On Sep 29, 5:44*pm, Owen wrote:
I have been exploring models of a quarter wave monopole over a set of
radials on 80m using NEC4 models.

If my models are valid, and they use 'average ground', the indication is
that while it may require a large number of buried radials (16) before
efficiency levels off a bit, similar efficiency can be obtained with
just three radials elevated more than 100mm above the soil.

This leaves me wondering why the popularity of extensive fields of
buried radials for the lower bands.

Comments?

Owen

I don't think the model is totally valid.. Partially though..
I agree that for a given number of radials used, slightly
elevating off the ground is better than buried.
But I don't agree that a small number of slightly elevated
radials is equal to a large number of buried radials, and
most certainly not equal to the same number of radials
highly elevated. IE: vs 1/4 or 1/2 wave or more up..
Three slightly elevated radials are not sufficient to lower
ground losses down to a low level over mediocre soil.

I always think in terms of wavelength when calculating
the approximate efficiency of an elevated radial set.
For instance, three radials at 1/2 wave up will be pretty
much equal to about 120 on the ground.
Three at 1/4 wave will be equal to about 50-60 on the ground.
Three at 1/8 wave might be equal to 15-20 on the ground.
Three at cigarette pack height will be equal to about twice
as many as actually used at best. "slightly guessing
on that one, but my real world tests seem to pretty much
agree".
So being as the increase is fairly small at such low heights
in wavelength, it is probably practical to just bury them so
people won't trip over them.. :/
If tripping is no issue, then it might be worthwhile to get
the slight edge in performance. But the increase over buried
will be fairly small with them only 100mm up.