G1YBB Disguised ultralight Cobweb antenna

At my location it’s very difficult to have any sign of HF antennas (or any antennas for that matter) up in the garden. I’m already using a covertly erected dipole after dark using this quick erect fishing pole mount. But I was very interested in an ATU free multiband antenna. The hexbeam is nice but too big and needing a rotator. So I looked at the G3TPW Cobwebb antenna. For those unaware this is a 5 band dipole based antenna horizontally polarised and roughly omnidirectional working on 10, 12, 15, 17 and 20m. The folded dipole style with shorting points seemed more complicated than I fancied so I looked at the simpler G3TXQ cobweb design.
This filled more boxes for me, single wires nice and easy to tune and a tidy looking feed box. However, it would still stand out in the garden due to it being some strange looking (to non hams) spoked wire thing. What I decided to try was upsweeping the spreaders to make the antenna look like a rotary washing line as there is already one in my garden. I was counting on the neighbours not noticing it had grown an extra arm and got a bit bigger. Except when actually in use I would keep it low down like a normal washing line such as this:
rotary washing line
I searched the internet to see what people had designed but no-one had done anything quite this style. I was sure it would work due to the success of the hexbeam, but to be sure I started a thread on qrz.com and got some advice from the man himself, Steve G3TXQ, confirming there should be no reason why it wouldn’t work. Thinking about it the wire positions on this design are quite similar to those on the successful hexbeam.

Looking at existing designs all seemed to be based on heavy aluminium plates and tubes to support the spreaders. My plan to use this on a fishing pole would preclude this sort of design. Mine would have to be ultralight to have any chance of working. The spreaders were easy, I would use the 2nd and 3rd sections from telescopic fishing poles like the ones I use for masts. These two sections are long enough (bearing mind the upswept angle means the spreaders need to be slightly longer than for a flat design) and are plenty stiff enough. At the bottom they are approx 20mm diameter tapering to 8mm at the tip. Five 4 metre poles were soon ordered from eBay at a cost of £37.70 with the delivery, making them just over £7.50 each. Here they are next to an 8m and the 10m fishing pole the finished cobweb will be used on:
5 poles for cobweb
Next problem was the centre piece which came to be known as the spider. I mentioned what I was looking to do with a non ham engineering friend and it turned out he was about to get a 3D printer on loan. A great answer to my problem, a custom designed 3D printed ABS spider would be perfect. I got straight onto to modelling up the antenna in a 3D design program. This would also allow me to be able to confirm the fishing poles would be long enough and see how it looked, find where the wires should be based on the wire lengths used by G3TXQ and also predict quite well the finished weight. After searching the web a lot for everything to do with the G3TXQ cobweb, many threads on qrz.com with posts from Steve himself, I designed it to have the feedbox in line with the 17m wire, making the 17m wire a square and all the others bunched into the feedbox.
Here is an animation showing how the antenna should look when finished:

And here is my original design of the spider:

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

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

The spreaders slot into the spider bores and need to locate on a pip in the bores to stop any rotation (seen in the spider images above). This is mostly for the feed box to keep it in position but also to securely locate all the spreaders. The ends of the fishing poles are not cut square so I marked a line to indicate the longest part and marked out for the slot to be made with a Dremmel 3000 and a small milling like bit:
spreader marked out
To Dremmel the fibreglass safely I set up the hoover as a dust extractor which was very effective:
hoover setup for fibreglass
Finished notch, which is done to all 4 spreaders and the feed box spoke:
spreader notched
So I knew the notch was deep enough I marked the spreader fitted before the notch is made, then added another mark 3mm up the pole (depth of the pip):
spreader before notching
Spreader fitted after notching:
spreader after notching

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

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

The feed box is an ABS box from Farnell, their part number 244-4686, manufacturers part number TW7-5-11B. Note that Farnell do free delivery to non company accounts now. This size was chosen to be the smallest usable and (hopefully!) fit the feed balun inside:
Feeb box
The buses for the wires I wanted also to be lightweight but not compromise on the amount of copper so I abandoned my plan A of some copper clad FR4 when I found some 0.32mm copper sheet. Perfect. That equates to 10 ounce copper where the FR4 copper would have only been about 1 ounce and I have no dead weight in FR4:

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

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

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

As I like things neat and tidy, I have taped the two copper bus plates back to back to drill a small pair of mounting holes through both together so they match:
copper plates for drilling
Here are the two bus bars fitted with M2x6mm screws:
bus plates fitted to box

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

The wire I used is 16/0.2mm stranded which measured to be pretty much the same as G3TXQ describes in his text though in his photos the coloured wire looks a little chunkier to me. For the actual lengths I started with the lengths given by G3TXQ here:
wire lengths
I then referred to his wire thickness adjustments for hex beam wires here:
wire size adjustmentsto see how much things changed for wire diameters then decided that an extra 3 inches each should hopefully be more than enough. I also took note of some predicted and measured figures for the amount the resonant frequency changes when trimming provided by Jacek SP3L in the disguised cobweb thread higher up the page:
trim length predictionsChanging the wires with my construction would be a nightmare so hoped this extra length would be plenty.

