Elevation Patterns of Ground Mounted Vertical Monopoles
Elevation Patterns of Ground Mounted Vertical Monopoles
(OP)
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Possibly of interest to some readers of this Forum, here is part of a post I wrote for an antenna newsgroup for amateur radio operators ...
Ground-mounted verticals up to 5/8-wave high used by ham operators have the same elevation pattern shapes as those used by broadcast stations. The peak radiation launched from all of them occurs in the horizontal plane, and reduces slowly and smoothly for lower elevation angles above the horizontal plane. It could well be that the DX you do work results from radiation at a much lower elevation angle than believed possible when looking at the usual NEC calculations and plots for that vertical antenna.
The first link below leads to a scan of a graphic from Section 10 of Terman's Radio Engineers' Handbook (1943). It shows the "takeoff angles" needed to serve various distances from a ground-mounted, vertical monopole radiator via its skywave, and the resulting skywave fields there for the conditions stated. The reflection coefficients apply to the E-layer.
Terman's work shows that the elevation pattern of such a radiator over lossy earth does not approach zero field near the horizontal plane -- as is a common interpretation when looking at their NEC evaluations.
Terman's text (p. 743) also states that the reduction in skywave field after a peak at ~130 miles results from the ERP at the elevation angles serving those ranges not compensating for the greater losses of those longer paths.
But the skywave fields at 1000+ miles with takeoff angles of 1 degree and less are far from approaching zero (no matter what we think NEC is telling us).
ht tp://i62.p hotobucket .com/album s/h85/rfry -100/Terma nFig55.jpg
Discussion invited...
RF http://rfry.org
Possibly of interest to some readers of this Forum, here is part of a post I wrote for an antenna newsgroup for amateur radio operators ...
Ground-mounted verticals up to 5/8-wave high used by ham operators have the same elevation pattern shapes as those used by broadcast stations. The peak radiation launched from all of them occurs in the horizontal plane, and reduces slowly and smoothly for lower elevation angles above the horizontal plane. It could well be that the DX you do work results from radiation at a much lower elevation angle than believed possible when looking at the usual NEC calculations and plots for that vertical antenna.
The first link below leads to a scan of a graphic from Section 10 of Terman's Radio Engineers' Handbook (1943). It shows the "takeoff angles" needed to serve various distances from a ground-mounted, vertical monopole radiator via its skywave, and the resulting skywave fields there for the conditions stated. The reflection coefficients apply to the E-layer.
Terman's work shows that the elevation pattern of such a radiator over lossy earth does not approach zero field near the horizontal plane -- as is a common interpretation when looking at their NEC evaluations.
Terman's text (p. 743) also states that the reduction in skywave field after a peak at ~130 miles results from the ERP at the elevation angles serving those ranges not compensating for the greater losses of those longer paths.
But the skywave fields at 1000+ miles with takeoff angles of 1 degree and less are far from approaching zero (no matter what we think NEC is telling us).
ht
Discussion invited...
RF http://rfry.org





RE: Elevation Patterns of Ground Mounted Vertical Monopoles
RE: Elevation Patterns of Ground Mounted Vertical Monopoles
RE: Elevation Patterns of Ground Mounted Vertical Monopoles
(Doesn't seem to make sense on its face.)
RE: Elevation Patterns of Ground Mounted Vertical Monopoles
RE: Elevation Patterns of Ground Mounted Vertical Monopoles
RE: Elevation Patterns of Ground Mounted Vertical Monopoles
RE: Elevation Patterns of Ground Mounted Vertical Monopoles
RE: Elevation Patterns of Ground Mounted Vertical Monopoles
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Agree. NEC will give ~ the same output result as developed by Terman and other early authors as long as its operation is understood, and it is used correctly for the model circumstances.
But a common belief when looking at the NEC far-field elevation pattern of a ground-mounted vertical monopole up to 5/8-wave high over real ground is that it radiates zero field in the horizontal plane. But this is untrue. If it was, then MW broadcast stations would have no daytime groundwave coverage, yet that field is the source of most of their income.
The error isn't the fault of NEC, but the operator.
RE: Elevation Patterns of Ground Mounted Vertical Monopoles
RE: Elevation Patterns of Ground Mounted Vertical Monopoles
More and longer radials weren't worth the investment for the small improvement in radiated fields that they could provide.
BL&E's findings were the basis for the FCC rules applying to AM broadcast station antenna requirements to the present day.
RE: Elevation Patterns of Ground Mounted Vertical Monopoles
I think I read somewhere that one of the advantages of NEC4 over NEC2 is the accuracy of the ground modeling. This seems to confirm that the ground modeling in NEC2 isn't 'The Last Word' on what must be a very complicated subject.
Then again, I'm not sure that a guy with a slide rule in the 1930s could have done much better either, no matter how smart he was.
RE: Elevation Patterns of Ground Mounted Vertical Monopoles
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BL&E's investigations were not a slide rule study, they used real hardware in the real world. And THAT is why their conclusions have proven valid in practice, ever since (some NEC conclusions notwithstanding).
RE: Elevation Patterns of Ground Mounted Vertical Monopoles
(Sorry, I wasn't specific.)