Tower Lift Failures - Are You Prepared?

First the good news. My new 140' tower is complete. At the time the adjacent photo was taken the only thing left to do was to tighten the top set of guys and realign the tower. There are no antennas on the tower at this point. A few of the yagis for the 15 and 20 meter stacks can be seen on the ground biding their time.

The reason I delayed completing the tower was to build the mast and rotation system which required keeping the top two sections on the ground. With that job completed the tower sections could be raised. More on that in a subsequent article.

Unfortunately the final lift was not without mishap. No matter how carefully you plan and execute an operation of this scale there is an ever-present possibility that something will go wrong. It is never routine.

Several of the hams who have generously given their time to this project have commented that I make these big jobs look easy. Of course they are not easy. It helps to have experience but that is no insurance policy. What experience does provide is a bag of tricks to avoid or recover from many of the things that can and do go wrong.

No one was injured and the toll on tools and equipment was minor. I enforce safety practices on site. By describing what happened and what may have precipitated the mishap I hope to instill a sense of respect in readers for towers big and small. Mistakes can be very costly.

Photo credit: all but two of the pictures in this article are courtesy of Alan VE3KAE who was assisting me that day.

Lift procedure

Like most hams I don't do tower lifts the way professionals do it. The cost of tools, equipment and manpower is too high and unjustified for a ham. For those without the ability to do the work it is worthwhile to hire those professionals. I won't say more about how they do these jobs.

Hauling 150 lb loads 150' vertically upward is not a job for a few muscular hams. A manual winch with a 4:1 or greater advantage isn't as easy as you might guess, and it takes a long time. Power is required. A vehicle or tractor comes in handy and I've used both over the years.

A pulley at the tower based turns the downward rope from the gin pole horizontal. Find a suitable attachment point (tow hook, trailer hitch, etc.), hook up securely and without risk to the vehicle and away you go. The biggest problem is that you have more power than needed. An automatic transmission with a hydraulic clutch helps modulate the power. A rope rather than steel cable provides elasticity that allows a safe and graceful recovery when the load inevitable snags a guy or other tower protrusion.

Failure

When the tower section was up about 90' the rope seized. The load would not move up or down. A brief inspection discovered that wheel on the bottom pulley had split in two. The rope was caught in between the broken halves and was partially severed.

No disaster at that point but not an easy problem to resolve. The axle kept the rope from popping out and dropping the load. Had it broken through the load would have dropped at least 40' and possibly hit a guy at the 65' level. Damage to the car was likely. Had the rope been severed the load would have gone into free fall, an even worse outcome.

Since the situation was stable I had a few minutes to consider the problem. We took care to stand to one side of the tower while doing this. Had the rope or axle broken we would have had time to jump away from ground zero. Hard hats and steel toe boots are no match for a free falling load.

Unfortunately there is no picture of the seized and broken pulley since we were fully occupied dealing with it. The picture shows the split wheel and axle after being extracted from the pulley during the recovery procedure.

Recovery

As the saying goes: necessity is the mother of invention. The come-along (hand winch) and a bunch of old guy grips were at hand in preparation to pull in the top set of guys. While a poor fit the grip was wrapped on the top side of the rope, a thimble inserted and the the come-along hooked to the tower bottom.

Once the tension was transferred the load was safely suspended. The pulley was then broken apart and the rope freed.

A new and larger pulley was attached next to the old one on the same cable wrapped around the tower base. The rope was wrapped around the pulley wheel and the pulley was reassembled. Only then did we pause to have a close look at the rope cut.

No more than 25% of the rope fibres were severed. It still had ample capacity to support the load. The car was backed up to take up the tension and test this assessment. Had it broken through the come-along would have held the rope.

The rope was again inspected under load. We decided to continue the lift with the damaged rope and new pulley.

Completion

The lift was completed without incident. Before climbing up the come-along was reattached to the rope. This eliminated further risk from the damaged rope. My helper used the come-along to lower the tower section into place when I was in position.

The two pictures were taken at almost the same moment. Alan took the one on the left -- one of the rare pictures of me in this blog. You can see me retrieving or replacing my phone for the picture on the right.

Notice that the gin pole has taken some abuse during this problem plagued lift. It looks bad but all that happened is that the pole rotated and pivoted on the top pin so that it is no longer perfectly vertical. This has happened before and is not a risk. All that said it is safer for the rigger to be at the top before the lift, staying above the load rather than climbing below it. On that day the ideal wasn't attainable.

After clearing the tower top the load typically dangles on the far side of the gin pole, only occasionally drifting in the breeze to where you see it in the pictures. The tower has only one climbing face so I cannot climb another face as the load drifts. We monitor it in case something untoward occurs.

A few minutes after reaching the top the section was lowered and bolted in. The guys were then lifted and attached to the segments on the top section. Success at last. After a break we pulled the guys to the anchors and called it a day.

Aftermath

Equipment doesn't come with a best before date. Everything should be inspected before an operation. Had I looked closely at the pulley it's possible I'd have seen something. Often the damage isn't visible so you must rely on the quality of the hardware.

The pulleys have seen lengthy service: lifting 300' of tower; tramming yagis; and a variety of other heavy lifts. Each has passed many thousands of feet (or meters) of rope and cable. No equipment lasts forever, not even when the working load capacity is never exceeded. Since an identical pulley is on the gin pole I brought it down and inspected it. Unlike the broken one there is no evidence of stress. Despite that the pulley will no longer be used at critical locations for heavy loads.

The 100 meter long polypropylene twist rope is approaching end of life, and that's okay since I planned to discard it once the tower was up. There is UV damage (polypropylene is very sensitive to UV) and fraying. Considering what I paid for it I have no complaint. I'll can buy another reel of it or a better product.

I subsequently spoke to a local tower pro. He showed me the rope and pulleys they use. These are very expensive and look awesome. I found it interesting that they never use steel cable, only rope. I will hunt for suitable products at a better price point.

For critical lifts I will be more diligent about using keepers. These are loosely bound ropes or cables that "catch" lifting ropes should the hardware fail. For example, a keeper for the recent failure would be a cable around the tower pillar that passes on the outside of the pulley. Even if the rope comes completely free the load will not fall. Unfortunately the mechanism to recover from a severed rope is not so easy to implement. The answer to that is to use better rope.

As to why the pulley wheel failed I have a likely failure mode. These pulleys are made for rope. As the loaded rope passes over the wheel it compresses and spreads the load over a large cross section of the wheel surface. Steel doesn't behave this way. Since it is thinner (for the same capacity) the force is focused on a narrower area of the wheel.

Second, aircraft cables are hardened steel that abrade the wheel surface, thinning it and reducing its load capacity. Steel cable should not be used on rope pulleys or the pulleys should be discarded sooner and inspected before each use. In future I will try to avoid steel cable for lifts and tram lines. The former I haven't done for a long time anyway.

None of us is perfect. By dissecting this mishap I hope to provide a lesson to myself and to others. Learning by direct experience alone can be deadly. Be safe out there.