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

To solder the wires to the copper bus plates I removed them from the box and placed them onto a piece of MDF to prevent heat sinking away. Before doing so I drew around the box and marked the wire entry points so I would be soldering the wire in the right places. The pre-cut to length wires were then threaded into the box treble checking the order before soldering:
ready to solder wires
Using a 100 watt Weller mains power soldering iron with a 6mm chisel tip I was easily able to solder the wires on with sound looking joints and without melting the previously soldered joints:
wires soldered to bus
Once cool I fed the wires back into the box and fitted the plate and repeated for the other side:
ready for balun

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

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

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

Once the box was fitted to the pole I could then fit the balun. I wanted to fit the feed box to pole first in case once the balun was fitted it was blocking the access to the screws (quite likely). To try and reduce the damage to the edge of the box during soldering (the iron ALWAYS finds a way of melting the box when you are working inside no matter how carefully) I cut up a Pepsi can (other canned drinks are acceptable!) and folded it around the edges, hoping it would make a good heat shield:
ready for balun soldering
For the feed balun I used the exact same  FT 140-61 ferrite toroids as G3TXQ and RD316 (which is just RG316 with a double screen)

4 lengths of RD316 taped out for marking exactly the same lengths. Apparently the outer jacket of RD316 is repellent to all marker pens including biro, Steadler permanent markers and sharpies. So I marked the line to strip the braid off with masking tape then slit down between each piece to leave a strip on a marker:
making the balun 1
Outer jacket removed and bits of heatshrink added to keep the 2 coaxes together. This also helps stop the coax curling up all the time:
balun 2
Close up showing quite closely matching outer jacket length remaining:
balun 3
Both 1:1 chokes wound:

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

balun fitted in feed box

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

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

3D printed wire guides

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

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

wire to string detail

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

Cutting and tuning results

MetroPWR FX700 antenna analyser

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

cobweb SWR on 20m band
cobweb SWR on 17m band
cobweb SWR on 15m band
cobweb SWR on 12m band
cobweb SWR on 10m band
cobweb SWR on all bands

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

disguised cobweb on mast

cobweb looking up mast

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

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

 

Easy building of a moxon antenna with 4NEC2

As we are still on lockdown and my 50MHz yagi is literally too huge to fit in the garden let alone erect on my lockdown lash-up system I decided I needed to make something smaller to use at home. I didn’t have any aluminium tubing at home long enough to make a small yagi so I decided to make a moxon antenna on the recommendation of a friend. These are very compact and easy to make so it seemed like a plan. I decided on a wire based version as although I have some 12mm tube I could cobble together I didn’t have anything I could get today for the corners. Wire it is.

I’d already looked around the web and compared the various online moxon calculators and the AC6LA Moxgen program (link) and the Moxgen program seemed to be the best fit for the suggested spreader angles. (Even though I’m not using spreaders as such.) It’s dead easy, just put your desired frequency in and the wire size and click calculate:
Moxgen calculated values for 16AWG wire
That’s it, job done. Almost…

I’m using normal insulated wire but the calculator doesn’t cater for the change in velocity factor from insulated wire. So I decided to run it through the free 4NEC2 simulation software (link) to make the required adjustments to the dimensions so it would work with minimal fiddling after. I love building, hate fiddling. Now, before you start backing away from the PC this is quite easy to use and just needs some really simple maths to do this. Stick with me. Look at the image above and see I have selected Format NEC on the right. You just do that and click the Generate Model button and save a file ready to open in 4NEC2. Run 4NEC2 and click Open and load the file you just made.
4nec2 main screen
Click that green calculator looking icon to bring up the next screen, choose frequency sweep and check the start and end frequencies are a useful range and that the step size is not too large, then click generate:

We then get a plot showing us the expected SWR curve of the antenna:
SWR of Moxgen design as supplied
Oddly minimum SWR at 50.1MHz rather than 50.2MHz but looking good. We can click the green calculator button again and this time plot the azimuth plot we are interested in:
generate 4NEC2 far field pattern
Which results in this plot:
Gain of Moxgen design as supplied
We can see the moxon should have about 6dBi gain and the amazing front to back ratio it is known for. Next to nothing off the back.

