Re: NEC-LIST: Monopole above soft water

Hello,

Just regarding your question about the litterature. Ronold King has
(some years ago) published some articles on this topic. I only have the
reference of the first one:

"Electromagnetic field of a vertical dipole over an imperfectly
conducting half-space", Radio Science, vol 25, pp 149-160, 1990

There are other article after this one, especially one where he compared
results from various type of soils, but I can't remember where I've put
them :)

Regarding your NEC modeling, in my opinion, there might be a problem
depending on what is exactly your frequency: if you are in the lower
part of the VHF band, you will have to take into account the surface
wave mode (this is done in King's articles), and not only the
(classical) space wave mode. If not, well, much simpler case.

Regis

Le lundi 06 juin 2005 à 12:06 -0500, Alexandre Kampouris a écrit :
> Hello,
>
> A relative of mine complains of poor results while attempting to track a
> small buoy floating on softwater lake at VHF.
>
> As far as I can gather, the antenna is probably a monopole, and the lower
> part of the antenna is formed by the immersed buoy.
>
> I've given her already a couple of tips on how to improve reception, but
> I'd also like to have a look at the situation with NEC2, to see if I should
> expect shadow for a distant observer close to ground.
>
> Qualitatively, the soft water's surface should be something of a magnetic
> wall, forcing the tangential H field to zero (if my brain hasn't turned to
> mush). So I suppose that a vertical monopole may behave quite differently
> than one would expect on say, salt water.
>
> So here are my questions :
>
> 1) Is NEC's ground model applicable to something like softwater
> (epsilon~=80, relatively low losses)? I've never used SOMNEC before, so
> this is something new for me.
>
> 2) Modelling the immersed part is impossible with NEC2, but I consider
> testing two things :
>
> a) Model a monopole just in contact with the water's surface, like NEC2
> allows (I'm only interested in the radiation pattern, not in calculating
> the input impedance).
>
> b) Instead of a discrete contact, have a network of short radials
> converging to the base of the monopole.
>
> What do think above approaches? Can one neglect the underwater component of
> the buoy, or is my approach pointless?
>
> 3) Do you know of any literature on this or a comparable problem? (eg:
> propagation studies on inland navigation).
>
> Thanks in advance,
>
> Alexandre
>

        
        
                
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