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Old Dec 09, 2010, 08:56 PM
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Mini-HowTo
The Skew-Planar Wheel circular polarized omni antenna

These antennas are now available as DIY kits and fully assembled units. Kits can be ordered from: Video Aerial Systems and fully assembled units are available from: Video Aerial Systems and Ready Made RC.

With all of the attention circular polarization is getting, it's about time for a circular polarized omni directional antenna. So far there have only been two in the FPV world: Old Man Mike's CPOD and the Skew planar wheel first built by Nigel (Devonboy).

I had tried to develop a turnsile antenna with a little help from blupp which we called the "bluppnik" based on the attic antenna. While quite robust, we found it to be not useful as a TX antenna.

However, with the availability of circularly polarized patches in the 2.4 and 5.8 GHz band, it only made sense to pursue one that could be built for these bands.

There are other tutorials on this antenna. I found this one to be quite good: http://www.igs.net/~graham/SkewPlanarAntenna/

Warning: This antenna is very delicate and isn't very easy to build for a first timer. I would suggest building an inverted Vee first if you are a first time antenna builder. The reason it is so difficult is joining 4 wire ends to a single point on the coaxial line is rather difficult. I have a few ideas on how to overcome this, but showing how to do it will not be easy.

Lawmate RX problem: - The skew planar wheel does work with Lawmatre 1.2GHz recievers. This problem was unique to my particular setup which I fixed easily.

Demo video: This shows the advantages of a circularly polarized system. The performance difference is staggering.

IBCrazy's "New System" - Omni directional antennas (4 min 30 sec)


EDIT: Geometry video by Terry74:

The Skew-Planar Wheel (SPW) circular polarized omni antenna by IBCrazy (1 min 11 sec)


-Alex
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Old Dec 09, 2010, 09:01 PM
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Materials

You need two items:

- Some sort of stiff wire conductor (2 lengths of it just over 2 wavelengths each)
- A length of coaxial cable

You will want to use a good stiff wire. Copper is a bit too soft. I tried music wire, but I had to weld it (not solder but WELD) to get it to stick together. .030-.045 mig welder wire is great and you can probably get it from your local machine/weld shop for free

OldManMike used gold plated "memory wire" from Hobby Lobby.

I used .030" welding wire for the wheel and RG316 coaxial cable for the feed.

-Alex
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Old Dec 09, 2010, 09:18 PM
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Calculations - Your element dimensions

The antenna is made from two lengths of wire whose lengths are:

Wire length in inches = 23675/f in MHz

Or for you metric folks

Wire length in mm = 601345/f in MHz

So for:

910MHz = 26"/660mm
1280MHz = 18.49"/469.8mm
2.4GHz = 9.66"/245.5mm
5.8GHz = 4.08/103mm

Now you need to calculate your quarter wavelength which is simply 1/8 of your wire length.

Quarter wavelength in inches = 2960/f in MHz

Or

Quarter wavelength in mm = 75168/f in MHz

So for:

910MHz = 3.25"/84mm
1280MHz = 2.31"/60mm
2.4GHz = 1.2"/31mm
5.8GHz = .51"/13mm

You may notice this is a little longer than the true electrical quarter wavelength such as that is used in the BiQuad tutorial. Admittedly, I don't know why this is the case, but it appears to work best 1-2% longer than the electrical wavelength, so we'll go with it.

-Alex
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Old Dec 09, 2010, 09:26 PM
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Building the antenna - Making the S-curve

Now it's time to start building. You will start out by making an "S" curve.

Measure back from each end of the wire one quarter wavelength (as calculated above) and bend each end in opposite directions 90 degrees. You now have an elongated "S" with tips equal to your calculated quarter wavelength.

Next, we complete the "S". Measure back from each bend TWICE your quarter wavelength and bend 90 degrees in the same direction as your previous bend on that end. Do this to both ends to form an "S"

Repeat this on both lengths of wire. They should be identical.

-Alex
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Old Dec 09, 2010, 09:34 PM
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Building the antenna - Making the pinwheel blades

Now we need to bend the radius in our "S". I did this by taking my pliers and making small bends all the way around the 1/2 wavelength side until the end met with the middle of the antenna. The tip of the wire should meet the center at a ~105 degree angle. It will not (and should not) intersect at 90 degrees.

Do this to both wires. They should again be identical and should look like a figure "8".

Now take your figure "8" and twist one side 90 degrees along the central axis of the element. One radius should be flat and the other should be upright. Do this to both elements. They should be identical.

-Alex
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Old Dec 09, 2010, 09:50 PM
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Building the antenna - Soldering it all together

Now this is the hard part. Soldering this without overheating the coaxial cable is difficult.

First, mark the centers of the pinwheel blades. Now place them over top of each other 90 degrees apart. Each of the blades should set at a 45 degree angle from the "X". Solder the point where the flat lengths of wire cross. No radius should be flat at this point. If one is, you can always rebend after soldering.

You should notice that all of the tips come together at the center at 45 degree angles with the plane of the "X" and 90 degrees apart from each other. Now is a good time to tin the tips if you haven't done so already.

Connection

Now you must connect your coaxial cable. While it is probably easier (and certainly better) to do this from underneath with a really short piece of coaxial line I opted to feed mine from the side. The reason I side fed mine is because the antenna is quite large on 1280MHz and I want to lay it flat on top of my wing. Bottom feeding will be more efficient and easier. Side feeding should only be done with 900MHz-1.3GHz.

Strip about 1/2" or so off of the end of your coaxial line and pull back the shield. Wrap the shield up into a straight tail, then wrap the shield around the center of the "X" so the cable rests against the side of the "X". Solder the shield to the center of the "X" being careful not to let the elements move.

Now strip the insulation off of the center conductor leaving 3-4mm of insulation on to prevent shorting out to the shield. All 4 of the tips must be soldered to this. It isn't easy. I did this by turning up the conductor and then held the elements to it by spring tension and soldered them all in place.

That's it! You now have a circularly polarized omni antenna!

-Alex
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Old Dec 09, 2010, 09:52 PM
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Q&a

I will try to answer questions here:

Q: Will you build this for me?
A: Yes. These are part of my "new system" of FPV antennas. As much as I'd like people here to build it themselves, I understand that it is not easy and intimidating.

