Tuesday, June 20, 2017

Antenna Swap: How They Play

I write this article with a light heart since at long last there is significant progress on my 150' tower. That story I will leave for another time since it is an interesting and lengthy tale. With that progress note I will return to my most recent antenna project. It has now been close to a week with the new antennas on the Trylon tower, enough time to speak about how they are performing and my immediate plans.

6 meters with the redesigned A50-6

On the very first DX opening I worked 9 new countries, and another the next day. This brings my total to 30 DXCC countries on 6 meters. This does not include the many more countries I worked back in the 1980s. I chose to reset my DX counters to zero when I returned to the hobby in 2013 after a 20+ year hiatus.

From my experience in the pile ups and marginal openings that the A50-6 up almost 24 meters is competitive with respect to big guns in this area of the continent. While there are better equipped stations and sporadic E propagation is fickle enough to confound easy comparisons I feel confident in stating that I have a very good signal on 6 meters.

Looking north from the top of the tower
The pattern is sharp, the F/B excellent and the SWR is not perfect but reasonable. Compared to testing on the ground the frequency of minimum SWR moved upward from 50.3 MHz to 50.9 MHz. Either the gamma match was disturbed while lifting it or there is interaction with the TH7 antenna lying 2.5 meters below it. I may yet push the A50-6 a little higher on the mast.

This success is despite using 40 meters of ancient RG213 that has more loss than new coax. Compared to the AVA7 Heliax I intend to use on VHF I estimate at least -2.5 db loss. That hurts a little, especially on transmit. In addition to the main run there is ~6 meters of LMR400 equivalent Ultraflex for the rotation loop and run up the mast and down the boom.

The old RG213 is contributing to the impedance problem since it measures ~47 Ω. For now I am using the rig's ATU to allow full power at the low end of the band by taming the ~1.7 SWR.

To alleviate common mode I used two snap-on ferrite cylinders at the feed point plus a 1-turn coax loop. It isn't perfect but the best I could do with what I had on hand. The clean pattern I am experiencing is a good sign.

I am eagerly anticipating the remainder of the sporadic E season. Unfortunately it is unlikely I'll have the AVA7 installed before band fades away. That requires a trench, burying it and other cables that are not yet in hand, and figuring out how I will terminate the ground end of the Heliax. I am not sure I want to bring this 1-⅝" coax through the wall and into the house! I would like to do all coax terminations and switching outside the house.

TH7 performance

This long boom tri-band yagi is performing about as well as expected. The difference between it and the short boom Explorer 14 it replaced is not something that is evident without a carefully done A-B test. This is impossible since I cannot have them both up at once. Suffice it to say that it certainly seems to perform at least as well. That's good.

What isn't good is that the match on 15 and 10 meters is not as it ought to be. On 15 meters the SWR minimum is at 21.375 MHz and on 10 meters it is 28.550 MHz. Both are too high and are not what they should be based on the measurements from the manual. On the other hand 20 meters resonates exactly as it should.

It is possible that there is a trap problem or I have somehow made an assembly error. Another area of concern is the rotation loops for both it and the 6 meter antenna since both run near the phasing lines between the two driven elements. This may be creating some imbalance and thus mismatch, and it would tend to be more noticable at higher frequencies. But I really don't know.

What I will do is raise the TH7 several inches to provide more clearance from the tower top. This will allow routing of the rotation loops in a way that would reduce interaction with the phasing harness. It will also reduce the likelihood of the rotation loops snagging the tower legs.


It is conceivable though unlikely that the balun I installed at the feed point is part of the problem. I replaced the Hy-Gain BN86 voltage balun with the more appropriate current balun from Balun Designs. It is wider than the BN86 so the arms of the feed point had to be spread a little.

Aside from that it fits surprisingly well and is a superior solution to common mode than a scramble wound coax choke. Although I do notice less computer and other local noise on receive compared to the scramble wound coax I had on the Explorer 14 there are likely too many variables to confidently say that the balun has significantly improved common mode rejection.

Loss of 40 meters for the summer

Taking down the XM240 certainly reduces my capability on 40 meters. This is acceptable for the remainder of the summer months when low band activity is lower than other times of the year. The only significant impact that I see is during next month's IARU Radiosport contest. Since I haven't decided whether to enter that contest I am not too worried. In a pinch I can put up an inverted vee.

The yagi has been disassembled and will remain in storage until I decide what to do with it. For expediency I may put it up at the top of the 150' tower. There is also the possibility that I will convert it to a W6NL Moxon. I'll wait and let circumstances dictate what I'll do when the time to act arrives.

An antenna for 40 meters at the height it was on the Trylon -- 21 meters, or λ/2 -- is needed for contests since it is a good height for short haul paths such as the US, Caribbean and even Europe. I intend to address that lack with a side mount antenna (to be determined) on the big tower.

Mast and tower load

With the swap of antennas on the Trylon I am now more comfortably set for storm force winds. The high wind load of the TH7 (approximately 12 ft²) is right at the top of the tower, which is far better than the 10 ft² of the Explorer 14 that had been 2 meters up the mast.

The wind load of the A50-6 is 3 ft² and it is only slightly higher than the Explorer 14 former height. Better yet, the maximum projected areas of the antennas are orthogonal to each other: on the elements for the TH7 and on the boom for the A50-6. Therefore they are never both present at one time.

In advance of doing a detailed calculation it appears to the best to turn the antennas orthogonal to high winds so that the booms face the wind. Back in the 1980s I had a similar arrangement with a TH6 at the top of the tower and the A50-6 10' (3 meters) above the tower, on the very same mast. That tower was lighter duty than the Trylon yet survived some fierce wind and ice conditions.

However that is no guarantee of future success. All is takes is one strong gust of wind to take it all done. If you wait long enough there will always arrive weather conditions that will take down any tower and antenna combination. The more conservative your approach the longer you will wait. All anyone can do is make that wait longer than your lifetime, and do regular maintenance.

One point about the current arrangement bothers me: the TH7 boom. The XM240 it replaced has a larger diameter boom that has also been strengthened per W6NL's prescription. Although thick walled the TH7 boom flexes quite a lot in the wind. When combined with the brake play of the Tailtwister rotator there is a substantial movement of the antennas and mast when the wind rises. Although not an immediate concern this sets up the possibility of oscillatory load adding to ordinary wind load. I plan to watch this closely.

Part of the larger plan

With the completion of the change from temporary yagis to a more permanent arrangement I am one more step along the road to realizing my antenna farm plans. For the summer my attention will be focussed on the big tower.

