since this whole pandemic issue is going on, I am mostly at home tinkering around. I thought about creating a coil for portable use. Something like the buddistick coil but for a 6m pole and a wire antenna.
The problem was how to tap the coil since the coil is pretty small so the distance between each winding is. The coil is 5cm in diameter, around 10cm tall and has around 58 windings, which should be around 59microH. Apparently enough for a wire resonant on 20m to reach 80m with the coil. I have not tested the coil yet. But since that is not the first one I made, I assume it works. Only the tuning should take some amount of time (counterpoise + radiator).
The tapping points are printed and taped with copper tape, the clip that goes on the tapping points is also 3dprinted with taped coper around it.
The radiator banana plug is 3mm, the counterpoise banana is 5mm. You also need some rubber band or bungee cord and copper tape of course.
You can download the thing here: 80 40 30 20 vertical antenna SOTA by Koppo - Thingiverse
I’m open to ideas on how to improve it. Especially the tapping of the coil could need some improvements. After initial tuning, you should mark the position on the coil somehow, since the rubberband will slip after time.
The coil form looks quite well suited to the task. As to coil clips on narrow gauge wire I would suggest small alligator clips or a mini test clip such as this.
Hope that is helpful!
73 de KE6MAK
Yes those miniclips look quite useful for that task Thanks! Ordered!
As a suggestion for tapping the coil, could you have a piece that is similar in shape to the piece that currently attaches to the elastic but that instead is used to push between the wires of the coil? If it located in the slot in the coil former that is facing the camera in the picture, I imagine it could be reasonably secure as you could make it just the right size to push back against the wire.
I thought about that but the problem is, the copper wire is not springy, so if you push something in between the wire won’t bend back, therefore there will be no contact any more.
The other problem is that the distance between the wire is so small that I can’t print such small parts.
You can also buy the clips from Buddipole folks.
Instead of a single layer cylindrical coil you could try a basket wound coil.
Because the winding is shorter the mutual inductance is higher i.e less wire is used.
Also the staggered nature of basket windings makes them easy to tap.
To give you an idea 25turns of 1mm on 75mm basket is 61uH