Category: Equipment

As I was planning to resume 144MHz contesting but this time full backpacking style I wanted a decent beam that was suited for repeatedly assembling and disassembling. I have a Cushcraft Boomer and also a pair of homebrew DJ9BV yagis but neither are really ideal for the job. After nearly two decades away from radio yagis have moved on and researched showed the DK7ZB yagis were very popular. His designs seemed ideal for my purpose.

I settled on the 9 element long yagi as it is not too long but with decent gain and also has a good flat SWR curve. The RSGB Backpackers section we wanted to participate in only allows one antenna so stacking shorter yagis was out.
The dimensions are available on Martin DK7ZB’s site:

I went for the 10mm elements as a compromise between size and weight and best performance. I was also able to find 10mm clips to suit my intended design.

You can buy some of the DK7ZB yagis ready made and also in kit form, but I didn’t really think the parasitic element mounting methods were ideal for repeated building especially in cold weather. Also the driven element was a problem as it’s not ideal at all for disassembly. There was one example of a driven element designed for taking apart on DK7ZB’s site but I couldn’t find any parts like they were using. I was already building my own lightweight portable mast so I decided I may as well design the yagi from scratch too. So I modelled the full antenna down to every nut and bolt in 3D CAD software. This enables me to know exactly what materials I need and also predict pretty accurately the weight, bearing in mind I plan to backpack this up hills:

To source the main raw materials I found that it was cheaper to buy from https://shop.nuxcom.de/ in Germany than anywhere I could find in the UK! I went for the 20mm square boom and 10mm elements. My 3D CAD model told me I wanted two sections of boom 1.72m long and one section 1.62m long. (After ordering I noticed that is the same lengths Attila uses in his 9 element kits!) I didn’t go for a kit as there were several parts in the kit I didn’t need and I wanted to order a few spares of the elements just in case I cocked up some of the cutting. Nuxcom sell the boom in 1.5m and 2.0m lengths but the 2.0m lengths cost more than double the shipping, so I asked Attila if it was possible to buy 2.0m lengths but have them shipped in two pieces, 1.72m and 28 cm lengths. He did this for me at no extra cost which is good service. The offcuts would be useful for doing tests later.

First building task was to cut the parasitic elements to size. Although I’m pretty good with a wood saw I’m a bit rubbish with a hacksaw and I didn’t want to use a pipe cutter as certainly for the driven element I needed no deformed ends to the tube, so I managed to borrow a mini circular disk cutter like so:

With this I was able to make nice square cuts. To measure them I used a metre ruler (tape measure for the reflector-checked against the metre rule first) butting both up against a stop to get an accurate measurement. I checked that the first mm was a true mm before starting as some rulers have a dubious first mm:

And checking D2 (ever so slightly short if anything by a fraction of  a mm):

After cutting the parasitic set I fitted end plugs from Nuxcom for a nice finish. (Elements in bottom box, spare elements and boom sections in top):

Next to assemble the boom. I bought the Nuxcom boom joiners and I must say they are very well recommended. The fit onto the 20mm boom sections is a snug push fit and the extrusion is thick enough to be strong yet still light. I got them with the M4 bolt and wing nuts. The one thing I didn’t like so much was the massive hole for M4 which was 6.5mm diameter. However, once I modelled up the joiners and dropped them into the antenna assembly I could see that a 4mm hole at the top of the 6.5mm hole would be pretty much bang on centre of the boom, and mean the boom could not move up in the joiner. I also added a vertical bolt on each side of the joiner too as shown below. That meant the boom section was forced into the joiner tightly ready to drill the holes. I drilled from each side, using the 6.5mm hole as a stop for the 4.0mm drill bit:

The above picture is showing the boom joiner fitted to the centre section. Both joiners are fitted to the centre section and will stay there permanently so I have used socket cap heads and nylocs, all stainless steel, bolts cut to minimum length. (The four supplied wing nut bolts will be used to attach the end sections on the hill top). With both joiners fitted, the centre section then is pretty much the same length as the outer sections (by design). I also bought the square boom end caps from Nuxcom to finish them off nicely:

The boom was then assembled in my hallway and the centrelines of the element positions scribed on. I used a tape measure masking taped to the boom to ensure it never moved and starting at the 100mm mark on the tape measure to eradicate any errors from the tape measure hook end.

