70cms RG179 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 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.

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

Icom IC-9700 Contesting review

Icom IC-9700

I bought the Icom IC-9700 at the time the second batch of this radio to hit the UK were being hotly sought after. I had recently got the IC-7300 before it, which I also love, so I was pretty keen to get this one to add to my portable contesting stable. In it’s early days there was a LOT of negative talk about dynamic range and frequency drift, I’ll touch on that at the end.

I can honestly say right now, I love this radio! Review done.

Oh you want to know why? OK headline points for me…

Functionality.
The IC-9700 has brilliant functionality for VHF contesting. The spectrum display is the biggest new thing to me (on 144MHz and up). Whilst this is brilliant for spotting signals on the band (and for this reason I think everyone ELSE should have one to find me!) not only that it has made the biggest gain to my 144MHz performance since getting the 9700. The way it actually did this, apart from the signal spotting ability, is to highlight why I was getting so much QRM on 144MHz. I always blamed other club members out portable nearby, line of sight, and some using FT-991 radios. Whilst they did batter me there were some nights I couldn’t find who it was killing me on the old school radio I was using. The 9700 soon showed me:
9700 bandscope showing pager QRMI was getting awful QRM and the OVF warning in regular all night long pulses, as you can see all over the band, but particularly hammering me where I usually run (144.265). That’s no ham! We determined the source to be a local (100 metres away) pager system. For so long I had suffered this QRM without realising the true source. It took me a while but after buying one filter that wasn’t sharp enough I borrowed another bandpass filter that took out this pager QRM and left me with a bandscope a little healthier looking!
9700 with pager QRM filtered outCouple this with the excellent receiver the 9700 has and it has truly transformed my 144MHz operating, and also on the other bands based on the receiver.

In the first QRM image above you can see I have the inbuilt memory buttons showing. The IC-9700 has these for voice and CW (maybe data?) and these are a complete godsend. I use two for contesting and one for general calls pre-contest. They auto repeat and you can get an external box to replicate the first 4 buttons. (Another build in the future)

You can connect the 9700 to your PC with a simple USB cable and get CAT control and data in out for things like digital modes, computer reading and sending of CW etc. So much easier than buying a rig interface box. I just use CAT when I am contesting.

The 9700 will also record both sides of a QSO as you go onto the SD card. Useful for DXers and the RSGB recommend doing this for contests. I guess it would be good for resolving disputes.

Those are probably the biggest plus points for me that I use all the time. Receiver functionality like adjustable filters and notch filters etc are there but not unique to this radio of course.

Performance.
As I touched on above, the radio performs excellently in my opinion. It won’t match a top HF rig into a high spec transverter of course, and may not have the optional roofing filters some radios have, but I have done very well with mine and I have seen quite an improvement in my scores since getting this and the 7300 (which I also love and has basically the same features). I find the receiver excellent and pretty good at withstanding some strong QRM locally as we have a pretty good turnout in the UKACs at Hereford ARS.

This radio does satellites (I know nothing about that) and can receive on two bands, but one of the first things I did when I got it out of the box was turn off the sub-receiver never to be used since. Until this March! March sees the RSGB March 144/432MHz where you need to operate on both bands at the same time. Not possible simultaneously as a single op but I set up with two antennas and two amps and ran on 144MHz and 432MHz, using CAT control from Minos to change bands by changing logs. Worked so well. However one thing I didn’t realise it could do was receive on one band while transmitting on the other. In the video below the 9700 is sat on top of the 70cms amp that you hear click when I Tx

I’m pretty impressed by that (as you can tell).

The “Bad Things”
When the IC-9700 was first announced there was a lot of talk about insufficient dynamic range to handle huge signals whilst receiving weak ones. Now whilst this might show up in a contest like 144MHz Trophy (IARU Region 1 in rest of EU) with huge signals from multiple antenna arrays and QRO amps (in fact our club station had such a complaint from a fairly close line of sight 9700 user) I can say that I have never had this that I can recall from another radio amateur. The only time my 9700 has shown OVF (overflow) is from the local pager mentioned above and from the Clee Hill radar station on 1296MHz. Bear in mind that I operate 11km away from G4ASR who has been known for being a very strong signal for many, many, many decades. (hehe Dave). I get strong signal QRM from him if too close in frequency when pointed at each other, but he has never put the 9700 into OVF (That is NOT a challenge Dave)

