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Magnum14E Media Converters Installation and User Guide (10/02)
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media has a PDV of about 1 BT per meter of length. The Magnum 14E has a PDV of 20 BT.
Therefore, in shared Fast Ethernet applications, the 14E uses about 80 meters of equivalent
cable distance to convert from TX media to fiber FX media, i.e., it consumes almost as much of
the available PDV as a Class II repeater. Since a 512BT collision domain will almost always
include at least one repeater and two media segments, the remaining amount of Bit Times left
after allowing for a 14E and a length of fiber media indicates that the available fiber length will
be much less than the 412 meters that is the known maximum for fiber. Therefore, in shared
environments, Magnum 14E Media Converters will be of benefit when they allow the use of
fiber media, but not to gain distance by facilitating use of fiber media instead of twisted pair.
As a sample calculation, consider the question of what fiber cable distance
(connected by a pair of Magnum 14Es on each end) can be obtained that will interconnect two
100Mb hubs where the twisted pair cables to the user nodes are 10 meters in length.