Bidirectional OTDR Testing in Fiber Optics | Fluke Networks

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Bi-Directional Testing - DTX Compact OTDR Module

If your launch lead has a different backscatter coefficient than the cable you are testing, you may well end up with a suspiciously low loss value for your launch event (first connector). You may even observe a negative loss. An example of this from the DTX Compact OTDR is shown below:

Bi-directional Testing with DTX Compact OTDR

You could make a launch lead using the same fiber as you are testing. Alternatively, you could make the measurement in the opposite direction and take the average. This is defined in IEC 14763-3 and is referred to as bi-directional testing.

Bi-directional
testing

  • Set the launch + receive fiber compensation - click here for details.
  • Rotate the dial on the DTX CableAnalyzer to SETUP.
  • Highlight Fiber OTDR and press ENTER.
  • Move to Tab 2 and make sure Testing From says End 1.
  • Rotate the dial to AUTOTEST.
  • Go ahead and test the link.
     
    Bidirectional OTDR Testing
     
  • Save it as 001 (or your own Cable ID scheme).
  • Continue to test the rest of your links whilst saving them to the DTX CableAnalyzer.

  • Rotate the dial on the DTX CableAnalyzer to SETUP.
  • Highlight Fiber OTDR and press ENTER.
  • Move to Tab 2 and make sure Testing From says End 2.
  • Rotate the dial to AUTOTEST.
  • Swap ends with the DTX CableAnalyzer (leave the launch/recieve fibers in place).
  • Go ahead and test the first link again.
     
    Bi-Directional Testing - DTX OTDR 
     
  • Save it as 001 (or whatever you chose previously)
  • Continue to test the rest of your links whilst saving them to the DTX Cableanalyzer.
  • The bi-directional calculation is done within the LinkWare Software. Go ahead and download your OTDR results into LinkWare.
     

  • Fluke Networks LinkWare Software
     
  • The two measurements made in different directions are recorded as one result.
  • Click on Utilities > Generate Bidirectional OTDR Results; the following window will open:
      
    Generating Bidirectional OTDR Testing Results
     
  • Select the Cable IDs you wish to implement bi-directional averaging on and click OK.
  • You will now see your test result calculated using bi-directional averaging:
     
    LinkWare Software - Fluke Networks
     
     
  • Looking at the result, we see:
     
     OTDR Testing
     
  • The loss at each connector is 0.20 dB using bi-directional averaging in accordance with IEC 14763-3. Note the 0.02 dB reported when the measurement was made in one direction only.
  •  

Learn About:
- OTDR

Author: Adrian Young

Creation Date: 2014-02-28

Last Modified: 2014-02-28

 
 
 
 
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