My conundrum is that I expect equal power intensity at the the measuring
point from the isotropic source whether a ground plane is involved or
not and that I also expect equal intensity from a vertical dipole in
free space and a quarter wave vertical on the ground plane (except for
the ground absorption at the real ground plane).
To add to my confusion? if I take an infinitesimal vertical radiator an
infinitesimal distance above the origin, such as a radiator of wire
0.00001 ft diameter spanning from 0.0001 to 0.0002 feet elevation with
one segment at 1 MHz with ground plane I see a gain of -57 and a
fraction dBi and in free space a gain of -60 dBi and the same fraction.
Then if I make that an isotropic source by adding two more wires of the
same length at the height of the middle of that first wire, one parallel
to the X axis and one parallel to the Y axis and spaced one wire length
from the middle of the vertical wire, I get -100 dBi gain over the half
sphere over a ground plane or -100 dBi gain in free space. Each wire has
a source in it.
73, Jerry, K0CQ
On 1/7/2011 5:07 PM, Steve Hunt wrote:
Jerry,
Then we'll probably have to agree to disagree :)
On 07/01/2011 22:53, Dr. Gerald N. Johnson wrote:
I fear its not a commonly held view though I'd think in broadcast
circles NEC would be held in contempt because it seems by my analysis to
predict twice the field power than would be measured in the real world.
Not so!
If you calculated the power density you would expect to see at that
range from an isotropic radiator in Free Space - one which radiates
uniformly in all directions - then apply the predicted EZNEC dBi figure,
it should match the power density you measured.
As I see it, it's not a problem with EZNEC, it's how you define the
reference power density; and your definition seems to be out of step
with all the engineering references I can find.
73,
Steve G3TXQ
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