This test measures only the loss of the mated pair of connectors between the launch reference cable and the cable being tested plus any loss of the fiber in the cable being tested. The detector in the power meter is so large it captures all the light and therefore has no loss - when we measure either the output of the launch cable or the cable under test.
We can test the connector on the other end of the cable by reversing the cable to test. Do this to check both connectors.
Reference Standard: FOTP-171
Since "dB" is a relative logarithmic scale, lower power will be a more negative number, so if your reference is -20.0 dB and your measurement is -20.3 dB, your loss is 0.3 dB.
1. Disconnect the launch cable from the meter.
2. Using a mating adapter, attach the cable you want to test to the end of the launch cable.
3. Attach the other end of the cable to the meter.
4. Read the value on the meter display. The difference in power between this measurement and the reference measurement will be the loss.