This is all very well but I’m not make it with bare wire so my antenna will not look like this without some tuning. First of all we need to add in the insulation so we can see what the effect will be. On the main screen, to the left of the green calculator is a red book, for editing the information that defines the wires making up the simulated moxon. Select the Source/Load tab, and tick Show loads. We then add two lines selecting as shown below from the offered selections. For Tag, First & Last we put 0 (zero) which will apply the setting to all parts of all wires. My tri-rated wire has insulation 3mm in diameter so I enter the radius, adding the mm to ensure correct scaling is used:
parameters for coated wire added
Once done we can click the green calculator on that screen, select frequency sweep again, but widen the scale. I’ve gone 5MHz either side of 50MHz. You can see the resonant frequency has moved 2.5MHz due to the effect of the insulation’s velocity factor:
frequency shift with insulated wire
So if we had built to the Moxgen dimensions using my insulated wire we’d be looking at an SWR of about 2.2:1. So we need to make some simple adjustments. The dimensions of the wires are on the Geometry tab below. Looks complicated but it’s just a few repeated co-ordinates. Some with a minus ( – ) sign to make the equal around the center of the axis to plot correctly:
original design geometry
What we are going to do is put those numbers into symbols, or what we would call variables in programming. When you look above there is only actually 4 different numbers used so it’s not complex. You can give them any name you like, even Harold but I have gone similar to the Moxgen image further up. Just click the Symbols tab and enter as shown below. You’ll see a 5th value called Vf. I’ve already tuned it by now but pretend I haven’t:
values changed to symbols
Now we need to flip back to the Geometry tab and put the letters (W, E, DirS, RefS) where the numbers used to be:
geometry changed to symbols
If you were to run the SWR plot again now, it should be exactly the same, best SWR on 47.5MHz. But finally we add in the velocity factor. To the end of each of the letter symbols add without spaces
*Vf    (star V f):
velocity factor applied to design
Now we can run the SWR plot and it will apply a Vf correction to every dimension. I found 0.945 by trial and error. They say Vf for wire is between 0.95 and 0.98. I knew mine would be the lower end as it is quite thick. Now if we run the SWR plot, changing back to the 49 to 51MHz range we get this plot:
velocity factor corrected SWR plot
Back in business. A point to note here. I’m aiming for the SSB section of the band, but if I wanted to cover more of the band I would still aim at the lower frequency with this design. You can see the SWR curves rises steeply on the LF side but gently on the HF side. Anyway, if we run the far field plot we now get this:
velocity factor corrected gain plot
As you can see this has changed. A bit less forward gain because we are chucking some out the back now. Now as I mostly do contesting this doesn’t bother me at all but it is interesting nonetheless.

So now we have redesigned the original dimensions to my real world application of actual wire, we should be shooting for success. We just need to apply the scaling factor of 0.945 to the original sizes with a calculator and a little rounding to sensible numbers:
Moxgen adjusted values for 16AWG wire
So for the reflector we need a wire 2051+384.5+384.5 – 2820mm long and for the driven element 2 wires 1025.5+305.5 = 1330.5mm long.

Now we can build the antenna and have a good chance of it working!

I decided to make it from a small length of 20mm boom left over from VHF yagis and find some plastic pipes from the DIY shop to support the wires in the A dimension and just stretch them between the pipes for the E direction:
material costs receipt
I bought a terminal block strip with the intention of using the brass inserts with nylon rope to join the ends at the C direction but didn’t after so total cost of parts not lying around £3.87. I used my red yagi elemt plates to mount the pipe clips and snapped the pipes into them after cutting to size. They didn’t really grip the pipes so I just taped them on to stop them sliding sideways.
I fitted a short tail of RG223 to an N-type plug, split the other end into braid and core and soldered the two halves of the driven element on and threaded those into a hole drilled in the centre of one pipe. After testing I sealed this with liquid insulation tape:
driven element entry detail
I had a better idea for the ends of the elements at dimension C. I quickly modeled up a small plastic part like so and sent two to the 3D printer:
wire ends connecting strip 3DThe holes are a snug fit, tight enough to hole the wire until final testing. I marked lines on with a Sharpie 60mm apart and fitted the wires. Once tested I locked off with cable ties:
wire end connecting strip
So, the acid test. What does it measure like?
SWR as designed
SWR plot is very close but shifted down in frequency. This is because of the plastic pipes which I can’t (or don’t know how to) model in 4NEC2. Not a problem as I expected this and knew that now the wires would be ‘too long’. So I cut 10mm off the end of each element half (4 ends) and ended up with this:
SWR plot with 10mm trimmed off(just noticed my analyser clock is way out LOL)

Pretty much an exact match to the simulation with 30 seconds of trimming. Just how I like it!

The finished antenna looks like so. It actually looks better than this because this is before cutting the 10mm off each wire end.:
finished moxon up for testing

Lockdown lash-up mast base

The coronavirus outbreak of 2020 put a stop to all portable radio activities so like many people I was forced to adapt and overcome and set up something at home. For non rotating mast systems I strapped a mast to the YL’s parasol base:
old umbrella stand base
This worked for smaller dipoles but I wanted something a bit sturdier and the YL wanted her umbrella back! So I decided to make a new one. I thought about making something from scratch but after asking the local club members for ideas it was suggested to use a tamper that builders would bash sand down before laying slabs or bricks. A quick Google located one in stock in the local Toolstation:
roughneck tamperThis is a cast iron 10″ base and a fibreglass handle. Cost me about £35 which is cheaper than some of the suitable umbrella bases I was looking at. I click and collected it. It didn’t seem that heavy at all to be honest but I’d already planned to fit it to a paving slab so wasn’t an issue. A quick session with the drills and the tamper was securely fixed to one of those heavy council style paving slabs:
new mast base fitted to slab
The fibreglass handle feels pretty strong with some give but also felt like it would snap before that slab budged! This would normally only be used as the support until guys are attached anyway.

