Inputs
Large: 3 columns · Small: 2 · Mobile: 1All values are in dB/dBm unless noted. Use allowances to reflect construction-site routing, temporary masts, and environment.
Formula used
- Free-space path loss (distance in km, frequency in GHz):
FSPL(dB) = 92.45 + 20·log10(dkm) + 20·log10(fGHz)
- EIRP:
EIRP(dBm) = Ptx(dBm) + Gtx(dBi) − Ltx-feeder(dB)
- Received power:
Pr(dBm) = EIRP + Grx − Lrx-feeder − FSPL − (Lmisc + Lrain + Latm + Lpol)
- Fade margin:
Fade Margin(dB) = Pr − PthPth is receiver sensitivity (threshold). Higher margin means better resilience to fading.
- Optional sensitivity estimate:
Pth(dBm) = −174 + 10·log10(BWHz) + NF + SNR + IMBW is channel bandwidth, NF is noise figure, SNR is required demodulator SNR, IM is implementation margin.
How to use this calculator
- Enter the link distance and frequency.
- Provide transmit power, antenna gains, and feeder losses.
- Add allowances for rain, atmosphere, and site-related misc losses.
- Choose Sensitivity Mode: manual threshold or computed from BW/NF/SNR.
- Set a required fade margin and press Calculate.
- Review PASS/FAIL and export CSV/PDF for documentation.
Note: This tool is a first-pass budget. Real deployments may require terrain, diffraction, multipath, and regulatory checks.
Example data table
Sample values for a short construction backhaul link.
| Distance (km) | Frequency (GHz) | Tx Power (dBm) | Tx/Rx Gain (dBi) | Total Allowances (dB) | Sensitivity (dBm) | Estimated Margin (dB) |
|---|---|---|---|---|---|---|
| 12 | 11 | 20 | 30 / 30 | 1.5+1.5 feeder, 2 misc, 5 rain, 0.5 atm, 0.5 pol | -75 | ~ 28 (varies with inputs) |
Link budget context for construction deployments
Microwave backhaul is often used to connect offices, CCTV towers, batching plants, and gate systems where fiber is unavailable. This calculator consolidates distance, frequency, power, antenna gain, and losses into an actionable budget. By quantifying received level and fade margin, teams can select radios, confirm heights, and justify allowances for dust and re-aiming.
Key inputs that influence received power
Received power is driven by EIRP, path loss, and total allowances. Increasing antenna gain or transmit power raises EIRP, while feeder loss reduces it. FSPL rises with both distance and frequency, so short links at higher bands can still be viable if antennas are aligned and losses are controlled. Allowances for rain, atmosphere, polarization mismatch, and miscellaneous losses help represent real installation conditions.
Sensitivity selection and calculated mode
Fade margin compares received power against the receiver threshold. If a vendor sensitivity is known for the intended modulation and throughput, use manual mode. If only RF specifications are available, calculated mode estimates sensitivity from bandwidth, noise figure, required SNR, and implementation margin using thermal noise power. This provides a consistent baseline for early-stage planning before final radio profiles are locked.
Interpreting fade margin and availability targets
Higher fade margin generally improves link availability during multipath fading and heavy weather. Site policies may set different targets by criticality: a safety system backhaul may require a higher margin than a noncritical Wi‑Fi relay. If the calculator returns FAIL, reduce losses, shorten the path, increase antenna gain, or revisit bandwidth and modulation assumptions. Always validate against local regulatory limits and equipment ratings.
Reporting, audits, and handover documentation
Construction projects often require rapid approvals and clear records. The CSV export captures every input and computed result for review in spreadsheets, while the PDF export provides a lightweight attachment for submittals and commissioning packs. Pair exports with photos of antenna alignment, mounting details, and cable routes. This combination supports troubleshooting later, especially when equipment is relocated or a site expands.
FAQs
1) What does fade margin represent?
Fade margin is the difference between received power and receiver sensitivity. It is the “headroom” available to absorb fading, rain attenuation, and installation variability while still maintaining a stable link.
2) Which sensitivity mode should I use?
Use manual mode when your radio datasheet provides sensitivity for the exact modulation and channel width. Use calculated mode for early estimates when you only know bandwidth, noise figure, and SNR targets.
3) Why include rain fade as an allowance?
Rain can add significant attenuation at microwave frequencies, especially on longer paths and higher bands. An allowance helps your budget reflect weather risk and supports higher availability targets.
4) How do feeder losses affect the result?
Feeder losses reduce EIRP on the transmit side and reduce received power on the receive side. Improving connectors, shortening cables, or using better waveguide directly increases margin.
5) What should I adjust first if the link fails?
Start with controllable items: verify antenna gains, reduce feeder and misc losses, and check alignment assumptions. If needed, shorten the path or choose a lower bandwidth or more robust modulation profile.
6) Is this calculator a substitute for a full path study?
No. It is a fast budget tool. Final designs should consider terrain, Fresnel clearance, diffraction, interference, and regulatory constraints, plus vendor-specific performance at the intended throughput.