wrote:

On Jan 24, 2:45 pm, "mpm" wrote:
On Jan 23, 8:29?pm, "Kaimbridge" wrote:

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.

If I understand what you're asking, your question really centers
around how to calculate Free Space Loss. The Friis Equation will
allow you to do this, and it is a relatively simple matter to
derive Free Space Path Loss in decibel form from the Friis Equation.

I'm not su Is this the same (or at least related to) W/m^2?
The problem I see with these is that, as distance approaches 0, KW
approahes oo and what I'm looking for shouldn't be greater than the
transmitter's erp.
What got me on this idea, is a few weeks go I was visiting up in the
NH White Mountains and was checking out the AM/FM bands (I'm a radio
geek! P=). When I got home, I went to the FCC site to create a
bandscan of the area. The designation used was the radius from a
point.
I quickly realized that this was less than ideal, as--using 100 km
radius, as an example--100 W stations at that distance would be listed
along with 50 and 100 KW! What would be much more useful would be a
listing of stations that provide--st least the theoretical baseline
value (i.e., not considering intervening local terrain or one's
receiver sensitivity and antenna gain)--a given mV/m or mW at that
point (thus listing 100 W stations out to 15 km, whereas 50 KW
stations out to 75 km and 100 KW to 130 km would be listed).
Think of it this way: If you turned on a 100 W lightbulb in the
middle of a field at night and held a book page right up to it, you
would be able to read it clearly; if you moved about 10 feet away
(with the book page still facing the lightblb, unobstructed), you
would have difficulty trying to read it, as only about the equivalent
of (e.g.) 50 mW of light may be hitting the page.

~Kaimbridge~

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Unless i am more mistaken than usual, the basic reference distance for
radiated power is 1 meter from the phase center of the antenna. Of course
depending on wavelength / frequency this could mean sub-near field
measurements to normal (semi-far to far field) measurements.

--
JosephKK
Gegen dummheit kampfen die Gotter Selbst, vergebens.Â*Â*
--Schiller