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

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

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

70cms RG179 & RG302 DK7ZB match cutting jig

This cutting jig will enable you to cut RG179 75ohm PTFE coax accurately and repeatably to the length required to make DK7ZB 28ohm matches. RG179 is chosen as it is easy to work with and is best used for antennas that will only be used as part of an array, or lower power use only. It should be good for about 300W PEP on 432MHz. This jig arrangement gives you enough braid to solder to with a very short length of exposed PTFE dielectric. At 432MHz you want to be keeping your ‘tails’ short and tidy for best results.

Design goal:
3D stripped cable
Reality:
RG179 one end prepared

Building the jig.

You need to print the following from the files supplied:

1x           Part1
1x           Part2
1x           Part3
2x           Part4
2x           Part5

I used PLA at 0.1mm layer height and printed them in the orientation that they are used:
3D printing layout
Download the RG179 STL 3D print files

I fitted them to a metal plate so I could clamp them to my bench. Holes for M3 bolts are included in all pieces. Small wood screws could be used to screw to a board.
jig and tools

To set the overall length (finished braid and cut for 2nd end) I used 2 pieces of tube the  closest size to fit RG179 inside I could find which I found in a model shop and is brass tube 4mm diameter x 0.45mm wall thickness. Code BT4 M by Albion Alloys.

One needs to be cut to 120mm (¼wave for RG179) and one to 132mm. The 120mm is a critical dimension. The 132mm wants to be pretty close. Varying by a small amount is not game over but it means the stripping lengths may not be 100% symmetrical so worth looking out for this.
Edit: I have since re-calculated the length for RG179 and other 75ohm PTFE cables and found that it comes up with 121.4mm. I used this to make abnother yagi and the match was spot on.

These tubes need fitting into Part4 & Part5. I ran a 4mm drill through both parts to clear the prints for the tube, and a 1.6mm drill through Part4 only for the coax. This hole needs to take the PFTE dielectric with a nice close fit but not too tight. Dielectric should be 1.55mm so 1.6mm drill should be about right.
NOTE: when running a 4mm drill through Part4 (if required) only drill 7mm deep to clear the blue highlight below. The bore opens up inside after 7mm to ensure there is a flat surface for the brass tube to sit against internally:
Part4 showing internal to drill

Part4, Part5 and the brass tubes then make assemblies like below. I used Loctite 243 sparingly on the tube before ensuring it was pushed completely home into Part4 then on Part5 when that was fitted. Part 5 is just a support and needs to be about 10mm from the tube end.
120mm tube assembly

Using the jig.

Part1, Part2 & Part3 are designed to be used with a craft knife with the type of blade where you can break sections off, like this one:
stanley craft knife

Extend the blade far enough to easily span the two guide slots. Only light pressure with a sharp blade is required. Do not ‘saw’ with the knife, instead rotate the coax. Start with a length of coax about 150mm long.
knife shown in jig

Step 1 – strip the outer jacket.

Insert one end of the coax into Part1 until it hits the blind end, insert the knife and rotate the coax. I found the jig worked perfectly as printed, but in case near each guide slot for the blade is a hole that will take an M3 grub screw to fine tune the blade height. This cut is the tightest tolerance one.
Part1 for cutting jacket

The outer jacket should be scored not fully cut through. This is to ensure no braid strands are cut. Gently flexing the coax should snap the jacket easily without damage to the coax.

DO NOT FULLY REMOVE THIS PIECE YET.

Carefully slide the jacket towards the end to reveal about 10-12mm of braid:
jacket moved to solder braidNow lightly tin the braid with solder. Enough to wet all the strands all the way round but not too much to increase diameter. I find ‘real’ solder with a lead/tin mixture better than the lead free stuff. Once done the jacket piece can be removed fully. Lightly tin the rest of the braid:
braid fully tinned

Step 2 – cut the braid to length
cutting the braid

Insert the braid into Part2 until jacket stops and again fit knife and rotate the coax at least once full turn.

Again this will only score the braid, in order to ensure the PTFE is not damaged.

Also again, gently flexing the braid at the score mark should fracture the soldered braid cleanly at the score mark. Braid can now be removed easily.
braid stripped

Step 3 – cut the dielectric to length

Insert the coax into part 3 until the braid stops on the inner stop:
cutting the PTFE dielectric

As before, fit knife, rotate coax at least one full turn. The PTFE inner will be scored but should easily twist off, shearing at the score line neatly. Lightly tin the stranded inner conductor.

