A "transmission line" carries radio frequency signals from the station to the antenna and between the various pieces of equipment in the station.
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Characteristic Impedance is determined by the physical dimensions of the line. Length, frequency or load have nothing to do with it.
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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.
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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.
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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.
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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.
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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.
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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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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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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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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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"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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"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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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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"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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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'.
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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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"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.
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"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).
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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.
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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.
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'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.
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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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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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Poor connections can also lead to intermittent electrical contact (evidenced by an erratic or 'jumpy' Standing Wave Ratio (SWR) reading at the station).
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Coaxial cable, with its shielded and grounded outer conductor, is not affected by conductive soil. It is also not affected by nearby metallic objects.
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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.
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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.
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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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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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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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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.
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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.
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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.
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"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.
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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.
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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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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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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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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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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.
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'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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'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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'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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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 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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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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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 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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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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