User's Manual

Remote Fiber Node (RFN) User Manual

Figure 13

Note: Allow for 0.25 dBo loss for every interconnection.

FORX discussion

On the opposite side, complimenting is the fiber optic receiver (FORX) which converts the

optical input to an electrical output for the downlink (DL) path. By also adding an OADM in

the receiver side only matching light goes through while rejecting all others.

Most photo detector optical input limits are about 8 dBm, but the system receivers will never

see such high levels, with practical values at 5 dBm or much lower due to the external fiber

medium optical loss which is around 4 dBo.

Further explanation, with a 7 dBm source optical power at the Headend which is split 4-Ways

(-7dBo) then the OADM thru loss (-2 dBo) and a typical (-4 dBo) loss thru fiber medium,

putting the upper optical input limit of the fiber receiver at -6 dBm. So the upper limits are un-

reachable into FORX.

Alarm threshold for excessive optical loss is set to -14 dBm which is a 4 dBo margin from the

expected fiber medium maximum loss of 8 dBo.