Low Band DXing: You Snooze, You Lose

Those who have been reading this blog lately will know that I've been very busy lately with tower and antenna work. That time mostly comes from that devoted to operating so that the rest of my life isn't impacted too much. However there are many DXpeditions this month that do entice me to make an occasional effort.

One of those DXpeditions was ZK3A Tokelau. Although I have ZK3 worked and confirmed I wanted to log it on the low bands where it is a new DXCC entity for me. After working ZK3A on CW and SSB on 40 and 80 meters there was just 160 meters left to be worked.

I did try one time early in the DXpedition when I was awake during a sunrise enhancement. They were very strong for perhaps 10 to 15 minutes. Despite having a good antenna and running a kilowatt I was not successful. Indeed few in this part of North America had success that morning since East Asia, especially Japan, had the better signals.

As the sun climbed above the horizon they faded into the noise. Not being a morning person I tried only once or twice more. Each time they were not on 160 meters. I didn't fret since I was happily busy with other things and the DXpedition was scheduled to last until October 11.

On the 8^th a friend called and told me how he'd worked them early that morning on 160. Rather than wait for sunrise he got up a little past 4 AM (0800Z), a time when it was daylight in Asia and most North Americans are asleep. The sun rises 30 minutes later in JA and the competition rapidly escalates. He planned it well and deserved the contact.

Our conversation motivated me to give it a try. A little after 4 AM the next night I got up and wandered in the shack. I turned on the rig and tuned around. About the only DX was a very weak T30GC making a few contacts with the west coast. There was no sign of ZK3A. In fact they were not spotted on any band.

Before giving up I checked one of the European DX news sites where the first item was that the DXpedition ended early. The boat arrived early for an unrelated medical evacuation so they tore the station down and jumped on board. I had missed my chance for good.

My friend commiserated with my bad luck by suggesting I'd have more opportunities in the future. But for him at his more advanced age, he explained, he might not have another shot at ZK3 on top band so he had to make the effort. It worked for him.

As the cliche goes: you snooze, you lose. Being a DXer isn't always comfortable not even when you have big antennas and power. The DX calls the shots, not you, and you must be flexible if you want to work them. I knew that yet I passed on the opportunity each night in favour of a good night's rest. Until next time.

Aluminum Yagi Construction: Materials and Methods

Be warned: after reading this article you'll probably abandon your home brew HF yagi project and buy a commercial product instead. I am not that sensible. I'll keep building them despite the difficult experience.

With that disclaimer out of way let's dive in. You will learn how I went about the physical construction of 5-element stacked yagis for 15 and 20 meters. The yagis are complete but not tuned. That's my next task. Then I have to raise them and put them to work. I am nowhere near done.

Perils of aluminum shopping

I envy Americans, at least when it comes to aluminum tubing. Despite Canada being among the biggest global producers of aluminum finding what a ham needs is challenging. On the positive side, aluminum tubes, pipes and other shapes are readily available and economical.

Nesting tubes for telescoping tapered elements requires close tolerance of inner and outer diameters. Milling and finishes affect the usability of tubes since the measured and published dimensions may not match or be consistent. The English dimensions used in the United States for tubes and pipes are most common in Canada due to the close trade relationship and despite this being a metric country. When it comes to yagis this fact is helpful. I have heard that telescoping available metric tube sizes can be difficult.

The 0.058" and 0.120" wall diameter high tensile alloy tubes in stepped ⅛" sizes work best for yagis. The former is unavailable here and the latter is uncommon. These tubes are classed as aerospace tubing and though widely available in the US must usually be imported from there. That can be costly since shipping can double the price. Shipping of longer tubes is especially expensive

To keep cost as low as possible I chose a taper schedule after discussions with local suppliers and after considering the tooling requirements to adapt tubes that were close to being suitable for telescoping. All my tubes are 6061-T6 alloy except for the 6063-T832 aerospace tubes I imported from the US. I did my own importing since in every case it was far cheaper than getting it via a local metal supplier.

I received an unwelcome lesson in the difference between mill and other aluminum finishes. More on that later. First I'll describe my taper schedule and construction techniques.

Element taper schedule

The longest half elements are the 20 meter reflector at 219.5" and 15 meter reflector at 143.4". Here are the half-element taper schedules. The centre 1" tube is twice the half-element length.

• 1" OD, 0.120" wall: 60" (20m); 30" (15m)
• ¾" OD, 0.125" wall: 60" (20m); 40" (15m)
• ⅝" OD, 0.058" wall: 36" (20m); 24" (15m)
• ½" OD, 0.065" wall: variable length element tips

All the local tubes were purchased in 20' lengths and cut to 10' lengths for transport in my vehicle. That explains the lengths of the 1" and ¾" tubes. The imported ⅝" tubes were purchased in 6' lengths to optimize shipping and cutting prices. Aerospace tubing comes in 12' lengths.

The approximately ⅛" wall for the inner segments increases the wind and ice survival. For those in the US, it may be more convenient to nest 0.058" tubes in adjacent ⅛" diameters. Ultimate survival was not calculated but interpolated from published designs. These yagis should survive this 135 kph wind zone with capacity to spare, even with modest icing.

The ¾" tube fits snugly in the 0.120" wall 1" tube with no friction at all. I consider this a lucky break since I expected 0.125" to be available yet the 0.120" was available and inexpensive. Since I bought so much they gave me a substantial discount.

The ¾" tubes were machined to fit a ⅝" tube at the outer end so it didn't really matter whether the wall was 0.120" or 0.125". More on that machining below. Fitting the ½" tips into the ⅝" tube with its 0.509" ID should have been easy but wasn't, as I discovered to my dismay.

In tandem with this major project I have also developed a taper schedule for 40 meter yagi elements that utilizes the same taper schedule for the outer halves of the elements. The inner halves will be substantially heftier. I'll leave this construction project for a future article until I've built one of these monsters.

Stepped diameter correction (SDC)

My EZNEC models for the yagis were updated with the final taper schedule for the elements. Using the built in SDC add-on for the NEC2 engine I adjusted the tip lengths to return the yagis to their original designed frequency ranges. This process retains the performance of the designs. For the lucky few with NEC4 although the SDC algorithm is superfluous it is still necessary to adjust the element lengths for the taper schedule.

You must scale the yagi elements since without the SDC for the final taper schedule the performance changes can be substantial. This was most evident when I scaled the 20 meter yagi. Surprisingly the 15 meter yagi, despite having the same taper schedule, required almost no change to the element lengths.

I found it helpful to scale the element in steps, starting with the inner tube section and working outward, checking yagi performance after each step. The changes at each step are not always in the same direction so that a later section change cancels the previous deviation. This is what happened when I scaled the 15 meter elements.

