Cloverleaf Antenna by RCExplorer

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Posted: August 1, 2012  |  61,970 views
INFLUENCE 88%

The Cloverleaf Antenna

The Cloverleaf antenna was brought to the FPV community by IBCrazy. Thank you for making circular polarized antennas accessible to the average FPV-flier.

Never heard about circular polarization? Read about the advantages of circular polarization here

The Cloverleaf is a closed-loop antenna, meaning that the signal and ground wires are connected. Measuring between signal and ground with a multimeter would read a short circuit. However it works great as an antenna. The cloverleaf has 3 lobes at 120° apart from each other in the horizontal plane and angled 45° in the vertical plane. It may look funky, but it’s an excellent transmitter antenna. In fact its one of the best FPV video transmitter antennas out there at the moment.

The Cloverleaf is best suited for the transmitter, and almost exclusively used for this purpose. It has an excellent radiation pattern and very low gain. It’s also possible to achieve a perfect 1.0 SWR, making it very efficient. It is not the ideal antenna to use on the receiver though. The reverse polarization rejection pattern is very erratic and varies between -8 and 19dBi. Therefore there are better antennas to choose for the receiver. This doesn’t matter for transmitting signals though, only for receiving them.

Gain: 1.2dBi
Lowest SWR possible: 1.0
Directionality: Omnidirectional
Difficulty to make: High
Best suited for: Video transmitter only

Downsides: Hard to make, comparably fragile, big, not very aerodynamic, not possible to trim to the right frequency.

Upsides: Possible to achieve SWR of 1.0, pretty wide band, good radiation pattern, low dBi

You need:
Stiff wire that is easy to solder.
RG316 coax cable.

(The antenna on the pictures in this guide is left hand polarized)


I use 0.8mm copper plated MIG welding wire. It’s stiff and holds its shape well. Yet it’s not to hard to work with in terms of bending and shaping and it’s really easy to solder. Therefore a good choice.


Enter the exact frequency
MHz
Cut the wires to:
mm
Start of by straightening the wire. Then using a wire cutter, cut 3 pieces of wire a little longer than the calculated length you got from the calculator above. Sand the ends of the wires down using sandpaper, a dremel or a file to the exact length. This technique is the best I’ve tried as trying to cut the wire to the exact right length with just a wire cutter is nearly impossible. Plus it doesn’t make a clean cut. Cutting a little longer than sanding it makes the ends nice and clean.


Now we are going to bend both ends 90° inwards creating a “U” shape with a flat bottom. The length at which you are going to bend is 1/4 wavelength from the ends of the wire, and can be calculated here:
Enter the exact frequency
MHz
Bend at:
mm



The three “U” shaped pieces

A tip on how to get good precision and speed up the bending is to use pair of calipers. Set the caliper to the length you wish to bend but subtract half the thickness of the wire. So if you’re going to bend at 59.96mm then set the calipers at 59.56mm if you’re using a 0.8mm wire. Place a pair of pliers on the inside of the calipers measuring arm and grab the wire and bend it. Perfect results every time.

Now it’s time to create the arc. The easiest way is simply using your hands and bend it to the right shape. The two tips should meet at a ~105° angle. They could not and should not meet at 90°.


Here is the ~105° angle visible. Be careful to make the curve as uniform and well shaped as possible.


Repeat with the two other wires as well.

Now it’s time to strip the coax cable. I highly recommend using RG316 as it’s much more heat resistant than RG58. Soldering this antenna can be quite a challenge and you don’t want the coax to melt on top of everything. Separate the shield into 3 pieces and place them at 120°. Strip the signal as close to the shield as you dare. If this part is to long it’s going to shift the frequency of the antenna. But be sure that the signal and shield can’t connect.

To simplify the soldering I made a simple jig out of food container lid. I simply taped down the lobes at 120° apart. Also make sure that the lobes are at 45° vertically (see video at the end of the guide for more detailed illustration). I recommend using “poster gummy” (green mass used to fixate posters to walls without using nails). It holds the lobes in place better and is easier to work with, but I didn’t have any at home at the time of this build. Notice the hole in the bottom. That is where the coax cable is fed through and soldered in place.

At this step you also decide which polarization the antenna is going to be. The picture shows a left hand polarized clover. For right hand polarization, simply flip the elements over to the right instead.

Solder the legs to the shield first. Be sure to get it properly soldered. Pre-tin both the wire and the shield. Use extra solder flux if you have any.

The trickiest part of the whole thing is to solder the 3 legs to the signal wire. I usually bend the lobes so that they align perfectly without having any strain on them while soldering. This eliminates the risk of one “plonking” off while soldering. An other technique is to use “helping hands” to hold the wires in place. Just make sure to pre-tin all wires and get a good solid solder joint. This is the part that’s most likely to break on this antenna and if it’s a cold solder joint, it’s going to break really easy.

Check all your angles now. The 120°, the 45° and when looking straight from above the top there should be a 10° separation between the legs thats soldered to the feed-point and the legs soldered to the shield. (See video at the end.)


I added some hotglue to support the solder joints so that they don’t fatigue or break as easy. Beware that hotglue will shift the resonance frequency slightly. But in my opinion, it’s a small price to pay for added durability.


Really neat looking antenna. People will think you know what you’re doing if you use on of these.


This antenna was measured to 1.05 SWR which made me really happy.


