For a long time now I am drooling when thinking of vertical whips with tappable loading coils. I got the 3 band vertical from QRP guys but the setup is really annoying. Especially when hiking and trying to set up the antenna on spots, where vegetation took over. Lying down the radials, setting up the wire on a pole or tree, it takes a lot of times and costs a lot of nerves. Often I end up cursing because everything got tangled into the bushes.
Wouldn’t it be great to have a whip for HF? Yes it would. But there is no way I am paying 130$ and more for that…
Well, there is this 3d printer in my basement and…
I could build my own buddistick!
First I wanted to make something like the WolfRiver coils, but sliding this ring up and down and searching for a resonant point would be annoying with time. Then I thought about those tap position like buddistick has and why not just copy their design (I checked, there are no patents on this 🙂 ).
I mean, building such an antenna would spare me over 100$ that could be spent elsewhere, right? Often the way to achieve something is more interesting than the goal itself, so they say.
First I bought the Buddistick/pole HF whip. It is 2.85m long! Very nice quality, it cost me about 30$ with shipping. I already checked Chinese vendors if they got such long whips, unfortunately not.
When I got it, the first problem arised. Those threads are not metric! I spent 2 days finding some good Ebay offers on 3/8 to metric adapters, no luck. Then I thought about buying a 3/8 tap to tap a pipe so I can screw the whip in. It costs 15$. In the end I decided to take a regular screw, drill a small hole in it and weld an M8 nut on it. I took the whip, filed of the thread and cut a fresh M8 thread in it. Voila!
While drilling the hole I missed the center. I really need a
For a 2.85m whip that goes down to 80m I need a loading coil of 75µH.
Using the calculators on:
I came up with a coil that’s 60 turns on 6cm diameter and 14cm length. using 1.3mm wire with 1mm spacing in between. Having those measurements, I could start designing the coil for 3d printing. I tried to stay simple because this is just a prototype to see how this will work out. I do not intend to take tripods with me, rather my telescopic 6m pole. I took the measurement on the 4th element of the pole, in around 2m height. Enough elevation and I can still reach up to change bands. Hence, the hole at the bottom of the coil fits perfectly on my telescopic
I left out an opening for the BNC socket and a path for the counterpoise. I want the counterpoise to be on the opposite site of the coax, so the weight is kind of evenly distributed, avoiding the whip to lean to one side only.
The print was quite straight forward. I used my crappy Gembird PLA which has horrible layer bonding and very bad layer adhesion to the printing bed. But I bought 1kg of it and it need to be used up, rather than throwing away. The print took about 6 hours. I used a lot of infill to make it sturdy. Then I screwed in the top and the whip get’s on perfectly.
Time for the wiring. If you decide to rebuild this, please calculate your length of wire before (2r x Pi x windings) going to the store. I bought 10m of wire and need 11m. So I have to buy another batch because you should not attach or solder additional lengths. They would not fit into the cuttings of the coil.
In the next article we will wind the coil and do the final work on it.