Advanced Qualification · A-007 Feedlines and matching · A-007-002-001
What kind of impedance does a quarter wavelength transmission line present to the source when the line is shorted at the far end?
- A A very low impedance
- B A very high impedance
- C The same as the characteristic impedance of the transmission line
- D The same as the output impedance of source
Correct answer: B — A very high impedance. From the official ISED question bank, verified word for word.
Why
When a quarter-wavelength line is shorted at the far end, the signal travels down, hits the short, and reflects back exactly out of phase, effectively cancelling the current at the source end while voltage remains high. The full explanation — and one for every question — is in Pro.
Practise this section
Feedlines and matching at the advanced level: transmission line theory, impedance transformation, stubs and matching networks.