On 01/10/10 03:51, Jim Lux wrote:

Thanks Jim.


I would think that the buried radials are more convenient (broad band,
etc.)

Yes, I understand that there are advantages to buried radials, but I
don't understand the preponderance of cases where I see 120 radials
pinned on the top of infertile dirt. They still present a trip hazard,
and less money spent on just a few elevated radials may perform just as
well.


Look at the performance of your ankle biting radials when the dimensions
are changed slightly.. For instance, if you shorten them by 5%, does it
make a big difference? For the buried radials, the length is very, very
non critical.

Yes, of course the feedpoint impedance is more sensitive to change in
length or conversely change in frequency.


Something else to look at is the sensitivity of "efficiency" (and your
definition of radiated power in the hemisphere/power into antenna is
fine) to soil properties.. if the soil conductivity or epsilon changes
(as it will with changing water content) does the efficiency change
rapidly?

Yes, efficiency is sensitive to soil parameters... for both types, but
not very sensitive.

Because of the impedance change mentioned above, the impedance
transformation needs adjustment for wide range frequency operation. Not
such an issue in the intended application, the DX window on 80m here is
just 50kHz.



Also, what about the loss in any matching components needed (e.g. if you
had a real efficient narrow band antenna, then operating off nominal
means you'll need a different matching network, and the loss in it might
be worth considering)

Matching network loss was not included in my analysis because both
quarter wave options present fairly similar load impedances that need
transformation to 50 ohms. The shortened verticle is slightly lower R
(23 vs 38 IIRC), and slightly more loss can be expected, but it is
practical to match with a shunt coil of copper tube and matching loss
should be real low in the system context, and in comparison of elevated
vs buried radials.

If I haven't got something quite wrong in the modelling, it would seem
worthwhile to prototype the shortened version with a view to extending
the system to a four-square if suitable.

I have still to read Rudy's papers... I am away from home (less
bandwidth) and I will download them later today when I get home. I
suppose that the proposed design challenges the norm of a very large
number of buried radials. In our case, part of the property is quite
rocky, and a configuration with just a few elevated radials offers
deployment opportunities that aren't suited to buried radials.

So, my original question is no so much suggesting everyone else got it
wrong, but why don't I seem more people doing it this way. Could I be
forgive in thinking that the popular, nearly universal, way is to uplift
the BL&E research at MF and apply it to 80m?

Owen