Circular versus linear polarization
 

On Aug 12, 2:17*am, Jeff Liebermann wrote:
On Tue, 11 Aug 2009 23:01:49 -0500, tom wrote:
Jeff Liebermann wrote:

Applied CP made simple:

1. *Circular polarization is like a drill. *Instead of bouncing off
the ionosphere, it drills right through it. *Therefore, little or no
skip with CP.

So the ionosphere knows the difference between CP and linear?

I suspect the decision making abilities of the ionosphere approaches
zero. *Attributing intelligence to inanimate objects is generally a
bad idea.

Interesting, since horizontal and vertical both reflect, and CP is a
combination of both.

Could you please explain what's happening with CP?

Ummm.... no, I can't.
Please read my other points and see if they pass a sanity check.

Incidentally #2 should read:
"If you're sending CW (not CP) with your right hand..."
Sorry(tm).

I just hate it when someone takes me seriously.

--
Jeff Liebermann * *
150 Felker St #D * *http://www.LearnByDestroying.com
Santa Cruz CA 95060http://802.11junk.com
Skype: JeffLiebermann * * AE6KS * *831-336-2558

Some people just have no sense of humor.

Jimmie

Circular versus linear polarization
 

On Wed, 12 Aug 2009 10:10:17 -0700 (PDT), JIMMIE
wrote:

On Aug 12, 2:17*am, Jeff Liebermann wrote:
I just hate it when someone takes me seriously.

Some people just have no sense of humor.
Jimmie

In my case, it's too much sense of humor. Answering questions with
accurate information is easy. Just Google the question, excavate
through the resultant debris field, and pontificate on what is found.
A dash of authority and a hint of arrogance provides a defensible
packaged answer. A few URL's are always useful.

However, that's too easy, no fun, and most important, can be done by
any mortal. What's more interesting is to supply a series of wrong
answers. In order to do that, one must know both the right answers,
how things really work, and enough about the problem to be able to
successfully misinterpret any data, phenomenon, and physics. That
requires considerably more skill than merely knowing or finding the
right answer. What looks like humor, is really an intellectual
exercise.

Note that supplying wrong answers is not limited to technical Usenet
newsgroups. Lawyers do it while presenting evidence to give the jury
a misleading packaged interpretation of the evidence.

There's also an educational benefit from providing wrong answers. If
one knows all the wrong answers, whatever is left, no matter how
complex or irrational, must be the right answer. Therefore, if you
study how thing do NOT work, you will have a default understanding of
how things actually do work.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Circular versus linear polarization
 

tom wrote:
Art Unwin wrote:
The majority of antennas used today are (commercial) circularly
polarized
Ham antennas remain in the linear domain (ala the Yagi and similar)
There are many reasons espoused in CP advantages in "point to point"
What is the main advantage hams hold over the more popular circular
polarized antennas in its "skip" type useage versus "point to point" ?

Please provide examples of commercial antennas that are CP. Space
communication antennas are not ok to include.

FM and TV broadcast.

Circular versus linear polarization
 

Art Unwin wrote:


Use your own thread to ask for assistance on your question.
Be prepared to answer why you are requesting this personal service .
I asked a question on this thread with respect to the main advantage
for hams that linear
polarization has over CP. I have no resistance to change if it can be
justified. I see
that it can pick up signals that linear antennas cannot hear because
of a 30 db attenuation
where as CP has only a 3 db attenuation!

Compared to what?

Circular versus linear polarization
 

On Aug 12, 3:21*pm, dave wrote:
Art Unwin wrote:

Use your own thread to ask for assistance on your question.
*Be prepared to answer why you are requesting this personal service .
I asked a question on this thread with respect to the main advantage
for hams that linear
polarization has over CP. I have no resistance to change if it can be
justified. I see
that it can pick up signals that linear antennas cannot hear because
of a 30 db attenuation
where as CP has only a 3 db attenuation!

Compared to what?

