Author: Steve G1YBB

I have had a few emails now from people asking for STL files to print themselves some of the wire guides I have used on my disguised cobweb or my 20m wire moxon. So I have uploaded 3D printed wire guides for moxon or cobweb antennas in various different sizes for free download.

I have no idea what size tubes other people are using so I have made a set that covers poles from 7mm diameter up to 25mm diameter in 1mm increments.

Each size should grip about a half mm diameter smaller than design and expand about a half mm bigger diameter.

They are designed for M3 machine screws and I recommend using nyloc nuts so they can be nipped up enough to grip without over tightening.

The wire holes are 3.5mm diameter which is bigger than the tri rated wire I used on my 20m moxon so should be fine for most people. Of course you can easily run a brill through the hole if you are using very thick wire but be aware of making it too weak for such thick wire.

To print orientation below is best for strength and doesn’t need supports. I recommend PETG and print with several walls also for strength. I print mine basically as 100% walls so there isn’t actually any fill as such.

Download the files from the link below

https://www.thingiverse.com/thing:6680276

If you like them, I’m always up for a coffee…
https://g1ybb.uk/buy-me-a-coffee/

Like many hams, when there is a lot of wind about outside I have to check on how the mast is doing. One thing I did not like was the way the wind rocks the beam back and forth on the rotator. I figured this cannot be good long term of the gears, especially as they seem to be mostly plastic. (Unverified)
When you have something like a 20m moxon up the play back and forth looks quite dramatic. So here I am sharing my YBB boom tether system idea.

For a couple of years now I have had a small arm attached to the stub mast and I guyed that down but it was very short and even with a lot of tension the boom still moved about in bigger winds. Also was quite a lot of  sideways downforce on the rotator (I don’t have a cage).

So in the design and build of my new 20/15/10m tri-band 2 ele beam I incorporated a tethering system on the boom itself at each end to have more effect and balance the side loading to the rotator.

This has proven to be very successful, keeping the boom practically motionless while the 20m moxon element dances all over the place. So I thought I would share it as an idea for others, especially those with a christmas tree stack of beams. I always retract the mast when not on the air, but I know others also retract their masts when high winds are due, and this could help then.

This is the mast retracted to about gutter level and the beam tethered. The left hand tether point is close to the 20m driven because the balance point of the beam is to the left of the 10m driven so it was a small contribution to try and reduce the imbalance on the mounting point.

The tether points are very simple. Some aluminium angle, a square U bolt and a round U bolt. These MUST be stainless. (Trust me I know!)
To hook the rope on these I use a plated steel (must NOT be stainless) clip from screwfix. I then file the head off the gate pin to remove that.

Then this is what they look like installed:

Once fitted they are just tensioned up with sliders as I use on all my guy ropes:

Now I know by now you are wondering how on earth I get them on and off?
Well that is quite simple and surprisingly easy. I use a telescopic fishing pole with some neodymium magnets taped to it to both fit them and remove them for winding the mast up:

All dead simple stuff but it is really effective.

This may not seem that radio related but an arbor press is a very useful tool, even if it is not used that often. Most recently I have used it to press in my YBB washers into Stauff clamps for an antenna build. I’m tuning it up in order to use a 5 inch vice based brake press set to do some sheet metal folding, mostly as I don’t actually own a vice to use the brake press set in but also because if I did I would only have a couple of inches of throat to bend whereas the arbor press will give me about 5 inches. These are great tools and not expensive but out of the box they don’t feel or work that great so I decided it needed a simple tune-up.

I actually bought an arbor press because I could get what I really wanted which was a lever press RS (Radio Spares) used to sell. If you have one of these in good condition, I need it!!

I used to have access to one of the RS punches in my previous company and used it to good effect to bend boom supports for my VHF yagi. That was the actual original reason I got the arbor press later, despite working now at a company with several fly presses, I like the control of a lever.