Drilling out thick wall tubes and pipes

The inner diameter of the ¾" tubes is ½". Although the thick wall means I didn't have to nest a ⅝" tube full length inside the outer end must be widened to fit a ⅝" tube. Alternatively a coupler could be used -- " on the outside or " on the inside -- both are troublesome due to needing to import ⅞" tube (0.058" wall) or finding thick wall or solid ½" inserts, respectively.

Reaming out the ¾" tubes to ⅝" must be done precisely. Ideally it is done on a metal lathe in a machine shop. They will do it but it can be costly since I have 40 half-elements to be machined in this manner. So I chose to do it myself.

My first attempt (left) did not go well. I simply put a ⅝" bit in my hand drill, lined it up by eye and had at it. The bit suffered a lot of chatter and even with frequent progress inspections the bit went off centre over the 3" depth of the cut. For my second attempt I first used a 9/16" bit then used the ⅝" bit. The tube wall is thicker, close to the ideal 1/16" since there was less chatter. Doing the cut in two stages help keep the hole almost perfectly centred.

I decided to keep going and do all 40 of them. It took some time. Each tube required at least 10 minutes of work. There were several that drifted off centre and had to be cut off and redone. The 2" to 3" shortening of these tubes has a negligible impact on the SDC. I learned a lot about drill rotation speeds for cutting aluminum and the dos and don'ts of lubricating aluminum. After an initial trial I discarded the lubrication and did the drilling dry, which went faster and with fewer mishaps.

Chuck driven reamers might have done a cleaner job but for the amount of material to be removed. It would have had to be done in more steps and at greater expense since I did not (yet) have any reamers.

I'd hate to do this job again but it did work out pretty well. That is, except for one difficulty which I did not entirely appreciate beforehand.

In the picture you can see the drilling jig and the two drill bits. The technique of screwing together two wood blocks to secure round tubes without crushing or marking them is one I learned a long time ago when I built a bicycle frame from very thin wall chrome-molybdenum steel tubes.

With a standard ¾" bit (not a wood bit) you make a hole as shown. Use a drill press to make it perfectly vertical. The halves are then unscrewed and a sander applied to one or both interior faces to reduce the diameter a tiny amount. Put the halves back together and lightly hold in a vise. Insert the tube and tighten the vise. The tube won't turn except under very high torque.

Pounding a round peg into a round hole

The problem in a nutshell: you can't fit a ⅝" tube into a ⅝" hole. Well you can, but just once since it won't come out after you've pounded it in. This is an example of a press fit and it is totally unsuitable for building yagis.

Even 0.001" makes a difference. My local machinist took one of my ¾" tubes and hand reamed the ⅝" opening to 0.626". The tube now fit though with some friction. After hearing his quote to do all 40 on the lathe I decided to order a reamer online and do it myself. I chose 0.627" to ensure the tubes could be pulled apart in the future.

I use the same ¾" jig to hold the tube. Since I don't have a handheld drill with a suitably large chuck I reamed the tubes manually. I used vice grips and protected the tool with a metal wrap. Unlike a fluted drill bit the reamer is very unlikely to wander off centre. Shaving 0.001" all around is doable by hand without only a little effort.

When the reaming was done the ⅝" tube slipped in easily and hand no discernible slop. Then I did the remaining 39. All this work did save on importing aerospace size tubing, however I might have chose otherwise if I'd thought through the troubles of reaming tubes.

The woes of mill finish

My reaming woes were not over! An unexpected and larger challenge lay ahead. The 200' (60 meters) of ½" tubes I purchases for element tips came with a mill finish just like all the other tubes locally sources. They did not fit into the ⅝" tubes. I was surprised since the 0.058" wall leaves an ID of 0.509", which should leave plenty of room.

Mill versus mirror finish

With a sample in hand I made another trip to the machinist. He put his precision calipers on it and found the diameter to be 0.508". However the diameter is not consistent. That's what you get with a mill finish.

He explained that this oversize diameter is quite common on small aluminum stock. Worse is that for a press fit of similar aluminum alloys a thin layer of material is pushed along the surfaces and can lock the tubes together. That is, once you press it in it won't come out again. I had already discovered this the hard way.

The aerospace tubing, the machinist explained, goes through a grinder that produces surfaces with precise tolerances and a mirror finish that the market demands. The consistent 0.009" gap allows easy nesting to any depth. But I had 200' of tubes I didn't want to waste so I took the reaming challenge.

This was a bigger problem that reaming the ¾" tubes since tips must be adjustable and that requires greater depth of insertion. I first ordered a 0.511" reamer reasoning that an additional 0.002" should be plenty. It wasn't. It was better than a press fit but not enough to allow the tubes to slip together without any binding.

My next step up was a 33/64" drill bit with a shank that would fit the chuck of my handheld drill. Reaming 0.509" to 0.5156" is difficult to do by hand so I chose to do it with power. I did experience binding of the bit inside the ⅝" tube when I rushed the job so I took it in easy steps, being sure to regularly allow the flutes to clear. It wasn't fun but finally it was done and the ½" tubes slipped in to 5" depth. In a pinch the tube can penetrate 7" since I went deeper with the 0.511" reamer.

To add insult to injury, after all the foregoing woe I ordered more of the ½" tubes for other yagi projects. It looked different: the finish was shinier and there was source and material lettering on the tubes, unusual with mill finish. After putting calipers on a sample and comparing with the previous order I grabbed a ⅝" tube and lined up the two. The new ½" tube slipped right through the ⅝" tube just as it should. I'm tempted to run back and pick up more in case they switch suppliers again. No reaming needed for this batch.

Joining tube sections

Apart from the element tips all tube joints are screwed together. This forms a reliable bond and because these joints are fixed there is no need to make them adjustable. Many commercial and home brew yagis use slotted tubes and hose clamps since they are easier to construct.

Each joint -- 1" to ¾" and ¾" to ⅝" -- uses two #8 stainless screws with a flat washer and nyloc. Two holes are drilled through at right angles, one near the edge and near the back of the 3" overlap.

I borrowed a trick from other yagi builders that achieves a superior mechanical and electrical connection. One side is drilled wide so that the screw head rests on the inner tube. When tightened the opposite sides of the tube are firmly pressed together. This is better than relying on screw torque to distort the outer tube so that it presses against the inner tube. With small screws and high tensile strength tubes it may be impossible to adequately distort the tube.

I made drilling guides out of PVC pipe with the hope of achieving enough consistency that tubes could be interchanged and the holes would be aligned. That didn't work out since that close a tolerance was too much trouble and not really necessary. I soon dispensed with them. However the tubes were clearly marked and stored in groups to avoid mismatches.

Because of the tight tolerances of tube diameters (see above) all holes were carefully deburred, inside and outside. All joints, including the screwed ones, were sanded to remove oxide and coated with an aluminum joint compound (I use Noalox, and there are many others on the market) for a good electrical connection and ease of sliding tubes together and, years in the future, sliding them apart.

