Saturday, December 24, 2016

Overhauling a Hy-gain Tailtwister Rotator

Earlier this year I purchased a Hy-gain Tailtwister rotator (or T2X for short) as part of a package from a local ham who was disposing of some equipment. Although I was not actually shopping for this rotator I didn't hesitate to take it since I knew with my upcoming move that it would surely find a use.

This rotator has its good and bad points, and hams certainly have opinions! However, like any piece of equipment it is important to understand its capabilities and limitations and only use it accordingly. It won't survive when tasked with turning the largest HF yagis and large stacks, but it is certainly good for mid-size arrays.

In this article I'll point out only some of the points of the overhaul process that I believe are worth describing. There are many other descriptions of the full overhaul process out there, and even some videos, so there is no need for me to do it.

Signs of trouble

I purchased the rotator fully aware that it needed an overhaul. It was poorly stored, possibly sitting outside on the ground for a while, and it showed on the outside. Since the terminal strip was badly rusted I replaced the 8 terminal screws and scraped off some of the corrosion. When I first connected the cable and turned it on it did turn, although grudgingly. Clearly the bearings were not in good shape. Since I was terribly busy with the pending move I put the rotator aside until later.

That time is now since I intend it for the Trylon tower where it will turn a couple of mid-size yagis. One evening during the early stages of tower construction I opened the rotator and was presented with a real mess.


All the balls on the bottom bearing were badly rusted. This bearing is effectively the weather seal in the gap between the rotating and static parts of the rotator. There were even signs of rust on the upper bearings. I tossed the lot of them and the ring gear into a vat of solvent. I let them soak for a couple of hours, with periodic agitation, while I cleaned the lower half of the rotator's innards. The upper half of the rotator (above the top bearing) was surprisingly clean and needed little attention.

When I pulled the parts from the solvent bath I was able to separate the balls from the plastic retainers without damaging the retainers to which the balls had been firmly attached. Vigourous brushing of the retainers removed the rust particles and dirty grease that remained. The balls of the lower race were barely recognizable as ball bearings: they were not at all spherical, plus they were completely rusted and deeply pitted.

Most of the balls in the upper bearings passed inspection. A ball that showed the smallest evidence of pitting or rust was discarded. Balls are cheap so don't develop an emotional attachment to these bits of metal. Otherwise you'll pay a higher price, later.

Inspection: what to look for

Here's a quick list of things I look for when inspecting Hy-gain rotators. Since my list is similar to that of others I won't spend much time on it.
  • Ring gear: Look for pitting, chipped or broken teeth and metal spurs. Most defects cannot be fixed so you'll have to purchase a replacement. This is not uncommon.
  • Brake teeth in the bottom housing: There should be no broken or heavily worn teeth. If you have much of this consider replacing the rotator since it's been heavily used and abused over the years.
  • Bearing races: Check all surfaces for deep indentations or fretting damage. Again, there is little that can be done here except replacing the rotator. If you try to sand the races you'll only introduce slop in the bearings and accelerate further damage. You can continue to use the rotator with some race damage but plan for replacement.
  • Brake solenoid and wedge: Look for deep scoring in the wedge's front and sides, and the solenoid housing where the wedge slides through. Consider replacing the brake since there is excess play that will accelerate further deterioration and eventual failure. That will damage transmission lines and could damage the antennas when the brake fails. Also inspect the return spring and replace as necessary. Operate the brake a few times with the rotator open and watch its action.
  • Reduction drive: Test for slop and tooth wear in the spur gears.
  • Indicator pot: The top surface of the windings should be clean and shiny with no evidence of wire abrasion. The wiper tension should be sufficient to press firmly against the winding at its lowest point. The tangs on top of the wiper must be symmetric and straight. Look inside the bell housing to check for abrasion of the tabs that engage the wiper. It's only aluminum and will wear over time can eventually fail to hold the wiper. Yes, this really does happen.
Hy-gain rotators are reasonably robust and give most hams many years of service. Those who operate a lot, especially contesters, and those pushing the rotator's capacity limits with large antennas or in windy or salty locations should inspect them periodically. Plan for that when you design your tower and mast system so that the rotator can be conveniently and safely removed for service.

Replacement ball bearings

To my surprise I found little information on the internet about the size of the bearings used in this rotator and the lower-capacity Ham series. Yes, it's out there but it's not as if anybody is drawing attention to this important detail.

Hy-gain itself doesn't say. So I'll say it:
T2X and Ham series ball bearings are ⅜"
Happily these are easy to find at any industrial bearing shop. They are half the price by mail order (Hy-gain sells replacement bearing kits as well) but I was not willing to wait the typical 2 week delivery time. Much to my surprise the bearing shop had only 38 in stock when I stopped by. They had thousands of other sizes but not ⅜".

Since this was Ottawa, where I no longer live, and could not easily drop by the next day to pick them up they offered to courier them to me for a nominal fee. Two days later 300 ball bearings arrived at my front door. About 70 of them went into the T2X. The rest are being stored for future Hy-gain rotator overhaul projects.

Cleaning it up

I was mostly concerned with loose debris and caked on dirt/grease on the bearing races. The former was removed with a small brush and a blower while the latter was removed with a rag dipped in solvent. The spur gears, motor and indicator pot were very clean and properly greased so I left them alone.

After cleaning the races with solvent I used steel wool to carefully remove any remaining debris until the races were clear and smooth. I tested by running a finger along the full circumference of both faces of every race. There was little evidence of fretting or undulations. The rust stains from the ruined ball bearings on the lower race required additional cleaning with the steel wool until they passed the finger test.

All cleaned up and ready for a fresh coat of grease

The remaining discolouration of the cast aluminum is not a concern. Do not keep sanding until it is shiny since that serves no purpose and can degrade the race. Do not use an abrasive stronger than soft steel wool, and even then use it lightly and sparingly. Avoid using sandpaper with a grit coarser than 1000.

Grease

Many types of grease are suitable for these rotators. White lithium grease is the one I use most often since it is easy to work with, is inexpensive and has decent all-season performance. This time I decided to try a synthetic grease for reliable performance in our frigid winters and adhesion out in the summer sun. We'll see how the experiment goes. Others report good results.

You do not need to use a lot of grease. Too much and it will be squeezed out during operation and possibly foul other components and bog down the reduction drive.

With your finger (use a plastic glove to keep yourself tidy) spread a thin layer of grease on the bottom and inner and outer edges of the ring gear and the flat surface on which it sits. Don't grease the top of the ring gear since it is affixed to the bell housing.

Do the same for all the bearing races. There are 6 race surfaces in the T2X, two for each for the 3 bearings. I like to also add a thin layer of grease directly to the ball bearings after they've been inserted into the retainers, but this is not strictly necessary. Be sure that if you do that the total amount of grease is not excessive. There should not be visible globs of grease anywhere.

Putting it back together

This is the task that most worries hams about Hy-gain rotator service. The T2X is no different, and is indeed done pretty much the same as the Ham series. Let's go through the way I (and many others) do it, with a few illustrative pictures. When you understand the trick of how to do it I hope you'll never again hesitate to open up one of these rotators.

In the picture at right the main body of the rotator is in proper configuration for attachment of the bell housing. There are 3 steps to get to this point:
  1. Turn the rotator in either direction until the limit switch cuts off the motor; I chose clockwise, as seen from above. This step positions the ring gear.
  2. Turn the wiper on the indicator pot by hand to the stop in the same direction you just turned the rotator.
  3. Install the upper bearing. The grease should keep it from sliding off.
Look into the bell housing and notice that there are 3 hooks at the perimeter that attach to the 3 protrusions on the ring gear. They are identical and allow the bell housing to seat in one of 3 positions. However only one is correct. You determine this by the tabs that engage the indicator pot. Look at the tabs and look at the pot, then rotate the bell housing in your hand so that it is approximately oriented to engage.

Now tilt the bell housing and you'll notice that all the ring gear tabs are approximately directly overhead those 3 protrusions on the ring gear. Pick one for reference and make a mark on the outside of the bell housing at the tab's centre. Use a felt marker or a bit of tape. This step is important since you must install the bell housing blind; that is, you can't directly see the hooks and tabs.

Gently lower the bell housing over the rotator body until it is an inch above the ring gear. Visually align the mark and the ring gear protrusion and, keeping the bell housing vertical and centred, lower it until it contacts the ring gear. You should only have to rotate the bell housing a tinyamount for the tabs to seat against the ring gear. If you've done this right the pot will also have properly engaged its tabs.

To test if the pot is properly seated run the rotator away from the stop for perhaps 10 degrees. You should see the indicator on the control box move with the rotation almost immediately. If not you should suspect a problem. Now rotate it back towards the stop. There should be no hesitation before the indicator moves. If the pot is not properly engaged it may take a second or two before the indicator shows movement.

If you got it right do a full rotation to the other stop and back again to whatever direction you wish for installation on the tower. Otherwise take the bell housing off and try again. Do not keep playing with rotation if the symptoms I mentioned are evident since you are likely to damage the pot wiper. As often as I've done this I still managed to get it wrong with this T2X. I was successful on the second attempt.

