Quad and circular polarization
 

Greets OMs,

yesterday i had a QSO with K2US - impressive antenna, by the way i'm using
the station of a local OM near my QTH with a 4 elements 5 band Quad.

The beautiful thing is the 9-9+20 signal around 20.45 UTC, far away in
magnitude from the others stateside signals, around S5-7. So i remember my
father that tell me one day in his opinion the circular polarization in the
better choice... lose no matter about 6 dB, with any kind of polarization
used at the other side except circular - and faraday torsion due to
ionosphere - and in my mind comes 2 questions...

- we take some advantage from the fact that both are using quad antenna ??
- in my non-knowledge of the facts, i have in the past believed that the
quad antenna is near a circular-polarized antenna. Reading books and hearing
some QSO in the air i learn that quad can be horizontal or vertical
polarized, regard the feed point of the quad.. so - the circular
polarization need some kind of "special" feed point or is merely a "circle"
antenna ??

Apologize for the english and for the questions, maybe trivials and stupids,
but i believe one esxperienced OM can say far better than 100 books.

73,
CQ -.-. --.-

Quad and circular polarization
 

"-.-. --.-" ha scritto nel messaggio ...

Yep, and not obviously information, because i'm used to write on the it.*
usenet ierarchy, the contact was made from central Italy :)

-.-. --.-

Quad and circular polarization
 

-.-. --.- wrote:
Greets OMs,

yesterday i had a QSO with K2US - impressive antenna, by the way i'm using
the station of a local OM near my QTH with a 4 elements 5 band Quad.

The beautiful thing is the 9-9+20 signal around 20.45 UTC, far away in
magnitude from the others stateside signals, around S5-7. So i remember my
father that tell me one day in his opinion the circular polarization in the
better choice... lose no matter about 6 dB, with any kind of polarization
used at the other side except circular - and faraday torsion due to
ionosphere - and in my mind comes 2 questions...

- we take some advantage from the fact that both are using quad antenna ??
- in my non-knowledge of the facts, i have in the past believed that the
quad antenna is near a circular-polarized antenna. Reading books and hearing
some QSO in the air i learn that quad can be horizontal or vertical
polarized, regard the feed point of the quad.. so - the circular
polarization need some kind of "special" feed point or is merely a "circle"
antenna ??

Apologize for the english and for the questions, maybe trivials and stupids,
but i believe one esxperienced OM can say far better than 100 books.

73,
CQ -.-. --.-



Circular polarization means you have equal H-Pol and V-Pol radiation,
with one polarization 90 degrees ahead (or behind) of the other.

A quad antenna is a folded dipole.

Quad and circular polarization
 

"-.-. --.-" wrote in message ...
Greets OMs,

yesterday i had a QSO with K2US - impressive antenna, by the way i'm using
the station of a local OM near my QTH with a 4 elements 5 band Quad.

The beautiful thing is the 9-9+20 signal around 20.45 UTC, far away in
magnitude from the others stateside signals, around S5-7. So i remember my
father that tell me one day in his opinion the circular polarization in
the better choice... lose no matter about 6 dB, with any kind of
polarization used at the other side except circular - and faraday torsion
due to ionosphere - and in my mind comes 2 questions...

- we take some advantage from the fact that both are using quad antenna ??
- in my non-knowledge of the facts, i have in the past believed that the
quad antenna is near a circular-polarized antenna. Reading books and
hearing some QSO in the air i learn that quad can be horizontal or
vertical polarized, regard the feed point of the quad.. so - the circular
polarization need some kind of "special" feed point or is merely a
"circle" antenna ??

Apologize for the english and for the questions, maybe trivials and
stupids, but i believe one esxperienced OM can say far better than 100
books.

73,
CQ -.-. --.-


a quad is generally linearly polarized, either vertical or horizontal. to
get circular polarization you need dual driven elements with the proper
phasing.

Quad and circular polarization
 

"Dave" ha scritto nel messaggio
...

a quad is generally linearly polarized, either vertical or horizontal. to
get circular polarization you need dual driven elements with the proper
phasing.

