GE ML1600 Manuel d'utilisateur télécharger pdf (Page 14)

QS–10 MULTILINK ML1600/2400 ETHERNET COMMUNICATIONS SWITCH – QUICKSTART GUIDE

QUICK START GUIDE

QS.4 Optical Power Budget

Inevitably the question that arises is “What is the maximum practical communication

distance when using a fiber optic cable?”. The answer isn’t straightforward, but must be

calculated as follows:

• First the "Optical Power Budget" is determined by subtracting the receiver’s rated

sensitivity from the transmitter’s rated power, both of which are defined in

decibels of light intensity. For example if a particular transmitter is rated at

minus15 db and the receiver’s sensitivity is rated at minus 31 db, the difference of

16 db is the "Optical Power Budget."

Xmt Output Pwr - Rcv Sens = OPB: Optical power budget

Magnum: ( -15.0 dB ) - (- 31.0dB)= -16 dB OPB

The Optical Power Budget can be thought of as the maximum permitted

attenuation of the light signal as it travels from the transmitter to the receiver,

while still permitting reliable communication.

• The next step is to calculate the worst case Optical Power Budget by subtracting

from the Optical Power Budget, 1 dB for LED aging and 1 dB for each pair of

connectors (referred to as "insertion loss").

Worst Case OPB = OPB - 1dB (for LED aging) – 1dB (insertion loss for

each pair of connectors) x number of pairs

The final step is to divide the calculated result by the rated cable loss per kilometer

to determine the maximum distance.

For costly installations it is recommended that you always measure the actual cable loss

before and immediately after the installation to verify that the cable was installed

correctly. To avoid damaging the receiver, ensure that the maximum optical input power of

the receiver isn’t exceeded.

• Worst case distance = {Worst case OPB, in dB} / [Cable Loss, in dB/Km]

where the “typical cable loss” for:

• 62.5/125 and 50/125ìm (M.m) is 2.8 dB/km

• 100/140 (Multi-mode, 850nm) is 3.3 dB/km,

• 9/125 (Single-mode, 1310nm) is 0.5 dB/km (a worst case industry number)

• 9/125 (Single-mode, 1310nm) is 0.4 dB/km ( LXSC25)

• 9/125 (Single-mode 1550nm) is 0.25 dB/km (ZXSC40, SSCX)

• 9/125 (Single-mode 1550nm) is 0.2 dB/km (ZXSC70) and

• 9/125 (Single-mode 1550nm) is 0.22 dB/km (ZXSC120)

These are typical cable losses. There will be deviations depending on the manufacturer.

Always measure the loss before installation.

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GE ML1600 Manuel d'utilisateur Page 14