Sunday, June 18, 2017

Tractor Pull

Putting up modest towers and antennas can be done with a little muscle. Gather some friends, set up a pulley or gin pole, and haul away. Some food and drink afterward completes a fantastic day of learning, fun and a bit of work for you and other local hams. I highly recommend it. Just be sure there's at least one person there with the expertise and standing to successfully direct many hands.

As the towers and antennas grow in size and weight there comes a point where human muscle is not enough, or there is insufficient safety margin. There are too many hams unwilling to use safety equipment (even if only a hard hat and gloves) or too willing follow their own whimsy rather than the team leader. It's a disaster waiting to happen. Don't be afraid to handpick your crew from among those you trust to do the job right.

When I raised the Trylon I dispensed with a crew entirely until it came time to top the tower and put up the 40 meter yagi. This suited me since it was winter, my new property is a long drive for my friends and I wanted to do the work during weekdays when most people are at work. I overcame the challenge by designing and building a winch driven system for lifting heavy tower sections and antennas.

It worked well but was slow going. By relying on muscle to operate the system a 4:1 mechanical advantage in the winch was mandatory. It took a lot of cranking. It was safe and effective though slow. There are better ways. Those involve engines or motors, whether used in a crane, winch or...a vehicle. Thus we come to tractors.

I've used small garden and lawn tractors and far larger farm tractors to raise towers and antennas. All can work well if you use them appropriately. Power is both a blessing and a curse. Countless people have been injured or killed by machinery improperly employed or maintained.


Over the winter I purchased a garden tractor for mowing the large country property I own. I made sure when I shopped that it also would be up to the task of plowing snow and doing tower work. Luckily the parents of a business colleague were retiring from a hobby farm to the city and had a lightly used garden tractor to sell.

A deal was quickly made and I arranged transportation. The tractor sat unused for the remainder of the winter. Amazingly it promptly started in the spring despite being out in the weather with no more protection than a tarp and without recharging the battery. It has since been used for its primary job: mowing the grass. I have also driven it into the hay field to create (hopefully) tick free paths to my tower excavations.

Ropes and pulleys

Using a tractor or any powered vehicle for hauling objects up and down a tower requires a few simple techniques. However they are very important for a safe and successful procedure. In the following picture the key aspects are visible.

Ground crew: Brian VE3CRG on the tractor and his wife Mollie who handled the tag lines

This is the Cushcraft XM240 immediately after it has been lowered by the tractor. The tractor held it above ground while the fragile capacity hats were removed. Notice the pulley attached to the bottom of the tower. The pulley two things. First, the forces at the top of the tower and mast (where there is another pulley) are kept vertical. Otherwise the bending moment on the tower could cause structural damage. I discussed this topic some time ago with regard to gin poles.

Second, a garden tractor is not so massive that it will maintain contact with the ground were the rope to angle upward. The pulley translated the vertical force to horizontal so that the tractor has maximum traction.

The pulley is attached to the tower since it is a convenient and strong place to take the large forces involved. The pulley pivots upward approximately 45°, so keep that in mind when choosing an anchor point. Since the antenna is only 75 lb (35 kg) I went with the simplest attachment option: ¼" aircraft cable with a couple of cable clips. A better choice is a chain to reduce chafing and stress for heavier loads. The only suitable chain on hand was used to couple the rope to the tractor frame.

Some go further and fabricate a heavy gauge steel bar across the tower base which eliminates pulley motion upward. Although the cable could be made shorter to limit upward motion its length reduces chafing of the rope against the side of the tower. This method has a limit since if the pulley moves up too high the tractor can lose traction.

Measure the work area

Before using a tractor in this fashion you must clear a path for it that is reasonably flat and long enough radially outward from the tower base. If you run out of room you're stuck with an antenna dangling midair and no where to go but back where you started.

The XM240 was mounted 21 meters (71') above ground. I measured 30 meters (100') out from the tower as the starting point for the tractor to lower the antenna. This is not only to ensure that the tractor does not run into the tower before the antenna reaches the ground but also to keep the tractor out from under the antenna when it drops to the ground. In the picture above the tractor started its journey at the line of trees in the background. You can see the tire tracks in the grass.

The rope is 200' (60 meters) of ⅜" nylon. This is the minimum recommended for this operation. With the pulley mounted 75' up there is 150' required to go up and down the tower and 30' on the ground for the tractor to stay clear of the antenna. Another 5' to 10' is used for harnesses to the antenna and tractor. Very little is left unused.

To lift the TH7, which is about the same weight and breadth as the XM240 the process is reversed. The tractor pull starts at the edge of the antenna and backs away to lift the antenna. Whether lifting or lowering the tractor operator is facing the tower and rest of the crew.

Power is dangerous

As I tell the ground crew: you can't argue with 22 horsepower. When something goes wrong and you put up a fight the tractor always wins. When antenna hardware snags in the tower the tractor keeps moving. When a crew member gets tangled in a rope the tractor keeps moving. When the antenna or tower section strikes the pulley atop the tower or gin pole the tractor keeps moving.

Modern small tractors for residential use are surprisingly forgiving machines. Say you brush against a building, tree or large rock. Often the tractor will "see" the resistance and let the clutch spin. While this helps keep the crew safe it should not be relied upon to avert a disaster.

Older tractors are less forgiving: they'll just keep going. That's when someone can be seriously hurt. For large farm machinery or a truck there are fewer if any safety features, and the power is far greater. You are better off employing the smallest machine that will get the job done.

I've used garden tractors to successfully lift 200 lb tower sections. Only use more powerful machines when the operator is sensible and experienced.

Tag lines

Use tag lines to direct load around obstacles and to prevent snagging hardware on the tower, guys and side-mounted antennas. Tower sections require only one tag line while yagis should have two. For tower sections tie the tag line near where the lifting rope or cable is tied but on the opposite side. For yagis place one on either side of the boom cradle. The two 100' tag lines are visible in the picture above.

It is generally better for only one crew member to handle the tag lines. Little force is required so this is not a problem. When there is a person on each tag line I can almost guarantee they will find it difficult to coordinate their attempts to steer the yagi..

The crew handling the tag lines will be the first to know when the load snags on something or is about to do so. Give them the authority to stop the operation immediately when they detect a problem. The tractor operator must be prepared to quickly react.

Crew taking a well earned rest
Traction

Tractor power is of no use if the wheels spin on the ground. Excess power only makes the problem worse. Garden tractor engines are designed to use the power for mowing, not so much for hauling.

On wet grass or snowy ground a small tractor can easily lose traction under load.  This occurs more often when lifting rather than lowering.

On uneven ground if one drive wheel has poor ground contact the differential will spin the lifted wheel and apply no torque to the other one. A tractor with a more sophisticated drive train is desirable if it is available. Otherwise plan the route for the tractor will extra care.