With the hardest part out of the way we are close to completing reassembly. There is only one special trick left to do.

Turn the rotator upside down, taking care to keep the bell housing firmly seated against the rotator body. You really don't want to do the alignment procedure over again, do you? Install the remaining two bearings on the rotator body.

If you have a quick disconnect plug on the rotator (all recent model T2X have a plug rather than a terminal strip, but not mine, alas) unplug it, or disconnect the wires from the terminal strip if that's what you have. Thread the cable through the bottom half of the housing and reattach the cable. We need to operate the rotator for the next step.

Lift the lower housing and position it over the rotator body. Lower it carefully, ensuring that it is vertical and centred. You will likely hit resistance when the lower housing contacts the brake wedge. You can drop it further if you position the brake wedge between two teeth, but don't do it this way since the housing will not be centred. The reason is that the spring forcefully extends the brake wedge further than the diameter of the lower housing. Don't fight with it: the solenoid spring is quite strong and you'll knock the bearings off the races.

With one hand on the control box retract the brake wedge. You can now easily lower the bottom housing until it contacts the upper (bell) housing. With the brake wedge still retracted rotate the lower body so that the bolt holes are aligned. You can now release the brake and bolt the rotator together.

I suggest doing this only finger tight and testing the rotator for full rotation. Only then would I tighten the bolts. Do not tighten the bolts in sequence; as one tightens move to one approximately opposite to it, to avoid higher stress on one side of the rotator. Admittedly the risk is low but why not when it's easy to do.

Done

As you can see I made only a perfunctory attempt to clean the rotator exterior . Its appearance is of no interest to me; I only care about the inside. Some hams like to make them nice and shiny and will even give them a new coat of paint. Do whatever moves you.

While it isn't clear in the photo the indicator is calibrated and set to point north, which is the rotation centre. That direction is convenient for setting the yagis correctly and for adjusting the length and position of the rotation (drip) loops in the transmission lines.

Now all that's left is to install it on the tower. But first I have to complete the tower. Weather and the holidays are making that difficult for the present. One of my friends told me not to worry about it too much since the bands are so lousy. We'll see.

Merry Christmas or whatever holiday you choose to celebrate.

Wednesday, December 21, 2016

Drilling a Tower Plate

It is a good thing that tower plates often come pre-drilled for popular varieties of bearings and rotators. For all other cases there is some effort required to do this right, including centering drilling templates, locating the mounting holes and finally drilling the plates.

There is no magic involved other than attention to detail and using the right tools. Get it wrong and the bearing or rotator will bind or at least experience stress for all or part of the rotation circle. That can lead to unexpected failure, although it might take a few years depending on the severity of the error and frequency of use.

Unfortunately the rotator and bearing plates on my Trylon tower are not drilled for a Hy-gain Tailtwister and a 4-hole bearing flange. There is a rotator plate on the top section that is drilled for the Tailtwister, which I am not using since I am mounting the rotator on the next lower section to allow stacking above the tower with a long mast.

I decided to take a few pictures of my work and write it up in case this could prove useful to others. There are other ways to do the job, some perhaps better than my way. However if you have never done it and you need to do it this article may give you some ideas and the confidence to do the work.

Preparation

The top plate for the 4T section and the 5 section (purchased used) are drilled for a 3-hole bearing flange. All the plates include a large circular opening for the mast, which is very helpful since that hole is not easy to machine in the typical ham workshop. Ordinary hole saws don't do well on steel!

The first task was to remove the two plates from the tower sections. These are the formed sheet steel plates that Trylon stopped producing about 25 years ago. New plates are flat and sit on angle brackets that bolt to the tower legs. Both have their challenges when it comes to drilling.

The rest of this article will be about the bearing plate. The rotator plate was done the same way. It is only chance I'm doing it this way since the rotator plate was already done and out in the snow with the tower section when I decided to write this article.

Finding the centre

To begin I taped a sheet of paper under the plate. This is needed since (obvious, I hope) the centre will fall within the large cutout. There are three lines drawn between the centre of each side and the opposite vertex. When it's done right the lines should cross at the same point. Don't cheat and draw only two of the lines since there are many ways the lines can be misdrawn and with only two you won't know if an error has been made.


A careful inspection of the plate shows that the three bends are not exactly the same; that is, the plate is not symmetric. All of my three plates are off a small amount. Therefore we cannot rely on the edges of the plates as accurate centering guides.

The best guides for these plates appears to be the bolt holes that attach the plate to the tower legs. There are six of these. They must be in the correct location of the tower section splice would be misaligned. Perhaps Trylon drilled the holes in a jig after bending the steel to account for type of small errors in the bend locations. For other tower brands you should be able to find and use other centering guides.

Since the top plates are adjacent to the splice holes the distance between holes on each vertical tab are almost exactly an integral number of inches: 15" in the case of the 4T bearing plate and 18" for the 5T plate. It isn't difficult with a steel carpenter's rules or square to bisect the line between the bolt hole centres and mark it with a pencil (not a pen). I then used the small square shown on the photo to project that point onto the plate surface.

A line is then drawn from that mark to the opposite vertex. You may need to use a similar method to bisect the line between the bolt holes adjacent to the vertex since there is no reliable landmark at the vertex to rely on. A small box is placed underneath the plate to allow the pencil to mark the paper.

If the lines don't cross within 1/8" or less check your work. Keep in mind that the angle of the pencil alongside the ruler or steel square can error cause an error of 1/16". Keep the angle constant while drawing and ensure it precisely hits the marks you made at each end.

Drilling template

Bearings and rotators almost always include a drilling template. However whether it is already on paper or you print it yourself do not rely on its accuracy. Scaling errors have a habit of creeping in from the original machinist's template to software to printer.

If you are lucky enough to have a bearing or rotator where the mounting holes stand clear of the body drawing the template is quite easy. Place it on a sheet of paper and with the pencil held vertical draw a circle around the inside of each hole.

For blind mounting holes found in most rotators and some bearings it is less easy though still straightforward.
My preferred technique is to tape a sheet of paper over the equipment itself and punch the holes with a pencil or by pushing the mounting bolts through the paper and engaging the threads. I used the former for the bearing and the latter for the rotator.

For either clear or blind holes use a ruler to draw lines between the centres of opposite holes. These ought to intersect at a point. If there are only two lines, in the case of 4 blind mounting holes, ensure that the four sides of the square formed by the holes are equal to confirm that the intersection point is truly the centre.

Overlaying the template

Since paper isn't transparent it is necessary to find a way to ensure the centres of the plate and template are aligned. One way (pictured) is to cut out the middle of the template and use a ruler to ensure the centre of each line on the template is located at the plate centre. Another technique is to push a small nail or tack up through the plate centre, support it on a solid surface and push the bearing template centre onto the nail.


Either way you now have a drilling template properly centred on the tower plate. You can rotate it to any preferred orientation (if you care). In my case it did matter since the existing holes on the plate had to be avoided. I reused one of the existing holes since the holes often overlapped and I could reduce the amount of drilling, and possible weakening of the plate.

Drilling

A centre punch in each template hole provides a dimple for the drill bit. I use a ⅛" bit to make a pilot hole before using a bit of the required diameter. I always use at least one step larger hole than the bolt shaft so that there is some play to allow final adjustment for mast alignment. The Yaesu bearing you see uses M8 bolts so I made the mounting holes ⅜" (9.5 mm).

Remember to deburr the holes to protect your skin and to ensure the hardware mounts flush against the plate surface. I used a round file to lengthen that one previously existing hole since it wasn't quite in the correct position.

When you're done turn the bearing or rotator upside down and place the drilled plate over it. The holes ought to align. If there is a small misalignment in one hole get to work with a round file or reamer.

Ready to go

When you're done you can be confident that the bearing or rotator is correctly centred on the plate. Mast alignment should require little additional work once everything is installed on the tower.


Above you can see the bearing mounted on the 4T top plate along with the bolts for reattachment to the tower section. The pencil marks can be left as is unless you enjoy doing unnecessary work. The weather will soon enough do the work for you.

Long masts

I'll leave you with one positive note. When a long mast is used the rotator is (and should be) mounted lower in the tower. Centering errors cause fewer problems as the distance between bearing and rotator increases. If you are unsure of your machining skills all you need do is mount the rotator lower. That will also put you in good stead should you later decide you want a longer mast.

Wednesday, December 14, 2016

Turning Skimmer Spots On and Off

Once again I joined multi-op VE2OJ for the recent ARRL 160 meter contest. This group only does this and the CQ WW 160 meter contest, gathering at an isolated cottage in west Quebec for a bit of fun and radio. The radio is modest but the receiving is very quiet. Well there was some noise this weekend since not all of the neighbours had yet abandoned cottage country for the winter.

As is usual this group operated in the assisted category, using the spotting networks to do the VFO tuning for us when we aren't running flat out. VE2 is not all that rare in contests yet we still manage to attract attention. The amplifier helps overcome the small inverted L's modest performance.

