Circular Polarized Antenna

[Pushrod]

I have a question about circular polarized antennas. This type of antenna seems to be overlooked. I am curious as to why. About 20-25 years ago, when I just starting to play around with radios, I bought an antenna that I cannot find any info about. It is called a Circular Polarized Goldenrod 45. It is different than what we see today as a Goldenrod 45. This funny looking antenna worked so much better than anything that was out at the time. Now that I am thinking about dusting off some of my old equipment The only thing I really need is an antenna. While doing research, I am surprised that this type of antenna has not evolved into something better. So what gives? There seem to be some very knowledgeable antenna gurus here. Why has this technology fallen out of favor?

Thanks

 

[AudioShockwav]

One way is you can use a beam that has dual polarization's ( a beam that has two coax connections on it ) like the comet, moonraker 4, shooting star or a PDL II and make it transmit and receive Circular Polarization.
What you have to do is feed both connecters (horizontal and vertical ) at the same time, but they must be fed 90 degrees out-of-phase with the other one.
You can not just hook both coax cables up, it has to be feed out of phase.
There is a very good write up about this on the web, I will find it and post it for you.
Another answer, is Lou Franklin had a set of plans to build a "CP" beam, I will look for that also.
Welcome to the forum.

73
Jeff

 

[AudioShockwav]

Here is Lou`s web site, It can be forund here

http://www.cbcintl.com/default.htm
He sells a lot of CB radio related books and kits.

Here is a direct link to the beam

http://www.cbcintl.com/CP_Beam.htm

73
Jeff




[FONT=century gothic,arial,helvetica].[/FONT]

 

[AudioShockwav]

Here is a Link to the Write up on CP beams I was refering to From Signal Engineering the guys that build Quad Antennas.
, Lots of good info on this site.


http://www.signalengineering.com/ultimate/circular_polarization.html


73
Jeff

 

[freecell]

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 and unless this earlier incarnation of the Goldenrod 45 was able to be used with dual feedlines it was not able to be operated in this manner. i never saw one.

http://www.firecommunications.com/se.shtml

 

[Pushrod]

Wow, you really peaked my interest. I went up into the attic and found my old Circular Polarized Goldenrod 45. It is in really poor shape from being moved around all these years. It is a mobile antenna similar to the current gr45. It does however transmit and receive both flat and vert at the same time. I used to use this to talk to my father about 100 mile away. I would drive up Mt Diablo (a local mountain top in the SF Bay area) and talk to my father. He only had a small three element flat side beam. This worked out great . It was great for dx also. I even took up a generator and tickled a couple of ceramic tubes through it one night (in my less responsible years ). This little antenna worked like nothing I have ever seen.

http://s226.photobucket.com/albums/dd30/pushrod777/radio/?action=view&current=cpgr45g.jpg

I am curious about the SE antennas you mentioned. I am a little unclear on the exact antenna you are referring to. Do you mean the Thunder XB 8? Or the Lightning 8. I am assuming you mean the Thunder XB 8. You said "the materials required for these modes of operation are not supplied by SE". What materials are you talking about? I do have a driver that I used to run two small amps, one to each antenna in a co-phase set up. Would that work? It splits the signal into two equal 50 ohm signals. This setup worked great for me when I first started driving trucks. It seems like that is all you would need.

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

A few more pics of the antenna and my amp setup are here.

http://s226.photobucket.com/albums/dd30/pushrod777/radio/

 

[freecell]

"It does however transmit and receive both flat and vert at the same time."

that's dual polarization, not circular.

 

[Pushrod]

How could the two circular loops be transmitting flat and vert but not be in a circular pattern? Wouldn't the Thunder XB 8, or any quad beam that requires two coax connections be a better example of duel polarization? For duel polarization, wouldn't that require two distinct types of signals (flat and vert) radiating at the same time? Wouldn't it also require two coax runs without a delay between the signals. The SE site suggests that a special harness is needed to hook up a CP antenna. It also say a delay is needed between those lines. It implies that only a quad beam type antenna is capable of CP. None of this really explains my old CPGR45 and why it works. I was always under the impression that the way the signal radiated off the antenna defined its polarization. If you take a GR45 Spider and shape the oval radials into more of a circular shape and angle them down 45* put a fiberglass divider rod at the bottom to keep the distance consistent, you have something very similar to what I have now. The coil at the top would be the exception. I must be missing something. I am not trying to be a smart a$$, I just truly do not understand.

