|Feb 11, 2011, 08:23 PM|
Build IBCrazy's Cloverleaf - The ultimate circularly polarized aerial antenna!
These antennas are now available fully assembled units called the "BluBeams" and are available from many FPV stores and are built by me and my team.
The best CP TX antenna: I give you the CloverLeaf antenna. Similar to the skew planar wheel, this antenna has one less lobe to it and is arranged at 120 degree angles. This allows the antenna to achieve better SWR (I got a perfect 1.0 on the first try!) compared to the Skew planar wheel’s best SWR of 1.2. Reverse polarization rejection is very erratic and can be as low as -8dbi, but can also be as high as 19 dbi depending on how the signal is received. Gain is only 1.2dbi, making it perfect for an aerial antenna. This antenna is best flown in conjunction with another circularly polarized antenna on the RX.
I write this tutorial in the name of my Lord and Savior, Jesus Christ. It is with His heart that I write this as a free gift to the FPV community.
Please enjoy, but if you have any human decency please do not market and sell this antenna without my (C. Alex Greve) expressed permission. I give this to the hobbyist to enjoy, not for a commercial business to compete with me. Competitors please in vent you own just like I did.
EDIT: Demo video - Here's a demonstration of why you should try this antenna. The video says it all.
Base fed how-to video!
Construction jig by Tretch5000
Geometry by Terry74:
|Feb 11, 2011, 08:24 PM|
First, a couple of thank you's
Before I begin I need to give a big thank you to Micheal (Mictronics) for his help in this venture. He took the time to figure out how to model this in 4NEC-2. Its people like him that make this hobby great.
I also want to thank the following people:
Old Man Mike For his excellent support of circular systems
Nigel (devonboy) For his discovery and research of circular omni antennas
Dave Albert (K4UAV) For his support in testing my antenna systems
Dan Greathouse (Owner of Lazertoyz.com RC store)
These are the people that support our hobby. I couldnt do this alone. Thank you, guys.
|Feb 11, 2011, 08:25 PM|
- Some sort of stiff wire conductor (2 lengths of it one two wavelengths and one just one wavelength)
- A length of 50 ohm coaxial cable
You will want to use a good stiff wire. Copper is a bit too soft, but copper clad steeel works really well. .020-.045 mig welder wire is great and you can probably get it from your local machine/weld shop for free. Memory wire from Hobby Lobby is also a good choice.
I used .035" welding wire for the wheel and RG316 coaxial cable for the feed. RG58 and RG174 work fine, too.
Not many materials needed for this one
|Feb 11, 2011, 08:27 PM|
The antenna is made from two lengths of wire. One is twice as long as the other. The lengths can be calculated:
Long Wire length in inches = 24175/f in MHz
Or for you metric folks
Long Wire length in mm = 614035/f in MHz
910MHz = 26.5"/675mm
1280MHz = 18.9"/479.5mm
2.4GHz = 9.86"/250.5mm
5.8GHz = 4.1/105mm
Short wire length = 12088/f in MHz
Or in metric:
Short wire length in mm = 307022/f in MHz
910MHz = 13.25/338mm
1280MHz = 9.44/240mm
2.4GHz = 4.93/125mm
5.8GHz = 2.08/53mm
Now you need to calculate your quarter wavelength which is simply 1/8 of your wire length.
Quarter wavelength in inches = 3021/f in MHz
Quarter wavelength in mm = 76755/f in MHz
910MHz = 3.32"/84mm
1280MHz = 2.36"/60mm
2.4GHz = 1.23"/31mm
5.8GHz = .52"/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. Hey, it hit a perfect 1.0 SWR on the first try, so apparently something is right.
|Feb 11, 2011, 08:30 PM|
Building the antenna - Constructing the elements
Now it's time to start building. You will start out by making an "S" curve from the long wire.
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"
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.
The wire should look like a figure 8.
