Portable 9 element 144MHz DK7ZB long yagi

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:
DK7ZB yagi dimensions
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:
Proxxon KG 50
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:
measuring stop
And checking D2 (ever so slightly short if anything by a fraction of  a mm):
D2 measuring
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):
parasitic elements cut ready
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:
boom joiner
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:
Boom sections ready
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:
element clipAnother 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:
element mounting plate
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:
masking tape slack filler
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:
clamped ready to drill
Once the first rivet was fixed, the clamp was no longer needed and the 2nd hole drilled and riveted:
element plate fitted
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:
finished parasitic elements
elements numbered
element in numbered location
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:
using clamps to mark centreline
cut lines marked
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):
element slits cut
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:
ferrules fitted to driven halves
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:
feed point box
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:
feed match taped out straight
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:
driven element feed box
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:
3D printed coax spacer
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:
dipole box support peg
Here is the feed match finished:
finished DK7ZB match

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:
boom to mast clamps

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):
boom to mast clamp
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:
20mm square tube bend test
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:
boom supports bent up
Checking the bends are matched:
both support strusses parallel
Then just a case of offering them up, drilling holes in the right places and fitting. Finished!
finished DK7ZB yagi

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:
SWR match at 144.150MHz
SWR match at 144.300MHz
SWR match at 144.500MHz
SWR match at 144.660MHz
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:
G1YBB 9 ele DK7ZB assemblyHigh 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.
DK7ZB yagi in action

Ultralight and ultra strong antenna mast guying ring

When I made my lightweight aluminium portable contest mast I designed up a very lightweight guy ring to use that was both strong and light. I designed it for my friend to injection mould in a fibreglass reinforced plastic that is really strong. The material is so strong I could not damage a 1.5mm thick long credit card size sample by hand even across the edge of a table. All I did was hurt my hands.

So with one eye on weight and one on strength this is the design I came up with. The design criteria was that these rings would hold up a mast carrying a decent sized 144MHz long yagi with at least a 5m boom on an exposed mountain summit in winds at least as strong as the tent will take but also be nice and light and small. They are very similar to many others you will see (there’s only so many ways a guy ring can be designed), but this is only 61.5mm outer diameter and 14.2 grams in weight:
injection moulded guy ring
I went for the simple 4 holes rather than extra holes for 3 point guying that some rings offer as it’s easy enough to just use 3 of the holes. Rope holes are 5.8mm which is plenty big enough for 550lb paracord or other ropes you would use with a lighter weight mast system. The centre hole is 20.5mm sized to fit the top section of my mast. For the lower thicker section it’s easy to open the centre hole with a step drill, in my case 26mm. 30mm is about as big as I would open it too though to retain full strength.

When the rings arrived in the post the first job was to test it for strength. I figured I would make a good test load. Just needed something to hang off and give it some welly. I am a good 170lbs, probably more with boots and big coat on. The rucksack is full of 2 litre bottles of water, probably a good 30lbs more easy. So about 200lbs bouncing weight on the guy ring. This is on a very short length of paracord. A longer length will absorb more shock like a climbing rope does:

Once I was happy with them fitted to the mast and the guy ropes tied on:
bushes and guy rings fitted
And in action:
mast and 144MHz yagi
These rings will also be very useful for SOTA activations where the very ultralight commercially available rings may be a little brittle without adding a noticeable weight penalty. Used for a fishing pole mast the mast will break long before these rings will!

I mentioned that these could be ideal for other radio hams doing SOTA activations and other portable operations wanting a very strong but lightweight guy ring he has made these available (pretty much any quantity) on his website:
https://imlmoulding.co.uk/lightweight-mast-guy-ring-strength-without-weight/
(25% discount code G1YBB25 will work until end of April 2016)

Guying down a lightweight portable antenna mast

Having just finished making a lightweight aluminium portable antenna mast for backpacking VHF contesting I wasn’t really happy with the initial way we were tying down the guy ropes.

