Return loss is the ratio of signal power injected from a source compared to the amount that is returned or reflected back toward the source. It is a critical performance parameter in both copper twisted pair and fiber optic cabling systems, because it can interfere with the transmitted signal and can contribute to an increase in the measured insertion loss (the amount of power that a that a signal loses as it travels along a cable link). If more power is reflected back to the source, less power is available at the far end of the cable. In some fiber optic systems, return loss can even damage the transceiver laser source.
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