"Richard Harrison" wrote
George, K6GW wrote:

"What is the easiest/fastest way to calculate received power out
of a very short non-resonant antenna?"

.. The dissipationless resistance of free-space (a ratio between voltage
and current) is 377 ohms. Attenuation due only to reduction of power per
square meter as the radio wave envelope expands in space is 6 dB every
time distance from the transmitter doubles. That means getting only 1/4
the previous power every time distance from the transmitter doubles.
(etc)
__________

The answer to the way I read the original question does not involve knowing
what the field strength is, or how it varies with distance or other factors,
but knowing the power it will produce via the receive antenna system.

Here is a paste from a spreadsheet I set up to calculate the field needed to
produce a defined power level at the input terminals of a receiver,using the
equation

µV/m = 10^[(dBmW - G + 20*(log F) + L + 75)/20]

where

-66.89 dBmW = signal level at receiver input in dB with respect to 1 mW
-2.14 G = receiving antenna gain in dBd
0.1 L = line loss in decibels
98 F = frequency in MHz


Solution for the values shown at the left margin above:

322.65 µV/m field required.

The equation could be rewritten to solve for power, given a field strength.

RF http://rfry.org