RF Link Budget Calculator
Complete RF link budget using the Friis transmission equation. Enter TX power, gains, losses and distance to get received power, SNR, link margin and system sensitivity. Essential for wireless system design.
About the RF Link Budget Calculator
A link budget is an accounting of all the gains and losses in a radio communication system from the transmitter output to the receiver input. It determines whether there is enough signal margin for the link to work reliably under the given conditions.
Free Space Path Loss
Even in a perfect vacuum with no obstacles, radio waves spreading out in all directions lose power as they travel. Free space path loss (FSPL) follows the inverse square law: FSPL = 20*log10(4*pi*d/lambda) dB. At 2.4 GHz over 100 metres, FSPL is approximately 80 dB. At 60 GHz (mmWave), the same distance gives 108 dB of path loss — one reason mmWave systems require high-gain directional antennas.
EIRP — Effective Isotropic Radiated Power
EIRP is the transmit power plus antenna gain, referenced to an isotropic radiator. A 20 dBm transmitter with a 5 dBi antenna has an EIRP of 25 dBm. EIRP is the figure that regulatory bodies (FCC, ETSI) limit for unlicensed devices. The higher the EIRP, the further the signal travels — but the regulatory limits exist to prevent interference between systems.
Link Margin
Link margin is the difference between the received signal power and the minimum required receiver sensitivity. A link margin of 10 dB means the system can tolerate 10 dB of additional loss (from rain, reflections, obstacles or antenna misalignment) before the link fails. Minimum acceptable margins are typically 10-20 dB for reliable outdoor links and 3-6 dB for indoor consumer devices.