If you are a contester you are familiar with the idea of operating assisted. Some like it and some don't. I had not done so until joining the VE2OJ group last winter. It was fun and interesting. Despite its attractions I have not decided whether I'm going to do much of it from my own station. First I need to build my station!

I won't repeat my operating style when assisted since I described it previously. What I want to focus on here is how we did, and didn't, use the spots.

Turning it off

For most of the first evening we were mainly running. I had the first shift and split running and S & P about 85% and 15%, respectively. The reason I did some S & P was that so many stations were running that there were unwanted periods of few responses to our own CQ: running depends on the presence of S & P operators. I relied on the band map of spots to click and call since, as I described in that earlier article, it was more efficient than turning the dial.

Spots come in two types: human entered spots and skimmer spots from the RBN. Most spots come from the latter source in CW contests. This is where we ran into difficulties.

Early in the contest almost every spot is a needed station. The result is a very busy band map. It is impossible to even tell what frequency stations are on without using the mouse to hover over the call signs. Worse is that quite a few of the spots coming from RBN are busted calls. For example, our call of VE2OJ might appear several times on the band map, under busted calls like VE2OO, VE2OP, VE3OJ and so on.

Phantom RBN spots can waste an inordinate amount of time, especially early on when the rates are highest. The group discussed the problem and came to the consensus of disabling RBN spots entirely. For S & P we found it more effective (higher S & P rate) to rely on human spots and spinning the dial.

Despite losing the majority of spots we stayed very busy that first evening. That early in the contest most of the lower quantity of human spots were for needed stations. In any case, most of the time we were running and usually only pursuing spots for DX multipliers. All agreed that we had made the correct decision.

Turning it on

The second evening the situation changed. QSO rate slows as the contest progresses since all the serious entrants have already been worked. The band map can look pretty empty since worked stations are filtered out of the band map; there is no good reason to see spots for dupes unless you have an urge to listen to the competition.

We had enough dupes as it was. Perhaps some stations had fallen victim to the busted skimmer calls by relying on RBN rather than copying our call directly. There's a lesson in that: use the spot to S & P but only log the call you directly copy from the other station. Better still, listen a moment before calling and delete the busted calls from the band map.

A brief and passionate discussion ensued. Should we turn skimmer spots back on? I argued yes, but not all agreed. However I was in the operator chair at the time and since it would be me and no one else who would be plagued by busted calls we agreed to give it another shot.

This time it worked in our favour. With dupes being filtered much of the clutter was gone. While there were still busted calls they did not cause as much wasted time (drop in rate). However they did remain annoying. We kept it on for the remainder of the contest.

The lesson is to be smart about using spotting networks. Adjust your assistance strategy as the contest progresses to get the best outcome.

Where did it go?

Something I've noticed since moving to my new QTH is that terrestrial wireless internet access has its ups and downs. One problem is EMI to and from the internet equipment. Wireless internet is used at both my QTH and at VE2OJ. The topology is similar in that the internet modem is located at the antenna and the cable running from the antenna into the house is Cat5e operating as powered Ethernet. The wall wart DC supply connects to the indoors termination of the cable adjacent to the RJ45 connector that plugs into the computer or router.

As with most home Ethernet cables they are perilous for the radio amateur. Not only do they pollute the HF bands (and even VHF) they are susceptible to interruption from our transmitters. The closer the cable is to the radio antenna the worse the mutual interference. This is despite the twisted pairs in the Cat5 cable that suppress EMI. That twisting is insufficient protection for low-noise receive and digital resilience at most ham stations.

The problem can be beat by wrapping the Cat5 and our radio transmission lines around common-mode killing ferrite toroids. But for the long runs associated with wireless internet many toroids are required. So far as I can tell shielded Cat5 cable is not typical in these installations. For my own station I have a large order of toroids on the way!

The result of all this mutual EMI at VE2OJ was that the router would lose its connection to the radio modem and would have to be reset at frequent intervals. Focussed as we were on the contest we often only noticed when the band map would begin depopulating some minutes after the internet connection was lost.

We got into the habit of paying close attention to the band map and the Telnet window. The operator would point out the loss to one of the idle operators who would take care of resetting the boxes. A minute later the Telnet connections could be reestablished.

Coming up...

Building of the new station is continuing. There is lots of blog fodder but nothing has reached a point where an article is worth writing. I have several in draft, all of which are awaiting associated activities to reach a conclusion. Hence the recent gap in blog posts.

Tower work is being interrupted for a while by a spate of frigid winter weather and work on the tower components to fit rotators and bearings. I need assistance to complete the work so I am dependent on the availability of others, which for most means weekends or the holiday week preceding the new year.

If all goes well there ought to be as many as 3 more articles before we ring in 2017.

In addition to radio related activity the long awaited house renovations have begun. I am living in a construction zone both inside and outside. This computer is temporarily sitting on a coffee table while the work goes on around me. Fun times.

Thursday, December 1, 2016

Trylon Gin Pole

The time has finally arrived to put up the Trylon tower. The concrete is well cured and the weather is not too unbearable. The snow has mostly melted (for now) so that I can find hardware and tools when I drop them. The next order of business was to build a gin pole.

A gin pole for the lower sections of a Trylon or similar self-supporting tower must be very robust. The heaviest section I am raising is the #11 section which lists as 168 lb (80 kg). This is substantially more than the 50 lb sections of DMX for my earlier gin pole. The structural requirements are challenging. Not only that, lifting that amount of weight safely and with enough maneuverability (to position the section for splicing) is also a challenge.

Pole and tower "hooks"

I have many lengths of 1.5" schedule 40 water pipe lying around that look suitably attractive for this purpose. It isn't especially light -- many prefer aluminum alloy pipe or tube -- but it's up to the task and I have it on hand. Water pipe is regularly dismissed as unsuitable for mechanical applications, such as masts for yagis, yet it perfectly usable when its limitations are kept in consideration. It also did well when bending large diameter rebar.

Since the forces are primarily axial rather than radial they can be used for gin poles. My only concern was getting the height right and being cognizant of the difficulty of handling its weight (2.7 lb/foot) from the bottom end when attaching and detaching it from the tower. The gin pole I constructed comes it at about 35 lb (16 kg) and 10' tall. It is cumbersome enough to easily get away from you when trying to hold it vertical from the bottom. You must be strong enough to handle it on your own or invite a friend up the tower with you.

I was offered the free use of a gin pole of my choice from the stable of tools kept by a local tower service company. However all of them were quite long and heavy and would require two people to manipulate. They, of course, make tools for large commercial towers which must necessarily be heftier. The gesture was appreciated nonetheless.

One nice thing about much of the scrap pipe I have is that it comes pre-drilled with ⅜" holes at top and bottom. (The pipe had previously served its previous owner as a long mast for a ground-mounted rotator, hence the holes for angle stock pipe splices.) There is therefore less machining required than with new pipe. Only one more hole needed to be drilled for the second attachment point to the tower.


To avoid the need for welding or metal bending I designed the gin pole to require little metal work. The detail of a tower "hook" is visible in the above photograph (close up adjacent), while the #11 section is being attached to #12 base section.

A 3" long ⅜" grade 5 bolt holds a sandwich of several parts. In order, from the inner side of the pipe:
  • 1"x⅛" steel stock 3" long with a ⅜" hole in the centre. This is a "keeper plate" to prevent clockwise rotation (as viewed from above).
  • Flat washer that butts against the tower leg.
  • Shaped 1"x1"x ⅛" angle stock 2.5" long that provides a seat for resting on a downward diagonal cross-member, and as a keeper plate to prevent counterclockwise rotation. The shaping allows further insertion into the leg interior before bottoming out on the smaller (upper) tower sections.
  • Flat washer. A lock washer is a poor choice since the angle stock must rotate slightly when attached to the tower because the diagonal orientations (angles) are all different.
  • Grade 5 Nut.
There are two identical hooks 30" apart. The distance is that of consecutive downward diagonals for sections #12 through #4. It goes on the left side of any face; the right side downward diagonals are lower down and would require a taller pole. Due to section design there is often a small gap under the upper or lower seat. I haven't yet needed to shim the gap since the pole leans very little until the seat firmly presses on the diagonal. However the seat and keeper plate must be long enough to avoid disconnecting from the leg.

Pole length and splice procedure

The next picture shows the 150 lb #11 section lifted and ready for splicing to the #12 section.

With this 10' pole the maximum lift is 6.5' (2 meters) above the lower section. This is enough for an 8' tower section. Since lower sections are so wide (3'+) any attachment to the perimeter of the section will result in the section hanging diagonally. As you go up the tower the lean will decrease as the ratio of height to width increases.

It is not difficult for even one person to grab and swing the section into vertical orientation. The bigger problem is judging whether the lift is just right for the section to be fitted. Due to the heavy weight there is only a small margin unless there are two strong hams up the tower.

