Calculating The Fiber-Optic Cable Power Margin For An Nfx350 Device - Juniper NFX350 Hardware Manual

NOTE: See the specifications for your transmitter and receiver to find the minimum transmitter
power and minimum receiver sensitivity.
2. Calculate the power budget (PB) by subtracting (P
–15 dBm – (–28 dBm) = 13 dBm

Calculating the Fiber-Optic Cable Power Margin for an NFX350 Device

Calculate the link's power margin when planning fiber-optic cable layout and distances to ensure that
fiber-optic connections have sufficient signal power to overcome system losses and still satisfy the minimum
input requirements of the receiver for the required performance level. The power margin (P
amount of power available after attenuation or link loss (LL) has been subtracted 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 all the parts of an actual system do not operate at worst-case levels. A power margin (P
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
insufficient power to operate the receiver. See the specification for your receiver to find the maximum
receiver input power.
Before you begin to calculate the power margin:
Calculate the power budget. See
on page 54.
To calculate the worst-case estimate for the power margin (P
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
(here, the link is 2 km long and multimode, and the (P
Table 25: Estimated Values for Factors Causing Link Loss
Link-Loss Factor
Higher-order mode
losses
"Calculating the Fiber-Optic Cable Power Budget for an NFX350 Device"
Estimated Link-Loss Value
Multimode—0.5 dBm
Single-mode—None
) from (PT):
R
) that is zero or negative indicates
M
) for the link:
M
) is 13 dBm):
B
Sample Link Loss (LL) Calculation Values
0.5 dBm
0 dBm
) is the
M
) greater
M
Table 25 on page 55
55