or
Subelement L06b
Transmission Lines.
Section L06b
• A ground wire
A transmission line
• The power cord

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:
• length of the line
• frequency at which the line is operated
• load placed on the line
physical dimensions and relative positions of the conductors

Characteristic Impedance is determined 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. If 10 metres were cut off, the impedance would be:
• 13 ohms
52 ohms
• 26 ohms
• 39 ohms

This is a catch. Characteristic Impedance does NOT change with line length. 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 coaxial line:
can be the same for different diameter line
• changes significantly with the frequency of the energy it carries
• is correct for only one size of line
• is greater for larger diameter line

The Characteristic Impedance of coaxial cable is determined 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 antenna transmission line can be buried directly in the ground for some distance without adverse effects?
• 600 ohm open wire line
Coaxial cable

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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The characteristic impedance of a transmission line is:
• the dynamic impedance of the line at the operating frequency
• the ratio of the power supplied to the line to the power delivered to the load
equal to the pure resistance which, if connected to the end of the line, will absorb all the power arriving along it
• the impedance of a section of the line one wavelength long

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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A transmission line differs from an ordinary circuit or network in communications or signalling devices in one very important way. That important aspect is:
• inductive reactance
• resistance
propagation delay
• capacitive reactance

Radio signals propagate (travel) slower in a transmission line than they do in space. 'Propagation Delay' is specific to transmission lines. Resistance and reactance can be found in many other components or circuits.

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 parallel wire transmission line does not depend on the:
• centre to centre distance between conductors
• dielectric
velocity of energy on the line

Key words: DOES NOT. Physical dimensions (radius and centre to centre distance) and dielectric influence 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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If the impedance terminating a transmission line differs significantly from the characteristic impedance of the line, what will be observed at the input of the line?
• An impedance nearly equal to the characteristic impedance
Some value of impedance influenced by line length
• An infinite impedance
• A negative 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 a parallel-conductor antenna transmission line?
• The radius of the conductors and the frequency of the signal
• The frequency of the signal and the length of the line
The distance between the centres of the conductors and the radius of the conductors
• The distance between the centres of the conductors and the length of the line

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 antenna transmission line?
• The diameter of the shield and the length of the line
• The diameter of the shield and the frequency of the signal
• The frequency of the signal and the length of the line
The ratio of the diameter of the inner conductor to the diameter of the outer shield

The Characteristic Impedance of coaxial cable is determined 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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What is a coaxial cable?
• Two wires twisted around each other in a spiral
A center wire inside an insulating material which is covered by a metal sleeve or shield
• Two wires side-by-side in a plastic ribbon
• Two wires side-by-side held apart by insulating rods

Coaxial: two concentric conductors, an inner conductor, a dielectric (insulator) and an outer conductor (braided or solid). 'Twin lead' (a type of parallel line) looks like a ribbon. 'Open wire line' or 'ladder line' (a type of parallel line) uses insulating rods. [ 'Twisted pair' is very rarely used in radio work. ]

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 parallel-conductor transmission line?
• Two wires twisted around each other in a spiral
• A center wire inside an insulating material which is covered by a metal sleeve or shield
• A metal pipe which is as wide or slightly wider than a wavelength of the signal it carries
Two wires side-by-side held apart by insulating material

"Two wires held apart by insulating rods (spacers or 'spreaders')" is also known as 'open wire line' or 'ladder line'.

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 antenna transmission line is made of two conductors held apart by insulated rods?
• Twisted pair
Open wire line
• Coaxial cable
• Twin lead in a plastic ribbon

"Two wires held apart by insulating rods (spacers or 'spreaders')" is also known as 'open wire line' or 'ladder line'.

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 does the term "balun" mean?
• Balanced antenna network
Balanced to unbalanced
• Balanced unmodulator

"Balun" is the contraction of "BALanced to UNbalanced". Dipole antennas and parallel lines operate in a BALanced mode (two conductors float above ground potential). A quarter-wave antenna, a ground-plane antenna and coaxial cable operate in an UNbalanced mode (with one side grounded). A BALUN interfaces balanced antenna to unbalanced transmission line OR balanced line to unbalanced line. A BALUN can also include impedance transformation.