To ease the process with just me up the tower, with or without someone working the winch, I first tie a rope around the gin pole and leg attached to the cable. This keeps the section near enough to vertical to allow fine adjustment of height for the remainder of the splicing operation. Despite appearances it is the other two legs that first contact the lower section when it is rotated to the vertical orientation.

When the outer legs are hanging inside the lower section legs I inserted bolts into the lower legs to prevent the upper section from sliding down. Thus when the section is lowered further to slip the inner leg into the lower section it is in near vertical orientation and is unlikely to jam due to excess lean. The bolts can then be removed and splicing can proceed to completion.

It's important to attach all 12 bolt loosely at first. If a bolt is tightened too soon it may be impossible to insert the bolts on the other face of the leg due to misalignment. Gradually tighten all 4 bolts per leg splice in a rotation to achieve maximum alignment.

Power lift

There are several possible ways of putting muscle into a gin pole to lift heavy sections:
  • Lots of friends, or at least two strong ones
  • Winch, motorized or manual
  • Tractor or similar motorized vehicle
Since I am so isolated at this QTH and the age of most hams it is not easy to go by muscle alone. My only motorized vehicle for the present is a car, which can be used although it is overpowered for the application and can be hard on the lawn. So I opted for a winch. I went with a manual winch since it is more economical and easier to operate without making any mistakes.

I purchased a winch capable of 1,400 lb working load. A smaller capacity winch would suffice but the ones I investigated didn't meet my expectations for spool capacity, ratchet quality or other criteria.

I am using 3/16" aircraft cable with a 6,600 lb breaking strength. Smaller cable is, again, sufficient but a poor choice due to the risk of pulley cage pinching, abrasion or kink failure and tangling. I happened to enough left over from a previous project. One end went onto the winch spool and the other was terminated in a forged steel hook with a thimble and cable clamps.


I constructed a platform and tower clamp for the winch out of surplus lumber and some bolts. The outside half holds the winch. The inside half is cut to fit underneath the upper diagonal and atop the one below. These two diagonal converge away from the tower leg so that when the two halves are bolted together the platform cannot move outward. Both halves sandwich the tower leg to secure it against slipping inward or outward. The inner half is 2x6 lumber and the outer is 2x10. There are 4 bolts tying them together. The outer half is wider so that the winch handle clears the tower leg.

On the right you can see the winch in action, fully supporting the weight of the #11 section. By running the cable onto the outside of the spool there is increased outward force on the platform. With a platform made of lumber there is some risk to doing this. However the bigger risks are abrasion of cable and tower and cable snagging were the cable run to the inside of the spool.

Progress

As this is written I have only 3 sections raised, sections #12 through #10. Weather and other tasks have delayed further progress until next week. It gets easier as you go up since the sections rapidly decrease in weight. The #9 section (see picture) is the last that is over 100 lb. Eventually I'll dispense with the winch and use a rope and muscle. I've already fitted a rope cleat to the tower, as I have done for all of my towers.

I have some work yet to finish on the rotator and bearing plates (#5 and #4 sections, respectively) so I needn't rush. There is also ongoing work on the LR20 150' guyed tower which I'll write about when it's ready to go. The gin pole for the Trylon requires only a few modifications to be used on the LR20 since both towers use a similar leg design.

If all goes well the Trylon should be fully built within two weeks. I can hardly wait to have a real antenna again. A simple, low antenna doesn't appeal to me the way it did when I returned to the hobby in 2013.

Saturday, November 26, 2016

W1AW/p Centenary WAS

Earlier this month the VA3/VE3 incoming QSL bureau notified me that I had a lot of cards to be mailed out and to please sends funds since this would blow through my previous deposit. I was a little surprised by this influx of cards since it seemed unusual. Nevertheless I forwarded the funds and my mailbox was soon filled by several heavy envelopes.

More than half of the cards were for the 2014 ARRL centenary celebration stations W1AW/p operating from every US state and overseas territories. I guess they had lots of cards printed and decided to confirm every QSO, even without any requests.

I do not as a rule apply for operating awards of any kind, not even DXCC, being happy to have worked the stations I want to work without requiring any more paper. This is why I was pleased to sign up for LOTW to escape paperwork, and especially unwanted task of filling out QSL cards.

Nevertheless my curiosity was piqued. In 2014 I was operating QRP with my KX3 and for the most part using simple wire antennas. I was certain I had worked all 50 states worth of W1AW/p stations just by habit of jumping in when I stumbled across them. It seems that being a DXer I am loathe to bypass any pile-up!

And so it seems I did indeed work all 50 states. Now they're confirmed (many twice) as well as most of the overseas territories. No, I am not curious enough to break it down by band! But I do know it was all CW.

Although the award itself does not interest me these cards make a nice memento. Kudos to ARRL for doing this.

Saturday, November 19, 2016

Planting the Trylon Tower

In the previous article I discussed forming and installation of the rebar cage for the foundation of my Trylon Titan T400 tower, nominally 72' tall. I am using this project as a vehicle to describe some of the important skills and activities involved in erecting a reasonably large self-supporting tower. This article will take us through to the concrete work, completing the planting of the tower.

It is my hope that hams who have never put up a tower with a concrete foundation, or even those who have, will learn something and perhaps gain motivation to take on a project of this size. Certainly I have learned new skills, including rebar form construction, and it's fun to pass that along to others. Ham radio is a fantastic opportunity to learn new skills and it would be unfortunate to avoid those opportunities by hiring someone to do it or going without.

Eventually I'll get back to antennas and operating. Since every antenna needs a support structure this long sidetrack is, in my opinion, well worth the time. I hope that readers will agree.

With that out of the way let's plant that tower in the ground. All the work up to this point will finally show tangible results.

Alternatives to positioning and securing the tower base

The base section and anchor stubs for the majority of towers of this type (typical for ham use) must hang rigidly suspended over the foundation excavation for the pouring of the concrete. Since magical levitation isn't an option we need a practical approach. There are a few objectives:
  • Position the tower, laterally and vertically, per the manufacturer's specification.
  • Support the weight of the tower without sag, movement or risk of tipping or other failure mode.
  • Cheap and effective, but not necessarily pretty.
  • Can be built and the tower placed by muscle alone.
  • Withstand the force of concrete pouring from a height and lateral flow.
  • Rapid adjustment of tower position, lateral or vertical angle, if and when concrete or other force shifts it.
  • Does not impede pouring of the concrete, whether by chute or wheelbarrow.
This is a long list! I have seen many systems, both good and bad, devised by hams over the years. Professionals have their own favourites. Here are the ones I am most familiar with:
  • Chairs: Concrete blocks -- they must be concrete -- are positioned at the bottom of the hole. The base section and stubs sit directly on those blocks. The base section must be guyed top and bottom to prevent movement and collapse of the chairs while the concrete is poured. From asking around this is option chosen by many hams with Trylon towers.
  • Side bracket: This method is only possible when the tower is next to a rigid structure. Enough tower is built (usually one or two) sections to allow bracketing to the adjacent structure. In this way the tower is suspended over the hole and held rigid. It is guyed or otherwise secured just above ground level. After the concrete sets the bracket and guys are removed.
  • Scaffold; Two or three lengths of lumber, steel or other rigid and strong material pierce the base section near ground level so that the horizontal or diagonal cross members between legs rest on them. These are in turn supported at either end so that the tower is correctly positioned. The scaffold should be clamped to the tower for best results. Top guys may be required.
  • Cradle: A steel or lumber cradle is built on the base section. The cradle is wider than the tower and rigidly attached. It is then carried or lifted by muscle or machine over the hole and supported at all corners. Top guys are not required.
In my situation a side bracket is not an option and chairs require at least 3 people for a tower of this size. Even a scaffold is difficult to install with fewer than two people. This is impractical for the Trylon Titan series since all the cross members are diagonals that would require 3 supports rather than just two.

A cradle is more elaborate but it only requires one person to do all the work. Also, since I've never built a cradle before that's what I decided to proceed with. I came up with a design that would work for the Trylon and bought the lumber I needed. Pretty much all the hardware was acquired from my junk box.

Cradle

Picture from an earlier article included for convenience
Unlike a scaffold a cradle is mechanically integrated with the base section. Its purpose is to suspend and secure the base section and stubs over the hole and to facilitate lifting the assembly upright into the hole. This is no simple task since the #12 section and stubs weigh in excess of 200 lb (90 kg) and the design of the Trylon tower diagonals makes attachment awkward. The cradle itself adds approximately 30 lb (14 kg). I had strong doubts whether I could manage the job by myself.

The cradle was built onto the #12 section with it lying on the ground and the stubs on the bottom legs resting on the hole casing. The construction of the cradle is captured below in a mosaic of views. The large picture on the left shows the tower immediately following lifting onto the skids and centred. The rear stub is not attached since it would strike the casing when the tower is levered upright due to its large turning radius. Draw it on a piece of paper and you'll see why that is so.


