Category: Construction

My portable HF 3 band linked dipole for SOTA activations I like to pack the wire away on a spool rather than a kite style wire winder. I find the figure of eight loops put kinks into the wire and I just prefer the wire to lie straight.

Since I made the dipole I have been winding both halves of the dipole onto one shared spool like so (picture is an older dipole but the spool is the same one I now use on the portable dipole):

I use this spool as it’s the smallest I have to hand and has the capacity for both wires including their integral guy strings each end. This is OK in that it keeps the wires lovely and kink free but it takes a while to wind them onto the spool, and bringing one half of the dipole to the other invariably involves unhooking it off every tiny thistle or twig on the ground. Also the two halves love to tangle together.

My dipole (described here) is for 20m, 30m and 40m with small bullet connectors for the links and is made from insulated 16/0·2mm wire with 3metres of 3mm nylon guy line attached at the end of each half.

So I decided to model a smaller dedicated single wire spool to separate the wires and make deployment and packing away easier and faster. This would be 3D printed by my friend Paul so the design needed to be suitable for that, ideally with no time consuming support structures needed during the printing. It would be in ABS so a two part (identical halves) design was used which would be cemented together. The cement works like a weld essentially melting the two parts together. Loading on this part is very minimal anyway.

This is the design I came up with:

The design features were to be:

• Lightweight. I wanted the two spools to be equal or less weight than the existing single grey spool. I am always aware of ‘feature creep’ upping the carry weight. A large central drum and shallower cheeks keeps weight down, as do the weight reducing holes.
• Function. Obviously I need it to take all the wire without overflowing but not have so much capacity I was carrying dead weight.
• Usability. I wanted to make it easier and faster to use. The larger internal drum size means more wire wound per revolution and the cross members in the sides are sized to allow a gloved finger from each hand to fit in quadrants 180° from each other to make a simple hand winding action. Additionally the larger weight saving holes were sized to allow the plastic guy locking buckle to pass through to make starting the winding up of the guy very easy.
• Bonus features. I realised when adding the weight saving holes that a good airy pattern of holes would greatly help with natural airing and drying out when packed away wet. I also added some internal locating lugs that would self centre each half during the cementing together process (a request from Paul after the prototype build).

The 2nd version soon arrived and was tested with the dipole. It was definitely much easier and faster to wind up the single dipole half which fitted nicely in the spool capacity (that’s an open 20m to 30m link sticking out):


Deployment is extremely fast as the spool is small enough still to use a thumb and finger of one hand as an ‘axle’ on the centre hole each side (sized to take a pen or pencil for when it’s too cold for dexterous hands) and as I can now deploy each half where I need it immediately with no tangles I’d say deployment is between 2 to 4 times faster which is appreciated when the wind and rain is biting.

Paul has made a small improvement to the design for printing purposes. My location lugs had such a small surface area they did not have time to cool down before layers so he has extended them lengthways but removed the vertical part of the lug to keep the volume (and thus weight) the same:

Here are a final pair to make one spool fresh off the 3D printer:

The final weight for the pair of finished 2 part cemented up spools is 44grams. 2 grams over budget but I can live with that for the much better overall system:

SOTA HF dipole ready to roll, literally:

Quick demo showing deployment and packing away:

If anyone with their own 3D printer is interested is making use of this design Paul has made it available on Thingiverse and Youmagine.
(Obviously your wire diameter and lengths will dictate suitability)

As I was looking to resume my contesting activities but SOTA style backpacking (for the RSGB backpackers contests) I needed a lightweight portable mast that is strong enough to stand up to some Welsh Mountain top wind and hold up a decent yagi. I looked around the Internet to see if anything was available already but nothing seemed to fit the bill for me. So I decided I would make one myself.

The biggest problem I had was finding tubing that was available and would telescope inside each other. The UK still mostly stocks imperial sized tubes, and each size seemed to be a fraction of a mm too big to fit in the next size up. I did find some metric tubes with a 2mm wall thickness in 5mm diameter step sizes. The sizes were 30mm, 25mm and 20mm. I would have preferred the smallest to be a little bigger like 25mm but I figured it would be OK well guyed.