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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Where would you install a balun to feed a dipole antenna with 50-ohm coaxial cable?
• Between the antenna and the ground
• Between the coaxial cable and the ground
Between the coaxial cable and the antenna
• Between the transmitter and the coaxial cable

"Balun" is the contraction of "BALanced to UNbalanced". Dipole antennas and parallel lines operate in a BALanced mode (two conductors float above ground potential. A quarter-wave antenna, a ground-plane antenna and coaxial cable operate in an UNbalanced mode (with one side grounded). A BALUN interfaces balanced antenna to unbalanced transmission line OR balanced line to unbalanced line. A BALUN can also include impedance transformation.

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 an unbalanced line?
• Transmission line with both conductors connected to each other
Transmission line with one conductor connected to ground
• Transmission line with neither conductor connected to ground
• Transmission line with both conductors connected to ground

key word: UNBALANCED. An 'UNbalanced' transmission line functions with one conductor connected to ground (like coaxial cable or 'coax' for short). A 'balanced' transmission line operates with both conductors floating above ground potential (like all types of parallel lines: twin-lead, open-wire line).

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 device can be installed to feed a balanced antenna with an unbalanced transmission line?
• A triaxial transformer
• A wave trap
A balun

"Balun" is the contraction of "BALanced to UNbalanced". Dipole antennas and parallel lines operate in a BALanced mode (two conductors float above ground potential. A quarter-wave antenna, a ground-plane antenna and coaxial cable operate in an UNbalanced mode (with one side grounded). A BALUN interfaces balanced antenna to unbalanced transmission line OR balanced line to unbalanced line. A BALUN can also include impedance transformation.

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 flexible coaxial line contains:
• four or more conductors running parallel
• only one conductor
• two parallel conductors separated by spacers
braided shield conductor and insulation around a central conductor

Coaxial: two concentric conductors, an inner conductor, a dielectric (insulator) and an outer conductor (braided or solid). "Two parallel conductors separated by spacers" are also known as 'open wire line' or 'ladder line'.

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 balanced transmission line:
• carries RF current on one wire only
• is made of one conductor only
is made of two parallel wires
• has one conductor inside the other

key word: BALANCED. A 'balanced' transmission line operates with both conductors floating above ground potential (like all types of parallel lines: twin-lead, open-wire line). An 'UNbalanced' transmission line functions with one conductor connected to ground (like coaxial cable or 'coax' for short).

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 75 ohm transmission line could be matched to the 300 ohm feed point of an antenna:
• with an extra 250 ohm resistor
• by using a 4 to 1 trigatron
• by inserting a diode in one leg of the antenna
by using a 4 to 1 impedance transformer

"Balun" is the contraction of "BALanced to UNbalanced". Dipole antennas and parallel lines operate in a BALanced mode (two conductors float above ground potential. A quarter-wave antenna, a ground-plane antenna and coaxial cable operate in an UNbalanced mode (with one side grounded). A BALUN interfaces balanced antenna to unbalanced transmission line OR balanced line to unbalanced line. A BALUN can also include impedance transformation. In this example, a '4 to 1' balun.

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 antenna transmission line can be constructed using two conductors which are maintained a uniform distance apart using insulated spreaders?
600 ohm open wire line
• Coaxial cable

"Two wires held apart by insulating rods (spacers or 'spreaders')" is also known as 'open wire line' or 'ladder line'. 'Twin-lead' is two conductors held apart in a plastic ribbon. Coaxial cable is two concentric conductors, an inner conductor, a dielectric (insulator) and an outer conductor (braided or solid).

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 does coaxial cable make a good antenna transmission line?
It is weatherproof, and its impedance matches most amateur antennas
• It is weatherproof, and its impedance is higher than that of most amateur antennas
• It can be used near metal objects, and its impedance is higher than that of most amateur antennas
• You can make it at home, and its impedance matches most amateur antennas

Parallel lines generally have Characteristic Impedances in the range of 300 to 600 ohms. Common coaxial cable have Characteristic Impedances of 50 or 75 ohms. Such an impedance is a direct match to transmitters and common antennas.

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 best antenna transmission line to use, if it must be put near grounded metal objects?
Coaxial cable
• Twisted pair

Coaxial cable, with its shielded and grounded outer conductor, is not affected by nearby metallic objects.