Your coax should now look like this:
RG179 one end prepared

Step 5 – trim overall length

Insert the stripped end of the coax carefully into the 132mm tube assembly, rotating it as you go to ensure the PTFE dielectric enters its hole and the braid sits up against the inner stop:
cutting 2nd end coax

Using flush cut wire cutters cut the coax nicely flush with the brass tube. The neater the better, this will determine the position of the 2nd jacket strip. You may want to grip the coax with the cutters using the brass tube as a guide then carefully pull out the coax from the tube as you cut it so there is some to grab hold of.
2nd end coax cut

Step 6 – strip 2nd end jacket

Repeat Step 1 above so you have this:
2nd end jacket stripped

Step 7 – cut 2nd end braid

Slide fully stripped end into the 120mm brass tube rotating it as you go to ensure the PTFE dielectric enters its hole and the braid sits up against the inner stop:
cutting critical braid length

Hold your sharp knife blade on an angle to match the blade’s cutting edge ground angle so the cutting edge is flush with the end of the brass tube and using gentle pressure rotate the coax by twisting the bare braid on the left letting the blade edge roll along the circumference of the braid. You are aiming to score it as in Step 2. Remove from the tube and gently snap the braid at the score line and remove as in Step 2. You should now have a braid length of exactly 120mm:
braid cut to 120mm

Step 8 – cut the dielectric to length

Repeat step 3.

You should now have a finished cable:
finished quarter wave RG179 cable

You can now repeat this process as many times as required and should get extremely similar pieces.
I always ensure I cut my matching segments for all antennas I might use together from the same reel of coax in case of any manufacturing differences.

To make the actual DK7ZB match I like to pair the cables with short lengths of adhesive lined heatshrink. One of the few things that tames that slippery FEP jacket. The pics below show how I connected up the short tails.

Match-N-type end
Match-dipole end

RG302 Version.
Since making the RG179 matches I have built a version using RG302 for better power handling.
Principal is exactly the same as above except I used 8mm aluminium tube (spare element tube) with 1mm wall thickness.

This is the result I got:
19 ele DK7ZB N-type box19 ele DK7ZB dipole box19 el DK7ZB SWR plot

Download the RG302 STL 3D print files

Yaesu FTDX-5000 transport case

THIS IS NOT A FLIGHT/SHIPPING CASE!!

As the FTDX-5000 is an expensive and heavy beast I designed and made a transportation/storage case to fit it. I’d looked at what you could buy and everything was huge and heavy, increasing the size of the 5000 by a considerable amount. Something simple, low profile and low weight was required.

Images are clickable for larger version.

Below is the resulting case. It’s powder coated aluminium, adorned with protective foam so the radio never gets scratched or dusty/wet (just care fitting the lid is all required) and has latches to quickly but securely lock the lid on. Once in the case it can be carried around without fear of accidental bumps, things falling on it, kids fiddling or rain (to and from car etc).
FTDX-500 transport case

The box is designed to enable the radio to be operated whilst still in the base, and even offers a handy place to hang the standard microphone:
FTDX-500 transport case
Rear connector access:
FTDX-500 transport case
Base showing foam support strips, foam side protection, and rubber grommet foot protection:
FTDX-500 transport case
Base strengthening and feet protection:
FTDX-500 transport case
Video showing fitting the lid. (I am extra careful with everything!):

Plugging yagi dipole ends to waterproof them

When making my yagis I like to plug the ends of the tubular dipoles so water cannot run down the tube and enter the dipole housing with its corrosive end results.

Many people do not like to add caps to the elements for concerns over altering resonance, so I just cut the cap off and push them in so they are fully inside but water cannot enter. Simples.

plugs for yagi dipoleThese plugs are from nuxcom.de

Accurately cutting yagi elements to size

I planned to build more 144MHz & 432MHz DK7ZB yagis for contesting to use in arrays so I wanted to ensure I could make them accurately and repeatedly and also without taking forever doing it! Thus I needed to come up with an efficient cutting jig.

I would use some threaded bar to adjust and set the length and steel angle for the supporting the aluminium tube and cutting the length. First I calculated the range of length between the longest reflector and the shortest director then a quick knock up in Solidworks gave me the length of stud required and ideal places to weld the angle to do the cutting. The studding is M12 because a nut for M12 will take a 10mm ali tube with a little clearance. The long M12 barrel nut (Screwfix, few pence) is locktighted in place. From the left the angle brackets have the following holes: 12.5, M12 tapped, 10.5, 10.5, 10.5:
144MHz element cutting jig

Some cutting, drilling and tapping later and I have this (the observant will note it’s not exactly the same as the intended design-more on that accidental stroke of luck later!):
cutting jig completed
Usage is very straightforward. First I G-clamp it to the bench then I used one piece of spare element tube as the setting piece, doing all elements in sequence, longest to shortest. So I set the jig and adjust, cutting and filing the setting piece until spot on then do all elements that length then onto the next element size using the same setting piece. Simple, but more importantly, very accurate and repeatable. I did try calculating the distance a fraction of a turn would give based on the thread pitch but with a simple tapped hole the thread backlash made it too unpredictable so found it easier to measure the amount the cutting piece protruded when setting for the next size down with the small vernier in the photos above and start from that point and fine tune on the thread and lock nuts.

