B Mode conditioning patch cord (fiber cables)
The following information applies to installations in which multimode fiber-optic cables are connected
to a Gigabit-LX port. Multimode cable has a design characteristic called “Differential Mode Delay”
which requires the transmission signals be “conditioned” to compensate for the cable design and
thus prevent resulting transmission errors.
Under certain circumstances, depending on the cable used and the lengths of the cable runs, an
external Mode Conditioning Patch Cord may need to be installed between the Gigabit-LX and the
multimode network cable to provide the transmission conditioning. If you experience a high number
of transmission errors on those ports, usually CRC or FCS errors, you may need to install one of
these patch cords between the fiber-optic port in your controller and your multimode fiber-optic
network cabling, at both ends of the network link.
The patch cord consists of a short length of single mode fiber cable coupled to graded-index
multimode fiber cable on the transmit side and only multimode cable on the receive side. The
section of single mode fiber is connected in such a way that it minimizes the effects of the differential
mode delay in the multimode cable.
NOTE: Most of the time, if you are using good quality graded-index multimode fiber cable that
adheres to the standards listed in Appendix B, there should not be a need to use mode conditioning
patch cords in your network. This is especially true if the fiber runs in your network are relatively
short.
Installing the patch cord
As shown in the illustration below, connect the patch cord to the HP transceiver with the section
of single mode fiber plugged in to the Tx (transmit) port. Then, connect the other end of the patch
cord to your network cabling patch panel, or directly to the network multimode fiber.
If you connect the patch cord directly to the network cabling, you may need to install a
female-to-female adapter to allow the cables to be connected together.
Figure 11 Example: connecting a mode conditioning patch cord for Gigabit-LX
Make sure you purchase a patch cord that has appropriate connectors on each end and has
multimode fibers that match the characteristics of the multimode fiber in your network. Most
important, the core diameter of the multimode patch cord must match the core diameter of the
multimode cable infrastructure (either 50 or 62.5 microns).
28 Mode conditioning patch cord (fiber cables)
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