The same as the output impedance of the source
  • The same as the characteristic impedance of the transmission line
  • Correct Answer
    A very low impedance

Line lengths that are multiples of a half-wavelength replicate the load impedance at the input regardless of the Characteristic Impedance: i.e., the input impedance equals the load impedance. Line lengths that are odd multiples of a quarter-wavelength behave as impedance transformers. Quarter-wavelength line sections are said to invert impedance: an open is reflected as a short and vice-versa. When used for matching right at the antenna, a quarter-wavelength line section is called a "Q Section" or "Quarter-Wave Transformer".

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

What kind of impedance does a half wavelength transmission line present to the source when the line is open at the far end?

  • Correct Answer
    A very high impedance
  • The same as the characteristic impedance of the transmission line
  • The same as the output impedance of the source
  • A very low impedance

Line lengths that are multiples of a half-wavelength replicate the load impedance at the input regardless of the Characteristic Impedance: i.e., the input impedance equals the load impedance. Line lengths that are odd multiples of a quarter-wavelength behave as impedance transformers. Quarter-wavelength line sections are said to invert impedance: an open is reflected as a short and vice-versa. When used for matching right at the antenna, a quarter-wavelength line section is called a "Q Section" or "Quarter-Wave Transformer".

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

What kind of impedance does a half wavelength transmission line present to the source when the line is shorted at the far end?

  • The same as the output impedance of the source
  • Correct Answer
    A very low impedance
  • A very high impedance
  • The same as the characteristic impedance of the transmission line

Line lengths that are multiples of a half-wavelength replicate the load impedance at the input regardless of the Characteristic Impedance: i.e., the input impedance equals the load impedance. Line lengths that are odd multiples of a quarter-wavelength behave as impedance transformers. Quarter-wavelength line sections are said to invert impedance: an open is reflected as a short and vice-versa. When used for matching right at the antenna, a quarter-wavelength line section is called a "Q Section" or "Quarter-Wave Transformer".

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What is the velocity factor of a transmission line?

  • Correct Answer
    The velocity of the wave on the transmission line divided by the velocity of light
  • The velocity of the wave on the transmission line multiplied by the velocity of light in a vacuum
  • The index of shielding for coaxial cable
  • The ratio of the characteristic impedance of the line to the terminating impedance

Velocity Factor is a ratio of wave travel speed on a transmission line with respect to wave speed in vacuum. It is expressed as a percentage or a decimal fraction because waves travel slower on lines than in space. The dielectric constant of the insulator between the conductors determines the Velocity Factor per this formula: 1 over the square root of the dielectric constant. Lines using polyethylene have a Velocity Factor of 66%, foam polyethylene brings it above 80%. Actual Velocity Factor can vary by as much as plus or minus 10%. Because of that delay in propagation, a given physical length will always seem longer electrically.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What is the term for the ratio of the actual velocity at which a signal travels through a transmission line to the speed of light in a vacuum?

  • Surge impedance
  • Standing wave ratio
  • Correct Answer
    Velocity factor
  • Characteristic impedance

Velocity Factor is a ratio of wave travel speed on a transmission line with respect to wave speed in vacuum. It is expressed as a percentage or a decimal fraction because waves travel slower on lines than in space. The dielectric constant of the insulator between the conductors determines the Velocity Factor per this formula: 1 over the square root of the dielectric constant. Lines using polyethylene have a Velocity Factor of 66%, foam polyethylene brings it above 80%. Actual Velocity Factor can vary by as much as plus or minus 10%. Because of that delay in propagation, a given physical length will always seem longer electrically.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What is a typical velocity factor for coaxial cable with polyethylene dielectric?

  • Correct Answer
    0.66
  • 0.33
  • 0.1
  • 2.7

Velocity Factor is a ratio of wave travel speed on a transmission line with respect to wave speed in vacuum. It is expressed as a percentage or a decimal fraction because waves travel slower on lines than in space. The dielectric constant of the insulator between the conductors determines the Velocity Factor per this formula: 1 over the square root of the dielectric constant. Lines using polyethylene have a Velocity Factor of 66%, foam polyethylene brings it above 80%. Actual Velocity Factor can vary by as much as plus or minus 10%. Because of that delay in propagation, a given physical length will always seem longer electrically.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

What determines the velocity factor in a transmission line?

  • Correct Answer
    Dielectrics in the line
  • The line length
  • The centre conductor resistivity
  • The terminal impedance

Velocity Factor is a ratio of wave travel speed on a transmission line with respect to wave speed in vacuum. It is expressed as a percentage or a decimal fraction because waves travel slower on lines than in space. The dielectric constant of the insulator between the conductors determines the Velocity Factor per this formula: 1 over the square root of the dielectric constant. Lines using polyethylene have a Velocity Factor of 66%, foam polyethylene brings it above 80%. Actual Velocity Factor can vary by as much as plus or minus 10%. Because of that delay in propagation, a given physical length will always seem longer electrically.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Why is the physical length of a coaxial cable shorter than its electrical length?

