tool · units
RF converters
Four converters with fields linked in both directions: type in any of them and the others follow along. Comma or dot for decimals, either works.
Frequency and wavelength
lambda = 299.79 / f(MHz), in meters
Length in free space, without shortening factor. To cut an antenna use the antenna calculator.
Power and voltage into 50 Ω
dBm = 10 log(P / 1 mW)
W = 10(dBm - 30) / 10; dBW = dBm - 30; voltage = √(P x 50 Ω); dBµV = 20 log(µV). Example: 100 W is 50 dBm; an S9 signal in HF, -73 dBm, is 50 µV at the receiver input.
S-meter
IARU standard: 6 dB per S unit
SWR and reflected power
|Γ| = (SWR - 1) / (SWR + 1)
Return loss = -20 log |Γ|; reflected = |Γ|²; mismatch loss = -10 log(1 - |Γ|²). Example: SWR 2:1 returns 11.1% of power, return loss of 9.5 dB. Modern radios usually reduce power on their own above 2:1 or 3:1.
Sources
The calculations run in your browser, nothing leaves here. Each formula was checked against the references below.
- IARU Region 1, Technical Recommendation R.1 (1981): S9 = -73 dBm in HF and -93 dBm in VHF, 6 dB per S unit
- ARRL Handbook, transmission lines chapter: SWR, reflection coefficient and return loss
- dBm and voltage in 50 ohms: P = V^2 / R (Ohm's law); 0 dBm = 1 mW. definition
- Speed of light: 299,792,458 m/s (BIPM)