Q: What is the radiation pattern like?
A: Similar to a 1/2 wave dipole. About 2 dbi or so gain.

Q: Is this right hand or left hand polarized?
A: It depends on which way you bent the pinwheel. It is the opposite direction of your hand. If you curl your fingers in the direction of the bend coming off the center pin with your right hand, the antenna is left hand polarized. Both Old Man Mike's and mine are LHCP.

Q: Why left hand polarized?
A: It's just how it came out. I didn't choose before designing it.

Q: What if I polarized it in the wrong direction?
A: Twist the pinwheel 90 degrees across each other.

Q: Why should I build this antenna instead of all the others?
A: Performance. Circular polarization on both ends (RX and TX) makes a huge dfference in video quality.

-Alex
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Old Dec 09, 2010, 10:34 PM
14s 180mah should be enough...
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Alex,

I just finished up a 2 element quad design for 7.150Mhz that, due to tower height, had to have part of the elements folded back in toward the center. I found that this significantly raised the frequency of resonance, though I don't know why either. I ended up between 7 and 10% longer to get it back where I wanted it. I have yet to come across an explanation for it, but if I do, I will share it.

Of course, we are wavelengths apart in our center frequencies, and particular antenna designs in this case, but I still find it interesting that we both have run into the same issue.

I wonder if there is some sort of loading effect in both cases?

I didn't see a reduction in bandwidth as one would expect with a loaded antenna, but I only got to sweep it a couple of times before I ran out of daylight....


Nice work, BTW!

Tim
AG4RZ

Quote:
Originally Posted by IBCrazy View Post
You may notice this is a little longer than the true electrical quarter wavelength such as that is used in the BiQuad tutorial. Admittedly, I don't know why this is the case, but it appears to work best 3-4% longer than the electrical wavelength, so we'll go with it.

-Alex
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Old Dec 10, 2010, 09:36 AM
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THX! Ib, gonna build one soon.

I found this tutorial for a 50ohm helix, just forgot about the dish.
http://ve2zaz.net/SatAnt/2400Dish.htm

-Hugo
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Old Dec 10, 2010, 09:39 AM
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Good idea to start a seperate thread dedicated to CP Alex.

Another good link regarding the Skew-Planar CP antenna is here:
http://www.slvrc.org/902band/skewplanar.htm

Both OMM and myself have had some correspondence with the authors of the links above, so please don't everyone with an interest start emailing them separately.

The Skew-Planar or PinWheel as OMM has called it, is very much an antenna in it's infancy and the more people who build and test them, the better and the greater will be our understanding of it.
Of all the CP antennas that might be suitable for the VTx, the S-P has a great omni-directional radiation pattern and near perfect match to 50 ohm coaxial cable.

To take full advantage of the Circular Polarity on the VTx, a same polarity CP antenna is required on the VRx.
If you have a decent CP patch, you're half way there (just make sure you know it's handing and make the VTx the same hand i.e. RH or LH).
Alternatively, a helical is not too difficult to build and even more gain can be obtained from a helical.

CP explained with pictures:
http://sv1bsx.50webs.com/antenna-pol/polarization.html

S-P plots

Azimuth



Elevation


Nigel.



Edit
Alex,
Your frequency numbers are off - from the links the calculations are +4% over normal frequency calculations and I quote:

N.B. Testing and analysis has shown that the elements should be
slightly more than one wavelength long ( WL x 1.0443 ).

The factors to use are: 31329 / F (centimeters) or 12334 / F (inches) long.

This antenna is broad in frequency response. In practice, element lengths are not supercritical.

/Edit
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Old Dec 10, 2010, 10:27 AM
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Nigel,

I think you should see how I built it. My numbers are double those numbers. Why? I'm using 2 wires instead of 4 Your factors are for each element. My wire encompasses 2 elements to make this easier to build.

-Alex
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Old Dec 10, 2010, 10:56 AM
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OK - get your idea now.

Only thing I can see is that the elements will be slightly off centred with your method.
I wonder whether this will have a detrimental effect to the CP pattern or not?

From my previous attempts at CP, the slightest deviation or miscalculation and CP is affected.

Both OMM and my builds were with 4 individual elements.

Nontheless, it's good to experiment

Nigel.
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Old Dec 14, 2010, 12:50 PM
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My first attempt, 2.4ghz pin-wheel:
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Old Dec 14, 2010, 01:28 PM
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Well done! What did you use for the wire?

-Alex
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Old Dec 14, 2010, 01:51 PM
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It's 20g copper wire, so the antenna is very soft. I made it for testing purpose only.

Then, I came with the idea of a radome or maybe even make a demi-sphere mold and encase the antenna is self expanding foam (insulation foam).

-Hugo
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Old Dec 14, 2010, 01:58 PM
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Good first effort.

I wouldn't encase it in anything - it will effect it's performance by adjusting it's resonant frequency and probably for the worse.

OMM had a good idea with the gold plated, spring steel type 'memory wire' you can get from online stores or as I did, a local 'beads and bangles' shop (women are predominant in these shops and I was questioned why I wanted the memory wire !!!).

2nd pic down in OMM's post
http://www.rcgroups.com/forums/showp...&postcount=256

Nigel.
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Old Dec 14, 2010, 02:13 PM
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Encasing it wouldn't be bad if you knew the dielectric constant of the material. Then you could compensate for the frequency shift. Typically the dielectric makes the frequency shift downward. However I would guess that a gorilla glue/water mix on the feedpoints would stiffen up the antenna significantly and not shift the frequency too much.

Maybe I should make a mock up and encase the whole thing. If anybody has access to an SWR meter or directional wattmeter, I'd be glad to make a few and do some experiments.

-Alex
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Old Dec 14, 2010, 02:39 PM
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Bad news with Gorilla glue or anything similar as it's hygroscopic (absorbs moisture) and will be like putting a damp sponge on the feedpoint.

Why not just leave it bare?

