Tuesday, October 6, 2015

For Future Consideration: Tower

Once again I am adding another chapter onto this series about actions I have taken towards my next, and bigger, station. All that Heliax now has a tower to attached to.

This past weekend was a busy one for me. It involved renting a large truck, driving over 1,100 km, picking up loads in two distant locales, then unloading and storing the truck contents on my property. In all, the weight of everything was somewhat over 2,500 lb (1,200 kg). Now I have a large tower, and much more.

The tower you see in the photo has 15 sections, each 10' high, including one base section. With overlap for section splices this tower would stand 144' (44 meters), plus around 15' (4 meters) of mast topped with a yagi.

The assembly resting atop the base section is a prop pitch motor fitted to a platform that mounts to the side of the tower. More about that in future. Just outside the picture frame is a large quantity of guying material, pipe and tubing. Most of the guys will be stripped for the usable parts, with most of the guy wire to be discarded; due to its past service it is necessary to purchase new guy wire for this tower.


This tower was manufactured by Leblanc & Royle (L&R), probably in the 1980s. L&R was in the business of designing, manufacturing, installing and maintaining tower systems for broadcast, military and other applications in Canada for many years. Many commercial towers across the country were once L&R, and many remain in service. While I don't know the details they were likely the victim of a changing industry, failing to successfully transition from previous tower applications to cellular communications. The tower requirements are quite different.

Used and surplus L&R tower can be found in many of the larger amateur radio stations in Canada. The tower I purchased comes from two other VE3 stations. The tower is used though appears to be in excellent condition. Most sections are painted in the familiar white and red colours for aircraft safet, while a few are bare galvanized.

One strong attraction of this tower to me is the many attachments that had been customized for amateur use. These include brackets for the (above) prop pitch motor for rotation of a heavy duty mast and side-mount yagis. These should not be overlooked since they will save me a substantial amount of time and money for design and custom manufacture. However, having seen long service, some maintenance is needed for the custom bearing assemblies and other components. This is something I will look at this winter, now that I have it close at hand.

LR20 specifications

Per the specification at right, my tower is "light duty" LR20 (the numerals are the face width in inches). It is conservatively rated and can comfortably handle ice and wind load when 150' high and holding several long boom HF yagis. Strict adherence to engineering guidelines for guying and loading is mandatory.

One thing that distinguishes this tower from a tower with round legs and diagonals is wind load. A tower has a substantial surface on which the wind acts, a load that the tower must support even without the additional load due to antennas. The engineering specs take this into account. Always always always follow the manufacturer's instructions for tower assembly, guys, anchors, base and load placement.

There are two girts per section, used for guy attachment, bearing plates, side mounted antennas and other loads. Guy yokes (custom U-bolts) are already attached to the girts on my tower that were previously used as guy stations. Depending on my final design I may need to move these.

This tower has a pier pin base, where the base plate is positioned over a 1" steel pin protruding from the reinforced concrete base. This is a common design element in large guyed tower to mitigate the stress on the tower caused by the torque of wind load on large antennas and bending in high winds. By allowing the tower base a limited amount of motion, the guys can absorb these dynamic loads. You can see an example for Rohn tower on W8JI's web site.

Also of note for those of us who do climb is that there are horizontal struts at ~18" intervals on one side of each section. That is a great convenience for climbing and working at height. The girts alone are inadequate since they are 5' apart. Ask anyone who has worked on, say, a Trylon Titan tower what they think of diagonal struts. It is of course important that the tower be built so that the horizontals are all on the same side. I prefer mine on the side that faces approximately southwest to keep the sun out of my eyes and the prevailing wind at my back.

A tower is not a toy

Do not be misled by any sense I might have unintentionally given that this tower is a plaything. Hams use towers to get the best from our antennas, just as we might use a kilowatt amplifier. Both can easily kill you. The only difference between falling off a 150' tower versus a 50' tower is the amount of time you have to think about it on the way down.

Safety is mandatory in the air and on the ground when working on any tower, and especially one of this size. Things always go wrong. It is our job to ensure accidents that do happen are not fatal to people or property.

The weight of the tower sections requires mechanical assistance. Do not rely on the muscles of two or more people. The risk is too high. Better to have one expert on site than a large crew of eager but inexperienced hams. This is not the place to trade safety to save money. Accept the fact that a tower this size is going to incur a substantial expense.

There are several options to put up a large tower. Use the one that works best for you, and that can be done safely and within budget.
  • Gin pole - This is the cheapest solution but expensive in time and potential safety events. The pole and attachments must be up to the task of lifting and manoeuvering heavy awkward weights. A tractor or similar device can provide the muscle with a suitable pulley system to minimize gin pole stress and permit horizontal pulling. Winches have been used but are not ideal due to the amount of cable required and the risk of slippage. Steel temporary guys are required before reaching the first permanent guy station, and even higher to reduce sway during construction.
  • Crane - The tower can be built on the ground and lifted all at once. A large crew is required on the ground to place the tower onto the base, plumb the tower and especially to secure and tension 12 or more guy wires. If any splice bolts slip the tower sections (typically near the centre of the span) will need to be redone once lifted but before the guys are fully tensioned. The crane will not be cheap, and you want a crane operator and ground crew who are sensible, experienced and safety conscious. If the crane boom is tall enough you can also include mast, rotator and even an antenna or two. The latter requires a second crane or a boom to mast clamp that permits 90° rotation.
  • Helicopter - This is similar to erection with a crane but far more expensive and should only be performed by professionals.
  • Hybrid - Use a small crane to lift part of the tower, to at least just above the first guy station. Splice slippage is kept to a minimum and only 3 or 6 guys need to be handled. The rest is done with a gin pole.
I have been involved in tower erections using the first and fourth methods. One of those was for an L&R tower of similar height to mine. While this gives me valuable experience it does not qualify me as an expert.

Before it goes up...

There is much to be done before my newly acquired tower goes up. One obvious need is the purchase of a large plot of land; this tower requires almost 1 acre of land, and more with mandatory setback from property lines. I must also perform ordinary maintenance on the tower sections to repair any minor flaws. All tower sections and guy yokes have passed my preliminary inspection. Always inspect tower sections, whether new or used. Inspection is easier on a tower with open steel members than it is on tower with tubular steel legs such as Rohn.

Mechanical work includes bearing repair and replacement, of which there are several: top plate and thrust bearings for the mast and beneath the drive bearing. The prop pitch motor may require maintenance and does require some work on the chain drive system. The motor itself works fine. The homebrew control electronics and positioning system may require an overhaul.

Guying hardware must be inspected and replaced where necessary. The tower came with a large quantity of turnbuckles, thimbles, guy grips, insulators and guy wire, mostly used but some new, in both ¼" and 5/16" sizes. I expect to discard most of the guy wire since its remaining service life is inadequate to my needs. The old guy wire that is in good condition may be used in other projects with less critical requirements.

From here on this is a winter project which I can temporarily set aside. I will now return to my fall antenna work. The 80 meter vertical is next on my schedule. CQ WW is fast approaching.

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