Typically I have tied off guys that don’t have tensioners with several half hitches. These are quick and easy but they are hard to tie tensioned properly and I have lost two 19 element MET yagis, a Yaesu rotator and an aluminium scaffold pole when one guy worked loose on a windy day. I didn’t want to use tensioners on this setup as they can work loose and we are going to be operating from a tent and won’t see any loose guys until too late most likely. Also I’m using for this mast lightweight paracord which is meant to be good to 550lbs breaking strain, but I am wrapping that around fairly sharp edged aluminium angle guy stakes which might create a weak point on the paracord. The mast is not massive and I have 2 sets of main load bearing guys but I want this to stay up on exposed windy Welsh mountain tops.

So I thought a round bar would be a better shape to tie the guys to and a clove hitch would be a good start knot as it can be tightened up. For the round bar I thought I would use some of my old climbing karabiners. And to attach those to the guy pegs I would use some small sized climbing rope about 6 or 7mm and use a clove hitch to quickly attach those to the pegs.

Here are the karabiners and rope loops. The rope loops were made from about 1m of rope each and a double fisherman knot used to make the loop:
guying karabiners
Once the karabiner was fitted to the guy peg it was very quick and easy to make a clove hitch and slip it on, tension, then lock off with a couple of half hitches:
guy tied off
guy tied off
This adds an extra 381grams to carry but I think it will be worth it in the long run. I could probably cut that down with newer smaller and more lightweight climbing karabiners (I’m not going to risk the cheapie ebay style mini ones) and probably a smaller rope would be OK to use:
karabiner extra weight
This is one way of many options, I’d love to hear your methods and tip and tricks!
(email explained on welcome page)

3D printed wire winding spool for SOTA HF dipole

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.
kinks from wire winder
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):
old spool
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):
spool full just right
spool fully loaded
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:
spool modified

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:
new spools versus old spool
SOTA HF dipole ready to roll, literally:
dipole ready to roll
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)

Lightweight portable aluminium antenna mast

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:
2.4m mast inside passat estate
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:
two operating heights
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:

clamp
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:
slits for clamping

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:injection moulded guy ring
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:
lower guy bush NB580
Custom made bush for 20mm top section:
custom made bush
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:
bush in action
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:
guy rope lengths
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:
inner sleeve screwed in
Close up of the bushes and guy rings before fitting the guys, which stay with the mast to make deployment faster:
bushes and guy rings fitted
First trial erection went completely to plan, set up on my own.
mast completed and erected
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:
mast and 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:
mast anti-rotation system

Lightweight carry case for Yaesu FT-857D portable operation

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:
FT-857D portable protectionThe 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:
base foamex marked out
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:
ready for folding
Both sides folded up:
base 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:
base rear view
base front view
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:
lid front half cut out
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:
front half of cover
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:
last section cut out
And folded up and glued to the front half:
last piece folded up
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:
finished and ready to go
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.

Ultralight seat for portable operation and SOTA activations

As I am using a Microsoft Surface Pro 3 for logging on some portable activations and have it on my knees when operating it means I am sat in a fairly stationary position for longer periods. I was using a foam garden kneeler as they are very light and nice and cheap. But a couple of hours on that and I had to pack up and go home due to a sore butt!

I decided something better was required. From my camping experience I have ditched the OK but lacking foam karrimat style sleep mat in favour of a Thermarest self inflating mattress so I looked for something from that type of seat. They came up with the goods in the form of the a Lite seat:
http://www.ultralightoutdoorgear.co.uk/equipment-c3/accessories-c10/seats-and-sitmats-c47/lite-seat-self-inflating-sitmat-p705

This is the seat:

But how does it weigh up to a lightweight kneeler?
Here is my kneeler:

And the new comfier seat:
2015-12-25 11.36.56
Only 9 grams heavier. But it packs down quite a bit smaller. This is the tube it came in, which I shall use to pack it, and it is pretty small. Next to a normal sized mug:
packing size
Looking forward to trying it out on my next portable SOTA activation.

Ultralight guy line winder

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:
winder 3D view
And here is it dimensioned up:
winder dimensions

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:
incorrectly wound
This is how they should be wound:
string wound on
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:
    finished winder
    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:
    fitted to 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:
    all guys ready to roll
    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.

