🧮 Radio unit converters
MHz ↔ wavelength, dBm ↔ watts, dB ↔ ratio, SWR ↔ return loss, S-units ↔ dBm.
Frequency ↔ wavelength
- Wavelength
- 2.05 m
- 6.71 ft
- Band
- 2 m
- ¼ wave
- 0.51 m
- 1.68 ft
dBm ↔ watts
0 dBm = 1 mW · 30 dBm = 1 W · 37 dBm = 5 W (a handheld) · 47 dBm = 50 W · 50 dBm = 100 W. Meshtastic radios run ~20-30 dBm. Right now: 37.00 dBm = 5.00 W.
dB ↔ power ratio
- Power ×
- 2.00
- times more power
- Voltage ×
- 1.41
- S-units
- 0.5
- 6 dB per S-unit
3 dB ≈ ×2 · 6 dB ≈ ×4 · 10 dB = ×10 · 20 dB = ×100. dBi − 2.15 = dBd (dipole gain). One S-unit is nominally 6 dB, so a 3 dB antenna gain is half an S-unit at the other end.
SWR ↔ return loss ↔ reflected power
- Reflected
- 4.0%
- of forward power
- Return loss
- 14.0 dB
- Mismatch loss
- 0.177 dB
- actually lost (not the reflected %)
2:1 reflects 11% but only costs 0.5 dB - most radios are happy to 2:1 and fold back power above 3:1. High SWR mostly matters for what it does to the finals and for extra coax loss, not the tiny mismatch loss.
S-meter → dBm
- HF (S9 = −73 dBm)
- -73.0 dBm
- VHF/UHF (S9 = −93 dBm)
- -93.0 dBm
- Into 50 Ω
- 50.1 µV
- HF