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

Unfortunately, it's not demonstrating circular polarization at all.

Circular polarization isn't the equivalent of 45 degree tilted linear
polarization. The polarization of a circularly polarized wave (RF,
light, or any other electromagnetic wave) rotates, one revolution per
cycle. So over each period, the polarization rotates from vertical,
through intermediate angles to horizontal, back to vertical but oriented
the other direction, to reverse-oriented horizontal, back to vertical
again. A 1 MHz field does this a million times per second.

If you view circularly polarized light through polarized sunglasses, the
intensity will be the same regardless of how you rotate the glasses. If
you pass circularly polarized light through one polarized lens, the
light is linearly polarized on the other side. So rotating the second
lens behind it illustrates only cross polarization of linearly polarized
waves.

If you have a purely linearly polarized field, say, horizontal, and
rotate a dipole in a vertical plane in that field (with the plane
oriented so the field is broadside to the dipole), the signal received
by the dipole will be maximum when the dipole is horizontal, zero when
it's vertical ("cross polarization"), and intermediate values in
between. This is the equivalent of the polarized sunglass experiment.
But if the impinging field is circularly polarized, the received signal
will be the same for any of the dipole orientations. This is because the
field is always aligned with the dipole for two instants every cycle
(when the antenna response will be maximum), cross-polarized for two
instants every cycle (when the antenna response is zero), and at some
intermediate relative polarization for the rest of the cycle (when the
antenna response will be greater than zero but less than the maximum).
And the proportion of each is the same regardless of which position the
dipole is rotated to. The 3 dB attenuation relative to a linearly
polarized, optimally oriented field is due to the fact that the
circularly polarized wave is cross-polarized to various degrees during
the cycle and is optimally polarized only for those two instants each
cycle. A dual situation exists with a circularly polarized antenna and
linearly polarized field: a linearly polarized wave of any orientation
is received equally with a right or left handed circularly polarized
antenna. Any plane wave can be divided into either vertical and
horizontal (or any two orthogonal) linear components, or into right and
left handed circular components. Any linearly polarized wave has equal
magnitude right and left handed circular components. Any circularly
polarized wave has equal magnitude horizontal and vertical linear
components. Hence the antenna responses discussed above.

Like a circularly polarized wave, a 45 degree linearly polarized wave
also has equal magnitude horizontal and vertical components. But this
doesn't make it the same as a circularly polarized wave. The horizontal
and vertical components of a 45 degree linearly polarized wave are in
time phase or 180 degrees out of phase; those of a circularly polarized
wave are 90 degrees relative to each other. This essential difference
causes the orientation of the linearly polarized field to stay fixed but
the orientation of the circularly polarized field to rotate. Put two
crossed dipoles close to each other and feed them in phase or 180
degrees out of phase, and you'll get a 45 degree linearly polarized
field broadside to the antenna. Feed them in quadrature (90 degree
relative phasing) and you'll get a circularly polarized field broadside
to the antenna.

Linear and circular polarization are limiting special cases of the more
general elliptical polarization. The polarization of an elliptically
polarized field rotates each cycle, but the amplitude can also vary
during the cycle. The ratio of the minimum amplitude to the maximum (or
vice-versa, depending on the reference) is called the axial ratio.
Circular polarization is the special case of elliptical polarization
having an axial ratio of one. Linear polarization is the special case
where the axial ratio is zero (or infinite, depending on the definition
used for axial ratio). A general elliptically polarized wave can have
different horizontal and vertical linear polarization components, and
different right and left hand circular polarization components.

Roy Lewallen, W7EL