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

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

DH8BQA voice keyer BX-184 for FT-817, FT857D, FT-897D mic MH-31

I was scrolling down my Facebook feed and spotted a post in I think one of the SOTA Facebook groups mentioning a BX-184 CQ Parrot. It looked interesting at first, then awesome! Within 20 minutes I had it ordered.

This is a modification to the standard MH-31 microphone that comes with the FT-817, FT-857D and FT-879D etc. It will record and playback a message, perfect for calling CQ Contest or CQ SOTA etc, but without the requirement to carry and connect up another gadget as it fits completely inside the microphone body. It was designed by Oliver DH8BQA and he describes it on his website here http://www.dh8bqa.de/bx-184/.

It is available for sale on the German Funk Amateur site here Funk Amateur BX-184. However they also do another kit that includes an MH-31 microphone body if you don’t want to disturb your original mic and that is the option that I took Funk Amateur BX-184M. The website is all in German so if like me you don’t speak German Google Translate will help a lot! There is also now a USA vendor here http://www.box73.com/product/2

It came pretty quickly and this is what you get in the box:
what is in the box
A complete kit with all you need. The PCB is part SMT (surface mount technology) and part through hole components. You just need to fit the through hole components.

The double sided PTH PCB is very nicely built.
Top:
PCB as supplied top
Bottom:
PCB as supplied bottom
Before it arrived I did some research and found some mods made by DG2IAQ on eHam which sounded worthwhile:

Mod 1:
I do always replace C8 (4,7µF) by a nonpolarised SMD 1,0µF to fasten up the AGC. With this Change the internal AGC works more as a mic compressor than as a (slightly delayed) mic Level limiter.”
Mod 2:
And for the first time I changed R4 (82k) into 56k to bring the sample rate from 8kHz up to 12kHz (by a shortened play time of 40s instead of 60s, but that’s still more than enough for my needs). This change gives even more punch for the replayed calls as the sound is a little more high-pitched afterwards. You simply can solder a 100k SMD in parallel to R4 instead of completely replacing it.”
I emailed Oliver DH8BQA for his thoughts on these mods and he confirmed they should be worthwhile.
So I decided an 0805 ceramic chip 1µF capacitor would fit best across the pads for the 4.7µF electrolytic it was replacing:
C8 fitted as 1uF
I should have fitted this first as the 15µF cap next to it made it awkward to get a good solder joint on the GND side of the capacitor due to the ground plane wicking the heat away. Got there in the end though:
1uF cap fitted
R4 is an 82K 1206 sized resistor located on the rear of the PCB (this is easy to locate as the kit comes with build instructions in German with a good circuit and layout supplied. English instructions can be downloaded here, page 5 onwards English Build Guide):
standard R4 as 82K
And with a 100K 1206 fitted in parallel (on top of the fitted resistor) as suggested above:
R4 with 100K added
With all parts now fitted (including a 1206 capacitor fitted across the supplied electret insert terminals) all that is left to do is mount the electret insert into the microphone body and solder that to the PCB.
Opening up the supplied microphone and removing the PCB revealed these 2 slabs of steel in the body. The only function of these I could see was to add weight to make it feel more substantial. So I got rid of those. No point in carrying dead weight:
empty mic shell
Next I hot melt glued the electret insert into the mic and filled up the void as the instructions said. Actually I filled more than the picture in the build instructions showed by mistake. Then solder the screened cable to the PCB and fit the IC and it’s ready to be assembled:
finished prior to assembly
As the replacement PCB does not have the two position slide switch, there is the unused hole in the back of the mic. For this I just used some good quality sticky label material I have to hand.
One piece inside:
switch hole covered up
And one on the outside.(not pretty but functional):
switch hole covered up ext
Once assembled I compared the standard supplied Yaesu MH-31 mic for weight against the BX-184 CQ parrot. A 40% saving in weight, I’ll take that:
Yaesu MH-31 v CQ parrot weight
I soon connected it up to the radio ready to go but there was no outgoing audio! What!? With several projects on the go I could do without time spent fault finding. What if I have cooked the electret soldering the capacitor on now it’s well and truly hot glued into place. Hmmm. Hold on, what was that pot trimmer for? I remembered when building it I couldn’t see any mention of it. A check of the circuit confirmed the obvious answer. It’s on the mic output to the radio. A quick check with the meter confirmed it was currently set to ground the mic line going to the radio. A quick tweak and we are back in business.
In fact the worst part was setting up to monitor myself. Eventually I had a reasonable system, FT-857D on 5Watts into a dummy load near the FT-897D with a 4mm banana plus as an antenna feeding into the sound card on the PC, with Audacity dealing with the recording. The recordings are not broadcast quality but are good enough for a comparison.
Here is a CQ call using the standard MH-31 mic:

Here is same CQ call live using the BX-184:

And the replayed recorded CQ call from the BX-184:

I might need some on air radio reports for final setting but it doesn’t seem to be clipping at all though does have a little more punch.

