Power margin of a fiber-optic system

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Discussion Overview

The discussion revolves around calculating the power margin of a fiber-optic system based on provided parameters such as transmitter power, connector loss, attenuation, total length, and receiver threshold. The context is primarily homework-related, focusing on the application of formulas to derive the power margin.

Discussion Character

  • Homework-related
  • Mathematical reasoning

Main Points Raised

  • One participant presents a calculation for power budget and power margin, arriving at a value of 13.5 dB.
  • Another participant agrees with the calculation but questions the validity of an external answer of 9.5 dB, suggesting it may be incorrect.
  • A third participant recalculates and suggests the power margin should be 12.5 dB, indicating a possible error in subtraction.
  • Subsequent replies express confusion over the discrepancy between calculated values and the provided answer, with participants seeking clarification on how the 9.5 dB result was derived.

Areas of Agreement / Disagreement

Participants generally agree on the calculations leading to 12.5 dB and 13.5 dB, but there is disagreement regarding the correctness of the provided answer of 9.5 dB, which remains unresolved.

Contextual Notes

Participants have not fully resolved the source of the discrepancy in the power margin calculations, and there may be missing assumptions or errors in the original problem statement or external answer reference.

MattH150197
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Homework Statement


Im going over some revision for fibre optics and I've come across an example question to calculate the power margin of the system with the following info is given:
transmitter power = -10dBm
Connector loss = 1.5dB
Attenuation = 3dB/Km
Total length= 2KM
Receiver threshold = -30dBm

Homework Equations


Power budget = Pt - Pr
Power Margin = PB - Total losses

The Attempt at a Solution


PB = -10 - - 30 = 20
PM = 20 - ((3*2) + 1.5)) = 13.5dB
However it says the answer is 9.5dB, i didnt write the formulas wrong did i when i was making notes or can you see where I've gone wrong anywhere?
 
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If you have written the problem correctly and completely, then I agree with your result and suspect that the "answer" is wrong.
 
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MattH150197 said:
PM = 20 - ((3*2) + 1.5)) = 13.5dB
Should be 12.5 dB. Unfortunately still not 9.5dB.
 
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Oops right, I didn’t subtract that properly in my head!
 
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I'd like to know how the given answer was obtained if you ever find out.
 
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  1. Oops! Sorry yeah I meant 12.5, I really have no idea where 9.5dB has come from and it was really frustrating why I was getting different. So thanks for clearing it up guys!
 

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