> Interesting thread, one poster mentioned work by John Wang / FCC
> on MF-AM
> field strength prediction curves.
>
> I don't recall sighting that work, but prior to the 1975 Regional
> Administrative Broadcasting Conference in Geneva (Regions 1 & 3)
> there was
> considerable work done, both theory and measurements, on "excess
> polarization coupling loss" which is a non-reciprocal phenomenon in
> propagation, dependent, amongst other things, upon the angle of
> propagationwith respect to the geomagnetic equator and proximity
> to the gyrofrequency.
> While there was much dispute as to magnitude, the existence of the
> phenomenon was always accepted and an algorithm was ultimately agreed.
>
> That algorithm was also accepted in the 1981 RABC in Rio de
> Janeiro for
> Region 2, although for international coordination purposes the
> value was set
> to 0.
>
> I seem to recall that Phil Knight of the BBC Research Department
> led much of
> that work and the RD reports are all now on-line.
>
> The algorithms have also been incorporated into the ITU-R P series
> recommendations for MF-AM Skywave field strength prediction. Do
> a google on
> "excess polarization coupling loss" also polarisation.
>
> Regards
>
> Sam Dellit formerly VK4ZSS now Canberra, Australia
>
Hi Sam,
thanks for more info on the subject. Indeed, the atmo/ionosphere is a
complicated medium, some dielectric, some conductor, some mirrors, some fiber
optics, some clouds like blotches, some nice uniform and "linear" behaving,
some.....
We are dealing with electromagnetic radiation through media that interacts with
it and is also affected by earth magnetic field.
Let me just throw another aspect - the polarization twist. When signals are
transmitted with one polarization and arrive at different. If the media is so
linear, how could that happen? How do you "prove" that effect with laser or
flashlight and perfect mirrors?
The point is that atmo/ionosphere is a complicated, almost "live" medium. The
lower the frequency, the more prone to refraction, ducting, spotlighting, etc.
Flatly stating that the is no "one way (enhanced) propagation" is contrary to
reality. There is, after carefull observations, effect where signals can be
enhanced or attenuated in different directions, following different paths,
being skewed, causing sometimes significant differences in signal levels.
No, it's not a (one way) diode.
Yes there are other factors that contribute to perceived diferences of signal
levels, like local noise, atmospheric noise, antenna patterns - angles, etc.
But there are also cases when all those factors are minimised, yet leaving
observable differences in signal levels going both ways.
Trivializing the behavior of radio waves propagation does not help our
experimenter's and curious nature image of hams. It reminds me the "famous"
frog experiment. You rip the frog's one leg off and say jump, frog jumps. After
you rip all four and frog doesn't jump the "obvious" conclusion is: "da frog is
deaf after you rip all its legs".
Propagation and its finicky nature, unpredictability (OK, modeling software
now "knows" everything :-) is one of the things that keeps us hooked on RF and
still going. I wish I had more time to dig deeper into the subject, but so far
I was satisfied with some of the "revelations" I observed, that I could use
while still doing serious contesting.
73, Yuri, K3BU.us
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