With the other wire you make a 110 degree arc. Measure back ¼ wavelength from each end of the wire and bend them inward to form a U shape. Once done, put an arc on the backside to form the element.
Now you need to twist your figure 8 wire. The direction will determine the antenna polarization. The polarization is determined by curling your fingers from the center of the element around the radius and pointing toward the tip. Which hand did you use? That is the polarization. The unit in the pictures is RHCP.
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.
Once done, you need to bend a 120 degree radius in the center of the bent 8. Set the antenna so the lobes are at 45 degrees to the ground and bend the center 60 degrees in one direction (It doesnt matter which way) to form a 120 degree bend.
For this you simply make 3 of the short elements. For this, jigs are easy to make or you can just bend by hand.
Easy to make Jigs
I have seen the most impressive jigs to make these antennas from Chad Kapper's on Flite Test to some vendors even selling commercial units. It isn't necessary... I have used a simple cheap wooden dowel for over a year now and it works really well. You simply drill a hole 1/4 wavelength deep into the center of the dowel and then cut a flat spot around the side 1/2 wavelength away.
To use: Insert the wire into the dowel and wrap around to the flat spot. It's that easy!
|Feb 11, 2011, 08:33 PM|
building the antenna - Putting it all together
Now this is the hard part. Soldering this without overheating the coaxial cable is difficult.
First you need to finish the cloverleaf. With the arc at a 45 degree angle to the ground, solder one point to the 120 degree bend in the other element. This completes the clover. No radius should be flat at this point. If one is, you can always rebend after soldering. All should extend upward at a 45 degree angle, 120 degrees apart.
Now is a good time to tin the tips if you haven't done so already.
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-2.4GHz. 5.8 GHz must be fed from the bottom.
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 antenna. Solder the shield to the center of the antenna being careful not to let the elements move.
Now strip the insulation off of the center conductor leaving 2-3mm of insulation on to prevent shorting out to the shield. All 3 of the tips must be soldered to this. It isn't easy. I did this by turning up the conductor and tinned it to stiffen it up. I then bent the very ends of the wires at 90 degree angles ~2mm back to create a hook. I hooked all the elements together and soldered them in place.
That's it! You now have a circularly polarized omni antenna!
|Feb 11, 2011, 08:35 PM|
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: A little less than 1.25 dbi.
Q: Is this right hand or left hand polarized?
A: It depends on which way you bent the pinwheel. It is the direction direction of your hand. If you curl your fingers in the direction of the bend coming off the center of the flat part of the antenna with your right hand, the antenna is right hand polarized.
Q: Why right hand polarized?
A: My system is RHCP.
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 difference in video quality and does not lose signal in a bank.
|Feb 11, 2011, 08:38 PM|
Of course, I could make this an evil antenna by twisting the elements 90 degrees.
Your antennas are under construction tonight as well, Jeff.
|Feb 12, 2011, 01:01 AM|
It's not difficult if you build it my way. I just tried Hugo's way and it took me forever! How he makes those direct attach to a fitting is beyond me. I need a short length of coaxial cable to solder to or it takes me over an hour just to get the soldering joint.
|Feb 12, 2011, 09:54 PM|
Is this the correct patch antenna?
edit: I also found this one by some guy who apparently likes to make antennae:
How do you think CP compares to an inverted v and an 8 db patch? Better range as well as better in banks?
|Feb 12, 2011, 10:38 PM|
I just did a mile on two cloverleaf antennas. This blows a Vee/patch out of the water. I also did a test with a 4 turn helix and a cloverleaf and turned around after 1.5 miles as I was running to the end of my radio range. No loss of signal in a bank, no multipath problems. Just solid video. I'm not used to video this clean.
Needless to say, I am VERY proud of this antenna!
|Feb 13, 2011, 04:36 AM|
United States, TX, Houston
Joined Feb 2007
What do you think about using the cloverleaf on 900mhz on a rc car "On vx and tx"?
Would this be an ideal for ground use, or should I be looking for somthing else?
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