As mentioned the tips are adjustable by putting two slots in the ⅝" tube and compressing with a stainless hose clamp. I took some care to cut the two slots straight and opposite to each other with two cuts with a hacksaw. The slots were cleaned with a triangular file and a short bevel placed at the bottom of the slot to reduce stress when compressed The twin slots are wide enough that when the hose clamp is tightened the ½" tips are firmly held.

Element to boom clamps

For 15 and 20 meter elements with 1" × 0.120" centre section the clamps don't have to be excessively large. Following the advice in W6NL's Physical Design of Yagis the plates are ¼ × 4" × 6" 6061-T6511. I cut the plates by hacksaw from a long length of the extruded alloy, thus saving cutting fees and getting a sore arm. High tensile strength aluminum isn't easy to cut.

Galvanized muffler clamps secure the plate to the boom. Each size of boom section, ranging from 2" to 3", has its own clamp size and bolt pattern. The galvanized u-bolts for the elements are the same. I could have used stainless hardware at more expense and order lead time, but it is not necessary. Electrical continuity is via aluminum to aluminum contact not through the hardware. Although there is no texture on the muffler clamps the torque from the element is modest even in a turbulent and strong wind so it shouldn't rotate on the boom.

Using the formulas in W6NL's book I calculated the effective diameter of the plate clamps -- 1.673" -- and inserted that into the EZNEC models. The SDC algorithm takes care of the rest. The boom under the clamp electrically shortens the element a small amount -- estimated ~6% of boom diameter by both W6NL and W2PV -- which is pretty well negligible when considered in combination with the effect of tower, guys, other antennas and hardware "bumps".

Gamma match

Originally I planned to use a beta match and acquired the fibreglass tubes needed to mechanically join split driven elements. Instead I am using gamma matches to reduce the mechanical complexity and to gain the gamma's modest ability to attenuate common mode on the coax shield. Beta and gamma matches are about the same amount of work to tune the impedance match and both require similar shortening of the driven element (capacitive reactance).

The prototype 20 meter gamma match is shown mounted on one of the 20 meter yagis. The gamma rod is ½" tube, making it half the diameter of the centre section of the driven element which is a typical (recommended) ratio.

The fixed spacer is PVC pipe mitered to the top 1" tube and secured with a tie wrap. The tie wrap will be replaced with a more durable clamp when the antenna is tuned. The gamma rod fits snugly through a hole in the pipe. The slider for impedance matching is a strip of 1/16" thick mild aluminum alloy.

There is as yet not coax connector or pigtail to terminate the transmission line. For tuning a variable capacitor will be mounted. After tuning it will be replaced with a hardier capacitor of the same value, either a high-Q, high voltage fixed capacitor or (more likely) a length of RG213 (with covering and braid removed) slid into the gamma rod. The latter method is popular since the gamma rod can be slid to adjust the capacitance. However it is not so convenient for initial coarse tuning.

The ends of the slider were manually wrapped around tubes to create the required shape. The wrap is stopped at approximately 330°, the end bent and the bolt holes drilled. When tightened the grip is very good. A conductive grease is recommended on the interior clamping surfaces.

A difficulty was encountered while forming the gamma rod end. I could put the bend in the right place at the beginning of the process but found it difficult to prevent the long straight section from creeping along the form during the last half of the forming. As a result a couple of the shorting straps are ¼" short. After recalculating the gamma match with the reduced values my concern was assuaged. The gamma capacitance value barely changed and the short position goes outboard no further than another inch.

Booms

The four booms were constructed from a mix of pipe and tube. I tried to find a balance between weight, wind load and cost. Most of my pipe is surplus and inexpensive. When I can't get what I want I either modify the boom design to use what I have or I buy new material as needed. Large tubes and pipes are readily available new and are not too expensive.

The side mount yagis use the largest diameter tubes. Their relatively thin wall makes them unsuitable for rotation at great height. These were built last year and stored until I was ready for them.

The rotatable yagi booms are heavier, narrower and have a modest wind area. They are a mix of surplus pipe and new tubes. The 20 meter rotatable boom is the heaviest with a centre section that is 2-½" schedule 40 pipe (2.875" OD). I made liberal use of my relative strength spreadsheet to contrast and compare alternatives.

Some choices were made based on good fit between various sized tubes and pipes. In one case I had couplers machined but those didn't work out and have been put aside for a future project. I am not bothering to describe details of the booms since my choices are unique to my circumstances.

Waste

Machining, drilling and cutting the elements, booms and clamps produces a lot of aluminum waste. Constant cleaning of the tools and work surfaces was necessary to avoid mishaps.

No matter how well I cleaned up each day aluminum shards appeared everywhere throughout the workshop, on my clothes and hair and in the house. The latter occurred despite cleaning of clothes and boots. The stuff is insidious.

Regrettably there isn't enough metal weight to make recycling worthwhile. However it does occupy a large volume since the shards, especially the strings and spirals spun off drill bit, pack loosely. It'll all be thrown out.

Of greater concern is steel waste since it is darker and therefore more difficult to see. That matters since it is far more likely to cause cuts and slivers than the softer aluminum. Fortunately there is less steel waste, the bulk of it from fabricating the rotation and support system for the mast and yagis.

Putting it all together

Here we have the first of the assembled yagis: the side mount yagis for 15 (left) and 20 meters. The gamma matches are not yet ready. That and initial tuning is coming up. It isn't a trivial task since the feed points are far out on the boom. Access to the feed point is required for every tweak to the gamma match. More on this later.

Element positions were previously marked on the boom. I attached the element clamps then the elements, tightened everything and sighted along the boom to align the elements. To do this properly the boom must be lifted above the ground. That will be enough height to clear the fragile gamma match. I use old cable reels for supports, in this case from 500' spools of EHS guy strand.

Was it worth it?

That's a very good question. For myself the answer is yes despite all the difficulties. It was a superb learning experience and, aside from the time invested, economical in comparison to commercial products. There is also a sense of accomplishment overcoming the challenges of design and fabrication.

Of course the project is not complete. After the tuning the yagis must be raised and fed for stacking. The switching system for choosing lower, upper and both for the 15 meter and 20 meter stacks will be a commercial product. Little money will be saved building my own and it will look and work better. There is no shame in buying some products even for a devout home brewer.

As I finish this article friends are scheduled to come over to assist me with tuning the yagis. Three are built and the fourth (20 meters) is awaiting completion of the boom. I'll have more to say once the next stage is completed. For the present I am relieved to have all this aluminum out of my garage workshop so that I can move around and access things that have been out of reach for weeks.

Cutting Pipe Square

I cut a lot of pipes and tubes building towers and antennas. Most of the time I do rough cuts with a hacksaw or cutoff saw since the angle of the cut is not critical. It may look ugly but once it's up in the air no one will know.

For small diameter thin wall tubes I use a pipe cutter which is quick and makes a square cut. Except that a pipe cutter does not cut cleanly since rather than removing material it pushes it to either side forming a ridge, inside and outside, and the cut itself has a bevel. These must be filed off. The squareness of the cut can be distorted if the file is not kept level.

