There's not enough information to calculate field strength. There's a
direct relationship between uV/m (field strength) and W/m^2 (power
density), providing you're in the far field and you know the intrinsic
impedance of the medium (about 377 ohms for free space). But you need a
distance from the source and the antenna gain in order to know what the
power density is for a given power (dBm). So at the very least, you have
to specify the distance from the source and the antenna gain to
calculate field strength from dBm. And then it's valid only in the far
field.

Roy Lewallen, W7EL

Ron J wrote:
Hey all,

I'm still skeptical about this formula:

Field Strength (uV/m) = 10 ^ ( (107 - |dBm| ) / 20 )

Is this valid? I saw this formula somewhere and jotted it down.

Thanks!