Author: Steve G1YBB

It’s time that the saying about sliced bread was replaced with 3D printers. They are right up there with the internet in ‘how did we manage without it’ in my opinion. For the radio amateur they uses are never ending!

The yagi below is completely a assembled with 3D printed parts. Not only that it’s mounted to a 30mm pole with 38mm U bolts using 3D printed reducers and the guy ring has an integral 3D printed plastic bearing.

Not only that the DK7ZB match coaxes were precision cut on a 3D printed cutting jig.

My HF inverted V dipoles and guys are wound up onto 3D printed spools and winders:

I just built a 20m moxon made with loads of 3D printed parts:

Including a custom made for the job dipole centre with strain relief and tie wrap slots for the wires and the choke:

The things you can make are really only limited by your imagination.

Here is a time lapse video of a yagi dipole box being printed:

Ok sales pitch over, you know you NEED one, what now?

Well first choose your printer. I went for the Creality Ender 5 which is at the higher end of the budget printers. Loads to choose from though.

To print anything first you need a design. This can often be downloaded from a site such as Thingiverse or you can design your own. To design your own you need 3D CAD software. Don’t panic, it’s not as bad as it sounds. There are many free options you can try like FreeCAD or TinkerCAD etc. I use Solidworks as I am lucky enough to use that for my job. Here is the box from the video in Solidworks:
Once you have your design file you export it as an STL file (downloads from Thingiverse already are STL files).

The STL file then needs to be sliced for the printer to print. That is turning the finished shape into many thin layers, or slices, to make up the final part. Again, software for this can be free. A lot of people use Cura which is a free download.

Here is the box above in Cura ready for slicing. It all sounds complicated but once you have told Cura what printer you are using and what type of filament you have you can often print with the default settings very well.

Here is the 18th layer of printing that would make up this box:

Once you slice your design you save the output to a card or send it via USB and pass it to the printer and the magic begins.

There is loads of help and advice on the internet for 3D printing but it is a really useful tool for the amateur radio home builder.

Having recently received my new (2nd hand) short contest callsign I was keen to air it and with probably the biggest contest in the world, CQ WW SSB, coming up I decided I would try a single band entry and build a moxon that was as lightweight as possible to use after how well my 50MHz moxon performed for me.

First step was the trusty Moxgen application and give it the wire size to get my start dimensions. As with the 50MHz moxon I then used 4NEC2 to recalculate the sizes for insulated wire as I was using.

This gave me this predicted radiation plot:

And an expected SWR curve like this:

Here is my NEC file for those wanting to work on their own version:
G1YBB_20m_Wire_Moxon.zip

Here are the calculated dimensions above applied to the 3D design described below. Note these dimensions apply to 16AWG/1.5mm2 tri rated wire. Other wire sizes with different insulation thicknesses will be different.

Once I had the dimensions I modelled up the wires in Solidworks to work out how long the spreader poles would be. This turned out to be about 4m so I ordered from eBay two types of 5m long fishing poles for evaluation. To do so I weighed a known length of the wire I was using to get an approximate weight each spreader would support and used something that weight to test how much sag there would be. The windjammer style pole had a thicker top section and was best.

Once chosen I could model up the poles themselves, weigh them and set their weight correctly in Solidworks.

To make the hub, rather than a thick metal plate and chunky U bolts and something to stop those U bolts crushing the poles I decided to use lightweight 1.5mm thick sheets of aluminium in a sandwich arrangement using 3D printed parts to grip the fishing poles without crushing them. I am a big believer in ferrite chokes at the feed point so I wanted a smaller support arm for that also. After my ultralight cobweb build which was unbalanced due to its 5th arm for the feedbox and choke I also wanted this antenna to be balanced, particularly as I intended to use this on the top section of my fibreglass push up mast which is 23mm in diameter.

Solidworks is great because it will also tell you the centre of gravity of your design, which I used to find the best places to put the boom supports on my yagi designs. So I was able to see how lop sided the design was, which was quite a bit. A ferrite toroid with coax wound around it on the end of a pole is a fair imbalance. To counter this I moved the mounting point towards the feed point so the main weight could help counter it. There was still a lot of imbalance so I decided there would have to be a support for the reflector to help counter the feed arm and it would also keep the reflector in better shape in the wind. Still not enough and I didn’t want to increase the aluminium plate sizes. Hmm. So I made a wire guide for the reflector support (exactly like the ones for the spreaders) but used a relatively fat chunky M6 bolt and washers for the mass and that pretty much balanced it according to Solidworks.

