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Plotly Graph
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Example Data Table
| Scenario | Distance (km) | Frequency (MHz) | FSPL (dB) | Gt/Gr (dBi) | Other Loss (dB) | Fade (dB) | Pr (dBm) @ Pt=20 dBm |
|---|---|---|---|---|---|---|---|
| Short Wi‑Fi | 0.1 | 2400 | 80.04 | 2 / 2 | 1.0 | 5 | -62.04 |
| Campus Link | 2 | 5800 | 113.27 | 10 / 10 | 2.0 | 10 | -85.27 |
| Microwave Backhaul | 15 | 11000 | 136.79 | 24 / 24 | 3.0 | 20 | -91.79 |
Formula Used
The 32.44 constant applies when distance is in kilometers and frequency is in megahertz. This calculator converts your selected units into those bases before computing loss.
How to Use This Calculator
- Enter the link distance and choose the correct unit.
- Enter the carrier frequency and select its unit.
- Optionally add transmitter power, antenna gains, and extra losses.
- Set a fade margin to reserve headroom for reliability.
- Press Calculate to view FSPL, wavelength, and estimated received power.
- Use Download CSV or Download PDF to export the latest result.
Article
Link Budget Context
Free space path loss estimates how much signal power spreads out as a radio wave travels in open space. It is a baseline term in a link budget for Wi‑Fi, microwave backhaul, satellite telemetry, and radar test ranges. For example, at 2.4 GHz and 5 km, FSPL is about 114.0 dB, meaning an isotropic transmitter’s power density is reduced by that amount before antenna gains and other losses.
Unit Choices and Conversions
This calculator accepts meters, kilometers, miles, feet, and nautical miles, plus frequency in Hz through GHz. Internally it converts to kilometers and megahertz to apply the standard constant 32.44. That constant keeps results consistent with engineering references and makes comparisons easy across bands, such as 900 MHz, 2.4 GHz, 5.8 GHz, and 11 GHz.
Frequency Drives Loss Rapidly
FSPL grows with 20·log10(f). Doubling frequency adds roughly 6 dB of loss at the same distance. A 5 km link at 1.2 GHz has around 108 dB FSPL, while the same link at 2.4 GHz is roughly 114 dB. This is why high‑frequency links typically require higher‑gain antennas, tighter alignment, or shorter hops.
Distance Scaling and Planning
Loss also grows with 20·log10(d). Doubling distance increases FSPL by about 6 dB. The Plotly curve helps you see how quickly margin erodes when a 2 km design becomes 4 km or 8 km. Use it to test “what‑if” scenarios before committing to tower height, dish size, or amplifier power.
From FSPL to Received Power
To move from loss to a full budget, add transmitter power and antenna gains, then subtract other losses and fade margin. With Pt = 20 dBm, Gt = Gr = 10 dBi, other losses = 2 dB, and fade margin = 10 dB, a 2 km 5.8 GHz link lands near −85 dBm. Compare that to receiver sensitivity to judge throughput or availability.
Engineering Use and Limits
FSPL assumes clear line‑of‑sight and no reflections, absorption, rain fade, or foliage. Real deployments may need extra loss terms for cables, connectors, polarization mismatch, oxygen absorption, or precipitation. Treat this calculator as the starting layer, then refine with terrain profiles, Fresnel clearance checks, and site measurements. Document assumptions so future recalculations match your commissioning report and logs exactly.
FAQs
What does free space path loss represent?
It represents ideal spreading loss in unobstructed line‑of‑sight space. It does not include antenna gains, cable losses, rain, foliage, or multipath; those are handled as additional terms in your link budget.
Why does the formula use kilometers and megahertz?
Using km and MHz allows the constant 32.44 to be applied directly. The calculator converts your chosen units into km and MHz so results match standard engineering references.
How accurate is the received power estimate?
It is a first‑order estimate based on your entered gains, other losses, and fade margin. Real systems may differ due to antenna patterns, pointing error, interference, and environment‑dependent attenuation.
What fade margin should I enter?
Choose a margin that matches your availability target and environment. Short indoor links may use 3–10 dB, while outdoor microwave links often reserve 10–30 dB depending on climate and path variability.
Can I use this for satellite links?
Yes. Enter the slant range and carrier frequency, then add antenna gains and system losses. For higher bands, also account for atmospheric absorption and rain fade, which are not part of FSPL.
Why does the Plotly graph use a log distance axis?
A log axis shows short and long ranges on the same chart and highlights the 6 dB change per distance doubling. It helps quickly compare scenarios across decades of distance.