The element clips I needed to find something that was quick to mount the elements and remove them again. The typical single bolt through the centre of the elements I didn’t fancy as it was a bit fiddly especially with cold hands on a windy hill top. My friend found these 10mm pipe clips that were ideal. Snap in and lock, and easy to open again to remove the elements. They will have a finite life but my test piece has had dozens of cycles and they come in a bag of 100 for under £6:
Another plus point of this is the element centre is a reasonable distance off the mounting surface which means I had good scope for getting the driven element to be on the same plane as the parasitic elements. I just need some suitable plates to mount these on nice and squarely on the boom. My friend offered to injection mould me some rather than my trying to accurately drill out several plates exactly.  So I modelled up a mounting plate to be made from glass fibre reinforced nylon which is extremely strong and stiff for its weight. The image shows the underside. The two ridges are to locate on the square boom:

Soon in the post came a parcel of element mounting plates. We decided riveting them on was a secure and lightweight fixing method. The two location ridges on the bottom had a slight amount of play when offered to the 20mm boom which of course would be amplified by the approx 100cm elements so I fitted two tiny strips of masking tape which made the plates a perfect fit. Once the rivets were in it doesn’t matter if the masking tape decomposes away:

The small hole in the very centre of the element plate is a sighting hole to align the element in it’s correct position on the boom. This was used to line up to clamp the plate on for the drill of the first rivet hole:

Once the first rivet was fixed, the clamp was no longer needed and the 2nd hole drilled and riveted:

Then a simple case of fitting the 10mm pipe clips and snapping in the elements in the right place centred on the boom. In order to easily locate the element centrally on the boom with out any time consuming I fitted to each element a piece of adhesive lined heatshrink to be positioned between the clamps. I also added some marking numbers for the 8 parasitic elements, numbered 1 to 8 from from to reflector:



Now the easy bits are done, time for the driven element. This was the biggest head scratcher on how to make it suitable for repeatedly taking apart and assembling. I needed to come up with a method that both left the electrical connections to the driven element halves but also enabled me to remove them for transportation. This meant a split in each half of the driven, but how to attach it?
I decided to come up with a system of employing a ferrule in the driven to join the two halves. With some custom made parts it would also be mounted on the same element mounting plate as the parasitic elements and is the reason the element plate is larger than a typical one, although that was also good for rigidity and build accuracy.

When I ordered my 10mm element tubing from Nuxcom I also ordered 1 metre of 8mm tubing to do this. But there were two issues with this. The first was this was the only piece of tubing that arrived with a bend in it. If I had planned to use it as an element I would have had to reject it. As it was I could cut out straight parts to use but the 10mm diameter 1mm wall thickness elements have a bore of about 7.92mm and the 8mm tube an outer diameter of about 8.10mm. No chance of a fit. Out with the calculator and it soon transpired 5/16″ should be a perfect size. I bought some T6 grade aluminium from eBay and it was a perfect fit. Sliding with no slop at all.

To cut slits in the 10mm tube to compress it with clamps to grip the ferrules I used two 10mm element clamps to mark a dot each end and each side of the clamp and joined them up to make cut lines to follow:


I’m not fantastic with a hacksaw to be honest but using the element clamps above to hold the tube in the vice I was able to cut (from both sides) fairly neat slits with a junior hacksaw (I wanted thin slits):

Then it was a case of fitting the ferrules into the outer halves of the driven elements and adding a screw to maintain a good mechanical and electrical grip:

Next to feed that driven element. I decided to straighten out the feed match to take the feed point a little closer to the centre of the yagi. I’m using WF100 75ohm coax which is fairly low loss for its size, and is not too big or heavy. Its claimed velocity factor is 0.85 so I worked out the length as so:

300/144.300 = 2.079m full wavelength
2079/4 = 519.75mm for quarter wave
519.75 x 0.85 = 442mm

DK7ZB gives a length of 440mm for this velocity factor, but I notice all his lengths are in multiples of 5mm so I wondered if he did some rounding down? I hope so!