 Can’t wait to try this out in a contest or SOTA activation. All in a great little kit well thought out and went together very well. The only small point is no actual mention of the trimmer function or setting which would be good as a reminder if nothing else. I know this kit is aimed at radio amateurs who should be able to look at the circuit and deduce why the pot is there so this is a very minor point in a great kit.
Edit:
I have since used this ‘in anger’ in 144MHz contests. The first contest I got some complaints about over driving and being wide (complainant was also wide to me for that matter!!). But I turned SSB mic gain down in the FT-817 and back at home I did turn down the audio output level on the microphone itself and did some tests between it and the standard MH-31. Subsequent contests have resulted in zero complaints but some good audio reports.

Lightweight Yagi beam element mounting plate

In order to facilitate the building of my backpacking lightweight 144MHz 9 element DK7ZB yagi with a friend I came up with this reinforced plastic element mounting plate.

The primary idea behind it was that it would make it easy to accurately position elements in the right position along the boom and also ensure the elements were mounted nicely perpendicular to the boom. This was the sought after benefit for my build, ensuring all elements were nicely parallel to each other and in the same H plane. Also it would allow easy use of specific element mounting methods particular to my variation of a DK7ZB 144MHz long yagi beam design. The mounting plate is specifically designed to work with 20mm square section boom.

Here is the 3D design of the element mounting plate:
element mounting plateAnd a dimensional drawing for suitability to other yagi build applications:
yagi element mounting plate
For my beam (linked at top) I was able to use this to mount both parasitic elements and the custom driven element:
element in numbered location
finished DK7ZB match
The element mount plate has location ridges underneath to align perpendicular with the 20mm square boom and has a small central sighting hole to align with a marked up boom for element centreline positions:
element plate fitted
Two fixing holes are provided to fix the element mounting plate to the boom. They are sized for 3.2mm pop rivets but can be easily drilled out for other sized bolts or rivets. The element mounting clip holes provided can also be easily enlarged. They are supplied undersize for M3 deliberately so that an M3 bolt has to be screwed into them thus providing a precision centre aligning of the bolt and hence element clip mount.

Here is a video of the element mounting plates in action:

The clips have now been made available for other radio amateurs wishing to do a similar build in sets at
https://dura-id.store/product/yagi-beam-element-plate

Portable 9 element 144MHz DK7ZB long yagi

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

I settled on the 9 element long yagi as it is not too long but with decent gain and also has a good flat SWR curve. The RSGB Backpackers section we wanted to participate in only allows one antenna so stacking shorter yagis was out.
The dimensions are available on Martin DK7ZB’s site:
DK7ZB yagi dimensions
I went for the 10mm elements as a compromise between size and weight and best performance. I was also able to find 10mm clips to suit my intended design.

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

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

First building task was to cut the parasitic elements to size. Although I’m pretty good with a wood saw I’m a bit rubbish with a hacksaw and I didn’t want to use a pipe cutter as certainly for the driven element I needed no deformed ends to the tube, so I managed to borrow a mini circular disk cutter like so:
Proxxon KG 50
With this I was able to make nice square cuts. To measure them I used a metre ruler (tape measure for the reflector-checked against the metre rule first) butting both up against a stop to get an accurate measurement. I checked that the first mm was a true mm before starting as some rulers have a dubious first mm:
measuring stop
And checking D2 (ever so slightly short if anything by a fraction of  a mm):
D2 measuring
After cutting the parasitic set I fitted end plugs from Nuxcom for a nice finish. (Elements in bottom box, spare elements and boom sections in top):
parasitic elements cut ready
Next to assemble the boom. I bought the Nuxcom boom joiners and I must say they are very well recommended. The fit onto the 20mm boom sections is a snug push fit and the extrusion is thick enough to be strong yet still light. I got them with the M4 bolt and wing nuts. The one thing I didn’t like so much was the massive hole for M4 which was 6.5mm diameter. However, once I modelled up the joiners and dropped them into the antenna assembly I could see that a 4mm hole at the top of the 6.5mm hole would be pretty much bang on centre of the boom, and mean the boom could not move up in the joiner. I also added a vertical bolt on each side of the joiner too as shown below. That meant the boom section was forced into the joiner tightly ready to drill the holes. I drilled from each side, using the 6.5mm hole as a stop for the 4.0mm drill bit:
boom joiner
The above picture is showing the boom joiner fitted to the centre section. Both joiners are fitted to the centre section and will stay there permanently so I have used socket cap heads and nylocs, all stainless steel, bolts cut to minimum length. (The four supplied wing nut bolts will be used to attach the end sections on the hill top). With both joiners fitted, the centre section then is pretty much the same length as the outer sections (by design). I also bought the square boom end caps from Nuxcom to finish them off nicely:
Boom sections ready
The boom was then assembled in my hallway and the centrelines of the element positions scribed on. I used a tape measure masking taped to the boom to ensure it never moved and starting at the 100mm mark on the tape measure to eradicate any errors from the tape measure hook end.

