Hi Tony,
> Although I don't really understand this area at all, it seems to me to
> be reasonable to assume that there are definite non-linearity's in the
> ionosphere.
That is easy to prove Tony, and because it is easy to measure and
prove it is also well documented the ionosphere is very linear.
The entire purpose of HAARP was an attempt to create non-linear
behavior, and it was unsuccessful. An operation with resources like
3 megawatt ERP transmitting systems and ionospheric sounders
pinging the ionosphere looks very closely for an effect for years on
end, such as even a tiny change in ionization with application of a
very dense EM field, and can not find it.
Yet we prove it through 5kW ERP transmitters pointed in random
directions and listening to a signal five minutes later?
I'm sorry, but if those high level effects occurred we would see
them in the path of VOA...or Radio Moscow...or troposcatter
stations using 100's of kilowatts. We would see them on a regular
basis, because the power levels are higher than ours and they are
LOOKING for those effects.
> How do the various layers change during day/night if the effect is
> truly 'linear'. Obviously the layers themselves are an indication of
> non-linearity.
How does a capacitor vary capacitance and remain a linear device?
How does a resistor do the same with resistance? Linearity (in this
context) does not mean the signal level is constant, it simply
means that power does affect the path loss of the ionosphere.
> Another non-linearity is the "Arctic Flutter" effect that is often
> heard when communicating with the northern part of Europe. This must
> be caused by some refractive effect (i.e. non-linearity).
Refraction has nothing to do with linearity. The flutter you hear is
effects of multiple signals arriving at the same time over different
paths. It is like the echo you would hear in a "hard" room, if the
walls were moving slowly in and out.
Picture the sound of an organ with a spinning speaker, it is the
same effect. Everything is linear, you simply have rapidly changing
multipath.
> Another non-linear observation - why is RTTY and PSK31 so unreliable
> when the path is close to the poles. Also I have experienced very
> non-linear RTTY signals (looking at a scope output) when simply
> transmitting over 'clean' paths in North America. Seems to me that
> this is not just a polar effect.
Again that is not linearity..it is amplitude and phase change. PSK
(and to a much lesser extent RTTY) is very sensitive to multipath.
Even so, where are you going with that? It has nothing to do with
power. Increasing power or decreasing power, with no other
changes, produces EXACTLY the same amount of echo!
> Maybe the term 'linear' should be better defined when talking about
> the ionosphere. I suspect (and am quite possibly wrong) that Tom W8JI
> and Tree N6TR are really talking about 'consistency of effect' rather
> than an 'electrical linearity'. Maybe I am barking up the wrong
> tree????
Actually you have that reversed!
Tree and I are talking about linear behavior (power vs level) and you
are giving examples long term phase or attenuation changes in a
path.
If power affected attenuation, signals would mix or there would be
other forms of distortion. We can see examples of this if we
consider simple devices or systems.
Consider a diode. At some part of the curve of applied voltage you
see resistance change abruptly. The resistance goes from nearly
infinite to a very low value with a change of only a few tenths of a
volt. If we plotted the resistance vs voltage we would see when we
get beyond a certain voltage the slope of the curve would become
very flat (linear). It would change directions at low levels at different
rates.
That is what you are claiming (or describing) the ionosphere does.
If it did that, signals would mix. Since signals do NOT mix, we
know that does not happen.
The real problem with this is when we see an effect, we stop
thinking about the many reasons we can see the effect and focus
on a single simple answer. Fortunately it is easy to measure
linearity, and prove out signals have no effect on the ionosphere's
ability to support propagation.
Believe me if the ionosphere was even a tiny bit affected by signal
levels, HF would be totally useless because of all the IMD! It
certainly behaves nothing like a diode, and not even like a "volume
expander".
73, Tom W8JI
W8JI@contesting.com
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