Calculator Inputs
Example Data Table
| Use Case | Distance | Frequency | Tx Power | Tx Gain | Rx Gain | Extra Loss | Estimated FSPL |
|---|---|---|---|---|---|---|---|
| WiFi Outdoor Bridge | 2 km | 2400 MHz | 20 dBm | 8 dBi | 8 dBi | 2 dB | 106.07 dB |
| Microwave Link | 15 km | 5800 MHz | 27 dBm | 24 dBi | 24 dBi | 3 dB | 131.24 dB |
| Satellite Planning | 35786 km | 12000 MHz | 40 dBm | 35 dBi | 40 dBi | 5 dB | 205.11 dB |
Formula Used
The free space path loss formula is: FSPL dB = 32.44 + 20 log10(distance in km) + 20 log10(frequency in MHz).
The received power formula is: Received Power = Tx Power + Tx Gain + Rx Gain - FSPL - Extra Losses.
Fade margin is: Fade Margin = Received Power - Receiver Sensitivity.
EIRP is: EIRP = Tx Power + Tx Antenna Gain - Cable Loss.
How to Use This Calculator
- Enter the link distance and choose the matching distance unit.
- Enter the operating frequency and choose the correct frequency unit.
- Add transmit power in dBm or watts.
- Enter antenna gains for both sides of the link.
- Add cable, connector, and other expected losses.
- Enter receiver sensitivity and your required fade margin.
- Press the calculate button to view the full link result.
- Use CSV or PDF export for records and reports.
Free Space Path Loss Guide
What This Calculator Does
A free space path loss calculator estimates signal reduction across clear space. It helps radio planners understand how much power is lost between antennas. The tool uses distance and frequency as the main factors. Longer distance creates more loss. Higher frequency also creates more loss. These two values shape the basic wireless link budget.
Why Link Budget Matters
A working radio link needs enough received power. The receiver must hear the signal above its sensitivity limit. Antenna gain can improve the result. Cable loss and connector loss reduce the result. Extra losses should be included for safer planning. Trees, walls, rain, poor alignment, and hardware limits may reduce performance.
Advanced Planning Value
This calculator goes beyond basic path loss. It estimates EIRP, received level, wavelength, and fade margin. Fade margin is important for dependable service. A weak margin may work only in perfect conditions. A stronger margin gives the link more room for weather, movement, and interference. Many designers aim for a practical safety margin before installation.
Good Input Practices
Use accurate distance values from maps or site surveys. Use the real operating frequency, not only the band name. Enter antenna gains from product data sheets. Include cable loss at the chosen frequency. Connector loss should not be ignored. Small losses can matter on long or high frequency links.
Reading the Result
The FSPL value shows ideal open air loss. Received power shows the estimated signal at the receiver. Fade margin compares that signal against receiver sensitivity. The status line checks your margin target. A passing result does not guarantee real world performance. It gives a clean starting point for planning. Field testing is still useful before final deployment.
Common Uses
The calculator is useful for WiFi bridges, microwave paths, telemetry links, amateur radio, satellite estimates, and point to point systems. It can compare different frequencies quickly. It can also show how better antennas or shorter cables improve the link. Use the export buttons when documenting proposals, checks, or engineering notes.
FAQs
1. What is free space path loss?
Free space path loss is signal reduction in open space. It assumes no walls, trees, hills, rain, or reflections. It is an ideal radio planning value.
2. Does higher frequency increase path loss?
Yes. Higher frequency increases calculated path loss when distance stays the same. This is why high frequency links often need better antennas or shorter paths.
3. What unit should I use for frequency?
You can enter Hz, kHz, MHz, or GHz. The calculator converts the value to MHz before applying the standard free space path loss formula.
4. What is fade margin?
Fade margin is the difference between received power and receiver sensitivity. A larger margin gives more protection against weather, obstruction, interference, and alignment errors.
5. What is EIRP?
EIRP means effective isotropic radiated power. This calculator estimates it from transmit power, transmit antenna gain, and cable loss before the antenna.
6. Why include cable and connector loss?
Cables and connectors reduce useful signal power. Even small losses can affect long distance links, especially at higher frequencies or low receive margins.
7. Is this result exact in real life?
No. It is an ideal estimate. Real environments include reflections, absorption, terrain, rain, trees, buildings, and equipment limits. Field testing is recommended.
8. Can I export the calculation?
Yes. After calculation, use the CSV or PDF button above the form. The exported report includes main input conversions and link budget results.