Anyway. You can see from the following video that as supplied they are a bit rough and ready:

Having seen videos on youtube about these already I knew it could use a strip down and clean up. So it was all stripped down and taken outside to clean the swarf from the tapped holes that hadn’t been done when it was made. As I don’t have an airline at home I used a steel tube and blew hard, after first spraying in some WD40 to loosen it and wash some out:

Once all the holes and bolts were cleaned up I used a fine file to smooth off sharp edges and machined faces that weren’t that smooth. The side to side slop adjustment of the ram is just two bolts that nip up onto the side of the ram so I also filed the ends of those smooth. Below is an after and before picture of the two bolts, one filed, one as supplied and fitted:

The adjustment screws that control the front to back slop act on a small plate but that plate was just guillotined sheet steel and not deburred at all so had a sharp edge on the pressure face so that was all filed smooth and flat too. (You can see that plate on the edge of the video below)

Once all the filing and cleaning up was done I first fitted the lever arm spindle and lubed it up:

I then greased up the 3 sides of the ram and fitted that and the front plate, and then adjusted all the adjustment bolts:

That will do for now, but there is a mod people do where they grind the bottom 2 teeth off the ram which allows you to be able to position the handle in the ideal position for the depth you are pressing. I will also drill and tap some holes for adding fixtures to the arbor press, such as the brake press kit (see below pic).

This was another Covid lockdown project in 2020 to enable me to do some over the air audio checks with locals and maybe give some points away in contests to the locals (my QTH is very poor for VHF/UHF). I wanted something small I could put in the attic. I figured a simple DK7ZB dual band 2m/70cm yagi in the loft with a single feeder would be ideal.

on this page:
https://www.qsl.net/dk7zb/Duoband/4+5_2m-70cm.htm

Martin DK7ZB describes his design for a single feed dual band yagi with 4 elements on 2m and 5 elements on 70cms on a compact 1m long boom.

I already have my element cutting jig  (see here) so cutting the elements was easy enough as usual. I went for the 8mm elements to make it nice and light.

To assemble it I decided I would 3D print not just the dipole box but also the element mounts themselves. The beauty of this over commonly used mounts like the Stauff clamps (see here) is I could design in a feature to ensure the elements are nice and perpendicular to the boom. I also don’t like drilling my tubular elements. For a start it weakens them and also adds a place for inaccuracies to creep in.

So this was my design for the element mount:

A snug fit onto the 20mm square boom and a friction fit for the elements. It was printed on its side so that the layers of the 3D print went around the element as printing as shown it may break off half of the tube pushing the elements in.

The are secured from below as seen here with an M3 bolt screwing into a captive hex recess in the mount:

I don’t like droopy dipoles on my yagis so I printed a dipole box to house the 50ohm choke that has integral clamps outside the box and also extra support inside the box:

I wanted the dipole box to also align on the boom but did not want to print it with supports as they are messy to clean up after so I used a simple locating spacer with 2 matching fixing holes in the dipole box. The 3rd hole in the spacer is a sighting hole that matches up with the scribed line on the boom for the dipole. This was also used as a drilling jig:

I used the dipole box spacer/jig to drill all the element fixing holes exactly centre of the boom and on the scribed line and assembly went to plan. I didn’t take photos inside the dipole box on this build but the following image is from a previous build of a 50ohm choke fed DK7ZB design. I hadn’t added the extra internal dipole supports here but I did print the choke former and re-used the design in this build.

Before final fitting of the elements I added a coax support guide. I usually use LMR400 as my feeder which is great but not super flexible and I like to take strain relief off the dipole box and N socket. This slips over the boom and supports the coax and also helps you align the N plus so you don’t cross thread it:
Here is an end on view showing the coax support perfectly concentric with the N socket and with a radius to match LMR400. When the feeder is fitted I then use a velcro cable strap, the ones with a slide through buckle you can tighten onto:
So finally we have the finished dual band yagi ready for testing. The boom to mast clamp is another G1YBB design for maximum flexibility and minimal RF footprint when looking along the boom. The guy ring is also G1YBB designed and seen on this link:

And how does it look on the antenna analyser? I like making antennas and try to make them precisely because I do NOT like fiddling and adjusting much (wire stuff is OK) so my methodology is to try and follow the design with high level of accuracy and hope results match the design.

144MHz SWR plot:

432MHz SWR plot:

Both are a little high in band especially 2m but the SWR curves are so flat it’s very usable on both. I ended up feeding this yagi in the attic with RG58 as it is easier to route so with the losses in that the radio sees no reflected power as it is mostly used in loss I imagine. However I have made QSOs using this antenna in the loft, fed with RG58 on 23cms using 10W from the IC-9700. I can’t imagine much of that 10W getting to the antenna and what does reach the antenna has to pass through the roof but QSOs have still been made several times.