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 are some reasons not to use parallel-conductor transmission line?
It does not work well when tied down to metal objects, and you should use a balun and may have to use an impedance-matching device with your transceiver
• You must use an impedance-matching device with your transceiver, and it does not work very well with a high SWR
• It does not work well when tied down to metal objects, and it cannot operate under high power
• It is difficult to make at home, and it does not work very well with a high SWR

key word: NOT. The high Characteristic Impedances and greater separation of the conductors in parallel lines DO permit high power and high Standing Wave Ratio (SWR) BUT nearby metallic objects can affect them and impedance matching is most often necessary at the transmitter end. Their high Characteristic Impedance permits carrying power with less current (P = R * I squared), less current implies less losses due to resistance.

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 common connector type usually joins RG-213 coaxial cable to an HF transceiver?
• A banana plug connector
• A binding post connector
A PL-259 connector
• An F-type cable connector

'RG-213' is the catalogue designation of common 10 mm (0.405 in.) coaxial cable. 'PL-259' is the catalogue designation of the male connector which matches the output connector found on MF/HF (Medium Frequency/High Frequency) transceivers. The 'SMA' connector is found on modern compact handheld transceivers. The 'Type-N' connector is the connector of choice above 300 MHz. The 'BNC' connector is found on larger size handheld transceivers.

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 common connector usually joins a hand-held transceiver to its antenna?
• A binding post connector
An SMA connector
• A PL-259 connector
• An F-type cable connector

The 'SMA' connector is found on modern compact handheld transceivers. The 'BNC' connector is found on older and larger handheld transceivers. 'PL-259' is the catalogue designation of the male connector which matches the output connector found on MF/HF (Medium Frequency/High Frequency) transceivers. The PL-259 connector fits on 10 mm (0.405 in.) coaxial cable such as RG-213. The 'Type-N' connector is the connector of choice above 300 MHz.

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 these common connectors has the lowest loss at UHF?
A type-N connector
• An F-type cable connector
• A BNC connector
• A PL-259 connector

The 'Type-N' connector is the connector of choice above 300 MHz. The 'BNC' connector is found on larger size handheld transceivers. 'PL-259' is the catalogue designation of the male connector which matches the output connector found on MF/HF (Medium Frequency/High Frequency) transceivers. The 'SMA' connector is found on modern compact handheld transceivers.

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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If you install a 6 metre Yagi on a tower 60 metres (200 ft) from your transmitter, which of the following transmission lines provides the least loss?
• RG-59
• RG-58
RG-213
• RG-174

'RG-213' is the coaxial with the largest diameter (10 mm or 0.405 in.) in this group. It has the lowest loss per 30 m length.

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 should you regularly clean and tighten all antenna connectors?
• To increase their capacitance
To help keep their contact resistance at a minimum
• To keep them looking nice
• To keep them from getting stuck in place

Poor connections can also lead to intermittent electrical contact (evidenced by an erratic or 'jumpy' Standing Wave Ratio (SWR) reading at 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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What commonly available antenna transmission line can be buried directly in the ground for some distance without adverse effects?
Coaxial cable
• 600 ohm open wire line

Coaxial cable, with its shielded and grounded outer conductor, is not affected by conductive soil. It is also not affected by nearby metallic objects.

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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When antenna transmission lines must be placed near grounded metal objects, which of the following transmission lines should be used?
• 600 ohm open wire line
Coaxial cable

Coaxial cable, with its grounded outer conductor, is not affected by nearby metallic objects.

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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TV twin-lead transmission line can be used for a transmission line in an amateur station. The impedance of this line is approximately:
• 70 ohms
300 ohms
• 600 ohms
• 50 ohms

50 ohms is the common Characteristic Impedance of coaxial cable. 600 ohms is the common Characteristic Impedance of 'open-wire line' (a.k.a. ladder line). 300 ohms is the Characteristic Impedance of twin-lead transmission line used with yesteryear outside television antennas.