A hacksaw cuts more cleanly. However to make the cut square it requires a miter stand or the tracing of a reference line when cut free hand. Better is to use a metal band saw. Since my cutting needs are modest I have not invested in a band saw for my workshop. Instead I use a variety of manual cutting methods.

For large diameter pipe, steel or aluminum, the challenge of cutting the pipe square is multiplied. Manual pipe cutters of such a large size are rare and expensive. Even if available they require a lot of muscle. A hacksaw can be used if a square cut can be traced beforehand on the surface.

This is not difficult if the pipe has a known square end to use as a reference. Surplus pipe often does not have even one square face. A different technique is therefore required. I did this recently when I required a square cut on a 3.5" diameter aluminum pipe. I took a few pictures to show how it's done.

Draw a circumference

It's quite easy to scribe a circle around a pipe. You start at point A, travel orthogonal to the axis and come back to point A. But without a guide the line will almost invariably be a ellipse and not a circle. That is, it won't be square and the cut will be at an angle.

We need a straight edge that wraps around the pipe and does not crinkle, warp or that can lie askew. Guides I've tried and rejected include: tape, hose clamps, another bigger pipe, steel and fabric tape measures and drawing a line with a fixed marker while the pipe rotates. They fail because they are not rigid, rigid but not when stressed, a better but less than accurate edge or mechanical instability while drawing.

After considering the problem I found what is perhaps the most unlikely solution and one that covers half the space of my office desk: paper. Although it is easy to crumple and warp it is also easy to have it sit flat when wrapped around the pipe with a bit of tape and care taken to avoid "bubbles". The paper edges are a great straight edge when supported on a rigid surface such as a pipe. Paper is flexible with dimensional rigidity and is superior to straight wraps such as hose clamps because the sheet is wide: if it has a warp it will be immediately visible and can be corrected.

The pipe in the picture is 3.5" OD so an 11" paper edge (standard North American sheet height) almost exactly makes a circumference -- 3.5 × π = 10.9956. In this case the sheet is a little short since it doesn't quite reach around the pipe.

Masking tape on the pipe makes it easy to trace a fine line. The line doesn't have to be perfect provided there are no paper tears. If the pen or pencil wanders just fill in the gap and continue.

Making the cut

Starting the cut is the most crucial step.

Lie the pipe flat on a stand where it can't roll but can be easily turned by hand. I use an ancient Workmate (40 years old!).

With your gloved hand (for protection) precisely guide the blade along the drawn line. Cut with light pressure, taking care to keep the blade from wandering. Correct any deviation immediately.

Rotate the pipe a bit and continue. When you've gone around once you have a shallow cut that will help keep the blade on the line. The tape will tear or be marked if the blade jumps as you cut, warning you to correct the mistake. This is most likely while the cut is shallow.

Continue cutting while rotating the pipe a little every few seconds. As the cut goes deeper you can use two hands on the hacksaw if the stand opening is wide enough that the blade's force doesn't rock the pipe.

As you go deeper take care to align the blade so that it doesn't lean to one side. Many hacksaws, such as the one shown, seat the blade at a small angle for improved work visibility and to counter a natural inclination to lean the hacksaw towards the dominant hand. A straight cut means less filing to remove a bevel and less chance of warping the pipe edge from excessive filing.

Eventually the blade will penetrate the wall of the pipe. Avoid the temptation to speed up and not rotate the pipe. Keep rotating the pipe and the cut will be cleaner.

Finishing

After completing the cut there is some filing to be done. Use a flat file across the full diameter of the pipe rather than filing one wall. This will keep the file flat and maintain the levelness of the surface. Burrs on the outside can be removed with the flat file and a half round file used on the inside.

The finished pipe stands perfectly vertical when on a level surface. When fit to the finished work the squareness of the cut was confirmed.

The use of this cut pipe will be described in a future article after I complete the new 140' tower. It forms part of the rotation system for the top mast. All the mechanical work to the top two sections is being done on the ground before being hoisted up.

One Step Forward

My one step back a few weeks ago continued to the point where I had just one HF antenna: the 80 meter vertical. This kept me off the air and focussed on rebuilding. The removal of almost every antenna was necessary to move and repair antennas in preparation for the next configuration of my antenna farm. It has been a very busy time.

With the help of friends I am again active on all bands from 80 through 10 meters. Until more antennas go up my flexibility is limited, so I cannot call this progress. That explains the title of the article. Over the next month there should be enough progress that I can truly claim that I have taken one step back and then two step forward.

For now it's just one step forward in which the station is different but at similar capability to what it was a month ago. In this article I'll run through the progress so far.

TH7: high tri-band yagi

I will have little to show for 10 meter antennas when this year's work is done. That is acceptable for the next year since signs of life on that band will remain elusive for at least that long. With a large tri-bander up at 43 meters this will give me flexibility during contests to target, say, South America at the same time as Asia on 20 meters. I am assuming my new 20 meter and 15 meter stacks on the new tower will be ready and I am working hard to make it so.

I really like this picture. The Hy-Gain TH7 dangles at the bottom of the tram line fully rigged and ready to be hauled over the hay field to the top of the big tower. Posing with the antenna is my trusty ground crew (left to right) John VE3NJ, Don VE3DQN and new ham Alan VE3KAE.

Notice how the antenna is well balanced so that the boom is level and the elements point straight ahead. This is the correct orientation to clear the guys and not strike the tower or mast. Those element tips are fragile. Two people lifted the boom as the tram line was pulled tight to prevent the elements from catching on the ground. Two people manually operated the haul rope during the lift. Power makes the job easier but increases risk of damage when the the antenna strikes an obstacle.

Many hams attach yagis to tram lines with custom made rigs that guarantee good orientation. I do it old style with ropes. With practice ropes work very well and allow for rapid removal and easy packing at the top of the tower, an important consideration. In this instance it worked beautifully as the close spaced driven elements of the TH7 slid right around the tower and mast.

One mistake I made was to point the antenna backwards. Although this is easy to correct by calibrating the prop pitch rotator controller the direction I dressed the cables and rotation loops is not compatible with a north centred rotation, which is the preferred method in this part of the world. I avoided rotation until it was fixed a few days later.

The TH7 was retuned to resonate lower in the band. SWR is a little higher than ideal at the low ends of 15 and 10 meter. but better than it was before. The boom is attached to the 3" mast using the same modification I used for the TH6. I shortened the DX Engineering saddle clamp on the top side to avoid it contacting the phasing line between the driven elements.

Other tri-band yagis

The reason the TH7 is up there and not the TH6 is because the close spacing of the driven elements does not easily permit tower side mounting. The TH6 is better for this. It was trammed to 75' and pointed roughly south to permit working Caribbean and Central American multipliers and the southern US, all of which are present during opening to Europe on the high bands. It uses the same side mount bracket as used previously for the Explorer 14.

The Explorer 14 is now gone to its new home where it will soon bring home the DX to its new owner. Although a small antenna it did well for me during the past several years.