When traction is lost determine the cause. Many problems can be solved with more weight over the wheels. Some tractors provide an area where weights (stones, bricks, etc.) can be placed. In a pinch have one or two crew member jump onto the back of the tractor.

If you can't solve the problem you'll likely have to lower the load back onto the ground and try something different. Larger tractors are unlikely to lose traction with the weight of loads hams typically lift, however there is greater risk of injury and damage from all that power.

Communication

I cannot overly emphasize the importance of communication between the tower crew, ground crew and tractor operator. Agree on hand signals or voice commands beforehand, and practice if you can. Handheld radios can be very helpful. They don't have to be ham band devices. However you do it remember that tractors are loud and so you cannot always rely on shouting to get the message across. We want the tractor operator facing forward at all times so that they can see and respond to directions from other crew members.

Although we are all friends there must be a command hierarchy. In this hierarchy the tractor operator is at the bottom. That is, when anyone else tells them to stop or go they do so. Make sure he or she understands this. Don't assume they'll obey. No one, no matter how responsible, should be allowed free reign over the power they are handling.

As with all tower work the highest authority goes to those on the tower. Next in line is the ground crew. As already mentioned, last in line is the tractor operator. This arrangement strikes a balance between vulnerability and the potential to cause harm.

Don't hesitate to call a temporary halt to the operation if anyone is having difficulty coping or there is a point of confusion. Everyone should have this authority and not be timid about using it. The tractor operator should know how to lock the wheels when necessary.

We did have a few instances of miscommunication even though we all understood what needed to be done. Corrections to our procedures were made as we went along. No harm was done.

Finished

In the picture the TH7 dangles atop the tower under tractor power, and a properly set brake. After taking this picture I climbed the tower (wearing a hard hat) and bolted the antenna in place. We used the tractor to adjust the antenna height by a few inches to put it exactly astride the mast bracket.

The A50-6 was hand lifted since it is light and relatively fragile. It is best to avoid tractor power in this and similar cases. Always use the right tool for the job. It went up first since it goes highest on the mast. The TH7 must be carefully handled so that it does not tilt upward and strike the smaller VHF antenna.

It was getting late so we quit once the antennas were in place and the tractor and ropes put away. The next day I went up on my own to finish the job. This involved pushing the 6 meter yagi higher up the mast, removing the pulleys, pointing the antennas, attaching the rotation loops and testing that everything worked. Back on the ground I disassembled the XM240 and stored it and the Explorer 14 out of the way until they are again needed.

Both antennas use the RG213 runs I already had on the tower. This was not my intention. I ran into some difficulty preparing Heliax runs in time. I'll deal with that later.

In my next article I'll report on how the antennas play. For now I will only say that I am generally pleased with their performance. For the foreseeable future these are the only yagis going on this tower. Other than perhaps a 2 meter yagi for VHF DXing. This is part of my broader plan for the station.

Next tractor job

I will next use the tractor with a gin pole to construct the 150' tower. Each tower section weighs 120 lb and there is additional hardware that is similar weight. With an experienced crew the tower should go up quickly, with the tractor providing most of the muscle.

I may use the tractor to tram yagis to the top and sides of the tower. Muscle power will be used to raise Heliax and other fragile station components. Sometimes 22 HP is too much power.

I love a crew that tidies up the job site without being asked

Tuesday, June 13, 2017

Spinning My Wheels

Activity on the station is happening yet I have little to show for it. Ambition and property are not enough. With little accomplished in the preceding weeks there is little to talk about in the blog. In any case summer is a time for being outdoors rather than sitting in front of a screen. Not all of my outdoor activity is amateur radio related.

I decided that rather than go quiet I would give a progress report of sorts. This is perhaps boring reading. All of this nothingness is however necessary prelude to concrete steps in fulfilling my ambitious plans for 2017. So if you can handle a little bit of boring reading continue onward and you'll see what has been going on at VE3VN.

Big tower

Nothing of note has happened. True spring weather has arrived and the ground has solidified enough for heavy equipment to work in the hay field. Unfortunately it didn't happen soon enough. Now the company doing the foundation work is busy with commercial projects. They are searching for a hole in their schedule when they can get over here and finish it off.

I have abandoned my own futile attempts to clear the winter-damaged excavations. The slumped soil is too waterlogged for shovel work. I had hoped to clear enough debris to ease the removal of all the steel in the anchor and base holes. Now we'll have to use the backhoe and risk damaging it, and taking time to repair the damage.

Growing hay between me and the 150' tower excavations

A further problem is that the hay is growing very high due to the record breaking wet spring. I cleared a few paths but it is still difficult moving around. Hopefully the hay will be harvested later this month. Worse still is that the high grasses are full of ticks. Even with protective clothing they find a way through. It is no fun dealing with these stealthy disease carriers. For the same reason I have put off work on the Beverage and other low band antennas until late summer.

The tower itself requires minor repairs to several sections which I've deferred until the concrete work and back filling are completed. I can only wait at this point.

Other towers

I like to trade favours by doing tower work for others. This may take the form of helping me with my tower work or other assistance. I never charge money. I never even expect favours to be returned though they almost always are. It's simply about hams helping hams.

I wrote about one small tower that I took down recently and I have another larger tower to take down in the next week or two. The make of tower is unknown so I had to take measurements on site and build a gin pole for it. This tower, too, is slated to go to another ham I know.

Preparing coax

Before going to Dayton I took a detailed inventory of all the Heliax in my possession. Some of the used runs have connectors on only one end because the other end was cut where it entered a building. All the coax, including my own ancient runs of LDF4, must be tested and refurbished, and connectors added as needed.

Testing Heliax in the garage. Notice the antenna analyzer. Gin pole construction on the left.

Most of the Heliax has N connectors, including a few UHF-N adapters, but some use 7-16 DIN. There is some weather damage that requires repair. Unlike braided coax water typically does not penetrate far into Heliax. But it still requires removing the connectors and cleaning them, cutting off the damages sections, then putting the connectors (or new ones) back on. It's a lot of work.

The cable itself must be tested, both before repair work and after. Large, heavy rolls of Heliax dwarf the test equipment. Larger equipment, such as transmitters and power meters must go to the coax since the Heliax cannot be brought into the shack! Luckily my garage is now built and electrified, and that is where the work is being done.

For the rotation loops I am using LMR400 equivalent Ultraflex cable. I have had too much trouble with RG213 in this application during the winter when the cold temperature stiffens the plastic.

Ordering aluminum and steel

Big yagis need a lot of aluminum for booms and elements. There is also the cutting and machining of plates and channels for the multitude of clamps. I have an assortment of surplus pipe arriving shortly that will serve as both boom material and potentially as part of a full size 40 meter yagi. However that yagi project is being deferred to the future.

