Mostly 3D printed discone antenna

Discone antenna - Side view render

Side view render

For a long time I wanted to listen in to some unencrypted radio frequencies (for example air band). When I discovered the RTL-SDR dongle I have bought it almost instantly. For such a low price, it has incredible possibilities.You can listen to signals that you are receiving ,decode them and observe their spectrum in range of about 500 kHz to 1.75 GHz. Unfortunately, as you can guess, the RTL-SDR without a good antenna can’t do much. I was looking for an antenna that would be relatively easy to build, lightweight and broadband (so that I don’t have to change the antennas every time I want to listen in to different frequencies). The antenna was designed in the way so that it can be built with use of 3D printer and some other tools that you probably already have. Unfortunately, as it turned out later, the antenna was not as easy to build as I thought it will be (there were a few problems that are already corrected in the final version of this project). The whole project was supposed to last about one day, unfortunately everything took me about 3 days. I am very happy with this antenna – it works exactly as expected. It receives signals very well in the range of about 85Mhz to 850 Mhz / 1GHz. Below I will describe the entire process of building such an antenna so that you can make one by yourself.


Design & some renders:

Discone antenna - Wireframe render

Wireframe render

As always, the entire project was created in the Autodesk Inventor software. The design of the whole antenna took about 2-3 hours. In addition, I have also designed some tools that will help in assembling this antenna (for example drill guides).The antenna has been designed for a minimum frequency of 85 MHz (if you want to change that to 100 MHz you can easily calculate new rods lengths over here ( the rest stays the same): https://www.changpuak.ch/electronics/calc_11.php). If you want to modify this project or check several dimensions, the CAD files can be found under the link which is placed at the bottom of this page. Recently I have discovered a nice view-style in Inventor which is called “wireframe view”. It looks very nice when combined with the white background  😉 . Below you can see several other renderings:

Discone antenna - Render

Render

Discone antenna - Bottom view render

Bottom view render

Discone antenna - Top view render

Top view render


Needed parts/tools:

  • Some M3 Bolts and washers
  • One M5 x 55 mm bolt (x50 mm should be fine too if you don’t use washers)
  • About 11 m  [(345 mm * 8)+(980 mm*8)] of  6 mm dia. aluminium rod (with 2.5 mm hole inside)
  • Drill
  • M3 Tap
  • 3D printer
  • Non etched PCB laminate / Copper plate (1.5 mm thick or less)
  • 50 Ohm coax cable
  • F-type RF connectors
  • PVC pipe 1/2″   (about 21,5 mm outer diameter in my case)
  • ASA filament  (or anything else that can survive in external conditions)

3D Printing parts:

Discone antenna - 3D printing the cone mount part

3D printing the cone mount part

Everything has been printed from ASA filament (similar to ABS, however it is more resistant to weather conditions). Remember to set a large infill because these parts will carry heavy loads, especially during a storm. All of the parts were printed in about 6-7 hours in my case. I didn’t have an idea for the name of these 3D printed parts, so I named them as follows:

  • Upper part that holds the disc aluminium rods – ” disc mount part”
  • Bottom part that holds the cone aluminium rods – ” cone mount part”

Recommended printing settings:

  • Layer height: 0.15 mm
  • Heated bed: 90 deg C or more
  • Printing speed: 40-60 mm/s
  • Filament: ABS/ASA
  • Infill: 80% or more
  • Outlines: 2 or more
  • Top/Bottom 100% layers: 3 or more
  • Support: Yes – Only for drill guides
  • Nozzle diameter: 0.4 mm
Discone antenna - 3D printing the disc mount part

3D printing the disc mount part


Putting it all together:

Discone antenna - Exploded view render

Exploded view render

On the render above you can see how the whole thing is assembled. Below I will describe the entire process of assembling this antenna step by step:

1) Drilling holes to size:

First, you have to drill all the holes in the disc and cone mount parts to make sure that they have correct diameter according to the dimensions below:

Holes dimensions:

  • Holes for aluminium rods : Ø6 mm
  • Holes for M3 bolts which clamp down these rods : Ø2,5 mm (You don’t really need to drill these because we will tap them anyway )
  • Center hole for main screw: Ø5 mm
  • 4 holes for attaching separator and bottom copper plate/PCB to the cone mount part : Ø3 mm
  • 2 holes in the mast mount part that are used to fix the PVC pipe : Ø3 mm

2) Tapping holes:

Discone antenna - Tapping holes for screws that hold aluminium rods

Tapping holes for screws that hold aluminium rods

You will need to tap all of the holes in the disc and cone mount parts that are used to clamp down aluminium rods with an M3 tap. You also need to make sure that every thread is straight because it might cause problems with alignment later.