  • The surge impedance is higher in the parallel transmission line
  • Skin effect is less pronounced in the coaxial cable
  • The characteristic impedance is higher in a parallel transmission line
  • Correct Answer
    RF energy moves slower along the coaxial cable than in air

Velocity Factor is a ratio of wave travel speed on a transmission line with respect to wave speed in vacuum. It is expressed as a percentage or a decimal fraction because waves travel slower on lines than in space. The dielectric constant of the insulator between the conductors determines the Velocity Factor per this formula: 1 over the square root of the dielectric constant. Lines using polyethylene have a Velocity Factor of 66%, foam polyethylene brings it above 80%. Actual Velocity Factor can vary by as much as plus or minus 10%. Because of that delay in propagation, a given physical length will always seem longer electrically.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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The reciprocal of the square root of the dielectric constant of the material used to separate the conductors in a transmission line gives the ____________ of the line:

  • impedance
  • hermetic losses
  • Correct Answer
    velocity factor
  • VSWR

Velocity Factor is a ratio of wave travel speed on a transmission line with respect to wave speed in vacuum. It is expressed as a percentage or a decimal fraction because waves travel slower on lines than in space. The dielectric constant of the insulator between the conductors determines the Velocity Factor per this formula: 1 over the square root of the dielectric constant. Lines using polyethylene have a Velocity Factor of 66%, foam polyethylene brings it above 80%. Actual Velocity Factor can vary by as much as plus or minus 10%. Because of that delay in propagation, a given physical length will always seem longer electrically.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

Tags: none

The velocity factor of a transmission line is the:

  • speed at which the signal travels in free space
  • speed to which the standing waves are reflected back to the transmitter
  • Correct Answer
    ratio of the velocity of propagation in the transmission line to the velocity of propagation in free space
  • impedance of the line, e.g. 50 ohm, 75 ohm, etc.

Velocity Factor is a ratio of wave travel speed on a transmission line with respect to wave speed in vacuum. It is expressed as a percentage or a decimal fraction because waves travel slower on lines than in space. The dielectric constant of the insulator between the conductors determines the Velocity Factor per this formula: 1 over the square root of the dielectric constant. Lines using polyethylene have a Velocity Factor of 66%, foam polyethylene brings it above 80%. Actual Velocity Factor can vary by as much as plus or minus 10%. Because of that delay in propagation, a given physical length will always seem longer electrically.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Waveguide is typically used:

  • Correct Answer
    at frequencies above 3000 MHz
  • at frequencies above 2 MHz
  • at frequencies below 150 MHz
  • at frequencies below 1500 MHz

Waveguides, used as transmission lines, are hollow pipes through which signals propagate as waves. The width or diameter of the waveguide must be slightly larger than a half-wavelength at the operating frequency. Below one gigahertz, dimensions become prohibitive. Signals with wavelengths too large for the physical size of the waveguide are attenuated: waveguides behave like high-pass filters, in other words, attenuation below the cutoff frequency. Waveguides do not suffer the conduction, dielectric or radiation losses that normal transmission lines present at microwave frequencies.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Which of the following is not correct? Waveguide is an efficient transmission medium because it features:

  • low radiation loss
  • low dielectric loss
  • low copper loss
  • Correct Answer
    low hysteresis loss

Waveguides, used as transmission lines, are hollow pipes through which signals propagate as waves. The width or diameter of the waveguide must be slightly larger than a half-wavelength at the operating frequency. Below one gigahertz, dimensions become prohibitive. Signals with wavelengths too large for the physical size of the waveguide are attenuated: waveguides behave like high-pass filters, in other words, attenuation below the cutoff frequency. Waveguides do not suffer the conduction, dielectric or radiation losses that normal transmission lines present at microwave frequencies.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Which of the following is an advantage of waveguide as a transmission line?

  • Heavy and difficult to install
  • Correct Answer
    Low loss
  • Frequency sensitive based on dimensions
  • Expensive

Waveguides, used as transmission lines, are hollow pipes through which signals propagate as waves. The width or diameter of the waveguide must be slightly larger than a half-wavelength at the operating frequency. Below one gigahertz, dimensions become prohibitive. Signals with wavelengths too large for the physical size of the waveguide are attenuated: waveguides behave like high-pass filters, in other words, attenuation below the cutoff frequency. Waveguides do not suffer the conduction, dielectric or radiation losses that normal transmission lines present at microwave frequencies.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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For rectangular waveguide to transfer energy, the cross-section should be at least:

  • three-eighths wavelength
  • one-eighth wavelength
  • one-quarter wavelength
  • Correct Answer
    one-half wavelength

Waveguides, used as transmission lines, are hollow pipes through which signals propagate as waves. The width or diameter of the waveguide must be slightly larger than a half-wavelength at the operating frequency. Below one gigahertz, dimensions become prohibitive. Signals with wavelengths too large for the physical size of the waveguide are attenuated: waveguides behave like high-pass filters, in other words, attenuation below the cutoff frequency. Waveguides do not suffer the conduction, dielectric or radiation losses that normal transmission lines present at microwave frequencies.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Which of the following statements about waveguide IS NOT correct?

