Use the figures for your radio and antennas to check one direction of a link. Start with free space as a reference, or enter a path loss from a measurement or propagation study.
Margin above receiver sensitivity
26.95dB
Free-space reference plus your additional loss allowance.
Check the values to see a result.
A positive margin is not proof of coverage. Check both directions and verify packet delivery at the installed locations.
Received dBm = transmit dBm − transmit loss + transmit gain − path loss + receive gain − receive loss
Estimated received power is -68.05 dBm, giving 26.95 dB above the -95 dBm sensitivity. Your 10 dB fade-margin target is met in this calculation.
Tip: Use receiver sensitivity for the actual data rate, bandwidth and modulation. Run the calculation again with transmitter and receiver roles reversed.
A link budget keeps the radio power, antenna gains and losses in one calculation. It estimates the power at the receiver input, then compares that with the sensitivity for the selected radio mode. Calculate the return direction separately: a strong Gateway transmitter cannot make a low-power sensor transmit further.
Free space is a reference, not a prediction for a plant room. Use a measured or studied path loss when you have one. A metal cabinet, moving machinery and nearby transmitters can change packet delivery without changing the distance between the radios.
EIRP = radio dBm − feeder loss dB + antenna gain dBi
Start at the radio connector. Include cable, connector and filter losses between that point and the antenna. If your datasheet already states EIRP, do not add its antenna gain again. EIRP describes the directional radiated power relative to an isotropic antenna; this tool does not check regulatory limits.
Free-space loss = 20 log₁₀(4πdf / c)
The ITU-R reference uses distance and wavelength in the same units. Here frequency is entered in MHz and distance in metres; the kernel converts frequency to Hz and uses c = 299,792,458 m/s. Far-field conditions depend on antenna size and wavelength. The entered range is not evidence that those conditions hold.
Received dBm = EIRP − path loss + receive antenna gain − receive feeder loss
A known path-loss input excludes the antenna gains and feeder losses entered in their own fields. If you infer path loss from RSSI, account for those gains and losses first. Add separately estimated obstruction loss only in free-space mode; known total path loss already contains the propagation loss.
Margin = received dBm − receiver sensitivity dBm
Keep the minus sign on sensitivity. A −80 dBm signal is 15 dB above a −95 dBm sensitivity. Reserving 10 dB for fading leaves 5 dB above that target. A target of zero leaves no deliberate reserve and a negative margin is below the entered sensitivity.
EIRP is 11 dBm. Received power is 11 − 100 + 2 − 1 = −88 dBm. That leaves 7 dB above receiver sensitivity, which is 3 dB below the entered 10 dB fade-margin target.
Margin above receiver sensitivity 7 dB Open in the calculator
Free-space loss is approximately 80.05 dB. The received-power estimate is −68.05 dBm and the margin is 26.95 dB. This example includes no walls, ground reflections or interference. It cannot establish that an indoor link will work.
Margin above receiver sensitivity 26.95 dB Open in the calculator
It means the arithmetic is above the sensitivity you entered. Sensitivity is measured for particular radio settings and an error criterion. Interference, fading, packet collisions and an obstructed path can still prevent reliable delivery. Check packet delivery and fresh timestamps at the actual installation.
Use the target from the link design or site study. The 10 dB starting value is an editable example, not a universal recommendation. More variable conditions need a justified allowance; no single number replaces a survey.
Use the radio settings and antenna figures for the exact device. The arithmetic applies to a single hop, not to mesh routing or network capacity. A LoRaWAN sensitivity figure must match its spreading factor, bandwidth and other radio settings. Run both uplink and downlink budgets where the application depends on both.
dB expresses a ratio. dBm expresses absolute power relative to 1 mW. dBi expresses antenna gain relative to an isotropic radiator. Adding gain or subtracting loss in dB changes a dBm power level; adding two dBm powers is not how powers are combined.