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Re: [TenTec] NEC, ground, grounds, and radials.

To: tentec@contesting.com
Subject: Re: [TenTec] NEC, ground, grounds, and radials.
From: "Dr. Gerald N. Johnson" <geraldj@weather.net>
Reply-to: geraldj@weather.net, Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Fri, 07 Jan 2011 18:20:59 -0600
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
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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