As the towers and antennas grow in size and weight there comes a point where human muscle is not enough, or there is insufficient safety margin. There are too many hams unwilling to use safety equipment (even if only a hard hat and gloves) or too willing follow their own whimsy rather than the team leader. It's a disaster waiting to happen. Don't be afraid to handpick your crew from among those you trust to do the job right.
When I raised the Trylon I dispensed with a crew entirely until it came time to top the tower and put up the 40 meter yagi. This suited me since it was winter, my new property is a long drive for my friends and I wanted to do the work during weekdays when most people are at work. I overcame the challenge by designing and building a winch driven system for lifting heavy tower sections and antennas.
It worked well but was slow going. By relying on muscle to operate the system a 4:1 mechanical advantage in the winch was mandatory. It took a lot of cranking. It was safe and effective though slow. There are better ways. Those involve engines or motors, whether used in a crane, winch or...a vehicle. Thus we come to tractors.
I've used small garden and lawn tractors and far larger farm tractors to raise towers and antennas. All can work well if you use them appropriately. Power is both a blessing and a curse. Countless people have been injured or killed by machinery improperly employed or maintained.
Over the winter I purchased a garden tractor for mowing the large country property I own. I made sure when I shopped that it also would be up to the task of plowing snow and doing tower work. Luckily the parents of a business colleague were retiring from a hobby farm to the city and had a lightly used garden tractor to sell.
A deal was quickly made and I arranged transportation. The tractor sat unused for the remainder of the winter. Amazingly it promptly started in the spring despite being out in the weather with no more protection than a tarp and without recharging the battery. It has since been used for its primary job: mowing the grass. I have also driven it into the hay field to create (hopefully) tick free paths to my tower excavations.
Ropes and pulleys
Using a tractor or any powered vehicle for hauling objects up and down a tower requires a few simple techniques. However they are very important for a safe and successful procedure. In the following picture the key aspects are visible.
|Ground crew: Brian VE3CRG on the tractor and his wife Mollie who handled the tag lines|
This is the Cushcraft XM240 immediately after it has been lowered by the tractor. The tractor held it above ground while the fragile capacity hats were removed. Notice the pulley attached to the bottom of the tower. The pulley two things. First, the forces at the top of the tower and mast (where there is another pulley) are kept vertical. Otherwise the bending moment on the tower could cause structural damage. I discussed this topic some time ago with regard to gin poles.
Second, a garden tractor is not so massive that it will maintain contact with the ground were the rope to angle upward. The pulley translated the vertical force to horizontal so that the tractor has maximum traction.
The pulley is attached to the tower since it is a convenient and strong place to take the large forces involved. The pulley pivots upward approximately 45°, so keep that in mind when choosing an anchor point. Since the antenna is only 75 lb (35 kg) I went with the simplest attachment option: ¼" aircraft cable with a couple of cable clips. A better choice is a chain to reduce chafing and stress for heavier loads. The only suitable chain on hand was used to couple the rope to the tractor frame.
Some go further and fabricate a heavy gauge steel bar across the tower base which eliminates pulley motion upward. Although the cable could be made shorter to limit upward motion its length reduces chafing of the rope against the side of the tower. This method has a limit since if the pulley moves up too high the tractor can lose traction.
Measure the work area
Before using a tractor in this fashion you must clear a path for it that is reasonably flat and long enough radially outward from the tower base. If you run out of room you're stuck with an antenna dangling midair and no where to go but back where you started.
The XM240 was mounted 21 meters (71') above ground. I measured 30 meters (100') out from the tower as the starting point for the tractor to lower the antenna. This is not only to ensure that the tractor does not run into the tower before the antenna reaches the ground but also to keep the tractor out from under the antenna when it drops to the ground. In the picture above the tractor started its journey at the line of trees in the background. You can see the tire tracks in the grass.
The rope is 200' (60 meters) of ⅜" nylon. This is the minimum recommended for this operation. With the pulley mounted 75' up there is 150' required to go up and down the tower and 30' on the ground for the tractor to stay clear of the antenna. Another 5' to 10' is used for harnesses to the antenna and tractor. Very little is left unused.
To lift the TH7, which is about the same weight and breadth as the XM240 the process is reversed. The tractor pull starts at the edge of the antenna and backs away to lift the antenna. Whether lifting or lowering the tractor operator is facing the tower and rest of the crew.
Power is dangerous
As I tell the ground crew: you can't argue with 22 horsepower. When something goes wrong and you put up a fight the tractor always wins. When antenna hardware snags in the tower the tractor keeps moving. When a crew member gets tangled in a rope the tractor keeps moving. When the antenna or tower section strikes the pulley atop the tower or gin pole the tractor keeps moving.
Modern small tractors for residential use are surprisingly forgiving machines. Say you brush against a building, tree or large rock. Often the tractor will "see" the resistance and let the clutch spin. While this helps keep the crew safe it should not be relied upon to avert a disaster.
