This test measures the loss of the connectors on both ends of the cable being tested plus any loss of the fiber in the cable being tested. We do this with two reference cables, one attached to the source and one attached to the meter.
Reference Standard: OFSTP-14 (MM), OFSTP-7(SM), EIA/TIA 568-B.3.
- IMPORTANT NOTE:
- Although we use both a launch and a receive reference cable, we still set our "0 dB" reference power the same way - at the output of the launch cable according to the TIA-568 standard!
- In the real world, there are some connectors that cannot be adapterd to a power meter to allow the launch cable reference, so international standards allow for referencing with both launch and receive cables or even aunch and receive cables plus a third reference cable.
- All three methods are acceptable in most cases, as long as the method is documented.
- The loss will be lower with these other methods, since 1 or 2 extra connectors will be included in the "0 dB" reference.
- Although we use both a launch and a receive reference cable, we still set our "0 dB" reference power the same way - at the output of the launch cable according to the TIA-568 standard!
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 receive cable attached 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.