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Calculate received signal power from transmit power, antenna gains, and path losses. Free RF link budget calculator for wireless, satellite.
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The fundamental link budget sums transmit power, antenna gains, and subtracts all losses including free-space path loss, cable attenuation, and connector losses.
Received_Power(dBm) = Tx_Power - Tx_Losses + Tx_Antenna_Gain - Path_Loss + Rx_Antenna_Gain - Rx_LossesFSPL depends on frequency and distance. Higher frequencies and longer paths increase loss exponentially.
FSPL(dB) = 20×log₁₀(d_km) + 20×log₁₀(f_MHz) + 32.44Compare received power to receiver sensitivity plus required SNR. Positive margin indicates a reliable link; 10 dB margin is typical for analog FM, 3 dB for digital modes.
Margin(dB) = Received_Power - (Rx_Sensitivity + Required_SNR)Updated: July 2026
A 5W HT on 146.52 MHz accessing a repeater 15 km away with rubber duck antenna.
→ FSPL: ~103 dB; received: ~-67 dBm; margin: ~50 dB — strong access
Working an FM satellite at 400 km altitude with 25W and a 7-element Yagi (10 dBi).
→ FSPL: ~129 dB; received at satellite: ~-75 dBm; viable for FM satellite uplink
NVIS operation on 80m at 300 km using 100W and a dipole at 15 ft height.
→ Received: ~-85 dBm; NVIS reliable for regional emergency comms
dBd is gain relative to a dipole (dBi = dBd + 2.15). Mixing units causes 2 dB errors. Always convert to dBi for link budget calculations.
RG-58 loses ~6 dB per 30 m at 440 MHz. Use low-loss LMR-400 or place the radio at the antenna mast for VHF/UHF weak-signal work.
HF ground wave and NVIS paths have additional ground absorption and ionospheric effects. FSPL alone overestimates received signal on HF.
An RF link budget accounts for every gain and loss between your transmitter and receiver to predict whether a signal will be copyable. Ham radio operators use link budgets for VHF/UHF repeater planning, satellite contacts, and weak-signal DX work.