I thought he said earlirer that it had a 3 db gain

Circular versus linear polarization
 

On Aug 12, 3:42*pm, JIMMIE wrote:
On Aug 12, 3:21*pm, dave wrote:

Art Unwin wrote:

Use your own thread to ask for assistance on your question.
*Be prepared to answer why you are requesting this personal service

Circular versus linear polarization
 

Art Unwin wrote:

Use your own thread to ask for assistance on your question.
Be prepared to answer why you are requesting this personal service .
I asked a question on this thread with respect to the main advantage
for hams that linear
polarization has over CP. I have no resistance to change if it can be
justified. I see
that it can pick up signals that linear antennas cannot hear because
of a 30 db attenuation
where as CP has only a 3 db attenuation!
So what is it on the other side of the coin is what this thread is
posing to those who are familiar with respect to radiators.

You stated that MOST commercial antennas are CP. Having been in that
business to some extent, I know that statement to be false. I'm simple
asking you to prove it.

Also where is this information that shows linear antennas have 30dB of
attenuation? When? How? What conditions?

And when do the CP antennas have 3dB by comparison? Give references.

I know you can't since all these things are figments of your addled brain.

tom
K0TAR

Circular versus linear polarization
 

On Aug 12, 3:42*pm, JIMMIE wrote:
On Aug 12, 3:21*pm, dave wrote:

Art Unwin wrote:

Use your own thread to ask for assistance on your question.
*Be prepared to answer why you are requesting this personal service

Circular versus linear polarization
 

Art Unwin wrote:
On Aug 12, 3:42 pm, JIMMIE wrote:
On Aug 12, 3:21 pm, dave wrote:

Art Unwin wrote:
Use your own thread to ask for assistance on your question.
Be prepared to answer why you are requesting this personal service .
I asked a question on this thread with respect to the main advantage
for hams that linear
polarization has over CP. I have no resistance to change if it can be
justified. I see
that it can pick up signals that linear antennas cannot hear because
of a 30 db attenuation
where as CP has only a 3 db attenuation!
Compared to what?
I thought he said earlirer that it had a 3 db gain

When I modeled my antenna the max gain was CP I then checked for
linear gains
on the same set up and they were 3 db down. I suppose I should have
set it up for max linear gain and then checked CP gain on the same set
up. (Made a note to myself for future). For end fed antenna, the gain
max was around 13 dbi but 10 dbi seemed to be more the norm. What
really pleased me was the near 50 ohm impedance feed.
The biggest advantage is that people with small yards will now have no
problems on getting on top band with directional antenna and be able
to use the whole band! However, regardless on the ideas I have checked
out on it I am very confident that hams will immediately will be able
to improve it in ways I have not thought of. As with all thoughts
others will say I knew that but I couldn't be bothered because once
the dots are connected
everything appears to be obvious. A jigsaw puzzle with all the parts
turned over is tremendously hard to solve. Once you have seen the
picture it is a different ball game.
The antenna is extremely quiet, and as I have mentioned before the
audio quality is such that I immediately look at the meter only to see
it on the low side. Perhaps the CP pickup
does not register the same as for linear. It is my hope that all will
tackle building one this fall
so that the improvement horizon will broaden while I am still around.

And except for his ridiculous claims he will give no details of the
antennas he makes the claims for.

You are a fraud Art.

tom
K0TAR

Circular versus linear polarization
 

dave wrote:
tom wrote:
Art Unwin wrote:
The majority of antennas used today are (commercial) circularly
polarized
Ham antennas remain in the linear domain (ala the Yagi and similar)
There are many reasons espoused in CP advantages in "point to point"
What is the main advantage hams hold over the more popular circular
polarized antennas in its "skip" type useage versus "point to point" ?

Please provide examples of commercial antennas that are CP. Space
communication antennas are not ok to include.

FM and TV broadcast.

I asked him, not you because he wouldn't know any answers.

Now you've given it all away!