The element clips I needed to find something that was quick to mount the elements and remove them again. The typical single bolt through the centre of the elements I didn’t fancy as it was a bit fiddly especially with cold hands on a windy hill top. My friend found these 10mm pipe clips that were ideal. Snap in and lock, and easy to open again to remove the elements. They will have a finite life but my test piece has had dozens of cycles and they come in a bag of 100 for under £6:
element clipAnother plus point of this is the element centre is a reasonable distance off the mounting surface which means I had good scope for getting the driven element to be on the same plane as the parasitic elements. I just need some suitable plates to mount these on nice and squarely on the boom. My friend offered to injection mould me some rather than my trying to accurately drill out several plates exactly.  So I modelled up a mounting plate to be made from glass fibre reinforced nylon which is extremely strong and stiff for its weight. The image shows the underside. The two ridges are to locate on the square boom:
element mounting plate
Soon in the post came a parcel of element mounting plates. We decided riveting them on was a secure and lightweight fixing method. The two location ridges on the bottom had a slight amount of play when offered to the 20mm boom which of course would be amplified by the approx 100cm elements so I fitted two tiny strips of masking tape which made the plates a perfect fit. Once the rivets were in it doesn’t matter if the masking tape decomposes away:
masking tape slack filler
The small hole in the very centre of the element plate is a sighting hole to align the element in it’s correct position on the boom. This was used to line up to clamp the plate on for the drill of the first rivet hole:
clamped ready to drill
Once the first rivet was fixed, the clamp was no longer needed and the 2nd hole drilled and riveted:
element plate fitted
Then a simple case of fitting the 10mm pipe clips and snapping in the elements in the right place centred on the boom. In order to easily locate the element centrally on the boom with out any time consuming I fitted to each element a piece of adhesive lined heatshrink to be positioned between the clamps. I also added some marking numbers for the 8 parasitic elements, numbered 1 to 8 from from to reflector:
finished parasitic elements
elements numbered
element in numbered location
Now the easy bits are done, time for the driven element. This was the biggest head scratcher on how to make it suitable for repeatedly taking apart and assembling. I needed to come up with a method that both left the electrical connections to the driven element halves but also enabled me to remove them for transportation. This meant a split in each half of the driven, but how to attach it?
I decided to come up with a system of employing a ferrule in the driven to join the two halves. With some custom made parts it would also be mounted on the same element mounting plate as the parasitic elements and is the reason the element plate is larger than a typical one, although that was also good for rigidity and build accuracy.

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

To cut slits in the 10mm tube to compress it with clamps to grip the ferrules I used two 10mm element clamps to mark a dot each end and each side of the clamp and joined them up to make cut lines to follow:
using clamps to mark centreline
cut lines marked
I’m not fantastic with a hacksaw to be honest but using the element clamps above to hold the tube in the vice I was able to cut (from both sides) fairly neat slits with a junior hacksaw (I wanted thin slits):
element slits cut
Then it was a case of fitting the ferrules into the outer halves of the driven elements and adding a screw to maintain a good mechanical and electrical grip:
ferrules fitted to driven halves
Next to feed that driven element. I decided to straighten out the feed match to take the feed point a little closer to the centre of the yagi. I’m using WF100 75ohm coax which is fairly low loss for its size, and is not too big or heavy. Its claimed velocity factor is 0.85 so I worked out the length as so:

