The second photo shows the element to boom assembly where I used the SS U-Bolts with saddles from DX Engineering. This really strengthened the assembly and did not squeeze the boom at all--very strong!
Element Strengthening
My station location is within 75 miles of the gulf coast and in the 85 to 90 mph minimum wind range. It is possibly with a direct hit from a hurricane that we could get winds well in excess of 100 mph. I used the techniques that W6NL recommends for strengthening this antenna. Check out Physical Design of Yagi Antennas, by David B Lesson, W6QHS (W6NL) book on strengthen this and other antennas. It is very good!
The 205's heavy duty boom (center sections) was in good shape with only a very slight bend, I did not bother to try to straighten it, just lined it up with the bend pointing down and will let the strut support pull it up and support it.
I also used the Hy-Gain Boom to Mast mount.
Loading Coils
The following are some pics of the coils of the 40-2CD. Bruce had replaced the self-tapping screw with a stainless steel bolt and nut. However corrosion had developed with the aluminum tubing, the copper lead to the coil and the stainless steel bolt met. I cleaned up the connections very good and used some Noloax to control the corrosion between the aluminum, stainless steel bolt and the copper wire, hopefully this will help control the corrosion.
The coils had two pop rivets on each side to holding these assembly together. Three of the four assemblies were loose on the fiberglass forms. I drilled the pop rivets out and used three pop rivets evenly spaced around the tubing on each side. One of the rivets had to be off center from the other two because they would not all fit inside the aluminum tubing.
Here are some pics of the work that was required on the coils:
For the new shrink wrap, picked up some 1 1/8" 3M shrink at the local electronic supply house. Used a small torch to shrink the tubing. Tried a hair dryer but it would not work on the thick material. When heated up, this shrink extruded a clear sealant that sealed the ends. I am sure that this was some type of water resistance sealant. I don't know what it will be like if I ever had to take it down--hopefully I won't have to find out! hi
Unfortunately, I did not make any pics of the finished coils. They really didn't look to much different that the original ones!
Here is a detailed drawing of the LCA
Dave, W6NL also posted the following article to the Tower Talk reflector regarding the coils. It is complete and you will do well to following these procedures.
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Improving the Cushcraft 40-2CD Loading Coils (by W6NL) The Cushcraft 40-2CD uses 4 loading coils, which they call LCA (Loading Coil Assembly). I had one that had burned out, and when I fixed it, I found a much better way to construct the assembly for mechanical stength. The LCA consists of a heavy-wall plastic tube, around which is would the tinned or plated copper wire of the loading coil. At each end, the plastic form telescopes into the aluminum element tubing. The coil wire is looped under self-tapping screws and the plastic form is fastened to the aluminum tube with 2 large rivets. The assembly is covered with a heat-shrink tube. My antenna, which was the subject of the QST article, has been through an extraordinarily stressful life and doesn't owe me anything. We've had winds up to 134 mi/h, and ultimately the 120' tower, which was overloaded by my commercial renters, broke a guy anchor rod and the whole thing came down. When I was salvaging the pieces to put the 40-2CD back up, I found that one of the traps had failed to an open circuit where the wire was terminated. The wire had a copper ball from melting in an arc, and my conclusion is that the failure had occurred before the crash. It appears that the wire had fatigued and broken because the rivets had become loose from flexing in the wind, allowing motion of the plastic form in the aluminum element tubing. The cracked wire then arced until the gap was too great to bridge. When I had originally built the antenna, I was aware that the self-tapping screws had a reputation of rusting out from moisture getting into the trap from the inside (although the outside is covered with heat-shrink, the inside is open to the weather through the element joints). I had replaced the self-tapping screw with a 10-32 x 1" pan-head stainless machine screw with internal-tooth lock washer and nut. I've heard that Cushcraft now uses an approach like this in new antennas. Because I've had some failures of stainless hose clamps have seen some rivets eat an oversized hole in element tubing, I now assemble all highly-stressed element joints with two stainless bolts with nylon insert locking nuts (whether I use a hose clamp or not; as an aside, I buy exact bolt lengths, such as 7/8" and 1 1/8", so I don't have anything sticking out of the nut to snag on guys or whatever). When I was reassembling the traps, I drilled out one of the rivets that was roughly at a right angle to the coil-terminating screw and put another 10-32 x 1" screw through the element and plastic form (at both inner and outer ends). This double shear and compression results in a very much stronger mechanical assembly that I believe will not become loose over time. If I were building the loading coil from scratch, on assembly I would also coat the tips of the form with something waterproof and rubbery such as polyurethane caulk (much better than RTV, butyl or silicone, but for some reason not easy to find). I would also consider using the heat-shrink tubing that comes with a meltable sealant on the inside surface. The only mechanical failures I had experienced with the original strengthened antenna were U-bolts eating their way through relatively thin element-to-boom plates and failure of inner ends of the outer boom sections, which were too thin to withstand the torsional load of the heavy reinforced elements. This is no knock on Cushcraft, as the antenna was exposed to winds far above even the 118 mi/h upgrade level I had worked to. For the reborn antenna, I used a single 24' length of extruded 2" diameter 0.12" wall 6061-T6 tubing for the boom, and made new element and boom mounting plates from 3/8" thick 6061-T6 plate. Both the elements and boom are mounted with 2" plated muffler clamps (with the heavy material, you can really tighten up, so there's no tendency for the elements to rotate on the boom). The boom is guyed from above with two cables on each side, after the fashion of the HyGain LP1009 (the guys come from a single point on the mast down to each end of an 18" aluminum angle attached to the boom as if it were a short dummyh element). This seems to prevent failure from rotary motion of the elements and boom, and is working out well on other antennas I have up. Dave, W6NL |
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Antenna HistoryI acquired this antenna from Bruce/WT4I in Florida, after it had fell from about 90' as a result of a hurricane in 2005. The boom broke at the mount, the aluminum struts were destroyed, the capacitance hats were all broken and the antenna tips were bent a little. I was lucky in that, AL/K3VN, from Florida, gave me the remains of a Hy-Gain 205CA that had crashed during a recent hurricane (2005). There was a good bit of damage to the elements outer pieces, but there was plenty of the larger tubing that was usable to strengthen the elements of the 40m antenna. I did have to buy a couple of specific sizes to finish the job, but all in all it was minimal. Thanks Bruce for the 2L40m and Al for the 205CA! |