And he said "the majority" which is untrue.

tom
K0TAR

Circular versus linear polarization
 

On Aug 12, 8:31*pm, tom wrote:
Art Unwin wrote:
On Aug 12, 3:42 pm, JIMMIE wrote:
On Aug 12, 3:21 pm, dave wrote:

Art Unwin wrote:
Use your own thread to ask for assistance on your question.
*Be prepared to answer why you are requesting this personal service .
I asked a question on this thread with respect to the main advantage
for hams that linear
polarization has over CP. I have no resistance to change if it can be
justified. I see
that it can pick up signals that linear antennas cannot hear because
of a 30 db attenuation
where as CP has only a 3 db attenuation!
Compared to what?
I thought he said earlirer that it had a 3 db gain

When I modeled my antenna the max gain was CP I then checked for
linear gains
on the same set up and they were 3 db down. I suppose I should have
set it up for max linear gain and then checked CP gain on the same set
up. (Made a note to myself for future). For end fed antenna, the gain
max was around 13 dbi but 10 dbi seemed to be more the norm. What
really pleased me was the near 50 ohm impedance feed.
The biggest advantage is that people with small yards will now have no
problems on getting on top band with directional antenna and be able
to use the whole band! However, regardless on the ideas I have checked
out on it I am very confident that hams will immediately will be able
to improve it in ways I have not thought of. As with all thoughts
others will say I knew that but I couldn't be bothered because once
the dots are connected
everything appears to be obvious. A jigsaw puzzle with all the parts
turned over is tremendously hard to solve. Once you have seen the
picture it is a different ball game.
The antenna is extremely quiet, and as I have mentioned before the
audio quality is such that I immediately look at the meter only to see
it on the low side. Perhaps the CP pickup
does not register the same as for linear. It is my hope that all will
tackle building one this fall
so that the improvement horizon will broaden while I am still around.

And except for his ridiculous claims he will give no details of the
antennas he makes the claims for.

You are a fraud Art.

tom
K0TAR

No, I am not Tom you are just extending your mouth. Obviously those
who give me a hard time don't get to share. There are others who do
not give me a hard time who get to share.
If you are an outsider to every thing then I understand why you lean
on the term "ridiculous"
Remember the discussion on Gauss? You never did reverse your position
which is against classical physics so you are an unproven quantity to
most with respect to antennas and radiation.
You could, ofcourse, provide a list of polarity changes upon collision
instead of your dart throwing which is never accurate. Why don't you
plonk me or are you just a nasty person?
Maybe you can start a separate thread for just you and me so you can
sound off, insult and have a good time.

Circular versus linear polarization
 

Art Unwin wrote:
No, I am not Tom you are just extending your mouth. Obviously those
who give me a hard time don't get to share. There are others who do
not give me a hard time who get to share.
If you are an outsider to every thing then I understand why you lean
on the term "ridiculous"
Remember the discussion on Gauss? You never did reverse your position
which is against classical physics so you are an unproven quantity to
most with respect to antennas and radiation.

I never expressed any opinion on Gauss. More of your mid slips.

You could, ofcourse, provide a list of polarity changes upon collision

What polarity changes? I have not been in the discussion about CP
reflections, just the claims you made about CP antennas being dominant
in the commercial market, which they are not.

instead of your dart throwing which is never accurate. Why don't you
plonk me or are you just a nasty person?

I only throw darts at targets, and you give many.

Maybe you can start a separate thread for just you and me so you can
sound off, insult and have a good time.

I'd rather insult you here, since this is where you are currently
spouting your nonsense.

And it's not a good time. I feel sorry for you and wish you'd get help.

tom
K0TAR

Circular versus linear polarization
 

In message
, Art
Unwin writes
On Aug 12, 3:42*pm, JIMMIE wrote:
On Aug 12, 3:21*pm, dave wrote:

Art Unwin wrote:

Use your own thread to ask for assistance on your question.
*Be prepared to answer why you are requesting this personal service .
I asked a question on this thread with respect to the main advantage
for hams that linear
polarization has over CP. I have no resistance to change if it can be
justified. I see
that it can pick up signals that linear antennas cannot hear because
of a 30 db attenuation
where as CP has only a 3 db attenuation!