The pink two way arrow shows the expected centre of gravity:

One beauty of 3D printing is you can make exactly what you need so I could make pole clamps the exact size for the fishing poles and also arrange the poles compactly together (needed for the balancing) that you couldn’t do with something like Stauff clamps. I was also able to save on a bolt per side, every little helps. I started with the main pole clamps so I could test if my thin sheet sandwich would work as expected. As the holes were all in odd locations I decided I would mark out by printing a 1:1 scale print of the 3D model of the plate and taping it to one of the sheets and centre marking the holes ready for drilling. I then taped then G clamped the two plates together to drill the holes exactly in the same place on both plates. The holes in the plates are 4.0mm and so are the holes in the 3D printed parts. All the M4 bolts fitted perfectly.

I assembled the poles on and gave the assembly shake. All seemed OK.

I was able to press on with the design and printing. To mount the antenna to a 23mm fibreglass pole without crushing it I got some 32mm U bolts and printed some load spreading clamp halves. Also I was able to print some stiff but light supports to join the ends of dipole halves. Pretty much had a full kit of parts.

Final drilling could now take place.

I did a test fit to the pole to ensure it fitted OK:

To connect the feeder I used a panel mount N type socket. I used RG316 to go to the feed point as it’s lighter than RG58,can handle more power being PTFE based and also being PTFE based can be soldered without it melting. I drew up and printed a plate for the feed point with holes to stress receive the dipole wires, slots for cable ties and clamping on the back to attach to the support arm.

Even though it’s “only” 14MHz I still like to keep the connections tidy.

The coax part done I can start final assembly. The N type socket had to be fitted first as it would be very awkward once built.

Once mechanically assembled I took it out the front of house to have enough room to rig up the wires. I allowed an extra 20mm on each end to allow for tuning. Another good thing about a full 3D model is I was able to fit my 3D printed wire guides tot he spreaders using measurements taken off the 3D model and as seen below all was spot on.

I collapsed the poles to carry it round into the back garden to fit to the mast. Once all re-extended the first thing I wanted to do was check the balance by extending the 23mm section fully to see if it leaned over. Looks good!

Pushing it up to about 30 feet to test I trimmed 10mm off each end to arrive at the below plot. Almost perfect match with the simulation.

Time to test it on the air. Hmm. SWR with real RF way up in the red. It couldn’t be but was. I wondered if the choke wasn’t just not working but was working against me? It was meant to be 17 turns of RG58 so I hoped tightly packed RG316 would have same effect. I tried a GM3SEK choke my end in the shack, no good. Hmm. Talking with a couple of friends one suggested taking the N type off the plate.

I couldn’t think this would have any affect but it was worth a try before I started cutting things.

Well snag my blade! All was good now. The metal plate attached effectively to the braid of the coax certainly had some negative effect!

So now I had a working 20m moxon beam.

As it turned out come CQ WW SSB weekend it was too windy for me to use the moxon, but I have had great success working USA on FT8 since. The below is where I was heard for a few hours with the moxon aimed for USA and working mostly USA and Canada.

Final weight of the finished moxon was 3.2kg and it does compact down small enough to go on a roof rack, possibly even inside my estate though it could be a squeeze. I aimed for the SSB section of the band but it would have probably been to aim lower in the band to get a more usable SWR at the CW end. But performance wise I’m very happy with the new moxon.

Edit: October 2021
Since the initial build I have since soldered a little wire to the end of all 4 wire ends to move the resonance down to the digital end of the band. And since that I have made a 3 section wind up aluminium mast and can now use a rotator instead of running downstairs and up the step ladder!
But more interestingly, I re-measured the moxon at about 12.3m above ground on the new mast with LBC400 coax so very low loss at 14MHz and the whole band is below 1:1.6.    (I really must set the date on the analyser!)

At my location it’s very difficult to have any sign of HF antennas (or any antennas for that matter) up in the garden. I’m already using a covertly erected dipole after dark using this quick erect fishing pole mount. But I was very interested in an ATU free multiband antenna. The hexbeam is nice but too big and needing a rotator. So I looked at the G3TPW Cobwebb antenna. For those unaware this is a 5 band dipole based antenna horizontally polarised and roughly omnidirectional working on 10, 12, 15, 17 and 20m. The folded dipole style with shorting points seemed more complicated than I fancied so I looked at the simpler G3TXQ cobweb design.
This filled more boxes for me, single wires nice and easy to tune and a tidy looking feed box. However, it would still stand out in the garden due to it being some strange looking (to non hams) spoked wire thing. What I decided to try was upsweeping the spreaders to make the antenna look like a rotary washing line as there is already one in my garden. I was counting on the neighbours not noticing it had grown an extra arm and got a bit bigger. Except when actually in use I would keep it low down like a normal washing line such as this:

I searched the internet to see what people had designed but no-one had done anything quite this style. I was sure it would work due to the success of the hexbeam, but to be sure I started a thread on qrz.com and got some advice from the man himself, Steve G3TXQ, confirming there should be no reason why it wouldn’t work. Thinking about it the wire positions on this design are quite similar to those on the successful hexbeam.

