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Twin X-Mount Dipole Idea

And if you want to see what any particular antenna will do, then by all means do so, give it a shot. I also understand why Lou would tell you to start with something simpler. It would, at the minimum, give you some experience dealing with tubing etc. Give you a 'feel' for what sizes can mean with weather etc.
Good luck.
- 'Doc

Thanks.
I had planned originally to make a CP beam with just a reflector and still might do that. Getting the antenna's impedance at the feed points looks mute without a analyzer though. However,there is no mention of using an analyzer to tune the antennas. A SWR meter is the sole device mentioned. The tuning process begins with adjusting the air-variable capacitor for lowest SWR and then the gamma match. It mentions to go back and forth from the capacitor to the gamma match to get the lowest SWR. It also mentions to use the SWR meter directly hooked up to the antenna with a coax jumper no longer than two feet long. It says to tune the antennas at their operational height. Personally,I'm not going to attempt that.
 
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Circular polarization can be beneficial in any case where the signal polarity between stations cannot be held stable and the polarization will be expected to change. This happens anytime a signal is reflected back to the other station rather than direct wave line of sight propagation. Examples include satellite communication, moonbounce, VHF and UHF signals experiencing multipath reflections off buildings or terrain and all skywave DX signals reflecting off the ionosphere.

I've used CP for working DX and it can be very helpful and difficult to construct properly. Some of the key construction points are using sets of elements that are as symmetrical as possible. Any imbalance between driven elements will skew the pattern and prevent the CP pattern from forming. The same is true if the phasing harness feeding the driven elements does not provide an exact 90 degree phase delay between the two. The result will be "elliptical polarization"

The idea that "you can't keep a CP antenna in the air very long on this band" is not true. Tens of thousands of "CP ready antennas" have been in the air for decades. Any dual polarity antenna from a PDL-II to the Laser 500 is all that needs to be in the air to make CP. It's how you connect the two feedlines together that determines the difference between CP or VP and HP.

Some people may not realize how often a DX signal will shift polarity on the receiving end. Depending on conditions this can happens dozens of time per minuet. The majority of signal fluctuation we see during DX conditions is not because the path between the two stations has improved or deteriorated, it's because the signal polarity is rotating in and out of a polarization that matches your antenna!

When the polarization is completely mismatched, the signal can easily be attenuated by 20 db. That's the difference from being full copy in DX when the polarization matches, to being lost in the pileup 10 seconds later when the polarity shifts. The advantage CP offers is keeping your station in ALL polarities at one time to prevent this signal loss due to polarization changes resulting from the signal being reflected.

The bad news is this advantage will also cost you 50% of your output power to create. Since you are driving two elements, the total output power will be split between them. That will cost you 3 db whenever the polarization matches the physical orientation of one of the sets of elements on your antenna. In other words if you are talking to a completely vertical of horizontal station, you will be 3 db lower using CP.
 
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Circular polarization can be beneficial in any case where the signal polarity between stations cannot be held stable and the polarization will be expected to change. This happens anytime a signal is reflected back to the other station rather than direct wave line of sight propagation. Examples include satellite communication, moonbounce, VHF and UHF signals experiencing multipath reflections off buildings or terrain and all skywave DX signals reflecting off the ionosphere.

I've used CP for working DX and it can be very helpful and difficult to construct properly. Some of the key construction points are using sets of elements that are as symmetrical as possible. Any imbalance between driven elements will skew the pattern and prevent the CP pattern from forming. The same is true if the phasing harness feeding the driven elements does not provide an exact 90 degree phase delay between the two. The result will be "elliptical polarization"

The idea that "you can't keep a CP antenna in the air very long on this band" is not true. Tens of thousands of "CP ready antennas" have been in the air for decades. Any dual polarity antenna from a PDL-II to the Laser 500 is all that needs to be in the air to make CP. It's how you connect the two feedlines together that determines the difference between CP or VP and HP.

Some people may not realize how often a DX signal will shift polarity on the receiving end. Depending on conditions this can happens dozens of time per minuet. The majority of signal fluctuation we see during DX conditions is not because the path between the two stations has improved or deteriorated, it's because the signal polarity is rotating in and out of a polarization that matches your antenna!

When the polarization is completely mismatched, the signal can easily be attenuated by 20 db. That's the difference from being full copy in DX when the polarization matches, to being lost in the pileup 10 seconds later when the polarity shifts. The advantage CP offers is keeping your station in ALL polarities at one time to prevent this signal loss due to polarization changes resulting from the signal being reflected.

The bad news is this advantage will also cost you 50% of your output power to create. Since you are driving two elements, the total output power will be split between them. That will cost you 3 db whenever the polarization matches the physical orientation of one of the sets of elements on your antenna. In other words if you are talking to a completely vertical of horizontal station, you will be 3 db lower using CP.
Thanks. I've read up on the things you said about CP antennas and I agree with you. The plans I purchased from CBC International - books plans kits modifications repairs for CB radios has exact measurements on how to build a three element CP Beam for CB. It also has formulas for any other band there is. Yes,there will be a 3db loss using this antenna but that can be overcome by doubling the power output. My CRE-8900 deadkeys 10 watts am where as my Galaxy DX-959 only deadkeys 4 watts. I figure it will still work good. I'll just do better as far as DX'ing goes plus it will be a big step up from my 1/4 wave SS whip that I'm presently using for a base antenna. I think that the 3db loss discourages a lot of folk from using CP antennas. I can't go wrong in making this antenna and I'll be buying some Maco parts(Gamma Matches) to simplify things.
 