Compared to what?

I thought he said earlirer that it had a 3 db gain

If you are horizontally polarized a vertical will be down 30db
theoretically than if it was horizontal and vica versa.

Where do you get 30dB from? 'Theoretically', it ought to be infinitely
down. In practice, because of reflections and things like that, it can
vary from 'a bit down' to 'a hell of a lot down'.

If the
radiator is set for CP transmissions other polarizations
will be down only 3 db theoretically.

This is correct. You are splitting the transmitter power - half power to
each orthogonal polarisation and, with a 90 degree phase shift,
producing a circularly polarised signal (instead of a 45 degree slant).

Seems obvious which is best to
have, except a lot of hams like long distance communication which
means you have to deal with reflections.
From this thread it is obvious to me that we are not sure, at this
point, what changes occur
when reflection comes about. Roy pointed out a "misconception" at
least to his findings but the fact is there is no list of known
changes that one can bank on for reflections of CP at least for the
present. If I am incorrect then please post your thoughts.
--
Ian

Circular versus linear polarization
 

On Aug 13, 5:21*am, Ian Jackson
wrote:
In message
, Art
Unwin writes



On Aug 12, 3:42*pm, JIMMIE wrote:
On Aug 12, 3:21*pm, dave wrote:

Art Unwin wrote:

Use your own thread to ask for assistance on your question.
*Be prepared to answer why you are requesting this personal service .
I asked a question on this thread with respect to the main advantage
for hams that linear
polarization has over CP. I have no resistance to change if it can be
justified. I see
that it can pick up signals that linear antennas cannot hear because
of a 30 db attenuation
where as CP has only a 3 db attenuation!

Compared to what?

I thought he said earlirer that it had a 3 db gain

If you are horizontally polarized a vertical will be down 30db
theoretically than if it was horizontal and vica versa.

Where do you get 30dB from? 'Theoretically', it ought to be infinitely
down. In practice, because of reflections and things like that, it can
vary from 'a bit down' to 'a hell of a lot down'.

Correct.
A reference supplied earlier by Jeff in this thread stated "real
world
20db to 35 db" (You used the term "in practice) A manufacturer used
the figure 30 db when I followed thru on his other references which
also appeared to me as being reasonable



If the
radiator is set for CP transmissions other polarizations
will be down only 3 db theoretically.

This is correct. You are splitting the transmitter power - half power to
each orthogonal polarisation and, with a 90 degree phase shift,
producing a circularly polarised signal (instead of a 45 degree slant).

Seems obvious which is best to
have, except a lot of hams like long distance communication which
means you have to deal with reflections.
From this thread it is obvious to me that we are not sure, at this
point, what changes occur
when reflection comes about. Roy pointed out a "misconception" at
least to his findings but the fact is there is no list of known
changes that one can bank on for reflections of CP at least for the
present. If I am incorrect then please post your thoughts.

--
Ian

Circular versus linear polarization
 

On Aug 11, 4:24*pm, Art Unwin wrote:
different options to what we already have.
* *All I ask of them is to share with the rest of us exactly what
happens to CP when it collides with anything in transit to a receiver.

And the information was so shared.

Jimmie

Circular versus linear polarization
 

JIMMIE wrote:
On Aug 11, 4:24 pm, Art Unwin wrote:
different options to what we already have.
All I ask of them is to share with the rest of us exactly what
happens to CP when it collides with anything in transit to a receiver.

And the information was so shared.

Jimmie

They split themselves from the conspiracy to keep Art un- and
misinformed. They will pay for that.

tom
K0TAR

Circular versus linear polarization
 

On Aug 15, 7:27*pm, tom wrote:
JIMMIE wrote:
On Aug 11, 4:24 pm, Art Unwin wrote:
different options to what we already have.
* *All I ask of them is to share with the rest of us exactly what
happens to CP when it collides with anything in transit to a receiver.

