Hi Richard,
On your referenced fields graph you caption "Measured vs. Calculated"
intensity, but the traces are not differentiated. Which traces on the
graph are measured and which are calculated?
73, Guy.
On Tue, Oct 2, 2012 at 2:58 PM, Richard Fry <rfry@adams.net> wrote:
> Conclusion: The less ground conductivity the higher is the antenna
>> elevation radiation angle. This is a negative impact for DX!
>>
>
> Cris, Tom, Paul et al
>
> This belief is common when looking at the far-field elevation pattern of a
> vertical monopole in MoM results, or in antenna textbooks. That pattern is
> what remains of the radiated field at an infinite distance from the
> monopole, over an infinite, flat ground plane.
>
> --> But in reality all vertical monopoles of 5/8-wavelength and less
> radiate their maximum relative field (E/Emax) in the horizontal plane.<--
>
> A NEC near-field evaluation can show the field produced in and near the
> horizontal plane closer to the radiator, for earth of defined
> conductivity/permittivity, and it will not be zero as is shown in a NEC
> far-field plot.
>
> The NEC study at the link below illustrates this. The groundwave field
> (0-deg elevation) is plotted out to 8 km. Note the good correlation
> between the NEC GW field and the GW field measured by a broadcast
> consulting engineer using an accurately-calibrated field intensity meter.
>
> On that same chart is plotted the field existing from that radiator at an
> elevation of 100 meters above the earth. Note that it is lower near the
> radiator than the GW field, because the relative field radiated by a
> 1/4-wave monopole at higher elevation angles is less than in the horizontal
> plane. In fact at the zenith it will be zero. At ~8km downrange it has
> reached the value of the GW field, and further downrange it will exceed the
> GW field.
>
> From the NEC chart it can be seen that the field at low vertical angles
> (less than 3 degrees) is at least as great as it is at zero degrees. There
> is no physical reason for that low-angle radiation NOT to continue on to
> the ionosphere to produce a skywave signal, given the right conditions.
>
> http://i62.photobucket.com/**albums/h85/rfry-100/Measured_**
> vs_NEC2D_Fields2.jpg<http://i62.photobucket.com/albums/h85/rfry-100/Measured_vs_NEC2D_Fields2.jpg>
>
> Supporting this below is a clip from the Radio Engineers' Handbook
> (Terman, 1943) showing this same reality, in that the angle at which
> radiation leaves that antenna for greatest 1-hop skywave range is less than
> 3 degrees.
>
> http://i62.photobucket.com/**albums/h85/rfry-100/**TermanFig55.jpg<http://i62.photobucket.com/albums/h85/rfry-100/TermanFig55.jpg>
>
> Probably the description "takeoff angle" commonly applied to vertical
> monopoles is a rather misleading specification.
>
> R. Fry
> ______________________________**_________________
> UR RST IS ... ... ..9 QSB QSB - hw? BK
>
_______________________________________________
UR RST IS ... ... ..9 QSB QSB - hw? BK
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