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 should you use only good quality coaxial cable and connectors for a UHF antenna system?
To keep RF loss low
• To keep television interference high
• To keep the power going to your antenna system from getting too high
• To keep the standing wave ratio of your antenna system high

Losses in transmission lines increase with length and operating frequencies. At Ultra High Frequencies (UHF, 300 MHz to 3000 MHz), keeping losses low is paramount.

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 are some reasons to use parallel-conductor transmission line?
• It has low impedance, and will operate with a high SWR
• It will operate with a high SWR, and it works well when tied down to metal objects
• It has a low impedance, and has less loss than coaxial cable
It will operate with a high SWR, and has less loss than coaxial cable

The high Characteristic Impedances and greater separation of the conductors in parallel lines DO permit high power and high Standing Wave Ratio (SWR) BUT nearby metallic objects can affect them and impedance matching is most often necessary at the transmitter end. Their high Characteristic Impedance permits carrying power with less current (P = R * I squared), less current implies less losses due to resistance.

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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If your transmitter and antenna are 15 metres (50 ft) apart, but are connected by 60 metres (200 ft) of RG-58 coaxial cable, what should be done to reduce transmission line loss?
• Roll the excess cable into a coil which is as small as possible
• Shorten the excess cable so the transmission line is an even number of wavelengths long
Shorten the excess cable
• Shorten the excess cable so the transmission line is an odd number of wavelengths long

key words: 60 METRES of RG-58. Forty-five extra metres (150 ft.) of unnecessary RG-58 (diameter = 5 mm or 0.195 in.) introduce 4 dB of loss at 30 MHz, that's the problem here. [ References to multiples of the wavelength only tap into urban legends. ]

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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As the length of a transmission line is changed, what happens to signal loss?
• Signal loss is the same for any length of transmission line
Signal loss increases as length increases
• Signal loss decreases as length increases
• Signal loss is the least when the length is the same as the signal's wavelength

Signal loss in a given transmission line AUGMENT with increased length or increased operating frequency. For example, 30 m of RG-58 introduce a loss of -3 dB at 50 MHz. Doubling the length, double the loss: 60 m of RG-58 lose -6 dB at 50 MHz. The original 30 m of RG-58 wastes -10 dB at 450 MHz.

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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As the frequency of a signal is changed, what happens to signal loss in a transmission line?
• Signal loss is the least when the signal's wavelength is the same as the transmission line's length
• Signal loss is the same for any frequency
Signal loss increases with increasing frequency
• Signal loss increases with decreasing frequency

Signal loss in a given transmission line AUGMENT with increased length or increased operating frequency. For example, 30 m of RG-58 introduce a loss of -3 dB at 50 MHz. Doubling the length, double the loss: 60 m of RG-58 lose -6 dB at 50 MHz. The original 30 m of RG-58 wastes -10 dB at 450 MHz.

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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Losses occurring on a transmission line between transmitter and antenna results in:
• an SWR reading of 1:1
• reflections occurring in the line
• the wire radiating RF energy

Losses in the line are merely transmit energy that does not get to the antenna to be radiated OR received signal which does not reach the receiver to be detected. The SWR reading is primarily dependent on the adequacy of the match between the load placed at the end of the line and the Characteristic Impedance of the line. Reflections, measured by SWR, are caused by an improper match at the end of the line.

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 lowest loss transmission line on HF is:
open wire line
• coaxial cable

300 ohms is the Characteristic Impedance of TV twin-lead transmission line. The high Characteristic Impedances and greater separation of the conductors in parallel lines DO permit high power and high Standing Wave Ratio (SWR) BUT nearby metallic objects can affect them and impedance matching is most often necessary at the transmitter end. Their high Characteristic Impedance permits carrying power with less current (P = R * I squared), less current implies less losses due to resistance.

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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In what values are RF transmission line losses expressed?
• Ohms per metre
dB per unit length
• Ohms per MHz
• dB per MHz

"Decibels per unit length". In North America, typically 'dB per 100 ft.' or 'dB per 30 m' at a given frequency. Loss rises proportionally with length. Loss goes up as frequency goes up.

