Free RF Power & Voltage Converter
Instant bidirectional conversion between dBm, Watts, RMS Volts, Peak-to-Peak Volts, and receiver S-meter levels across 50Ω and 75Ω systems.
📻 Input Signal & Impedance
1,000 mW • 0.0 dBW
The 0 dBm Benchmark: In a 50Ω transmission line, 0 dBm = 1 milliwatt produces exactly 0.2236 V_rms (224 mV) and 0.632 V_pp. Every +3 dB doubles power, and every +10 dB is a 10× power increase.
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RF Signal Conversion Mathematics
Radio frequency power is universally expressed logarithmically in dBm (decibels referenced to 1 milliwatt):
Power in Watts: P_watts = 10^( (P_dBm - 30) / 10 )
Voltage in 50Ω: V_rms = √( P_watts × Z_0 )
Peak-to-Peak: V_pp = 2 × √2 × V_rms ≈ 2.8284 × V_rms
dBμV: dBμV = 20 × log10( V_rms / 1μV ) = P_dBm + 107 (in 50Ω)
IARU S-Meter Calibration Standards
Under the international IARU Region 1 recommendation:
- HF Bands (< 30 MHz): S9 is calibrated to -73 dBm ($50 mu ext{V RMS}$ across $50 Omega$). Each S-unit represents exactly 6 dB (a factor of 2 in voltage, factor of 4 in power). S8 is $-79 ext{ dBm}$, S7 is $-85 ext{ dBm}$, etc.
- VHF/UHF Bands (> 30 MHz): Due to lower atmospheric background noise, S9 is calibrated 20 dB lower at -93 dBm ($5.0 mu ext{V RMS}$ across $50 Omega$).
Frequently Asked Questions
Why does 0 dBm equal 0.224 V in 50 ohms but 0.274 V in 75 ohms?
Ohm’s law dictates P = V^2 / R. For 1 mW (0.001 W) into 50 ohms: V = sqrt(0.001 * 50) = 0.2236 V. For 1 mW into 75 ohms: V = sqrt(0.001 * 75) = 0.2738 V.
What is the difference between dBm and dBW?
dBm is decibels relative to 1 milliwatt, whereas dBW is decibels relative to 1 Watt. Because 1 Watt = 1,000 milliwatts (+30 dB), the conversion is simply: dBW = dBm - 30 (e.g. +30 dBm = 0 dBW; +40 dBm = +10 dBW).
Can an oscilloscope directly measure high transmitter power?
Never connect a transmitter directly to an oscilloscope! A 100W HF transmitter outputs 200V peak-to-peak (+50 dBm). Standard 50-ohm oscilloscope inputs are rated for only 5V RMS (0.5W, +27 dBm) and will burn out the internal termination resistor instantly. Always use a high-power 30 dB or 40 dB calibrated RF attenuator.