Schematic Diagram

Upstream fiber links in a community antenna television (CATV) system are usually among the most difficult elements of the network to align properly.Set-top boxes and cable modems employ "long-loop" automatic gain control (AGC) (in other words, far-end power-control), which attempts to normalize the RF path end-to-end.

Alignment is very important because for every decibel of uncorrected optical loss, there's a 2-dB optical-modulation-index (OMI) variance at the transmitting node.