 

[W5LZ]

Circular polarization just isn't very practical at HF. Dual polarization is more common, but they are not the same thing at all. Your old antenna wasn't circularly polarized, and just going by the looks of it, it wasn't dual polarized either.
Those loops at the top of the antenna do not mean anything is polarized in any particular way no matter what the 'shape'. 'Shape' doesn't determine polarization. If you would change those loops to just straight lengths of conductor of the correct lengths, the antenna would behave in the same way as with the loops. It really isn't all that simple to explain unless you have more knowledge of electronics than the average person has (it also takes a good teacher, which I am NOT). A circularly polarized antenna for HF is not going to be very practical, it's gonna be large and complicated. And because of how HF behaves (as opposed to VHF/UHF) it typically just isn't very viable/necessary. Possible? Sure, but get your 'wide load' permit before mounting it on your vehicle .
- 'Doc

 

[AudioShockwav]

Wouldn't the Thunder XB 8, or any quad beam that requires two coax connections be a better example of duel polarization? For duel polarization, wouldn't that require two distinct types of signals (flat and vert) radiating at the same time?

Dual polarization is , 2, as in a horizontal AND a vertical polarization, with a seperate 50 ohm coax running to each, with no phase delay.
For Circular polarization you must feed both sides at the SAME time, but with one set 90 degrees out of phase.

This allows the signal to "fire" in a right hand, or left hand pattern (depending on how you build the phase harness) off the end of the antenna.
If you look at a SE quad, it has two feedlines, one for V one for H, but it is not a circular polarized antenna because there is no phasing harness.
Even if you feed both at the same time, it is not CP without the delay that the harness provides.

You could take the elements from a quad, and form them in a circle, rather than the diamond shape, and it would make no difference.
====
Here is the main point:

To get Vertical polarzation, you feed the 1/2 wave at the center of the element on the side.
To get Horzontal polarzation you feed the 1/2 wave at the center of the element on the bottom.

=====

To get CP, you must feed both, with one of them 90 degrees out of phase to the other.

=====
A yagi, with flat and vert elements can do CP as well, it is not necessary to have the elements in a circle/diamond shape.
Were you feed the element, and the phase shift between the two is the critical part.
=====



Just looking at the pictures of the antenna you posted, I would think that the wire loops at the top of the antenna serve as a top hat, or what is more often refered to as a cap hat or capacitance hat.

A vertical antenna, fed at the bottom, is a vertical antenna.

I hope this helps, if not post back, and I will search around on the web and see what I can dig up as far as info to explain CP a bit more.

73
Jeff

 

[freecell]

unfortunately scott is just as confused about cp as everyone else. a dual polarity antenna IS NOT REQUIRED to produce LH or RH CP. in the case of the Thunder 8XB, (not XB,8) this antenna is a vertically polarized bi-directional array and it produces NO HORIZONTALLY POLARIZED RADIATION PATTERN. the initial design of the 8XB provides 3 modes of operation, vertical omni, vertical EW and vertical NS bi-directional modes. there are no matching problems inherent with the use of dual feedlines and with the proper phase angle delay between the two lines both LHCP and RHCP are readily added to this antennas repertoire of operational modes.

simply put, it's not used because no one understands how it works or what is required to put it into proper use. there may be a lot of good information on the site but there's just as much bad information and sifting through it and sorting it all out is not something that can be done by the uninitiated. the material provided on the se site is riddled with error.

the site remains "The Ultimately "CONFUSING" Guide to 11 Meter CB Antennas".

 

[Happy_Hamer]

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

 

[freecell]

now there's a link to some useful and accurate information.

 

[Pushrod]

Wow, I will be the first one to admit that I am truly "uninitiated" . That math is way over my head.

I have read through most everything I can find on CP. So let me paraphrase what I am grasping. There are two ways to achieve CP. First is electrically, by manipulating the electrical connection. This still seems like it would radiate out more like duel polarized set up to me. That doesn't really mean anything except that I don't grasp the concept. Second is physically, by manipulating the way the signal radiates off the antenna. This is easier for me to understand. Especially when using the “beam” examples everyone is providing. Both of these examples have one thing in common, two physical connections to the antenna.

Everything I have read states that the "beam" concept is just one way to create a CP signal. Has anyone ever tried to make an "omni" CP signal? Could this be what I have? Might there be a way to generate a CP signal with one connection? The main issue in the examples I've read seems to be the "corkscrew" effect that is generated off of "beam" styles. Or rather the RHCP (Right Hand Circular Polarization) & LHCP (Left Hand Circular Polarization). How would this work with an omni? Would the rotation be "R" or "L" ? Since a signal is a wave, it would seem it has to be generated with some orientation.

I realize that CP may be way over my head. Some things are just not easily explained. I can live with that. However, the one thing that bothers me is the fact that my antenna still tx & rx both H & V signals at the same time with only one coax connection. How can this be? Certainly there has to be a logical explanation. If my little mobile antenna can do this, why can't a base antenna be built to work in the same way?

 

[freecell]

"Has anyone ever tried to make an "omni" CP signal?"
Yes. it has been successfully accomplished at HF frequencies.

"Could this be what I have?
No.

"Might there be a way to generate a CP signal with one connection?"
No.

How would this work with an omni?
the "corkscrew" pattern as you put it would be in the vertical plane. simply view the jp4 and jp5.gif images tilted 90 degrees in the CW position with the reflector grid at the bottom.