Discone Antenna

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About: I am corporate identity & branding specialist and telecom is my hobby & I build things from time to time.

The Discone Antenna

This is my first time on instructables.com, so I am a newbie here, sorry not being very meticulous in expressing the steps correctly. Building this antenna is difficult in general and finding the right or perfect materials is even more difficult.

There are several antenna calculators online but I used this: https://www.changpuak.ch/electronics/calc_11.php

I was limited by the Aluminum rods of 99cm and needed to cut off the brand engraving so ended up with 97cm to start with. The aluminum rods are those used for welding.

Step 1: Step 1: Preparing the Materials

1. Two (2) flat Aluminum pieces 6x6cm and cut them into an octagon by marking their edges after tilting them by 45 degrees.

2. Eleven (11) Aluminum Welding Rods 8 cut to 85 cm and 3 cut to 32 cm

3. PC (computer) main board-case plastic spacers x 4

4. Three (3) pieces of inner tire tube cut same size as the aluminum octagons

5. SO-239

6. About 10-20 Screws (with Drill-bit tip)

7. PVC rod to hold the antenna

8. Some Pieces of a trunking tube cut at 2 cm x 25 cm with a drilled hole at each end (to act as a guide for cone elements)

9. An open 4x4 piece of a square aluminum tube to act as a holder.

10. Two (2) flat pieces of flat aluminum pieces about 3 x 10cm to hold the antenna open box (above #9) to the tube

Step 2: Step 2: Drilling and Welding

Cut the paper octagons and paste them on the aluminum octagons, mark them with a nail and hammer (so drill bit does not slip while drilling). I soaked the paper with ATF-4 Transmission oil to ease drilling.

Octagon 1 (DISC): Made 8 holes for the top disc reflectors and 4 additional holes for PC Spacers and middle hole to weld the copper wire to the disc.

Octagon 2 (Cone): Same as above in octagon 1, but widened the middle hole to insert the SO-239 + 4 extra holes to screw the socket.

Welded the reflectors of Octagon 1 horizontally (shot rods @30cm) and Welded the rods for Octagon 2 Vertically (80++cm).

Step 3: Step 3: Assembley

(Error: the dimensions in the 2nd image are "cm" not "mm" (image is 1/10th scale)

Solder a copper wire to the middle element to the SO-239

Make sure to add an insulation of about 1 cm or less (I used 3 inner tire tubes that added up to about 8mm of thickness)

Cut through the rubber to let the plastic PC Spacers pass easily and then tighten the top disc with the bottom cone with plastic zip ties. And surely a middle thin hole for the copper wire to pass

Solder the copper wire to the top element (disc)

Screw the bottom element (Cone) to the open Aluminum box (holde) As you see best fits.

Step 4: Finalizing

After assembling all the parts and screwing the box (base) to the holders, you will need to add the bits and pieces of the truncating tube to almost the middle of reflectors (at almost 30 to 40 cm measuring from the top). This design is a bit flimsy and the truncating pieces would hold the cone reflectors from wobbling.

Although not intended for TX but rather as RX to be used with the RTL-SDR dongle as a scanner, but humbly it proved to have an SWR 1.5 @140.000 Mhz and SWR 2.0 @ 150.000 Mhz.

Again sorry for the missing details.

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7 Discussions

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tytower

Question 22 days ago

So what was your target frequency and what thickness were the welding rods ?
Its a little light on photos of the PL259 attachment and wiring points to follow easily ,can you add any more?
I would have left the brand name on the rods if you needed the extra length . On the outside it would have made no difference. Ah I see you did not need the length.
What is trunking tubing?
I don't see how the center conductor is attached to the driven elements or where?
Its a good contribution here and I would like to build it but just need it to be a bit clearer thanks.

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faditechtytower

Answer 15 days ago

Hi tytower
Thank you for your interest. As I said in the comments, I did not take lot of photos while doing the project since I did not intend to post it online, but a friend insisted.
I will try to answer all your questions:
1. Target frequency was 122Mhz and above and the rods are 2.68mm and I bought 11 rods from fix-it shop and there was no recognizable brand (Rods has the number 4043 on one side and 32 on the other side).
2. As for the center element I will draw it for you in the attached image. (I soldered a copper wire and passed it through 3 layers of rubber (from an old tire inner tube). See attached pics.
3. I followed this online calculator: https://www.changpuak.ch/electronics/calc_11.php
4. As for the higher frequencies, it is determined by the distance between the plates (8mm) which was not my concern, my focus was on the Lower Frequencies only.

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tytowerfaditech

Reply 1 day ago

In case I missed this thanks for the response.

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seamster

22 days ago

Ambitious project, I appreciate the work you put into this. Thank you for sharing your first instructable! : )

1 reply
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faditechseamster

Reply 22 days ago

Thank you @seamstr, I did not know I was going to post it here, a friend recommended I do so, if I knew I would have drawn better schematics and taken better pictures.

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faditech

Tip 22 days ago

Other Antennas I built
Dipole 144Mhz / Dipole 430 Mhz / Monopole 433 Mhz / FM 90° V / Dipole 144Mhz

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