To actually cut the elements (after using the jig to prepare one end of all elements to ensure it was nice and square and deburred) I just slide it through the 10.5 clearance holes into the long nut and hold it pressed against the long nut with one hand. With the hacksaw tilted slightly to start a cut just away from the steel angle to prevent sawing the face of the steel angle I start cutting then as soon as the cut is started square up the hacksaw. Cutting takes a few seconds:
element sawn rough size
Then it takes a few seconds more to file the element down flush to the steel angle. Over MANY elements the steel angle will gradually file down in thickness but such a large area and so much harder than the aluminium it will not affect the length between a batch (I checked):
element filed to size
Next to just finish off the end. In the picture above you will notice the countersink bit in the screwdriver handle and a pencil sharpener. Both employed very quickly to deburr inside and outside edges:
element finished end
The only thing left to do is check the length! I am lucky that my place of work happens to have a very large digital vernier. These will do, close enough for G1YBB…
882mm close enough1027mm close enough
Obviously most people won’t have such a measuring tool but it shows the jig can enable accurate results, more accurate than we can normally measure. I belive working as accurately as possible to follow the simulated design will enable the best possible results to be achieved. I have had fantastic results with my first 9 element DK7ZB working to that ethos.

About that lucky error in placement of the angles with the holes…
One thing I forgot to allow for when designing the jig was the driven dipole halves! But by a stroke of good luck (MOST unusual for me) fitting the middle guide hole angle in the reversed place turned out it was perfectly positioned for the dipole half:
driven half cut

I’ll be able make the 432MHz element cutting jig to cater for dipole halves and full elements easily because the threaded bar covers enough length with the 70cms elements being so small.

Simple inverted Vee wire dipole for 50MHz

Now it’s towards the end of June and I have been listening to the other club members I chat and contest with reporting on all the times 50MHz has been wide open on sporadic E, I decided today I would knock up a simple antenna for 50MHz for the garden. My location is not suitable for any real antennas due to neighbour issues so I thought I would make a wire delta beam and mount it fairly low as I have a suitable 2m length of plastic pipe I could use for the cross boom. A quick look at the design scuppered those plans as I had no suitable 75ohm coax here.

I then considered a simple aluminium dipole as I have loads of 1.5m lengths of 12mm tube in the garage. Then it came to me in a eureka moment. A good old trusty inverted vee would be easy to make and do the job nicely!

Since I made my first 20m inverted vee dipole I have since butchered it by cutting off the coax to use elsewhere and it has been lying around the garden for a year or so in the grass in the corner of the garden. Rescue that and put new coax on and I am good to go!
50MHz inverted Vee dipole centre
Next (as seen already above) I needed a pole. I took the bottom 3 sections from my 8m SOTA fishing pole which gives me about 3m of lightweight but stiff pole. In the garden there was fitted a rotary washing line with a two part stem set in the ground. Amazingly it was the perfect fit for the bottom section of the pole! The two sprung plungers even stopping it flapping around:
rotary washing line base section
Into the HF antennas odds and sods box and I got out one of the SOTAbeams lasered guy rings I bought to hang the dipole from. I slid it down to a reasonably but not excessively snug point and wrapped some tape around below that to stop drifting lower and possibly cracking as the plastic is fairly brittle feeling. I also sealed the feed point with liquid insulation tape which is great stuff and taped the coax down the pole to take the weight of the coax, which is longer than I need and only RG223 but I am just looking for something to get on the air and do some tests:
50MHz inverted Vee centre detail
With my HF dipoles I usually peg the other end to the ground with a length of string to insulate and keep the voltage maximum point off the ground but that really didn’t seem a plan. So that delta beam boom was called into play as a dipole spreader:
50MHz inverted Vee close up
It’s literally just lashed on with insulation tape:
50MHz inverted Vee spreader detail
At each end I drilled a single hole to thread the wire through which actually retained the wire quite well due to the tension and angle. But I backed that up with the ubiquitous cable tie. Also visible is a blob of the liquid insulation tape on the end of the wire to stop water seeping up the wire via capillary action:
50MHz inverted Vee end detail
Here is the finished set up ready for tuning. On the left of the image you can see the coax running into my custom wall mount coax connector box:
50MHz inverted Vee
Talking of tuning…
To ‘design’ the dipole I use done of my favourite sites I use for all my HF dipoles over at sotamaps.org. (Click on the 2nd tab for the calculator). I put in the centre height measurement from my set up and adjusted the end support height to get a little under a metre horizontal distance between mast and end support. You can set the wire type via the settings button. You can see it offers me  1.32m for each side. So I cut mine to 1.42m to start as it’s always easier to trim than add!!
50MHz inverted Vee design
First measurement showed beautiful resonance a little under 50MHz, so I trimmed 10mm off each end. Nearly at 50MHz, so 10mm more. Resonant now more in the CW end so I took off another 5mm. The final cut length is actually 75mm longer than the designer suggested, so it could be my  selection of wire should have been for a thinner one or thicker insulation than I chose. (that’s ex red wire with a dose of UV fading applied!):
50MHz inverted Vee SWR trimmings
SWR 1:1, zero reactive component and 49ohms resistive component (50 ohms a tad higher up the band but still in SSB section). I’ll take that!
50MHz inverted Vee SWR
Plugged into the trusty Yaesu FT-857D and a quick scan showed some Es stations calling. Found an EA station and called him, replied to me first time! As did the next 4 stations. Nice one!
first 5 QSOs all one call
So there you go. It is dead easy to get on 6m even with very awkward neighbours and small gardens. 50MHz truly is the magic band when those Es open up too!