The TH6 was inspected after removal from the tower. A couple of defects were discovered which I assume these were responsible for problems that began last winter. The worst was the poor design of the driven element clamps that connect wires to the balun and beta match line.

The tabs on the aluminum wraparound clamp bend when the bolt is tightened. There is no provision in the TH6 to prevent this so the wire studs don't sit flush against the tabs: they wobble. My antenna was particularly bad due to its great age.

I added two backing nuts to allow fine adjustment of the clamp pressure and squarely bond stud and tab. The TH7 is better than the TH6 in that it has one backing nut, but still not the two I used. The studs were weatherproofed after taking the picture since the tinning has deteriorated. The hardware is stainless.

I took the opportunity to move the yagi's optimum performance higher on each band. Previously it was set for CW so the SWR was poor at the upper ends of the SSB band segments. Not wanting to lose CW performance I opted to shift it slightly higher, just below the settings for "Lo Phone". Because there is only so much bandwidth possible with a tri-band trap yagi some compromise is necessary. Eventually the TH7 will be converted to a TH6 so the two can be stacked for added performance. The conversion is necessary to achieve a similar impedance and therefore good power division.

I made a mistake with the tram which at least doubled the time to raise it to its new home. The upper tram anchor and haul rope pulley were too close to the mounting position. Manoeuvering a big yagi in a stiff breeze with ropes getting in the way and pulling the antenna out of my hands was too much. We lowered the antenna and redid it properly. Expedience costs rather than saves time.

XM240 40 meter yagi

This small 40 meter 2-element yagi has been returned to its original location on top of the Trylon tower at a height of 21 meters. The lift went pretty well considering the necessity of dropping several above grade cable runs and navigating the long elements around the trees that have grown over the previous two summers.

A few modifications were made to improve the antenna. The previous owner modified the antenna to make it more robust in extreme weather. He did a fine job of it but he should have chosen better hardware when he replaced the Cushcraft element-to-boom clamps. The cheap galvanized muffler clamps do not have enough grip to prevent the elements from rotating.

I inserted galvanized mesh under the clamps to provide mechanical texture to improves the grip. While not ideal I could not simply use better clamps such as the flattened and textured DX Engineering Cycle 24 clamp since there is no reliable sizing of muffler clamps and I'd have to drill more holes in the aluminum channel. Too many holes risks weakening it. Time will tell how this improvisation deals with the wind.

The other improvement was to ground the reflector element to the boom. This is a popular mod to reduce precipitation static by providing a path to ground for the static charge. Performance is not affected. Precipitation static was a serious problem at 150'. We've had one rainfall since the antenna went back up and...there was precipitation static, though not as bad as in the past. I'll continue to monitor.

I adjusted the rigging to ease attachment to the mast. Ideally two on the tower eases installation of this unwieldy yagi but I made do on my own by adjust the rigging and the procedure. The lift was done the same day as the TH7 with the same ground crew. I spent two days beforehand to prepare the antennas and rigging on both towers to best utilize the time of my friends.

In the picture I am in the process of attaching the mast clamps. There are a few interesting features of the rigging that are worth mentioning:

• I attached the boom truss to the lift rope. This kept it out of the way during the lift, made it easy to slip onto the mast and by keeping it in one piece there is no risk of one end slipping out of reach while it is being assembled on the tower.
• Long ropes are looped over each side of the boom. These tag lines allow fine control of antenna orientation in tight spaces. When done pull one end of the rope and it falls to the ground.
• Precise positioning of the mast clamp needed to insert the clamps for an antenna this size is no easy task for one person. I used a couple of cargo straps as a third hand. I previously slipped all 4 clamps onto the mast and raised them one by one, top to bottom, for attachment. The rigging must keep the plate flush to the mast since there is nothing on the boom to grab onto to rotate it.

There are a few reasons for placing the XM240 at this new location. First, I need a directional yagi at intermediate height for contest work. Although side mounting it on the big tower is possible I do not have time this year to build a side mount suitable for almost full 360° rotation. Second, the Trylon is close to the house and there are many weak noise sources that are audible on 20 meters and above where the atmospheric noise level is low. This is not a problem on 40 meters. For long paths I have another plan for this autumn: a full size rotatable dipole above the TH7 on the big tower.

80 meter inverted vee

The 40/80 meter inverted vee that was on the Trylon is headed to its new (old) home on the 150' tower. However the 40 meter element of the fan dipole has been removed so that it's solely for 80 meters. It is no longer needed on 40 meters and it used to twist and tangle in the wind which would make it unusable on 40.

The tower mount has been improved from an ABS pipe to a steel angle bracket. The new bracket is far stronger and will take more tension. It is also a better mount for the balun (common mode choke). Strain relief for the wire legs keep stress away from the balun studs.

Modelling tells me the best pattern for short paths and low directivity is at a height at or a little above 30 meters. This will  also keep it well away from the other antennas on the tower. Unlike its original installation the two legs will go down into the tree line on the north end of the hay field, avoid ground anchors in the hay field. The model shows almost no effect on the pattern by doing this.

It should be a good antenna for the QSO rich northeast, mid-west and south-central US. After sunrise and before sunset a horizontal antenna often works better than a vertical on 80 meters on both short and DX paths. Unfortunately it's resonant frequency is ~3700 kHz, ideal for neither CW nor SSB. If widening the legs of the vee more doesn't help I'll lengthen it to lower the SWR below 2 within the range of 3500 to 3600 kHz. My primary use for the antenna is CW contests and DXing.

One step forward

Other antennas

With the bulk of the tramming on the 150' tower is done I deployed the radials for the 160 meter antenna and connected the over-ground coax. I kept the field free of trip hazards for the safety of the crew. The match is different each year I deploy this antenna. This year it resonated at 1800 kHz so I adjusted it to resonate at 1825 kHz. I believe the variability is due to the distance from the antenna from guy wires and the directions the radials run, neither of which are identical each year.

Work on the 80 meter vertical yagi is delayed. Since this antenna can be done by myself on the ground in the cold weather it is low priority. It's just a little frustrating that this project is taking two years to reach fruition. However I budget the time and energy I devote to amateur radio so that it doesn't become a burden. On the positive side it really is almost complete.

The last stage of aluminum work on the 20 and 15 meter long boom yagis is done. I have only to cut and insert the element tips, mount them on the boom, build gamma matches and raise them for tuning. October will be a busy month.

The mast bearing plates for the new 140' tower were assembled and declared unfit for use. I made an error in the template that requires modification in my workshop. This is a temporary obstacle. I expect to raise the top sections of the tower along with the mast and prop pitch motor by mid October.

When everything is completed I will be ready for the winter contest and DX season. Next year will be less busy with only a few large projects. More on those in the coming months. Right now I remain focussed on antenna building and becoming reacquainted with the HF bands since I did little over the summer other than 6 meter DXing.

