Earlier this week the tower was planted. Now I am waiting on the concrete to cure and the machine shop to fabricate a few needed items. Then I can proceed. With luck the tower will be up this fall. Luck includes good weather, friends to come out to help and no serious mishaps. It's doable.
This is my last big tower -- two is enough for me to do what I want without incurring excessive maintenance during my golden years. For those who have been following along, this tower was in my original site plan for this QTH, and is located within meters of that plan. The tower will be a nominal 140', and actually ~133', or 40 to 41 meters, taking into account section overlap for splicing and base pillar height. This is an excellent height for DX work since it is 1λ on 40 meters and 2λ on 20 meters, and not quite 3λ at the top of the mast for 15 meters.
Unlike the disaster that was the planting of the first LR20 tower this one took only 7 hours. That's remarkable. It is thanks to the presence of an old hand leading his large crew of four, lots of planning and preparation beforehand and a large measure of good luck.
While it might not seem necessary with this crowd in attendance I was very busy on site working and supervising work. I got a good deal on the crew since for most of them it was their first time planting a guyed tower and my tower was a training exercise. Everyone wins. But the inevitable mistakes had to be noticed and pointed out, then corrected. Fortunately I have lots of management experience.
In this article I'll mainly focus on why the work went so well in comparison to the first big tower, which was a months long expensive headache. This should be more interesting to read about than simple repetition. There are relatively few pictures because I was less motivated to take them. The young guys on the crew took many more to, I suppose, remember what was for them a novel event.
First, the updated site plan. The changes are the approximate final positions of the new tower and the 80 meter array in the north field. Placing the new tower to meet my many requirements was difficult. The major impediment was avoiding the trees and rock wall surrounding the yard while achieving an ideal orientation of one tower face aligned with Europe for side mount yagis. A similar orientation on a line through the original big tower allows experimentation with wire antennas for the low bands.
I got pretty close to my objectives. A lesser objective was to minimize the transmission line run from the tower to the Trylon tower within the yard (yellow ellipse), which is the location of the antenna switch. The distance is similar to that for the other big tower, depending on how I ultimately choose to route the cables, both underground and above ground. There are several approaches to do this while avoiding tree roots and other obstacles. I have until next year to decide.
Surveying was similar to what I did for the first guyed tower. I'll refer you to that article rather than repeat myself.
Pretzel machine
Once again I opted to do my own rebar cages for the anchor and base. This time I had no outside help at all. I recruited material on hand to make the bending jigs and did a few tests to ensure each bend was exactly where I wanted them. I'm getting much better at this compared to the first time.I again used an LR20 tower section and side mount bracket to build the jig for bending the rebar ties. I call it my pretzel machine. The design is an improvement over what I used before. It worked very well. The main challenge was determining how far the rebar would advance to the left as the hickey was rotated counter-clockwise on the leftmost stud. With that known it was easy to achieve consistent and accurate bends.
The circular stirrups were more of a challenge. The trick was to exploit the natural bend radius the jib imparted and repeatedly advance the rebar when the correct arc for a 12" circle was achieved. A circular template was used to check progress and to correct errors. The resulting stirrups aren't pretty but they're perfectly good.
When all was done I had 12 square pretzels, 18" on a side, and 5 circular pretzels of 12" diameter. Straight lengths of 20M rebar were cut and then combined with the ties and stirrups to form the 3 anchor cages and base pillar cage. The base platform grid is comprised of straight lengths of 20M rebar.
To bend the 20M bars for the base pillar (equivalent to US #6 bars) I needed a heftier jig. As in the past I recruited a suitable tree and steel pipes. After looking at several dozen trees (I have thousands on my property) I found a birch that was perfect. With this jig the 8 bars for the pillar were given a 90° hook on the end for joining to the base platform grid.
Notice the construction of the completed anchor cage. There are extra bars on the top and front that assist with distributing the tension of 4 guys across the load bearing faces of the anchor. Without them there is a risk that the concrete could split in the middle under severe wind load.
The cage is 18" × 18" × 90". This leaves a minimum 3" of concrete on all sides for the 2' × 2' × 8' reinforced concrete anchors. This is standard procedure to ensure long term corrosion protection of the rebar.
Excavation
I had a chance to chat with the backhoe operator before the tower crew arrived. He looked and sounded familiar. I soon realized that he was the plumber who came to my rescue when the house pressure system failed soon after I moved in. Turns out he had been laid off and returned to his earlier job as a backhoe operator.
While this is an interesting story what was more important is that I admired the skill and meticulousness he demonstrated on the plumbing job. He brought the same attributes to this job. There are ways to use a backhoe that can greatly improve the excavations, if the operator cares enough and has the requisite skill. This was my lucky day.