The remaining picture shows details of the cradle design and truing technique (next section). The front of the cradle consists of two lengths of 2x6 lumber, the inner one cut to fit inside the tower face and the outer one long enough to rest on the skids (2x4 nailed to two sides of the casing). The inner one butts up against the lowest diagonal on two sides, clamping the tower face between them. Scrap angle steel provides a hard surface for the diagonals to rest on to ensure they don't cut into the lumber.

The skids are worth a further look. These lengths of 2x4 on opposite sides of the casing serve multiple purposes. First, the keep the casing square by preventing any twisting. Second, the cradle is above the top of the foundation so that it cannot touch the wet concrete. Third, the wider surface is better for placement of shims to true the tower (next section).

The rear of the cradle is a single length of 2x6 lumber clamped to the tower leg with copper-plated steel strapping (it's what I had on hand). The choice of 2x6 lumber was determined by measuring the distance from the leg bottom to the supporting diagonals and adding the height of the 2x4 skids so that the manufacturer spec of 1" between the leg bottoms and concrete surface is met.

With everything done I manhandled the ridiculously heavy assembly until the front cradle was just past the edge of the rebar cage. There is little clearance so I had to get this right. I next adjusted the cradle's lateral position by eye so that the ends of the stubs were square to the hole. Otherwise one of the stubs will crash into the rebar cage when the assembly is rotated upward. That would be very bad.

Pushing up on the top tower leg I kicked a milk crate under the diagonal closest to my feet. That makes it easier to lift by giving lots of finger room underneath the tower. But here I experienced something unexpected: it was remarkably easy to lift the tower. The weight of the stubs and much of the cradle counterbalanced a significant portion of the 170 lb #12 section.

As it turned out I could have lifted the section with just one arm, rather than doing a power lift. The step in the operation I was most worried about turned out to be the easiest. I think I had a silly grin on my face as I lightly pushed the tower upright in a few seconds, even holding it up halfway while I ensured the position of the stubs was where they needed to be. What was to be a simple test of the cradle before I got on the phone to call up a friend to drive out to my place turned into the actual lifting. Lots can go wrong in tower work so it was pleasant to have this turn out so well.

The last task is to attach that last stub. I loosened both straps and inserted bolts into the two holes not covered by the straps. One at a time I lifted one side of each strap to insert the other bolts. This reduced the risk of the cradle slipping out. With the straps back in place but loose I dropped into the hole to attach the lock washers and nuts and tightened them.

Truing the tower

When I installed the casing for the tower foundation I got it almost but not quite level. With more fussing around with shaving dirt here and there I could have gotten it near perfect. But there is no need since even with the best of intentions there will be a problem elsewhere. In particular with the positioning system for the tower base over the hole. Such was the case with my cradle.

Truing the tower is the process of having it exactly vertical. With the cradle in place I had only to adjust it with shims. Although the cradle front and rear both used 2x6 lumber butting against the bottomost diagonal cross member the rear end used the bottom (vertical) of the L-shaped diagonal and the front used the top (horizontal). That is enough error for about the thickness of a lumber stud (less than 2").

As a result the rear leg sits higher on the skids than the front. Since it cannot be lowered the shims must go on the front. You can see them in the photo mosaic above.

For measurement I used a long carpenter's level. On towers with straight sections it is a simple matter to place the level along the vertical legs and ensure they are indeed vertical. On a tapered tower, which is typical for self-supporting towers, the legs are not vertical when the tower is vertical. The tower manufacturer often recommends taping a spacer at a prescribed position on the level as compensation for the taper.

My preferred techique is instead to aim for an equal error on all 3 legs. There is no spacer to make or attach (and lose). I learned this from another ham so far in the past I can't remember who it was. It's the method I always use and it has never failed me. However, there are things to watch out for:
  • Not all levels are properly calibrated. For this reason always use the same edge of the level to measure all the legs. It's a surprisingly common problem.
  • Wipe the level and tower legs since it takes only a small amount of dirt to skew the level.
  • Tower legs are not as perfectly straight as you might expect. This is especially true on towers with bent sheet metal legs such as the Trylon. When the level is against the tower leg you should not see any gap between them. If there is a gap move the level to a better position. The leg vertex is a better choice than one of the sides even though it is more difficult to set the level properly on it.
Securing the assembly

Secured, vertical and ready for concrete
One of the joys of a cradel is that the tower base is exceptionally stable against forces that would shift its position, either by accident of the flowing concrete. Other supports may not do as well. Of greater concern to me was the rebar cage.

With the tower in position and trued I dropped into the hole and wired each leg to the rebar cage in two directions. I then removed the temporary lumber spacers between the rebar cage and the hole walls. The rebar shifted a small amount which I adjusted by tightening the wires. Although the rebar cage weighs as much as the base section plus stubs the tower does not shift since it has the advantage of leverage.

Affix temporary guy wires to the top of the base section so that the tower can be adjusted back to vertical during the concrete work if tilts off vertical. Although the cradle was solid enough that I didn't expect to use them (and I didn't) I had them ready just in case.

Now, finally, it is time to call the concrete company.

Concrete work

In contrast to the step to this point the pouring of concrete goes fast. Perhaps too fast if you don't call a pause at sensible intervals. You usually have time since (here at least) for a given quantity of concrete you have the truck at your disposal for a set period of time. Only if you go beyond that will extra charges apply. That is unlikely to happen unless you are transported the concrete by wheelbarrow. (Someone did take a few pictures during the pour but I don't have them so there are none included here.)

Find out the required concrete strength from the tower specification. It is typically not an ultimate strength but that achieved after 28 days of curing in "normal" conditions. The Trylon requires 3,000 psi so I ordered 6 yd³ of 3,500 psi as a safety margin. Actually it was 4.6 m³ of 25 Mpa concrete since most business in Canada is conducted in metric. The truck of ready-mix arrives the same afternoon, after a wait because the driver got lost for a while (even locals occasionally have trouble finding this isolated QTH).

My preparation for the truck was quite simple. I called a friend to lend a pair of experienced eyes to the proceedings. This is very helpful since everything happens fast. Second, I cleared a path so the truck could easily back up right to the tower.

This brings up an important point: do you know where all your buried services are located? The truck is very, very heavy and can do a lot of damage. In the city the driver will often ask is there are any buried services he's being asked to drive over, and may insist you sign a waiver absolving the company if there is damage. Out in the country it can be different; our driver didn't ask. However I knew exactly what was where. Make certain you know.

Talk to the driver. Explain what you're trying to achieve. I told him I needed good flow to fill the flare at the bottom of the hole and to fully encase the chairs and rebar. A rented concrete vibrator can help, if you are willing to go to the bother and expense. I never have. You can achieve a lot by pumping a shovel up and down in the concrete and the driver adding some water to the mix. The small amount of added water slows the curing but does not weaken its ultimate strength.

Concrete is heavy and it is falling from a substantial height. Make sure the chute is positioned to miss the tower structure and rebar. The driver for my pour was careful and helpful. Concrete splashes so don't wear your best clothes! Cleaning your clothes is far easier when you wait for the stains to dry.

Keep an eye on things. Tell the driver to slow down when nearing the desired level. Many in the business talk of concrete being self levelling. Don't believe it. Use that shovel to move the concrete around, especially the voids behind the rebar. When the hole is full ensure there are no voids at the base stubs. Voids are typical where metal pierces the concrete and they are easily overlooked.

Adjusting the true of the tower during the pour can be a problem if you are unprepared. If you've attached those temporary guys that I mentioned earlier you're part way there. You have to do it quickly when necessary since, as I've said thing move fast during the pour. It can help to have a tensioner for the guys that is quick and easy to adjust. Look at the adjacent picture (and try not to laugh).

The guy is tensioned by adding or removing stones from the plastic crate that is attached to the rope guy mid span. This is far quicker than untying and tying knots or a turnbuckle. Silly but very effective. For the other guys (not shown) one is the #11 section (150 lb), which is moved back and forth to change the tension, and the other is a plank over the guy to which stone or bricks are added and removed. Again, silly and yet effective. Your friends may smirk and question your sanity but only until they see how fast you can true the tower.

The screw and chute have to be cleaned after the pour. Pick a good spot in advance for the driver to do this. They usually ask, but not always. It can be messy.

If you want a smooth finish mist the concrete and go to work with a trowel. Don't delay or it'll be too late. Do not clean the concrete on the tower, cradle, casing or elsewhere on the assembly until it dries. Should you try it when the concrete is liquid you'll only damage the surface of the foundation.

Shades of Cool Hand Luke

Digging a hole and filling it in again has been used as an instrument of torture. You may remember the scene in the movie Cool Hand Luke where the sadistic warden does this to Luke. In our case it isn't torture although there may be mixed feelings as you watch the hole fill with concrete. A lot of work went into the planning, digging and the rebar cage.

Relax and don't fret! Once the tower is standing proud and your yagis are singing and dancing on the bands you'll forget all about it. That is, until the next tower project.