It’s hard to photograph properly but the top of one lobe and the bottom of the next are 10° apart. (See video instead!)



Here is a video showing the geometry of the Cloverleaf antenna by Jayzy74

Observe that this video shows a right hand polarized antenna, while the previous pictures in this guide are of the left hand polarized version.

The key to success when making FPV antennas is to be meticulous. The more accurate you can make the antenna the better it will perform. Take your time and don’t rush things. This antenna is well worth the effort.



Comments

pranav.hosangadi March 16, 2013
Just tried this, with not-too-accurate measurements (to the millimeter)

The antennas look fine, and work fine when both are in the same orientation.

However, when I turn one of them, I get a whole lot of interference / static

In a weird reversal, the dipole antennas that came with the Tx / Rx work fine at any angle.

I'm going to try again on Monday (I'm all out of SMAs). Any suggestions about what might have gone wrong?

Looks like I'm in opposite-land :P
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pranav.hosangadi March 19, 2013
Update: New antenna works ok, still have some bad signal when Tx is around 15 degrees to the Rx. Dipoles still work fine at any angle.

Anybody know what's wrong?
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jivy43 March 25, 2013
What length did you make the coax?
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Rosario March 29, 2013
I am just getting into this FPV thing and the Antenna making (5.8) I have made a few so far just waiting on my RG316 to get here for testing but what I just noticed in the first part of this DIY it says the the center lead and the ground wires are connected and would look like a short if a DMM was used? you are talking about inside the Tx right?(has to be lol) as I dont see this in the build-sorry if this is a dumb question,but for somone just starting out (like me) this can be miss-leading
Thanks Guys for all that you do. BTW- I just found out that I ride thru the area you guys are in (on my HD) would like to stop by and see ya fly and have a chat sometime? is that possable
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ThiagoKern April 4, 2013
Can I use any kind of coper wire? Like a 1.7 mm ?
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747Pilot April 21, 2013
Head to ACE Hardware, Home Depot or LOWE's. Bring your calipers and wire strippers! In the electrical section you'll find all sorts of wire. Look for the spools of wire on the racks they sell by the foot. The higher gauge wire on those spools (16 or 18awg) usually has three (3) strands insulated and encased within another insulator. They will be a size VERY close to 1mm. Much better than 1.7mm. Best of all you can buy 1 foot of it real cheap and get 3 feet of copper wire from it.
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RandallJ August 19, 2013
best source of wire I have found is Harbor Freight.. buy a roll of copper plated welding wire (.035).. Careful about it trying to unspool when you take sections.. this roll of wire also works great as a "weight" for holding things down on the bench..
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TheThomass May 14, 2013
I would like to make a cloverleaf and skew planar for my 5.8ghz system (channel is 5.705ghz)
I wondered if the thickness of the wire has much influence on the performance, and what about the internal resistance of my RC305 receiver of 200mW transmitter from HK? Do I need to add a resistor?
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Hilton.viney June 19, 2013
Hi all, I want to know if you can just use normal television aerial cable? i think this is a RG58 cable. will this work for a 900mhz 200mW setup?
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Hilton.viney June 20, 2013
also will RG59 work? it is 75Ohm compared to 50Ohm of RG316.
Please Help urgently?
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RandallJ August 19, 2013
I have read that the answer is NO... Hop on EzeBay and search "RG316 Cables" and purchase male/male cables straight / 90º . You can typically get these at about $1 each (ends cost double that each). You can also get both 90 or both straight.. I prefer the mix.. Just make sure you get male/male
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Ivanlopezvergara July 3, 2013
This Comment Has Been Removed
Ivanlopezvergara July 3, 2013
Hi

We just made it for 900 Mhz and it works! Next step now is to make a helical for a ground station.

Thank you very much.

Regards
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elf128 September 25, 2013
Hi,

Thank you very much for tutorial. Small correction. During making of antenna, I've noticed that angle between wires in each leaf isn't even close to 105°. I've checked numbers. The length of bended part is ½ of wave length and radius is ¼. Which mean that arc is twice longer than radius and angle is 2 in radians ( ≃114.59° ). And that's exactly the angle I've got in practice.
Please correct it, some people may get confused.

Thanks,
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djentangle October 28, 2013
Hi, Is there a way to test the antenna's with a multimeter or some way of knowing if what I made will work without having to risk my fpv batbone tri?
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wilianamaral February 25, 2014
Do you guys can tell whats the pros and cons on cloverleaf and helical antennaes?
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mmazuera March 2, 2014
Has anyone tested the flux-core MIG wire to make the antenna?It's not solid copper. Does it work?
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bopiloot April 14, 2014
Hi,

Just a few quick question on the topic.
I have 2mm copper wire to make my antenna?
Good enough or overkill?
What could the influence be if one uses thinker wire?
Next question so it's a skew planar wheel antenna on the base station that communicates with a clover leaf antenna on the model, right?
Thx in advance and greetings,
bopiloot
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Boomex May 7, 2014
Hi erverybody,

I got a question, can I use the stock antennas wich came with the Tx or Rx as the basis for those CL antennas?

Regards
Michael
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zodrik February 27, 2013
thanks dave for the tutorial......so if this antenna work great for the transmitter what are your suggestions for the receiver?
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Point Blank RC May 9, 2014
The receiver equivalent is a skew-planar wheel antenna. It can be found near the bottom of this article on David's website. http://rcexplorer.se/?s=cloverleaf
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