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Radio signals attenuate with distance and frequency. FSPL increases 6 dB per doubling of distance and 20 dB per decade of frequency.
FSPL (dB) = 20×log₁₀(d) + 20×log₁₀(f) + 32.44 (d in km, f in MHz)Link margin = TX power + TX gain + RX gain − FSPL − receiver sensitivity. Positive margin means reliable link.
Margin (dB) = P_tx + G_tx + G_rx − FSPL − S_rxConvert mW to dBm: dBm = 10×log₁₀(mW). 25 mW = 14 dBm; 200 mW = 23 dBm; 1 W = 30 dBm.
dBm = 10 × log₁₀(power mW)Updated: July 2026
14 dBm + 2 dBi VTX antenna + 2 dBi RX − FSPL − (−90 dBm RX sens): reliable link to ~500 m–1 km line-of-sight on 5.8 GHz.
29 dBm + 2 dBi omni TX + 14 dBi patch RX: extended range to 5–10+ km LOS. Patch must be aimed — off-axis nulls drop signal rapidly.
Trees and terrain add 10–30 dB attenuation beyond FSPL. Halve calculated LOS range in wooded areas; use higher gain RX antenna.
Range is limited by the weaker link end. A high-power VTX with stock dipole RX antenna wastes power — upgrade RX antenna first for range gains.
Cross-polarization causes 20–30 dB loss — severe range reduction. Ensure VTX and goggles antennas match polarization and are both RHCP or both LHCP.
FPV video range depends on VTX power, antenna gain, frequency, obstacles, and receiver sensitivity. This calculator estimates line-of-sight range from transmit power, antenna configuration, and link budget.