RF Link Budget
Calculate the complete radio frequency link budget including all gains and losses.
About RF Link Budget
This RF link budget first calculates EIRP (Effective Isotropic Radiated Power) — the transmit power actually radiated toward the receiver after antenna gain and cable loss: EIRP = Tx_power + antenna_gain − cable_loss. It then subtracts the free-space path loss (FSPL), which grows with both distance and frequency, and adds the receiving antenna's gain to arrive at the final received power: received = EIRP − FSPL + Rx_gain. This is the standard method for estimating link feasibility for any RF system — WiFi, point-to-point microwave, or satellite.
Formulas
EIRP
EIRP = Tx_power + antenna_gain − cable_loss
Free-space path loss
FSPL(dB) = 20·log10(distance_km) + 20·log10(freq_GHz) + 92.45
Received power
received = EIRP − FSPL + Rx_gain
Worked example
With the default values below, RF Link Budget returns Received Power of -70.03. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Transmit Power
- 30 dBm
- Transmit Antenna Gain
- 10 dBi
- Cable Loss (Tx side)minimum 0 dB
- 1 dB
- Link Distanceminimum 0.001 km
- 5 km
- Frequencyminimum 0.01 GHz
- 2.4 GHz
- Receive Antenna Gain
- 5 dBi
Results
- Received Power
- -70.03 dBm
- EIRP
- 39.00 dBm
- Free-Space Path Loss
- 114.03 dB
Step by step
- 1Values used
- 2EIRP
- 3Free-space path loss
- 4Received power
- 5Received Power= -70.03 dBm
- 6EIRP= 39.00 dBm
- 7Free-Space Path Loss= 114.03 dB
Assumptions and limits
- The result is derived only from the 6 inputs listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or fees or charges into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
Why is EIRP calculated separately before applying path loss?
EIRP represents the actual effective power leaving the system in the direction of the antenna's main beam, which is what actually propagates through space and experiences path loss — it's more meaningful than raw transmitter output power alone, since antenna gain focuses that power directionally.
Why does path loss increase with frequency at the same distance?
Higher-frequency waves have shorter wavelengths, and for a fixed antenna size/gain, isotropic path loss increases with frequency — the FSPL formula's 20·log10(freq) term captures this, meaning a link at 5 GHz suffers roughly 6.5 dB more path loss than the same link at 2.4 GHz.
Is free-space path loss realistic for terrestrial links?
FSPL models an idealized, obstruction-free path and is a reasonable approximation for clear line-of-sight links (satellite, point-to-point microwave with a clean Fresnel zone), but real terrestrial links often experience additional loss from terrain, foliage, and multipath not captured by this simple model.
How does this differ from the microwave link calculator?
This calculator produces a full end-to-end received power estimate including antenna gains and cable loss. The Microwave Link calculator focuses specifically on the FSPL component itself, useful when you just need the path loss figure to plug into a separate link budget.