Older tractors are less forgiving: they'll just keep going. That's when someone can be seriously hurt. For large farm machinery or a truck there are fewer if any safety features, and the power is far greater. You are better off employing the smallest machine that will get the job done.
I've used garden tractors to successfully lift 200 lb tower sections. Only use more powerful machines when the operator is sensible and experienced.
Use tag lines to direct load around obstacles and to prevent snagging hardware on the tower, guys and side-mounted antennas. Tower sections require only one tag line while yagis should have two. For tower sections tie the tag line near where the lifting rope or cable is tied but on the opposite side. For yagis place one on either side of the boom cradle. The two 100' tag lines are visible in the picture above.
It is generally better for only one crew member to handle the tag lines. Little force is required so this is not a problem. When there is a person on each tag line I can almost guarantee they will find it difficult to coordinate their attempts to steer the yagi..
The crew handling the tag lines will be the first to know when the load snags on something or is about to do so. Give them the authority to stop the operation immediately when they detect a problem. The tractor operator must be prepared to quickly react.
|Crew taking a well earned rest|
Tractor power is of no use if the wheels spin on the ground. Excess power only makes the problem worse. Garden tractor engines are designed to use the power for mowing, not so much for hauling.
On wet grass or snowy ground a small tractor can easily lose traction under load. This occurs more often when lifting rather than lowering.
On uneven ground if one drive wheel has poor ground contact the differential will spin the lifted wheel and apply no torque to the other one. A tractor with a more sophisticated drive train is desirable if it is available. Otherwise plan the route for the tractor will extra care.
When traction is lost determine the cause. Many problems can be solved with more weight over the wheels. Some tractors provide an area where weights (stones, bricks, etc.) can be placed. In a pinch have one or two crew member jump onto the back of the tractor.
If you can't solve the problem you'll likely have to lower the load back onto the ground and try something different. Larger tractors are unlikely to lose traction with the weight of loads hams typically lift, however there is greater risk of injury and damage from all that power.
I cannot overly emphasize the importance of communication between the tower crew, ground crew and tractor operator. Agree on hand signals or voice commands beforehand, and practice if you can. Handheld radios can be very helpful. They don't have to be ham band devices. However you do it remember that tractors are loud and so you cannot always rely on shouting to get the message across. We want the tractor operator facing forward at all times so that they can see and respond to directions from other crew members.
Although we are all friends there must be a command hierarchy. In this hierarchy the tractor operator is at the bottom. That is, when anyone else tells them to stop or go they do so. Make sure he or she understands this. Don't assume they'll obey. No one, no matter how responsible, should be allowed free reign over the power they are handling.
As with all tower work the highest authority goes to those on the tower. Next in line is the ground crew. As already mentioned, last in line is the tractor operator. This arrangement strikes a balance between vulnerability and the potential to cause harm.
Don't hesitate to call a temporary halt to the operation if anyone is having difficulty coping or there is a point of confusion. Everyone should have this authority and not be timid about using it. The tractor operator should know how to lock the wheels when necessary.
We did have a few instances of miscommunication even though we all understood what needed to be done. Corrections to our procedures were made as we went along. No harm was done.
In the picture the TH7 dangles atop the tower under tractor power, and a properly set brake. After taking this picture I climbed the tower (wearing a hard hat) and bolted the antenna in place. We used the tractor to adjust the antenna height by a few inches to put it exactly astride the mast bracket.
The A50-6 was hand lifted since it is light and relatively fragile. It is best to avoid tractor power in this and similar cases. Always use the right tool for the job. It went up first since it goes highest on the mast. The TH7 must be carefully handled so that it does not tilt upward and strike the smaller VHF antenna.
It was getting late so we quit once the antennas were in place and the tractor and ropes put away. The next day I went up on my own to finish the job. This involved pushing the 6 meter yagi higher up the mast, removing the pulleys, pointing the antennas, attaching the rotation loops and testing that everything worked. Back on the ground I disassembled the XM240 and stored it and the Explorer 14 out of the way until they are again needed.
Both antennas use the RG213 runs I already had on the tower. This was not my intention. I ran into some difficulty preparing Heliax runs in time. I'll deal with that later.
In my next article I'll report on how the antennas play. For now I will only say that I am generally pleased with their performance. For the foreseeable future these are the only yagis going on this tower. Other than perhaps a 2 meter yagi for VHF DXing. This is part of my broader plan for the station.
Next tractor job
I will next use the tractor with a gin pole to construct the 150' tower. Each tower section weighs 120 lb and there is additional hardware that is similar weight. With an experienced crew the tower should go up quickly, with the tractor providing most of the muscle.
I may use the tractor to tram yagis to the top and sides of the tower. Muscle power will be used to raise Heliax and other fragile station components. Sometimes 22 HP is too much power.
|I love a crew that tidies up the job site without being asked|