Robert Brown wrote:
>
> Friends in Radio Land-
>
> Not having seen it stated explicitly elsewhere, let me use
> Newton's First Law of Motion as a guide and offer the following,
> perhaps as Maxwell's "First Law of Ionospheric Propagation":
>
> "Every electromagnetic wave front advances at constant speed
> and direction unless it is compelled to change that state by
> encountering ionization which is non-uniform over its spatial
> extent."
>
> If you disagree with that statement, speak now or forever hold
> your peace.
ok, i will, it is not only ionization that causes a change in velocity
of the wave front. you observe this every day as refraction and
reflection of light off various surfaces and through various
materials. and of course its not ionized materials that make up
the ground scattering part of multi-hop paths.
now, the next question is what do you consider the
'spatial extent' of a wave front? if you are refering to just the
plane surface that is normal to the direction of propagation then
the non-uniform part is not required since a wave can be affected
by encountering a uniformly distributed plasma. consider a transmission
from a vertical ionospheric sounder, the wave front is essentially
a plane when it encounters the ionosphere. now assuming that the
ionosphere is quiet and uniformly ionized above the sounder the
wave front will not see any gradients, but can still be reflected
back down to the receiver.
>
> For those who feel the need to invoke chordal hops or skewed paths
> to explain a short- or long-path contact during quiet geomagnetic
> conditions, let me suggest they refer to the International Reference
> Ionosphere (IRI) to see if CCIR or URSI models support your
> contention.
these are frequent events and well documented already. just don't
forget that the iri or other models are not meant to represent the
specific composition of the ionosphere at any particular time or
place. real propagation conditions, even with a quiet ionosphere,
are the result of many factors that vary widely around the world and
affect both the ionosphere both in density of ionization and the
height distribution. trying to describe it with a single curve or
model just isn't enough for even quiet conditions.
> Failing to find the needed gradient, in magnitude and direction, they
> should proceed to document the case fully:
>
> 1. Date
> 2. Time
> 3. Termini for the path
> 4. Operating frequency and antenna(s)
> 5. Solar/Terrestrial Indices
> 6. Proposed Ionospheric Gradient
> (geographic location, extent
> and electron density variation)
>
> then announce it publicly on the appropriate Reflector and submit
> a signed, notarized copy with three (3) technical endorsements to:
>
> Nobel Prize Selection Committee
> Royal Swedish Academy of Science
> Stockholm, Sweden
>
> Perhaps, with a lot of luck, they might be awarded the Nobel Prize
> for Physics by having found a new, unknown region of ionization
> and take a place beside Sir Edward Appleton in the history of the
> ionospheric research.
yeah, right. maybe if you came up with a good explanation for the
long delayed echo phenomenon that might be interesting enough for
a technical journal or two.
--
David Robbins K1TTT (ex KY1H)
k1ttt@berkshire.net or robbins@berkshire.net
http://www.berkshire.net/~robbins/k1ttt.html
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