Loop Antenna Copper Jumpers
I am planning to machine some copper jumpers to go between the copper loop and the vacuum capacitor. These can be soldered (or brazed) to create a solid connection with very low resistance.
![Loop Antenna Copper Jumpers](/content/images/size/w2000/2022/05/title_image.png)
I've had the loop antenna on the air a few times and I'm very satisfied with the results. The follow items are remaining before I can call this project complete:
- Add copper jumper to lower the resistance between the copper tubing the the vacuum cap.
- Finish the software for homing the stepper and automatically adjusting the tuning for each of the bands.
- (Optional) - I may choose to weatherize the antenna for longterm outdoor use.
First, I am going to start by finishing the design mechanically. The antenna uses some stranded copper wire between the tubing and the variable capacitor. This is a limitation – I have noticed the efficiency of the antenna has decreased over time and it especially decreased when I accidentally left it out in the weather overnight. Over time I've been able to improve the efficiency again by re-positioning and re-tightening the stranded wire connection – I would prefer if that wasn't necessary.
![](http://esorensen.com/content/images/2022/05/image.png)
I am planning to machine some copper jumpers to go between the copper loop and the vacuum capacitor. These can be soldered (or brazed) to create a solid connection with very low resistance.
First, I modelled up the brackets in Fusion 360:
![](http://esorensen.com/content/images/2022/05/image-1.png)
I modelled these as solid objects and did not use any sheet metal features. I then used the solid models as a reference to re-create the models in 2D:
![](http://esorensen.com/content/images/2022/05/image-2.png)
I generated toolpaths using the CAM functionality of Fusion 360 and cut the brackets out of some copper sheet using my benchtop mill:
![](http://esorensen.com/content/images/2022/05/IMG_2917.png)
![](http://esorensen.com/content/images/2022/05/IMG_2922-1.png)
I haven't cut much copper and the mill and the material was very gummy. It ended up cutting okay, but I had to spend some time removing a thick burr that formed on the edge of the part. I did a bit of sanding on the top and bottom surfaces and ended up with a couple of nice-looking parts:
![](http://esorensen.com/content/images/2022/05/image-3.png)
Here is one of the jumpers at the end of the piping, ready for solder:
![](http://esorensen.com/content/images/2022/05/image-4.png)
And here is the result after soldering. This was my first time soldering copper piping with a torch. The result is a bit ugly, but the connection is solid. I've since read that brazing may be a better approach to further lower resistance. I also let the torch heat up the body of the jumper in order to anneal it and make it more pliable for forming.
![](http://esorensen.com/content/images/2022/05/IMG_2954-1.png)
The round section of the copper jumper interfered with the plastic portion of my 3D print. I used an oscillating saw to cut away some of the material:
![](http://esorensen.com/content/images/2022/05/image-6.png)
And then finally I mounted the jumpers in place. I'm happy with how the pieces lined up and contribute that to modelling everything ahead of time.
![](http://esorensen.com/content/images/2022/05/IMG_2962.png)
Here is a final image of the re-assembled antenna with copper jumpers in place:
![](http://esorensen.com/content/images/2022/05/IMG_3232.jpeg)
And here is the SWR reading for 40M:
![](http://esorensen.com/content/images/2022/05/image-7.png)
Next step is to finish developing the stepper driver code and get it into regular usage.
Done for now.