How to build a 5.8GHz Helical Antenna
Introduction
A helical antenna consists of a conducting wire wound in the form of a helix mounted on a reflector (Figure 1).
The two key advantages to this design are circular polarization and high gain. In simple terms this means you can bank your plane without losing image and you can fly a long way away. The following instructions will help you construct just such an antenna.
Please check out forum for complete instructions.
Parts List
Part |
Part Code |
Price |
Blank Fibreglass Printed Circuit Board |
$3.95 |
|
1/16in Copper Round |
$3.35 |
|
Copper Sheet |
$17.00 |
|
SMA Reverse PCB – Plug |
$9.95 |
|
Total |
|
$34.25 |
Tools Required
- Bench Drill
- Hacksaw
- Side Cutters
- Soldering Iron
- Stanley Knife
Miscellaneous
- 15mm Ø Dowel
Build
Step 1: Print Guides PDF
- Print out Guides PDF and cut out Forma and Reflector Templates marked in blue.
Step 2: Construct coil
- Attach Forma Template to 15mm Ø Dowel.
- Wrap 1/16in Copper Round around 15mm Ø Dowel marked in black to form coil.
- Using a pair of side cutters, cut where indicated (Figure 2).
Step 3: Construct Reflector
- Using a hacksaw, cut a 50mm x 50mm square from Blank Fibreglass Printed Circuit Board.
- Attach Reflector Template to 50mm x 50mm square.
- Using a bench drill, drill 1.5mm holes marked in green and a 3mm hole marked in red.
Step 4: Solder SMA Reverse PCB-Plug to Reflector
- Remove Reflector Template and insert SMA Reverse PCB–Plug into rear of reflector (Figure 4).
- Using a soldering iron, solder pins where indicated (Figure 5).
Step 5: Construct Wavetrap
- Using a Stanley Knife, cut a 3.2mm x 6.4mm rectangle from Copper Sheet.
- Using a soldering iron, solder rectangle to coil where indicated (Figure6).
- Using a soldering iron, solder coil to remaining pin where indicated (Figure7).
Thank God for IB Crazy
Thanks for the comment. There are two reasons that I can think of for not using a spring. First and foremost, a spring is made from spring steel which doesn't lend itself well to being reformed. Secondly, copper is a fantastic conductor which is what you want for an antenna.
Regards
DM
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I would suggest using 15mm or slightly smaller. The critical factor is the material you are going to use to form your coil. If you find after winding it that it slightly expands then by all means use a forma less than 15mm. Hope this helps.
Regards
DM
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The first 1/4 turn of the coil does not sit 2mm above the reflector because I've found that given the size of the 5.8GHz helical it was impractical to achieve. Just my personal experience.
As for the 0.8mm MIG Wire. I would suggest this would be too thin. Most hobby shops stock 1/16in Copper Round and it is inexpensive.
I hope this helps.
Regards
DM
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What kind of gain is expected and what is the usefull angle on these?
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The Helical Antenna is wide band. In simple terms this means the above design will suite numerous channels/frequencies in the 5.8GHz range.
Gain is affected by the number of turns. The greater the number of turns the higher the gain. Ideally Helical Antenna's are in the region of 3 - 12 turns.
The angle of the antenna depends on far away you intend to fly and how high. To give you an example, if you fly 8km away and in the region of 250m - 500m high then your antenna should be at an angle 2.5 - 5°.
I would highly recommend reading IBCrazy's thread on Helical Antenna for a more in depth discussion.
Cheers
DM
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Does it matter if a use a copper sheet and not the pcb one? Is 1.8mm wire still ok?
Thanks
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Yes you are correct, the more turns the greater the gain but the narrower the angle of radiation.
Yes copper sheet will do fine. Just make sure that it is relatively stiff so as not to deform.
Yes 1.8mm copper wire will do fine. The thicker the better generally speaking.
Hope this helps.
Kind Regards
DM
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I found some in a mates shed. You could ask a friend with a wood lathe to turn a piece up. You could look at another material all together such as plastic or alloy. Hope this helps.
Regards
DM
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Thanks so much for posting this tutorial, I'm going to get onto making one of these soon for my 5.8GHz FPV system too. I am using the fatshark goggles and just bought these (http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=27750). Would the antenna you have built above be a good substitute for the skew planar from Hobbyking in the link above? Is it the right kind of 'handed polarisation'?
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http://users.ece.gatech.edu/~az30/Downloads/Helix_EuCAP_07.pdf
...is the page that shows how it works and the dimensions required.
http://flitetest.com/articles/Video_TX_RX_Frequency_Chart
...shows the frequency length of whatever frequency you use.
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