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

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

This is the length of the braid. I hate stripping and cabling up coax so did all I could to avoid twisting bits of braid about. I cut the braid and dielectric off square and about 5mm or so of the outer jacket to reveal the braid. With a very large tipped iron of unknown wattage I was able to tin the braid nicely with no apparent melting of the foam dielectric. I then made a small tinned copper plate to bolt to the N-type socket and solder to the braids making a good earth. For good measure I added a loop of braid from some RG223 soldered all round. Then made the inners as short as I could and soldered to the N-type:
feed point box
To tame the annoying curling coax I found yet another good use for the short boom offcuts I asked Attila to include. I taped the coax out straight to measure the 442mm finished length:
feed match taped out straight
You can see I am using red adhesive lined heatshrink to keep the coaxes tidy and together. In the picture above the tiny box for the driven element connections is threaded on ready for the stripping and fitting of connections. I used a similar method as on the feed end with some copper sheet to join the braids and solder tags to connect to the element halves. This was a very fiddly job but hopefully worth it keeping the connections as short as I could manage:
driven element feed box
To support and space the feed off the boom as recommended by DK7ZB (although this is going to be used for QRP almost exclusively) I got some ABS spacers 3D printed which I placed in position and then wrapped tightly with insulation tape. The idea is to keep the coax off the boom (which it is miles away from) but also as far away as possible from the element plate rivets but also as far from the element the coax passes under:
3D printed coax spacer
The driven element box is supported solely by the driven element inner pieces themselves, but I added a very small 3D printed pillar to make everything secure:
dipole box support peg
Here is the feed match finished:
finished DK7ZB match

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

I used a small 3mm aluminium plate in usual manner and bought some 20mm square U-bolts for the 20mm boom itself. As the 20mm boom again is quite small for a long yagi I was again concerned about over tightening the U bolts and creating a weak and potential failure point so I added some small 3mm aluminium plates to allow it to be tightened up nice and tight without any fear of crushing the boom. Here is the finished boom to mast mount. (The two unused holes visible are there to use with the lower 20mm boom mounting holes for a 25mm boom yagi I have):
boom to mast clamp
I used a similar arrangement for the boom support to mast fixings, the aluminium clamps and a slightly smaller aluminium plate. Just a simple M4 bolt per half of the boom support and another plate to help strengthen it all up. The intention is that the boom supports will also help offer a little sideways strength against the wind as well.

To bend up the boom supports I first tried to bend some 20mm square section (same as the boom) in my workbench jaws (seen above in the first picture after cutting the elements). They were not strong enough to bend it! Note this is not a proper vice as such, more of a drilling and cutting bench with jaws. I then thought I might use a bottle jack to apply the force but couldn’t think of anything solid I could jack onto. Then I remembered we have a small 3000lb lever press at work used for punching small holes in sheet metal. I soon made up a jig using a 10 inch square of ¼” steel with some small aluminium blocks and I used the spare offcuts (yet again) to work out the right amount of packers below the centre to give me the bend angle I needed:
20mm square tube bend test
I used 10mm MDF to spread the load from the press and protect the 20mm square tube and a strip of bare FR4 as a bearing and protection to the underside. Once tests were done I quickly and easily put the bends in the actual supports:
boom supports bent up
Checking the bends are matched:
both support strusses parallel
Then just a case of offering them up, drilling holes in the right places and fitting. Finished!
finished DK7ZB yagi

Now for the moment of truth, how does it measure on the antenna analyser? Well to me it looks to be best match at 144.660MHz but is showing SWR of 1.1:1 and 51Ω at 144.300MHz so I’ll take that thanks:
SWR match at 144.150MHz
SWR match at 144.300MHz
SWR match at 144.500MHz
SWR match at 144.660MHz
Here is a real time video showing how long it takes to assemble the elements (I have not shown the boom assembly as nothing unusual or new about the boom assembly):

Finally, here is an assembly drawing:
G1YBB 9 ele DK7ZB assemblyHigh quality PDF version of assembly drawing
Full Bill of Materials PDF

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

Edit: I have done my first contests with this now and it seems to work really well and I got good reports all round. Even with a low loss feeder the radio was not indicating any SWR reading at all on transit. I have come 2nd and 1st in the low power section of the first two UKAC contests I have entered so I am really pleased with the way this yagi performs. It ‘feels’ even as good or better than our 2x 19 element MET yagi array.
DK7ZB yagi in action