As I proceed through antenna modelling and mechanical design of yagis for this year and next I build spreadsheets to count up the sizes and lengths of aluminum and some structural steel I'll need. Since tubes and pipes come in standard lengths I have to figure out where the cuts are to made in advance so that I make maximum use of the material. Tubing and pipe isn't inexpensive.

I have in hand all the guying hardware for the big tower, and also for the future 80 meter array. That's a lot of steel. I'll have more to say on this later since it is an important and interesting topic. Building of the guy cables, complete with breaking into non-resonant lengths will only be done after the tower concrete work is done. I tend to practice JIT (just in time) for all my projects.

Antenna swap

The Hy-Gain Explorer 14 and Cushcraft XM240 on the Trylon are coming down very soon. These were temporary antennas to get me through winter and spring contests and general operating. Both will be going elsewhere, once I have more towers raised.

Friends are coming over to be ground crew for this. Both antennas are heavy enough to benefit from mechanical assistance. This time I will dispense with the winch and human muscle power and put my garden tractor to work. I'll take some pictures and perhaps write an article about how to do it.

Once these antennas are down I'll be raising antennas that will be more permanently attached to the Trylon. These are my recently redesigned and rebuilt Cushcraft A50-6 and the Hy-Gain TH7 I have had in storage for past year. The TH7 is assembled, tuned and mechanically refurbished. I completely replaced the boom truss since the old hardware was badly rusted and missing a key component. In Dayton I purchased bag fulls of replacement trap covers and element tips for my several Hy-Gain yagis and for the XM240.

TH7 ready to go

The TH7 will go just above the tower top plate (where the XM240 currently resides) and the A50-6 will go about 3 meters above it. In future I may add VHF and UHF yagis in between. Both antennas will be fed with Heliax: LDF7 for VHF/UHF and LDF4 for the TH7. If I don't have time to prepare the Heliax I'll stick with the RG213 runs for the present. The Heliax can be put up later.

I desperately want the 6 meter antenna before I miss more of the Sporadic E season. The redesigned A50-6 up 24 meters should do well for long haul DXing. The TH7 is for general operating and for short haul paths, such as the US and Caribbean, during contests. Bigger and higher antennas for Europe and long haul DX (low elevation angles) will go on the big tower.

Grounding

That's a 10' (3 m) long ground rod
Towers and lightning are inseparable. Protective measures are mandatory with size of towers I have going up. I've been planning how to go about the task to assure that protection with a reasonable amount of cost and effort.

As a first step I have grounded the Trylon and the bracketed tower for internet access. Pounding a 10' ground rod into the ground is not easy. I would whack at it with my sledge hammer a little each day. The hardened tip of the rod can break small rocks on the way down.

Eventually I got it in all the way. Fasteners are commercial quality and supplemented in some cases with stainless steel parts to avoid dissimilar metal corrosion. I have an ample supply of heavy gauge copper wire that I've saved over the years.

Locations for trenches for cable burial are being planned. I have a difficult job with that due to the many trees (roots!), a stone wall ringing the house and farm equipment working the fields. Although no cables can be buried for their full length I expect to be able to bury them all from the towers for some distance. That will help dissipate lightning discharges. I will rent a trencher to do the hard work.

Depending on how I do antenna switching and control the protections added near and around the house are not final.

Renovations and much more

A big distraction is the ongoing renovations of the house. Although not directly related to ham radio this is added a lot of stress and demands constant attention. This phase of the renovations should be complete before the end of June.

Aside from living space disruptions and endless decisions to be made the renovations have incurred some small disasters. The worst was failure of the sump pump system that resulted in shallow flooding of the basement. I was not pleased. Once the workers leave I will have more time and energy to devote to the station. I am not operating much these days.

The only part of the renovations which is radio related is ensuring that partitions and services in the basement are compatible with the main shack to be located down there. It will be have at least two operating positions for contests and amenities for the operators. Power for amplifiers, stations and work bench has been planned with the help of an old ham friend who is a retired master electrician.

A 50 acre property requires more maintenance than a small city lot. Although little of it requires regular attention there are several acres that need to be maintained. None of it is difficult, it is just something that consumes time and the purchase and maintenance of gasoline powered tools.

I have landscaping and other grounds projects planned, though I expect not this year. This year is dedicated to towers and antennas. Renovating the rest of the house will happen no sooner than this coming winter, once the outdoor station work is finished for the season.

And of course it is summer after all and that means simply getting out and enjoying the weather. I do not apologize for putting amateur radio aside when the outdoors beckons. The station work will get done. It is a hobby not a job.

Tuesday, June 6, 2017

Entertaining the Neighbours

Here we are now, entertain us
--Nirvana
While I was effecting repairs earlier this spring there were a few workers below who were building my garage. Several times I noticed them looking up towards me. During breaks they'd sit there having a smoke and again gaze upward. They seemed especially interested when I manually twirled the stack of yagis back and forth through their full rotation to test the coax rotation loops.

The crew lead had a smile on his face when I was back on the ground and commented on how much fun I seemed to be having. Curiosity is natural and I'm used to this kind of attention when I climb towers. In turn I often found myself watching them go about their jobs, also out of curiosity, and with a eye to learning how they do what they do.

Even without any nearby neighbours in this remote rural area a few times while on the tower I noticed passing cars slow down to watch me for a few seconds before continuing on their way.

I was reminded of this behaviour once more when I recently took down a small TV tower that a fellow ham had his eye on. He wanted it and the owners wanted to be rid of it. For me it was the pleasure of helping others and distracting myself from the ongoing delay in resuming my own tower work. The rain is pouring down as I type these words.

This last case was a picturesque neighbourhood on a lake shore with a mix of permanent and part-time residents. As we got to work a small crowd gathered. Several of the owners' neighbours came by to chat and watch me work. What was for me a routine task was for them a novelty. Over the 45 years of being a ham I've become used to this sort of thing.

I first noticed this phenomenon back in 1974 when I put up my first tower. Nearly every time I climbed the tower I noticed a few people come out on their decks, sit with their chairs in my directions and quietly watch. Occasionally I would catch a glimpse of a face peering out at me through a window. This suburban area of bungalows in Winnipeg (VE4) was newly built so there were no trees to impede the view.

As I did an increasing amount of tower work for others, back in Winnipeg, then Ottawa and elsewhere, the same thing would occur. Inevitably there were watchers in the neighbourhood. A few would come over to chat with the tower owner though most were content to sit and watch from their own yards.