Lightweight 80m Inverted Vee dipole

My local club Hereford Amateur Radio Society has been embracing the RSGB VHF and UHF activity contests but also some members have been taking part in the RSGB 80m CC series of contests which have SSB, CW and Data sessions. I wanted to join in so needed at make an antenna, which I decided should be a trusty inverted vee dipole.

My first consideration was how was I going to support the centre high enough. I have an 8m and 10m fishing pole but neither are really high enough on their own. So my solution was to attach the 10m fishing pole to the top of my VHF portable mast (a 6m scaffold pole) which will get me the centre of the dipole about 14m high:pole fitted to contest mast
Off to the SOTAmaps dipole calculator website (link on my useful links page) to calculate the lengths:
80m dipole calculations
The fishing pole is pretty flexible using the upper sections so I have a pair of guys lower than the dipole to stabilise it a little made from thin but strong cord. These will go at 90° to the dipole, using the dipole itself to steady the very top of the pole:
80m dipole pole guy winders
Typically it was a pretty windy day when I set it up on my favourite test setup hill:
Dipole erected and tuned
As the wire is quite thin it’s fairly narrow band but I got a reasonable match mid band:
tuned for centre of band
All ready to go.

Apart from the fact that my favourite test site and intended 80m CC portable operating site Westhope Common, that I have been using on and off for about 35 years now has a resident that hassles everyone and anyone who goes up there, and has hassled me each time I have been there lately. So I need to find another site.

Portable 6 element 50MHz DK7ZB long yagi

Towards the end of 2016 the rules and days for the UKAC series of RSGB contests were changed. The 50MHz and 70MHz UKAC events were moved to the 2nd and 3rd Thursday of the month respectively. This opened up more opportunities for me as working a Tuesday night contest means rescheduling my Tuesday to a Wednesday and means my Wednesday is busy as heck and it’s at least Thursday before I can even look at the tablet to get the log updated. But a Thursday I am usually free so I can get on another band. As I have no 70MHz Tx capabilities I decided 50MHz was the way forward for me. I have an old home made 5 element yagi we used to use but I wanted a newer better performing yagi. I am getting awesome results with my 144MHz 9 element yagi I decided another DK7ZB sounded ideal.

I chose the 6 element 7.2m boom version as I plan to only use it car portable and it’s only 1m each end longer than the 144MHz yagi I’m using. Also it has a great SWR curve. All dimensions are available on Martin DK7ZB’s site:
6 ele DK7ZB yagi dimensions
This design only had figures for 12mm elements. That was OK as I can get 12mm pipe clips like I used in the 144MHz yagi. But it turns out buying 12.0mm tube in lengths greater than 2000mm in the UK is exceedingly difficult. It had been suggested to me to use 12.7mm tube as that would be easy to buy in the UK but would require recalculating the element lengths. Not only that it would prevent me from being able to use the fast fit pipe clip I wanted to use. After much searching and asking in various places I had to admit defeat and arrange with Attila at nuxcom.de to ship (at some considerable expense) some 3000mm lengths of 12mm tube, along with several other antenna parts and also some 3000mm lengths of 10mm element tube.

