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| What is headroom for optical fiber cable? I know what it is for copper. I had a contractor return the test results for optical fiber cable and one of the test categories was headroom.
John Kendra RCDD |
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| ACR is the difference between NEXT and the attenuation for the pair in the link under test. Since it is fiber, where is the NEXT?
John Kendra RCDD |
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| | The tester was probably a Fluke tester as I have seen similar results submitted to me from Fluke testers. The headroom they are referring to is the difference between the result the tester observed and the test parameter that was plugged into the tester. From what I have seen, the default parameter that they test to is 3.50 dB. So if you have 1.7 dB headroom, it most likely means you had an optical loss of 1.8 dB. This can be a useful tool if the tech sets the tester to meaningful parameters. Since my projects require less than 0.5 dB per mated connector and runs typically are less than 1000 feet, the pass/fail should be set more like 2.1 dB or less to be applicable and should change depending on the length of the fiber. If you are looking for whether a specific system will run on the fiber, you can change the tester to look for the dB loss the system can tolerate (go back to the TDMM to calculate the acceptable loss) Good Luck Dave Golner |
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| That makes sense. It was a Fluke tester.
John Kendra RCDD |
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| | Headroom is the term used to distinguish the difference between the minimum requirement and the over perfromance delivered. The minimum requirement is met by delivering a channel to support the transmission requirement of any application it must carry. For example 10G Ethernet on Lazer optimized 50/125 is stated by IEEE as 2.6dB max loss (the requirement). Centralized fiber has a max channel loss of 2.55dB giving headroom of 0.05dB between the fiber performance and the application requirement.
Steve Banks RCDDNightlake Ltd U.K. |
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| When reviewing test results, you should look into the test parameters that are in the test set. If not set correctly, any margin or Headroom results may be skewed. Test results should be submitted in the form as recorded by the test set so that the manufacturers software may be used to dig into the results. Viewing a .pdf version may not tell you the whole story.
My 2--cents |
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