Relative Strength

Any ham with a tower or who has home brewed yagis will know there are a variety of software tools available to help with mechanical design. There are mast stress calculators to determine wind and ice survival of various grades and sizes of steel masts. Other calculators will determine stress on yagi booms and elements with attention to wind and ice loads. For the experts there are FEA (finite element analysis) engineering packages that handle most complex structures such as towers, both guyed and free standing.

Most of these tools are not used when buying commercial products. Instead we rely on manufacturer specifications and recommendations. Unfortunately some knowledge of various standards may be required since many advertisements attempt to place products in the best light and therefore choose to highlight specifications that may mislead even when accurate. Buying is not always worry free.

Guessing, optimism and hope abound among hams, including myself. I often calculate but other times times I rely on extrapolation from known designs and existing installations. If done carefully it can produce good results.

This is not an article about all those software and web tools for doing the heavy lifting for those mechanical calculations. Instead I want to discuss how I resolved a common question I deal with all the time when doing these calculations:

What happens when I change X?

X is a variable regarding a pipe or tube choice that may include but not limited to:

• Strength: bending, axial or other load limit
• Weight
• Wind load
• Cost

All have a bearing on the choice of boom, mast and yagi element structural members. It is helpful to play the game of What if? to see if the change is helpful or deleterious with respect to those criteria. Sometimes I choose pipes based on what best fits!

The relationship among those values can be complicated since, for example, reducing pipe diameter reduces strength and weight but also reduces wind load and cost. Trying alternatives can be enlightening, just like when using antenna models or electrical circuit simulators. Going by intuition and guesswork is faster but unwise. Using the engineering models spits out results but it is left up to the user to numerically compare among multiple scenarios.

As a design aid I use spreadsheets for calculations that may be inconvenient to do in other ways. Examples include: coils size, Q, wire length and inductance; transmission line impedance for wire diameter and spacing; wire coordinates under rotations for use in antenna models; and much more.

I wrote one for pipes, to calculate the parameters listed above. It compares two pipes to facilitate review and assessment. It makes it easy to discover the trend of pipe strength as diameter and wall thickness are varied. Wind force and pipe weight can change to a surprising degree. It's all excellent data to have in hand.

The first example compares two aluminum tubes of different diameter and the same wall thickness. Notice the better than 60% strength increase for a tube only 25% larger. Since the wind load increases in proportion to diameter the wind speed and ice survival is superior. Cost of large pipes and tubes is approximately in proportion to weight so this, too, is reasonable at 27%.

Notice that the spreadsheet doesn't calculate the actual strength of each pipe or the force for a specific wind speed and ice coating. There are ample tools available to do those calculations and I use them. This spreadsheet is a supplement not a replacement or consolidation. The spreadsheet assumes both pipes are the same alloy with identical strengths.

The spreadsheet works in English units since the large majority of pipes and tubes used in Canada are sized in these units despite this being a metric country. Industry inertia is strong, as is trade with the US. It would not be difficult to convert the spreadsheet to metric. The spreadsheet was calibrated using trade data for steel and aluminum pipe and tubes. Differences among alloys and tempers are negligible and are ignored.

The second example compares nominal 2-½" steel pipes, one schedule 40 and the other schedule 80. The heavier pipe is 26% stronger but weighs 32% more. This is poor economy. However on plus side the wind area is identical so the additional strength comes with no wind load penalty.

These first two examples illustrate the well-known rule that for a similar quantity of material (cross section or weight) it is better to increase diameter than wall thickness.

The final example compares a 2" schedule 80 aluminum pipe to a larger diameter 2-½" schedule 40 pipe. Again the thinner wall pipe of larger diameter is the better choice. Strength is 45% better for an increase of 21% is wind load and 15% in weight and approximate cost.

I don't always use the optimum pipe or tube, choosing to use what I have available or can acquire at a good price. The spreadsheet helps me understand the implications, in particular where I run the risk of poor economy. Ideally I should include alloy and temper in the spreadsheet to broaden the range of experimentation. Perhaps I will do so eventually.

Although I have not included the specific formulas used in the spreadsheet they are straight-forward to derive or look up. I extracted the strength calculation from a public domain beam spreadsheet. Surface area is simply length multiplied by diameter, after which you must apply the widely available wind load calculation for long cylinders. Circular cross section is the area of the outer diameter less the area of the inner diameter. Multiplying that by a constant gives the weight.

One Step Back

Progress is not continuously upward. There can be setbacks and there can be planned retreats. At my station the latter is the case. I am taking one step back as a prelude to major progress

Before I can reconfigure the station and raise new antennas it was necessary to remove all the HF yagis from the towers. With the help of friends this stage is now complete. Unfortunately that temporarily leaves me with only 3 antennas: 80 meter vertical, 40/80 meter inverted vee and 6 meter yagi. That's it.

Since the next few weeks are not filled with major contests and rare DXpeditions, or sunspots, I don't expect to suffer too much. With low band activity just beginning to stir from the summer lull I have little incentive to turn on the rig. This leaves me to concentrate on tower and antenna work.

The TH6 and XM240 which just came down from the 150' tower are lying in the hay field. The tri-bander requires service since there is an intermittent, most likely located in a trap in the 10/20 meter director. The XM240 will undergo a few modifications but is otherwise working. I had suspected an intermittent connection this winter that instead is due to a relay in the 2×8 antenna switch and a loose N connector.

With the help of friends antenna removal using the tram line went pretty well due to two innovations: radio communications and anchoring the tram line on a large tree. All were overjoyed not to have to shout, whether from the ground or on the tower. Rigging the tram line on the top side is more fraught than lifting yagis due to the difficulty of testing and correcting the rigging.

Every job on the tower requires more effort than on the ground. With advance planning I managed to complete this job with just two climbs: one to prep the antennas and rigging and one to do the job and clean up. Even so my combined time on the tower was approximately 5 hours.

The XM240 was improperly rigged which caused the capacity hats to tangle the top guys. I had the guys haul the antenna back up so that I could correct my mistake. Better that than losing those fragile aluminum rods. Time lost was no more than 30 minutes and was well worth it.

At the bottom of the tram line I hacked a short distance into the bush and attached a winch to a large tree. I took the above picture after the winch was taken off the board but you get the idea. The long outrigger prevents the winch from being twisted by the steel cable which can rapidly devolve into a dangerous situation.

The rope you see is a safety line to prevent the tram line from collapsing if the winch fails or is mishandled. It is tied to a thimble on the bottom end of the tram cable. The winch cable is attached with a shackle.

With a bit of luck the TH6 and XM240 will be back in the air within a couple of weeks. I am half convinced to convert the TH7 into a TH6 so that these tri-banders can be stacked. A similar impedance curve is required for equal power division.

After trying a couple of different element tuning schemes for the TH7 I've concluded that the TH6 is better suited to my needs. Conversion involves removal of one driven element and the phasing harness, changing the length of the beta match stud, shifting a few elements along the boom and adjusting element tip lengths. It's pretty straight-forward.

