B-006
Subelement B-006
Section B-006-001
Section B-006-001
What connects your transceiver to your antenna?
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A radial wire
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Correct AnswerA transmission line
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A ground wire
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A counterpoise wire
A "transmission line" carries radio frequency signals from the station to the antenna and between the various pieces of equipment in the station.
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 characteristic impedance of a transmission line is determined by the:
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Correct Answerphysical dimensions and relative positions of the conductors
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load placed at the end of the line
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frequency at which the line is operated
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length of the line
Characteristic Impedance is determined mainly by the physical dimensions of the line. Length, frequency or load have nothing to do with 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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The characteristic impedance of a 20-metre piece of transmission line is 52 ohms. What would the impedance be if 10 metres were cut off?
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Correct Answer52 ohms
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26 ohms
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104 ohms
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13 ohms
Why can coaxial cables of different diameters have the same characteristic impedance?
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Their characteristic impedance depends on operating frequency
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Characteristic impedance is set by the choice of conducting material
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Characteristic impedance is independent of line diameter
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Correct AnswerTheir characteristic impedance depends on the ratio of conductor diameters
The Characteristic Impedance of coaxial cable is determined mainly by the ratio of the outer conductor to the inner conductor. Different diameters of lines can have the same Characteristic Impedance as long as the RATIO is preserved.
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 commonly available transmission line can be buried directly in the ground for some distance without adverse effects?
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Correct AnswerCoaxial cable
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75-ohm twin-lead
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300-ohm window line
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600-ohm open-wire line
Because the outer conductor of a coaxial cable is operated at ground potential, it can be buried. Parallel lines operate differently with both conductors at some voltage above ground.
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 transmitter is delivering radio frequency (RF) energy into a coaxial cable with a characteristic impedance of 50 ohms. The cable is terminated by a purely resistive load. What value of load resistance will absorb all the RF energy it receives?
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25 ohms
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200 ohms
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Correct Answer50 ohms
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100 ohms
If a resistor of the same value as the Characteristic Impedance of a given line is placed at the end of that line, no energy is reflected. 100% of the incoming energy is dissipated in the terminating load.
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 major factor influencing the velocity factor of a coaxial cable?
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Size and spacing of the conductors
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Center conductor material
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Correct AnswerDielectric material
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Use of a solid or braided shield
Radio signals propagate (travel) slower in a transmission line than they do in space. The velocity factor is the relative speed of a wave in a line when compared to free space. The type of type of dielectric between the conductors determines that factor.
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 characteristic impedance of an open-wire transmission line depends, in part, on the diameter of its conductors. What other dimension determines its characteristic impedance?
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Distance to metal structures
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Length of the line
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Height above ground
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Correct AnswerSpacing of the conductors
Physical dimensions (radius and centre to centre distance) determine Characteristic Impedance. The speed at which waves travel on the line (velocity) is another characteristic altogether.
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 transmission line is terminated by an impedance that differs significantly from the characteristic impedance of the line. What impedance will be measured at the input of the line?
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Correct AnswerA value of impedance influenced by line length
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A zero impedance
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An infinite impedance
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An impedance nearly equal to the characteristic impedance
A transmission line offers an input impedance similar to the terminating impedance when the impedance placed at the end of the line matches the characteristic impedance of the line: in short, a 50 ohms impedance at the end of a line with a characteristic impedance of 50 ohms will present a 50 ohms impedance to the transmitter, regardless of line length. If the terminating impedance is mismatched, the impedance seen at the input of the line will depend on terminating impedance AND line length: the line acts as an impedance 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 factors determine the characteristic impedance of an open-wire transmission line?
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The frequency of the signal and the length of the line
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The distance between the centres of the conductors and the length of the line
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The radius of the conductors and the frequency of the signal
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Correct AnswerThe distance between the centres of the conductors and the diameter of the conductors
Physical dimensions (radius and centre to centre distance) influence Characteristic Impedance. It is independent of line length or operating frequency.
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 factors determine the characteristic impedance of a coaxial transmission line?
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The diameter of the shield and the frequency of the signal
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Correct AnswerThe ratio of the diameter of the outer shield to the diameter of the inner conductor
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The diameter of the shield and the length of the line
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The frequency of the signal and the length of the line
The Characteristic Impedance of coaxial cable is determined mainly by the ratio of the outer conductor to the inner conductor. It is independent of line length or operating frequency.
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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