Like a calculated piece of coax used to drive the 2nd element 90 electrical
degrees after the first ??

-.-. --.-

Quad and circular polarization
 

Dave wrote in
:

-.-. --.- wrote:
Greets OMs,

yesterday i had a QSO with K2US - impressive antenna, by the way i'm
using the station of a local OM near my QTH with a 4 elements 5 band
Quad.

The beautiful thing is the 9-9+20 signal around 20.45 UTC, far away
in magnitude from the others stateside signals, around S5-7. So i
remember my father that tell me one day in his opinion the circular
polarization in the better choice... lose no matter about 6 dB, with
any kind of polarization used at the other side except circular - and
faraday torsion due to ionosphere - and in my mind comes 2
questions...

- we take some advantage from the fact that both are using quad
antenna ?? - in my non-knowledge of the facts, i have in the past
believed that the quad antenna is near a circular-polarized antenna.
Reading books and hearing some QSO in the air i learn that quad can
be horizontal or vertical polarized, regard the feed point of the
quad.. so - the circular polarization need some kind of "special"
feed point or is merely a "circle" antenna ??

Apologize for the english and for the questions, maybe trivials and
stupids, but i believe one esxperienced OM can say far better than
100 books.

73,
CQ -.-. --.-



Circular polarization means you have equal H-Pol and V-Pol radiation,
with one polarization 90 degrees ahead (or behind) of the other.

A quad antenna is a folded dipole.

Except the top and bottom arms of a horizontally polarized quad element
are far enough apart to provide some gain and to slightly lower the
pattern from that of a dipole at the quad's central height. In a four or
five element design this can be quite effective. I was on the far end of
the QSO (at VE8ML) back in 1965 when OH8OS tested some very large quads
on 15m. They were impressive.


--
Dave Oldridge+
ICQ 454777283

Quad and circular polarization
 

"-.-. --.-" wrote in message ...

"Dave" ha scritto nel messaggio
...

a quad is generally linearly polarized, either vertical or horizontal.
to get circular polarization you need dual driven elements with the
proper phasing.

Like a calculated piece of coax used to drive the 2nd element 90
electrical degrees after the first ??

-.-. --.-

Hi MG

It isnt at all so simple as feeding one radiator 90 degrees later than
another to get "circular" polarization. For instance two linear radiators
can be fed in phase to get "CP". And two linear radiators can be fed with
one 90 defrees earlier (or later) than the other.
Look at wikipedia http://en.wikipedia.org/wiki/Circular_polarization

I'd expect that you can feed two Quads in phase to get CP along the axis
of their mounting boom. You'd space them appropriately and conect their
fed points appropriately.

Jerry KD6JDJ

Quad and circular polarization
 

"Jerry" wrote in message
...

"-.-. --.-" wrote in message ...

"Dave" ha scritto nel messaggio
...

a quad is generally linearly polarized, either vertical or horizontal.
to get circular polarization you need dual driven elements with the
proper phasing.

Like a calculated piece of coax used to drive the 2nd element 90
electrical degrees after the first ??

-.-. --.-

Hi MG

It isnt at all so simple as feeding one radiator 90 degrees later than
another to get "circular" polarization. For instance two linear
radiators can be fed in phase to get "CP". And two linear radiators can
be fed with one 90 defrees earlier (or later) than the other.
Look at wikipedia http://en.wikipedia.org/wiki/Circular_polarization

I'd expect that you can feed two Quads in phase to get CP along the axis
of their mounting boom. You'd space them appropriately and conect their
fed points appropriately.

Jerry KD6JDJ


Jerry has both bad eyes and bad code. I now see CQ and not MG. Sorry!

Jerry KD6JDJ

Quad and circular polarization
 

Dave wrote:

Circular polarization means you have equal H-Pol and V-Pol radiation,
with one polarization 90 degrees ahead (or behind) of the other.

That's not a very good description, although it's correct. You can
separate a circularly polarized field into vertically and horizontally
polarized components, the sum of which is the circularly polarized
field. And if you do that, you'll find that the two components are 90
degrees out of phase with each other.

