Re: LF: RE: Top load coil at ground level?

[Dick Rollema <dickrollema@casema.nl>]

Dear Jim, LF Group,

I also had difficulty in understanding how it works.  I therefore tried to 
construct it in 4 steps.  They follow here and I hope they explain the idea 
without further text.  Please read also what Peter Martinez
73, Dick PA0SE
Topload 1.jpg
Topload 2.jpg
Topload 3.jpg
Topload 4.jpg


At 15:38 20-4-06, you wrote:
> Dear Dick, LF Group,
>
> I am puzzled as to how the top-loaded vertical antenna plus stub is 
> supposed to operate. In Fig 1, the elevated loading coil is in series 
> between the vertical element and the top loading, which is perfectly 
> reasonable ? but I can?t see how the stub in Fig 2 could produce an 
> equivalent series inductive reactance, especially since one terminal of 
> the stub is unconnected.
> I can see that Dex?s antenna works (I presume the arrangement in Section 
> 2.12 of ON7YD?s antennas page), but I don?t think it is equivalent to an 
> elevated loading coil. The vertical wire from the hot end of the loading 
> coil to the top loading section will be at high voltage along its whole 
> length, leading to much the same displacement currents flowing to ground 
> and in the mast, and therefore the same current distribution, as would 
> occur with a conventional inverted-L with a ground-level loading coil. 
> This contrasts with a top-loaded vertical with elevated loading coil at 
> the top of the vertical section, where all the vertical part of the 
> antenna is at low RF potential, and only the top loading section carries a 
> high RF voltage. The main effect of using the mast and the additional 
> vertical wire from the top of the mast to the cold end of the loading coil 
> as part of the antenna system would seem to be to add their distributed 
> inductance to the cold end of the loading coil. In other words, you would 
> achieve an almost identical result by grounding the cold end of the 
> loading coil to the bottom of the mast, and adding some extra turns to the 
> cold end of the loading coil.
> Cheers, Jim Moritz
> 73 de M0BMU