When the first units were received there was a lot of talk about temperature based frequency drift. It was the end of the world as we know it. Icom has since come up with a firmware upgrade to assist and GPS locked board and mods are available. I feel it’s worth mentioning I am using one of the very early units and it is as it came out of the box. No firmware updates have been applied. None have had anything I felt I needed. I don’t do data modes (to date) just primarily SSB. I have never had anything mentioned to me about drifting and never noticed anything on receive. That’s on all 3 bands. I do only normally use the radio on 10W on each band so I probably generate less of a temperature change. (They say it multiplies up on 1296MHz)
So if you want to actually talk to people yourself rather than letting a computer do it for you, the 9700 works. Works well.

One real issue that has reared its head with me is the single PTT output for driving amps and transverters etc. There is only one contact available that grounds on Tx for all three bands. People have designed units that read the C-IV data and generate a band specific PTT output and I do plan to build one of these myself. For a recent dual band contest however I did something a little more old school:
9700 PTT switch front view9700 PTT switch rear view9700 PTT switch side view
Summary.
I am really happy with the purchase of the IC-9700 to accompany the also great IC-7300. One thing I like is the matching form factor. They are practically identical so I can alternate them in my portable box depending on the band I’m using.
G1YBB portable contest box

My suggestion is to think carefully about what the naysayers are actually saying and decide if their nays will actually have anything to do with what you want to do with the radio. For example, I’m not currently interested in EME or data modes like FT8 so the drift ‘problem’ doesn’t bother me. If I decide to do data, then there are firmware and hardware solutions ready to solve that.

Did I mention I love my Icom IC-9700?

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!

Car portable cable access

Nearly all of my radio is done portable in one way or another. When I am car portable like many people I bring the cables in through one of the car windows. As I like to operate both through the winter and in the summer I wanted to keep the cold and rain out in winter and the flies out in the summer.

My simple solution to this is a strip of 1 inch thick closed cell foam with a shallow slit in one edge to fit on the top of the window, and a notch for the cables. Simple but works for me. It also doubles as rattle reducing packing on the way up and back!

car portable cable entry

UK and Europe VHF Contesting Maidenhead Locator Map

With the introduction of the B2 scoring system in 2017 I decided it was time to update my VHF contesting map that I use to help me aim the beam and find multipliers and bonus squares when out portable.

I have beam heading marked centred on my portable locations. They are close enough together at this scale to us just one point.
G1YBB Locator map
I usually take an A4 print of this map with me to refer to but the PDF file is fairly high resolution and should be printable at least A3 size at decent quality. Here is a 100% view of the map to see the detail:
100% scale view of detail

You can download it if you wish but if you wanted one centred on your location you can always email me (my email is on the home page here). The annotations are all done in vector layers and can easily moved around to suit. Here is my PDF for a look but it’s probably only any use to David G4ASR and other portable stations in my area.

G1YBB B2 Contesting Locator Map of UK & Europe (15.4MB PDF)

Edit:
Several people have asked for a copy of the map centred on their locator so one of these below may be of use for you. The centre point of the beam headings covers a couple of squares around the actual centre so one near yours. If not you can always email me.

NEW MAPS APPEAR AT THE TOP. Below those is a sorted list of previous maps, and below those are 2017 B2 (boooo hissss) maps.

Latest Maps
G1YBB Contesting Locator Map of UK & Europe from IO62JF
G1YBB Contesting Locator Map of UK & Europe from IO83RU
G1YBB Contesting Locator Map of UK & Europe from IO65QE
G1YBB Contesting Locator Map of UK & Europe from IO83WO
G1YBB Contesting Locator Map of UK & Europe from IO84SA
G1YBB Contesting Locator Map of UK & Europe from IO91IQ
G1YBB Contesting Locator Map of UK & Europe from JO00HW