In the early days I admit that I was annoyed by the attention. I couldn't help wondering if they were hoping I'd fall, damage houses through carelessness or had other unworthy reasons. Perhaps they were busybodies looking for a reason to call the authorities and make trouble for me. Those were the days when TV RFI was a commonplace phenomenon and I was always a bit on edge when meeting the neighbours. Being young and unsure of myself didn't help.

Over time I learned to relax. In conversations with some of the watchers I learned that to most people towers are quite intimidating. A few told me of their concerns of an accident occurring and couldn't help paying attention in case their assistance was needed. Others told me of their fascination with an activity that, to them, appeared both dangerous and intriguing. No one was against me.

At worst I provided a mild form of entertainment and at best it was an ice breaker.

I will now preach. But just a little bit. While entertaining the neighbours is harmless it also serves as an opportunity to demonstrate that amateur radio operators are considerate, dependable and knowledgable neighbours. Over the years I have taken to improving my safety practices and those I work with, especially so when working on others' towers, and even more so if the tower owner is not a ham. I have discovered a sense of duty for our hobby.

It inspires confidence when we show up with and use safety equipment. This is not limited to climbing harnesses. Hard hats are incredibly cheap and I make sure I have enough on hand to pass around to the ground crew. I insist on their use. I explain to everyone, including spectators, what I am doing and why I am doing it. This includes the deployment of safety lines and other precautions to prevent property damage.

There will always be those without an interest in the details, though most appreciate that explanations are given. They may only be interested in understanding that the job is being done competently despite being performed by amateurs. In this most recent job I went so far as to explain why some of the equipment I use would never be used by professionals due to increasingly strict workplace practices regulation.

Well, that's enough preaching. Be safe out there and be sure to use tower work as a form of community outreach. We want hams to be seen in a good light. So don't mind the attention we attract, or the entertainment we provide.

Thursday, May 25, 2017

Dayton Hamvention Recap

Rain was one of the defining characteristics of this year's Hamvention. It got very wet out there in the grass fields used for parking and the flea market. The rain even followed me home, making for a somewhat gray and depressing drive. That is, other than the conversations with my fellow travellers.

Rain also featured on my return. On Monday (a holiday in most of Canada) the tower service company called and delayed completion of the foundation work for my big tower, again. And then again midweek. We apparently got several centimeters of rain while I was away and more is in the forecast. May rainfall has broken all historical records in much of eastern Ontario.

While the rain falls and tower work is delayed I have a few moments to write down my experience of Dayton. It's been 25 or 26 years since my previous attendance and much has changed. When you frequently attend an event changes might not be obvious since each step is small. In my case it was one very large step crossing from one generation to the next. Already by 1990 the Hara site was deteriorating so the move to Xenia is appreciated and needed.

I'll quickly step through my experiences, touching only lightly on each to keep this article brief. I do not need to repeat what everyone else has had to said about the Hamvention.

Mud: The reports about it are true. Continuous traffic in the wet turf parking areas turned them into lakes of mud. Rev the engine with the wheels on solid turf to gain the momentum to get over the hill of mud and reach pavement. The messy flea market kept many people away on Saturday but not enough to bring down prices! In the hope of great deals I waded into the muck. Even so I still enjoyed myself. I crossed off many of the lines on my shopping list.

Access by road: Friday was hell and then got remarkably better on Saturday. I got out of the car on that first morning and walked the last few miles. I'm a distance runner and cyclist so this was no great effort. Aside from the pleasant walk past the miles of cars it was a surprising opportunity to meet old friends and make new ones. I was frequently slowed by pleasant conversation.

Flea market: There was less junk than I remembered. I expect most of the old, heavy equipment is now in landfills. The equipment on display was of more recent vintage, and the selection was great: from parts for the QRP experimenter to big gun equipment such as prop pitch motors and Alpha amplifiers.

I stocked up on Heliax connectors and adapters even though most of what was available was 7-16 DIN. These are great connectors but I need more N connectors at the tower and station ends. I can use DIN to splice lines, especially at the tower bases for grounding cables. There were few extreme bargains in the flea market, though I found a few. The DIN to N adapter was a pleasant surprise. The free DIN to something adapter next to it remains a puzzle. The seller didn't know either so he kindly made a gift of it to me. Conversation in the flea market was friendly and unhurried. It was well worth the mud spatter.

Getting around: Because I carpooled to Dayton I did not have my own transportation while there. This became a problem since I was dependent on others and could not attend everything I wanted and had to travel even when not convenient. I walked when the distances weren't too great. Others were happy to help out in a pinch, for which I'm grateful. These included Glenn VE3XRA, the president of RAC, a ham from HamNation in a vehicle with WKRP TV plates, and of course from my fellow Ontario contesters I shared rooms with. Next time I plan to take my own car.

Forums: I attended a few of these. It's something I eschewed in years past since I generally was more interesting in shopping and meeting people rather than sitting and listening to presentations. Perhaps I changed. Without going into detail I'll mention the best talks I heard. The best was by Dr. Tamitha Skov of Space Weather fame. She was informative and entertaining and spoke well to a ham audience despite not being one. Second best was by W5OV of the CQWW contest committee who took on the disqualification controversy with panache and humour. I suspect that even the guilty parties would have enjoyed the talk. Talks I disliked were thinly disguised sales pitches.

Contest hospitality: I attended the hospitality suite Saturday evening after the contest dinner. I did not attend the contest dinner since I am bored by speeches and turned off by the food. Reports indicate I was right on both scores. However I did miss out on some interesting table conversation. The hospitality suite itself was very tame. Years ago it was often a wild affair with bathtubs full of ice and beer, impromptu pizza orders, pursuit of operators for multi-ops and less savoury activities in the wee hours. But we were all younger then, and it is much the same people. With age many like their comforts and the level of organization, while commendable, made it a somewhat dull affair to my eyes. That said, there was much enjoyable conversation to be had.

Attendees: Most attendees were like me: white, male baby boomers. But not all. There were far more women in attendance and all people of all colours and ethnicities. More young people than I expected were there, far more than are seen at Canadian events. US hams are doing a better job recruiting youth, and I hear that Europe is doing even more. However ham radio will not be the same once the older generation passes. For the present the numbers and activity levels are there, and well represented in Dayton.

People: I rubbed shoulders with some well known hams. I'll mention two. One was Nodir EY8MM. I made a point of speaking to him since he has a long acquaintance with a good friend of mine who asked me to pass on his regards. Notice the camera in his hands. On his web site you'll see some of the excellent photographs he has taken, many of which are from the DXpeditions he's been on. If you're a DXer you've certainly worked him. The other person is Richard K0XG of rotating tower fame. A pleasant chat with him ensued in the course of my friend negotiating the purchase of a prop pitch motor in the flea market muck.

