AdvancedA-007-002-002
What kind of impedance does a quarter wavelength transmission line present to the source if the line is open at the far end?
B
Answer
Interference, EMC, and safety
Type
A
A very high impedance
B
A very low impedance
C
The same as the output impedance of the source
D
The same as the characteristic impedance of the transmission line
Answer Notes
A quarter-wavelength transmission line acts as an impedance inverter. It transforms the impedance connected to its far end into its exact mathematical opposite at the source end.
Because the far end of this line is an open circuit, it has an infinite or very high impedance. The quarter-wave line inverts this infinite impedance, making it appear as a short circuit, or a very low impedance, to the radio source.
Distractors suggesting the impedance remains high or matches the characteristic impedance are incorrect because they ignore the unique 90-degree phase shift and reflecting properties of a quarter-wave line that cause this inversion.
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What kind of impedance does a quarter wavelength transmission line present to the source when the line is shorted at the far end?
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What kind of impedance does a half wavelength transmission line present to the source when the line is open at the far end?