Custom coax connector exterior wall mount box

I decided for home I wanted a box just outside where my radio sits that I could plug different antennas into easily, so I looked for a tidy way to run antenna feed lines through the exterior walls. Most were running to a large waterproof box that the antenna feeders plugged into but were a lot larger than I wanted. The box would offer a socket and be cabled through the wall and into the back of the radio. I also wanted it to be basically waterproof and compact.
There are many waterproof boxes on the market of course, but none I felt would be ideal. Then a good friend then got his hands on a 3D printer so we decided to print me a box to my design.

First step is to draw it up. I planned for 2 connector positions (one for each output from the FT-897D) and made it suitable for both single hole bulkhead type connectors and 5 hole panel mount connectors. It will take SO-239 and N-type (my preference) connectors. Both will be cable mount and crimped, which I use in my day job at L Band and above and much prefer to pretty much all other cable fitments for flexible coax.
SO239 panel mount crimpN-type bulkhead socket crimp

The coaxes will be fed through a hole straight through both skins of the house through a vertical mortar joint at an upwards angle and the wall plate part of the box fixed to the wall with two fixings into the horizontal mortar line. (My bricks require an SDS drill to drill holes in, plus this is easier to repair if removed later).
fitted to wall
A simple slide on cover open only at the bottom extending down past the connectors will shield it from even the most horizontal rain.
with cover fitted

Now to send the files over to my very generous friend Paul for 3D printing. He did an initial print of my design exactly as drawn, which took some time for the cover as we didn’t print it the most efficient way up. We got it done, but before I had chance to fit it discovered it was printed in PLA rather than the ABS we thought it was. So Paul decided to redesign it with printing in mind in smaller parts that would be cemented together, having already proven on my Cobweb antenna that this approach was a better plan.

Paul’s design was four pieces rather than my two:
Paul's design
Here is some of the 3D printing and assembly:

The two parts of the weather cover:
2 part cover
For the feeder from the coax box outside to the radio I wanted to add a hi band and mid band ferrite choke as described by GM3SEK here. I wound one with RG223 which was a springy slippery nightmare and one on RG58 which was much easier. There was no way to get the coils of either sitting tidily with just cable ties so I used masking tape to keep things tidy. As where they will come through the wall is very hard to get to I need to wind them on first and will have to pass the shorter tails out through the wall and fit the connectors outside.
hi and mid band chokes

Holes all drilled from outside, and short tails pulled through from inside using the smaller drill and some wire:
coaxes pulled through
Connectors fitted. As well as remembering to fit the crimp ferrules make sure you feed the coaxes through the hole in the coax box BEFORE fitting the first N-type type connector beautifully. Otherwise it needs to be cut off and wasted. Grrrrr. The final SO239 and N-type socket fitments are not as tidy but electrically good:
Coax box fitted to wall
Antenna cable and rain cover fitted. I have also smeared the cables and backs of the connectors with a good layer of vaseline in case any water does manage to run down the wall and down the cables:
ready to use
From concept to reality. Cool.

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.

Base station mount for fishing pole mast

My current circumstances preclude my having a permanent mast up for antennas so I am having to stick up a portable style telescopic fishing pole with an inverted vee dipole when it gets dark, and take it down again before I go to bed. Quite tiresome but better than nothing.

I started by strapping my 8 metre fishing pole to the rotary washing line that is installed in the garden but it’s a bit of a faff in the dark and I get covered in cobwebs, and it’s a bit wobbly. Also its location means I don’t have room for a 40m inverted vee, and the locations I have for the ends of the dipoles are not in line with the pole so that means it is always stressed and bent over quite a lot. So I needed another solution.
Mast on washing line
Using the very useful Link Dipole Calculator on the SOTA Mapping pages I was able to calculate that there is room for a 20/40m inverted vee if I use a 10m fishing pole and mount to to the corner of a 6 foot brick wall in the back garden and I can arrange the ends of the dipoles to be in a straight line with the mast to relieve stress on it. Both solutions have one end of the dipole coming close to building which is not ideal but the higher pole will help and at least it’s a bungalow so most if not all the actual radiating elements should be above the roofline.
Mast on brick wall
Next challenge is to come up with a quick and simple arrangement to erect it. After looking around and some thinking I decided I needed some sort of cup to sit the bottom of the mast in and a sleeve higher up to extend the mast into giving it secure support. Scouring the DIYs the closest I could find for the upper sleeve was some black 50mm downpipe. This also had suitable wall fixings that keep it fairly close to the wall. However it turned out to be a beautiful fit for the top of the bottom section (no use to me), but sloppy on the next section up.
slack fit on pole
I was trying to think of ways to line the pipe to get a better fit and how I might secure it in the pipe and in talking to a friend who is very good at engineering solutions he suggested heating the pipe and bending it inwards in several places. Perfect!