Product: As noted everywhere there were numerous products introduced at Dayton. I saw it all although I avoided the lineups and crowds around those exhibitor booths since it is not the best way to learn about the products. I'll wait for the reviews. One display of note was Flex Radio that had several Maestro remotes connected to stations around the continent that you could listen and tune around on. That was a nice touch.

LUSO120US (I believe)
The only other product I'll touch on is the Luso crank up tower you see pictured here. From all the other cameras present I'd guess it was the most photographed product at the Hamvention. It looks impressive with a price to match.

Without deriding Luso I do question the value for money. With transportation, heavy equipment, concrete and other costs I strongly suspect that for those hams that do not climb towers it would be less challenging and more cost effective to go with a conventional guyed tower and pay a professional climber to raise and maintain antennas and related equipment.

Of course there was a lot that I missed in the flea market, exhibits, forums and social venues. I picked my spots and did not rush about more than necessary. I expect that I'll attend again next year or the year after.

Wednesday, May 17, 2017

Surrounded By Turkeys

In my remote QTH there is ample wildlife. Deer, foxes and coyotes are the most frequent visitors. Beavers are a local pest since they damn creeks and wetlands causing road washouts and other problems. Countless chipmunks make homes in the piles of dirt I have lying around from all the tower excavations.

In the past couple of weeks I have getting increasing numbers of another species of wildlife: turkeys.


The smartphone camera doesn't do them justice. They were closer than the picture would make it appear. And they're big. Up to a dozen at a time can be found foraging in my hay fields. Despite popular lore about these birds they are not so stupid as to fall into any of the remaining tower excavations.

Speaking of excavations, completion of the tower concrete work has been scheduled. Assuming success I can start erecting the 150' tower at the end of this month. I'll have more to say on the topic as soon as I'm ready to go.

On a final note, I will be at the Dayton Hamvention for the first time in 25 years. Aside from shopping for parts and equipment I'll most likely be haunting the contest venues. If you see me there say hello. I'll be wearing this:


Sunday, May 14, 2017

Correcting Tower Lean

I've straightened towers that have developed a lean. It's usually a routine repair job. However like any structural work on a tower it can be hazardous if you become careless. If you are at all uncertain of how to go about or if your knowledge of towers is weak I suggest hiring an expert.
In an earlier article I mentioned that my Trylon tower is not vertical. In this one I'll talk about correcting lean in general and how I corrected the lean in my current tower.

Effects of wind, ice and time

Over time self-supporting towers can develop a lean, sometimes quite pronounced. Most often in my experience the lean is away from the direction of prevailing winds. For most hams this means a lean towards the east since in mid-latitudes the prevailing wind is from the west. Major storms are the exception, which can push the tower in almost any direction.

If the tower was perfectly vertical when installed lean can develop for a variety of reasons:
  • Poor quality or missing fasteners: Unrated or improper fastener selection is almost always trouble waiting to happen.
  • Inadequate torque on splice bolts or other fasteners: Do you know how many inch-pounds of torque splice bolts require? Tightening large bolts while strapped onto a tower is difficult but must be properly done. Large size grade 5 hardware requires a lot of torque.
  • Excess antenna load: Overloading a tower might not bring it down but it will place it under severe stress that can bend structural components, and shift or shatter fasteners. I've seen many leaning towers that lean directly away from the prevailing wind direction.
  • Inadequate foundation: Some hams fail to construct a proper base for reasons of cost or inconvenience, or are simply negligent. A compromised base must be dealt with immediately; that is, the tower must be taken down before it chooses the time on its own.
Towers can be curved or lean when first built due to construction problems:
  • Bent or improperly aligned sections: Towers like the Trylon that rely on bolts to connect all the structural components must be properly aligned during construction, whether by the factory, the dealer or you. Do it wrong and the tower will lean. Bent components have a similar effect. Even when properly built rivets and bolts can wear or loosen and welds can crack.
  • Poorly seated section splices: If the upper section is not sitting on all the splice bolts it will not align with the lower section. This can occur since the holes are typically larger than the bolts.
  • Crane lifts: Many hams splice many tower sections on the ground and lift the assembly by crane. While faster and less dangerous than using a gin pole an improper lift can severely stress the tower. Splice bolts slip or, worse, structural members bend or break.
Problems can be delayed or entirely avoided with regular tower maintenance. Check all fasteners and structural components at least once each year. In areas with extreme temperate swings between summer and winter consider doing it twice yearly. After a severe wind or ice storm sight along each tower leg and face to look for changes. Use a long level if you don't trust your eyes.

On a guyed tower regularly measure the pre-load tension in all guys. Guying hardware may be failing or the anchors may have shifted due to faulty design or construction, or soil movement due to floods and seismic events. Guy tension drops and the tower wobbles or leans. There is a substantial risk of structure failure.

Considering a repair

If you discover or suspect the tower is leaning immediately perform a thorough inspection. Identify the locations where the tower deviates from a straight line. Most often it'll be a section splice. That's the type of repair I'll cover in this article. Other damage such as broken rivets, bolts and structural components or a shifted or broken foundation are more serious and must be dealt with before the lean can be addressed. It may be unwise to climb a tower with damage of this type.

Let's proceed under the assumption that the lean is due to nothing more serious than splice slippage. Before we begin it is recommended that all splice bolts be inspected for proper torque and structural components for cracks and bends. If a splice has slipped it is possible that there is less visible trouble lurking elsewhere due to the same stress event(s).

My tower

The lean in my tower is mainly due to the way I put it up. The gin pole I built had a few design flaws, one of which caused the pulley to occasionally jam against the section as it was being slipped into the one below. The low width-to-length ratio of the lower sections made it difficult to get them to sit vertically well enough to seat itself on the bolts. The ⅝" bolts for the bottom splices were difficult to torque since I have only one 15/16" wrench and it isn't nearly long enough.

The winter was cold and I did not always take time to correct errors when they occurred. Although I did notice most of the problems as they occurred each on its own seemed minor. Deviations from the vertical are amplified as you go up, and that caused a noticable lean. Well, at least I noticed it. None of the hams who've visited noticed it without me drawing it to their attention.


The photography skills to capture the lean is beyond my skill. These pictures underplay the extent of the problem. I added a closeup of the southwest leg since that is the leg with poorly seated splices. The southeast leg is seen on the right.

The worst splice is between the #10 and #9 sections. The splice between the #12 and #11 sections is more subtle but contributes a lot to the lean since it is the base section. Although there are a few smaller deviations higher up the tower they are not of immediate interest. It is the two mentioned splices that I intended to correct.