Looking at existing designs all seemed to be based on heavy aluminium plates and tubes to support the spreaders. My plan to use this on a fishing pole would preclude this sort of design. Mine would have to be ultralight to have any chance of working. The spreaders were easy, I would use the 2nd and 3rd sections from telescopic fishing poles like the ones I use for masts. These two sections are long enough (bearing mind the upswept angle means the spreaders need to be slightly longer than for a flat design) and are plenty stiff enough. At the bottom they are approx 20mm diameter tapering to 8mm at the tip. Five 4 metre poles were soon ordered from eBay at a cost of £37.70 with the delivery, making them just over £7.50 each. Here they are next to an 8m and the 10m fishing pole the finished cobweb will be used on:

Next problem was the centre piece which came to be known as the spider. I mentioned what I was looking to do with a non ham engineering friend and it turned out he was about to get a 3D printer on loan. A great answer to my problem, a custom designed 3D printed ABS spider would be perfect. I got straight onto to modelling up the antenna in a 3D design program. This would also allow me to be able to confirm the fishing poles would be long enough and see how it looked, find where the wires should be based on the wire lengths used by G3TXQ and also predict quite well the finished weight. After searching the web a lot for everything to do with the G3TXQ cobweb, many threads on qrz.com with posts from Steve himself, I designed it to have the feedbox in line with the 17m wire, making the 17m wire a square and all the others bunched into the feedbox.
Here is an animation showing how the antenna should look when finished:

And here is my original design of the spider:

I sent the CAD file over to my friend for 3D printing and the printer reported it would take 95 hours to print! So he decided to strip it down to just the 6 bores (five spokes and bore for the pole) and rebuild it from separate parts that would be glued together after printing. The glue should be stronger than the ABS he assured me.
My design was originally based on the main spider with a slightly tapered bore suitable for the 5th section down on my 10m pole. Not where I planned to use it, but hedging my bets until I got one working and mounted on the pole. I would then use one of 3 sleeves to move the antenna up a section per sleeve. During the redesign we were able to come up with a better idea using end caps and also save a bit of weight, all good.
This is the new design:

And on this page the printing process and spider assembly is detailed in more detail.

The spreaders slot into the spider bores and need to locate on a pip in the bores to stop any rotation (seen in the spider images above). This is mostly for the feed box to keep it in position but also to securely locate all the spreaders. The ends of the fishing poles are not cut square so I marked a line to indicate the longest part and marked out for the slot to be made with a Dremmel 3000 and a small milling like bit:

To Dremmel the fibreglass safely I set up the hoover as a dust extractor which was very effective:

Finished notch, which is done to all 4 spreaders and the feed box spoke:

So I knew the notch was deep enough I marked the spreader fitted before the notch is made, then added another mark 3mm up the pole (depth of the pip):

Spreader fitted after notching:

Once this stage was finished I extended each spreader and feed spoke in turn and marked the smaller section at the end of the larger section to indicate how far it fitted, then took them back apart and applied some varnish to the part of the smaller section that makes the joint and extended them again adding a little extra force to ensure they are jammed nicely and hopefully the varnish should ‘glue’ them together. I then added some varnish to the outside of the joint to seal against water running down the joint and inside the spoke pooling in the ferrule. You can see in the picture below that the spreader on the left is going to need another application or two of varnish to seal that gap:

The feed box fits on the feed spoke suspended underneath the feed spoke pole. The angle of the feed spoke bore on the spider is slightly steeper to align the wire entry of the 17m straight in, one nice advantage of 3D CAD design.

The feed box is an ABS box from Farnell, their part number 244-4686, manufacturers part number TW7-5-11B. Note that Farnell do free delivery to non company accounts now. This size was chosen to be the smallest usable and (hopefully!) fit the feed balun inside:

The buses for the wires I wanted also to be lightweight but not compromise on the amount of copper so I abandoned my plan A of some copper clad FR4 when I found some 0.32mm copper sheet. Perfect. That equates to 10 ounce copper where the FR4 copper would have only been about 1 ounce and I have no dead weight in FR4:

As copper sheet is pesky to solder to I wanted to tin one side before trying to solder even more copper to it in the form of the balun and wires. First attempt with a heavy iron and a hot plate was not very successful. The solder looks awful and you can see the copper discolouration on the bare part before we gave up:

A plan B was required! A multi zone reflow oven and some solder paste was much more successful! Not something everyone has access to but I do so I may as well take advantage of it. The scratches are from scraping off the flux:

To mount the copper flat to the base of the box to maximise space for the balun and simplify the build I needed to Dremmel off the four PCB moulded mounts. For good measure I removed the same mounts from the lid. No point carrying dead weight even if small!

