Re: NEC-LIST: Re: RF Voltage Levels

Quoting Duncan Baker <apc_at_acenet.co.za>, on Fri 28 Dec 2007 11:38:23 AM PST:

> Dear all,
>
> Peter has it quite correct. Many years ago I had a peculiar
> situation on a somewhat
> poorly designed HF log-periodic antenna. With about 10 KW input, it
> arced across the
> insulators in the active region and burnt off the catenary.
> Investigation by modelling
> and a redesign of the LPA solved the problem.
>
  Behalf Of P Dettmann
> Sent: 28 December 2007 07:49 PM
> To: nec-list_at_robomod.net
> Subject: NEC-LIST: Re: RF Voltage Levels
>
> For radiation, the voltages are not of interest, but for the
> practical consideration of voltage stress on support insulators, or
> to avoid corona, it is important to know the level of voltages involved.

This is an interesting question. I'm not sure that the NE actually
gets you where you want to be, at least in a simple way. You could
specify very close spacing on the points for the NE card, then
numerically integrate (i.e. sum the field in each increment). And,
for run of the mill corona things, you could just look for where the E
field is > 3E6 V/m.

However, is the data coming back from a near field analysis valid
everywhere. For instance, if my grid is on 1mm ticks, and I have a 1
cm diameter wire, does the field go to zero "inside" the wire? I can
see NEC being good quite close to, but not touching the conductor,
subject to things like roundoff and precision errors.

Jim Lux

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