3Com 2000 TR manual Does the Cable Provide Sufficient Bandwidth?, Example

C-2APPENDIX C: TR-IN-FE MODULE TECHNICAL SPECIFICATIONS

Specification	Description
Output power (from transceiver)	-20 dB minimum
	-14 db maximum
Receiver power	-31 dB minimum sensitivity
	-14 dB maximum sensitivity

Maximum attenuation includes attenuation and the loss induced by other components such as connec- tors, splices, and the mating of unlike fiber types.

Although some 2 km (1.25 miles) cables have a total attenuation of less than 11.0 dB, the 2 km (1.25 miles) inter-station distance must be maintained to comply with modal bandwidth requirements.

The maximum attenuation value in this table is based on a cable diameter of 62.5, 80 or 100 μm.

The following table shows alternative Multi-Mode fiber types that can be used.

Core (mm)	Cladding (mm)	Numerical Aperture
50	125	0.20
50	125	0.22
85	125	0.28
100	140	0.29

If you are using fiber with a diameter of 50 μm and have 3Com equipment at both ends of the link, sub- stitute 8.0 dB for the maximum attenuation. If 3Com equipment is only at one end, substitute 6.0 dB for the maximum attenuation value.

If you are using equipment at the end of the link from a vendor other than 3Com, you must perform a sepa- rate loss budget analysis. Contact the vendor(s) for values to use in your analysis.

Does the Cable Provide Sufficient Bandwidth?

Bandwidth for multi-mode fiber is referred to as modal bandwidth because it varies with the modal field (or core diameter) of the fiber.

Modal bandwidth is specified in units of MHz.km, which indicates the amount of bandwidth supported by the fiber for a 1 km (0.625 miles) distance. Your cable must have a Modal bandwidth of 500 MHz, which allows the cable to support end-to-end band- width of 250 MHz at the maximum 2 km (1.25 miles) distance.

To check that the bandwidth of your fiber is within an acceptable range:

1Divide the amount of bandwidth available according to the fiber specification by the total length of fiber (km).

2If the result is lower than 250 MHz, the link may be prone to bit errors. You should shorten the length of the fiber or use a different fiber until the result of the calculation reaches 250 MHz.

Example

A cable with modal bandwidth of 500 MHz.km will have 250 MHz of bandwidth at 2 km (1.25 miles).