NOTE: See the specifications for your transmitter and receiver to find the minimum
transmitter power and minimum receiver sensitivity.
2. Calculate the power budget (P
B
) by subtracting (P
R
) from (P
T
):
–15 dBm – (–28 dBm) = 13 dBm
Calculate the Fiber-Optic Cable Power Margin for an MX10004 Router
Before you begin to calculate the power margin, calculate the power budget.
Calculate the link's power margin and distances when planning your fiber-optic cable layout. This will
ensure that fiber-optic connections have sufficient signal power to overcome system losses and satisfy
the minimum input requirements of the receiver for the required performance level. The power margin
(P
M
) is the amount of power available after you subtract attenuation or link loss (LL) from the power
budget (P
B
).
When you calculate the power margin, you use a worst-case analysis to provide a margin of error, even
though none of the parts of a configured system 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 does not
exceed the maximum receiver input power. This means that the link will work. A power margin (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.
To calculate the worst-case estimate for the power margin (P
M
) for the link:
1. Determine the maximum value for LL by adding estimated values for applicable link-loss factors. For
example, use the sample values for various factors as provided in
km long and multimode, and the (P
B
) is 13 dBm.
Table 38: Estimated Values for Factors Causing Link Loss
Link-Loss Factor
Estimated Link-Loss Value
Sample Link-Loss Calculation Values
Higher-order mode
losses
Multimode—0.5 dBm
0.5 dBm
Single mode—None
0 dBm
99
