A gigabit single-mode link between two substation buildings: does it pass on worst-case component losses, on typical losses, and what changes if 1000BASE-LX10 optics are used?
| Transceiver | 1000BASE-LX SFP, 1310 nm: Tx min −11.5 dBm, Rx sensitivity −19 dBm |
| Fibre | OS2 single-mode, 0.4 dB/km at 1310 nm, 3.2 km |
| Connector pairs | 4 (patch cord into panel and panel to switch, at each end) |
| Splices | 2 (pigtail fusion splices at the two panels) |
| Safety margin | 3 dB |
Transceiver figures are representative datasheet values; use the actual module's datasheet for a real design.
The connectors take 3.0 dB of the 7.5 dB budget — more than the 3.2 km of fibre.
With factory-polished connectors (0.5 dB) and fusion splices (0.1 dB):
A 1000BASE-LX10 module with Tx min −9.5 dBm and Rx sensitivity −19.5 dBm gives a 10 dB budget.
| Check | Requirement | Actual | Status |
|---|---|---|---|
| 1000BASE-LX, maximum losses | Margin ≥ 0 dB | −0.38 dB | ✗ FAIL |
| 1000BASE-LX, typical losses | Margin ≥ 0 dB | +1.02 dB | ✓ PASS |
| 1000BASE-LX10, maximum losses | Margin ≥ 0 dB | +2.12 dB | ✓ PASS |
| Reach (IEEE 802.3) | 3.2 km ≤ 5 km (LX) / 10 km (LX10) | 3.2 km | ✓ PASS |
Key insight: On short single-mode links the connectors, not the fibre, use most of the budget.
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Open Fibre-Optic Link Budget Calculator calculator →Yes. Splicing the trunk straight to the equipment pigtails or removing an intermediate panel removes 0.75 dB per pair on the design basis.
No. The calculator takes the strongest transmitter (−3 dBm) and a low estimate of the link loss (about 2.2 dB), giving about −5.2 dBm at the receiver — below the −3 dBm overload level.