Open circuited quarter wave transmission line

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Discussion Overview

The discussion revolves around the analysis of an open-circuited quarter wave transmission line, focusing on the calculation of voltage and impedance in this specific configuration. Participants explore various methods for solving the problem, including impedance calculations and the use of ABCD parameters.

Discussion Character

  • Homework-related
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant claims to obtain 10V across the open circuit but is unsure about the correctness of this result.
  • Another participant suggests calculating the impedance at the open end of the transmission line, indicating that it is not infinite and that a mismatched quarter wave transmission line behaves like a transformer.
  • A different approach is proposed using ABCD parameters to analyze the system, which can accommodate mismatches and various line lengths and terminations.
  • A participant expresses understanding of the problem after receiving feedback.
  • One participant compliments another's handwriting, which appears unrelated to the technical discussion.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the best approach to solve the problem, with multiple methods being discussed and no clear agreement on the correctness of the initial voltage claim.

Contextual Notes

There are indications of missing assumptions regarding the transmission line's characteristics and the specific conditions of the problem, such as the termination impedance and the nature of the mismatch.

reddvoid
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Homework Statement



attachment.php?attachmentid=54441&stc=1&d=1357318145.jpg


The Attempt at a Solution


I m getting 10V as one side is O.C so the whole voltage come across it...correct me where i m going wrong
 

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You're going about it wrong. First calculate the impedance at the open end of the transmission line. Hint, it's not infinite. A mismatched 1/4 wave transmission line acts like a transformer. After you calculate the impedance at the open end, then calculate the ratio of that impedance to the 50 ohms of the generator. Lastly, how does the ratio of voltages compare to the ratio of impedances of a transformer? If you first find the ratio of impedances then from that you can find the ratio of voltages. Once you've done that you would just multiply the input voltage by the voltage ratio.
 
I would use ABCD parameters, concatenating the ABCD parameters for the 50 ohm source resistor with the abcd parameters for the xmsn line. This method can handle any kind of oddball mismatches, such as in this case the 300 ohm xmsn line to the 50 ohm source, and any desired length of line (here λ/4) and far-end termination impedance (here ∞).

I'm sure that's overkill here & that there's an esier way, as skeptic2 is suggesting. Just pointing out that abcd parameters can handle the most general cases.
 
got it :)
attachment.php?attachmentid=54473&stc=1&d=1357392250.jpg
 

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Your handwriting is cool. :biggrin:
 

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