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5-8
Performance Tests
Test 4. Optical Input Return Loss
FC/APC patchcord loss
The effect of having loss in the FC/APC patchcord 1 to 2 connector pair is to under
measure the return loss by twice the FC/APC patchcord 1 to 2 loss. For example, if
this connector pair loss is 0.5 dB, then the actual return loss caused by the 14.6 dB
Fresnel reflection is 15.6 dB, but we enter 14.6 dB as an R value. Then, if the
device under test return loss is exactly 40 dB below that of the 14.6 dB Fresnel
reflection, the optical return loss module will display 53.6 dB because the 0.5 dB
connector pair loss (seen twice) is removed. In reality, the return loss is 54.6 dB
(exactly 40 dB below 14.6 dB), better than that displayed.