Waiting and preparing

Keep the exposed concrete damp. Experts agree that hydration speeds curing and can increase the ultimate strength. If the temperature approaches or dips below freezing it's a good idea to cover the concrete with plastic or other covering that inhibits evaporation and ice formation.


The casing can be removed as soon as the next day. I like to leave it be for two days. Since I had to be away I did it the third day. For those who like a tidy look to the concrete you can use a cold chisel to remove ridges and other protrusions.  Do not use a file since aggregate in the concrete (such as sand) can quickly ruin the file . Once you're happy with it you should restore the lawn around the tower to appease spouse and neighbours. Appearances matter.

After removing the casing I applied a fast-drying concrete repair compound to fill the voids I missed on the inside of the stubs (note the wet spot in the picture above). The cradle made it difficult to do properly while the concrete was being poured. You can use the compound to build a shallow slope so that water flows away from the legs. Pooling water over the years can initiate corrosion.

Now is a good time to call your friends to arrange a tower raising party. Borrow or build a gin pole and do other tasks to prepare. You'll want everything in place so that no time is wasted when the time comes.

I would wait at least 7 days before constructing the tower. There is really no need to delay longer since by then the concrete is sufficiently cured for all but the most severe weather with a heavy antenna load. Concrete curing is a long-term process with no definite date when it stops strengthening.

As I write these words several days of snow are forecast. There will be a delay.

Sunday, November 13, 2016

Reinforced Concrete: Rebar for Towers

Concrete is basically man-made rock. Rock is strong in compression and weak in tension. That is, it makes strong columns and weak beams. This is why, for example, ancient Greek and Roman architecture had so many columns filling open spaces in their buildings: it was only those short spans that allowed the beams to support roof and floor loads, including their own massive weight.

The integration of steel into manufactured concrete building components corrected this limitation. The steel enables concrete to remarkably increase its tension capacity. We see this in bridge spans, office building floor slabs and even in our garage floors and house footings. Reinforced concrete is a major component in all but the smallest towers we use in amateur radio.

There is substantial tension present in self-supporting towers when faced with a strong wind and in the guy anchors and bases of guyed towers. So when we dream of big towers and big antennas we need to reinforce concrete.

Rebar

Steel rebar (reinforcement bar) is specified in the foundations of towers and guy anchors by the tower manufacturers to meet the engineering requirements for their products to support themselves, the loads (antennas) and couple those loads to ground. Rebar is not an option, so we need to do it right.

I ordered over 1,000' (300 meters) for rebar of various sizes to include in my Trylon self-supporting tower, the LR20 guyed tower and extra to get me started on a third tower. For these big orders go with an industrial supplier since their prices are far lower than the retail outlets, including the big box stores, and delivery is often free or they charge a nominal amount.

The amount required can be surprisingly large. For the Trylon #12 base section foundation I needed 200' of rebar: 20x5' verticals and 5x20' ties. The weight is substantial, coming in at ~200 lb (90 kg).

These are convenient lengths since rebar in Canada and the US the standard length is 20', even for the metric sizes we use in Canada. Where US rebar sizes are specified the tower manufacturers recommend rounding up to the next largest metric size.

Cutting rebar

Small diameter rebar used for ties can be cut to length with bolt cutters. Since the largest bolt cutters I have have a ⅜" capacity (up to #3 rebar) that was not an option. A hacksaw is too slow and tedious for the amount of cutting I needed to do. This is a job for power equipment. My tool of choice for cutting rebar is a circular saw with a 7" steel cut-off (abrasive) disk. A cut-off saw with an abrasive disk is easier and more accurate if you happen to have one.

Cutting steel this way can be dangerous when not done properly. The steel that is thrown off by the tool is a fast, dense stream of hot particles accompanied by metal vapour. Skin, eye and breathing protection is required. If you are feeling lucky the last can be omitted if done outdoors and the wind is at your back. The rebar will be very hot following cutting so do not touch it anywhere near the cut and use thick gloves of natural fibre such as cotton. Toss it aside to cool while you move on to the next cut.

I lay out several scraps of lumber on the ground to support the full length of the rebar and both sides of the cut. The end of the measured length of rebar butts against an immovable object to avoid errors due to inadvertent movement. My booted foot presses down on the other side of the cut as the tool does its work. Cut straight and keep some pressure on the steel for maximum safety and speed.

To reduce waste I did not cut each 20' length of 20M rebar into 5' lengths. I cut one 5' length for a Trylon vertical and cut the remaining 15' into two 7.5' lengths for the LR20 anchors. Thus there is no waste. I need 21 of those for the 3 anchors. I now have 19 in storage for a future guyed tower of similar size. If you do have waste it can be used for surveying stakes, supporting tree saplings or other jobs around the house.

Tools to bend rebar

Readily available tools to bend rebar include hand tools, mechanical benders and hydraulic benders. The latter two are expensive for the modest amount of rebar bending that the typical ham will need. Hand tools are far cheaper but are not well suited to making bends of the required radius, angle and position, and their capacity is typically limited to #5 rebar. Searching the internet for advice turns up far too many useless techniques that are either too ad hoc or require expensive equipment. I needed a better way.

I have never bent rebar before. This is perhaps surprising since I've put up so many towers over the years. In the past, where rebar was involved, it was done by someone else and all I had to do was make sure it was in position and guide the pouring of concrete. So this project was also a learning experience for me.


I purchased a "hickey" bending tool by mail order. As you can see it is basically a snipe with hardened steel pegs to hold and bend the rebar. The typical application of a hickey is hold the rebar against a hard surface with your foot (stiff boot) and pull up. I did an experiment to see how this would work out. I wrapped the bend area with masking tape, marked the pins with a pencil to see where the rebar would bend in relation to the tool.

It was not a happy experience. The leverage was enough to lift me off the ground and the resulting bend radius was far too large. The ties for the Trylon cage need a much sharper bend (small bend radius). For the time being I tossed the hickey aside to reconsider how I'd bend the ties and turned to attack the 20M verticals. These are too large for a hickey in any case so I designed my own tool.

Two trees and 3 pipes

20M rebar (slightly larger than #6) is not easy to bend without mechanical assistance. The substantial leverage required is difficult to achieve with hand tools and readily available supports. But where there's a will there's a way, with a little ingenuity.

The 20 verticals in the Trylon rebar cage require a hook to match the flare at the bottom of the foundation (see Trylon drawing above). Although perfection isn't mandatory we want to get close so that the flare area doesn't crack when the tower is subjected to extreme load. So don't skip this task because it seems too difficult.

The simple jig I constructed required two small trees near to each other and enough room to swing a 10' pipe acting as a snipe. The picture shows the large picture subsequent to bending one of the 20M verticals. If you study the picture I expect you can discern how the jig works. A close up of the bend zone is in the next picture.


Both pipes are 1.5" schedule 40 water pipe. Graded steel isn't necessary. Inside one pipe is a 2' length of ¾" pipe whose inner diameter is slightly greater than the 20M rebar (19.5 mm). That inner sleeve ensures that above the desired bend zone the rebar doesn't get bent. To get the 12" from the bend zone to the bottom I measured 13" (leaves partially hides the rebar) and carefully position the movable pipe just less than 1" from the fixed pipe.

In action the movable pipe is moved right until the rebar is locked by friction and gripped by the trees. Then the movable pipe is pulled, hard, until it taps the barrel. By happenstance the barrel is perfectly positioned to achieve the desired bend angle.

Once I got the jig built and tested the bending of the verticals was very quick. All 20 20M verticals were done in 35 minutes. Stacked together they make a pretty sight. They are almost exactly identical.

With the verticals done I returned to the problem of forming the ties. Unhappy with the action of the hickey alone I built a jig to hold to hold the smaller rebar and provide a hard edge for the hickey to work against. As it turned out there was a piece of steel mounted to one of the LR20 sections that appeared ideal for my purpose.

The angle steel is ¼" thick and attached to a tower girt with ⅜" bolts. It served as a bracket for a side-mounted yagi (and may yet again). To grip the rebar I installed ⅜" bolts with two ½" nuts serving as the surface for holding the rebar. All hardware is grade 5. The tower section is sandwiched between other sections to hold the jig during the bending. Even at 120 lb per section I periodically had to reassemble the sandwich. That's a lot of torque!

As in my previous attempt I covered the bend area with masking tape and marked all the key points. The forward (closest to the jig) pin on the jig was positioned about ½" from the edge of the angle steel. The test bend turned out perfectly. I measured the distance from the jig to the outside of the bent rebar to determine how to position the rebar for the tie formation.

I made two bends in this fashion then flipped over the rebar and did the final two bends from the other end. This way most of the rebar's weight and length does not have to be supported while bending. It's important to get the sides the correct length, square and in a plane. Get it wrong and it'll be difficult to correct, as I discovered. Don't waste 20' of rebar due to carelessness.

The result is quite good. The tie sides are 53" (outside edges), which is 7" less than the hole's sides. Rebar should be no closer than 3" from the sides of the concrete form or there is risk of moisture incursion which can crack the concrete and corrode the rebar after several years. I added an extra 1" margin.

