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Link Budget Calculator

Calculate received signal power from transmit power, antenna gains, and path losses. Free RF link budget calculator for wireless, satellite.

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Inputs that matter
Tx Power, Tx Antenna Gain, Rx Antenna Gain, Path Loss
Output to expect
Link Budget Calculator
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

Link Budget Equation

The link budget sums all gains and subtracts all losses in the signal path from transmitter to receiver. The result must exceed receiver sensitivity plus required fade margin for reliable communication.

P_rx(dBm) = P_tx + G_tx - L_tx - FSPL - L_misc + G_rx - L_rx

Free Space Path Loss (FSPL)

FSPL is the dominant loss in most links. It increases with both frequency and distance according to the Friis transmission equation. At higher frequencies, more directional antennas are needed to compensate.

FSPL(dB) = 20log₁₀(d) + 20log₁₀(f) + 32.44 (d in km, f in MHz)

Fade Margin

Fade margin is the excess signal above receiver sensitivity to maintain link availability during atmospheric fading, rain attenuation, or multipath. Typical targets: 10-15 dB for 99.9% availability, 20-25 dB for 99.99%.

Updated: July 2026

Example Scenarios

Outdoor WiFi bridge using directional antennas for building-to-building connectivity.

Tx Power: 20 dBmFrequency: 5.8 GHzDistance: 2 kmAntenna Gain: 23 dBi each

→ Received power: ~-47 dBm (well above -80 dBm sensitivity)

Long-range IoT sensor communication in rural area.

Tx Power: 14 dBmFrequency: 915 MHzDistance: 10 kmAntenna Gain: 6 dBi

→ Received power: ~-102 dBm (within LoRa -137 dBm sensitivity)

Common Mistakes to Avoid

Ignoring cable and connector losses

Coaxial cable loss at 5 GHz can be 0.3-1.0 dB per meter. A 3m cable run with 2 connectors adds 2-4 dB of loss. Use low-loss cable (LMR-400 or better) and minimize connector count.

Not accounting for rain fade at frequencies above 10 GHz

Rain attenuation becomes significant above 10 GHz. At 60 GHz, heavy rain can add 20+ dB/km of loss. Include ITU-R P.838 rain attenuation models for frequencies above Ku-band.

FAQ

For 99.9% availability: 10-15 dB margin. For 99.99% (carrier-grade): 20-30 dB. For indoor/short-range: 5-10 dB is often sufficient. Under-designing margin leads to intermittent outages during weather events.

Higher frequencies have greater free-space path loss (6 dB more per octave of frequency). However, higher frequencies enable physically smaller antennas with the same gain, and more bandwidth is available. It's a system-level tradeoff.

EIRP (Effective Isotropic Radiated Power) = Tx power + antenna gain - cable losses. Regulatory bodies limit EIRP, not just transmitter power. High-gain antennas require reducing Tx power to stay within legal limits.

Yes: use higher-gain antennas (most effective), reduce cable losses (shorter runs, better cable), improve receiver sensitivity (lower noise figure LNA), or reduce operating frequency for less FSPL over the same distance.

About Link Budget Calculator

Calculate the power budget for an RF communication link by summing transmitter power, antenna gains, and subtracting all path losses. Determines whether the received signal exceeds the receiver sensitivity threshold with adequate fade margin for reliable operation.