SFI > 250 or bust!

I know that many readers have been holding their breath since last year’s sneak preview. Finally I finished this project.

When we bought this house, there was no cable TV. That was the very first thing we ordered and had installed. Not so much for TV but for broadband internet. The previous owner, an old widow, used a rusty satellite dish and some disintegrating VHF/UHF antennas. These were mounted on a six meter high steel tower that held another two meter mast on top. I couldn’t care less for the antennas but the structure was a nice bonus for someone who had to build an amateur radio station from scratch. It held the first dipole legs and later on L wires and elevated radials up high for many years. But as I said: the TV antennas were falling apart. The tower itself was completely corroded. Not a trace of galvanizing or paint. Cracks were appearing in several places. And the installer didn’t spend much on the concrete base. The foundation was simply too small and the whole tower sank away together the sinking base. A few degrees closer to the ground each year. Needless to say this was bound to go wrong one day.

I removed the TV antennas ten years ago. I didn’t like climbing this small tower nor put a ladder against it because the tubes may have been rotting from the inside. I had been wondering what to do when I removed the old tower. After all it was a vital point in my low band system. And how to get rid of this dreaded heap of rust? Without damaging the hedge, the fencing, the house, the crops on the adjacent lot…

The replacement issue was simple: I would make my own small steel tower. Not that I have a bucket list, but if I ever had one, ‘weld yourself a tower’ would have made the list. I am not a welder nor a fabricator but I file myself under ‘wannabe metal worker’. I had to decide how high. Six meters would do, like it is now, with some tubing on top. Triangular or square? I settled for square. Since I cannot get more than three meter lengths on my trailer, I decided to make two sections each three meter long and then weld them together. It would cost me more to have six or eight meter sections delivered to my doorstep than the bill for the steel itself.

I wanted a lightweight (relative of course) structure that I could tilt over. Light means I’d better not climb it. Tilting it over means easy access for antenna experiments and safer when yet another record storm is upon us. I calculated the weight of two designs. A triangular model with round tubing and diagonal cross bracing or a square model with L shaped flat stock. Since the weight for the same length was about the same for both models, I opted for the square design since that seemed easier to weld inside the construction.

I made the base for the tilting in summer 2015. I also made an anchor with six M16 threaded rods that I put in a new concrete base. By the end of last year’s summer I had given the base three coats of quality paint and bolted it to the concrete base. And I finished the lower section of the tower. That was the end of summer and the tower section hibernated in the garage. When my 2016 summer holidays started I wanted to finish this project ASAP.

Welding the second tower part was easy now that I knew how and how not. I had made a jig to keep the corner profiles at the exact spacing when welding the cross members. Joining the two parts in a straight line and not warped was a real PITA. In the end I just yelled ’To hell with it’ and welded away. A few hits with the hammer and the result was pretty acceptable. It would of course be much easier if I had a loooooooong welding table and not just a 80×80 cm plate. I had to use a ladder on each end to support the ends and then try to align both sections in the middle on the table. All by myself. If I had to start over I would first join the individual L stock and then weld the six meter long tower in one piece. Actually, knowing what I know now I would probably go for the triangular model with round tubing, with what I know now.

Next up: painting. One layer of anti-rust base coating. Two layers of high quality finish. Dark green for the lower quart, the other part mat gray. This turned out to be a pretty good choice to minimize visual impact. The base section blends in the crops and trees. The upper section blends in the sky. Painting this construction with a brush was no fun. It’s only corners and edges. For the finishing I decided to dilute the paint a bit and used the paint gun. I should have done this for the primer and the other layers too.

I had planned to remove the old tower and install the new all by myself. I knew this wasn’t a smart plan and in the end I asked my neighbor to give me a hand. We have done many jobs together here and at his place. He’s my age and a real DIY-guy too so I knew his assistance would be very welcome. It took us half an hour to remove the old tower. I cut the tubes with an angle grinder. This is the machine I fear the most. Especially since I didn’t know how the tower would behave. I was afraid the cutting disk might jam when the slicing through the tube. My assistant kept the tower tensioned in the direction it needed to fall. No margin for error! I decided not to cut through all the pipes and lattice bars. In the end the tower was just held by a few points. I whacked it with my heavy hammer and suddenly it snapped and fell right where it needed to land. What a relief, really! I cut the thing in half and loaded it on the trailer. Good riddance! The plan is to clean the mess at the base and cover the concrete with something (woodchips? gravel? huge flower pot?).

Then it was time to put the new tower on its tilting base. Last year’s sneak preview movie is the evidence that it should fit and actually it did. But there is no way I would have done this without the help of my neighbor-friend. Not even the XYL would have been of any use (sorry my dear). When the hinging bolt was in place and secured, I put the tower straight up vertically. I was very glad to see it was straight. The construction was not bent and it was square with respect to the horizon. This was confirmed by holding a level against it. This was important to me because I see things being level, straight and square as good craftsmanship as opposed to the poor work of a quack.

To end the job I only had to mount the three meter aluminum tube on top. This is in fact the boom of my old three element monoband yagi for 28 MHz. It holds two pulleys. One for the L-wire for 160 and one for who knows what. I also put an eye bolt in one of the cross members. This holds the rope to tension one of the 80m elevated radials. To make the tilting easier I looked for some counterweight at the base. I had some old fitness weights lying around. I used a threaded rod to make a ‘weight satay’. This counterweight helps but some more weight would be welcome as it’s pretty hard to get it down or up. I will look in the scrap container for some heavy stock next time I’m at the steel yard. Or just fill a PVC conduit with concrete and put a rod through it.

This project took a big bite out of my spare time. Time for the hobby but during which I didn’t get to fill the log. I’m very glad the old crooked tower is gone. And I’m glad with the result of this construction project. Time will tell if I did the job right. Will it last as long as the tower I just cut into pieces..?

One Response to New small tilt over mast

  • Really nice setup. What is your low bands antenna setup? I’m trying to figure out a way of covering effectively 80-160 but need some ideas.

    Thanks

    Stefano

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