Building the rebar "cage"

Professionals build the rebar cage above ground, in a jig, then transport it to the tower site and place it in the hole. I considered doing it that way until I realized that the rebar cage would weigh close to 200 lb (90 kg). That's a two man job and I didn't want to inconvenience anyone else. Besides which I don't have a jig and didn't want to build one.

Since the hole is, of course, almost exactly the precise shape required I used that instead of a jig. By building it in place I avoided having to carry it and, somehow, lowering it into the hole. But it did mean several hours spent sitting in a hole in the ground!

To begin I dropped all 5 ties and 4 verticals into the hole. In the hole I lifted the top one, resting one side on a ladder (the one I used to get in and out of the hole). With that as support I wired the opposite corners to two verticals leaning against the sides of the hole. Then I did the ones by the ladder. The ladder had to be removed since it wasn't quite the correct height. I did the remaining ties much the same way, working from the top to the bottom. After the second tie was in place the 4 verticals were stable enough to hold the partially-complete cage.

For my tower (see the #12 foundation detail above) the ties are ~12" apart. The verticals are ~10.5" apart on average. Precision isn't critical, but utter sloppiness must be avoided. Don't fret over minor inequalities in the spacing.

All the crossings are wired for the first 4 verticals and the ties. The remaining 16 verticals do not require 100% coverage. I wired all of them at the top and bottom ties. For the remaining 3 ties I alternated one wired crossing (middle tie) and two wired crossings. Never skip two crossings in a row.

My wiring technique was sloppy at first. It got better. I used steel rebar wire (very cheap and widely available). Using pliers I followed the common wiring techniques I discovered on the internet. It is important to ensure the crossing rebars are pulled tight against each other so that the corrugations lock them together. These connections only need to survive the pouring of the concrete since they are not mechanically needed after the concrete has set.

Since some of my bends were imperfect a few of the verticals needed to be repositioned so that all the crossings had good contact. Squeezing them together by hand isn't always possible or advisable.

When I was done I was pleased to find that I achieved the requisite 3" spacing from all 4 walls of the hole. There were a few spots where I had to shave some dirt off the walls to get it right.

There are lots of crossings so take the time to check them all. Don't skip this step or the foundation can develop cracks in a few years due to water incursion and corrosion.

As you can see in the picture the rebar cage is not perfectly rigid. Each side has some play since the wired crossings don't fully lock the rebar. For that you'd need to spot weld the rebar. I lifted the rebar verticals from the bottom to move the cage in small steps until the bottom tie was the correct distance from all the hole walls. Scrap lumber wedged between the tops of the verticals and the walls temporarily squared the cage. In this way I confirmed the dimensions were correct for the entire cage. The props were removed for the next step.

Rebar chairs

Rebar cannot sit on the ground. Like the rest of the rebar they must be separated at least 3". This requires what are called rebar chairs. These can be as simple as concrete blocks, although there are commercially available chairs made of plastic and concrete. Concrete chairs have protruding wires so they can be attached to the rebar. Do not use stone, wood or other random material since they will decay or fail to bond with the concrete.

Since plastic is a poor choice for a cage of this weight, are difficult to get the concrete into during the pour, and I couldn't easily find proper concrete chairs, I went with concrete bricks. I found a suitable product at a local brick factory I was directed to by a contractor working on my house. Placed on their sides they are 3.5" tall, which is perfect. They were also unbelievably cheap. Do not use clay brick!

Not every vertical needs a chair. Use enough to ensure the chairs can hold the cage without sag or shifting of the cage. I used less than 10 bricks. Add or shave dirt under the bricks as needed to keep the cage level and all them taking their share of the weight.

Securing the cage

If you look closely at the previous picture you can see a tower stub sneaking into the frame. Clearly my pictures are not quite in chronological order. However it is useful for this next step.

The #12 section base stubs clear the inside of the rebar cage by only a few inches. The sides of the cage are ~53" on the outside and less than 51" on the inside. The stubs on the #12 tower section flare out to almost 46", leaving a gap as small as 2.5" (8 cm). It was therefore necessary to reinstall the temporary lumber blocks at the top of the cage when the base section and stubs were manoeuvred over the hole.

With the tower and stubs in position per the manufacturer's drawings I wired the stubs to the rebar cage. The tower section with stubs weighs close to 200 lb (90 kg) so pulling the wire tight did not shift it. The lumber blocks kept the rebar cage from shifting while I tightened the wires. I made sure there was good tension in all directions and removed the blocks. Some adjustment of the wires ensured that the tower and cage were in position and stable against moderate force.

In the next article I'll back up a step to show how I suspended the tower base section over the hole. That deserves an article of its own.

Cleaning up

When you're all done there is one more small task to perform. It is a good idea to use a steel wire brush to remove surface rust on the rebar and to remove any mud and dirt clinging to the rebar. Even newly delivered rebar will have some rust on it since steel readily oxidizes. Rust will weaken the bond with the concrete. Although a little bit of rust is not a problem cleaning takes only a few minutes. Not all the rust will come off and it needn't.

Mud and dirt will block concrete from reaching the rebar and can be a greater problem than rust. Dirt from the walls will find its way into the gaps where rebar crosses, whether tied or not, from banging and dragging against the sides of the hole during construction and positioning of the rebar cage. If the wire brush can't get into these small spaces use something smaller.

Monday, November 7, 2016

Digging a Hole for a Tower Foundation

You've selected a site for your tower, dealt with the legalities and the time has come to stick a shovel in the ground. What's the first thing you need to think about? It probably isn't what you might guess.

Debris removal

The base of the Trylon tower I am putting up requires 6 yd³ of reinforced concrete. Of course that means digging a hole that will displace the same amount of soil. That's a lot of dirt and rock! Where will you put it? How will it get there? You cannot easily hide that much on a typical suburban lot.

If you don't already have one, borrow or buy a wheelbarrow. Mine has a rated capacity of 6 ft³, which is not quite ¼ of a yd³ (27 ft³). In reality you will not and should not approach the rated capacity; 3 to 4 ft³ is the limit for safety and what the average, healthy person can handle. In other words, about 50 wheelbarrow loads.

The topsoil you will start with has some value. Put it in your garden or offer it to your neighbours. Unfortunately that will rarely amount to more than 2 yd³. Below that you will encounter rock, sand or clay, or some mixture of them. Putting up a sign on your lawn offering "Free Clean Fill" is unlikely to make the problem disappear.

On my rural property I have many available solutions to this problem. The stonier soil has gone to repair the ruts on my 100 meter long driveway. The soil will be used to fill low spots on the lawn. The large stones will go to the stone wall or will be used as paving stones when I get around to doing landscaping around the house.

I am fortunate. Chances are you are not. So think very carefully before you start digging.

Excavation alternatives to consider

Picking up a shovel and having at it is one way to dig a hole. Although it is hard physical labour it comes with a certain sense of accomplishment. One benefit is that you do it on your own time, when and how you want. Buy some refreshments and invite over your strongest ham buddies and you've got a social event!

Digging may seem simple but it comes with risks. If you are in poor physical condition or if you don't know your limitations or you use poor technique you can injury yourself. Mistakes multiply when you're tired. Take frequent breaks and know when to call for assistance if you're in over your head. Don't be stubborn where your health and safety are concerned. There are ample references to consult on tools and tool use so I will not give a tutorial on safe, efficient digging technique.

The second alternative is the same but with hired help. I'll bet that you, like me, know a few teenagers in the neighbourhood who would welcome the opportunity to earn pocket money. This helps them and you, and neighbours may look more kindly on your tower knowing that you've given their or their neighbours' kids an opportunity. However if you're fearful of liability in case of injury you may want to reconsider.

The final alternative is machinery. A small backhoe and a skilled operator can almost surgically dig a hole with straight walls and square corners. Some touching up afterwards with a shovel and you're done. Don't hire a fool or you'll pay the price of an unusable hole and a mess to clean up.

If you are sitting on rock or (worse) bedrock, you have a predicament. Rock can be removed with hand tools, though it's brutally hard work even when you use appropriate tools. You won't find those tools at the typical big box hardware store. I've dug several holes this way when I was much younger. You can rent a pneumatic breaker (sometimes called a jackhammer). Using this tool is harder on the body than you might guess. Take frequent breaks. And remember that the tool breaks the rock but doesn't remove it. You'll still have to shovel.

Backhoes with hydraulic breakers can be expensive and large. A small one is preferable for a typical city lot though they take more time. I've hired both for excavation outside the realm of amateur radio. The big ones are impressive (and loud) machines to watch. They're also very expensive and will assault your family's and you neighbours' eardrums. They won't like it. Be prepared.

One last note about safety: an open pit is an accident waiting to happen. Even if someone's pet, or worse a child, falls into the hole you could be in big trouble. Around here the hole is what the lawyers call an "attractive nuisance." Put a barrier around the hole when you are not working on it, or at least wrap some bright warning tape around the stakes.