Nigel.
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Old Dec 15, 2010, 05:28 AM
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Encasing will add tons of drag to the plane


I love this thread and all the info IBCrazy is sharing about antennas (in this thread and in all the others), thanks mate!

I´d like to build a tx antenna for 5,8ghz, but I´m not sure what would be the best option. My doubt is between the Skew and the Vee (90 degrees), but the vee should be at least 5/2 wavelenght, and I want an antenna as uniform (spheric pattern) as possible, because what I mostly enjoy is flying close range, around obstacles, and doing stunts

I´m good soldering but know nothing about RF

What do you recommend me to build?
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Old Dec 15, 2010, 05:38 AM
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Quote:
Originally Posted by AndrésMtnez View Post
I want an antenna as uniform (spheric pattern) as possible, because what I mostly enjoy is flying close range, around obstacles, and doing stunts

What do you recommend me to build?
For 5.8GHz and your requirements, the CP S-P antenna should work the best providing you make your VRx CP as well.
Another S-P on ther VRx should do well for you.

Nigel.
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Old Dec 15, 2010, 06:14 AM
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Sounds to me like the skew-planar wheel is the best choice for you. It is nice and small at 5.8GHz. I wouldn't recommend a Vee at this frequency as it is very hard to get correct. I have coaxial cables and the welding wire to make these. if you need it, I can mail it to you.

-Alex
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Old Dec 15, 2010, 10:21 AM
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Quote:
Originally Posted by IBCrazy View Post
Maybe I should make a mock up and encase the whole thing. If anybody has access to an SWR meter or directional wattmeter, I'd be glad to make a few and do some experiments.

-Alex
I have an anritsu antenna analyzer that goes from Khz to 6Ghz. I would be happy to plot graphs for you. Maybe we could skype conference call and collaborate?

-dave
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Old Dec 15, 2010, 11:09 AM
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I you both agree I can´t go wrong with the SP

Thanks!

And Alex, thanks twice for the offer, but I´m sure I can get it here without messing you around, with this thread you´ve done more than enough for me
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Old Dec 15, 2010, 01:08 PM
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Quote:
Originally Posted by dalbert02 View Post
I have an anritsu antenna analyzer that goes from Khz to 6Ghz. I would be happy to plot graphs for you. Maybe we could skype conference call and collaborate?

-dave
PM me your address. I have many antenna designs I would like tested The Vee has already proven itself and the BiQuad has empirically when compared to a patch or Yagi.

If you could document your findings it would greatly help the community. I am constantly researching new antenna systems.

-Alex
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Old Dec 15, 2010, 05:59 PM
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I PM'ed you. I would be happy to test anything for you or anyone else provided it does not cost me anything. I did make a mistake above; my Anritsu only goes from 25Mhz to 4Ghz. I do have an MFJ antenna analyzer for the kilohertz stuff but I can not test 5.8Ghz gear yet. I am trying to purchase a new antenna analyzer and spectrum/serivce monitor that goes to 14Ghz but money is tight where I work. I can justify the purchase as we are now doing Ku sat comms, but if there is no money, there is no money regardless of the need or desire.
-dave
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Old Dec 15, 2010, 07:11 PM
14s 180mah should be enough...
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K4UAV de AG4RZ

RE the MFJ analyzers...after having a couple and being less than impressed with them (mighty fine junk...had to rework the boards in both, and they were assembled with sub-standard components...) I gave in and bought the Mini VNA Pro.. http://www.miniradiosolutions.com/miniVNA_PRO.php
Give it a look if you find yourself in need of a good 200Mhz and down analyzer!

Tim
AG4RZ
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Old Dec 15, 2010, 07:13 PM
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Encasing will add tons of drag to the plane
I'm a Newbie when it comes to FPV flying, but I am passingly knowledgeable about fluid dynamics, and what I know tells me that any wire hanging out in the wind creates turbulence, and thus, drag. (This, incidentally, is why you see those strange disc and "airfoil" style spoked wheels on racing bicycles. Traditional wire-spoke wheels create far too much drag.)

In order to minimize drag you want to keep as laminar a flow around the outside of your plane as possible, and thus keep it's profile as smooth and solid as possible.

Encasing an antenna of this type in some kind of dome shape would be best if you want to minimize drag. Provided the dome was worked into the profile of the plane as smoothly as possible. Something akin to a "UAV" style camera bubble would work nicely for an antenna such as this. As long as you have solid landing gear to protect it, that is.

Of course, none of that speaks to weight or signal attenuation, both of which are going to be issues on a super lightweight and low-powered craft like a model airplane.
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Old Dec 15, 2010, 07:50 PM
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@IFLYOS I have read that some people have had a hard time with their MFJ. Luckily I have not had any issues with mine, it compares favorably and repeatably with results obtained with my Bird 43 and my Anritsu S331D antenna analyzer. Thank you for your suggestion though, if my MFJ ever dies, I now have a good suggestion for an alternative.

@wearyman, I agree with your assessment. I plan to mount my antenna entirely inside the fuse (Sig Kadet Senior). I guess that is why all the support wires on old biplanes are flattened and not round, all that drag adds up!

-dave
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Old Dec 16, 2010, 04:00 AM
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Quote:
Originally Posted by Wearyman View Post
I'm a Newbie when it comes to FPV flying, but I am passingly knowledgeable about fluid dynamics, and what I know tells me that any wire hanging out in the wind creates turbulence, and thus, drag. (This, incidentally, is why you see those strange disc and "airfoil" style spoked wheels on racing bicycles. Traditional wire-spoke wheels create far too much drag.)

In order to minimize drag you want to keep as laminar a flow around the outside of your plane as possible, and thus keep it's profile as smooth and solid as possible.

Encasing an antenna of this type in some kind of dome shape would be best if you want to minimize drag. Provided the dome was worked into the profile of the plane as smoothly as possible. Something akin to a "UAV" style camera bubble would work nicely for an antenna such as this. As long as you have solid landing gear to protect it, that is.

