Quad and circular polarization
 

-.-. --.- wrote:
So thanks all for replies. Wikipedia at this page
http://en.wikipedia.org/wiki/Circular_polarization show more, and now i have
also clear in mind the fact that circular polarization is first made by a
physical, circular design of dhe radiant element and i can also have
clockwise or counterclockwise sense of the polarization.

By the way, due to wavelenght we are playing in the HF, i doubt that can be
realized a true circular polarization antenna for HF spectrum. Maybe
something can be realized on VHF and up.
Merely theory dreams in my mind, as in the real life i'm working HF with a
couple of butterfly dipoles covering from 80 to 10 m... :)

Thanks anyway to pay me attention.

73 folks,

-.-. --.-


"A circularly polarized wave may be resolved into two linearly polarized
waves, of equal amplitude, in phase quadrature (90 degrees apart) and
with their planes of polarization at right angles to each other."
-(from your wikipedia link)

Quad and circular polarization
 

-.-. --.- wrote:
. . .
By the way, due to wavelenght we are playing in the HF, i doubt that can be
realized a true circular polarization antenna for HF spectrum. Maybe
something can be realized on VHF and up. . .

I agree. My experience is that:

1. It's difficult to generate circular polarization in more than two
opposite directions at HF. With something like crossed dipoles fed in
quadrature (sometimes called a turnstile), the polarization is circular
only at right angles to the plane of the dipoles. It's linear to the
sides and elliptical elsewhere.
2. Even after you generate a circularly polarized signal, ground
reflection tends to make it linear. It's difficult or impossible to
avoid ground reflection over an HF path.

Roy Lewallen, W7EL

Quad and circular polarization
 

"Roy Lewallen" wrote in message
treetonline...
-.-. --.- wrote:
. . .
By the way, due to wavelenght we are playing in the HF, i doubt that can
be realized a true circular polarization antenna for HF spectrum. Maybe
something can be realized on VHF and up. . .

I agree. My experience is that:

1. It's difficult to generate circular polarization in more than two
opposite directions at HF. With something like crossed dipoles fed in
quadrature (sometimes called a turnstile), the polarization is circular
only at right angles to the plane of the dipoles. It's linear to the sides
and elliptical elsewhere.
2. Even after you generate a circularly polarized signal, ground
reflection tends to make it linear. It's difficult or impossible to avoid
ground reflection over an HF path.

Roy Lewallen, W7EL

Hi Roy

Just for conversation, I submit that an antenna with good hemispheric CP
coverage could be made with 4 dipoles.

Jerry KD6JDJ

Quad and circular polarization
 

Jerry wrote:

Hi Roy

Just for conversation, I submit that an antenna with good hemispheric CP
coverage could be made with 4 dipoles.

Jerry KD6JDJ

Yes, there's the quadrifilar helix which I believe fits that
description. Another, which I built decades ago at 450 MHz, is the "skew
planar" antenna which resembles a cloverleaf but with the "leaves"
rotated 45 degrees. Although I haven't seen either one constructed at
HF, on reflection I don't see any reason you couldn't.

There's still the problem of ground reflection, though. I didn't state
it very well in my last posting -- what I meant was that the sum of the
direct and ground-reflected rays tend to produce a linearly or nearly
linearly polarized wave even when you start out circular.

Roy Lewallen, W7EL

Quad and circular polarization
 

"Roy Lewallen" wrote in message
treetonline...
Jerry wrote:

Hi Roy

Just for conversation, I submit that an antenna with good hemispheric
CP coverage could be made with 4 dipoles.

Jerry KD6JDJ

Yes, there's the quadrifilar helix which I believe fits that description.
Another, which I built decades ago at 450 MHz, is the "skew planar"
antenna which resembles a cloverleaf but with the "leaves" rotated 45
degrees. Although I haven't seen either one constructed at HF, on
reflection I don't see any reason you couldn't.

There's still the problem of ground reflection, though. I didn't state it
very well in my last posting -- what I meant was that the sum of the
direct and ground-reflected rays tend to produce a linearly or nearly
linearly polarized wave even when you start out circular.

Roy Lewallen, W7EL

Hi Roy

I say with some humor - Have you considered the DCA as described in the
Feb2008 QST? For most conditions the DCA performs better than a
quadrafilar helix and it is much easier to construct.

Jerry KD6JDJ

Quad and circular polarization
 

Jerry wrote:

Hi Roy

I say with some humor - Have you considered the DCA as described in the
Feb2008 QST? For most conditions the DCA performs better than a
quadrafilar helix and it is much easier to construct.