3) Cutting aluminium rods and drilling holes in them:

At first you need to cut these rods to the right length and then smooth their ends with a file.If you are building this antenna for minimum frequency of 85 MHz the rod lengths are:

  • 345 mm (8 pieces) for disc
  • 980 mm (8 pieces) for cone
Discone antenna - Cutting aluminium rods to size 2

Cutting aluminium rods to size 2

Discone antenna - Cutting aluminium rods to size

Cutting aluminium rods to size

Next, we have to drill a hole in each of the rods that will be used to fix it in the disc/cone mount part . For this purpose, we will use previously printed drill guides. Drill guide consist from the 3D printed part and a piece of aluminium rod reamed to 3 mm inside. Both parts should be connected together using hammer or a vise (tight fit). Then you need to insert the aluminium rod into the drill guide ,and lock the whole thing firmly it in the vise. After locking it, you have to drill the holes with addition of some oil to lubricate the drill guide (to prevent wear of it).

Discone antenna - Parts needed for an drill guide

Parts needed for an drill guide

Discone antenna - Assembled drill guide

Assembled drill guide

Discone antenna - Drilling holes in aluminum rods with help of drill guide and a vice (cone rods)

Drilling holes in aluminum rods with help of drill guide and a vice (cone rods)

Discone antenna - Drilling holes in aluminum rods with help of drill guide and a vice (disc rods)

Drilling holes in aluminum rods with help of drill guide and a vice (disc rods)

Next you need to put on the 3D printed end caps. Below you can see how cone and disc aluminium rods should look like when they are finished:

Discone antenna - Finished aluminium rods

Finished aluminium rods

Discone antenna - All aluminium rods with drilled holes

All aluminium rods with drilled holes

4) Cutting and drilling copper plates / PCB,s:

The next step is to cut out the plates that will be used to connect electrically all of the rods together. They can be cut out from a copper sheet or PCB laminate (1.5 mm thick or less). All dimensions can be found in CAD files. If you need some technical drawings please let me know in the comments . In addition, I have tinned all of the plates to ensure better contact with the bolts and improve resistance to the weather conditions.

Discone antenna - Cutting and drilling [copper plates/PCB,s]

Cutting and drilling [copper plates/PCB,s]

Discone antenna - Tinning [copper plates / PCB,s] with soldering iron

Tinning [copper plates / PCB,s] with soldering iron

Discone antenna - Tinning [copper plates / PCB,s] with soldering iron

Tinning [copper plates / PCB,s] with soldering iron

Discone antenna - Tinning [copper plates / PCB,s] with soldering iron

Tinning [copper plates / PCB,s] with soldering iron

5) Assembling the disc:

Assembly of the disc begins by checking if all the rods fit to their holes. All rods should fit very tightly (they can’t be loose because they could vibrate in windy conditions). Each rod is bolted down separately with an M3x12 mm bolt , be careful to don’t damage threads in 3D printed parts. Below you can see how the whole disc should look like after it is finished:

Discone antenna - Top disc assembly - inserting and bolting down aluminium rods 2

Top disc assembly – inserting and bolting down aluminium rods 2

Discone antenna - Top disc assembly - inserting and bolting down aluminium rods

Top disc assembly – inserting and bolting down aluminium rods

Discone antenna - Top disc finished

Top disc finished

Discone antenna - Top disc finished 2

Top disc finished 2

6) Assembling the cone:

Proceed as above (but this time use M3x16 mm bolts to secure the aluminium rods), however, additionally you need to bolt down the separation plate at the top of the cone mount part using three M3x25 mm bolts. Leave one hole empty (this hole will be used to clamp down the coax braided shield to the bottom plate) .You only need to press the M3 nut into the heaxagonal hole at the bottom of disc mount part.