As there is quite a bit of play I used strips of cereal bar box and masking tape to build up the pole to a nice fit on the tube to keep it centred around the pole.
masking tape spacers each endmasking tape build upnice snug fit
Then a bit of masking tape over the outside to keep it still.
pipe secured to mast
Once set up I used a heat shrink gun to heat up small areas of the pipe and used a teaspoon to press the soft pipe against the pole and hold it there until the plastic cooled a little. I kept the teaspoon in a cup of ice water between uses to keep it cool and cool the pipe quicker. I did three sets of four indentations. Set one at 0° 90° 180° and 270°, 2nd set at 45° 135° 225° and 315°, 3rd set as the first. Then I took off the top card and masking tape and pushed the top edge in as well for a bit more support. I left the bottom entry oversize for easy entry.
pipe with support points
This worked better than I expected! The fit is very close. If I had known how good the pipe would keep the new shapes, I would have wrapped a sheet of printer paper around the pole to have a little freedom on the fit. However, it works and here is the pole standing upside down with the pipe fitted showing it gripping the pole.
pipe fits pole
The cup for the base of the pole took a bit more searching for. Nothing was quite the right size, or if it was it was flimsy plastic. It doesn’t need to be industrial but will need to stand the leverage the top 8 metres or so of pole exerts when the wind blows. After much looking and considerably over budget at £10, I got a metal camping mug from Mountain Warehouse. Of all the metal cups I found it was the only one that was close to the right size and also was parallel sided, which would be useful.

First the handle had to come off. I wasn’t sure how it fixed on so I started sawing it off. First cut through just plastic, then the 2nd hit metal as I cut closer. I decided to just try and break it off. Came off easily and I was able to see it was only a tab spot welded on. So the other was off in seconds.
handle removedspot welded handle
I had also though of how to attach it to the wall as screws through the side wouldn’t work as the heads would be in the way of the pole and the wall thickness of the double skinned cup are very thin anyway meaning it would deform. So it had to be fixed at the base. A simple metal shelf bracket was chosen, cheap and plenty strong enough. In order to line up correctly with the black pipe, the centre of the cup needed to be 55mm from the wall. To make it easy to do I drew a circle a little smaller than the cup base, and positioned the centre of it 55mm from a base line, printed and cut it out, and taped it to the base. It was then easy to line the shelf bracket up with my centreline and the upright part with the base line (left in the photo) so I could mark where the new holes in the shelf bracket needed to be (it goes without saying the ones already in it were no use).
template for bracket
I was then able to drill the bracket and the cup with new holes for fixing the cup to bracket, and a couple extra for rain drainage. As the metal is very thin I also cut a disk of 1.5mm aluminium sheet to spread the load of the screws. I just printed a circle the right size, cut it out, taped it to the aluminium and cut round it with tin snips. A quick file of the corners and it was sorted.
cup and disk drilled
Now just needs bolting up together. I used nyloc nuts so I can do it up tight enough to be sure but not need to crush the cup getting the nuts to stay tight. The disk and bracket spread the load well anyway, but I know they should never come undone. All the fittings are A2 stainless steel so should last a while outside.
mounting bracket fitted
So the pole can sit in the cup but not rest on the heads of the screws I cut a sheet of rubber matting to raise the pole base off the heads. May help absorb some (tiny fraction of) shock if the mast happens to collapse down one day. Ready to go on the wall now.
screw heads covered
All set and just need to screw these to the wall. And a rubbish picture taken in the dark with my phone with the mast in situ.
mast erected