Previous Maps
G1YBB Contesting Locator Map of UK & Europe from IO74AU
G1YBB Contesting Locator Map of UK & Europe from IO81AS
G1YBB Contesting Locator Map of UK & Europe from IO81EP
G1YBB Contesting Locator Map of UK & Europe from IO82WT
G1YBB Contesting Locator Map of UK & Europe from IO83LC
G1YBB Contesting Locator Map of UK & Europe from IO83MN
G1YBB Contesting Locator Map of UK & Europe from IO83SB
G1YBB Contesting Locator Map of UK & Europe from IO83VT
G1YBB Contesting Locator Map of UK & Europe from IO84JX
G1YBB Contesting Locator Map of UK & Europe from IO91CL
G1YBB Contesting Locator Map of UK & Europe from IO91RU
G1YBB Contesting Locator Map of UK & Europe from IO92ET
G1YBB Contesting Locator Map of UK & Europe from IO92JP
G1YBB Contesting Locator Map of UK & Europe from IO94DR
G1YBB Contesting Locator Map of UK & Europe from JO01BA
G1YBB Contesting Locator Map of UK & Europe from JO01EF
G1YBB Contesting Locator Map of UK & Europe from JO01JP
G1YBB Contesting Locator Map of UK & Europe from JO02JN
G1YBB Contesting Locator Map of UK & Europe from JO02RK
G1YBB Contesting Locator Map of UK & Europe from JO02UL
G1YBB Contesting Locator Map of UK & Europe from JO03AH

Old B2 Maps
G1YBB B2 Contesting Locator Map of UK & Europe from IO70SS
G1YBB B2 Contesting Locator Map of UK & Europe from IO70TQ
G1YBB B2 Contesting Locator Map of UK & Europe from IO70UM
G1YBB B2 Contesting Locator Map of UK & Europe from IO71LX
G1YBB B2 Contesting Locator Map of UK & Europe from IO71VO
G1YBB B2 Contesting Locator Map of UK & Europe from IO76XA
G1YBB B2 Contesting Locator Map of UK & Europe from IO82KR
G1YBB B2 Contesting Locator Map of UK & Europe from IO82PC
G1YBB B2 Contesting Locator Map of UK & Europe from IO82RJ
G1YBB B2 Contesting Locator Map of UK & Europe from IO83MR
G1YBB B2 Contesting Locator Map of UK & Europe from IO83PN
G1YBB B2 Contesting Locator Map of UK & Europe from IO85NS
G1YBB B2 Contesting Locator Map of UK & Europe from IO86GB
G1YBB B2 Contesting Locator Map of UK & Europe from IO86JV
G1YBB B2 Contesting Locator Map of UK & Europe from IO90HX
G1YBB B2 Contesting Locator Map of UK & Europe from IO90WX
G1YBB B2 Contesting Locator Map of UK & Europe from IO91QN
G1YBB B2 Contesting Locator Map of UK & Europe from IO91WP
G1YBB B2 Contesting Locator Map of UK & Europe from IO92FI
G1YBB B2 Contesting Locator Map of UK & Europe from IO92IR
G1YBB B2 Contesting Locator Map of UK & Europe from IO92PU
G1YBB B2 Contesting Locator Map of UK & Europe from IO93EG
G1YBB B2 Contesting Locator Map of UK & Europe from IO93KE
G1YBB B2 Contesting Locator Map of UK & Europe from IO93KH
G1YBB B2 Contesting Locator Map of UK & Europe from IO93MG
G1YBB B2 Contesting Locator Map of UK & Europe from IO93RF
G1YBB B2 Contesting Locator Map of UK & Europe from IO93TB
G1YBB B2 Contesting Locator Map of UK & Europe from JO01JK
G1YBB B2 Contesting Locator Map of UK & Europe from JO02KM
G1YBB B2 Contesting Locator Map of UK & Europe from JO02MA

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

Updates to portable car table

I have been using a piece of ply for years as a car portable operating table in many cars and still do, described here:
http://g1ybb.uk/simple-car-portable-operating-table/

After I made a post on the UK VHF Contest group on Facebook I got a reply from Dave G3WCB showing his cool car portable setup. I had already very recently thought of doing something similar but seeing his setup gave me an idea for a simple and quick update to my plank of wood.

I already locate it over the steering wheel for some security to stop it toppling over and trashing my radio gear but seeing Dave’s set up I realised I could secure the other end with two simple locating pegs and make it virtually idiot proof. Out with the 3D design and quickly knocked up a tapered peg to fit the headrest sockets. I included a recessed hex to take an M4 nyloc to save having to over tighten a bolt onto wood and split it:
3D modelled headrest peg
Shortly sent the file to my very generous friend Santa Paul who 3D printed me some and they were in the post!

A quick measure in the car and drilling and job done:
pegs fitted to board
Fitted to top of driver’s seat:
fitted ready to use
Just needs a radio and rotator controller:
ready for radios