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Antenna Factor Calculator

Turn an antenna's gain and frequency into its 50-ohm antenna factor, and use a measured receiver level to estimate the incident field strength.

MHz, 0.1 to 40000
dBi in the direction being measured, -20 to 40
dBµV at the receiver, -20 to 160; leave blank to skip field strength
Enter a frequency and gain to see the antenna factor.

The antenna factor is the field strength in volts per metre divided by the voltage the antenna delivers into a matched 50-ohm load, usually quoted in dB/m. For a 50-ohm antenna in the far field it follows from the gain as 20·log₁₀(9.73 / λ) − G, where λ is the free-space wavelength in metres and G is the gain in dBi, so a higher gain lowers the factor. Field strength is the received level in dBµV plus the antenna factor in dB/m; the linear value converts as 10^((E − 120) / 20) V/m. The estimate assumes a free-space far field, a 50-ohm match, a lossless feed and the gain you enter; it does not include cable, balun or mismatch loss, and above 1 GHz the calibrated factor from the antenna's data sheet is more accurate. Everything runs in your browser with no storage, uploads or network access.