Of course, none of that speaks to weight or signal attenuation, both of which are going to be issues on a super lightweight and low-powered craft like a model airplane.
But that´s not the correct comparison. The comparison would be if the wire-spoke wheel would have to move perpendicular to the disc, or the bike moving sideways, that would be the correct comparison with our case

I know a wire have drag, but I think it´s much less than if you block completely the air. With a case you´re higly increasing the friction surface, not like the wheel of a bike, in that case scenario the friction surface is always the same, so the disc help becasuse the surface is smoother, but with the SP antenna the surface would increase a lot, and thus the drag.

But please correct me if I´m wrong
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Old Dec 16, 2010, 07:50 AM
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Quote:
Originally Posted by AndrésMtnez View Post
But that´s not the correct comparison. The comparison would be if the wire-spoke wheel would have to move perpendicular to the disc, or the bike moving sideways, that would be the correct comparison with our case

I know a wire have drag, but I think it´s much less than if you block completely the air. With a case you´re higly increasing the friction surface, not like the wheel of a bike, in that case scenario the friction surface is always the same, so the disc help becasuse the surface is smoother, but with the SP antenna the surface would increase a lot, and thus the drag.

But please correct me if I´m wrong
You would be AMAZED at how much drag there is from a "simple" wire.

Read the book......

Basics of R/C Model Aircraft Design by Andy Lennon.... chapter 12, page 52.
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Old Dec 16, 2010, 09:49 AM
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You would be AMAZED at how much drag there is from a "simple" wire.

Read the book......

Basics of R/C Model Aircraft Design by Andy Lennon.... chapter 12, page 52.

Well said.

The trick, as I noted above, is to keep the airflow "laminar". That is, uninterrupted and smooth. The size of the object in the fluid flow is actually far less of an issue than the shape and the way it allows the fluid to flow around it. While surface friction can be a problem, it is less of an issue than that of a wire hanging out and breaking up the airflow into a turbulent pattern.

If you really wanted to go hog-wild with it, studding the dome surface with golf ball style pocks would go even further to reducing drag as this creates a "buffer" of air around the dome, allowing airflow to be even less disturbed and smooth.

Something else that has occurred to me is that unless you will be using VERY stiff and hard wire, an antenna shape such as this would be very prone to air pressure distortion if left hanging out in the wind. Since this kind of antenna is shape-dependent for it's function, distortion could put it out of phase and keep it from working correctly. So a very thick and stiff (and heavy, relatively speaking) wire would have to be used.

Even then, it would be prone to vibration and it's attendant stresses on all of the solder points, making mid-flight failure a serious possibility.

No, I think that some kind of "dome" or "pod" would almost be a necessity for this type of antenna.
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Old Dec 16, 2010, 10:38 AM
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All very good arguments, but the aerodynamics of an FPV ship is already that of a brick !

Nigel.
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Old Dec 16, 2010, 11:38 AM
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... No, I think that some kind of "dome" or "pod" would almost be a necessity for this type of antenna.
Not necessarily true based on the flying I've done with my implementation of the antenna. A few points should be noted.
  1. The steel gold plated memory wire is only 0.022 inches in diameter. With the hemisphere type construction, the antenna is very resistant to distortion. It can support a 6 ounce paperback book laid on top without any damage. It will compress a little but springs right back when the book is removed.

  2. As a quadcopter flyer, the maximum speed I've ever seen is 40 miles per hour for a 45 degree power dive. With the very small diameter wire, there is just not enough wind resistance at that speed to cause a problem. Here is an approximate measure of the wind resistance:

    45 mph exerts a force of approximately 3.3 lb/sq foot for a cylindrical object like wire. About 4 inches of the 0.022 inch wire is exposed for any direction of travel which is about 0.01 sq foot. So the total wind force on the antenna is only 0.5 oz. The antenna can handle 10 times that amount. With only 0.5 oz of force, there will be no significant distortion of the antenna.

  3. Of course wind resistance increases with the square of the speed so if you are flying a jet or very fast plane then this is probably not the antenna for you.

  4. Finally I have made a lot of flights with this antenna on my quad measuring the Polarity Axial ratio and noticed no redution of peformance when flying fast or slow. Any significant distortion of the antenna would have noticeably reduced that ratio.
OMM
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Old Dec 16, 2010, 01:05 PM
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Not necessarily true based on the flying I've done with my implementation of the antenna. A few points should be noted.
  1. The steel gold plated memory wire is only 0.022 inches in diameter. With the hemisphere type construction, the antenna is very resistant to distortion. It can support a 6 ounce paperback book laid on top without any damage. It will compress a little but springs right back when the book is removed.

  2. As a quadcopter flyer, the maximum speed I've ever seen is 40 miles per hour for a 45 degree power dive. With the very small diameter wire, there is just not enough wind resistance at that speed to cause a problem. Here is an approximate measure of the wind resistance:

    45 mph exerts a force of approximately 3.3 lb/sq foot for a cylindrical object like wire. About 4 inches of the 0.022 inch wire is exposed for any direction of travel which is about 0.01 sq foot. So the total wind force on the antenna is only 0.5 oz. The antenna can handle 10 times that amount. With only 0.5 oz of force, there will be no significant distortion of the antenna.

  3. Of course wind resistance increases with the square of the speed so if you are flying a jet or very fast plane then this is probably not the antenna for you.

  4. Finally I have made a lot of flights with this antenna on my quad measuring the Polarity Axial ratio and noticed no redution of peformance when flying fast or slow. Any significant distortion of the antenna would have noticeably reduced that ratio.
OMM
Interesting.

I would imagine that the steel wire you are using is probably more than stiff enough to prevent any deformation, and based on your real-world observations apparently is.

I suppose I erred in assuming that copper wire was going to be the construction material. Since that metal is so soft, one would have to use a heavy gauge wire to prevent deformation. Steel is unlikely to have issues with that.

Also, I wouldn't expect there to be much of a turbulence issue on a quadcopter arrangement anyway, as it is basically a "brute force" type of flight mechanism, so the entire process is a turbulent one already.

Of course, as DevonBoy mentions, many FPV systems are already severely compromised on aerodynamics already, so it might not end up making a difference. (Although I do wonder if a little more attention to smoothing out the lines of the craft might increase flight times and handling characteristics. Or at least tone down those uber-loud pusher engine planes a bit.)