For this yagi, unlike the 9 element for 144MHz, I had no plans to take it backpacking portable so I decided it only needed a 2 part boom. I was easily able to get 5000mm lengths of 20mm boom for this. 20mm is quite small sized boom for a yagi of this size but my element mounting plates are designed for 20mm boom only. I’ll be using truss supports and side supports if required to stop it flexing too much. The 5.1m long 2m yagi was nice and sturdy with its trusses in high winds on the top of the Black Mountains. Although it’s only 1 metre longer each end, it makes for a big boom!
7.2 metre long boom
Once the element positions were marked up the 5 parasitic element clips were fitted in the same manner as the 144MHz 9 element. On this yagi the driven is too big for the element clips so that will need a more conventional box:
element clips fitted to boom
For the feed box I decided to go for a beefed up version of that I did with the 144MHz 9 element. I chose an ABS box from Farnell as it is quite thick walled and with a decent lid should be pretty stiff and is also IP65 rated (before I start drilling it). In order to get a suitable height so the driven element 16mm sections could be on the same plane as the parasitic elements it came in quite large at 200 x 150 x 55mm but that is OK as the driven on this 50MHz is quite big:
Farnell 1526658 box
Here it is marked up for drilling. Marking needs to be spot on as this is what makes the driven element parallel with the parasitic elements in both planes so is crucial!
driven box marked for drilling
This is the centre point of the dipole box used for locating it on the boom in exact position:
dipole box centre locating hole
To enable stability and strength for the 3 metre driven element I am using some 19mm angle. The sighting hole above lines up with the centre of the scribed line:
dipole box supporting angle
To mount the two halves of the dipole I got my good friend Paul to 3D print some two part clamps in ABS to my design so the centreline height of the driven element above the boom matches the parasitic elements so all elements are in the same plane. Here are the clamps after drilling and fitting to the box with some 16mm tube to check alignment:
driven element clamps fitted
To fit the dipole box I drilled and tapped an M2 hole in the centre point of the boom on the scribed line as seen above and screwed the dipole box in place using the 2mm sighting hole. I then fitted the reflector and first director and ensured they were all parallel and drilled the box to fit the two angle pieces:
fitting dipole box to boom
When I bought the element materials from nuxcom.de I also bought their dipole centre for 16mm tubing:
nuxcom 16mm dipole centre
Which is very chunky and strong. But the 16mm tubes fit inside the joiner and I couldn’t see how one would get a good secure contact to the elements. So I got another good friend Ed to turn up a piece that would fit inside the elements like the nuxcom one for 10mm elements does. Here is the mechanically finished dipole centre:
finished dipole centre
The eagle eyed may be wondering what the red things are in each end. Well as I am using jubilee clips to clamp the 16mm tubes down onto the 12mm main driven element parts, once they are removed for transport (this yagi is for portable use remember) the jubilee clips are free to fall off unless clamped down. So my I got some plugs 3D printed to clamp onto to retain the jubilee clips and also prevent any dirt ingress during transport and storage:
jubilee clip retainer plugs
Now the dipole needs the DK7ZB match. I’m using the same WF100 75ohm coax I used on my 144MHz DK7ZB, 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:

300/50.150 = 5.982m full wavelength
5982/4 = 1495.5mm for quarter wave
1495.5 x 0.85 = 1271mm

As before I used a section of boom to tame the curling of the coax to allow accurate measurement and cutting of the lengths:
making the DK7ZB match
DK7ZB match one end
DK7ZB match other end
One end of the match fitted:
dipole wired to DK7ZB match
A picture of the process in operation in the ‘workshop’:
the G1YBB construction workshop
Other end of the DK7ZB match completed:
coax feed box
Apart from the bracing the antenna is pretty much complete except for the fact that the element mounting plates are not really man enough for 3 metre long 12mm elements. They were designed for the 144MHz yagi and only 1m long 10mm elements, which they are perfect for. With the larger elements this is how they were flexing with gentle persuasion:

A quick chat with Paul and he drew up a two part brace that he could 3D print me and soon they were in the post!They utilise the same holes already in the element plates and wrap underneath adding strength without interfering with the element clips at all. I used M4 nylon screws to add extra fixings without adding extra metal, the only metal nut and bolts holding the element clips on:
element plate brace fitted
After fitting the new bracing parts this is the flex with quite boisterous provocation:

Much better!

My next consideration is bracing. Long supports were made and fitted utilising the same fittings as on the 144MHz yagi. In fact as I write this I have started work on a 70MHz yagi. All three will fit on the same fittings on the portable mast, and the 70MHz yagi will re-use one of the 144MHz yagi braces and one of the braces for this yagi. The angle of the supports is quite narrow but they do support the boom and keep it straight. This yagi also will need side guys to protect it from the wind. I have several bottom sections of 4m fishing poles left over from HF antenna projects so I utilised two of those. Again Paul quickly produced some parts for me. Some ‘plugs’ to fit to the mast plate to mount the poles onto:
side guy pole fittings
And some stoppers to go in the end of the poles for the 3mm dacron cord, which is very strong and has very little stretch. The stoppers are a good interference fit:
side guy rope stoppers
side guy with rope fitted
Side guy poles fitted to the mast. These are a friction fit to the ‘stoppers’ and quickly assembled on site:
side guys poles fitted
The sides guys clip onto a plastic bushed (thanks Paul!) bolt on the boom supports with a single karabiner each end. Very quick to deploy:
side guys and supports fitted
Next step was to test it! This was done after work on the Wednesday before the first 50MHz UKAC in Jan 2017 the following day! It was reading 1:15 throughout the SSB portion of the band, which was slightly disappointing. There was no time to look into this as I needed to get back home (testing was done in a mountain’s car park) and pack for the next night’s contest!

On the night of the contest the in radio SWR reading was quite low so I was happy the radio was feeling OK about the match and used the new antenna for the first 50MHz contest I have done in 20 years. The yagi seemed to work pretty good and I even managed to beat G4CLA in the AR section of the RSGB 50MHz UKAC January 2017, which I was delighted with!

Here is the beam on my portable setup. Longer than the mast is…
50MHz 6 element DK7ZB yagi