"Kaimbridge" wrote:
I've seen the different conversions for mW, mV, mV/m, dBm,
mostly based on 50 ohms. What I'm interested in is converting
a given field strength mV/m, at a given distance for a particular
frequency, to the equivalent (decayed) baseline wattage.
_________________

The radiated power needed to generate a given, free-space field strength of
course depends on the length of the propagation path to that value of field
strength.

Re-arranging the FCC equation to solve for the radiated power needed to
generate 562 mV/m when distance in kilometers is known gives

P = D^2/0.1552

So if there is a need to limit the field strength to 562 mV/m at a location
1 km from the antenna, we see that ERP cannot exceed ~6.44 kW.

Another way of doing it is to massage this "classic" equation.

Field Strength in dB above 1 microvolt/meter =
104.77 + ERPi - 20 log (D)

where ERPi = Effective Radiated Power in dB referenced
to 1kW from an isotropic radiator
D = Distance in kilometers

It gives the same answer as the simpler equation above.

I think this will answer your question, if I understood it right.

RF