I wanted the mast to be telescopically erected like I do with the SOTA fishing pole mast so I worked out how high I could reach and modelled up the mast in 3D CAD to find out what the end result would be and what length tubes to order. Also so I knew what lengths and total length of guy rope to buy. Also by applying correct materials to each item and modelling them exactly it enables me to know with pretty good accuracy what I am letting myself in for weight wise for the entire system:

I decided to make the top section longer, both to get a little extra reach and to have a little extra to leave the antenna fittings permanently attached to reduce assembly time. It’s a little long to carry at 2.5metres but should be OK:

It does fit inside my Passat estate very nicely though:

Using these lengths and with 300mm of pole overlap a maximum height of 5.65m is achievable. Removing the thickest section enables me to keep it to the 4m limit nicely for backpackers and save about 1kg of weight:

To clamp each section I planned to slit the ends in the normal way and use jubilee clips (worm drive hose clamps). Talking to a friend he suggested a different type of hose clamp with a bolt so it would ultimately be stronger. eBay came up trumps and I ordered three clamps like this:

Then I just had to cut slits for the clamps to compress the tube down. The difference in diameters are 1mm so I needed to lose at least 3.141mm off the outer tube. Four 1mm hacksaw cuts did the job. The heavy duty hose clamps are nice and wide (20mm) which helps increase the clamping area:

I wanted 3 sets of guys for the full height mast, one at the top of each section. I would be using 4 guys rather than 3 as it suited my expected erection method. No commercially available guy rings I could find would fit so I discussed options with my friend and he offered to injection mould me some from a very strong and light plastic which would be perfect. I modelled that up and sent him the design:
More details and load test of the guy ring are here. As two rings would be on the 20mm section it would be moulded to fit that and I would enlarge the bore for the next section down with a step drill.

To sit the guy rings nicely I added some nylon bushes to hold them above and clear of the hose clamps and also to enable practically friction free rotation. I was able to find online an existing bush to fit the 25mm pole but not the 20mm pole. Luckily I have another friend who works in a tool room who turned me up what I needed in some nylon.
Commercially available bush, 25.5mm bore for mid section:

Custom made bush for 20mm top section:

Section view of bush in use (bush in blue). The idea of the bushes are they lift the guy ring away from the hose clamps to reduce risk of guy ropes snagging on the clamp, add a low friction intermediate interface between the aluminium tube top or the hose clamp and offer a flat surface for the ring to seat on to reduce the chances of the ring jamming diagonally across the pole:

For the guys themselves I looked at various ropes and cords available and decided on 550lb paracord. It’s light and strong and not too expensive. From the 3D model I was able to buy the right amount and predict where to place them allowing me to scope out my intended site to make sure I had room to set the antenna system up:

Whilst things were coming together I decided to calculate the wind loading on the 9 element DK7ZB I was also building. The loading on the 20mm square boom alone was quite frightening at typical Welsh mountain top wind speeds and as I am using trusses to support the boom that increases the boom height above the guy point and I was concerned about the small diameter top section. So I got a short length of 5/8″ T6 alloy (the whole mast is T6) that was a perfect fit in the 20mm tube so added that to the top section to span a decent amount either side of the guy point. An M2 countersunk screw was used to just hold it in position:

Close up of the bushes and guy rings before fitting the guys, which stay with the mast to make deployment faster:

First trial erection went completely to plan, set up on my own.

The finished weight of the mast INCLUDING guy rings AND guy ropes is about 3.5kg. It’s actually currently weighing 3.7kg but that includes some aluminium blocks and plates, and stainless steel bolts, that are part of my yagi mount so not actually part of the mast. It doesn’t include the guy pegs and hammer of course. However for backpackers contests I can save nearly another 1kg by leaving the 30mm section behind and still achieve the 4m height limit. For the guy pegs I bought some 25x25x2mm aluminium extruded angle and cut them into 50cm stakes. The 4 stakes weight 387grams for all four including a bit of mud still on them.

And with a 144MHz yagi:

In order to stop it spinning in the wind as I was using Armstrong Rotator method, I came up with a simple clamping system using some 3D printed half round pressure clamps and a bicycle quick release to lock/unlock it. Arm fixed in place to the ground with a simple guy peg:

As I use my new Yaesu FT-857D for portable operations including backpacking for things like SOTA activations I wanted a way to transport it securely to keep it from getting damaged. I have seen the select knob broken off on FT-857Ds so did not want that to happen. And keeping it from getting bashed and scratched would be nice whenever possible.