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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If the length of coaxial transmission line is increased from 20 metres (66 ft) to 40 metres (132 ft), how would this affect the line loss?
• It would be increased by 10%
• It would be reduced to 50%
It would be increased by 100%
• It would be reduced by 10%

If line length is doubled, the incurred signal loss is doubled. Loss for transmission lines is specified as "decibels per 100 feet (30 m)" at a certain frequency. Signal loss in a given transmission line AUGMENT with increased length or increased operating frequency. For example, 30 m of RG-58 introduce a loss of -3 dB at 50 MHz. Doubling the length, double the loss: 60 m of RG-58 lose -6 dB at 50 MHz. The original 30 m of RG-58 wastes -10 dB at 450 MHz.

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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If the frequency is increased, how would this affect the loss on a transmission line?
• It is independent of frequency
• It depends on the line length
• It would decrease
It would increase

The higher the frequency, the higher the loss. Larger diameter coaxial cables are recommended at VHF (Very High Frequency) and UHF (Ultra High Frequency) to minimize losses. Signal loss in a given transmission line AUGMENT with increased length or increased operating frequency. For example, 30 m of RG-58 introduce a loss of -3 dB at 50 MHz. Doubling the length, double the loss: 60 m of RG-58 lose -6 dB at 50 MHz. The original 30 m of RG-58 wastes -10 dB at 450 MHz.

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 does an SWR reading of 1:1 mean?
The best impedance match has been attained
• An antenna for another frequency band is probably connected
• No power is going to the antenna
• The SWR meter is broken

SWR is a measure of the impedance match in the antenna system. A Standing Wave Ratio (SWR) of '1 to 1' is an ideal condition indicating no reflected energy. The impedance of the load at the end of the transmission line matches the Characteristic Impedance of the line. Impedance Match has been achieved. A Standing Wave Ratio (SWR) of '1.5 to 1' would indicate a fairly good match while a very high SWR would indicate a short-circuit or an open-circuit somewhere along the transmission line.

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 does an SWR reading of less than 1.5:1 mean?
• An antenna gain of 1.5
A fairly good impedance match
• An impedance match which is too low
• A serious impedance mismatch; something may be wrong with the antenna system

SWR is a measure of the impedance match in the antenna system. A Standing Wave Ratio (SWR) of '1.5 to 1' is a totally acceptable condition indicating little reflected energy. A '1 to 1' ratio would indicate a perfect match while a very high SWR would indicate a short-circuit or an open-circuit somewhere along the transmission line.

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 SWR reading may mean poor electrical contact between parts of an antenna system?

SWR is a measure of the impedance match in the antenna system. A 'jumpy' (erratic) reading resulting from the sometimes on, sometimes off electrical contact would indicate a loose connection in the antenna system.

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 does a very high SWR reading mean?
The antenna is the wrong length for the operating frequency, or the transmission line may be open or short circuited
• The transmitter is putting out more power than normal, showing that it is about to go bad
• There is a large amount of solar radiation, which means very poor radio conditions
• The signals coming from the antenna are unusually strong, which means very good radio condition

SWR is a measure of the impedance match in the antenna system. A very high SWR, indicating that most if not all energy sent up the line is reflected back indicates that the antenna is cut for a totally different frequency OR that a short-circuit or open-circuit exists somewhere along the line.

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 does standing-wave ratio mean?
• The ratio of maximum to minimum inductances on a transmission line
• The ratio of maximum to minimum resistances on a transmission line
• The ratio of maximum to minimum impedances on a transmission line
The ratio of maximum to minimum voltages on a transmission line

'Standing Waves' result from the interaction of the forward power sent from the transmitter towards the antenna and the reverse power reflected back by an improper impedance match. The interaction produces a repeating pattern of voltage peaks and troughs along the line. SWR is also known as 'Voltage Standing Wave Ratio (VSWR)': it is a measure of the peak voltage to the minimum voltage on the standing wave.

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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If your antenna transmission line gets hot when you are transmitting, what might this mean?
• You should transmit using less power
• The conductors in the transmission line are not insulated very well
• The transmission line is too long
The SWR may be too high, or the transmission line loss may be high

Line losses, possibly compounded by high Standing Wave Ratio (SWR), waste energy as heat.

