The guy in the helicopter measured pretty much a straight vertical line.
The curve in the bottom graph drops 2.5 db by the time it's up 2.5
degrees. Not straight. If helicopter guy was measuring at 540 kHz, then
maybe the height of a 5/8 wave radiator at 540 was in play and flattened it
out for his descent.
And you have NEC4.2 saying one thing in one graph and a different thing in
the other. Are the graphs displaying orthogonal concepts and the two can
merely be added together? Is the process creating the sky wave plot
incapable of producing the lower data? Or is the lower data produced
exclusively to service ground wave analysis at the ground, and the data
above an invalid extrapolation from a process specifically aimed at
standing-man-with-meter? There are lots of things we can't do in the
models that produce skewed results. Is using near field calculations at
500m above ground at 2.8 km more than some height/distance/angle one of
those things we can't do? Like putting a source in a segment adjacent to a
complex joint?
Standing-man-with-meter would not be reporting the above as an issue to
anyone as long as shoulder height was telling him same thing as the models
and FCC was happy and the power bills were down. Takes a controversy like
this one to be looking at dust balls way under the bed with a flashlight.
Like an answer I once got reporting a trouble to IBM on it's mainframe OS,
"Why on earth do you care about that?" with a sincere, genuine quizzical
tone in his voice.
Lower curve shows 2.5 dB dip at 2.5 degrees elevation.
What is the lower curve up to 5 km at 30 km distance? Same shape?
Run the lower graph at helicopter guy's frequency and then blank the
frequency out before you publish. Do we get the same curves?
There are still a lot of things rattling around in this box.
73, Guy.
On Tue, Oct 9, 2012 at 11:52 AM, Richard Fry <rfry@adams.net> wrote:
> Mike W4EF wrote:
>
>> So again my question - if this low-angle ground-wave (aka surface-wave)
>> energy dies off so quickly (e.g. down 20dB at just 20 miles), how does any
>> of it get to the ionosphere where it can be useful for topband DX?
>>
>
> The field over real earth that exists within a few kilometers of a
> monopole is not very much less for an elevation angle of 10 degrees than it
> is for the peak radiated field from that monopole.
>
> This is shown in the link in my Topband post earlier today, which I'll
> repeat here:
> http://i62.photobucket.com/**albums/h85/rfry-100/NEC_FF_**with_Surf_Wv.jpg<http://i62.photobucket.com/albums/h85/rfry-100/NEC_FF_with_Surf_Wv.jpg>
>
> In this case the field existing 2.8 km from the monopole at an elevation
> angle of ~10 degrees is 86% or about -1.3 dB of the maximum field (at 67
> degrees). Earth conductivity in the NEC model was set to 5 mS/m, d.c.13
> (about average).
>
> It is such low angle fields existing close to the monopole that continue
> on to the ionosphere to produce useful skywave service under the right
> conditions -- not the groundwave field 20 miles downrange.
> ______________________________**_________________
> 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.
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