Topband: Measuring field strength (for the purpose of radialevaluation)

[Telegrapher9 at aol.com]

Rick and Tom (W8JI),

thanks for the great information! 

In NEC I have not been able to create a symmetrical radial field in which the 
impedance rises with additional radials. The radial lengths explored varied 
from 45 to 180 degrees. However, I have seen the input impedance increase with 
some unsymmetrical radial installations - like the ones we hams must use 
around our houses. In fact, the N30X radial field does this. And this is the very 
radial field for which I recommended the "decreasing input impedance method" of 
evaluation! N30X and I wondered about these results. I though originally that 
it was due to the system current maxima occurring along the ground system, 
rather than at the feedpoint, but this is not the case

So, I stand corrected on being too loose with the method. I should have 
pointed out the limitation of the "decreasing input impedance method." And that 
limitation is that the radials must be symmetrical and all of the same length.

Now it sounds like even this is not the case with actual measurements. Have 
you measured increasing input impedance for additional radials in a symmetrical 
arrangement? If so, I would like to understand this. Understanding and 
getting sims to match measurements (and vise versa) is what I do.

I have NEC-4 on the way and I hope that this will help with this. I so take 
the NEC-2 radials simulations with a grain of salt. I have a work-around for 
some limited cases. Using NEC-4 I hope to greatly refine these work-arounds so 
that those with NEC-2 can obtain useful simulations of ground mounted verticals.

This debate is just the thing to educate the members (most of all myself) of 
the reflector and dispell some myths and rules-of-thumb. 

    Dave WX7G