dBW to dBuV

Converting from dBV to dBW requires a defined impedance. Usually for RF work this is 50 ohms, and 1 volt across 50 ohms represents a power of 0.02 Watts. So:

0 dBV = 1 Volt = 0.02 W (across 50W) = -17 dBW

0 dBuV = 1 uV = 0.00000002 uW = -107 dBm

To convert from dBuV across 50 Ohms to dBm, subtract 107.0

For other system impedances:

To convert from dBuV across 75 Ohms to dBm, subtract 108.8

To convert from dBuV across 300 Ohms, subtract 114.8

Field Strength (dBuV/m) to Power Flux Density (dBm/m² )

Signal levels are often expressed in dBuV/m, an archaic unit favoured by broadcasters as it is easy to measure and allows easy calculaton of the receiver voltage for a standard antenna.

dBm/m² = dBuV/m - 115.8

from: P=|E|²/Z_o
Where Z_o is the free space characteristic impedance in W equal to 120p

NB. All the above only applies for a plane wave, that is, in the far field of the antenna.

dB