Installation guide

Planning and Designing RIO Cable System
56
890 USE 101 00 October 2006
Attenuation Considerations in an Optical Path
Overview Attenuation that occurs on an RIO fiber optic link is independent from attenuation on
the coaxial cable system. Signals that are attenuated no more than 35db after
traveling through a coaxial cable section are converted in the fiber repeater circuitry
to levels usable in the fiber link. Attenuation takes places on the fiber link and
receiving fiber repeaters convert the signal back to a full strength coaxial cable
signal. 35db will be available for use over the next copper section.
As with coaxial cable, size and components used will determine a fiber link
attenuation. The table below shows allowable attenuation or power loss budget for
the connecting repeaters to operate properly. The specified power loss budget is in
addition to loss introduced by two ST-type connectors. Other components such as
splices plus the fiber cable loss must be subtracted from the budget.
To illustrate, an uninterrupted run of 50/125 μm fiber cable that has attenuation of
3.5 db/km could be 2 km long.
Minimum
Distance
between
Repeaters
There is no minimum distance requirement when using 50/125 or 62.5/125 μm fiber
cable. If the larger diameter 100/140 μm cable is used, it is possible to overload a
repeater’s receive port circuitry. When no components are added in the fiber link
made up of this sized cable, minimum distance between repeaters is 1.2 km. Fiber
link length may be reduced proportionately as components are introduced.
Core Diameter Attenuation Optical Power Loss Budget
50/125 μm 3.5 dB/km 7.0 dB
62.5/125 μm 3.5 dB/km 11.0 dB
100/140 μm 5.0 dB/km 16.5 dB
Note: For those performing measurements, repeater transmitters have a
maximum optical power of -4 dbm when 100/140 μm cable is used. Maximum
repeater received signal is -10 dbm for any size cable used.
This document provided by Barr-Thorp Electric Co., Inc. 800-473-9123 www.barr-thorp.com