"Jim" wrote in message
om...
Wouldn't that provide a better coverage with less fading compared to
traditional approach? Or is it that shortwave needs ionosphere to
work at all? Thanks.

Seems to me that the signal would have a pretty difficult time penetrating
the ionosphere at HF frequencies.There are of course complications to that
answer, such as MUF and incident angle, but in general if the ionosphere
acts to reflect earth originated signals, it will do the same to space
originated signals.

Dale W4OP

The ionosphere isn't anything like a perfect mirror.
RF at or below the MUF still penetrates, some fo it
refracts.
A friend just received her PHD in astrondomy and her
thesis was based on observations on the 2 HF
radio astronomy allocations.
Even with the MUF right above either of these 2 freqs,
signals stll penetrated the ionosphere.

I will ask Ms C how mcuh attenuation there was.
From conversations, it wasn't as much as I thought.
It seems that even at best, less then 10% of the RF
refracts in the ionosphere, the rest "punches" through.

Terry

In article .com,
wrote:

The ionosphere isn't anything like a perfect mirror. RF at or below
the MUF still penetrates, some fo it refracts. A friend just received
her PHD in astrondomy and her thesis was based on observations on the
2 HF radio astronomy allocations. Even with the MUF right above
either of these 2 freqs, signals stll penetrated the ionosphere.

I will ask Ms C how mcuh attenuation there was. From conversations,
it wasn't as much as I thought. It seems that even at best, less then
10% of the RF refracts in the ionosphere, the rest "punches" through.

The mechanics of how EM waves "bounce" off the ionosphere is a good
question for a PH.D. The current explanation of refraction seems
likely. If it is refraction then I would expect most of the energy to
be refracted and the rest lost in heating the ionosphere. When I have
used prisms with light waves in experiments most of the light energy was
bent to the same path (little scattering) depending on wavelength so if
the ionosphere is doing the same thing with radio waves then I would
expect the same with the difference of possibly higher loses in the
ionosphere itself.

I would expect all the radio wave energy to follow the same path until
there is significant heating of the ionosphere by the radio wave energy,
which at that point would be modifying the ionosphere medium.

The refraction concept has the EM waves incident to a boundary of
dielectric change. The wave path is bent according to the frequency of
the EM wave and the delta of the change in dielectric constants. Another
factor to consider is the angle of incidence so three factors are
involved that determine the outcome of where the energy goes but it
looks to me that most of the energy follows the same path so if 10% of
RF only gets refracted then I just don't understand what is going on
with radio waves and the ionosphere.

--
Telamon
Ventura, California