Knowing that the anchor holes were to be 2' × 2' × 8' he brought a 2' bucket on the front. He was able to made these 3 excavations between 24" and 27" wide. That's excellent. This was so accurate that I had to get the crew to use their shovel to clear 3" around all sides of the rebar cages, including squaring the bottom corners. There was little margin for error with this quality of backhoe work.
The advantage is that the quantity of concrete was kept to a minimum, which saved me a few hundred dollars. While it is possible to build casings for the anchors it is more costly in labour and materials, and if the casing is to be removed it is necessary to bring back the backhoe a day or two later to backfill the holes. Using what they call "mud holes" is faster and cheaper. But to do it you need the right soil and soil conditions and a good backhoe operator. On this day everything went right. Casing was only used for the base.
Concrete
Readers may remember the fiasco with concrete delivery for the first big tower. The truck got stuck in the boggy November hay field. It and the concrete had to be rescued by backhoe. I had no intention of letting that happen again.When the driver arrived we did a walkabout to decide what to do. The backhoe has a big bucket (front end loader) for concrete delivery, if necessary.
The driver declared the ground just fine and drove onto the hay field. His judgment was good. Despite the 5 m³ of concrete onboard there were only light indentations left in the field.
Delivering the concrete direct to the excavation by chute is by far the superior method of delivery. It avoiding shifting of the steel when dropping concrete from the bucket and leaving time to push concrete into all the nooks and crannies to minimize air pockets. It is also much faster.
A handheld electric concrete vibrator made it easy to encourage the concrete to flow into all those spaces and level the surface. There is also less risk of shifting the rebar when shovels are used to pump the concrete.
Alignment
The crew did not spend time checking my surveying. There was no need. The crew leader aligned the anchor rods the old school way, with a string. In his experience it's the fastest and most reliable way of doing it. Too often he's found that transits are out of calibration or improperly used, but a string never lies.
When I did my surveying I measured the levelness of the ground. In one case I adjusted the distance to the anchor to account for the 18" drop in that direction. This ensures that the angle of all guys of each set come down from the tower at the same angle. My low tech method was to use a long level on a platform at the future position of the base pillar. Point it to a marked stake at the anchor site, ensure the level is level, then sight along it to measure the elevation difference.
More modern tools were used to set the 38° angle of the anchor rods. Every member of the crew would pull out their smart phones, lay them on rods and use inclinometer apps to adjust the angle. The angle was checked during and after the concrete pour.
The rule of thumb I was taught was that there are 30 minutes after the concrete is poured to move and align the anchor rods. Allow 2 hours before back filling over the exposed concrete, which allows it to firm up.
Back fill
When all but the back filling was complete the crew left, leaving me and the backhoe operator. While we waited for the concrete to firm up I had him move dirt around. This was the excess soil and subsoil from the excavations displaced by the concrete.
Some was left in small piles at the four excavations. I will use those to level the surface once the soil settles. That will take until spring. Since I forgot to leave extra soil at the excavations for the first big tower I also had him leave some at those four locations. I had done some wheelbarrow work in the spring but gave that up since it was tedious manual labour.
As the clock advanced we proceeded to back fill the three anchors. These were done in the same order they were filled with concrete and first poked to check firmness. He started slow with granular soil until the concrete was covered to 1' depth and the space under the anchor rods was filled. For the latter I used a shovel. This helped to prevent the weight of the back fill from pushing the rods downward to a lower than intended angle.
Over the next two days I spent a few hours raking and shovelling the extra soil. Large stones were removed by wheelbarrow. Last year I chose a spot within the bush to place the displaced soil and stones from the excavations.
Pier pin
The pier pin for the base section was embedded at the centre of the pillar soon after the concrete was poured. The pin in this case is a standard pipe with an OD ~1.3". The opening on the base section is 1.625". I may add a shim to fill the gap, however that is not really necessary.
One day later I filled the pipe with no-shrink grout and cleaned the pipe of stray grout and rust. It will be painted before the load bearing plate is slipped over the pin and grouted.
As you can see the 10' ground rod is already in. It was placed at a corner of the excavation then hammered down into the undisturbed soil. They crew would normally drive it below ground level and fill around it with gravel for future access. I prefer the ground rod to poke up a few inches. The difference in lightning protection is not large. I can drive it down later should I change my mind.
With that we're done! All that's left is final preparation of the tower sections and building upward. That stage of construction is scheduled after the CQ WW SSB contest. It should go faster than the first tower since the rigging can be reused and the lifting process has become routine. Hopefully I can get the same hams out to serve as ground crew. It's a race against winter.
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