Enter RF Link Inputs
Example Data Table
| Scenario | Frequency | Distance | Tx Power | Tx/Rx Antenna | Total Extra Loss | Received Power | Link Margin |
|---|---|---|---|---|---|---|---|
| Licensed backhaul example | 5800 MHz | 12 km | 27 dBm | 29 / 29 dBi | 4.40 dB | -53.69 dBm | 20.31 dB |
| Campus bridge example | 2400 MHz | 3 km | 20 dBm | 17 / 17 dBi | 2.20 dB | -40.29 dBm | 34.71 dB |
| Urban rooftop example | 1800 MHz | 8 km | 30 dBm | 18 / 18 dBi | 6.50 dB | -58.11 dBm | 16.89 dB |
Formula Used
FSPL (dB) = 32.44 + 20 log10(frequency in MHz) + 20 log10(distance in km)
EIRP (dBm) = Tx Power - Tx Losses + Tx Antenna Gain
Received Power (dBm) = EIRP - Total Path Loss + Rx Antenna Gain - Rx Losses
Noise Floor (dBm) = -174 + 10 log10(Bandwidth in Hz) + Noise Figure
Available SNR = Received Power - Noise Floor
Effective SNR = Available SNR - Implementation Loss
Link Margin = Received Power - Receiver Sensitivity
Operating Margin = Link Margin - Required Fade Margin
These equations combine antenna gain, feeder losses, propagation losses, receiver sensitivity, and SNR targets to show whether a planned wireless path should operate reliably.
How to Use This Calculator
- Enter the operating frequency, path distance, and transmitter power.
- Add real feeder losses, connector losses, and both antenna gains.
- Include environmental penalties such as rain fade or polarization mismatch.
- Provide receiver sensitivity, bandwidth, noise figure, and required SNR.
- Set the fade margin target that matches your availability objective.
- Press the calculate button to view received power, margins, and the plot.
- Use the CSV or PDF export buttons to document the design.
FAQs
1. What does an RF link budget actually measure?
It tracks signal power from the transmitter to the receiver by adding gains and subtracting losses. The result shows received power, margin, and whether the link is likely to meet performance targets.
2. Why is free space path loss so important?
FSPL is usually the largest loss term in a clear line-of-sight path. It rises with both distance and frequency, so even strong radios can fail if antennas or margins are undersized.
3. What is the difference between link margin and fade margin?
Link margin is the spare power above receiver sensitivity. Fade margin is the reserve you intentionally require to survive fading, rain, interference, and real-world instability over time.
4. Why does the calculator include noise figure and bandwidth?
Those inputs estimate receiver noise floor. A wider channel collects more noise, and a poorer receiver raises the floor further. Both reduce available SNR and can limit modulation choices.
5. Should I include rain fade for every wireless link?
Not always. Rain fade matters far more at higher microwave and millimeter-wave bands. Short links at lower frequencies may need only a small value, while long high-band links may need much more.
6. What is a good operating margin?
That depends on the service objective. Critical backhaul links often aim for strong positive operating margin after fade allowance, while short noncritical links may accept tighter reserves.
7. Why can a link show positive power but still be weak?
Received power alone is not enough. The link also needs adequate sensitivity margin and enough SNR after implementation losses. Stronger absolute power can still fail if noise is also high.
8. Can this calculator replace a full propagation study?
No. It is excellent for planning and screening designs, but terrain, Fresnel clearance, interference, clutter, multipath, and regulation checks still matter in final engineering work.