Teaching myself 4NEC2 and have most of it under control, which is good.

Regarding radials & grounds, i've been learning the "rules" NEC(2) has, summarised below.

4.1. Free space.

In the simulations in free space, logically there is no ground. Normally, the results will be similar to those one may find in the textbooks.

4.2. Perfect ground.

The perfect ground consists of a perfect electrical conductor ground plane, without losses. It is a good option to make simulations omitting the losses of the ground, a task which may allow to evaluate those losses comparing the results with further simulations using more realistic ground types.

The wires of a model can touch the perfect ground.

4.3. Fast ground.

With the fast ground type, NEC-2 uses a method based on complex reflection coefficients.

The wires of the model cannot touch the fast ground.

In the case of the horizontal wires, it is necessary to observe a height over the ground of at least one tenth of the working wavelength

[Ref.4,8]: Zs > (lambda / 10) for horizontal wires.

4.4. MININEC ground.

The MININEC ground model assumes a perfect ground for the computation of the currents and changes to a dielectric ground for the computation of the far field patterns (ground without losses). With the MININEC ground, hybrid calculations designed for the first generation of less powerful computers are used.

The vertical wires can touch the MININEC ground.

The horizontal wires cannot touch the ground. They must be placed at a height over the ground of at least one fifth of the working wavelength:

[Ref.4,8]: Zs > (lambda / 5) for horizontal wires over MININEC ground.

If this rule is not observed, the simulations with NEC-2 will provide as a result erroneous impedances and anomalous high gains, especially for horizontal polarisation.

4.5. Sommerfeld-Norton (S-N) ground.

The Sommerfeld-Norton (S-N) is the most precise ground model, with the highest computational cost and is the best method to simulate horizontal wires very close to the ground.

Using the S-N ground it is important to take into account that both the vertical and the horizontal wires cannot touch ground.

It's nice to use "fast ground" and define radials in 4NEC2's ground-tab, but it wont be accurate having the vertical wire touch the ground in the model per NEC2's rules, i could use Sommerfield-Norton ground, which is more accurate, but i'd have to elevate the radials (ground plane), which doesn't match reality (this is for a 1/4wl ground-mounted monopole).

I could draw/define them in the geometry tab i guess, but it would be handy to use fast-ground if i could get reasonable accuracy, to leverage it drawing many radials in, with equal spacing (just a pain to do it manually, especially for large numbers of radials).

To achieve reasonable accuracy, is there any middle-ground (pun unintentional lol), or is it basically one or the other?

  • $\begingroup$ Actually we'd rather that you //would// list or summarize the NEC(2) ground types, for two reasons: 1) it makes the question easier to read, and 2) links rot. $\endgroup$ – rclocher3 Jul 20 at 14:29
  • $\begingroup$ Fair point rclocher3. Question updated. $\endgroup$ – t252 Jul 21 at 11:56
  • $\begingroup$ @KevinReidAG6YO I meant to do that but you did it first ;) $\endgroup$ – rclocher3 Jul 22 at 23:30

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