Topband: Modeling the proverbial "vertical on a beach"

[Guy Olinger K2AV]

Just to mention that the prior opinion is controversial and not universally
agreed upon. Nor to date has anyone surfaced with actual measurements made
at the distances (25 to 50 km) and with span of altitudes (0 to 10 km) to
either prove or disprove either side.

It remains unproven modelling from NEC at those distances either way. This
situation may, alas, persist this way, because the precise subject
resolution appears to be without benefit to any commercial interest and
therefore without funds to pay for some pretty expensive experimenting
involving precision measurements from aircraft.

Additionally, there is considerable suspicion that moving from LF to MF in
this general subject involves a ground modal change of some sort that would
render 50x10 km measurments at 0.5 or 1 MHz unlike those at 2 MHz,
rendering commercial measurements at low and possibly high BC of no value
for extrapolation to ham use.

Arguments on both sides remain basically intuitive. I have "reasonable"
arguments to BOTH concur with Richard AND to not. NEC near field
calculations over sea water at 50 km follow Richard's assertions, and the
same over "average" ground does not. The model clearly thinks that 50 km
over most types of ground slowly dissipates low angles resulting in the
controversial "notch" in low angle elevation patterns.

So NEC based modelling cannot be used as a proof text to decide an argument
NEC has with itself.

73, Guy K2AV.


On Sat, Aug 9, 2014 at 7:23 PM, Richard Fry <rfry at adams.net> wrote:

> Just to note that the low-angle radiation produced by monopoles is not
> accurately shown by a NEC model/study that does not include the surface
> wave, regardless of whether one or two ground-plane media are specified in
> the model.
>
> Below is a link to a NEC study of the low-angle fields of a monopole
> __including the surface wave__ for three values of earth conductivity
> ranging from extremely good to very poor.
>
> The curves there all show maximum relative field in the horizontal plane.
>
> If the surface wave had not been included in these studies then all of
> those fields would have a zero value in the horizontal plane, and reduced
> fields at low angles just above the horizontal plane.
>
> Reality is that radiation leaving the monopole at elevation angles of at
> least 5 degrees decays at a 1/r rate.  Therefore that radiation is a space
> wave which propagates in a ~ straight line to reach the ionosphere, where
> (with suitable conditions) it can return to the earth as a skywave.
>
> NEC analyses of a vertical monopole of 5/8-lambda and less, and not
> including the fields of the NEC surface wave do not recognize the radiation
> sector capable of producing the greatest single-hop skywave service range
> that can be provided by that monopole.
>
> http://s20.postimg.org/9xqgzu9d9/Monopole_Low_Angle_Radiation.jpg
>
> R. Fry
> _________________
> Topband Reflector Archives - http://www.contesting.com/_topband
>