Free RF calculator
ERP and EIRP calculator
Effective radiated power from the transmitter power, the feedline loss and the antenna gain, or the other way round: the transmitter power a licensed ERP allows. Give both and it checks the install against the license.
ERP is referenced to a half-wave dipole (47 CFR 90.7); dBi = dBd + 2.15, and EIRP = 1.64 x ERP as OET Bulletin 65 states it.
Runs in your browser; nothing you enter is sent anywhere. The same math the Sentinel RF product uses, tested against it. A planning figure, not an engineering sign-off.
The math
power at antenna (W) = TX (W) x 10^(-line loss dB / 10)
ERP (W) = power at antenna x 10^(gain dBd / 10)
EIRP = 1.64 x ERP dBi = dBd + 2.15
Solving for transmitter power runs the first two lines backward from the target ERP.
Reading the result
ERP on a land mobile license is referenced to a half-wave dipole (47 CFR 90.7), so a gain quoted in dBi is converted to dBd before it is used. EIRP is referenced to an isotropic radiator, which is why it always reads higher.
Leaving the line loss out overstates ERP. That errs toward caution when you check a license ceiling, and toward optimism everywhere else, such as a coverage estimate or a link budget.
In Sentinel RF
In the product the licensed ERP loads from the license itself, the feedline comes from the same cable model, and the result carries into the coverage studies and link budgets without being typed twice.
Other free calculators
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- Coax loss calculatorMatched-line loss by cable, frequency and run length, with connectors.
- Fresnel zone calculatorZone radius, 60% clearance and earth bulge at a point on the path, plus knife-edge loss.
- Near-field and far-field calculatorWhere the reactive near field ends and the far field begins, and which one a point is in.
Forty-five calculators, and the FCC data behind them.
The product runs these against real licenses, real towers and real terrain, and prints the result under your operation's name.