I guess I was just thinking more along the lines of "general rule of thumb" when it comes to airflow and overall efficiency.
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Old Dec 16, 2010, 01:38 PM
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I suppose I erred in assuming that copper wire was going to be the construction material. Since that metal is so soft, one would have to use a heavy gauge wire to prevent deformation. Steel is unlikely to have issues with that.
Copper wire can also be used.
You can use 'hard drawn' copper wire.
I have an HF long wire, with a trap (for 40 metres) part way along, that has been in use for more than 10 years and never broken. The wire is 2mm (14 gauge) and 56 feet long.

Nigel.
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Old Dec 16, 2010, 07:16 PM
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Did anyone tell you it looks like a flower....
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Old Dec 17, 2010, 12:23 AM
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Did anyone tell you it looks like a flower....
It looks most like a PinWheel. It even functions like a pinwheel since the circular polarization matches the way a PinWheel turns in the wind.

I most often refer to the antenna as a Pinwheel.

OMM
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Old Dec 17, 2010, 03:10 PM
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OMM and IBCrazy, any thoughts on a egg beater antenna? Would that not be easier to construct and just as good for our purposes?
-dave
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Old Dec 17, 2010, 03:46 PM
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OMM and IBCrazy, any thoughts on a egg beater antenna? Would that not be easier to construct and just as good for our purposes?
-dave
Nope. I've built one and found that it just does not maintain a good axial ratio at low elevations. The ground plane requirement would also make it more difficult to mount on the air platform.

OMM
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Old Dec 17, 2010, 04:01 PM
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I also replied to you over on RC-Cam forum.

Quote

The eggbeater by ON6WG is mostly end fire (for CP) and the clue is at the foot of page 1 of this pdf
http://on6wg.pagesperso-orange.fr/Do...Part1-Full.pdf

I quote:
"At the horizon the polarization is linear and horizontal. As the elevation increases, the polarization
becomes more circular, proportional to that increase in elevation."

It also has the complexity of requiring a quarter wave coax to achieve phase shift.

/Qoute.

Nigel.
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Old Dec 17, 2010, 04:43 PM
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It looks most like a PinWheel. It even functions like a pinwheel since the circular polarization matches the way a PinWheel turns in the wind.
I have difficulties to tell left or right polarisation of the pin wheel.
The one I posted in the beginning..., can you tell me which way it is?
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Old Dec 17, 2010, 04:54 PM
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Hugeone - Yours is Right Hand Circular Polarisation (RHCP)

Looking at the antenna sideways on - if the elements 'point' upward to the right, it's right hand (RHCP).
If the element 'points' upward to the left, it's left handed (LHCP)

Nigel.
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Old Dec 17, 2010, 08:43 PM
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Thank you OMM and Nigel for your input, I appreciate it.
-dave
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Old Dec 18, 2010, 09:03 AM
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Another way to figure out polarization is what I call the "hand wrap rule". Take your hand and curl your fingers around the bend in the antenna toward the flat part. Which hand did you use? Polarization is opposite of that hand.

-Alex
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Old Dec 18, 2010, 09:22 AM
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Thx Nigel aqnd Alex!

I'm looking for a good rx antenna to go with it.
The flytron's CP patch look small and light, 11dbi is great. However I'm not sure about it's performance as far as CP goes, is it LHCP or RHCP? I emailed them about it, no anwser.

Or a DIY helix, I have a gut feeling they might do better than CP patch.

-Hugo
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Old Dec 18, 2010, 11:46 AM
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I just sent a helical antenna out for testing today. I hope to have the results back by the first of the year or so. dalbert is doing the testing.

The problem with the helical antenna is that the impedance is about 140 ohms. You can match 100 ohms with A split run of 75 and 50 ohm coaxial cable, which will get you close. However, I tried an impedance transformer as proposed by Jason Hecker. We will see how well it works.

-Alex
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Old Dec 18, 2010, 11:51 AM
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I seen a guy that use copper strip that follow the first quarter of turn at a precise distance from the reflector, see it here:



He say it bring the impedance to 50ohms.

I found some reading on it:
http://www.rac.ca/tca/2005-11-Articl...e%20Fowler.pdf

-Hugo
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Old Dec 18, 2010, 01:12 PM
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I have seen tons of ways to match it.

- One used a shunt (which I actually tried and calibrated but couldn't get it to work well)
- Another used a single wire for the reflector rather than a plate
- Another used a triangular impedance transformer (Jason Hecker)
- Another used a close parallel wire as one turn to make a 50 Ohm matched transmission line.

While I see how all of them would work in theory, practice as we all know is totally different. We shall see how my helical turned out soon enough

-Alex
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Old Dec 27, 2010, 09:29 PM
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I tried an impedance transformer as proposed by Jason Hecker. We will see how well it works
Jason's design have measurement based on antenna coil floating in air, however his helix is wound around a PVC pipe...?


I made another pin wheel from memory wire, however I'm wondering about the part where I solder the ground. See, I solder over the shoulder of the coax crimp (0,033") thinkness. Does the element measurement need to start where it leave the ground? I know I may be spliting hairs, however I plan to build one for 5.8ghz...

-Hugo
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Old Dec 27, 2010, 10:08 PM
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Jason's design have measurement based on antenna coil floating in air, however his helix is wound around a PVC pipe...?
PVC will lower the resonant frequency a bit but it is hard to say how much without measurement. It probably is not that significant and the Helix is fairly broadband anyway.


Quote:
Originally Posted by Hugeone View Post
I made another pin wheel from memory wire, however I'm wondering about the part where I solder the ground. See, I solder over the shoulder of the coax crimp (0,033") thinkness. Does the element measurement need to start where it leave the ground? I know I may be spliting hairs, however I plan to build one for 5.8ghz...

-Hugo
The construction looks good to me, at least for 1200 Mhz. In general I have found that the Pin Wheel antenna most often resonates a bit lower in frequency when cut to the recommended formula. I suspect it is mostly from the extra length of center conductor adding to the loop. 5.8 Ghz is really getting up there where even the amount of solder used makes a difference.

