M Squared 40M4CDD Setup Guide

The club recently acquired a M^2 40M4CDD antenna by donation from KI6HIG. It got its first use on Field Day 2026. This antenna is a beast!

Table of Contents

M Squared 40M4CDD Setup Guide

Overview

This page captures the club-specific assembly, mounting, testing, teardown, and storage steps for the 40M4CDD.

The 40M4CDD is large and at times unruly. Putting it together requires a bit of care as the elements and boom are long, and it’s easy to bend them.

The loading coils are fragile and must be treated with care. There are special packing and unpacking instructions.

There are also special packing and unpacking instructions in order to keep the antenna from breaking or losing parts.

Being taken apart and put together once a year is not really what the 40M4CDD is designed for. This is why there are some parts of the design that makes repeated assembly/disassembly difficult.

Each of the elements are supported by a truss. To facilitate this, each element’s center portion includes a truss mount. Because the elements are so long, instead of removing the elements from the boom, we remove each half-element from the center connector.

The antenna’s formal manual is available here.

Required Tools

7/16” Socket, for the three sections of the boom, and the bolts connecting the elements to the mast
#2 phillips screwdriver, for the element tip clamps
3/8” (TODO: Check this) socket, for bolts on the element truss mounts
3/8” wrench, for areas that sockets won’t reach
9/16” socket, for mounting plate U-bolts
1/2” socket, for mast U-bolts (TODO: check this)

Markings and Modifications

We have etched position indicators into all eight half-elements (1 being the director, 2 the front driven element, etc.)
The element tips collapse into the elements. We have marked where they should go with a scratch awl. You can tune the antenna with the element lengths.

Unpacking

The antenna is stored on top of the box trailer. It’s stored wired down, with elements facing opposite directions. This is so that the loading coils can be offset from each other. The loading coils are wrapped in neoprene which is taped around them.

The antenna is split into parts:

4 pairs of elements (really, half-elements). They should be taped together in pairs for each full element
3 sections of boom, several truss ropes (element and boom), phasing straps

Remove the neoprene sleeves from the coils on the elements and keep them in a safe place.

Assembly

The boom is split into three pieces. There’s paint demonstrating which should go where in different colors. a. Unforutnately, the rear (TODO: check if it’s front but I think it’s rear) driven element’s center section/truss mount is positioned right over the bolt connecting the two boom sections. This means that in order to assemble the antenna, first, you must remove that one center. There are four 7/16” (or 3/8”) bolts for this. They have to be taken all the way out. Immediately put it back on after the boom is assembled b. Make sure to apply grease to the boom sections before pushing them together. c. The upside of this approach is that we never need to locate the elements along the boom. They’re already in the right places.
Now, the boom should be put together and on sawhorses. Next, match each element to its correct location. The elements are symmetrical, so it doesn’t matter which is the left and which is the right.
The driven elements have plastic (nylon?) insulators which stop the halves of the elements from shorting against the mast. They are held on with zip ties, for reasons that will become evident later. Remove the zip ties.
Attach all the elements. They are long, and it may help to have a sawhorse underneath each element, or to have a friend hold it up. a. There is a single 7/16” bolt on each element, which is stored on the element side, not on the truss/center side. This is because each element has a stiffening sleeve inside it and we store the antenna with the sleeves safely stored inside the elements. This is also why we zip tie the insulators onto the center section rather than using the bolt to hold them in place. b. It’s very easy to misalign the holes in the sleeve while pushing the element onto the center section. The easiest way to make sure this doesn’t happen is to put a scratch awl, or other similar long thin device through the holes while you push the element on, and only remove it once the center section will not move further with it in. c. If you find that it’s not moving, or the sleeve and element half seem siezed, hold up the outer end of the element so it’s even across its length. Make sure to periodically apply a lubricant between the sleeve and the rest of the element.
Attach the phasing straps and balun. The phasing lines go through the clamps on each driven element. a. There is a single 3/8” bolt tightening each clamp. It’s difficult to get a socket around them, so you may want to use a wrench. b. The phasing lines are not symmetrical. The wider “Y” section goes to the side that the balun is attached to. c. There is only one place and direction that the balun will fit. The balun wires should go through the holes in the clamps, and onto the bolts there. The bolts are 3/8”.
Attach the trusses to each element, tying the ropes onto the clips
Tune the lengths of the elements. Each element has a single clamp for its tip. Loosen it with a #2 phillips screwdriver, extend the element to the scratch-all line, and tighten it back down.
Attach the support truss to the boom.
Loosen the bolts attaching the mounting plate to the boom so that it can rotate not quite freely. This will make it easier to catch the mount when it’s time. (only applicable if mounting in a way that requires rotation such as the tower trailer)
Level the elements. Choose one (usually the front) to act as the reference, and, keeping one level on the reference, use a second level to check that all the elements are level to each other.

