Last Updated: August 21, 2019
It’s fair to say most assembly houses test the optical loss of a single mated pair using a launch cable connected to the DUT with the far end of the DUT plugged directly into the power meter via the adapter cap. To complete the test, the DUT is flipped and the second connector is then tested. Here is where people envision the time savings. Won’t it be great to run the test in both direction and not have to swap the cable and run the test again? Well yes, but here’s the rub: you have one side attached without a launch. Bi-Directional test requires the use of a launch AND a receive cable, so when it light it shot in one direction there is a launch and when it’s shot in the opposite direction there is also a launch.
So if you aren’t already using the launch and receive cable method of testing you’ll have to change your test method to fully utilize the Bi-Directional feature. The launch and receive jumper method for optical loss give the loss of the entire jumper in one direction.
One more key point to consider is the testing of dissimilar connector styles, i.e. SC to LC. During referencing the launch and receive cables need to be connected and if they aren’t the same they can’t be connected using a standard adapter. There are hybrid adapters, but these don’t provide the best mating and can introduce high losses during the referencing which can inflated, or maybe it’s more appropriate to say they deflate (watch out Patriot’s fans) the measured readings. In other words, when you artificially increase the amount of loss during reference, you get artificially better and inaccurate test results.
So when does Bi-Directional make sense? If you can use the launch and receive test method and your jumps have the same connectors on each end. Some good product types for this are MTP to MTP jumps and large multi-channel cable reels where moving the cables is cumbersome. There certainly are other, but please give us a call and we can recommend the best test configuration for your application.
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