Topband: Skywaves from Monopole Surface Waves

[Guy Olinger K2AV]

The tangle of tree roots in woods or forest is a discontinuity.  It's
an immediate discontinuity if the antenna IS in woods or forest (like
mine). A vein of sandy soil that angles into the ground going away
from a radiator is a discontinuity (like in my NW back yard and the
only reason this property would percolate for a septic field).  We
persist in using a model for our thinking that applies to broadly flat
farmland and other quite large cleared spaces.

W3LPL seems to have an advantage at very low angles on 160 that
exceeds his 4 square.  Just my sense from being up against him in
contests for years. Notably his antennas are out in a very large
cleared grassy area. No close discontinuities.

I have anecdotes that would agree with the idea of a blend that fills the notch.

But to prove it we can't use standing-man-with-meter. He may just be
sensing the current in the ground just below his feet that will never
be airborne. We need sitting-man-with-meter-in-helicopter to go up
there and prove that what you get from the ground up to twenty
thousand feet out 20 miles is a blend, and not a notch.

I find it curious that some of those that so insist on
standing-man-with-meter in affairs regarding performance of antennas
are willing to accept a considerable logical reach on "upward
launching" of ground wave without the appropriate metric **at
altitude**.  And at how many places would this flying experiment have
to be run all over the US to detect patterns of blend-defeat for some
cause at which we currently could only guess?  Would it blend at 30
mS/m and be utterly absent at 1 mS/m.  Or the dead opposite?

My gut lurch is toward some kind of conditional, less than common
blending.  But I got no proof, no measurements, no RBN, no ad-hoc
reasonable comparisons.  I don't find the arguments on logic from
either side particularly convincing.  I'm waiting for someone to nail
this one way or the other. Who do you know that owns his own
helicopter and looks for any excuse to fly it on a pretty day?

73, Guy.

On Wed, Oct 3, 2012 at 2:11 PM, Michael Tope <W4EF at dellroy.com> wrote:
> I have long had a suspicion that some fraction of the power in surface wave
> must be "converted" to skywave as the surface wave encounters
> discontinuities in the ground medium (both physical geometry and dielectric
> parameters). Some folks I know from work were doing research on low-loss
> dielectric waveguides for microwave and millimeter waves (somewhat analogous
> to an optical fiber for RF). The degree to which these dielectric waveguides
> won't radiate despite not having a conductive outer shield is a function of
> how smooth the bends are and the degree to which discontinuities are
> minimized.
>
> Another way to look at this is to ask the question - how would a vertical
> perform if it were installed on a perfectly uniform ground of average
> conductivity that conformed to the ideal geoid as compared with a more
> realistic installation - hills, mountains, lakes, and other abrupt changes
> in characteristics of the surface wave medium? In the former case, would the
> surface wave contribute less or more to the skywave power at low angles than
> in the latter case?
>
> 73, Mike W4EF......................
>
>
> On 10/3/2012 9:05 AM, Richard Fry wrote:
>>
>> The elevation patterns of vertical monopoles over real earth has been
>> discussed in recent threads here
>> (http://lists.contesting.com/archives//html/Topband/2012-10/msg00140.html).
>> The common belief based on NEC far-field elevation patterns for those
>> conditions shows little relative field at low vertical angles, and zero
>> field in the horizontal plane.  However the surface wave must be included in
>> a complete analysis of monopole performance, because it contributes
>> substantial low-angle radiation that will reach the ionosphere to generate
>> skywave service under the right conditions.
>>
>> Below on this topic is part of an e-mail exchange of a few months ago
>> between Gerald Burke of Lawrence-Livermore National Laboratory and me, and
>> is quoted with his written permission.  As many will recognize, Mr. Burke is
>> co-author of the software engines used in NEC computer programs.
>>
>> This text applies to NEC surface wave plots attached to my e-mail to him.
>>
>>>> Hello Mr. Burke -
>>
>>
>>>> Would you expect the fields at elevation angles of 1 to 10 degrees
>>>> in these plots to continue on to the ionosphere, and under the right
>>>> conditions be reflected back to the earth as skywaves?
>>
>>
>>>> R. Fry
>>
>>
>>> The low angle 1/R fields should reach the ionosphere, although perhaps
>>> not
>>> accurately predicted by NEC, since it does not include the effects of
>>> earth
>>> curvature and the ionosphere.
>>>
>>> Regards,
>>> Jerry Burke
>>> LLNL
>>
>>
>> _______________________________________________
>> Remember the PreStew coming on October 20th. http://www.kkn.net/stew for
>> more info.
>>
>>
>
>
> _______________________________________________
> Remember the PreStew coming on October 20th.  http://www.kkn.net/stew for
> more info.