But here's a little more complete description: The electric (E) field of
a horizontally polarized wave is horizontal, and the E field of a
vertically polarized wave is vertical. But the E field of a circularly
polarized wave rotates at the transmission frequency, one revolution per
cycle. The instantaneous amplitude of a vertically or horizontally
polarized field is sinusoidal, varying at the transmission frequency.
The amplitude of a circularly polarized wave is constant.

A quad antenna is a folded dipole.

No, it's not.

Roy Lewallen, W7EL

Quad and circular polarization
 

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,

-.-. --.-

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?

Quad and circular polarization
 

On Dec 1, 8:28*am, Dave wrote:

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

Here's a link to one example for VHF and UHF TV...

http://www.kathrein-scala.com/catalog/HDCA-5CP.pdf

Of course the Lindenblad, or even 1/2 of one could be used, also.
Using half a Lindenblad would make it true c-pol only in two
directions, but if you can aim it in the right direction that may be
OK.

RF

Quad and circular polarization
 

On Dec 1, 9:07*am, Richard Fry wrote:
Here's a link to one example for VHF and UHF TV...

Oops. That one is VHF only.

Quad and circular polarization
 

"Richard Fry" wrote in message
...
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


RF

Hi Richard

The Lindenblad is Omniazimuth CP. The QHA is hemispherical CP. Some
explanation of the DCA is shown in the Feb 2008 QST.

Jerry

Quad and circular polarization
 

Roy:

[snip]
"Roy Lewallen" wrote in message
treetonline...
Dave wrote:

Circular polarization means you have equal H-Pol and V-Pol radiation,
with one polarization 90 degrees ahead (or behind) of the other.
..
..
..
That's not a very good description, although it's correct. But here's a
little more complete description: The electric (E) field of a horizontally
polarized wave is horizontal, and the E field of a vertically polarized
wave is vertical. But the E field of a circularly polarized wave rotates
at the transmission frequency, one revolution per cycle. The instantaneous
amplitude of a vertically or horizontally polarized field is sinusoidal,
varying at the transmission frequency. The amplitude of a circularly
polarized wave is constant.
[snip]

Hmmmm....

Roy, I don't believe that is a "complete" description of circular
polarization either.

My understanding is that circular polarization is what we call the
polarization of electromagnetic radiation when the electric field vector E
rotates with an angular velocity rather than oscillating back and forth in a
single (linear) direction.

Roy, your description of circular polarization above seems to imply that the
angular velocity of the E vector of a circularly polarized wave is always
"synchronized" with the signal frequency since you stated that it rotates at
one revolution per cycle, or one radian per radian per second.

This of course is the (normal?) situation if the antenna is say a helix
firing along its axis or say crossed dipoles fed with a 90 degree phase
shift, but... to be more complete, we should note that...

Circular polarization does not have to be "synchronous"!

Consider...

What would you call the polarization type of the radiation emitted by the
following radiator?

An ordinary linear dipole fed with RF from a feedline through two slip rings
arranged such that a mechanical drive is able to rotate the dipole at some
arbitrary mechanical angular velocity completely unsynchronized with the RF
carrier.

For example, say it's a 5m dipole driven with 30MHz carrier signal and
mechanically rotated at 1000 revolutions per minute.

Such an arrangement would result in circularly polarized radiation with the
E vector having angular velocity of 1000 revolutions per minute and a
carrier frequency of 30MHz which definitely is not one revolution per cycle.

Thoughts, comments?

--

Pete
Indialantic By-the-Sea, FL

Quad and circular polarization
 

"Peter O. Brackett" wrote in message
m...
Roy:

[snip]
"Roy Lewallen" wrote in message
treetonline...
Dave wrote:

Circular polarization means you have equal H-Pol and V-Pol radiation,
with one polarization 90 degrees ahead (or behind) of the other.
.
.
.
That's not a very good description, although it's correct. But here's a
little more complete description: The electric (E) field of a
horizontally polarized wave is horizontal, and the E field of a
vertically polarized wave is vertical. But the E field of a circularly
polarized wave rotates at the transmission frequency, one revolution per
cycle. The instantaneous amplitude of a vertically or horizontally
polarized field is sinusoidal, varying at the transmission frequency. The
amplitude of a circularly polarized wave is constant.
[snip]

Hmmmm....

