Tom,
SKYCOM (Version 1.0) and its Version 2.0, known as PropLab Pro, include
ray-tracing programs. Those programs are in two-dimensions (SKYCOM) and
three-dimensions (PropLab); they make use of the International Reference
Ionosphere, with the latest revisions of both the CCIR and URSI model
ionospheres. You can get a copy of IRI-90 from the folks in Boulder or
PropLab from The Solar Terrestrial Dispatch in Canada. A real neat job!
The PropLab version includes effects of the geomagnetic field, through
the Appleton-Hartree formulation of magneto-ionic theory. In calculations
using that set-up, one can see natural skewing and ducting from the
effect of the geomagnetic field on refraction perpendicular to the ray
path. See the next issue of the Low Band Monitor for a short article on
long EF hops, for radiation angles just above the Pedersen Ray for the
night-time E-region. That is in 2D and serves as the basis for another
article, just now completed, showing how ducting can take place (between
105 and 150 km altitude in the electron density valley above the E-region
at night and for distances the order of 4,000 km) on the path from VK2 to
VE7.
I was trying to tell you about this when you sent off your posting. So I
have been sitting back, watching the words fly by. Stay tooned; I have a
nice ray-trace which shows ducting in the geomagnetic field. Then the
field is turned off in the program and "Voila, ducting stops!" This
will be something new for you to look at and ponder. But I have no
doubts about ducting and chordal hops on HF; why should it be any less
possible on 160 when refraction in the ionosphere goes roughly inversely
with the square of the frequency? Hmm? And it happens naturally, thanks
to the geomagnetic field!
Finally, MUFs have nothing to do with propagation on 160 meters as the
critical frequencies are ALWAYS greater than 1.8 MHz, even in solar minimum.
The VK0IR operation was wonderful testimony for that!
Enuf said, CUL OM. 73,
Bob, NM7M
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|