Hi Jim,
I must respectfully disagree. And warn any reader that using NEC ground
media to simulate a conductive roof is a very troubled procedure with
significant issues.
Using the first media to simulate an elevated conductive plane for any
purpose is a problem. Using it to simulate radials is simply the ubiquitous
recurring error (out of a class of errors) that W7EL specifically lists as
the example in self defense. You are putting forth a rare invocation of
this same NEC weakness.
In order to estimate your hypothesis you need to create a building shaped
cage of dielectric wrapped, resistively loaded, interconnected wires. It is
necessary to bookkeep in the model that the roof, as conductor, is
connected to a vertical conducting face on four sides and then to ground.
These faces electrically are at least in the quarter to half wavelength
range vertically and can radically effect the appearance of the roof as
conductor. These faces can have significant radiation. These faces can be
the majority radiator with the dipole serving mainly as a matching device
to the building as majority radiator.
It is not inconceivable that the combination could function more like a big
dummy load.
73, Guy K2AV
On Monday, August 10, 2015, Jim Brown <jim@audiosystemsgroup.com> wrote:
> Actually, what he says is not use the high level media to model a RADIAL
> system.
>
> While playing with this model, I changed the characteristics of the higher
> level media to have far less conductivity. The result suggested that my
> model was good for what I was trying to understand -- that is, the very low
> far field lobe was unaffected by the conductivity of the high level media
> (that is, the roof).
>
> 73, Jim K9YC
>
> On Mon,8/10/2015 6:48 PM, Guy Olinger K2AV wrote:
>
>> There is a rather stern W7EL caution in the EZNEC doc about using two
>> ground media. He particularly nixes using the inner media as sea water
>> to mimic a high conductive surface.
>>
>
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