For my initial SOTA activations and portable operations I carried the FT-857D in a Lowepro camera rucksack inside my main backpacking rucksack. This kept it nice and safe but weighs over 1kg total and takes up a lot of space so I needed a better option. I didn’t like the look of any of the tube based manpack builds I saw on the internet a lot so I decided I needed to make something as I could not find a suitable lightweight container I could use. Talking with my friend he suggested some Foamex sheet that he uses as it is quite light and strong. This seemed like a plan so I drew up a two part cover using some 5mm Foamex which seemed strong enough to support the weight of the radio:
The pink half will be fixed to the radio using the mobile mount screw holes and the green cover will slip on and be retained by a Velcro strap. The fixed base protection will allow it to be used on grass and stones without any damage or dirt ingress. The green cover protecting the knobs from damage in transit in the rucksack. The microphone will be retained in the space at the front, in a bublewrap bag. The 3D modelling predicted the total weight of the two parts of the protection to be about 500 grams.

I planned to use heat to form the shape of the parts, so marked out a sheet for cutting first using masking tape:

Next I took it up to my brother and got it cut out on a bandsaw then scraped all the sharp edges off with a steel ruler (my favourite deburring tool). Next job was to fold up the sides. My brother already made me a piece of MDF to match the width of the FT-857D to fold it around. I used a heat gun to soften the foamex and fold it up, holding in shape till cooled with a glass worktop saver:

Both sides folded up:

Next drill some holes in the sides to mate with the mobile mount holes on the FT-857D. The rear extension will protect the DC input filter and the front will carry the microphone:


The sides are higher than the radio for the lid to clear the band Up Down buttons when fitted. Unfortunately the foamex panels I have available were not big enough for the lid as it has flaps on four sides making it take up more real estate. So I decided to make it in two halves and cement them together. The front half will be the more complicated one as it has to go around the tuning knob bulge so I started with that half:

The folding up of this part was more complex with staggered shapes but the length of the folds were shorter so at least it was a bit easier. It took a little reheating to get the shapes to sit exactly where they needed to be so the cosmetic appearance was not as good as I would like but mechanically the material still seemed structurally sound:

As the rear half of the cover was simpler I decided to cut it out with a knife rather than take it up to my brother to cut it with a band saw. It was straightforward enough just a bit heavy on one hand and shoulder:

And folded up and glued to the front half:

The join felt a little weak to be so I decided to glue some strips of thinner foamex along the top to strengthen it, and also make it a feature I could take advantage of. I could stand the base on the cover when operating to raise the operatin heaight and angle up and use the strengthen strips to locate the base so it didn’t slide or get knocked off. I added feet to the base to locate on the strips and finally drilled some airflow (and lightening) holes either side of the PA heat sink and along the base to recover some of the added weight from the strips. The video below shows the strips and feet in action. I decided to ditch the bubblewrap bag for the microphone and utilise the button for mic clips and drill a hole in the base for that to locate in and secure the mic in position with a small piece of foam. Finally two 10mm strips of Velcro keep the lid securely on and are located in small notches to stop the Velcro from moving in transit:

I’m looking forward to getting out and using this soon. The only cost to me was the Velcro from eBay and the glue, the foamex I am lucky that a friend had some to give me. I think the 540grams extra weight is worth the piece of mind knowing the radio should be safe and it takes up very little extra room than the radio itself and a lot less room than the current bag I have used to transport the radio. It’s not as cosmetically attractive as I would ideally like but this is the first time I have used this foamex and formed it with heat.

Finally here is a video showing how it looks in action and how it goes together for use and transport.

Edit: To assist others who may want to make their own version, I have added below the drawings I worked from to mark out and cut the two halves:
Base Drawing
Top Drawing

For my SOTA activations and HF portable backpacking operating I am using a 3 band link inverted V dipole and winding the dipole up onto a small round spool. Now the colder and darker months are here I was interested in the wire winders a lot of people use. My friend 3D printed me one to try out, but I did not like the kinks it puts into the wire so I decided to keep to my spool method as it keeps the wire lovely and straight. But we thought we would evolve the winder into one suitable for the 4 string guys I use to keep the mast up.Up to date I have been looping them up and tying the loops with a loose overhand knot. This works quite well and adds no weight at all. However it can be fiddly with gloves and although unfurls nicely 90% of the time but sometimes does get a knot or small tangle, which I can do without now winter is upon us.

