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Calculate the Fiber-Optic Cable Power Budget for a PTX Series Router
Calculate the link's power budget when planning fiber-optic cable layout and distances to ensure that
fiber-optic connections have sufficient power for correct operation. The power budget is the maximum
amount of power the link can transmit. When you calculate the power budget, you use a worst-case
analysis to provide a margin of error, even though all the parts of an actual system don't operate at the
worst-case levels.
To calculate the worst-case estimate for the fiber-optic cable power budget (P
1. Determine values for the link's minimum transmitter power (P
For example, here (P
(dBm):
P
= –15 dBm
T
P
= –28 dBm
R
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
–15 dBm – (–28 dBm) = 13 dBm
Calculate the Fiber-Optic Cable Power Margin for a PTX Series Router
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 don't 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.
) and (P
) are measured in decibels, and decibels are referenced to 1 milliwatt
T
R
B
) by subtracting (P
) and minimum receiver sensitivity (P
T
) from (P
):
R
T
) that is zero or negative indicates
M
B
) for the link:
) is the
M
) greater
M
108
).
R
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