Method 1: Power Meter + Sensor (Most Accurate)
Diode or thermocouple sensor detects average power Accuracy: ±0.03 dB (traceable to national standard) Frequency range: 10 MHz – 110 GHz (with appropriate sensor) Measurement: P_load = P_sensor × (1 − |Γ_sensor|²) / (1 − |Γ_source·Γ_sensor|²) Mismatch uncertainty: ±20·log₁₀(1 ± |Γ_s|·|Γ_sensor|) ← use matched sensor Best for: absolute power calibration, efficiency measurement, EIRP
Method 2: Spectrum Analyzer
Measures power in a resolution bandwidth (RBW) Accuracy: ±0.5–1.5 dB typical (worse than power meter) Advantage: frequency-resolved (can see sidebands, harmonics) Power conversion from SA display: P_total (dBm) ≈ SA_reading + 10·log₁₀(OBW/RBW) [for wideband signal] P_carrier (dBm) = SA_reading at carrier peak [for CW signal] Best for: spectral analysis, harmonic measurement, relative power comparison
Method 3: VNA S-Parameter Approach (Relative)
VNA measures |S21|² = P_delivered / P_available If P_source is known: P_load = P_source × |S21|² Not for absolute power — only relative power ratios Best for: insertion loss, gain characterization, matching verification
Common RF Power Level Reference
| dBm | Watts | Application |
|---|---|---|
| −174 dBm/Hz | 4e-21 W/Hz | Thermal noise floor 290 K |
| −100 dBm | 0.1 pW | Minimum detectable signal |
| 0 dBm | 1 mW | VNA test power, reference |
| +30 dBm | 1 W | LTE handset peak TX |
| +43 dBm | 20 W | Small cell TX power |
RF View dBm Calculator: Convert between dBm, watts, and milliwatts in RF View's Utilities tab. Includes dBuV conversion for EMC measurements. Free offline on Android.