Optical Loss Testing in a Multimode Network

The accepted best practice for testing link loss in a multimode network calls for the most accurate and repeatable test set up: the one-jumper reference method.
 
While this method uses two test jumpers to determine the losses of the patch panel connections at each end of the cable link under test, it is called a one-jumper reference because only one of the two cords is used as a reference.
 
Prior to testing — or even connecting your jumpers — you should clean your test ports and the connectors on your test reference cords (TRC). A single dirty connector will contaminate your test reference cords and transfer that dirt to other connectors – possibly causing damage or excess loss.
 
A one-jumper reference test is performed as follows:
 



Connect the TRC to the optical light source and to the power meter.
 
‘Zero out’ your power meter by pressing the zero or reference (Ref) button. The screen should report 0 dB or 0 dBm.
 



Disconnect the TRC from the power meter end only. Do not disconnect from the light source or you will need to repeat the previous step to zero out the power meter again.
 

 

Clean and connect a second TRC or good quality jumper to the power meter. With an adapter, connect it to the first TRC still connected to the light source.
 
Note: Treat this loss reading as a quality check for your test cords. This is a good value to track, in order to determine when your reference cords need replacing.
 
Disconnect the two test cords from each other. Do not disconnect the end plugged into the light source.
 



Connect the first TRC (plugged into the light source) to one end of the link under test. Connect the second TRC (plugged into the power meter) to the far end of the link under test.
 
Now, you can take your loss readings, and continue to test the links in this network.
 
If at any time you turn off your equipment or disconnect your reference cords, you must re-reference your test equipment before taking measurements again.