wrote
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On 9 mayo, 10:02, Szczepan Bia©©ek wrote:
U¢¯ytkownik napisa©ø w
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On 8 mayo, 10:35, Szczepan Bia©øek wrote:

I start reading about acoustic analogy.
I found that: "Over long distances, the atmosphere can cause the
polarization of a radio wave to fluctuate, so the distinction between
horizontal and vertical becomes less significant."
From:http://whatis.techtarget.com/definit...843762,00.html

The my question a
1. What means "long distances" in km (or miles),
2. What is the best orientation of the antenna for long distances.
S*
Hello,
Under normal circumstances, polarization change in line-off-site

conditions (think of max 40 mile) is not that much, so antenna
polarization does matter (unless you use at least circular
polarization on one side).

In a propagation path that is dominated by multi-path effects

(reflection at buildings, hills, foliage, etc), you get almost random
polarization and then the polarization is not that important. Your
cell phone and indoor WIFI are examples.

Extreme weather conditions can also lead to polarization changes or a

random polarization component (ducting superrefraction).

For sea water up to VHF, reflection depends on polarization. For

ground-ground links (for example ship shore) mostly vertical
polarization is used (as the sea water helps in this case). So if you
want to receive these communication, you use a vertical polarized
antenna.

The largest change in polarization you will get when the waves have to

travel through the ionosphere. At HF (ground-ground link via
ionosphere), the polarization vector rotates many times. This is due
to Faraday rotation. Also ground-satellite links suffer from this
effect. The higher the frequency, the less the change in polarization.
For example at 100 MHz you should think about 30 full rotations (that
is more then 10k degrees), while at 10 GHz the change in polarization
will be about 1 degree. Circular polarization may help to mitigate the
influence of Faraday rotation.

At HF sky wave (100....1000 mile via ionosphere) polarization of the

antenna matters. This is not because of the polarization change of the
waves due to Faraday rotation, but because of the reflection
characteristics of mother earth. In HF antennas, reflection on mother
earth is used (in combination with antenna height) to get the required
elevation radiation pattern of the antenna. Reflection on earth
depends on polarization.

Hopefully this helps you a bit.

You do not use the words "transversal" and "EM". The only evidence of
polarization is antenna directional sensitivity.

You talked about radiowaves, that are EM waves. In free space, only
progapation mode is transversal (that means both E- and H-field are
perpendicular to the direction of energy propagation. With regards to
audio, in gas, only lossless propagation mode is longitudinal
(molecule movement and pressure vectors are parallel to the direction
of energy propagation) .

EM is the hydraulic analogy (by Heaviside). It is a "piece to teach" a field
method.
In that time the electricity was incompressble and massles. Now the
electrons are compressible and have mass.
We need a new analogy. It can be call the Gas analogy or Acoustic analogy.
In www.tetech.nl is wrote that are many analogies for EM.

In the acoustic analogy a radio waves are normal spherical electric waves
emitted from the two sources (ends of the dipole).
So the sources are polarised, not the waves. Waves interfere. Do you
agree?

Not agree, the waves are also polarized, that can be physically
measured. Polarization is determined by the E-field vector.

A dipole has the E-field (in electrostatics). The equations are by Gauss.
The same equations we can use for the Hertz dipole. The E-field will be
alternate.
At long distances the frequency in receiving antennas will be twice more.

See my topic "frequency doubling" . I am only a science hobyist.

The second question was: " What is the best orientation of the antenna
for
long distances?
For old radio antennas. Very long horizontal wire.

On UHF (for example 2450 MHz), long distance can be 20 km, but on HF
500 km is not called long distance. So the meaning of long distance
depends on the frequency band.

You should distinguish between the actual polarization of the antenna
and the physical appearance. depending on how you feed it, a very long
horizontal wire can be sensitive to vertical or horizontal polarized
waves.

Though the equations for acoustical waves look similar to those of EM
waves, the orientation of the field components is completely
different. When you require a more specific answer, you should make
your question more specific. I tried to give you a general answer for
the various forms of radio wave propagation.

Now is XXI century. EM is a beautiful theory from XIX century. In Tetech
products no incompressible massless fluid.
So the most specific and important question is:
How is frequency in receiving antenna. Is it doubled?

Best regards, and sorry for my style
S*