Feedlines and Antenna Systems
concept of impedance matching
What device might allow use of an antenna on a band it was not designed for?
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Correct AnswerAn antenna tuner
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An SWR meter
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A low pass filter
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A high pass filter
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What does an antenna matching unit do?
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Correct AnswerIt matches a transceiver to a mismatched antenna system
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It helps a receiver automatically tune in stations that are far away
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It switches an antenna system to a transmitter when sending, and to a receiver when listening
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It switches a transceiver between different kinds of antennas connected to one feed line
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What would you use to connect a coaxial cable of 50 ohms impedance to an antenna of 35 ohms impedance?
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An SWR meter
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Correct AnswerAn impedance-matching device
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A low pass filter
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A terminating resistor
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When will a power source deliver maximum output to the load?
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When air wound transformers are used instead of iron-core transformers
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When the power-supply fuse rating equals the primary winding current
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Correct AnswerWhen the impedance of the load is equal to the impedance of the source
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When the load resistance is infinite
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What happens when the impedance of an electrical load is equal to the internal impedance of the power source?
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The electrical load is shorted
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Correct AnswerThe source delivers maximum power to the load
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No current can flow through the circuit
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The source delivers minimum power to the load
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Why is impedance matching important?
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So the load will draw minimum power from the source
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To ensure that there is less resistance than reactance in the circuit
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To ensure that the resistance and reactance in the circuit are equal
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Correct AnswerSo the source can deliver maximum power to the load
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To obtain efficient power transmission from a transmitter to an antenna requires:
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high load impedance
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low ohmic resistance
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Correct Answermatching of impedances
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inductive impedance
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To obtain efficient transfer of power from a transmitter to an antenna, it is important that there is a:
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high load impedance
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Correct Answermatching of impedance
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proper method of balance
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low ohmic resistance
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If an antenna is correctly matched to a transmitter, the length of transmission line:
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must be a full wavelength long
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must be an odd number of quarter-wave
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must be an even number of half-waves
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Correct Answerwill have no effect on the matching
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The reason that an RF transmission line should be matched at the transmitter end is to:
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ensure that the radiated signal has the intended polarization
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Correct Answertransfer the maximum amount of power to the antenna
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prevent frequency drift
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overcome fading of the transmitted signal
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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?
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2:1
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4:1
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10:1
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Correct Answer6:1
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