The initial design used was based on one download from a 3D print site, but I wanted to make some improvements by extending the length and deepening the scoop in the middle and adding some function for an elastic loop to keep the string tidy when wound up.

This is the model Paul came up with during our discussions. Deep winding Vees and deep scoop, but with minimal weight. It will be printed in PLA not worring about it’s longevity as will not be outside for long at a time and a nice bright conspicuous red:

And here is it dimensioned up:

To use these winders you need to wind them in a figure of 8 fashion both to unwind nicely and also to not introduce twists like this:

This is how they should be wound:

And when wound like that this is how easily they are unwound:

1. To retain the string nicely some elastic cord from eBay was added. A loop tied in the middle to make fitting and removal of it easy. Finished bare winder weighing in at 10 grams which tied up with the 3D model prediction:
   
   To save having to tidy them up and possibly misplace these in the field I have attached the guy through one of the loops in the frame in the same loop that will go around the guy peg. This will actually also help me to slide the tensioner up the line easily with gloves on as I like to pack them away with the tensioner at the bottom of the guy:
   
   All four guys tidy and ready to be deployed quickly. The longer part of my guys are the white cord, the last 3metres are in hi vis yellow to hopefully reduce chance of them being tripped over:
   
   These are nothing new of course but it was nice to make them exactly to my requirements. Similar winders can be bought from places like SOTAbeams etc, though this unit is similar in size to the midi winder SOTAbeams sell but a third of the weight and the deep arch allows the string to lie nicely and has loads more capacity than my guys need and they guy an 8 metre fishing pole.

If anyone with their own 3D printer is interested is making use of this design my friend Paul has made it available on Thingiverse and Youmagine.

Following my first wire dipole which is too heavy for portable and I am using it at home, I am making a multi band link dipole for portable use for SOTA activations on the hills and mountains.
Instead of traps it will have links where we can make or disconnect sections of wire in to be resonant on different bands. It will be cut for 20m, 30m, and 40m. The 30m dipole should work as 5 half waves on 6m, and the 40m dipole should work as 3 half waves on 15m.

Via the SOTA reflector I found this very useful link dipole designer:
http://www.sotamaps.org/extras.php
and used it to design the dipole like so:

The 4 foot support at the ends will be my trekking poles, which enable me to keep the end elevated with a lesser ground footprint, which needs 61feet as it is.

I decided to adopt a very similar design as my first dipole (here) with a flat plate centre and cable ties. The plastic I used before I found to be a little brittle so I don’t expect it to last repeated portable batterings on hills. So I found some bare FR4 board and used that.

Coax stripped back and wires attached. I decided to not go for the loop of coax at the top many go for to stop water ingress, but go for a simpler style and will waterproof it with some liquid electrical tape. I have gone for RG58 as it’s less lossy and mechanically good and not that heavy really. It can always be lightened up if really necessary later.

Showing the soon to be 20m antenna wire.

To mount the dipole on the fishing pole mast I have made this piece of uPVC which is very light and pretty strong which slips down over the thinner section and sits on top of the thicker section below like so:

And attached to the dipole itself:

I have to put a word in for the Barenco crimp PL-259 connectors I got for RG58.
I prefer crimp to any other style due to the reliable retention on the braid (if you have good braid-the Barenco supplied RG58 has a good braid).
This connector also has a reduced diameter tip which lets you use the iron on the outside to transfer heat and keep the main contact section clean of solder.
It also comes with a stiff plastic strain relief that is such a good fit I didn’t think it would fit, but can be fitted and looks like it will give some support.
Product link

Next job is tuning it up and adding sections.

Off to a local hilltop common to set up the mast and antenna and tune the dipole sections.

I’m using an 8m fishing pole and will mostly use it guyed. I decided the middle size guy ring from SOTAbeams was the best option as it sits nicely on a joint and is a nice height but also not too steep an angle to collapse the pole, hopefully. I have a ground stake to strap the pole to for assisting in erecting it and holding the base steady. I tied four guys, but may use just 3 depending on location.

