VK2YU Home brew M0MCX DX Commander

Home brew “DX Commander” 7m antenna – November 2021 … Australian date & time

Firstly, this build is a copy of a commercial antenna so ALL credit to the design and effort of the idea all goes to the designer:

Callum McCormick, M0MCX https://www.m0mcx.co.uk

The original build information is here https://www.m0mcx.co.uk/wp-content/uploads/DXC-Rapide-User-Guide.pdf

Note there are several YouTube videos that should be viewed as well as reading through the build document above. (YouTube videos are referenced in the document written by Callum above). Do this prior to construction as this is the underlying information you need to know for the build.

This document describes my particular build process, tuning outcomes and what I found building my copy. I also list the Australian parts suppliers I used.  The antenna is a copy of Callum’s DX Commander 7m Rapide design which he sells from his website listed above. I decided to cut elements for the following bands (as Callum also documents in his build guide in the 40m Adjustment section on page 4.):

• 10m
• 12m
• 15m
• 17m
• 20m
• 40m

To note there are different cut lengths if you are building the standard antenna vs the 40m adjustment so make sure you use the correct one for what you want to build. (I added another 5cm to each of Callum’s cut lengths just to be safe.)

Parts:

Part	Link	Quantity
7M Haverfords squid pole	https://haverford.com.au/collections/telescopic-squid-poles/products/7m-telescopic-poles-multi-purpose	1
Element Guide plates (3)-Made from Chopping boards	https://www.rejectshop.com.au/p/plastic-chopping-board-37x23cm	2
Wire Each of these can be bought by the role (100m)–24 x 0.2mm heavy duty hookup wire (Jaycar).	WH3041 (Black): https://www.jaycar.com.au/black-heavy-duty-hook-up-wire-sold-per-metre/p/WH3041WH3040 (Red): https://www.jaycar.com.au/black-heavy-duty-hook-up-wire-sold-per-metre/p/WH3040WH3042 (Green): https://www.jaycar.com.au/black-heavy-duty-hook-up-wire-sold-per-metre/p/WH3042	105m total (Maybe 110m for wastage and over cutting)
4mm Shock cord -tensioning elements	https://www.bunnings.com.au/grunt-4mm-x-5m-black-shock-cord_p4310533	1
4mm Paracord-you will only need around 8m total for the guy ropes	https://www.bunnings.com.au/grunt-4mm-x-30m-para-cord_p4310740	1 -The quality of this rope is pretty poor. Better quality “Paracord” can be found on ebay but is a bit more expensive
3mm Paracord-For use to tension elements (use with the shock cord)This is lighter weight than 4mm paracord and also a bit more visible. You will use around 4-5m.	https://www.bunnings.com.au/grunt-3mm-x-15m-para-cord_p4310741	1
Plastic shock cord ends(carabiners)	https://www.ebay.com.au/itm/313369938081	1 (set of 10)
Plastic number beadsfor element identification (optional)	https://www.ebay.com.au/itm/334153760807	1 (250 in a pack)
Ground and driven element plates(150mm x 3mm disc)	https://www.ebay.com.au/itm/274564411102?var=574781856591or (cheaper but with shipping)https://www.ebay.com.au/itm/112763328879	2
Aluminium plate150mm x 50mm x 3mm for extending Angle mounting (next item)-This item is cut in half to make 75mm x 50mm x 3mm plate.	https://www.ebay.com.au/itm/294442541589?var=593034496844	1
Aluminium angle-for mounting RF connector (BNC connector)	https://www.bunnings.com.au/metal-mate-30-x-30-x-1-5mm-1m-aluminium-angle_p1130510	1
Hose clamps(Sizes to suit Squidpole sections)	https://www.bunnings.com.au/prime-22-38mm-solid-butterfly-screw-band-hose-clamp_p3110907	3
Eye terminals	https://www.jaycar.com.au/eye-terminal-crimp-5-3mm-yellow-pk-100/p/PT4715	13 minimum (Similar to these.) For ground radials you will need eye terminals big enough to accept 4 wires
Zip ties (100mm long)	For holding end loop in elements while tuning. Once tuned use glue impregnated heatshrink to permanently secure.	Depends how many times you need to cut elements
Nuts, bolts, washers and wing nuts	All 5mm stainless.  BOLTS -Standard hex head (16mm long is a good size)NUTS -Nylock version as these wont come looseWASHERS to suit.WING NUTS	21211313
BNC Panel connector (9.5mm mounting hole)You could use an SO-239 if you wanted. I happened to have a few BNC’s spare	Wherever you buy your connectors from!	1

Creating the plastic element “spreaders”

!This was a very messy exercise resulting in a LOT of fine plastic residue to clean up. Use a vacuum attachment if you have one!

On a piece of A4 paper draw an 18cm diameter circle.

Use the process here to create a hexagon: https://www.youtube.com/watch?v=shVumum36k4

Cut out the paper hexagon template then use this to draw onto the plastic chopping board with a sharpie marker. Use the opposing points of the hexagon and a ruler to mark the centre of the hexagon for hole drilling.

Cut the hexagons out of the chopping board (I used a jigsaw with 18TPI blade) -Make 3 of these.