Jerry KD6JDJ

No, I haven't built a circularly polarized antenna for over 30 years.

Roy Lewallen, W7EL

Quad and circular polarization
 

Hi Roy

I say with some humor - Have you considered the DCA as described in the
Feb2008 QST? For most conditions the DCA performs better than a
quadrafilar helix and it is much easier to construct.

Jerry KD6JDJ

No, I haven't built a circularly polarized antenna for over 30 years.

Roy Lewallen, W7EL

The conversation reminds me, in 1947, I lived in Dayton, OH. Not far from
Columbus, OH and the home of Kraus. He was the guest speaker one evening at
the Engineers club in Dayton and I attended. He did his usual trick, a 400
MHz tone modulated oscillator and a receiver, both with plain vanilla
dipoles. Spaced across the audfitorium, he would hold up a piece of
cardboard between the two and stop the signal. Then he hooked both to a pair
of his helix antennas and tried but could not stop the signal. Of course, he
had a Faraday shield between TWO layers of cardboard. Some, who had looked
into his background more deeply than I, told him what he was doing. To me it
was remarkable.

NOT more remarkable than a ham in Dayton, call unknown, who had erected a 4
turn square helix for 20 Meters at his home in honor of the occasion. Made
of Aluminum downspout pipe, 16 foot on a side, complete with reflector of
chicken wire and supported on a long length of 2 x 4. Before the days of
CDR, but rotated with a prop pitch motor. I'm not certain of what the
neighbors thought of it, but it sure looked impressive to me at age 22.

W4ZCB

Quad and circular polarization
 

On Nov 29, 2:18*pm, Roy Lewallen wrote:
Jerry wrote:
*Just for conversation, I submit that an antenna with good hemispheric
CP coverage could be made with 4 dipoles.

Yes, there's the quadrifilar helix which I believe fits that
description. Another, which I built decades ago at 450 MHz, is the "skew
planar" antenna which resembles a cloverleaf but with the "leaves"
rotated 45 degrees...

Getting back to Jerry's idea - yes, four linear dipoles can generate
nearly perfect omnidirectional c-pol. This is a design of Nils
Lindenblad many decades ago, and I've done some NEC-2 modeling of it.
The link below leads to a rendered view of that model.

http://i62.photobucket.com/albums/h8...adRendered.gif

There's still the problem of ground reflection, though. I didn't state
it very well in my last posting -- what I meant was that the sum of the
direct and ground-reflected rays tend to produce a linearly or nearly
linearly polarized wave even when you start out circular.

This isn't true at least at VHF and UHF, where the ground reflection
mostly just reverses the polarization sense of the incident wave.
This have been demonstrated by the much-improved images seen on analog
TV receivers in city centers when using c-pol transmit and receive
antennas, because multipath reflections ("ghosts") tend to be
suppressed by the receiving antenna.

RF

Quad and circular polarization
 

On Dec 1, 8:15*am, Richard Fry wrote:
On Nov 29, 2:18*pm, Roy Lewallen wrote:

Jerry wrote:
*Just for conversation, I submit that an antenna with good hemispheric
CP coverage could be made with 4 dipoles.
Yes, there's the quadrifilar helix which I believe fits that
description. Another, which I built decades ago at 450 MHz, is the "skew
planar" antenna which resembles a cloverleaf but with the "leaves"
rotated 45 degrees...

Getting back to Jerry's idea - *yes, four linear dipoles can generate
nearly perfect omnidirectional c-pol. *This is a design of Nils
Lindenblad many decades ago, and I've done some NEC-2 modeling of it.
The link below leads to a rendered view of that model.

http://i62.photobucket.com/albums/h8...adRendered.gif

There's still the problem of ground reflection, though. I didn't state
it very well in my last posting -- what I meant was that the sum of the
direct and ground-reflected rays tend to produce a linearly or nearly
linearly polarized wave even when you start out circular.

This isn't true at least at VHF and UHF, where the ground reflection
mostly just reverses the polarization sense of the incident wave.
This has been demonstrated by the much-improved images seen on analog
TV receivers in city centers when using c-pol transmit and receive
antennas, because multipath reflections ("ghosts") tend to be
suppressed by the receiving antenna.

RF

Quad and circular polarization
 

Richard Fry wrote:


This isn't true at least at VHF and UHF, where the ground reflection
mostly just reverses the polarization sense of the incident wave.
This have been demonstrated by the much-improved images seen on analog
TV receivers in city centers when using c-pol transmit and receive
antennas, because multipath reflections ("ghosts") tend to be
suppressed by the receiving antenna.

RF

Can you show us one of these C-POL receive antennas?