Calculator Inputs
Choose a calculation mode, enter link parameters, and submit to estimate received power, path loss, maximum range, or required transmit power.
Example Data Table
This sample shows a point-to-point radio link using received power mode.
| Parameter | Value | Notes |
|---|---|---|
| Transmit Power | 30 dBm | Equivalent to 1 watt. |
| Frequency | 2.4 GHz | Common unlicensed band. |
| Distance | 3 km | Clear line-of-sight path. |
| Transmit Gain | 18 dBi | Directional panel or dish. |
| Receive Gain | 18 dBi | Matched directional antenna. |
| Total Fixed Loss | 4 dB | Feeders and extra losses combined. |
| FSPL | 109.59 dB | Computed from distance and wavelength. |
| Received Power | -47.59 dBm | Before weather or obstruction fading. |
| Receiver Sensitivity | -75 dBm | Minimum usable receiver input. |
| Link Margin | 27.41 dB | Healthy reserve for stable operation. |
Formula Used
The Friis transmission equation estimates received power for ideal free-space propagation:
In logarithmic link-budget form:
Free-space path loss is calculated as:
Wavelength is calculated from frequency:
Meaning of symbols
- Pr = received power at the receiving antenna input.
- Pt = transmit power from the radio output.
- Gt and Gr = transmit and receive antenna gains.
- R = separation distance between antennas.
- λ = wavelength associated with the operating frequency.
- L = feeder, polarization, and extra system losses.
How to Use This Calculator
- Select the calculation mode that matches your link-design task.
- Enter frequency and distance using the most convenient units.
- Add transmit and receive antenna gains in dBi or linear form.
- Include feeder, polarization, and extra losses for realism.
- For received power mode, supply receiver sensitivity to obtain margin.
- For maximum range or required transmit power, enter the required receive level and desired fade reserve.
- Press Calculate to display the result section above the form.
- Use the export buttons to save the computed metrics as CSV or PDF.
FAQs
1. What does the Friis equation assume?
It assumes ideal free-space propagation, matched polarization, and clear line-of-sight conditions. Real links may experience additional fading, absorption, multipath, terrain blockage, or connector losses not captured by the base equation alone.
2. Why does higher frequency often reduce range?
At the same distance, higher frequency produces a smaller wavelength and therefore higher free-space path loss. Unless antenna gain or transmit power rises, the received signal generally becomes weaker.
3. Should I enter gain in dBi or linear form?
Use whichever format you have. Data sheets typically list antenna gain in dBi. If your model provides linear gain, the calculator converts it internally before performing link-budget calculations.
4. What is link margin?
Link margin is the difference between calculated received power and receiver sensitivity. Positive margin means the signal exceeds the minimum usable level, while larger margin usually improves reliability.
5. What losses should be included?
Include feeder loss, connector loss, polarization mismatch, radome loss, duplexer loss, filter loss, or any other predictable attenuation between the transmitter, antennas, and receiver front end.
6. Is this suitable for satellite or microwave links?
Yes, as a first-order estimate. It is useful for microwave backhaul, satellite paths, and line-of-sight radio links, but advanced designs still need atmospheric, rain, and implementation losses.
7. What is the maximum range mode doing?
It solves the Friis equation in reverse. Using power, gains, losses, and required receive threshold, it estimates the farthest ideal free-space distance that still meets the design target.
8. Why add a target fade margin?
Fade margin reserves extra signal strength above the minimum threshold. This helps the link stay operational during rain, alignment drift, interference, or short-term propagation changes.