New project on www.sm0vpo.com - 3D Printed Portable HF Antenna

Hi Harry,

sad to hear about your illness. I wish you to recover ASAP.

Umbrella sticks and spokes are often made of stainless steel (anticorro). They cannot be drilled nor soldered using common methods. But it may differ one from another.

VBR from Ivan

Hi Ivan,
My flagpole had a ball at the bottom that was screwed into the bottom of the telescopic antenna. I just unscrewed that and stuffed a suitable machine screw into it.
It did not fit the M3 screw on the coil, so I took a bit of metal plate, about 8mm wide and 3cm long. Made two holes and then folded it it into a U-shape. Then I could use two different bolts . one for mounting on the coil, and the other for the screw into the antenna.

When I played witht he capacity hat I only had about 300mm wire for each spoke of the hat, but I used many of them. Mine were perfectly mechanically stable, although I never tried them in gale-force winds. One thing I DID notice was that I could just clip them on and the previous tappings of the coil were ok. There MUST have been small differences, but they did not seem to affect the tuning. So I do not think that stability of the hat is so critical.

I rarely used my antennas (including the original 5m antenna) in strong winds so I have never bothered about guying these portable antennas. But I would guess that it was wise to leave that option open. In my experience, if you leave an option open then you never need to use it  

BTW - for the past 4 days I have been sick as a dog with a terrible cold. I have not ben able to do anything at all in the house since last Tuesday, not until today. I am still not healthy, still have a runny nose, coughing and sneezing, but nothing like as bad as it was even yesterday.

But I will catch you later. So glad that the new project is useful. I hope that others can use it to advantage. Sometimes all it needs is a spark of an idea for someone to "run with the tech" and develop something better.

While writing this I had a little thought. I have several broken umbrellas. I am too mean to throw them away if there is a possibility that I can fix them. The centre of the umbrellas are all hollow, so perhaps I can do something with one of them - Remove the canvas, use the frame, solder a nut to the centre tube so that I can slip it over the top of the antenna and use a single screw to fix it in place. Just need to solder a few joints so there is nothing loose. The unbrella spokes can also be mounted upside-down to get a little extra height (and less cancellation). One of the unbrellas I have has a thick tube as it was also a walking stick.

Catch you later. BR Harry - sm0vpo

Hi Harry,

the case of the falling hat has been solved using a piece of polyester cord and some glue. It is ugly a bit, but it works. Here is a photo of the antenna with a hat in collapsed and deployed state:






I left the small loose wire triangle on the flagpole. It might be useful for eventual guying. Do you think it matters much?

My flagpole probably has no thread at its bottom. The cap with a small ball is just pressed into the bottom tube. I have to find how to attach it to the coil former and how to connect it to the coil.

VBR from Ivan

Hi Harry,

thank you. I did the calculations for 3,5 MHz band. Maybe it has no sense, the antenna would be too lossy on this band.

VBR from Ivan

Hi Ivan,
I had calculated that using 1.5mm coil wire Diameter copper wire, and a 2.5 meter telescopic whip, I would need around 26uH as the base loading coil, without the capacitance hat.
30 turns would give me about 33uH, which woiuld give resonance at about 6.5MHz. This gives a bit of leeway for error and can cover the whole 7MHz band. The minimum length of the telescopis must be about 1.75 metres to cover 7MHz (1.6m at 7.2 MHz).

Sorry, hagta go now, lunch meeting in 7 minutes in Maörsta centrum.

BR Harry

Hi Harry,

sm0vpo wrote:The coil is 7cm mean diameter and 4mm between turns. The coil length is 13cm. The end of the bottom turn is at least 1cm from the base plate, with plastic between the wire and the plate.

My calculations showed something around 10 cm dia and 50 cm length. It is probably due to my aiming at 7 MHz and maybe even 3,5 MHz. My idea was to make the antenna mounted on a light tripod, with 3 long radial wires, so that it would be suitable e.g. for backpacking - not dependent on a car.

Plasic drainpipe 7cm in diameter will work, and there are also pre-made plastic caps to fit them.

I had a 110 mm PVC drain pipe and caps in mind.

My capacity hat experiment was nothing more than an experiment, but it worked very well indeed. I had four crocodile clips, each with about 250mm of 0.8mm Diameter copper magnet-wire. So there was a horisontal cross at the top,

My hat is about 4x 600 mm when extended. The telescopes are attached to a metal cross, but they tend to fall down from their horizontal position. I have some ideas how to improve it, but not tested yet.

So please let me know if you want me to print a former kit for you?

You are very kind indeed, but sending the parts would make the thing too complicated. I prefer using local sources, you know. No, thank you.

I bought a resin UV printer (Creality Halot) recently, I am just collecting knowledge how to use it. It seems to be more suitable for railroad modelling than a filament printer. Maybe your files could be printed on it as well?

BTW did you know, that original Prusa printers are developed and manufactured in Prague?

VBR from Ivan

Hi Ivan "2- you wrote a perfect article again!" thank you very much, that is praise indeed  

The coil is 7cm mean diameter and 4mm between turns. The coil length is 13cm. The end of the bottom turn is at least 1cm from the base plate, with plastic between the wire and the plate.