The geometry of improper section splicing

The small amount of play in the splice bolt holes can have a surprising impact on the straightness of a tower. It can be approximately modelled by a rectangle representing the face of the upper tower section.

In the domain of small angles we can simplify calculations using the approximation:
x = sin x = tan x, where x is the angle in radians
The upshot is that the ratio between the bolt slippage and section width (W) is equal to the ratio between the offset at the top of the section and the section height (H). The approximation works well whether you measure W at the top or bottom of a tapered tower section.

For example, with bolts sitting 1/16" high in the splice holes, W = 24" and H = 96" the top of the section is offset by ¼". The lean angle α = 0.15°. If there are 6 sections above the improperly done splice the offset will be 1.5" at the top of the tower.

In my case the lean is worse since there are two sets of poorly seated bolts and one has an error worse than that of the above example. Standing on the top of the tower the lean is very noticable.

Lean correction procedure

I waited for a day with little wind, no rain and no one in the vicinity except me. This took a while because of the horrid weather we're having and the regular presence of workers doing house renovations.

I tied a rope between the southwest leg ⅔ up the tower and a suitable anchor to the southwest. The impromptu anchor is a post supported a balcony on the house. The strength of the rope and anchor is not critical since the required tension is only in the tens of pounds. The balcony is in no danger. We want just enough force to encourage the tower to sit back onto the splice bolts when they are loosened.


The 2 ton winch is certainly overkill. I used it because it made it easy to finely adjust tension on the rope. You can set the tension by hand if you prefer, in which case I suggest using a temporary rope cleat to allow a similar and rapid method of adjusting tension. The ladder you see in the picture belongs to the renovators, not me. To the left you can see a few elements of the Hy-Gain TH7 I am assembling.

To begin we put some tension on the rope. I prefer rope over steel cable because it is more forgiving of excess zeal. Stop when there appears to be just enough tension to draw the tower back when the splice bolts are loosened.


For the next step it is necessary to loosen some of the splice bolts. The picture shows the #11-#12 splice on my tower. At the centre is the southwest leg. All 4 bolts on that leg are loosened, but only enough for the lock washers to relax. Do the same for the nearest 2 bolts on the adjacent legs. This allows the tower to pivot on the back legs without stressing the steel. The 4 bolts on the opposite face are not touched.
Note: The bolts you loosen are different on towers with tubular legs (e.g. Rohn) or towers with bolts on one surface of the legs (e.g. DMX). Even so the basic procedure is the same. It is fair to say that adjusting the Trylon is the more complicated of the three because of the leg shape. The big guyed tower I am putting up this year, the LR20, has the same splice bolt and leg pattern as the Trylon. The procedure is similar on the LR20 but with modifications due to its being guyed.
Don't be surprised if you see no movement of the tower when the bolts come loose. The amount of downward motion is slight and may occur in small steps as each bolt is loosened. With the selected bolts loosened I returned to the winch. I discovered that the rope was quite slack, so obviously the tower shifted in the desired direction. Looking up the tower from the bottom the shift was visible. I put tension back on the rope in small steps until I was satisfied that the bolts were fully seated. On the tower I could tell by the fact that the bolts were being pushed down. I used a level to confirm I had the result I wanted.

I tightened two of the southwest leg splice bolts, one on either side of the leg, and left the others as is for the rest of the procedure. I then repeated the rope tension and bolt loosening procedure for the #9-#10 spice further up the tower. The rope slackened less this time when the tower sat back towards the southwest so I added more tension to the rope. With the bolts fully seated there was some residual lean at that splice.

Perhaps the #9 section is improperly aligned or something else is going on. Adjusting a misaligned section is not a task that can be safely done on an erected tower. I therefore chose the next most desirable approach which was to slacken the rope a small amount and loosen the remaining 4 splice bolts. At this point all 12 splice bolts are loose, but not so loose as to allow the tower to wobble freely and fret at the bolt threads (the bolts are harder than the tower steel). It is at times like this that you appreciate doing this job on a windless day.

Despite that warning this procedure is safer than you might expect since the tower is trapped by the bolts and can move only a small amount, an amount that is in general not a danger. The danger that does exist increases the further down the tower this is done and less the further up, due to the amplification of the lean upward from the splice being repaired.

With all the splice bolts loose I added tension to the rope in small steps, visually inspecting the tower after each increase. When the tower was about as close to vertical as I could reasonably expect I went back up the tower and tightened all the splice bolts, first at the #9-#10 splice and then the remaining 2 bolts at the #11-#12 splice.

The bolts opposite the southwest leg on the #9-#10 splice are no longer sitting on the bolts. When the bolts were tightened it was the pressure between the two legs that held the sections in position. This is not ideal but acceptable under the conditions I found. There is the possibility that due to ordinary load forces that over time the section will slump and sit back on those bolts. That will reintroduce a small amount of lean.


In the end I had a tower that had ~95% of the lean corrected. The couple of small deviations on the upper sections is not a concern since the absolute amount of lean is very small. I declared success and put my tools away.

Aftermath

I remain unhappy with a few remaining issues with the tower. The ⅝" bolts on the #11-#12 splice and the splice of the #12 to the base stubs need more torque. Using a long level there is a small error in the base section's vertical orientation that was not there when built. It is amplified over the height of the tower. I will buy the tools I need to deal with those large bolts.

There are a few small areas of rust where the cold galvanizing paint isn't up to the job. Those will need touching up. Alignment issues remain with a couple of upper sections, including the #7-#8 splice. The splice problems can be dealt with in the same manner I described in this article. There are also a few diagonals that have resisted repair and ought to be replaced.

As I said, these are minor concerns.

Does it matter?

A few years ago I went on a road trip back home to VE4. An emergency road closure rerouted us and thousands of others to the more northerly highway 11. It's actually a shorter route but more isolated and less scenic than the 17. One stretch in particular, 200 km long, was devoid of towns or service stations. That's what we get for living in a large country with a modest-size population.

The route is not entirely wild. In addition to numerous indigenous communities and wilderness recreation areas off to one side or the other there are regularly spaced maintenance depots, for road work and other services. They are interconnected by radio links. This requires antennas up high to reach its neighbours over the rough terrain.

With little other than forests, hills and lakes for this long stretch those depots drew my eye. Each had a Trylon tower, perhaps 70' to 80', with a collinear VHF antenna. What surprised me is that pretty much every one of those towers was not vertical. They deviated from vertical by a few degrees, which is a lot. It was readily apparent to my eyes and I expect by anyone who takes the trouble to look.

This is an example of incompetence. If not for the light load those towers would not survive long. Ham towers are more susceptible since their owners often push the load to the limit, and beyond. Leaning towers are also not much fun to climb.

