How to derive impulse response from characteristic impedance

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Discussion Overview

The discussion revolves around deriving the impulse response of a coaxial cable used for data transmission, specifically in relation to its characteristic impedance (Zo), source impedance (Z_source), and load impedance (Z_load). The focus includes the implications of impedance mismatches on bit error rate (BER) and the effects of reflections in digital communication.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant inquires whether it is possible to derive the impulse response as a function of Zo, Z_source, and Z_load.
  • Another participant warns against impedance mismatches, stating that reflections can lead to errors in digital communication, particularly if the bit rate width is not significantly longer than the coax line.
  • A different participant mentions that while they plan to match the impedances, they want to analyze the effects of mismatches on BER using impulse response to determine tolerable levels of mismatch.
  • One participant suggests that understanding the receiver's input threshold is crucial and references the significance of transmission line reflections, noting that typically only the first reflection is the most substantial and correlates with the mismatch.

Areas of Agreement / Disagreement

Participants express differing views on the implications of impedance mismatches, with some emphasizing the importance of matching impedances to avoid errors, while others focus on analyzing the effects of mismatches on performance metrics like BER. The discussion remains unresolved regarding the best approach to derive the impulse response and the impact of mismatches.

Contextual Notes

Participants highlight the need to consider the receiver's threshold and the nature of reflections in transmission lines, indicating that assumptions about the system's behavior under different conditions may not be fully addressed.

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i have a coax cable that will be used in data transmission. i have measured the open and short impedance and then characteristic impedance(Zo) for the cable. Eventually I will have a transmitter with Z_source in one end of the cable and receiver with Z_load at the other end of the cable. Is it possible to derive impulse response as a function of Zo,Z_source and Z_load?
 
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Unless the bit rate width is much longer than the coax line, it is not adviceable to to mismatch the source, line and termination impedance. Reflection will create a step change on the logic level and cause error.

In digital communication, you don't deal with standing wave and those, either you have it or you don't.
 
They all will be matched but i want to analyze the effects of mismatches on BER using impulse response to see how much mismatch is tolerable.
 
To do that, you have to know the threshold of the input of the receiver first, that is the most important thing. Then look up the transmission line reflection on step function. Usually only the first reflection step is the biggest and is proportion to the line and termination mismatch.
 

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