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Circular Polarized Antenna

Is it possible that there is a small coil at the top of my CPGR45 that is similar to a top loaded fiberglass whip? That the ground has been isolated to not make contact with the mounting bracket like most mobile mounts? That the two circular wires on top are in fact radials like on a ground plane antennas? Wouldn’t this have an effect similar to a physical CP signal?

http://s226.photobucket.com/albums/dd30/pushrod777/radio/?action=view&current=cpgr45f.jpg

I am just trying to understand why my antenna works the way it does.
 
"the two circular wires on top are in fact radials like on a ground plane antennas?

No.

"Wouldn’t this have an effect similar to a physical CP signal?"

No.

"I am just trying to understand why my antenna works the way it does."

it (the SE GR45) exhibits some horizontal polarization response because of the physical orientation of the capacity hat and the fact that signals that are propagated in one polarization are not necessarily intercepted in the same plane due to rotation and or reflection whether they be transmitted via direct wave, ground wave or sky wave.

even an omnidirectional antenna would require that at least a minimum of two elements be actively fed to produce circular polarization.

that should be clear by now.

what you "have" as indicated by the picture on photobucket is basically a mess. that it "works" at all is a miracle. this is the gr45:

http://www.signalengineering.com/Gr45+B.jpg
 
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Hmm, I wonder who made my antenna. Could I have an antenna that perhaps was made by Avanti before the buyout? I seem to remember reading, in a different thread, that SE bought Avanti. Maybe my antenna fell by the wayside like the Sigma 4.

...it (the SE GR45) exhibits some horizontal polarization response because of the physical orientation of the capacity hat and the fact that signals that are propagated in one polarization are not necessarily intercepted in the same plane due to rotation and or reflection whether they be transmitted via direct wave, ground wave or sky wave.


So, it could almost be called a virtual dp antenna. It has the characteristics of both while lacking the physical and electrical properties. That would make the SE GR50 http://www.signalengineering.com/gr50.jpg more of a strictly vert. antenna. That would explain the change.

what you "have" as indicated by the picture on photobucket is basically a mess. that it "works" at all is a miracle.

I admit it is a mess in its present condition. It is a rather delicate antenna. It has been moved and abused the last 15+ years sitting on various shelves, rafters and attics. However, when it was in service, it was in much better condition and it worked very well. So, with the above statement, could it also be said that my antenna (the CPGR 45) could be considered a virtual CP antenna? While lacking the physical and electrical characteristics, it exhibits some of the practical results.

that should be clear by now.

Clear as mud, but I am starting to understand more. Thanks for taking the time to walk me through all of this. Maybe I should email SE directly and see what they have to say about my antenna.
 
i have seen that antenna with the two drooping loops somewhere before, i just cant remember where i saw it,
you can clearly see the coil below the two hoops similar to the gr50 coil
what the secret is to the gr45's 1/8wave shaft with a certain inductance and hat above the shaft i aint figured out yet but i will be experimenting with the idea when we get decent weather.
 
This really doesn't explain why. It does, however, state that this antenna is capable of both V & H usability. I would still like more info on my exact antenna. There were quite a few of them around in the SF bay area (mostly in the east bay) when I got mine. Though, I'm realizing now the CP claim must have been just sales hype.

From http://www.signalengineering.com/goldenrod_45.html

"The GoldenRod 45 is the ultimate mobile antenna! High Tech design patterned after Signal Engineering's broadband, high power military antennas. Features a specially designed top section, which extends signal range by directing it to the horizon, instead of wasting it at high angles, like conventional mobile antennas. One to two S-Unit increase in signal strength over base and top loaded antennas. Broadband match with SWR less than 1.5:1 across all US & UK channels and well into the 10 meter amateur band with 12 KW power handling capability. Responds to horizontally polarized signals unlike any conventional vertical whip, thus extending the useful range of a mobile enormously!

The benefits must have been limited to just mobile antennas. This explains why this has never migrated over to base antennas.

"Has anyone ever tried to make an "omni" CP signal?"
Yes. it has been successfully accomplished at HF frequencies.
I am curious as to what an omni cp HF antenna would look like. Can you point me in the right direction?

the only antenna currently available from signal engineering capable of circular polarization (or more correctly, left-handed or right handed circularly polarized rotating magnetic wavefront mode) is the Thunder 8XB. the materials required for these modes of operation are not supplied by SE
Is all that’s required the "Special harness to produce Circular Polarization. Lead / Lag"?
 