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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If the characteristic impedance of the transmission line does not match the antenna input impedance then:
• the antenna will not radiate any signal
standing waves are produced in the transmission line
• heat is produced at the junction
• the SWR reading falls to 1:1

'Standing Waves' result from the interaction of the forward power sent from the transmitter towards the antenna and the reverse power reflected back by an improper impedance match. The interaction produces a repeating pattern of voltage peaks and troughs along the line. SWR is also known as 'Voltage Standing Wave Ratio (VSWR)': it is a measure of the peak voltage to the minimum voltage on the standing wave.

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 result of the presence of standing waves on a transmission line is:
• lack of radiation from the transmission line
reduced transfer of RF energy to the antenna
• perfect impedance match between transmitter and transmission line
• maximum transfer of energy to the antenna from the transmitter

High SWR add to line losses and lead to energy wasted as heat.

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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An SWR meter measures the degree of match between transmission line and antenna by:
comparing forward and reflected voltage
• measuring the conductor temperature
• inserting a diode in the transmission line

'Standing Waves' result from the interaction of the forward power sent from the transmitter towards the antenna and the reverse power reflected back by an improper impedance match. The interaction produces a repeating pattern of voltage peaks and troughs along the line. SWR is also known as 'Voltage Standing Wave Ratio (VSWR)': it is a measure of the peak voltage to the minimum voltage on the standing wave.

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 resonant antenna having a feed point impedance of 200 ohms is connected to a transmission line which has an impedance of 50 ohms. What will the standing wave ratio of this system be?
• 6:1
• 3:1
• 5:1
4:1

key word: RESONANT. A resonant antenna (reactances cancel each other at resonance) does not present any reactance (X) but only a 'radiation resistance'. In such a situation, SWR can be computed as the ratio of the impedances. In this example, 200 / 50 yields a ratio of '4 to 1'. SWR is normally a ratio of maximum to minimum voltage on the standing wave.

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 type of transmission line best suited to operating at a high standing wave ratio is:
600 ohm open wire line
• coaxial line

The high Characteristic Impedances and greater separation of the conductors in parallel lines DO permit high power and high Standing Wave Ratio (SWR) BUT nearby metallic objects can affect them and impedance matching is most often necessary at the transmitter end. Their high Characteristic Impedance permits carrying power with less current (P = R * I squared), less current implies less losses due to resistance.

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 would you use to connect a coaxial cable of 50 ohms impedance to an antenna of 17 ohms impedance?
• A terminating resistor
An impedance-matching device
• An SWR meter
• A low pass filter

The impedance mismatch could be corrected by an 'impedance-matching device'.

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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To obtain efficient power transmission from a transmitter to an antenna requires:
matching of impedances
• inductive impedance

Impedance Match: maximum power transfer occurs when the impedance of the load matches the internal impedance of the source. For example, A transmitter designed to work into an impedance of 50 ohms, will delivered maximum power if the antenna system offers an impedance of 50 ohms.

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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To obtain efficient transfer of power from a transmitter to an antenna, it is important that there is a:
matching of impedance
• proper method of balance

Impedance Match: maximum power transfer occurs when the impedance of the load matches the internal impedance of the source. For example, A transmitter designed to work into an impedance of 50 ohms, will delivered maximum power if the antenna system offers an impedance of 50 ohms.

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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If an antenna is correctly matched to a transmitter, the length of transmission line:
• must be a full wavelength long
• must be an odd number of quarter-wave
• must be an even number of half-waves
will have no effect on the matching

IF a mismatch is present at the end of the transmission lines, certain lengths may introduce an 'impedance transformation' effect. With a correctly matched antenna, line length is immaterial except for line losses if the line is unnecessarily long. [ References to multiples of the wavelength only tap into urban legends. ]

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 reason that an RF transmission line should be matched at the transmitter end is to:
• ensure that the radiated signal has the intended polarization
• prevent frequency drift
• overcome fading of the transmitted signal
transfer the maximum amount of power to the antenna

Impedance Match: maximum power transfer occurs when the impedance of the load matches the internal impedance of the source. For example, A transmitter designed to work into an impedance of 50 ohms, will delivered maximum power if the antenna system offers an impedance of 50 ohms.

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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If the centre impedance of a folded dipole is approximately 300 ohms, and you are using RG8U (50 ohms) coaxial lines, what is the ratio required to have the line and the antenna matched?