903-0628-00 Rev. 1
Model 903-HD User's Guide – FMB-X-2.5
Focal Technologies Corp.
Page 6-7
Figure 6-6: Power Budget Test Setup – Link Threshold Measurement
3. Disconnect the end of the VOAT that is connected to the console FMB-X-2.5 and measure the optical
power (P2) received (received sensitivity) by connecting that end of the VOAT to the optical power
meter. The difference between the transmit power (P1) and the receive power (P2) is an estimate of
optical power budget (P1-P2). (Add a spool of SMF-28 fiber with the VOAT to simulate dispersion
over long cables if necessary.)
Figure 6-7: Power Budget Test Setup – Received Sensitivity Measurement
4. Repeat steps 1-3 with connections reversed for the 1550 nm downlink (console to remote), ensuring
the optical power meter is set for 1550 nm. Often, the 1310 nm uplink fails before the 1550 nm
downlink, so the test will only determine a worst case for the 1550 nm link. If an exact measurement
of the 1550 nm power budget is required, use external WDMs to isolate the 1310 nm and 1550 nm
links on separate fibers.
Example Power Budget Calculation:
1310 nm Uplink Power Budget (measured)
1550 nm Downlink Power Budget (measured)
Rem_Tx_Pwr = -4.0 dBm (P1)
Con_Tx_Pwr = +1.0 dBm (P1)
Con_Rx_Pwr = -29 dBm (P2)
Rem_Rx_Pwr = -25 dBm (P2)
Power Budget =
-4.0 dBm - (-29 dBm) =
25 dB
Power Budget =
+1.0 - (-25 dBm) =
26 dB
Summary of Contents for Focal 903
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