You can wind the coil yourself using multistrand house wiring cable 2.5mm diameter (including insulation - (1.5mm conductor cross-sectional area). Use another wire 1.5mm diameter to regiment and guide the turns spacing. Use super-glue every two turns while winding, but use plenty of super-glue under each and every turn when installing the wire connection loops.

Plasic drainpipe 7cm in diameter will work, and there are also pre-made plastic caps to fit them.
Instead of a cone to support the antenna element you can use a second (shorter, about 6cm) piece of drainpipe with a hole in the top to fit the antenna element.


"I got stuck, when the hat repeatedly collapsed by itself"

My capacity hat experiment was nothing more than an experiment, but it worked very well indeed. I had four crocodile clips, each with about 250mm of 0.8mm Diameter copper magnet-wire. So there was a horisontal cross at the top, and it was always repeatable. I rarely use 7MHz and 10MHz, so I do not use them. My hat reduc ed the coil turns quite a lot so the VSWR with short telescopes improved to unmeasurable.


I can not promise anything to 100% as my 3D printer is a getting a bit old and tempramental tempramental; it is in use 24/7 printing out a 1300mm long RC boat, with all the fittings. But I will see if I can print out the plastic parts if you want me to give it a try? I hope that soon I will be buying a new 3D printer. The present one prints at 50mm/second, but I screwed it up to 60mm/second. New printers today print at typically 260mm to 300mm per second and cost less than 1/2 the price.

So please let me know if you want me to print a former kit for you? Is it for the 14mm diameter portable telescopic flagpole? Or some other diameter?

Very best regards from Harry

Hi Harry,

1- your ceiling probably needs re-painting;
2- you wrote a perfect article again!

I tried to make a collapsible vertical from the 2,5 m flagpole and four shorter telescoping antennas forming a capacitive hat some weeks (months) ago. I got stuck, when the hat repeatedly collapsed by itself, and I shelved the project. The other problem was making a coil former with groove, not having a 3D printer nor a lathe. What are the dimensions of your loading coil? It seems to be smaller than I expected.

VBR from Ivan

Hi again all,
I have had a lot of problems sleeping recently, just lying there looking at the cracks in ceiling in the semi-darkness. From one angle I can see Jesus with his foot in a bucket, but from a different angle I can see a duck holding a rifle. Since I stopped working I am not doing so much physical work, tramping around 5km a day in the laboratory complex.

Two days ago I got up at 3AM and stopped worrying about not sleeping. I have made loads of projects, some of which I have not published, were on the list, but shelved. Working full time and being socially active, plus many holidays abroad always seemed to fill my time.

Just before Maj-Lis passed I bought a packet of telescopic antennas. All had 6mm diameter bottom sections, with M3 threaded base. They vary in length from about 600mm to 1500mm in length. At the time I thought that 1500mm is in the same "order of magnitude" as a ¼-wavelength for 30MHz, and double that length is 14MHz. Then there was the HF multiband antenna with base-loading coils.

Ok, so 1500mm is not as efficient as an MFJ-1979 5 metre telescopic, but it should (and proved to be) surprisingly useful. It gave a good account of itself. On the first day I worked a station in Iwate, Japan. Since then I bought a gay-pride flag with a 2500mm telescopic "portable flagpole". The flag itself went in the bin, but the flagpole went on the portable antenna base-loading coil that I printed on the 3D printer.

So now I have documented the project, complete with STL printer files for download. I have included both antenna support cones for both 6mm telescopic antennas and the 14mm portable flagpole.

The antenna is bolted onto a 500mm x 500mm metal plate with super-magnets at each corner, so it will stick to the roof of a car like a limpet, but you should put some protection on the car roof before dropping this mag-mount antenna an the roof. The antenna can be deployed in about 30 seconds, in fact it takes longer to plug in the radio than it takes to plonk the antenna on the roof. When retracted, the antenna will even fit in the boot (trunk) of my little Mazda MX5 RF sports car.

I have found a lovely little man-made hillock about 4km from my house. It is elevated, with no surrounding trees or buildings. Lovely clear sight of the horizon all round. 100 Watts, with no ATU, covering 7MHz to 30MHz. It should also work on 50MHz and 70MHz. VSWR is almost 1:1 (that is to say I can hardly see any reflected power). Since the vertical has rather low angle radiation, especially when mounted on a car roof, this is a reasonable DX antenna for portable use.

I have put it on the homepages at sm0vpo.com, the URL is https://sm0vpo.com/antennas/hf-portant_01.htm

Have fun with it. Hope you like it. I will go back to my lab USB card and see what other projects I may have overlooked.

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Finally, if you see any weird characters in any other projects then please let me know. They seem to look like this 30°C when they should look like this 30°C.
The reason these have started showing on the homepages is that mkodern browsers do not behive like the old Internet Explorer, or Netscape. My html files were saved in "UTF8" format, but now they have to be "UTF8 with BOM".


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Very best regards from Harry Lythall - Märsta - sm0vpo


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PS - I have yet to update the altervista mirror site. Sorry!!
/H