OMM
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Old Dec 27, 2010, 10:48 PM
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instead of thick PVC I've seen this antenna that uses a very thin, clear plastic:

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Old Dec 28, 2010, 09:28 AM
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I just got some results back from dalbert. It appears the helical is truly wide band. however VSWR goes all over the place bouncing from 2.1 to 1.15 in a 300 MHZ wide band using the Hecker impeadance transformer.

Coming soon: Bluppnik (designed by Blupp), turnstile, Caltrop (my own design), helical, and cloverleaf.

Just when I thought I was done with antenna tutorials, there are 5 more to research and write. I'm never going to get any sleep...

-Alex
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Old Dec 28, 2010, 11:12 AM
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I'm never going to get any sleep...
Have childs? if not, you ain't see nothing

Did you saw this helical tutorial?
http://safe-pc.net/helical.html

He built it with a size factor of 0.67, because he claim PVC lowered resonant freq. significantly.

-Hugo
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Old Jan 19, 2011, 05:18 PM
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Hugeone, is your antenna also LHCP? Any flight reports with it yet?
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Old Jan 19, 2011, 07:31 PM
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Hugeone, is your antenna also LHCP? Any flight reports with it yet?
Mine is RHCP, I built two and made a few indoor test and found it reduce ghosts in the image (caused by multipaths) Flight tests will be this spring for me.
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Old Jan 21, 2011, 10:04 AM
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I finally figured out how to tell polarization. It is basically just the angle of the "blades" in the pinwheel. Can't wait for flight tests.
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Old Jan 21, 2011, 10:47 AM
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The construction looks good to me, at least for 1200 Mhz. In general I have found that the Pin Wheel antenna most often resonates a bit lower in frequency when cut to the recommended formula.
I noticed this too and it was confirmed by Dave (dalbert02) I made one for 2510 MHz and it resonated best at 2450MHz. I have since adjusted my formulas to reflect this.

-Alex
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Old Jan 25, 2011, 07:46 PM
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Kinda big.

So here is mine. I hope to build the helical to go with it later this week. It wasnt as hard as I thought, just a little tedious.

The steel I used is very strong. It is like music wire but it comes out of power/phone lines or something (my dad salvaged it). It is very stubborn and hard to bend and .060" thick.
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Old Jan 25, 2011, 08:01 PM
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Does this seem ok? Really wasnt sure of any options other than moving the Vtx big time.
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Old Jan 26, 2011, 03:56 AM
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Put that antenna in the center of the airplane. The drag on it is surprisingly high. Build another one for your RX now and watch how great the world of circular polarization can be

-Alex
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Old Jan 26, 2011, 07:01 AM
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Will it be ok right next to te esc? In the center of the plane, it will be right over it.

I plan on building the lowest gain helical to try, but yes, another SP might be a good starting point..!
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Old Jan 26, 2011, 08:59 AM
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Right over the ESC should be fine. I see no reason why it wouldn't be. The antenna is so large that the coupling effects of the ESC should not deter the antenna. Also you are using such low power I seriously doubt the antenna will adversely affect the ESC.

Please do try a 3 turn helical with this. It will have almost the same range as a Vee and a patch but it will be much cleaner video.

-Alex

-Alex
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Old Jan 26, 2011, 09:39 AM
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So here is mine. I hope to build the helical to go with it later this week. It wasnt as hard as I thought, just a little tedious.

The steel I used is very strong. It is like music wire but it comes out of power/phone lines or something (my dad salvaged it). It is very stubborn and hard to bend and .060" thick.
How did you solder the steel together, or did you have to weld?
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Old Jan 26, 2011, 09:45 AM
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Strangly this steel is easy to solder with a 40w iron. But it is not the type of steel you get at the hobby store. It is TOUGH, hard to bend, and less malleable (it breaks easily if bent a couple of timer). It must be high carbon, or tempered or something. Very strange, but it comes out of phone lines so it must be designed for tension.

I also have mig welder wire as Alex mentioned. I did not try it as mine is flux core I think, but it is much easier to work with.
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Old Jan 26, 2011, 11:44 AM
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Any ETA on flight tests? I am getting a bit pissed off at the manufacturer of my CP patch. They don't state if RH or LH and I am trying to find out but no answer back from them in over a week. I am beginning to wonder if they are selling a cross polarized antenna instead of a true CP antenna.
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Old Jan 26, 2011, 12:01 PM
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If weather is ok this weekend. I am gonna try to build the helical tonight to go with it. At minimum another SP.

Unfortunatly I do not fly long range here in the city, so I will not have any distance test info for you but mybe video quality will be revealing.

Most Antennas have the polarization in the part number, right? My 2.4 patch PN is HG2409PCL-SM..the CL means Circular Left, I think, as the right hand one is HG2409PCR-SM

http://www.nghobbies.com/cart/index....roducts_id=163 & http://www.nghobbies.com/cart/index....roducts_id=164

Or are you talking about Cercom? I am not sure of its polarization but from looking at the pics of it uncased it looks much like the rccam GP patch, which was an attempt at CP that ended up being just linear....
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Old Jan 27, 2011, 03:26 PM
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They got back to me, but don't know the polarization so I assume it isn't true CP. Here is a dumb question... I know that the gain of an antenna is the shape of the beam, not the distance, but is it related to distance at all? In other words is there anyway to judge relative distance performance between antenna types by the gain? Ie will a 14dBi CP patch perform the same as a 14dBi CP helical?
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Old Jan 27, 2011, 05:58 PM
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They got back to me, but don't know the polarization so I assume it isn't true CP. Here is a dumb question... I know that the gain of an antenna is the shape of the beam, not the distance, but is it related to distance at all? In other words is there anyway to judge relative distance performance between antenna types by the gain? Ie will a 14dBi CP patch perform the same as a 14dBi CP helical?
It's not really a fair comparison, but here's how you need to look at it:

An antenna covers a volume of space we'll call "V".

Now the gain of an antenna is how much that volume is compressed and directed. Every 6 bd increase doubles the effective range in the antennas main lobe. So a 14 dbi has a single oblong lobe that stretches out to 4X the range of the 2dbi whip.