  • In the transverse electric mode, a component of the magnetic field is in the direction of propagation
  • In the transverse magnetic mode, a component of the electric field is in the direction of propagation
  • Waveguide has low loss at high frequencies, but high loss below cutoff frequency
  • Correct Answer
    Waveguide has high loss at high frequencies, but low loss below cutoff frequency

Key words: IS NOT. Signals with wavelengths too large for the physical size of the waveguide are attenuated: waveguides behave like high-pass filters, in other words, attenuation below the cutoff frequency. In free space, waves are known as transverse-electromagnetic: the electric field, the magnetic field and the direction of travel are all perpendicular to one another. In a waveguide, waves bounce from wall to wall thus travelling in a zigzag manner. Only one of the electric or magnetic field can be truly perpendicular with the length of the waveguide; the mode, transverse electric or transverse magnetic, describes which field is purely perpendicular.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Which of the following is a major advantage of waveguide over coaxial cable for use at microwave frequencies?

  • Correct Answer
    Very low losses
  • Frequency response from 1.8 MHz to 24GHz
  • Easy to install
  • Inexpensive to install

Waveguides, used as transmission lines, are hollow pipes through which signals propagate as waves. The width or diameter of the waveguide must be slightly larger than a half-wavelength at the operating frequency. Below one gigahertz, dimensions become prohibitive. Signals with wavelengths too large for the physical size of the waveguide are attenuated: waveguides behave like high-pass filters, in other words, attenuation below the cutoff frequency. Waveguides do not suffer the conduction, dielectric or radiation losses that normal transmission lines present at microwave frequencies.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What is printed circuit transmission line called?

  • Ground plane
  • Correct Answer
    Microstripline
  • Dielectric substrate
  • Dielectric imprinting

A Microstrip transmission line is a type of line consisting of a thin and flat strip of conductive material separated from a ground plane by a dielectric. A double-sided printed circuit board lends itself to the construction of microstrip lines: traces on top with a ground plane underneath. Characteristic Impedance is determined by trace width, dielectric thickness and dielectric constant. One side of the line is exposed to air, external shielding may be required when high isolation is required. Stripline uses a similar thin and flat conductor but sandwiched between two parallel ground planes.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Compared with coaxial cable, microstripline:

  • must have much higher characteristic impedance
  • Correct Answer
    has poorer shielding
  • has superior shielding
  • must have much lower characteristic impedance

A Microstrip transmission line is a type of line consisting of a thin and flat strip of conductive material separated from a ground plane by a dielectric. A double-sided printed circuit board lends itself to the construction of microstrip lines: traces on top with a ground plane underneath. Characteristic Impedance is determined by trace width, dielectric thickness and dielectric constant. One side of the line is exposed to air, external shielding may be required when high isolation is required. Stripline uses a similar thin and flat conductor but sandwiched between two parallel ground planes.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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A section of waveguide:

  • operates like a low-pass filter
  • operates like a band-stop filter
  • is lightweight and easy to install
  • Correct Answer
    operates like a high-pass filter

Waveguides, used as transmission lines, are hollow pipes through which signals propagate as waves. The width or diameter of the waveguide must be slightly larger than a half-wavelength at the operating frequency. Below one gigahertz, dimensions become prohibitive. Signals with wavelengths too large for the physical size of the waveguide are attenuated: waveguides behave like high-pass filters, in other words, attenuation below the cutoff frequency. Waveguides do not suffer the conduction, dielectric or radiation losses that normal transmission lines present at microwave frequencies.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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Stripline is a:

  • family of fluids for removing coatings from small parts
  • Correct Answer
    printed circuit transmission line
  • small semiconductor family
  • high power microwave antenna

A Microstrip transmission line is a type of line consisting of a thin and flat strip of conductive material separated from a ground plane by a dielectric. A double-sided printed circuit board lends itself to the construction of microstrip lines: traces on top with a ground plane underneath. Characteristic Impedance is determined by trace width, dielectric thickness and dielectric constant. External shielding may be required when high isolation is required. Stripline uses a similar thin and flat conductor but sandwiched between two parallel ground planes.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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What precautions should you take before beginning repairs on a microwave feed horn or waveguide?

  • Be sure propagation conditions are unfavourable for tropospheric ducting
  • Be sure to wear tight-fitting clothes and gloves to protect your body and hands from sharp edges
  • Correct Answer
    Be sure the transmitter is turned off and the power source is disconnected
  • Be sure the weather is dry and sunny

With the possibility of shorter wavelengths to reach deeper into the body or to produce resonances in smaller structures, such as the eye, be extra careful not to expose anyone to microwave radiation. The significant gain available from physically small antennas also turn low power levels into definite risks. Heating is one known effect of RF on body tissues, other effects are possible.

Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.

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