Cristi YO3FFF wrote:
From Terman (as Richard Fry mentioned):
http://i62.photobucket.com/albums/h85/rfry-100/TermanFig55.jpg
First hop distance on E layer reflection for given angles is:
20 degrees = 300miles, 30 degrees = 200miles
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But note that Terman shows much longer 1st-hop skywave paths at elevation
angles below three degrees -- where a NEC far-field pattern of a vertical
monopole over real earth shows very low relative field from a vertical
monopole.
A NEC far-field pattern of a vertical monopole over real earth also shows
zero field in the horizontal plane, but clearly that is incorrect. If it
WAS correct, then AM broadcast stations would have zero daytime coverage by
their surface (ground) wave. Yet a 50 kW station on a low frequency can
provide useful groundwave service beyond 200 miles from their antenna site,
in many cases.
The surface wave MUST be considered when evaluating skywave performance of a
monopole, because that surface wave contains significant radiation at low
elevation angles capable of producing skywave coverage.
This was shown clearly in the NEC4.2 plot posted by Paul Christensen earlier
in this thread, at http://72.52.250.47/images/160m.jpg , and also in my link
http://i62.photobucket.com/albums/h85/rfry-100/Measured_vs_NEC2D_Fields2.jpg
R. Fry
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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