As I like things neat and tidy, I have taped the two copper bus plates back to back to drill a small pair of mounting holes through both together so they match:

Here are the two bus bars fitted with M2x6mm screws:

Instead of nuts and bolts to join the wires on I wanted to minimise weight again so just soldered directly to the copper. Not so good to replace wires but I like to bridge cross problems if and when it’s needed. As I didn’t want to waste space in the box and add extra weight there are no spacers for mounting the copper bus bars. They will sit flat on the bottom of the box. But as I will be soldering with it in situ, especially for the fiddly to fit Guanella current balun, I have added some Kapton tape to the box to hopefully protect it from the heat a little.

The wire I used is 16/0.2mm stranded which measured to be pretty much the same as G3TXQ describes in his text though in his photos the coloured wire looks a little chunkier to me. For the actual lengths I started with the lengths given by G3TXQ here:

I then referred to his wire thickness adjustments for hex beam wires here:
to see how much things changed for wire diameters then decided that an extra 3 inches each should hopefully be more than enough. I also took note of some predicted and measured figures for the amount the resonant frequency changes when trimming provided by Jacek SP3L in the disguised cobweb thread higher up the page:
Changing the wires with my construction would be a nightmare so hoped this extra length would be plenty.

Where the wires exit the feed box I’d planned to use Hellerman H20 rubber sleeving but it was too loose a fit to the wire, so instead I used adhesive lined heatshrink which would also prevent water ingress between sleeve and wire.

To solder the wires to the copper bus plates I removed them from the box and placed them onto a piece of MDF to prevent heat sinking away. Before doing so I drew around the box and marked the wire entry points so I would be soldering the wire in the right places. The pre-cut to length wires were then threaded into the box treble checking the order before soldering:

Using a 100 watt Weller mains power soldering iron with a 6mm chisel tip I was easily able to solder the wires on with sound looking joints and without melting the previously soldered joints:

Once cool I fed the wires back into the box and fitted the plate and repeated for the other side:

I’m using an N-type socket for the feed input connector as I much prefer them over the SO-239 and PL-259 UHF connectors.

Having created the design in 3D CAD I was able to use my model to tell me how long to cut down the fishing pole for the feed box arm. Using the end of the centre spider tubes as an ideal reference point for a tape measure told me the spot to mark for cutting, in [inches] and mm:

As things worked out the position for the feed box happened to span the joint of the telescopic pole. I had originally planned to use saddle clamps to attach the feed box to the pole, using the same screws for those to hold the bus plates in but I needed two sizes neither of which I could find and to save making them I just bolted the box to the pole with 2x M3 screws and nylocs. I used nylocs so I could tighten up without crushing the fibreglass pole but not have the nuts work loose.

Once the box was fitted to the pole I could then fit the balun. I wanted to fit the feed box to pole first in case once the balun was fitted it was blocking the access to the screws (quite likely). To try and reduce the damage to the edge of the box during soldering (the iron ALWAYS finds a way of melting the box when you are working inside no matter how carefully) I cut up a Pepsi can (other canned drinks are acceptable!) and folded it around the edges, hoping it would make a good heat shield:

For the feed balun I used the exact same  FT 140-61 ferrite toroids as G3TXQ and RD316 (which is just RG316 with a double screen)

4 lengths of RD316 taped out for marking exactly the same lengths. Apparently the outer jacket of RD316 is repellent to all marker pens including biro, Steadler permanent markers and sharpies. So I marked the line to strip the braid off with masking tape then slit down between each piece to leave a strip on a marker:

Outer jacket removed and bits of heatshrink added to keep the 2 coaxes together. This also helps stop the coax curling up all the time:

Close up showing quite closely matching outer jacket length remaining:

Both 1:1 chokes wound:

To fit the balun into the feed box I first loosened the four screw holding the two bus plates in so I could slip some thin card (from a cereal bar packet) under the ends of the bus plate where I would solder the coax (paralleled end) then soldered the coax to each plate. Then I removed the card and tightened the screws back up on the bus plates and added a drop of varnish to each one. I then fitted the other end (the series part of the balun). This job didn’t turn out to be as much of a stressful procedure as I expected. The heat shields worked perfectly and the box survived without any damage! I used some Hellerman rubber sleeves where the wires exited the feed box

As this project has taken me so long because I started make VHF & UHF yagis for contesting and doing lots of contesting, in that period I have moved away from using the fishing pole as I now have a more heavy duty pole this can go on. I did test mount it on the fishing pole and it is still viable. But it fits even better onto my 23mm diameter 3mm wall mast top section. To do this I designed and 3D printed adapter washers and simple locking collars to fit top and bottom. In the first photo you can see that without my glasses on I have fitted the collar upside down as the ridge is supposed to mate with the groove.