And the information was so shared.

Jimmie

They split themselves from the conspiracy to keep Art un- and
misinformed. *They will pay for that.

tom
K0TAR

I am just waiting for his new contraption that is going to produce
circular polarized waves on 160M and you could haul it in the trunk of
your car. I hope that when I am as old as he says he is that I will
have morre interesting things to do wiith my time than tilt at
antennas.

Jimmie

Circular versus linear polarization
 

I have been looking for a decent CP design to try out on my
repeaters .
For many years I have been looking at the reasoning for FM
broadcasters having used CP pol with great success.

I also have a small indication that linear antennas (eg:linear
collinears)and non-linear antennas(eg:folded loop dipoles) by design
may have slightly different characteristics in the far field that
tend towards a greater degree of cross/CP from the mechanical design .

Anyone had good success with installing a CP repeater antenna(2m or
70cm) to assist with the deap fade nulls in mobile uplink to the
repeater.
I want to try rhp for TX and lhp for RX - anyone tried this
combination before?

Circular versus linear polarization
 

wrote in message
...
I have been looking for a decent CP design to try out on my
repeaters .
For many years I have been looking at the reasoning for FM
broadcasters having used CP pol with great success.


In the UK, Band II VHF FM sound radio broadcasting began to fixed receivers
using horizontal polarisation (HP) for reasons including a belief that
interference from car ignition systems was predominantly vertically
polarised, and because it was found easier to achieve a good
omni-directional pattern in the horizontal plane from a transmitting antenna
based on a vertical slot (Babinet's principle) - several such slot antennas
were stacked vertically to obtain some gain and to avoid illuminating the
sky.

Later, as transistors became available and vehicular VHF receivers of
sensible size became practical, a new market emerged but it was poorly
served by the HP transmissions*. When local radio was launched in the UK,
in Band II, the new transmitters were equipped with antennas that radiated a
VP component as well as HP, and in time all Band II transmissions were
converted to mixed polarisation. Circular polarisation is one example of
mixed polarisation, but its ability to provide cross-polar discrimination is
not used in FM broadcasting.

Take a look at: http://downloads.bbc.co.uk/rd/pubs/reports/1970-35.pdf

The experience in other countries has probably been similar - same physics.



I also have a small indication that linear antennas (eg:linear
collinears)and non-linear antennas(eg:folded loop dipoles) by design
may have slightly different characteristics in the far field that
tend towards a greater degree of cross/CP from the mechanical design .


Huh?

* HP is less effective than VP for VHF communication with mobiles because
the ever-present ground reflection has reversed polarity (i.e. it's in
antiphase with the signal propagating over a direct path).



Anyone had good success with installing a CP repeater antenna(2m or
70cm) to assist with the deap fade nulls in mobile uplink to the
repeater.
I want to try rhp for TX and lhp for RX - anyone tried this
combination before?

If you use the same antenna for transmitting and receiving, and it is
fundamentally circularly polarised, then it will provide and respond to the
two different senses of CP automatically because the definition of the sense
of circular polarisation depends on the direction of propagation. But do
you think the horizontally-polarised component will help with deep nulls?

Chris

Circular versus linear polarization
 

christofire wrote:
. . .
* HP is less effective than VP for VHF communication with mobiles because
the ever-present ground reflection has reversed polarity (i.e. it's in
antiphase with the signal propagating over a direct path).
. . .

Reflection of a CP wave results in a reversed CP wave only when the
reflection is directly normal to the reflecting surface. That's not at
all the case for typical ground reflections. What you actually get from
ground reflections is an elliptically polarized wave, likely having the
same sense as the impinging wave. In experiments I ran about 35 years
ago, I found nearly linearly polarized waves resulting from reflection
of a CP wave from a vehicle top.

A little time spent with a modeling program such as EZNEC+ can be very
educational in understanding the generation and reflection of CP waves.

