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SketchUp for RC Aircraft Design Tutorial #7
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Never heard about circular polarization? Read about the advantages of circular polarization here
The Skew-Planar Wheel is very alike the Cloverleaf antenna, but instead of 3 lobes it has 4, positioned at 90° apart from each other.
The Skew-Planar Wheel is best suited for the receiver, but will work pretty well as a transmitter antenna as well. It has an excellent radiation pattern and very low gain. The reverse polarization rejection pattern is much better and more uniform than the Cloverleaf, making it excellent for the receiving end. The lowest SWR possible is 1.2.
Lowest SWR possible: 1.2
Difficulty to make: High
Best suited for: Video receiver
Downsides: Hard to make, comparably fragile, big, not very aerodynamic, not possible to trim to the right frequency.
Upsides: Pretty wide band, good radiation pattern, low dBi, good reverse polarization rejection.
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.
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.
Here is one of the “U” shaped pieces. This one is a little croocked (demonstrated here by mr jelly frog). If this happens, don’t worry, simply grab both 90° bends and twist them.
Twist until the piece lies nice and flat agains the table.
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°.
Grab the wire at the 90° bends and bend them until they meet.
If you bend it a little to far the arc is going to look like the one on the right. Don’t worry we’ll fix that.
Here is the ~105° angle visible. This is what we’re aiming for.
To fix the over bent arc simply grab it between you index finger and thumb and squeeze while pulling. Be careful to make the curve as uniform and well shaped as possible.
Repeat with the other three pieces.
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.
I use a scalpel to remove the plastic.
Be careful not to cut to deep and damaging the shield. A tip is to bend the coax while cutting. This way you’ll notice when the plastic is cut before you’ve cut too deep and damaged the shield.
Separate the shield, by unlacing the strands, into 4 pieces and place them at 90°, twist the strands together as seen in picture. 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 fixated the lobes at 90° 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.
At this step you also decide which polarization the antenna is going to be. The picture shows a left hand polarized Skew-Planar Wheel. 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 the wire and wrap the shield around the wire. Use extra solder flux if you have any.
The trickiest part of the whole thing is to solder the 4 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.
All soldered up.
Now is a good time to check your angles now. The 90°, the 45° and when looking straight from above the top there should be a ~17° 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 easily. Beware that hotglue will shift the resonance frequency slightly. But in my opinion, it’s a small price to pay for added durability.
It’s hard to photograph properly but the top of one lobe and the bottom of the next are ~17° apart. (See video as well)
Here is a video showing the geometry of the Skew-Planar Wheel 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.