Guy Olinger wrote:
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.
The r-f current flowing in real earth at a given distance beyond a few
wavelengths from a vertical monopole did not travel through the earth from
the monopole site to get there. It is the result of the EM wave radiated by
the monopole through space, at the earth boundary of that wave.
Here is Terman's description: "The electric vector of the wave produced at
the surface of the earth by a vertical antenna possesses a slight forward
tilt. As a result the electric vector has, in addition to the normal
vertical component a slight horizontal component parallel to the surface of
the earth, and lying in the direction of propagation. ... The component of
the electric vector lying parallel to the earth's surface that is present
because of wave tilt represents a voltage applied across earth's surface.
This voltage causes a current to penetrate down into the earth."
So those r-f currrents in the earth don't ORIGINATE radiation into space,
rather they are a consequence of it.
As for helicopter measurements, below is a clip from a website used mostly
by broadcast engineers, containing part of a post I made and a response to
it from an active, full-time broadcast engineering consultant. The
consultant's comment should be enlightening. Not only does he recognize the
validity of my NEC analysis, he reports his experience with helicopter
measurements confirmiing what is shown in that NEC analysis.
CLIP:
The link below was prepared using values generated by 4nec2, but plotted in
other software. It shows that even NEC2 can be used to accurately calculate
low-angle fields radiated by a monopole over real earth -- and that the NEC
fields are very close to the accurately measured fields for those conditions
shown in the plot at the bottom of that page.
The NEC plot also shows that very significant space wave (skywave) is
generated by radiation from a monopole from elevation angles down to about
one degree, where a NEC far-field plot shows very little relative field.
http://i62.photobucket.com/albums/h85/rfry-100/Measured_vs_NEC2D_Fields2.jpg
R. Fry
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Re: Monopole Radiation Patterns
Post by XXXXX » Thu May 17, 2012 7:16 pm
Interesting. As a side note I learned early on the hard way that when taking
FI readings in a helicopter to do the vertical calibration at least a couple
KM away from the antenna, otherwise all you're measuring is the vertical
plane radiation pattern and you end up somewhere on the left end of the
green line on the graph and screw everything else up.
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