How Does Bad/Poor Fiber Connection to My OTDR Affect Test Trace Results?

Enable "Front Panel Check" in Setup to avoid wasting time testing with bad or poor fiber connections.

Poor Optical Connector mating will result in inaccurate test results.  Poor OTDR connection can result in higher-than-normal insertion loss and/or high initial reflection. Modern connectors' end faces are either Ultra-Polished (UPC) or 8-degree Angle-Polished (APC). Mated UPC connectors will typically have 0.2 to 0.5 dB insertion loss and better than -50 dBm reflectance. Mated APC connectors will typically have 0.3 to 0.5 dB insertion loss and better than -60 dBm reflectance.

There are two ways to know whether your fiber connection is good, poor or outright bad:

  • Method 1 - VeEX OTDRs' Front Panel Check feature will automatically alert if the initial scatter level is lower than expected or if the initial connection reflection is worse than -45dB.
  • Method 2 - Zoom onto the initial connection of the trace and verify the linear scatter level (dB/km) is between green launch level bar on the vertical axis and the initial connector event table reflectance value is within expectations for that connector polish.

Bad Launch

There are many reasons for a bad initial connection: Dirt/contamination, loose internal connector, bad coupler (weak spring lock or cracked ceramic sleeve), bad universal adapter and, on occasion, bad laser or internal coupler/splices. No matter the reason, when this situation occurs, the OTDR will not work properly.