For now either the TH6 and TH7 (or 6!) will go on top of the 150' tower for the winter season. The other will be side mounted at around 75' and fixed to the US south. That should cover all the short path openings to the US 4, 5 and 8 districts, and some of 7, 9 and 0. Eventually the TH6 stack will be rotatable between 150° and 270° for increased utility.

Now that I've taken a step backward it's time to take two forward. Apart from efforts to get these antennas refreshed and back up the towers I am now focussed on completing the 20 and 15 meter stacks this fall. That's a bigger challenge than taking down antennas. With a sprinkle of good fortune I'll soon have directional and multiple antennas on 80 through 10 meters.

Weighing Yagis

As I get closer to raising the stacks of 15 and 20 meters yagis onto the new tower I am increasingly sensitive to the mechanical challenges. Not only are they large size they weigh a lot. That is a primary consideration in the decision of how to accomplish the lift. Since I am far enough along in construction to weigh the antennas, albeit as a collection of pieces, I have done so.

Not surprisingly the booms comprise approximately half the weight of each yagi, more for the 20 meter yagis than for 15. The longer booms for the 20 meter yagis (12 meters or 40') and the heavier elements need to be stronger than the shorter 15 meter yagis (9.5 meters or 32'). Similarly the rotatable yagis at the top of the tower need to be stronger than the lower fixed yagis. The elements and element-to-boom clamps for each band are identical for both yagis.

Their measured weights are as follows:

• 20 meter side mount yagi: 36 lb (16.5 kg)
• 20 meter rotatable yagi: 60 lb (27 kg)
• 15 meter side mount yagi: 25 lb (11.5 kg)
• 15 meter rotatable yagi: 45 lb (20.5 kg)

I weighed them by subtracting my weight from the combined weight of me holding the boom. It is important to provide a solid and level support for the scale to achieve reliable accuracy. I took at least two measurements to eliminate method errors.

It is no accident that the booms for the side mount yagis are lighter. They are lower and thus subject to less wind stress, a concern since they have a larger surface area. In this case larger diameter does not mean stronger because for most of their lengths the wall thickness is less.

Next up were the elements, which I weighed in the same manner. There is some uncertainty in these quantities because of their low weight. Element-to-boom clamps are included in the weights.

• 20 meters: 8 lb (3.5 kg)
• 15 meters: 5.5 lb (2.5 kg)

The ratio is about what you'd expect for the wavelength ratio. Tube sizes are the same, following the same taper schedule, with shorter lengths of each on 15 meters. They taper from 1" down to ½". I'll have more to say about the element design and construction in a future article.

Putting it all together I can estimate the total weight of each yagi:

• 20 meter side mount yagi: 115 lb (52 kg)
• 20 meter rotatable yagi: 80 lb (36 kg)
• 15 meter side mount yagi: 58 lb (26 kg)
• 15 meter rotatable yagi: 85 lb (38 kg)

The weights include an allowance for gamma matches, boom trusses and boom-to-mast clamps which are not complete. The side mount yagis do not include boom-to-mast clamps since tower brackets are separately lifted and installed.

Lifting options

Antenna weight is the major consideration for choosing a lift method. Both side mount yagis are light enough to be trammed using my existing hardware. The 15 meter yagi is moderately heavy and the 20 meter yagi, although very heavy, is being lifted only halfway up the tower (20 meters high). The rotatable yagis are another matter. At 85 lb the 15 meter yagi is close to the limit I'd want to lift to 140' (43 meters) with my existing tram, and the 20 meter yagi is substantially heavier.

My choices are to make a stronger tram or to lift the antennas in pieces and assemble them on top of the tower. The latter is not as daunting as it sounds. It's a method used by many hams. I have the mechanics of the process thought through since when I eventually build my full size 40 meter yagi it will be lifted in this fashion. That antenna design is not yet complete but I have enough of the components to estimate a weight in excess of 200 lb (90 kg). A crane can do the job but at substantial expense.

Wind load and yagi survival

I have not done detailed engineering calculations to determine wind and ice survivability of these yagis. Instead I interpolated boom and element strength from documented designs to achieve my strength objectives. The only calculation I did was to estimate boom strength using software for simple beams with a load on the extremity.

The lighter side mount yagis have the greatest wind load due to being 3" diameter end-to-end. The booms of the rotatable yagis are lower diameter but with thicker wall to compensate. In general there is a greater strength benefit from increasing tube diameter than increasing wall thickness. However, the strength is not only adequate the lower surface area reduces the wind force and ice load.

Projected cylindrical surface areas for the yagis are as follows:

• 20 meter side mount yagi: 10 ft²
• 20 meter rotatable yagi: 8 ft²
• 15 meter side mount yagi: 8 ft²
• 15 meter rotatable yagi: 6 ft²

The elements are identical for side mount and rotatable yagis. Their wind surface areas are estimated as follows, representing an average since each element has a different ½" tip length.

• 20 meters: 2.0 ft²
• 15 meters: 1.25 ft²

Multiplying by 5 (each antenna has 5 elements) we get 10 ft² and 6.25 ft² for 20 meters and 15 meters, respectively.

Maximum wind load occurs when either the boom or elements are orthogonal to the wind direction, with a smooth and shallow dip between those extremes. Obviously the side mount yagis have to contend with whatever weather occurs while the rotatable yagis can be rotated to lessen the impact. Boom and element strengths must also be considered but I don't have those calculations yet.

I live in a 135 kph (85 mph) wind zone. Over the decades I've lived in this region the strongest wind I can recall peaked at 120 to 130 kph. At 85 mph the wind force on a long cylinder is approximately 20 lb per ft². Therefore the booms must withstand from 120 lb to 200 lb wind force (shortest and thinnest to longest and fattest) plus gusts and turbulence. Each element must similarly withstand 25 lb or 40 lb wind force, which sums to 125 lb or 200 lb per 15 meter and 20 meter yagi, respectively.

The booms carry the force from the elements and the sum appears at the mast and tower. For the side mount yagis these forces are well within the capability of my tower. The only significant concern is the rotatable 15 meter yagi mounted 3 meters above the tower on the mast. For my selected mast (diameter, wall thickness and tensile strength) initial calculations are favourable.

However you can never say never. Although I intend to pin down the survivability calculations that won't delay the project. It is more important that the yagis go up this fall.

Moving forward

With this data in hand I can confidently move forward with my plans to lift the antennas. The rotatable antennas will be turned with a prop pitch motor which is more than adequate to handle these behemoths. Tower plates for the motor and bearings are currently being machined in my workshop.

One difficulty is tuning the antennas. With the driven elements so far from the mast and tower that job could be more difficult than the lift alone. Tuning will require multiple lifts to a low height or a mechanism to rotate the antenna, without tangling guys, to repeatedly access the feed point. This, too, is being planned.

Big yagis look impressive up in the air but getting to that point is a lot of work! I still think it's worth the effort. That puts me in a small minority of hams, even among committed contesters.