How to convert the power EIRP -13.03 dbuv/m at 300m to dBm

Guys,

I have case that I need to know the value of the power in watts,
in toher words I need to convert the power:

EIRP -13.03 dbuv/m at 300m to dBm

could you help me?

Field strength V/m = 10^(dBuV/20)
Power density = V/H W/m^2
H = impedance of free space, 120*pi = 377
For your values
Field strength = 10^(-13/20)*1e-6 = 2.23E-7 V/m
Power density = 2.23E-7 / 377 = 5.9E-10W/m^2

To get to the received power you need to know the effective capture area of your antenna

try searching for field strength to power density

A reference that might help you
https://www.semtech.com/uploads/.../...d_strength.pdf

dBuV/m is not a measure of power (or EIRP) but a measure of electric field E.

Considering the spherical radiation the electric field in far field can be calculated distributing the power over a spherical surface. If the radiation is not spherical you have to multiply the power by the (linear) gain of the antenna in the direction you want to calculate the electric field. The multiplication of power by gain is the EIRP.

It's easy to calculate E(V/m)=sqrt(30*EIRP)/d where EIRP is in W, while d is in meter.

-13.3 dBuV/m = 10^(-13.3/20) uV/m = 0.22 uV/m = 2.2e-7 V/m as already calculated by G4BCH

Then EIRP(W)= (E*d)^2/30 = (2.2e-7*300)^2/30 = 145.2 pW

EIRP(dBm) = 10*Log10(145.2e-12*1000) = -68.4 dBm VALID ONLY IN FAR FIELD