Staking the hole and breaking ground

You've found the perfect spot for your tower, as far as possible from noise sources but not too far for your transmission line attenuation, clear of utilities and approval from family and city, and at least tolerance from your neighbours. It's almost time to break ground.

Purchase or make 4 wood stakes, or even scrap metal rods if you happen have them (re-bar works well). Mark the corners of the square excavation, setting back a bit from the corners so that they stay put when you start digging. Getting the stakes in the correct positions is not entirely trivial. Your ground may slope and making a square requires more than simply measuring each side.

Using a carpenter's square to make right angles doesn't work so well on the ground. Error will easily creep in over several feet. Start by pounding in a stake for one corner. Next measure the side of the hole and place the second stake the same way. For appearance sake you may want to choose a side that you can make parallel to a fence, house wall or other property feature. It will give a more professional and pleasing look to non-hams.

Now mark the positions of the final two stakes, but do not pound them in yet. We need to square the hole first. There is a simple technique from the building trade to help us out. In a square or any rectangle the diagonals will only be equal if the corners are all square. Measure them. The exact values don't matter, only that they agree. I've even used a yagi element and my thumb position to quickly and easily check diagonal equality since it's easier to use than a tape measure for this task.

I can almost guarantee that no matter how careful you've been you'll have some error. Move those final two stakes so that the diagonals are equal and all four sides are the required length. Only then should you pound in the stakes.


Get our your long-handled spade and push it into the ground right around the excavation perimeter. When you have the spade lines agree with the staked lines it is time to break up the sod and remove it. This can be harder than it looks since vegetation binds the soil into a solid mat. This is how vegetation prevents erosion and is used to reclaim deserts.

Proper digging technique and tools

Go to any hamfest and you'll notice that too many hams are unfamiliar with physical labour, or have left it behind in their distant youth. Digging is hard work. Big DXCC and contest scores are great motivators but they do not confer physical strength and endurance. Be prepared: use the right tools and techniques to do it safely and at minimal risk to your comfort and health. Otherwise hire the job out.

I will not give a tutorial on digging. There is so much to say and many have said it better than I ever could. Besides, would it really help you if I listed out a couple dozen pointers? That's a lot to keep in mind and learn to apply as you go about the job. Lists are no substitute for experience. Watch, learn and do, in whatever way works best for you, whether it be internet video or other online resources or simply watching someone else go about it.

Dealing with hard clay and rock

Organic-rich topsoil doesn't go down forever. Even out in the rich agricultural land of the Canadian prairie where I first dug tower holes it may only go down perhaps 3' (1 meter). Beyond that we had to deal with dense clay that was more difficult to remove. At my current QTH the topsoil quality is poor, thin (1') and only suitable for hay and pasture. After that is clay, rock and bedrock.

After removing the top 6" I again probed for stone and rock since I could get down that extra depth. What I discovered was worrying. To understand whether this was bedrock I dug a narrow pit that reached down 3' below grade. This went quite fast since the volume of soil being removed was small. Getting a shovel into the narrow hole was not easy and I eventually resorted to a hand spade. When I hit solid rock I stopped and tested what I'd found.


Most of the tools you're looking at were laid out for the purpose of the picture and do not necessarily should how I did the work. What did matter at this point was the large cold chisel and hand sledge. I got down on my belly, leaned into the hole and tested the rock hardness. It was a mix of shale, rock shards and hard stones. It didn't seem to be bedrock so while I was disappointed I was not entirely discouraged.

The next day I excavated down to that rock layer. Notice that the pile of dirt beside the hole is growing.

Luckily what I found was not bedrock. The soil at this depth transitioned to the hard stone-infested clay mix I talked about before. The stones became numerous and irritating. Even the small ones rarely succumbed to the shovel, instead requiring chiselling them loose. The bigger ones had to be dug around until the chisel could get underneath and pry them loose.

You cannot leave this rock behind when it's poking out the sides of the hole. Concrete does not bind to rock without chemical assistance, so water will creep over months and years and erode the concrete and re-bar.

In a way the large rocks were a blessing. As the depth increased I had to resort to using the chisel throughout the excavation to first break the soil so that the shovel could get purchase. Rocks simplified the work. That is until you encounter a very large rock.

Monster rocks

There are rocks, and then there are rocks. The one that the probe and pit uncovered was one of those. The size is what made me think that I'd hit bedrock. But it was difficult at first to ascertain its size. Trying to dig around it seemed fruitless for a while. Finally I discovered that it was somewhat flat, with a height less than its width. I breathed a sigh of relief until I realized how heavy it was.

When it did shift from its ancient position I found it too heavy to lift. With effort I could move it but I could not by muscle alone lift it out of the hole. I estimate its weight at 70 to 80 kg. One strong person or two of me could have done it. Since I was on my own and I did not want to wait a day or two for a friend to drive out to help I improvised.


A 6 foot length of 2x10 lumber I had lying around served as a ramp. My decades old hand-operated winch (which I once used to tension guy wires), a small tree and a rope were my helpers. The only problem was that the cable wound on the winch wasn't long enough to pull the rock far enough.

The middle panel showed my first attempt which ended in failure. I tried it this way so that I'd be close to the rock to check it in case it slid sideways and the ramp tilted. But the winch caught on the top edge of the lumber. For my second attempt the winch went above ground and I stopped frequently to check the rock's position.

The rock still could only be lifted a foot shy of the top of the ramp due to that short winch cable. I couldn't push it well enough from below so I pulled on the rope from above using the full strength of my leg muscles strengthened from years of cycling and running. It was enough, barely. I ended up sacrificing the corner shake which happened to be on the path of least resistance.

Although I did have a better winch it was one that was not set up for this style of operation. It's the one that I'll be using to lift heavy tower sections. The point is there is always a way if you have good mechanical sense, a large junk box of mechanical aids and a scrupulous attention to safety.

No shortcuts

Digging is hard work. Even if you hire teenagers with shovels or a backhoe you need to supervise, measure, direct and finally clean up any errors. As the bill climbs higher or you become impatient you may be tempted to tell yourself that it's good enough and rush to the next step. When you do it yourself your inclination to be hasty is increased. Your body and mind conspire to convince you that you've done enough.

Except you have not done enough. Don't be hasty and take shortcuts. Do it right. Here are a few items to watch out for:
  • The hole isn't square, either horizontally or vertically. Fix that, even if it means you'll need to order more concrete.
  • The hole is undersized at some depths. See the previous point.
  • Most foundations specs call for a flare at the bottom. Too many hams try to convince themselves it isn't needed. Hint: it is.
  • A large rock is sticking out from the side of the excavation. Remove it. Stone binds poorly to concrete and the boundary is a place where water will slip in to degrade the concrete and erode the re-bar.
  • As you go deeper the shovel will seem to bounce off the compacted soil, and what you do dig up has to be lifter higher to get it out of the hole. It only gets harder. You may try to convince yourself you've gone deep enough, or that you can go wider and shallower provided the concrete volume is equal. Don't! That it gets harder is a good sign since it indicates that you've reached soil with greater bearing capacity, and that's makes for a stronger foundation. Follow the spec. 
I'm sure you can think of more items to add to the list. Take no shortcuts. We can move on to the next and more interesting tasks when the hole is properly completed.

Casing the top of the base

When you're done with the digging you must also build a casing above ground so that the concrete surface is above grade. Do not skip this step. If you leave the base at grade water will easily pool and eat away at the tower galvanizing. Sooner than you realize it will begin to rust. Yes, It happens quite frequently, especially in colder climates where spring thaw can leave the base submerged in an ice/snow/water mix long enough to do real damage after several winter seasons.


The casing should be square, level and secure from movement while the tower is moved in position over the hole and while the concrete is being poured. If the ground is uneven you'll have to use wood or other material to fit the grade and ensure that on all sides the base is raised sufficiently above grade.

You can see my cased hole in the picture. The 2x4 skids on two sides are nailed in a fashion to hold the casing square and will serve as supports when the bottom section and stubs are suspended for pouring of the concrete. This will be described in more detail in a later article. The weights on the near corners are part of that plan.

Since the ground slopes a few inches I used a 2x10 on the near side and 2x6 on the other sides. The gaps are filled with other lengths of lumber. The casing and fillers are held in place with stone and dirt from the excavation. Alternatively stakes can be used to hold the casing in position and square, and larger lumber on the sides could be used at the cost of stripping sod on the high sides to keep it level. I used what was available and helpful for the next stops.

Once you're done...

Try not to leave the hole unfilled for too long. The longer the hole remains the more likely an accident will occur. In my experience I always feel some reluctance to see yards of concrete sliding into the hole into which I put so much effort and time. But there's only so much admiring you can do for what, in the end, is just a hole in the ground.

The only significant casualty of my open hole was an unfortunate field mouse. Perhaps the fall killed it or perhaps it was a combination of injury, exposure and hunger. Tak care that nothing larger becomes a victim of your hole.

We are getting close to the end. The next steps are to build and position the re-bar cage, suspect the base section over the hole and, finally, pour the concrete. That's coming up.