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

Bill Otten wrote:

Not necessarily. The planet Jupiter emits a signal that can be heard at
about 15 meter wavelength, about 21 mhz or so. That signal penetrates the
ionosphere pretty nicely. See
http://radiojove.gsfc.nasa.gov/libra...discovery.html for more
info...

bill
KC9CS

Receiving the 21-Mhz HF (shortwave) energy from Jupiter depends on it's
altitude above the observer's local horizon and the MUF (maximum usable
frequency) for the particular area of the ionosphere where the signal is
trying to penetrate to the ground. In the first case, when Jupiter is
near the horizon, it's radio signal may not penetrate the ionosphere
because of the shallow incident angle. The energy is refracted off the
top of the ionosphere back into space like skipping a stone on water. In
the second case, if the local MUF is too high, it won't allow the 21-Mhz
energy to penetrate to the ground from space regardless of the incident
angle.
The best time to radio observe Jupiter is when the conditions are the
opposite of the first two cases above, or particularly when it's high in
the sky at night. This is when the signal passes through the ionosphere
at a more vertical angle to the observer (no skipping) and the local MUF
is at it's lowest for the day, which happens some time after sunset.
It's also best when the solar flux is low, near sunspot minimum, as it
is now. This insures a low MUF (well below 21-Mhz) so Jupiter's signal
can reach the surface of the earth more often.

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In article . com,
wrote:

Telamon wrote (in part)

snip

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
--------------------------------------- My "10%" figure is based on
conversation with our astronmy friend and also from an reffrence book
that I have misplaced, that goes in to great detail on EM wave
intereaction in the ionosphere. Back in the 70' several satellites
with HF recivers were used to measure ionospheric penetration. This
book detailed theresults. I can't even remember the name right now, a
mind is a terrible thing to lose. It was published by one of the big
Brit(Oxfor comes to mind) universities. I haven't thought of that
book in a long time. Damn I hope I have't really lost it!

Terry

Looks like we are going to have to read up on this Terry. I've got a
book I have not read yet called "Radio Frequency Principles and
applications" that may shed some light on this. I'll let you know.

--
Telamon
Ventura, California

Telamon wrote:


Looks like we are going to have to read up on this Terry. I've got a
book I have not read yet called "Radio Frequency Principles and
applications" that may shed some light on this. I'll let you know.

--
Telamon
Ventura, California
--------------------------------------------
I went through my technical library last night with no success.
Our friend Ms. C. will be comming through Lexington Sunday
afternoon, to pick up her AOR7030+, and I will see if I loaned
the book to her. As a rule, I don't loan books, too easy to lose
them, if you want to read one, be prepared to read it here, or
go with me to a photocopy machine and copy it.

Terry

"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.

Aside from the propagation issues, the usual antenna for satellite work is
highly directional. Antenna size is proportional to wavelength and SW
wavelengths are a hundred times or so bigger than the usual satellite
wavelength.

Frank Dresser