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Specifications
Mode Conditioning Patch Cord
N o t e
A-6
Mode Conditioning Patch Cord
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 transmitting device 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 switch 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.
Most of the time, if you are using good quality graded-index multimode fiber cable
that adheres to the standards listed in this appendix, 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 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.
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