Mounting

We typically mount the 40m monobander on the tower trailer. Follow the tower trailer guide to set up the tower trailer.

This is the heaviest and largest antenna that we mount on the tower trailer, so it’s very important to make sure the legs are set in a stable place, with an appropriate amount of tension on the chains.

The tower trailer has a stub mast. The U-bolts on the antenna should fit. They are 9/16”. Slide the antenna on, then slide the truss clamp on. Tighten down the truss clamp near the end of the mast, and use it to set the tension on the truss.

Go back to the tower trailer setup guide, and check the “hoisting” section.

Teardown

Teardown is essentially the reverse of assembly.

Remove the antenna from whatever mast it is mounted on, and place it on sawhorses.
Remove the boom truss by undoing the clamps and removing the rope. Keep it near the mounting plate.
Retract the tips of the elements into the elements. Tighten the clamps back down so the element tips don’t move too much.
Wrap the neoprene foam around the coils and secure with tape. It is easier to do this while the elements are still attached to the boom.
Remove the element trusses. You can leave the end on the boom side attached.They will be stored there.
Remove the element-halves. There is one 7/16” bolt per half-element, on each side of the boom. a. Remember that there is a sleeve underneath the element. If you need to remove the element and then the sleeve, that will work just fine but you may want to lubricate the sleeve before putting it back in. b. Because the elements have significant mass, you will find that it’s much easier to remove if you have someone hold the outside tip of the element level while it’s being pulled off c. Keep the bolt with the element, not with the center, in order to make sure the sleeve doesn’t go anywhere. That is to say, put the bolt back through the hole on the sleeve/element-half side, not with the center piece
On the two driven elements, put a zip tie through each side of the center element attachment point to keep the “donut” insulators from going anywhere
Remove the phasing straps. Loosen the clamp bits with a 3/8” (TODO: check) wrench (You probably will not be able to get a socket over them), pull the lines out, and tighten back down.
Remove the balun The balun wire is attached to the same bolt as the clamps for the phasing straps. Undo the U-bolts and remove the balun. Tighten the bolts back down so we don’t lose nuts.
Stack all the half-elements in opposite directions, so that the coils are slightly offset from each other. It’s best to keep the pairs of half-elements together.
Now we have to deal with removing the one center truss holder, in order to deconstruct the boom. Remove the four 7/16” bolts to take off the center piece, break apart the boom, and put the center piece back.
Break the boom at the other joining area. There should now be 3 pieces of boom, each with the 7/16” bolts stored through their holes.
Secure all the loose bits down - this is all the various truss bits and the phasing line.
Finish by checking that the element pairs, truss pieces, and boom sections are all tied together for transport.

Common Gotchas and FAQs

Be extremely careful with the support sleves inside the element halves. It is easy to “lose” the holes and have them not line up
Apply a protective conductive grease (e.g. Penetrox) to all the aluminum components that will sit next to each other. Once surfaces cold-weld themselves together, it’s almost impossible to get them apart.
The antenna’s phasing lines are not symmetrical. The wider “Y” section goes to the side that the balun is attached to.