Field Tool
Optical Loss Budget
Add up optical link loss, compare it with the optics, and show headroom and loss-limited reach.
Within budget: 2.10 dB headroom. Design loss 25.90 dB.
Design Loss
25.90 dB
22.90 dB link loss plus 3.00 dB margin, against GPON Class B+ (28 dB maximum).
| Item | Basis | dB |
|---|---|---|
| Fiber | 9.144 km × 0.35 dB/km | 3.20 |
| Splices | 8 × 0.10 dB | 0.80 |
| Connector pairs | 4 × 0.50 dB | 2.00 |
| Splitters | 1×32 | 16.90 |
| Other | WDM, filters, panels | 0.00 |
| Link loss | Sum of the rows above | 22.90 |
| Design margin | Planning assumption | 3.00 |
| Design loss | Link loss + margin | 25.90 |
| Headroom | Budget 28 − design | 2.10 |
- Max reach at this design (loss only)
- 15.14 km (49,681 ft)
Loss-limited only: it does not check the optics' rated reach, dispersion or the PON class's reach. The transceiver datasheet and the owner's design rules govern.
Show the Math
link = L·α + Ns·Ls + Nc·Lc + splitters + other design = link + margin headroom = budget − design max reach = max(0, (budget − (design − L·α)) ÷ α)
L is the route length in km (1 ft = 0.0003048 km; 1 mi = 1.609344 km) and α is the attenuation in dB/km. Ns and Nc are the fusion splice and mated connector pair counts, with loss Ls and Lc each. For PON, the budget is the class maximum; link loss below the class minimum warns about receiver overload on short links. Max reach: Loss-limited only: it does not check the optics' rated reach, dispersion or the PON class's reach. The transceiver datasheet and the owner's design rules govern.
Status
- Headroom of 1 dB or more: good.
- Headroom from 0 to 1 dB: warning.
- Headroom below 0: critical (over budget).
- The 1 dB warning band is a FAHMY planning threshold, not a standard; the owner's design rules govern.
Defaults and Where They Come From
- Attenuation planning defaults: 1270 nm → 0.40 dB/km, 1310 nm → 0.35 dB/km, 1490 nm → 0.27 dB/km, 1550 nm → 0.25 dB/km, 1577 nm → 0.25 dB/km. Typical cabled G.652.D (
ITU-T G.652). Use the cable spec sheet. - Splice and connector maximums: 0.3 dB per fusion splice and 0.75 dB per mated pair . The tool's 0.10 dB and 0.50 dB are example values.
- PLC splitter typical maximum insertion loss without connectors (manufacturer datasheets): 1×2 4.0 dB, 1×4 7.4 dB, 1×8 10.7 dB, 1×16 13.7 dB, 1×32 16.9 dB, 1×64 21.0 dB. Use your splitter's datasheet.
- Design margin 3.0 dB for repairs and aging is a planning assumption. Use the owner's margin where one is set: design margin.
- PON classes (minimum–maximum optical path loss): GPON Class B+ 13–28 dB ; GPON Class C+ 17–32 dB ; XGS-PON N1 14–29 dB ; XGS-PON N2 16–31 dB ; XGS-PON E1 18–33 dB ; XGS-PON E2 20–35 dB .
- Point-to-point budget: minimum transmit power minus receiver sensitivity, from the transceiver datasheet. The 15 dB value is an example.
Assumptions
- Check the worst direction. Upstream (1310 nm for GPON, 1270 nm for XGS-PON) usually sees the most fiber loss.
- When you test, compare measured loss with the link loss before margin. Typical practice; the owner's test specification sets the acceptance value and method.
Sources
FAHMY tools give planning estimates. The owner's specifications, the authority having jurisdiction and the manufacturer's data govern every job. Values marked "Planning assumption", "Planning default", "Typical maximum", "Rule of thumb" or "Example" are editable starting points, not requirements; "Per owner spec" fields take the owner's value.