TopBand: Ducting

[Robert Brown]

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

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