Now with true circular polarization, theoretical gain is about 3db or so less than linear. patches are seldom truly circular, where helicals are circular. So your helical will likely do better with a circular on the plane than the patch. However the patch will likely do better with a linear on the plane than the helical.

-Alex

BTW - I just made a demo video of two skew-planar wheels against the Vee and whip. The improvement is nothing short of staggering.
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Old Jan 27, 2011, 05:59 PM
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Are you posting it here? Look forward to that.
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Old Jan 27, 2011, 07:35 PM
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Demo video

I'll let the video do the talking. Flown today from my backyard.

IBCrazy's "New System" - Omni directional antennas (4 min 30 sec)
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Old Jan 27, 2011, 07:49 PM
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Wow. Well there it is!
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Old Jan 28, 2011, 09:47 AM
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Confused...I skimmed through a bunch of the posts and pics here and can't find info that says what goes where on the plane and ground station?

I understand that you want to go circular-VTx to circular-VRx but does that mean you have to have one of these one the plane and on the ground? Where on a plane would you mount something like this? How does it hold up to 50mph winds? ...I would imagine a 910mhz version would be too big and ungainly for an RC plane?? I watched Alex's video but it didn't really show what was mounted where.

Thanks for any guidance...photos and/or video would be great!
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Old Jan 28, 2011, 09:50 AM
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Ok my bad...I see it in Alex's video now. It flashed by so fast that it took a few passes before I realized what I was looking at.

Still it would be great to see more examples photos and video!

Quote:
Originally Posted by AdamChicago View Post
Confused...I skimmed through a bunch of the posts and pics here and can't find info that says what goes where on the plane and ground station?

I understand that you want to go circular-VTx to circular-VRx but does that mean you have to have one of these one the plane and on the ground? Where on a plane would you mount something like this? How does it hold up to 50mph winds? ...I would imagine a 910mhz version would be too big and ungainly for an RC plane?? I watched Alex's video but it didn't really show what was mounted where.

Thanks for any guidance...photos and/or video would be great!
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Old Jan 28, 2011, 09:56 AM
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The best deal is CP on plane and GS. If you have one CP and one linear, you automatically have a 3db loss. However, that loss is pretty constant, so you theoretically do not have a higher loss than that in a bank, where with linear the more you bank the more out of polarization you are.

I can get pics tonight for you but I mounted mine on my Stryker just in front of the motor, dead center of the plane on the top. Mine is 1280 mhz and is pretty big at probably 5" diameter and 2.5" tall. It is draggy, but a choice you have to make. My Stryker seems to fly fine without it, but I'm sure you would feel it on a glider.

According to a previous post by OMM ( I think in this thread actually), it does not have enough surface area to deform under most regular wind conditions, both in his calculations and actual testing. On my Stryker which probably acheives 50mph, I had no problem so far.

I would say at 910mhz it would be unweildly for many smaller planes. I would just guess it is 30 ish% bigger than mine so 6.5" x 3" or so. But i am just guessing, you might run the calculations to be sure.
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Old Jan 28, 2011, 10:00 AM
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I hope to do a LOT of flying Saturday morning to really see what she can do. I may move it to my E* since it has OSD and I can see range, alt, speed, etc. Weather is supposed to be good.

Look up a few posts to see the SP on my Easy Star. Also see Alex's thread on helical antennas to see his version of a CP RX antenna. Mine is on there too.
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Old Jan 28, 2011, 11:40 AM
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Derek, I don't know if you have an LRS system or not, or at least a RTH feature, but it would be nice to see performance out 3 mile or so. Not sure if you normally fly that far out, but my concerns are if the omni directional nature of the SP signal doesn't decrease effective performance at greater distances. I guess that is where the high gain of the helical comes in to pull in a weaker signal. That fact that you don't have the 3dB loss anymore, probably really helps here. Can't wait for more video.
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Old Jan 28, 2011, 12:00 PM
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Unfortunatly I fly 72 mhz, no RTH (no OSD either usually) so 1 mile is my personal best, and I had a few PCM glitches at that distance here in the city. I may need to invest in a LRS but I have had a lot of fun within that range.. Once the Thomas Schrerrer LRS is in stock at RMRC I may have to get one.

Either way I will not be able to test it to that extent and share with you guys. My RC control just isnt capable. Maybe Alex will in time reveal some more experience with us on LR performance since he has a DL I think.
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Old Jan 28, 2011, 02:11 PM
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I am living a bit vicariously through others as the winter weather here sucks big time. I will be able to fully test once the weather breaks. I am just a bit worried now as I think I have no true CP GS antenna now.
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Old Jan 28, 2011, 03:28 PM
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Originally Posted by Derek_S View Post
Either way I will not be able to test it to that extent and share with you guys. My RC control just isnt capable. Maybe Alex will in time reveal some more experience with us on LR performance since he has a DL I think.
Still waiting on the dragonlink... that's fine, though. I have a lot of fun at mile 2 mile limit. You guys saw me tree skimming 2000 feet out

-Alex
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Old Jan 28, 2011, 03:33 PM
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Originally Posted by cherokee180c View Post
I am living a bit vicariously through others as the winter weather here sucks big time. I will be able to fully test once the weather breaks. I am just a bit worried now as I think I have no true CP GS antenna now.
What's the weather got to do with it? Come on. Brave the cold! Do what I do

I ride my motorcycle in sub freezing temperatures... and then get sick for several days with a serious lyctic fever... Literally.

I made those flights with the skew-wheel while running a fever of 101 degrees. I nearly collapsed on my way back in the door. I woke up earlier that morning soaked in sweat and shivering uncontrollably. All because I wanted to take the motorcycle out in the cold Sunday...

On second thought, stay inside where it's warm. Stay healthy

-Alex
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Old Jan 28, 2011, 06:09 PM
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Cold has nothing to do with it, we have been flying all winter, but the field is a swamp right now with 1' of wet snow on top. I am more worried about frying some electronic gear on my plane during landing. I am thinking an SP on the plane with a high gain CP helical, or CP patch maybe great for long distance and close by. Thanks for all the hard work and hope you feel better.
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Old Jan 28, 2011, 11:02 PM
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Built another one. I though building it in 4 parts on a pcb would be easier. Not really. the only difference is that it now does not have overlapping elements, maybe for the better, but build difficulty was similar. If I do more I will go with Alex's method, unless a performance gain is painfully obvious.
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Old Jan 29, 2011, 11:59 AM
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Ok, here it is. My 1st Antenna for 5,8GHz. I am not totally happy with the tolerances...but that is definitly the lower size limit that i can handle. Or maybe i just have to go to Alex' "Bending and Soldering"-Training camp ;-)

That thing is damn tiny, but i am proud as hell

Will report how it behaves.

