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

To: tentec@contesting.com
Subject: Re: [TenTec] NEC, ground, grounds, and radials.
From: Rsoifer@aol.com
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Fri, 7 Jan 2011 18:53:19 -0500 (EST)
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
When I was an undergraduate at MIT, there was a requirement for a  
Bachelor's degree thesis.  Mine was about bouncing 2m  signals  off Echo II 
(see my 
QST articles about that in 1962).  Anyway,  they invited three prominent 
professors, all of them hams, to be on my thesis  committee.  They quickly got 
into an argument about whether 20 dB (voltage)  was the same thing as 10 dB 
(power).  I just kept my mouth shut, and  got an A.  True story.
73 Ray W2RS
In a message dated 1/7/2011 10:30:17 P.M. GMT Standard Time,  
steve@karinya.net writes:


Please don't think I'm trying to be contentious, but  your comment 
challenged my established view of what "dBi" represents. That  led me on 
a literature search starting with my (very old) Masters Degree  notes, 
antenna engineering reference books, and web sites. I can't find  any 
material where the Isotropic reference power density is defined as  
anything other than the transmit power spread over a *complete sphere* -  
not a hemisphere - even where the antenna being compared is over real  
ground. In other words, consistent with EZNEC.

In some cases the  interpretations were explicit - for example "...... 
compared with the  power density of an isotropic radiator in Free Space"; 
in others it could  be inferred from the underlying maths.e

That's the interpretation I was  taught, and yes it would certainly lead 
to a 3dB higher figure than your  interpretation.

I'm trying to understand whether your view is commonly  held, or rather 
something you feel strongly about; if it's a commonly held  view perhaps 
you could point me to some literature. I presume that someone  like IEEE 
must have an unambiguous definition?

Steve  G3TXQ

On 06/01/2011 17:07, Dr. Gerald N. Johnson wrote:
>  As for the effects with ground planes and my claim of error. I base it
>  on this: Model a quarter wave vertical on a perfect ground plane. It
>  will show 3 dB more gain than a half wave dipole in free space. Yet  the
> theory of images in the ground plane insists that the quarter  wave
> vertical on the ground plane has a image of the other half making  it the
> exact equivalent of a half wave dipole. I claim that while the  program
> in free space is comparing the signal intensity from the  antenna to that
> of a perfect isotropic radiator located at the 0,0,0  origin of the axes,
> that when the ground plane is present it cuts that  isotropic radiator in
> half, shielding half of its radiated power and  so the reference to a
> full isotropic radiator is 3 dB in error. 3 dB  too much  gain.
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