Roy, I don't believe that is a "complete" description of circular
polarization either.

My understanding is that circular polarization is what we call the
polarization of electromagnetic radiation when the electric field vector E
rotates with an angular velocity rather than oscillating back and forth in
a single (linear) direction.

Roy, your description of circular polarization above seems to imply that
the angular velocity of the E vector of a circularly polarized wave is
always "synchronized" with the signal frequency since you stated that it
rotates at one revolution per cycle, or one radian per radian per second.

This of course is the (normal?) situation if the antenna is say a helix
firing along its axis or say crossed dipoles fed with a 90 degree phase
shift, but... to be more complete, we should note that...

Circular polarization does not have to be "synchronous"!

Consider...

What would you call the polarization type of the radiation emitted by the
following radiator?

An ordinary linear dipole fed with RF from a feedline through two slip
rings arranged such that a mechanical drive is able to rotate the dipole
at some arbitrary mechanical angular velocity completely unsynchronized
with the RF carrier.

For example, say it's a 5m dipole driven with 30MHz carrier signal and
mechanically rotated at 1000 revolutions per minute.

Such an arrangement would result in circularly polarized radiation with
the E vector having angular velocity of 1000 revolutions per minute and a
carrier frequency of 30MHz which definitely is not one revolution per
cycle.

Thoughts, comments?

--

Pete
Indialantic By-the-Sea, FL

Hi Pete

Your idea of rotating a linearly polarized 30 MHz dipole at 1000 RPM does
not relate to the term "Elyptical Polarization" which is often called
Circular Polarization. The Wikipedia information is fairly complete as it
defines CP..

Jerry KD6JDJ

Quad and circular polarization
 

Peter O. Brackett wrote:

Hmmmm....

Roy, I don't believe that is a "complete" description of circular
polarization either.

My understanding is that circular polarization is what we call the
polarization of electromagnetic radiation when the electric field vector
E rotates with an angular velocity rather than oscillating back and
forth in a single (linear) direction.

Roy, your description of circular polarization above seems to imply that
the angular velocity of the E vector of a circularly polarized wave is
always "synchronized" with the signal frequency since you stated that it
rotates at one revolution per cycle, or one radian per radian per second.

This of course is the (normal?) situation if the antenna is say a helix
firing along its axis or say crossed dipoles fed with a 90 degree phase
shift, but... to be more complete, we should note that...

Circular polarization does not have to be "synchronous"!

Consider...

What would you call the polarization type of the radiation emitted by
the following radiator?

An ordinary linear dipole fed with RF from a feedline through two slip
rings arranged such that a mechanical drive is able to rotate the dipole
at some arbitrary mechanical angular velocity completely unsynchronized
with the RF carrier.

For example, say it's a 5m dipole driven with 30MHz carrier signal and
mechanically rotated at 1000 revolutions per minute.

Such an arrangement would result in circularly polarized radiation with
the E vector having angular velocity of 1000 revolutions per minute and
a carrier frequency of 30MHz which definitely is not one revolution per
cycle.

Thoughts, comments?

That certainly doesn't fit the classical definition of circular
polarization. Circular and linear polarizations are special cases of
elliptical polarization, which all fields actually have, and which is
universally defined in terms of polarization change over each period.
Whatever you want to call the field your mechanical arrangement is
producing, it's not circular polarization in the sense universally used
in the literature.

Roy Lewallen, W7EL

Quad and circular polarization
 

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 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.

The polarization reversal on reflection occurs only when the wave is
normal to a large (in terms of wavelength) flat surface. If it reflects
at a glancing angle, the sum of the direct and reflected rays end up
being nearly linear, or at least elliptical, depending on the reflection
angle and reflection coefficient. Glancing reflections from ground are
just about impossible to avoid at HF, but the also occur at VHF and above.

Roy Lewallen, W7EL