Roy Lewallen, W7EL

Circular versus linear polarization
 

On Mon, 28 Sep 2009 14:13:31 -0700 (PDT), wrote:

I have been looking for a decent CP design to try out on my
repeaters .
For many years I have been looking at the reasoning for FM
broadcasters having used CP pol with great success.

I also have a small indication that linear antennas (eg:linear
collinears)and non-linear antennas(eg:folded loop dipoles) by design
may have slightly different characteristics in the far field that
tend towards a greater degree of cross/CP from the mechanical design .

Methinks you'll be better off with eliptical polarization, where
perhaps 70% of the power is vertically polarized, and the rest is
horizontal. The idea is that most of the energy will be properly
recieved by the traditional vertically polarized mobile antenna. The
remainder will be to fill in the gaps, where the polarization changes
to something not so vertical.

Search Google patents:
http://www.google.com/patents
for "omnidirectional circular polarized antenna". Also, look at FM
broadcast xmit antennas. Some really strange stuff there.

Anyone had good success with installing a CP repeater antenna(2m or
70cm) to assist with the deap fade nulls in mobile uplink to the
repeater.

Yes. I can't find my previous rant on the subject, so I'll try again.
Around 1968 thru 1970, I was at Cal Poly Pomona doing some experiments
with CP UHF antennas. The problem was that the local repeater was
experiencing deep Raleigh fading as mobiles moved along the San
Bernardino Freeway. The ideas was that CP would reduce these fades so
that listening to the repeater didn't sound like it was accompanied by
a machine gun. It worked but with a price. The fades were
dramatically reduced, but so was the coverage area. Antenna gain was
down at least 3dB as was maximum range for the repeater. I thought it
was a good tradeoff, but not everyone agreed. The stations that were
marginal (usually because they were too lazy to install a proper
antenna) were gone. However, the reliability of the local mobiles was
greatly improved. Range won over fade reduction and the antenna was
replaced after a few months of testing.

There was an article on the subject in "The Practical Handbook of
Amateur Radio FM and Repeaters" by Bill Pasternack and Mike Morris.
1981 by Tab Books.
http://openlibrary.org/b/OL4421123M/practical_handbook_of_amateur_radio_FM___repeaters
http://www.alibris.com/booksearch?qsort=p&isbn=0830612122
Sheesh. I paid about $5 at a hamfest.

Since it's not online, I scanned the applicable chapter, chopped out
some irrelevant junk, and posted them to:
http://802.11junk.com/jeffl/circular-polarization/
I'll convert them to a single PDF after I figure out why Irfanview is
generating garbage. Bug me if you have trouble reading the JPG's.

I want to try rhp for TX and lhp for RX - anyone tried this
combination before?

Yep. I tried that to improve TX-RX isolation. I gave up. Mounted on
a single pole, with separate phasing harnesses, I never could get the
antennas anywhere near 50 ohms. There was also just too much coupling
between the RH and LH sections for that to work. Another explanation
might be that at the time, I didn't have a clue what I was doing, but
we won't go there. The rather high VSWR certainly didn't help with
the isolation as it detuned the tx and rx cavities (formerly a
duplexer). Some rather crude testing showed that we were better off
with a single antenna, the stock duplexer, and a single CP
polarization. There was also a problem with distant stations. They
wanted to use CP on the base station to reduce the effects of
multipath (usually off the infamous L.A. smog inversion layer). That
would have required two antennas for each base station. I suggest
that you stick with one circular polarization for now.

Incidentally, note the scanned photo of the Loop Mountain site
http://802.11junk.com/jeffl/circular-polarization/cp-02.jpg
and compare it with the previous intermod factory and post-storm
removal exercise at:
http://802.11junk.com/jeffl/pics/Old%20Repeaters/slides/LoopMtn02.html
http://802.11junk.com/jeffl/pics/Old%20Repeaters/slides/LoopMtn03.html
One of the reasons I'm current intact and still sane is that I don't
own any repeaters and find excuses not to do any tower work.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Circular versus linear polarization
 

"Roy Lewallen" wrote in message
...
christofire wrote:
. . .
* HP is less effective than VP for VHF communication with mobiles because
the ever-present ground reflection has reversed polarity (i.e. it's in
antiphase with the signal propagating over a direct path).
. . .

