ISE Magazine, July 2019
ISE ICT SOLUTIONS EDUCATION 36 FIBER TESTING Are you using APC or UPC connectors What is the connector type s On the link patch panels On the OTDR output As you likely know launch and receive fibers need connectors compatible with your OTDR and with the connectors on the patch panels Are you connecting an OTDR at the far end Remember OTDRs do not actually measure loss they measure changes in backscatter So when you are splicing fiber reels together any backscatter differences will show up in addition to the change in signal level through the event The only way to obtain accurate event loss measurements is to test from both ends and average the loss values of each event from A to B side and then from B to A side A B B A 2 This means if you are A side and your test partner is B side your launch fiber is Bs receive fiber and Bs launch fiber is your receive fiber Key Question 3 How do you optimize the connections Optimizing connectivity for testing is simple in concept but it can be a challenge in practice The goal is to have low loss and low reflectance connections at both ends of the link For this to occur we need 3 things 1 An OTDR output port that is pristine no end face contamination or damage 2 A launch fiber with a connector matching the OTDR also in excellent condition no contamination or damage 3 Inspection and cleaning practices in place to ensure 1 and 2 above are achieved A Quality digital inspection probes with the right connector tips and automatic pass fail grading capability IEC B Cleaning sticks for bulkheads and connectors pen style cleaners C Cleaning tapes for connector launch receive connector end faces Figure 1 Trace with poor launch causes lower signal noisier trace Figure 2 How to measure loss at a connector Figure 3 OTDR interface visual Poor vs good launch
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