Thanks, Wes-- when originally considered it was looking at the moon
in terms of approaching a point source (the surface of the moon
being relatively small TIME-WISE- but the surface to the edges
being relatvly HUGE in distance , per Wavelength would allow a
distortion of a reflection. As I said , its dangerous to get me
thinking too hard (I tend to fall asleep)! Tho, hadn't considered
the (Cheezy) effect! makes me wonder if linear circular would be
the way to go, or would it distort as bad as other signals
(do to Faraday Rotation- the skewing of the signal's polarization)?
Just curious. The linear circular refers to circular yagi construction
rather than as a Helix? Or is this tilting at windmills? Jim - NN7K



Wes Stewart wrote:
On Tue, 5 Apr 2005 02:44:10 -0700, "Ed Price" wrote:


"Wes Stewart" *n7ws*@ yahoo.com wrote in message
. ..

On Mon, 04 Apr 2005 00:27:17 GMT, Jim - NN7K
wrote:

[snip]

|Thanks, Cecil -- what got me thinking about it was a friend
|brought up this discussion of , say Moonbounce , with say
|Lefthand circular polarization , as observed from Earth.
|(which on reflection should be RIGHT HAND circular polarization
|upon return to earth, if to a Linear , Flat plane, like a billboard)
|and one of the experts there said to him "NOT so fast about the
|signals being 100 % out of phase" ( think had to do with
|Faraday effect)

Faraday rotation takes place in the Earth's ionosphere. The less than
perfect 180 degree phase shift in polarization is caused by the fact
that the lunar surface isn't a flat metallic surface but is instead,
as everyone knows, a lumpy green cheese ball.

On Tue, 05 Apr 2005 15:33:42 GMT, Jim - NN7K
wrote:

|Thanks, Wes-- when originally considered it was looking at the moon
|in terms of approaching a point source (the surface of the moon
|being relatively small TIME-WISE- but the surface to the edges
|being relatvly HUGE in distance , per Wavelength would allow a
|distortion of a reflection. As I said , its dangerous to get me
|thinking too hard (I tend to fall asleep)! Tho, hadn't considered
|the (Cheezy) effect! makes me wonder if linear circular would be
|the way to go, or would it distort as bad as other signals
|(do to Faraday Rotation- the skewing of the signal's polarization)?
|Just curious. The linear circular refers to circular yagi construction
|rather than as a Helix? Or is this tilting at windmills? Jim - NN7K

Linear circular is an oxymoron. When you phase two crossed Yagis to
generate circular polarization, it is just as "circular" as a helix.

It's been 20 years (how time flies) since I was operating EME but I
remain interested. There is a current school of thought that
switchable polarization has an operational advantage. I remain
unconvinced when the complexity and degradation of performance is
factored in. I don't know of anyone who is using true circular
polarization (at VHF) even though their antennas are capable of
generating it.

The reason to have switching capability is speed up the QSO. With
fixed linear polarization, at any given time, there can be spatial and
Faraday rotation caused polarization mismatch between two stations
located on different parts of the Earth. Switching polarization at
one end can overcome all or part of this mismatch. Usually, if one
waits long enough the always changing Faraday rotation will bring the
mismatch to zero or near zero without any switching.

So there is a trade of complexity for speed. In the modeling I've
done, I have yet to see a case of high gain, crossed-element Yagis
that were not degraded by the presence of the stacking hardware.

Thanks, the ones was considering are the yagis with the elements bent
into loops, but, from what I see, wouldn't really make a differnece.
note some of the 1296 antennas shaped like that, at any rate!
But, again, when I think-- dangerous things tend to happen!
Never have done it- tho WA7TDU lived about 4 blocks from me when
in K.Falls, and K7XC, down here in Reno also has done it.
Keep thinking of giveing it a try, but dont knowif ever will happen.
Jim NN7K

Wes Stewart wrote:
On Tue, 05 Apr 2005 15:33:42 GMT, Jim - NN7K
wrote:

|Thanks, Wes-- when originally considered it was looking at the moon
|in terms of approaching a point source (the surface of the moon
|being relatively small TIME-WISE- but the surface to the edges
|being relatvly HUGE in distance , per Wavelength would allow a
|distortion of a reflection. As I said , its dangerous to get me
|thinking too hard (I tend to fall asleep)! Tho, hadn't considered
|the (Cheezy) effect! makes me wonder if linear circular would be
|the way to go, or would it distort as bad as other signals
|(do to Faraday Rotation- the skewing of the signal's polarization)?
|Just curious. The linear circular refers to circular yagi construction
|rather than as a Helix? Or is this tilting at windmills? Jim - NN7K

Linear circular is an oxymoron. When you phase two crossed Yagis to
generate circular polarization, it is just as "circular" as a helix.

It's been 20 years (how time flies) since I was operating EME but I
remain interested. There is a current school of thought that
switchable polarization has an operational advantage. I remain
unconvinced when the complexity and degradation of performance is
factored in. I don't know of anyone who is using true circular
polarization (at VHF) even though their antennas are capable of
generating it.

The reason to have switching capability is speed up the QSO. With
fixed linear polarization, at any given time, there can be spatial and
Faraday rotation caused polarization mismatch between two stations
located on different parts of the Earth. Switching polarization at
one end can overcome all or part of this mismatch. Usually, if one
waits long enough the always changing Faraday rotation will bring the
mismatch to zero or near zero without any switching.

So there is a trade of complexity for speed. In the modeling I've
done, I have yet to see a case of high gain, crossed-element Yagis
that were not degraded by the presence of the stacking hardware.

On Wed, 06 Apr 2005 01:35:34 GMT, Jim - NN7K
wrote:

Thanks, the ones was considering are the yagis with the elements bent
into loops, but, from what I see, wouldn't really make a differnece.
note some of the 1296 antennas shaped like that, at any rate!

Hold on. Those are "Loop Yagis." They are not circularly polarized
any more than a quad is. When an approximate one-wavelength loop is
fed at the bottom, it has linear horizontal polarization. Period.


But, again, when I think-- dangerous things tend to happen!
Never have done it- tho WA7TDU lived about 4 blocks from me when
in K.Falls, and K7XC, down here in Reno also has done it.
Keep thinking of giveing it a try, but dont knowif ever will happen.
Jim NN7K

I don't have all of my old logs computerized but I seem to remember
working 'TDU. I have K7XC in the log on two-meters. My ragchewing
tropo range was about 400 miles and my best DX was 10,000 miles [g].
ZS6ALE who completed my 2-M WAC.

"Wes Stewart" wrote:
I don't know of anyone who is using true circular
polarization (at VHF) even though their antennas are capable of
generating it.
________________

Most FM broadcast stations in the US use some form of dual polarization,
which they think of as "circular" but usually is not due to differing H&V
pattern distortions from the mounting structure supporting their antennas.
Paper 6 at http://rfry.org discusses this in the form of NEC-2 studies.

In some cases, several FM stations all use a common antenna at a master FM
site. An array of "cavity-backed radiators"* used in these cases can
provide a c-pol axial ratio of 2dB or less for all polarization planes.
Antennas of this design are used as master FM antennas in Houston, Dallas
and St Louis, where they radiate approximately eight FM stations of 100kW
ERP each. Sears Tower in Chicago has a number of them installed in a
vertical stack for use by individual FM stations.

*crossed, wideband dipoles in phase quadrature, installed in a circular,
wire mesh cavity about 1/4-wave deep and less than a wavelength in diameter
and arrayed in groups of three or four around a triangular or square
cross-section tower. Several levels (often 8 or 10) are used to provide
elevation gain for the array.

RF