[600MRG] NDB Antenna Calculator

[Edward R Cole]

Rudy,

I assumed when you write ground resistance you mean for the ground, only.

When I originally calculated my ERP in 2012, I used EZNEC to provide 
the radiation resistance which was about 0.83 ohms and I measured 
ground resistance with my modified MFJ analyzer by tuning the loading 
coil until I got R +j0; R read 20-ohms.

Rr/Rg is used in the calculation of EIRP.

So if the variable given in the "NDB calculator" is Rg+Rr that should 
be made clear instead of saying "ground resistance".    It seems this 
imprecision in specifying variables is what keeps the analysis from 
being accurate.

73, Ed

At 03:22 PM 10/5/2015, Rudy Severns wrote:
>Steve, he's going to have a real problem.  Rg depends not only on soil
>electrical characteristics and details of the radial system but also on the
>antenna over the radial system.  If you have NEC4 determining Rg from
>modeling is easy.  Direct calculation is also possible, I've done it, but
>it's complex because you have to start by deriving the E and H field
>intensities associated with the antenna in the near-field.  From that you
>can calculate the soil losses which determine Rg for a given Io.
>
>
>
>Too many people believe that a given radial system, at a given frequency,
>with given soil characteristics, has a fixed Rg.  This is false.  Rg will
>depend on all those things plus the details of the vertical.  This is
>carefully explained in section 3.2.3 of the 22nd edition of ARRL Antenna
>Book which shows among other things the dependence of Rg on the vertical
>height for a given ground system.
>
>
>
>73, Rudy N6LF
>
>
>
>
>
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73, Ed - KL7UW
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