This is the length of the braid. I hate stripping and cabling up coax so did all I could to avoid twisting bits of braid about. I cut the braid and dielectric off square and about 5mm or so of the outer jacket to reveal the braid. With a very large tipped iron of unknown wattage I was able to tin the braid nicely with no apparent melting of the foam dielectric. I then made a small tinned copper plate to bolt to the N-type socket and solder to the braids making a good earth. For good measure I added a loop of braid from some RG223 soldered all round. Then made the inners as short as I could and soldered to the N-type:

To tame the annoying curling coax I found yet another good use for the short boom offcuts I asked Attila to include. I taped the coax out straight to measure the 442mm finished length:

You can see I am using red adhesive lined heatshrink to keep the coaxes tidy and together. In the picture above the tiny box for the driven element connections is threaded on ready for the stripping and fitting of connections. I used a similar method as on the feed end with some copper sheet to join the braids and solder tags to connect to the element halves. This was a very fiddly job but hopefully worth it keeping the connections as short as I could manage:

To support and space the feed off the boom as recommended by DK7ZB (although this is going to be used for QRP almost exclusively) I got some ABS spacers 3D printed which I placed in position and then wrapped tightly with insulation tape. The idea is to keep the coax off the boom (which it is miles away from) but also as far away as possible from the element plate rivets but also as far from the element the coax passes under:

The driven element box is supported solely by the driven element inner pieces themselves, but I added a very small 3D printed pillar to make everything secure:

Here is the feed match finished:

As I plan to use this on a lightweight mast section only 20mm in diameter I didn’t think the usual U-bolt clamps would be able to create enough friction to stop the beam spinning on the mast without being so tight to possibly crush or weaken the 20mm ali mast. I bought some plastic 20mm clamps for large yagi elements from Nuxcom to try but they do not have enough friction. So I drew up some half round clamps to be made out of aluminium:

I used a small 3mm aluminium plate in usual manner and bought some 20mm square U-bolts for the 20mm boom itself. As the 20mm boom again is quite small for a long yagi I was again concerned about over tightening the U bolts and creating a weak and potential failure point so I added some small 3mm aluminium plates to allow it to be tightened up nice and tight without any fear of crushing the boom. Here is the finished boom to mast mount. (The two unused holes visible are there to use with the lower 20mm boom mounting holes for a 25mm boom yagi I have):

I used a similar arrangement for the boom support to mast fixings, the aluminium clamps and a slightly smaller aluminium plate. Just a simple M4 bolt per half of the boom support and another plate to help strengthen it all up. The intention is that the boom supports will also help offer a little sideways strength against the wind as well.

To bend up the boom supports I first tried to bend some 20mm square section (same as the boom) in my workbench jaws (seen above in the first picture after cutting the elements). They were not strong enough to bend it! Note this is not a proper vice as such, more of a drilling and cutting bench with jaws. I then thought I might use a bottle jack to apply the force but couldn’t think of anything solid I could jack onto. Then I remembered we have a small 3000lb lever press at work used for punching small holes in sheet metal. I soon made up a jig using a 10 inch square of ¼” steel with some small aluminium blocks and I used the spare offcuts (yet again) to work out the right amount of packers below the centre to give me the bend angle I needed:

I used 10mm MDF to spread the load from the press and protect the 20mm square tube and a strip of bare FR4 as a bearing and protection to the underside. Once tests were done I quickly and easily put the bends in the actual supports:

Checking the bends are matched:

Then just a case of offering them up, drilling holes in the right places and fitting. Finished!

Now for the moment of truth, how does it measure on the antenna analyser? Well to me it looks to be best match at 144.660MHz but is showing SWR of 1.1:1 and 51Ω at 144.300MHz so I’ll take that thanks:




Here is a real time video showing how long it takes to assemble the elements (I have not shown the boom assembly as nothing unusual or new about the boom assembly):

Finally, here is an assembly drawing:
High quality PDF version of assembly drawing
Full Bill of Materials PDF

Only job left now is to take this up a mountain top and do some contesting!

Edit: I have done my first contests with this now and it seems to work really well and I got good reports all round. Even with a low loss feeder the radio was not indicating any SWR reading at all on transit. I have come 2nd and 1st in the low power section of the first two UKAC contests I have entered so I am really pleased with the way this yagi performs. It ‘feels’ even as good or better than our 2x 19 element MET yagi array.

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