Reflection of a CP wave results in a reversed CP wave only when the
reflection is directly normal to the reflecting surface. That's not at all
the case for typical ground reflections. What you actually get from ground
reflections is an elliptically polarized wave, likely having the same
sense as the impinging wave. In experiments I ran about 35 years ago, I
found nearly linearly polarized waves resulting from reflection of a CP
wave from a vehicle top.


No doubt, but what I wrote above was about horizontal and vertical _linear_
polarisations, HP and VP. I did wonder after I sent it if 'polarity' would
be misread as polarisation.

Chris

Circular versus linear polarization
 

christofire wrote:
"Roy Lewallen" wrote in message
...
christofire wrote:
. . .
* HP is less effective than VP for VHF communication with mobiles because
the ever-present ground reflection has reversed polarity (i.e. it's in
antiphase with the signal propagating over a direct path).
. . .
Reflection of a CP wave results in a reversed CP wave only when the
reflection is directly normal to the reflecting surface. That's not at all
the case for typical ground reflections. What you actually get from ground
reflections is an elliptically polarized wave, likely having the same
sense as the impinging wave. In experiments I ran about 35 years ago, I
found nearly linearly polarized waves resulting from reflection of a CP
wave from a vehicle top.


No doubt, but what I wrote above was about horizontal and vertical _linear_
polarisations, HP and VP. I did wonder after I sent it if 'polarity' would
be misread as polarisation.

Chris

My mistake, I apologize for misreading it. Yes, HP does reverse
polarity, exactly as you say, when reflecting from the ground.
Furthermore, the amplitude of the reflection is nearly the same as the
incident wave (that is, the reflection coefficient is nearly -1), even
when ground conductivity is relatively poor, especially at low angles.
So the sum of the incident and reflected waves is near zero.

Unfortunately, the sum of a vertically polarized field and its
reflection from finite conductivity ground is also nearly zero at low
elevation angles, for different reasons. There is a component that
propagates via surface wave, but it attenuates to essentially zero in a
very short distance at VHF.

Roy Lewallen, W7EL

Circular versus linear polarization
 

Ok all noted on the many ideas.

Here is one for you boffins:

After having a look at the circular turnstile type antenna with a
groundplane ,I sent a request to the main manufactureers regarding
using this in an inverted state for what I wanted to do on the
repeater.Still yet to get a reply and after a few months I guess they
are still thinking about it.

If they advertised it so great for horizontal to near vertical
satellite work then the same principle should apply if inverted.

Style of eggbeater looking at .
http://pagesperso-orange.fr/on6wg/Do...Part1-Full.pdf

What do the Boffins suggest.

Circular versus linear polarization
 

wrote in message
...
Ok all noted on the many ideas.

Here is one for you boffins:

After having a look at the circular turnstile type antenna with a
groundplane ,I sent a request to the main manufactureers regarding
using this in an inverted state for what I wanted to do on the
repeater.Still yet to get a reply and after a few months I guess they
are still thinking about it.

If they advertised it so great for horizontal to near vertical
satellite work then the same principle should apply if inverted.

Style of eggbeater looking at .
http://pagesperso-orange.fr/on6wg/Do...Part1-Full.pdf

What do the Boffins suggest.


1. How are you thinking of mounting it whilst upside down? Even if you
were to use a dielectric swan neck of some kind, you'd still have the feed
line passing through the volume into which the antenna is intentionally
radiating, so the radiation pattern would be upset to some extent. Of
course, if you were willing to modify the antenna you could probably pass a
co-axial feed line through an axial tube - but if you were going to that
much trouble you might as well build the thing yourself.

