When you calculate the power margin, you use a worst-case analysis to provide a margin of error, even
though all the parts of an actual system do not operate at worst-case levels. A power margin (P
M
) greater
than zero indicates that the power budget is sufficient to operate the receiver and that it does not exceed
the maximum receiver input power. This means the link will work. A (P
M
) that is zero or negative indicates
insufficient power to operate the receiver. See the specification for your receiver to find the maximum
receiver input power.
Before calculate the power margin, see “Calculating the Fiber-Optic Cable Power Budget for an MX10016”
on page 118.
To calculate the worst-case estimate for the power margin (P
M
) for the link:
1. Determine the maximum value for link loss (LL) by adding estimated values for applicable link-loss
factors; for example, use the sample values for various factors as provided in Table 47 on page 119 (here,
the link is 2 km long and multimode, and the (P
B
) is 13 dBm).
Table 47: Estimated Values for Factors Causing Link Loss (LL)
Sample Link Loss (LL) Calculation ValuesEstimated Link Loss ValueLink-Loss Factor
0.5 dBmMultimode—0.5 dBmHigher-order mode
losses
0 dBmSingle-mode—None
0 dBmMultimode—None, if product of
bandwidth and distance is less
than 500 MHz/km
Modal and chromatic
dispersion
0 dBmSingle-mode—None
This example assumes five connectors. Loss for five
connectors: 5 (0.5 dBm) = 2.5 dBm.
0.5 dBmConnector
This example assumes two splices. Loss for two
splices: 2 (0.5 dBm) = 1 dBm.
0.5 dBmSplice
This example assumes the link is 2 km long. Fiber
attenuation for 2 km: 2 km (1 dBm/km) = 2 dBm.
Multimode—1 dBm/kmFiber attenuation
This example assumes the link is 2 km long. Fiber
attenuation for 2 km: 2 km (0.5 dBm/km) = 1 dBm.
Single-mode—0.5 dBm/km
1 dBm1 dBmClock Recovery Module
(CRM)
119
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