The wires are fitted to the spreaders with some 3D printed guides I drew up and printed. The wires pass through holes so the spreaders should self centre and tension be equalised all along the wire.

As my design is closely following the build of Steve G3TXQ I was able to use 3D CAD to determine where the wires should be attached to my spreaders if all goes to plan and at the very least give me a good start point. This could of course change if my wire turns out to be thinner or have a different velocity factor from the wire Steve used. These are the positions using the same wire lengths as on Steve’s page:

To join the ends of the dipole I used nylon cord as used on bathroom light pulls only a bit thinner, thin, strong and light. I used a tight fisherman’s knot in the cord to grip the wire and taped the string to the wire ends to keep the wires straight at the ends whilst tuning then locked off once tuned with a cable tie as well.

Tuning I did with the extremely useful MetroPWR FX700 antenna analyser, taking notes of how much I cut off each time affected the resonant frequency. I decided my target tune frequencies would be somewhere near midway between the SSB and data portions as from home data modes is very family friendly with no shouting to annoy anyone.

SWR results are as follows, measured at about 30 feet above ground.

Finished antenna pretending to be a washing line. It sure looks like one but I don’t think I quite have the disguise cracked…

As this started off to be an ultralight cobweb it’s worth stating the weight. Weighing myself alone and with the cobweb complete on the bathroom scales it comes out as 1.2kg overall.

Final Note:
It is with sadness that this took me so long to complete, and during that time Steve G3TXQ succumbed to illness and is now SK. Steve had some thoughts on the antenna that we exchanged, both via email and in this QRZ thread. It’s a great shame for me he never got to see the finished antenna he inspired. However the QRZ thread did stimulate some good experimentation on cobwebs and is well worth a read through for that alone.

The coronavirus outbreak of 2020 put a stop to all portable radio activities so like many people I was forced to adapt and overcome and set up something at home. For non rotating mast systems I strapped a mast to the YL’s parasol base:

This worked for smaller dipoles but I wanted something a bit sturdier and the YL wanted her umbrella back! So I decided to make a new one. I thought about making something from scratch but after asking the local club members for ideas it was suggested to use a tamper that builders would bash sand down before laying slabs or bricks. A quick Google located one in stock in the local Toolstation:
This is a cast iron 10″ base and a fibreglass handle. Cost me about £35 which is cheaper than some of the suitable umbrella bases I was looking at. I click and collected it. It didn’t seem that heavy at all to be honest but I’d already planned to fit it to a paving slab so wasn’t an issue. A quick session with the drills and the tamper was securely fixed to one of those heavy council style paving slabs:

The fibreglass handle feels pretty strong with some give but also felt like it would snap before that slab budged! This would normally only be used as the support until guys are attached anyway.

Before fetching the tamper I liked this design as the 4 webs I thought would be good for locating the bottom of the pole for lashing with a bungee. But in the end I decided to design and 3D print a locating guide that would stop the pole from twisting in relation to the yellow handle. Quick bit of CAD:
The hole on the side is to clip the first end of the karabiner bungee into while I lash it tight. Once a few turns of bungee are overlaid there is little stress on the plastic but it feels pretty strong anyway. This I printed in PLA which is easy to work with though ABS or polycarbonate would probably be better. There’s not a lot of stress on these parts so should be fine.

The biggest problem I had fitting these was getting the rubber handle off! it’s only glued on at the domed top but pesky to remove. Got there in the end and fitted the guides. they were a beautiful fit, close sliding fit. So close in fact the label halfway down stopped the slide  so I had to open it up a bit. Couple of small M3 stainless screws and nylocs and job done. Two bungees and we’re ready to rock and roll:

Close up of the top guide:

All fitted a treat.

You may be thinking all well and good if you have a 3D printer of course. You could do the same with bits of wood I’m sure but I do heartily recommend a 3D printer. They are amazingly useful and very affordable now, although the filament at the moment is doubled in price due to the high demand when the 3D printing community was mass producing PPE equipment for the NHS.