B-006
Subelement B-006
Section B-006-009
Section B-006-009
How is a parasitic antenna element energized?
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By direct connection to the transmission line
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Correct AnswerBy induction or radiation from a driven element
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By inductive coupling from a wave trap
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By direct connection to a driven element
The term 'parasite' means "feeding off something else". For instance, in a Yagi, there is only one 'driven' element where the transmission line attaches. The 'reflector' and 'director' capture energy off the 'driven' and re-radiate it.
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 can the directivity of a half-wave dipole be increased?
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Correct AnswerBy adding one or more parasitic elements
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By using a radiating element with a larger diameter
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By adding traps to the radiating element
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By lengthening the radiating element
If a half-wave dipole is converted to a Yagi by adding a slightly shorter parasitic element, in what direction(s) does the radiation strength increase?
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From the new element towards the dipole
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Correct AnswerFrom the dipole towards the new element
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In both directions at right angles to the elements
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In both directions parallel to the elements
Key words: PARASITIC, SHORTER. A 'slightly shorter parasitic' element is the description of a 'Director'. A dipole and a 'director' in front of it make up a two-element Yagi. Radiation will be enhanced towards the 'director' at the expense of the back.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
If a half-wave dipole is converted to a Yagi by adding a slightly longer element, in what direction(s) does the radiation strength increase?
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From the dipole towards the new element
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In both directions at right angles to the elements
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Correct AnswerFrom the new element towards the dipole
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In both directions parallel to the elements
Key words: PARASITIC, LONGER. A 'slightly longer parasitic' element is the description of a 'reflector'. A dipole and a 'reflector' behind it make up a two-element Yagi. Radiation will be enhanced away from the 'reflector', towards the radiating element (the dipole, the 'driven').
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 property of an antenna that defines the range of frequencies to which it will respond, is called its:
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antenna aperture
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Correct Answerbandwidth
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front-to-back ratio
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beamwidth
What is the approximate gain of a half-wave dipole in free space relative to an isotropic radiator?
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Correct Answer2.1 dB
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3.0 dB
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1.0 dB
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1.5 dB
An 'isotropic radiator' radiates equally well in ALL directions ( radiation pattern is a 'sphere'). A dipole in free space has a radiation pattern similar to a donut ( maximum radiation broadside from the antenna, none towards the ends ). This concentration of radiation produces a gain of 2.1 dB over an isotropic antenna.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What is meant by antenna gain?
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The ratio of the power radiated by an antenna compared to the transmitter power
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Correct AnswerThe ratio of the radiated signal strength of an antenna to that of a reference antenna
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The ratio of the signal in the forward direction to the signal in the back direction
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The power amplifier gain minus the transmission line losses
Antenna Gain is a ratio, expressed in decibel, of the radiation of a given antenna against some reference antenna. For example, the expression 'dBi' means decibel over an isotropic radiator.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
What is meant by antenna bandwidth?
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The angle formed between two imaginary lines drawn through the ends of the elements
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Correct AnswerThe frequency range over which the antenna may be expected to perform well
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The angle between the half-power radiation points
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Antenna length divided by the number of elements
In free space, what is the radiation pattern of a half-wave dipole?
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Correct AnswerMaximum radiation broadside from the antenna
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Hemispherical radiation pattern
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Maximum radiation from the ends of the antenna
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Omnidirectional radiation pattern
A dipole in free space has a radiation pattern similar to a donut ( maximum radiation broadside from the antenna, none towards the ends ). This concentration of radiation produces a gain of 2.1 dB over an isotropic antenna.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
The gain of an antenna, especially on VHF and above, is quoted in dBi. The "i" in this expression stands for:
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integral
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ionospheric
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interpolated
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Correct Answerisotropic
Antenna Gain is a ratio, expressed in decibel, of the radiation of a given antenna against some reference antenna. For example, the expression 'dBi' means decibel over an isotropic radiator.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
An antenna is said to have a gain of 4.1 dBi. How much gain is this over a half-wave dipole antenna?
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4.1 dB
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Correct Answer2.0 dB
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1.1 dB
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3.0 dB
A dipole in free space has a radiation pattern similar to a donut ( maximum radiation broadside from the antenna, none towards the ends ). This concentration of radiation produces a gain of 2.1 dB over an isotropic antenna. This other antenna has an advantage of 2.0 dB over a dipole.
Original copyright; explanations transcribed with permission from Francois VE2AAY, author of the ExHAMiner exam simulator. Do not copy without his permission.
Tags: none
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