Jim - NN7K wrote:

Think what he may mean is: if you use a Circular
polarization , it will receive both horizontal,
and vertical polarization signals, equally well
tho at a decrease of 3 dB in signal , vs. horizontal
to horizontal, or vertical to vertical
polarization. A good way to observe this
optically, for LINEAR polarizations, would
be to find an old pair of sunglasses, useing
polarized lenses. break them in two, and then look
throuh BOTH lens's . As you rotate one, keeping
the other stationary, note the loss of light thru
them. At 90 degrees, it should be almost black!
but at 45, degrees, the degree of darkness (this
is for the stationary lens) will be about the same
if the rotated lense is moved either + or - 45
degrees (the equivalent of circular polarization
in an optic field. Don't know if this explaination
helps, but migh give it a try-- Jim NN7K

I was thinking about something I read a while back
in Paul Nahin's book "Science of Radio" about
synchronized transmitters and receivers,
and about something in Richard Feynman's QED.

Roy Lewallen said several things that for a moment
made me wonder whether quantum entanglement
could be demonstrated in radio waves as it can be
for light. I'll have to re-read Nahin's book.

Karo brand corn syrup has an interesting property.
It will rotate the linear polarization of light passing through it
by different amounts depending on the frequency.
This can easily be seen by placing a small jar of
Karo syrup between to linear polarizers and rotating
them. Different angles between the linear polarizers
will result in a different color being seen in the Karo jar.
Note the color seen also depends on the thickness of
the jar, so if you use a round jar you will see several
different colors but they will still change when you rotate
the polarizers. I was wondering if a radio receiver could be
frequency tuned based on polarization in such a manner.


Green Egghead wrote:
Roy Lewallen wrote:
I don't have any link handy, but it's easy to explain.

Ground isn't necessary. Consider a horizontal dipole in free space.
Position yourself directly in line with the antenna, some distance away,
so all you see of the antenna is a dot. Now, move directly upward or
downward. The antenna now looks like a vertical line(*). The radiation
from the antenna at the point where you are is purely vertically
polarized, for the same reason it's purely horizontally polarized when
you're directly broadside to the antenna.

The only directions in which the dipole will radiate a purely
horizontally polarized signal are in the horizontal plane of the
antenna, or exactly at right angles (broadside) to the antenna. In the
vertical plane containing the antenna, it's purely vertically polarized.
In all other directions, it's a combination of the two. (In other words,
the polarization angle of the total field is neither vertical nor
horizontal.)

Here's an illustration you can do with the demo version of EZNEC. Open
the Dipole1.ez example file, which is a dipole in free space. In the
main window, click the Desc Options line. In the Desc Options dialog
box, select the Plot and Fields tabs if not already active, and select
"Vert, Horiz" (not "Vert, Horiz, Total") in the Fields To Plot frame.
Then click Ok to close the box. (Note: The "Vert, Horiz" option, without
the "Total", isn't available in EZNEC v. 3.0, including EZNEC-ARRL.)

The example file is set up to plot the pattern in the horizontal plane
of the antenna. If you click FF Plot, you'll see only a horizontally
polarized field. That's because the field is purely horizontally
polarized in the horizontal plane of the antenna, as I mentioned
earlier. The ends of the antenna are up and down on the plot, and
broadside is to the left and right.

Now in the main window, change the elevation angle to 45 degrees. Do
this by clicking on the Elevation Angle line, entering 45 in the dialog
box, then clicking Ok. This moves the observer above the horizontal
plane of the antenna. The observation point (assumed very far from the
antenna) follows a circle which is equidistant from the antenna and the
horizontal plane containing the antenna. That is, it maintains a
constant distance and an angle of 45 degrees above horizontal from the
antenna. Click FF Plot to see the result. Now you can see that when
you're directly broadside to the antenna (left and right on the plot),
the field is purely horizontally polarized -- the vertical polarization
component is zero. But directly in line with the ends of the antenna,
the polarization is purely vertical. The top and bottom directions of
the plot correspond to the position you were in when you saw the antenna
as a vertical line.

Vertically and horizontally polarized components reflect differently
from the ground. So in directions where both are present, one can be
reinforced while the other is attenuated, resulting in a different mix
after reflection. (But reflection won't change a horizontally polarized
component to vertically polarized or vice-versa.) For example, a
vertically polarized field reinforces when reflecting from a perfect
ground at a low angle, while a horizontally polarized signal cancels.
This ends up enhancing the vertically polarized component at low angles
when both are present. (Remember, though, this is perfect ground -- real
ground, except salt water, behaves quite differently.)

Finally, let me emphasize that there's really only one E field from the
antenna, with one polarization angle. Separating it into vertically and
horizontally polarized components is simply a convenience used for
calculations and as an aid in understanding, much like separating two
currents into common and differential (even and odd) mode components.
The principle of superposition allows us to conceptually split the field
into components, analyze each separately, then recombine the results,
getting the same answer we'd get if we had done the analysis on the
total field.

Are there multipath solutions using circular polarization
between double side band supressed carrier components?

(*) More precisely, the projection of the antenna on a vertical plane
passing through your position is a vertical line. Visually, you can't
tell if the antenna is a short vertical wire or a longer horizontal one
you're seeing end-on. The nature of the radiation in your direction is
also the same for the two situations.

Roy Lewallen, W7EL

lu6etj wrote:
Dear friends:

Could you give me me a link to some reference material (in the net)
about vertical polarized radiation of horizontal dipoles near ground?
(not feed line radiation)..
Thank yoy very much in advance.

Miguel Ghezzi (LU 6ETJ)