Well....as in everything there are pros and Cons

You looking to do this as a base i take it
Also looking to use HF frequencies

Circular polarity in some cases are the Best
in many cases not

For HF frequencies they are extremely large
Circular beams are more for VHF and UHF
(particularly for satellites)

i didnt look at link to your antenna
elsewhere on the thread it was mentioned that it actually wasnt a circular beam

However you did ask what if any advantages there are to that antenna

if you have 2 people talking on a beam and both are set up on the flat side (horizontally )
then those 2 people will find it fairly easy to talk to each other
they may even find that other people (using vertical antennas) do not or can not hear them

most antennas are vertical in their radiating signal
as such these vertical antennas also receive best (typically ) vertically also

beams (most of which are horizontally radiated) concentrate the power they radiate in a far smaller slice then that of a typical vertical (which is usally a 360 degree footprint)

many beams are set as vertical so they gain the greater concentration of power radiated in their desired slice (beam-width)
the reason or advantage to using a vertically radiated beam is that most other antennas are that most other antennas are vertical (ground planes or dipoles)
as such they easily receive the whole signal from the other vertical antenna

think of say a skinny person
talking to you standing in front of you
you see their entire body (shoulder to shoulder)
if however you remain as you are and the other person turns 90 degrees from you
although you will still see them
you will see far less of them and not see anywhere near the amount of detail you had seen
when both of you were directly facing each other
(now if that person was a block from you you would see and recognize far less)

Now back to the antennas
think of a cross
where the vertical and horizontal meats it is a simple dot for the most part
if i had 2 vertical or 2 horizontal antennas some 500 feet apart
then both antennas would see each other very good
(same for the signal being radiated between them)

now go vertical to horizontal and suddenly one antennna does not persay see the other
(or hear the radiated signal of the other) anywhere as well as when
2 verticals or 2 horizontal antennas saw each other

so in best world happenings
2 verticals will talk best to each other
or 2 horizontal antennas will talk best to each other

but what happens if the 2 like antennas are no longer simply 500 feet apart
what if not even 5000 ft apart

what if is 500 miles or more apart

then at this point many other factors come into play
now what started as a vertical or started as horizontal signal
is now bounced around and or reflected off other parts of the atmosphere

in other words
light travels only in a straight line
yet put a mirror in its path and we can turn or rather reflect it to a different location

back to signal from antennas and the atmosphere does this to a antennas signal
by water and gas molecules or different layers heck even planes and such

so now what may have started as vertical signal radiated from a vertical antenna may well have been reflected or scattered into many other directions then the signal was originally sent

typically though
vertical stays radiating vertical
horizontal stays horizontal

so if a vertical is talking to a horizontal antenna
then because of the differences the antennas give out and receive signal
then there is either a loss between different planes of radiation
(or no loss between antennas of same plane of radiation)
the actual number if memory serves me is 3 DBi or Dbd difference

Now finally to your circular beams
it or they are using both planes
as such they are only ever at worst 1.5 DBi or DBd
they also have the most consistent signal going through the atmosphere
given the are both equally in vertical and horizontal planes

a circular beam may well realize the least amount of fade in a signal

however due to the size needed they are typically not used often for HF or mobile

if you look at say ham bands in the VHF or UHF
you will notice nearly all repeaters are having their signals sent out via vertical antennas
but most contesting or DXing is used with horizontal antennas
(rarely do the 2 planes mix)

most satellite work is used with true circular beams
(then there are many variations of these antennas)

to realize ho best to use these antennas
happy hammer's link was rather good

http://www.qsl.net/sv1bsx/antenna-pol/polarization.html

I tried to keep the math out of it
and give you a bare bones answer to your original question
 
Most circularly polarized antennas are found at VHF/UHF frequencies. The boom length for some/most of those antennas are more than 1 wave length long. The diameter of them are something like 1/2 wave length. So, convert those 1/2's and full wave lengths to feet at HF. The thing isn't exactly a very commonly found size anymore, is it? One such antenna for 11 meters is 'do-able'. The hard part is going to be supporting the thing, though. For bands lower than 11 meters, you start getting into really, really huge antennas. And the real question is will it all be worth the effort? In my opinion, nope. Probably much cheaper to rent a '747 and use a trailing-wire antenna...
- 'Doc
 
"I am curious as to what an omni cp HF antenna would look like. Can you point me in the right direction?"

can you see this image of the SE Thunder 8XB?

mth8.jpg


then you're looking at an HF Omni (one of three original operating modes) Antenna that is readily adaptable to LHCP & RHCP operation and at no time do the dimensions deviate from what you see here.
 
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CP antennas cost you afew db but keep your signal from fading as much as it changes from vert to horz. This is my understanding. tell me if im wrong.
 
I've glanced at this thread but haven't had the time to fully dive into it.

That Goldenrod antenna with the loops is just top loading. Because part of the loop is in the horizontal plane, would speak for the, "Responds to horizontally polarized signals unlike any conventional vertical whip" comment.

To have circular polarization, you need two out of phase signals. The Goldenrod antenna does not have this.

The 8XB is a bi-directional antenna capable of an omni pattern based on switching. I don't see where it is circular polarized. If anything, the antenna would resemble an "Eggbeater" with an overhead circular polarized pattern if the two elements are 90 degrees out of phase from eachother. If this is true, then it would have a horizontal omni pattern at the horizon. Unfortunately, the picture is not clear.
 
CP antennas are required when orientation of antennas vary

Old topic, so if anyone is interested. CP antennas are required when orientation of antennas vary as in satellite to land based antennas, i.e. GPS, etc. Because there is tremendous difference in gain when polarization between antennas is orthoganal, circular polarization helps prevent polarization diversity loss. On land based systems its usually not employed as vertical polarization is most often used, skip propagation vary anyways in polarization, and where horizontal polarization is used to reduce vertical polarized noise when talking with another antenna of horizontal polarization. Hope this helps.
 

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