On 10/03/2010 07:31 PM, Owen Duffy wrote:

I have explored what you have said in an NEC4 model of a quarter wave
monopole with three quarter wave radials at varying heights over 'average
ground'. The results are summarised at
http://www.vk1od.net/lost/Clip053a.png . The reference for the graph is
the efficiency of the same antenna with 120 buried radials in the same
soil type.

If the models are correct, laying just a few radials on or very close to
the ground (eg the popular method of pinned into the turf) would appear
to be a very poor option. The model indicates efficiency improves with a
very small increase in height above the dirt, just 30mm is a 6dB
improvement of lying on the dirt, just half a metre achieves 90% of the
available efficiency.

Owen

Thanks Owen for the Clip053a.png
The results are just amazing.

But I just cann't understand why the current in the radials, don't
induce a significant current in the earth, that ends as an important
lost power.
--
Alejandro Lieber LU1FCR
Rosario Argentina

Real-Time F2-Layer Critical Frequency Map foF2:
http://1fcr.com.ar