> To sum things up, the advantage of salt water is more in the decreased
> pseudo-Brewster angle than in the local ground loss. Local ground loss can
> be fixed using miles of radials but your signal is at the mercy of the
> far-field ground.
One question I've asked of others in the past without a conclusive answer:
At what distance is the far-field ground conductivity no longer relevant
with a vertical radiator? IOW, there's some distance from a vertical
radiator where the low angle lobe is launched to such a distance and height
that the ground beneath the field no longer matters.
Also, I keep seeing references in some recent on-line presentation material
that the quality of ground conductivity has no relevancy on the shape of the
radiated vertical profile from a vertical radiator -- and that only field
strength changes as a function of ground conductivity. However, the effect
of changing profile shape as a function of ground quality is shown in the
vertical profile sketches in the ARRL Antenna Book, among other references.
The vertical profile over salt water shows a flat, compressed radiation
pattern over the surface of the earth. By contrast, that same radiator over
average soil shows an upward elevation lift of the low angle profile with a
gap of FS disparity at low angles of radiation. Accordingly, the vertical
profile shape (at low angles) must change as a function of ground
conductivity.
If FS measurements are taken at say 1 km from the radiator, variances in
ground conductivity over a 1 km path must also affect the shape of the
vertical profile. Testers who are making these measurements within a few
hundred feet of the radiator seem to be missing this and are drawing the
conclusion that the profile does not change when they are taking FS
measurements inside the lobe of the profile. Measurements taken too close
to the radiator will not reveal changes in low-angle radiation. So, it
seems to me that any performance tests that include low angle of radiation
(less than 5-10 degrees), needs to be taken at some far distance from the
radiator.
Paul, W9AC
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