Edit: Alex, THANKS FOR ALL YOUR EFFORT
Best regards
Christian
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Old Jan 29, 2011, 12:03 PM
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Looks really good in the pictures...beyond my patience probably Hopefully it works great, let us know!
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Old Jan 29, 2011, 12:53 PM
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Originally Posted by Lonestar78 View Post
Ok, here it is. My 1st Antenna for 5,8GHz. I am not totally happy with the tolerances...but that is definitly the lower size limit that i can handle. Or maybe i just have to go to Alex' "Bending and Soldering"-Training camp ;-)

That thing is damn tiny, but i am proud as hell

Will report how it behaves.

Edit: Alex, THANKS FOR ALL YOUR EFFORT
Best regards
Christian
That looks AWESOME! I think it'll do great.

The part that's the hardest for me is joining the for wires at the center of the antenna. Perhaps a small crimp collar would make it easier? You can run all 4 loops straight for a short run without affecting performance.

-Alex
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Old Jan 29, 2011, 01:03 PM
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Thanks for the flowers, Alex ;-)

For the lower "cross" i made two corresponding hollows in the two wires by filing. Then i soldered the two parts together.

After that it is actually quite easy to join the four wire ends due to the size of the antenna. Just bended them for as long as it took to align them.
Spring force does the rest :-)

The Antenna wire goes last.
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Old Jan 29, 2011, 02:22 PM
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I made my original 5.8GHz S-P in 4 parts and soldered them individually to the RG316 3mm (1/8") coax - it has Teflon jackets, and doesn't melt when you show it your soldering iron
RG316 is not rated to 5.8GHz but it was all I had at the time (worked OK as best I can tell).
I now use CLF200 coax at 5.8GHz but have to be careful as the inner jacket will melt easily.

Pics attached...

Nigel.
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Old Jan 29, 2011, 02:39 PM
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Derek, What happened to your flying today? Did you not get to go?
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Old Jan 29, 2011, 02:47 PM
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Well, I went, and had some problems so I ditched. My field was having a youth soccer game, and I avoid flying around cars and people if I can. Also, I had annoying servo glitching on my Stryker's HS82mg servos which I did not recall from the other day. Maybe i just didnt notice. I moved the SP antenna forward away from them wich helped, but not perfect.

I need to find better servos before I fly safely it I think I did do one flight, but it was uneventful. I can upload that vid if you like to see anyways?

I am now at home reworking my EasyStar to include the CP antenna, a 12v stepup for the 1280 tx, and some other things. Maybe it will be a good day tomorrow.
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Old Jan 29, 2011, 08:52 PM
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I've never actually built an antenna before, maybe this was not such a good entry point I do not envy anyone who has to build one of these for 5.8ghz, because I just tried it. They are dinky! Don't worry about the blobs on the elements, that is just some kicker that I did not wipe off from when I strengthened the joints with CA.

At 26mm wide, it is small enough to fit inside a ping-pong ball for mounting on my quad. How would this affect it's performance?
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Old Jan 29, 2011, 09:06 PM
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Sarge - that looks great especially for a first antenna! Bending the ends in is fine. geometry on this antenna isn't super critical, but element length is.

You can put it inside a ping pong ball without problems.

I can't wait to hear about the flight tests. Perhaps the next antenna for you is a helical for your RX?

-Alex
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Old Jan 29, 2011, 09:58 PM
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Hey, that would be cool, split a ping pong ball and mount it inside and then glue the ball back together. Kind of like a Doppler Radar ball on the plane.
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Old Jan 29, 2011, 10:23 PM
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It would be nice! The 1280 antenna is just a little big. I wish mine were that size.
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Old Jan 29, 2011, 11:06 PM
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I have made a second one so that I can have the same at both ends. When I do a video shoot I tend to do a whole area at once rather than going for distance, so I prefer omni's over a patch. If I had a tracker that would change the story but not at the moment.

My second one is better than the first in terms of element length and proper angles, I presume that these are more critical on the TX end?
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Old Jan 29, 2011, 11:12 PM
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Can you tell me what 5.8 system you are using and what you thinK? Range, quality, intereference, etc? Are you having multipath probs, thus the CP antennas?
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Old Jan 29, 2011, 11:31 PM
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I'm using the Foxtech 200mW system which is available at a bunch of places under different names. Build quality is good, when it is clear of interference the picture is fantastic. I have heard that 5.8ghz is prone to multipathing so I am going to try these to see the difference. I know that I can often fly through fuzz and get clear picture shortly after. If this is multipathing then the CP's should improve things. Time will tell.

ibcrazy: What should the impedance be on this antenna for 5.8Ghz? I have been warned against using unmatched antennas.
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Old Jan 30, 2011, 02:18 AM
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Nice built :-)
I also use the foxtech/sky-rf 5,8Ghz rx/tx combo.
Pretty good in terms of picture quality.

Ahh, and btw: good idea about the pingpong ball.
Will try that as well.
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Old Jan 30, 2011, 04:09 AM
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When the dimensions and shape are correct, the Skew-Planar is a good match for 50 ohm systems.

Nigel.
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Old Jan 30, 2011, 11:51 AM
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Been busy

From left, 2.4-2.5 and 5.8ghz

Mines are built in four pieces. I slot the sma ferule in a + shape, so the wires are held in the slots.

-Hugo
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Old Jan 30, 2011, 07:06 PM
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Hugeone, are you making them to attach directly on top of the VTx transmitter? Does this antenna need any height to avoid the signal being blocked by the batteries and other things on the plane? I had to elevate my V antenna up to avoid blind spots caused by certain gear on the plane.
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