Well put Shockwave. (y)

You say you've use CP for DX work. Was it a yagi like the PDL II fed out of phase?
Did you have it switched to select between right and left handed?

I think doc was suggesting that the lack of performance would incite the operator to replace with a different antenna not some mechanical weakness.
ghz24,
I think the simplest 'confirmation' is that you don't see many/any used on CB or HF in general. Wouldn't you think that if they were beneficial at all that someone would be selling them? Or at least using them?
I don't have the facts and figures to confirm my opinion, but if you do a little researching I'll bet you could find them. What's the purpose of a circular polarized antenna? Where is it commonly used? That alone should give you an idea of why I don't think it's worth the bother. This circular polarization isn't 'new' by any means, and it's been discussed before.
Are you obsessed with "new" I haven't tried to show you anything new. Maybe I'll try soon. Give you a "new" fix.
But I have seen the "bond two yagis booms together with a quarter wave stagger" offered as a technique to get CP which as it turns out is pretty flawed. at 0.44 for an axial ratio.

I don't think I really need to point out that your argument against circular polarizations usefulness at HF has more to do with circular reasoning than circular polarization. I actually asked for supporting evidence/data for your assertion that CP is not useful at HF. But you give the old google is your friend !?
Are you really that obtuse you think I haven't done that?
Makes me think you haven't!
I've seen phasing harnesses sold that claimed to convert PDLII type yagis to CP.,and the author of this thread bought plans to 3 CP antennas
SO I guess someone is selling /using them.

Here is a site about someone using CP at 75 meters and reporting benefits even at that low frequency Circular Polarization on HF
Here's a nice site that includes calculating the mismatch loss from two antennas of different axial ratios and the same "sense". http://www.attplus.cz/hamradio/projekty/article/cppl_b.pdf
 
Wave Polarization and Antenna Polarization



http://www.science-bbs.com/69-electronics-design/84c3e43f1557a69a.htm

">"Antennas with orthogonal elements that are combined in phase
>quadrature such as the crossed dipole with external 90 degree hybrid
>coupler. This type of antenna can produce right-hand and left-hand
>circular polarization simultaneously."
>"Simultaneously"? Can anyone explain how this works? What is the
>confguration of the coil and how is the signal applied to produce this
>effect?

In a crossed dipole system, you can produce either RHCP or LHCP
signals depending on how the phasing harness is connected.
However, if you bring down both the horizontal as well as the vertical
dipole signal on separate cables to the RF amplifier (and possible to
the IQ down mixer), you can then create both sum and difference
signals to get both RHCP as well as LHCP signals.
IQ and MIMO (Multiple Input, Multiple Output) might be usable keywords
to limit the Google search. "
 
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An 'X' config instead if a '+'

Making RH circ and LH circ polarized antennas

"I also seem to remember seeing a system where by you mounted the antennas in an 'X' formation, rather than a '+' formation, and again you adjusted the lengths of coax. to give the correct phase delay characteristics. That could give LHC, RHC, vertical and horizontal options as well.

I'll see if I can dig some references out..."
http://www.amsat.org/amsat/archive/amsat-bb/200601/msg00143.html
http://www.amsat.org/amsat/archive/amsat-bb/199911/msg00138.html
http://www.qsl.net/i0jx/4pol.html
http://www.qsl.net/dk7zb/Cross-Yagi/crossyagi.htm
http://hjem.get2net.dk/ole_nykjaer/oz2oe/xyagi/xyagi.html
http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=4045
http://www.nitehawk.com/sm5bsz/polarity/simplesw.htm
 
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I could be wrong but MIMO doesn't use CP.. CP is not even allowed on 2.4 GHz (Legally).
MIMO does use polarization diversity to create multiple "channels "
All CP antennas create some cross-polarized component. This is undesirable and degrades the axial ratio.
I'm pretty sure "simultaneously" was misused to say the sense can be switched without physically altering the antenna. A linear polarized antenna shows exactly equal left and right handed components. But the "sense" is zero instead of 1 or -1
 
I could be wrong but MIMO doesn't use CP.. CP is not even allowed on 2.4 GHz (Legally).
MIMO does use polarization diversity to create multiple "channels "
All CP antennas create some cross-polarized component. This is undesirable and degrades the axial ratio.
I'm pretty sure "simultaneously" was misused to say the sense can be switched without physically altering the antenna. A linear polarized antenna shows exactly equal left and right handed components. But the "sense" is zero instead of 1 or -1

Well,I'm a noob at all of this so I am the student. I'm doing research and am learning about all if this. At this moment,I'm checking up on switching relay systems that can allow me to run the CP antenna either linearly or in a CP mode of operation. Here's a diagram I found that supports this
.
P.S. here's the link for this diagram. Looks promising.


http://www.qsl.net/i0jx/4pol.html

http://www.nitehawk.com/sm5bsz/polarity/polcal.htm
http://www.nitehawk.com/sm5bsz/polarity/polcal.htm#AMPADJ
 

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