Drill holes for the driven elements near each point (4.5mm and then use a debur tool or a larger drill to slightly countersink each hole on either side to remove sharp edges.)

The centre holes were made according to where they sit on the squid pole. These sizes allow each plate to stop at the bottom of the pole section just resting on the top of the next lower pole. The holes were drilled with a speed bore and these conveniently came in the sizes I used below.  Make sure the speed bore is sharp otherwise it will melt the chopping board and be a bit messy to clean up.

For my squid pole the hole sizes were:

• Upper plate (left) 18mm (could be 19.5 – 20mm depending on where you want this plate to sit. Mine sat a little further up the pole section than expected but works fine.) 
• Middle plate (middle) 28mm
• Lower plate (right) 35mm (also used to guy. Guy holes (x3) were 8.5mm)

Check the fit of each plate on the squid pole sections. The plates should sit at the bottom of each of the following pole sections:

Lower (& Guy) plate -Sits bottom of section 2 -just above section 1. There is also a hose clamp installed at this section as it is a guy plate and exerts additional downward force and would pull down without the hose clamp.

Middle plate -Sits bottom of section 4 -just above section 3

Upper plate -Sits around 1/3 the way up section 6 (or you can enlarge the hole by a mm or two and it will sit at the base of section 6) – I only had an 18mm speed bore so I settled for where this plate ended up.

Ground and element plates (Aluminium)

Mark the centre of the 2 aluminium plates and bore a hole that suits the lower diameter of your squidpole.

For mine I went for:

• 38mm for the driven element plate (and then had to file out the remainder carefully to make a snug but not contacting fit around the pole)

• 51mm for the Ground/Radial plate. This is fairly loose around the bottom of my squidpole but this doesn’t matter. It also means the pole can be pulled up from the base and laid flat to adjust elements without disturbing the elements.

I used a hand drill and metal hole saw ($7 for a small set from Bunnings) to cut the hole and this was a bit messy, so if you have a drill press this would be a lot neater (or a lathe would be the best!)

Hose clamp above driven element plate to prevent it from slipping up squidpole when elements are under tension with shock cord fitted. Marked the band connection points on the driven plate with a Dymo labeller and band elements with plastic numbered beads.

The BNC connection is the centre conductor of the BNC socket on the ground plate.

Middle element spreader (Shockcord for 10m element point as element end sits lower than this spreader). A good idea is to mark the bands as shown (40 is hidden) on each of the spreaders as this makes it easier to keep track of where each element should be placed.

3mm Paracord (red) and 4mm Shock cord to tension elements. Shock cord length approx. 30cm unstretched seems to give enough tension without over stretching wire. Use the 3mm Paracord to make up the distance required to reach the spreader it connects to plus a little spare as you will typically cut the wire elements back to tune you will need a little more 3mm paracord than what you begin with.

The element in the foreground (17m) is temporarily held with a zip tie as had not been tuned at this point.
The element on the left side is 20m. (40m element had not been installed at this point)

The 40m band setup.

In Callum’s documentation he describes the 40m conversion whereby he suggests creating a 14 turn coil at the lower squidpole section and continuing the remainder of the 40m element up the pole. I decided I didn’t want the coil on the squidpole itself as this makes it impossible to disassemble due to the snug fit of the driven element plate.

I found a piece of 40mm (ID) PVC tube which I used as the coil former and after some experimenting found 7 turns was around what I needed for 40m.

This coil former was then taped to the squidpole where Callum suggested. (Long term install will likely be with zip ties and will prevent water from accumulating around the coil and tape)

Setup for tuning

Base of antenna. 
Showing:

• A few of the (6x) 4 bundled ground radials (3.2m long) connected to the ground plate at bottom.
• The centre conductor from the BNC socket connected to the driven element plate via a short piece of wire
• Driven element plate with elements connected (marked with numbered beads) and under tension via the shock cord above. You can also see the hose clamp above the driven plate to prevent it sliding upwards.
• The orange rope is installed to stop the base from wandering and is tied off to the ground stakes.

Tuning

Tuning was (is still underway) done using a 24m length of RG58 terminated with BNC plugs (it was lying around) and this was connected to a Rig Expert AA-600.

The initial sweep of bands 40 – 10m showed the ugly SWR plot:

As all elements were cut VERY long this was expected.

Slowly working through each band/element the results below (so far) were achieved. (I will continue to tune these to the desired target frequencies)

Things of note:

• Using the Rig Expert made tuning VERY easy. If you have access to one or something similar they are excellent.
• Callum references an element tuning calculator in his build document. This is an excel sheet with some simple formulas in it. Its VERY helpful.
• Make sure when tuning you keep all elements nicely tensioned as this minimises SWR anomalies.
• Make sure to tape each squidpole section at the join to the next one as when under tension they will tend to self collapse!
• Tuning is a long process! Take your time and the results will be worth it.
• Under a lot of load the plastic element clips popped the shock cord so 2 knots are required in the ends there.
• My build is not pretty. This was more a first go and I would suggest using a drill press especially on the aluminium plates. I only had hand tools but I had enough to make it work. Buying the aluminium discs saved a LOT of hassle
• The cost of materials is high as there is a lot of unused parts. If you can split the cost to make additional antennas this will make it better (cheaper).

Simon VK2YU – November 2021