2. Their statement that: 'Each of the two loops forming the antenna has an
impedance of 100 ohms, and when coupled in parallel, they offer an ideal 50
ohms impedance. We will use the properties of a quarter wavelength coax line
to achieve a 90 degree phase difference between the two loops in order to
obtain circular polarisation.' is a bit suspect. This would be true for a
half wavelength of line, indeed that is the basis of a very common form of
balun, but a quarter wavelength of transmission line will cause an impedance
transformation. If they use 50 ohm cable then a quarter wavelength will
transform 100 ohms down to 25 ohms, and when this is connected in parallel
with another 100 ohms the result will be 20 ohms which is presented to the
feed line. Not a particularly good match!

My suggestion is: if you intend to purchase, proceed with caution and keep
asking the proprietor the questions you want answered.

Chris

Circular versus linear polarization
 

"christofire" wrote in message
...

wrote in message
...
Ok all noted on the many ideas.

Here is one for you boffins:

After having a look at the circular turnstile type antenna with a
groundplane ,I sent a request to the main manufactureers regarding
using this in an inverted state for what I wanted to do on the
repeater.Still yet to get a reply and after a few months I guess they
are still thinking about it.

If they advertised it so great for horizontal to near vertical
satellite work then the same principle should apply if inverted.

Style of eggbeater looking at .
http://pagesperso-orange.fr/on6wg/Do...Part1-Full.pdf

What do the Boffins suggest.


1. How are you thinking of mounting it whilst upside down? Even if you
were to use a dielectric swan neck of some kind, you'd still have the feed
line passing through the volume into which the antenna is intentionally
radiating, so the radiation pattern would be upset to some extent. Of
course, if you were willing to modify the antenna you could probably pass
a co-axial feed line through an axial tube - but if you were going to that
much trouble you might as well build the thing yourself.

2. Their statement that: 'Each of the two loops forming the antenna has
an impedance of 100 ohms, and when coupled in parallel, they offer an
ideal 50 ohms impedance. We will use the properties of a quarter
wavelength coax line to achieve a 90 degree phase difference between the
two loops in order to obtain circular polarisation.' is a bit suspect.
This would be true for a half wavelength of line, indeed that is the basis
of a very common form of balun, but a quarter wavelength of transmission
line will cause an impedance transformation. If they use 50 ohm cable
then a quarter wavelength will transform 100 ohms down to 25 ohms, and
when this is connected in parallel with another 100 ohms the result will
be 20 ohms which is presented to the feed line. Not a particularly good
match!


OK - I've just noticed they specify RG62 for the quarter wavelength of line,
and that has 93 ohms characteristic impedance. It would transmform 100 ohms
down to 86.5 ohms which, in parallel with the other 100 ohms, would yield
46.4 ohms. Better.

Chris

Circular versus linear polarization
 

Regarding the mounting , running the feeder out from a concrete
microwave tower one can run the feeder from the top or bottom of the
antenna.

Circular versus linear polarization
 

wrote in message
...
Regarding the mounting , running the feeder out from a concrete
microwave tower one can run the feeder from the top or bottom of the
antenna.

Hi Brad

How is the eggbeater performance superior to that of a Lindenblad?

Jerry KD6JDJ

Circular versus linear polarization
 

Hi Jerry

Very good question ,and I do not have any information regarding their
comparison.

On this tower due to the size and isolation I would have to split the
feeder and have a minumum of two or more antennas around the tower .
(Toer is 10m in diameter with steel reinforcing - high front to back
isolation)

For this specific case , a Lindenbald would perhaps have too much
horizontal space to mount a number of them around the tower.

Unless you are assuming that one uses one antenna split over the 4 ,
equally spaced around the tower.
Again this is a good question as under normal circumstances one does
not have the high isolation between the elements .

I could use a 1:4 wilkoson and mount folded dipoles at skewed angles ,
so at any one time a distant station should see at least two of the
4 .

This is a lot to ponder about .