To add to what PA3DJS has observed:

I have seen the use of near-field measurements to determine directivity and
gain at the (then) NBS in Bolder, Col. A huge x-y table was used to move a
probe over the face of an energized microwave antenna. Lasers (with cycle
counters and mirrors) were used to measure the actual coordinates of the
probe! A staggering amount of data was collected over a long period of time
and then digested over another long period of time. This was done inside of
a very large building where reflections were minimal.

To use this technique at, say, 10 MHz with a yagi would be improbable, but
not impossible.

73, Mac N8TT

--
J. McLaughlin; Michigan, USA
Home:
"Wimpie" wrote in message
...
On 7 ene, 04:25, (Richard Harrison) wrote:

snip
Hi Richard,

You can determine radiated power and radiation pattern by near field
measurements (theoretically). Please search for "poynting theorem"
and "Huygens principle", "Huygens Source" or "Fresnel diffraction
theory". Most texts require differential vector calculus.

Because determining radiated power based on E- and H-Field measurement
is generally not feasible for amateurs (and even for many
professionals), I suggested another approach based on E-field
measurements and EM simulation.

As absolute E-field measurement and EM simulation are within the reach
of amateur radio operators, one can both tune for maximum field and
determine absolute radiated power.

Of course you don't know how much power is dissipated in nearby
structures (buildings, etc).

Best regards,

Wim
PA3DJS
www.tetech.nl