Discone antenna - Bottom disc assembly (cone) 3

Bottom disc assembly (cone) 3

Discone antenna - Bottom disc assembly (cone)

Bottom disc assembly (cone)

7) Preparing coax cable:

  1. Remove first layer of insulation from the cable [about 30 mm or more]
  2. Twist the braided shield
  3. Remove most of inner insulation core [leave about 10 mm or less]
  4. Bend the core wire by 90 deg.
  5. Put on some heat shrink tubing to insulate the core from the braided shield
  6. Make a loop from copper core wire so that M5 bolt can fit in it
  7. Prepare the other end and install an F-type connector
Discone antenna - Preparing coax cable: Insulation removal

Preparing coax cable: Insulation removal

Discone antenna - Preparing coax cable: Twisting the braided shield

Preparing coax cable: Twisting the braided shield

Discone antenna - Preparing coax cable: Removing inner insulation core and bending copper core wire by 90 deg

Preparing coax cable: Removing inner insulation core and bending copper core wire by 90 deg

Discone antenna - Preparing coax cable: Putting on some heat shrink tubing to insulate the core from the braided shield

Preparing coax cable: Putting on some heat shrink tubing to insulate the core from the braided shield

Discone antenna - Preparing coax cable: Making a loop from copper core wire

Preparing coax cable: Making a loop from copper core wire

Discone antenna - Coax cable with a M5 bolt inside the copper wire loop

Coax cable with a M5 bolt inside the copper wire loop

Discone antenna - Preparing coax cable for putting on an F-type connector

Preparing coax cable for putting on an F-type connector

Discone antenna - Coax cable with a F-type connector on its end

Coax cable with a F-type connector on its end

8) Assembling the whole antenna:

Next you need to put the wire, M5 bolt and braided shield through the mast mount part and then tighten everything .Then you have to clamp down the braided shield to the bottom plate using an M3 screw and a washer (you have to use hole that we previously left empty)

Discone antenna - Putting coax braided shield and a M5 bolt through the mast mount

Putting coax braided shield and a M5 bolt through the mast mount

Discone antenna - Clamping down a coax braided shield to the bottom plate with a bolt and a nut

Clamping down a coax braided shield to the bottom plate with a bolt and a nut

Discone antenna - Checking if everything fits together

Checking if everything fits together

Discone antenna - Bolting down mast mount

Bolting down mast mount

9) Checking for continuity:

After everything is finished you have to check if every aluminium rod is connected to coax cable with a multimeter. If any of these rods is not connected properly, you have to fix it.

10) Mounting in desired place:

After everything is finished you can mount your antenna in desired place:

Discone antenna - Mounting on the balcony

Mounting on the balcony


How well it works?:

Discone antenna - SDRSharp 70cm Ham Band spectrum

SDRSharp 70cm Ham Band spectrum

The number of signals that this antenna receives (in whole band for which it was designed) exceeded my expectations. The antenna receives several signals at once in the Air Band, because of that I am able to listen to the conversations of many pilots without any problems. I also receive a lot of strange signals in the Ham radio bands and anywhere else. Answering to the question above: it works very well  🙂 .

Discone antenna - SDRSharp Air Band spectrum

SDRSharp Air Band spectrum

Discone antenna - SDRSharp Air Band spectrum 3

SDRSharp Air Band spectrum 3

Discone antenna - SDRSharp 33cm Ham Band spectrum

SDRSharp 33cm Ham Band spectrum

Discone antenna - SDRSharp Air Band spectrum 2

SDRSharp Air Band spectrum 2

Discone antenna - SDRSharp FM Broadcast spectrum

SDRSharp FM Broadcast spectrum

Discone antenna - SDRSharp weird signal spectrum

SDRSharp weird signal spectrum


[Update] Corrections of minor issues:

Discone antenna - Bolt clamping a coax braided shield

Bolt clamping a coax braided shield

I improved the design to make it easier to clamp down the braided shield to the bottom copper plate. Now the nut is on the other side , because of this you can easily squeeze the braid with a screw and washer.


Final effect:

Discone antenna - Mounted on the balcony 2

Mounted on the balcony 2

Discone antenna - Mounted on the balcony

Mounted on the balcony

Discone antenna - Discone antenna completed

Discone antenna completed


Links to .STL & CAD files

If you want to make this antenna by yourself you can find all CAD and STL files over these links:

  1. Grabcad: https://grabcad.com/library/mostly-3d-printed-discone-antenna-1
  2. Thingiverse: https://www.thingiverse.com/thing:2909028

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