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:
> 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.
> Steve G3TXQ
TenTec mailing list