Antenna attached, will be at 23 feet above ground.

As I prefer to take the weight hit and reduce coax losses, I am using RG58. To save it bending the thinner top of the pole with the weight hanging away from the pole, I am using velcro cable ties to keep the coax against the pole to below the guy ring.

Raising the mast. This is SO much easier than hoisting a 20 foot aluminium scaffold pole on your own!

I used the MFJ269C for tuning the 20m section of the dipole. What an amazingly useful bit of kit!

Once the wire was trimmed to nearly be resonant in band I tied on the string I am using to make the link supports. This shortened the dipole making it closer to resonance, then a final trim to tune. It actually read and SWR of 1.2:1 at both band edges, with 1:1 to 1.1:1 in the SSB portion, where I will be operating. Then trim off the ends the same amount as the length of the 2mm bullet connectors I am using for the links. I used the sockets on the ‘uphill’ side of the links.
Soldering the link on, literally ‘in the field’.

I’d pre-cut the next sections and already fitted the plug of the bullet connectors, so the link was soon made. I don’t think you’ll get much lighter link supports than these!

We soon had the 30m dipole tuned up nicely, and ends prepared for soldering. Except the brand new gas iron G1YFC had bought failed to work again. Managed literally two solder joints! That’s going back. So I will need yet another dipole building session tonight, as I plan to be using this tomorrow for SOTA activations.

We took the opportunity to work some stations on 20m and test the battery supply. We started on 50W, then 75W, and in the end went for 100W. Why not…
We used about 1.1Ah in about just over an hour. We’d use more contesting or calling CQ more often, but we were scanning the band and calling into other stations.

Final round of antenna making.

Bullet connectors now soldered on at home I headed back out to add the 40m sections of the dipole. First I checked the match of the 30m dipole to check it wasn’t different from the previous install as this time I set the pole and antenna up on some grass near my home and wanted to see if there was much difference. All seemed fine. At least the dog walkers and cars driving by were amused. Or was it bemused…

Anyway, tip of the day if you are using string for your links is to make sure you tie the knots with enough slack. I made one link string a little too short so it was same length as the link, which meant with stretch the connector may pull out.

One problem of a double fisherman’s knot tied in wire and thin nylon cord is it’s pretty much impossible to untie them. I couldn’t cut either as I’d have to start over, so I had to tie a couple of knots in the link string to make it shorter.

Once done I could trim the 40m wires to resonance. I thought I was near so I tied the final knot to join in the bottom guy string, leaving (I thought) plenty of trailing wire to trim.
Wrong. I trimmed as much of the wire as I dared but was resonant pretty much at 7.000MHz, and I will be using SSB. My only option now (as I was getting tired of it now anyway) was to shorten the wire by adding knots. That did do the trick.

Next stop, some summits.

As part of my plans for SOTA (Summits On The Air)  operation I want to operate on 144Mhz SSB with a small lightweight yagi.

After much research and a lot of reading up on lightweight yagis (I’m more used to building long high gain yagis for contesting) I have decided to go for a DK7ZB design. A 5 or 6 element yagi with max boom length of 2 metres.

So I headed off to Wickes to see what they have, only choosing Wickes as it was less across town to battle through the traffic coming back. I was looking for PVC pipe and pipe fittings.

Most of the smaller bore pipes less than 38mm seemed just too floppy. The 38mm waste pipe was nice and rigid, but probably was heavier than a suitable aluminium boom would have been. I kept looking and discovered there were two types of 22mm pipe and one was floppy, but one seemed rigid enough. It was a 2m length and although I was thinking of two 1m lengths for portability, I am leaning towards the single piece boom for now.

Next element clips in the form of pipe clips. The design of the pipe clips varied, I needed ones with flat sides to drill for the elements. Some have a central rib about as wide as the 3mm elements would be and it was clear it was unlikely I could drill spot on through it. So I managed to find some that didn’t have the rib. A big bag for 59 pence.

I also got a pair of T pieces. My thoughts here are to mount the boom through the T piece permanently and drill a hole in the T part to drop over my fishing pole mast.

to be continued……