Jerry,
With respect, the "industry standard" Isotropic reference definition
*doesn't* change in the presence of ground - it remains at a power
density of Pt/(4*Pi*r^2) in all cases.
It may be that leads to some "condrums" for you, but they follow from
the definition - it's not an error in EZNEC, which is simply applying
the standard interpretation.
For me there is no conundrum. If I model a quarter-wave vertical over
perfect ground I see a maximum Gain of 5.15dBi - the 2.15dBi I would
expect due to the elevation pattern (same as a half-wave dipole), and
3dB because all of the transmitted power is now constrained to one
hemisphere rather than the two hemispheres "occupied" by the reference
Isotropic source. I see no problem there.
73,
Steve G3TXQ
On 08/01/2011 20:13, Dr. Gerald N. Johnson wrote:
What I see is that the changes in isotropic reference definition in the
presence of a ground cause the program to show greater gain numbers that
make the casual user conclude that there is a gain caused by the
presence of the earth that is not there when signal strength in the main
lobe is measured compared to that antenna in free space.
73, Jerry, K0CQ
On 1/8/2011 6:48 AM, Steve Hunt wrote:
Jerry,
I can understand that the interpretation of dBi which appears in most
engineering texts (and possibly the IEEE definition?) throws up
conundrums with which you are uncomfortable. But what I think is unfair
is to claim that EZNEC is in error, simply because it adopts the
"industry standard" interpretation rather than an alternative that you
might prefer.
I make widespread use of EZNEC, and when I saw someone as authoritative
as yourself state that it is 3dB in error I felt it needed further
investigation!
73,
Steve G3TXQ
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