Calculator Inputs
Use the responsive grid below for radio path and link budget inputs.
Formula Used
This calculator estimates ideal line-of-sight attenuation and then extends the result into a simple link budget review.
Free Space Path Loss
FSPL (dB) = 32.44 + 20 log10(distance in km) + 20 log10(frequency in MHz)
Effective Isotropic Radiated Power
EIRP (dBm) = Tx Power + Tx Gain - Tx Cable Loss
Received Power
Received Power (dBm) = Tx Power + Tx Gain + Rx Gain - FSPL - Tx Cable Loss - Rx Cable Loss - Misc Losses
Link Margins
Raw Margin = Received Power - Receiver SensitivityAvailable Margin = Raw Margin - Fade Margin Target
The model assumes free space conditions. Terrain, clutter, diffraction, rain, connectors, and polarization effects should be added through the loss fields where appropriate.
How to Use This Calculator
- Enter the operating frequency and choose its unit.
- Enter the radio path distance and pick the correct distance unit.
- Add transmitter power, antenna gains, and any cable or miscellaneous losses.
- Enter receiver sensitivity and your required fade margin target.
- Submit the form to display path loss, received power, delay, EIRP, and margin values.
- Use the chart to see how attenuation and received power move as distance changes around the selected point.
Example Data Table
These rows show sample planning cases for quick comparison.
| Scenario | Frequency | Distance | Tx Power | Tx/Rx Gain | Total Losses | FSPL | Received Power | Margin vs -80 dBm |
|---|---|---|---|---|---|---|---|---|
| Campus Bridge | 2.4 GHz | 1 km | 20 dBm | 8 / 8 dBi | 3 dB | 100.04 dB | -67.04 dBm | 12.96 dB |
| Backhaul Spur | 5.8 GHz | 5 km | 23 dBm | 15 / 15 dBi | 4 dB | 121.69 dB | -72.69 dBm | 7.31 dB |
| Rural Link | 900 MHz | 15 km | 30 dBm | 17 / 17 dBi | 5 dB | 115.05 dB | -56.05 dBm | 23.95 dB |
Frequently Asked Questions
1. What does free space path loss represent?
It represents the signal attenuation caused only by distance and frequency in ideal unobstructed space. It excludes clutter, reflections, weather, diffraction, and interference.
2. Why does path loss increase with frequency?
Higher frequencies have shorter wavelengths, so the same link distance produces greater spreading loss in the standard free space model. The formula captures this with the frequency logarithm term.
3. Why include antenna gains and cable losses?
Path loss alone is not enough for deployment decisions. Gains and losses convert the attenuation estimate into a practical link budget, showing expected received power and usable margin.
4. What is a good available margin?
There is no universal value, but positive available margin is usually the minimum target. Many planners prefer at least 10 dB, while higher reliability links often reserve 20 dB or more.
5. Does this calculator handle obstacles or terrain?
No. It is based on ideal free space propagation. Use the miscellaneous loss field to add rough allowances, but detailed terrain and clutter studies need more advanced propagation models.
6. What is receiver sensitivity?
Receiver sensitivity is the minimum signal level your device needs for acceptable performance at a chosen modulation, coding rate, or data throughput target.
7. Why does the chart use a range around my distance?
It helps you see how quickly loss and received power shift when the path becomes shorter or longer. This is useful during early planning and sensitivity checks.
8. Can I use this for satellite or microwave links?
Yes, for first-pass estimates. Just use suitable frequency, distance, gains, and losses. For final design, add atmospheric absorption, pointing loss, polarization loss, and regulatory constraints.