So it can matter. Keep it vertical and eliminate the concern. If your antenna load is light in comparison to the tower capacity don't fret about it too much. But I'm the sort of person who walks into a room and straightens the pictures hanging on the walls.

Tuesday, May 9, 2017

My Last QRP Plaque

If you've never placed highly in a contest you may be surprised to learn how long it can take for the plaques to be sent to the winners. This month I many other winners are receiving plaques for the CQ WW SSB 2015 contest. That was 18 months ago, and the results have been out for 12 months.

It made me smile to receive a plaque so long after I decided to exit from QRP contesting, and SSB QRP contests in particular. This made for a special photo opp since I won in the SOAB QRP category two years in a row.


Very pretty. My thanks to the CQ WW outgoing and incoming contest committee and the plaque sponsors. The sponsor, as you can see, is once again Jeff N5TJ.

I do not expect to win a third plaque in this category since QRP is no longer my focus. The best I've done in the CW weekend of CQ WW is #2, which is nice but does not earn a plaque, and now I most likely never will. QRP is a challenge and I salute the QRPers who continue to turn in fantastic contest scores.

If you are a QRP operator please call when you hear me in a contest. Copying QRP signals can be difficult (as I know all too well) but I welcome the challenge. And the points.

Saturday, May 6, 2017

Planning Around Guy Wire Interactions

Guy wires make great antennas. Except that we don't really want that since they will interact with our actual antennas, and interactions are rarely beneficial. To get around the problem there are several approaches that hams use when planning towers that call for guy wires:
  • Break up guys into non-resonant lengths
  • Use non-conductive guys
  • Crank-up towers (keep them lowered in high winds and when not being used)
  • Very heavy duty free-standing towers
Each has its pros and cons with respect to each ham's unique situation. In my case a crank up or large free-standing tower is expensive and unnecessary since I have lots of land for guys. On suburban properties they can be the best option to achieve heights. Of course one can shelve those plans and learn to live with small towers and antennas. But that's not why I moved to this remote QTH.

This leaves us with using guyed tower, and the choice of conductive or non-conductive guys. Steel is often the least expensive and worry free option in comparison to kevlar/aramid composites such as Phillystran and fibreglass rod. I know hams who use non-conductive guys and they are happy with their choices. This choice frees them to focus on interactions between antennas and not with the guys.

I looked closely at the pros and cons of each approach and how others deal with them in their stations. Based on that I chose to go with steel guys. This article is how I am going about the challenge of designing the guys to minimally interact with antennas on the tower. Soon enough my swimming holes will be converted into foundations and tower raising will commence.

Hardware

Apart from the terminations at tower end and anchor end each guy segment boundary requires 1 egg insulator and 2 guy grips. Many segments are required to make the guys non-resonant for most cases, which adds up to a lot of guying hardware.

If you choose your supplier with care the cost of a steel guy broken into non-resonant segments is cheaper than non-conductive guys of equal strength. After considering cost one must also realize that there is substantial work involved in cutting and splicing the segments. When done properly a steel guy built in this manner will be no less strong than a single run of steel guy wire.


Do not use clamps, crimps or other methods of terminating a steel guy wire. Guy grips, though they may look questionable to the untrained eye, are state of the art. On a guy wire broken into many non-resonant segments the risk of disaster with lesser quality terminations is high. Guys do break. I've seen it firsthand. Do not take chances with guying hardware.

Expectations

From experience and the large body of work published by others I enter this experiment with a range of expectations.
  • Yagis at the top of the tower will have negligible interactions with the guys except, possibly, on 10 meters with the top one or two guy segments.
  • Gain will be affected little by guy interactions since all the selected guy segment lengths are non-resonant on the bands of interest. It would take a resonant or near resonant guy wire segment to have a large enough mutual impedance to affect gain.
  • Similar to gain, SWR should only show small deviations due to guy interactions. That is, I expect SWR (impedance) to be a poor indicator of pattern distortion.
  • F/B and F/S will be degraded when the yagi is side mounted; that is, mounted below the top set of guys, even when induced currents on the guy wires is relatively small in comparison to the currents on the parasitic elements. It is the minor lobes of a yagi that are most susceptible to interactions since a finely tuned distribution of phase and current is needed for fields to cancel.
  • Interactions are greatest on guys that approach being parallel (or in a parallel plane) to any yagi element.
  • The most problematic interactions will be on 10 meters, modest on 15 meters and negligible on 20 meters. I am not testing 40 meters at this time since interactions are unlikely with the guy segment lengths I chose.
By the end of this article we'll see whether my expectations were met. At least, that is, for the range of models I'm selecting in this first study.

Guy wire segment lengths

The amateur radio literature has quite a lot of material on guy wire resonance. Some make bald statements about what lengths to use or avoid while others dive deeply into specific cases. Below are a couple of example charts. On the left is the ARRL Antenna Book and on the left is from an NCJ article by N2IC.


Without meaning to be unfair to the authors these charts exemplify what I said above. The ARRL chart implies that there are good lengths and bad lengths. The N2IC chart makes it seem that any length longer than 12' (4 m) for the 10 meter example are problematic, at least to some degree. The authors in both cases do provide deeper discussion about the issues, and that is very good.

Yet in my years of discussing this matter with many hams of my acquaintance the discussion is usually lost on them. They only remember the simplicity of a single chart. That drives their decision process, unfortunately. I hope to do a little better with my modelling effort.

The lengths I will use in my first model are from the aforementioned sources. My initial choices are, from the top of the guy: 5' (1.5 m), which is 4' plus half the tower width; 6' (1.83 m) for the next 2 segments; 19' (5.8 m) for the next 3 segments; and 43' (13.1 m) for the final segment. For the upper guys another 43' segment may be required, plus a final segment of variable length to the anchor, but this is not modelled since it is far enough away from the yagis to be of far lesser concern.
Note: These lengths do not consider the 12, 17 and 30 meter bands. The primary purpose of my tower is for contests, which does not include those bands. In any case coming up with non-resonant lengths for all HF bands is nigh impossible. If that's important to you I strongly suggest you use non-conductive guys.
The reason the shortest lengths are at the top is because they are adjacent to antennas mounted directly above them -- either at the tower top or side-mounted. It is good practice to place large wind loads near guy stations. Short lengths of under 10' (3 m) have essentially no interactions on any HF band. As the guys go out farther from the tower they are more distant from the antennas and consequently have lower mutual impedance. By distant I mean with respect to wavelength, not an absolute measurement.

Building a model

A complete computer model of guys and antennas is excessively complex and large. It isn't strictly necessary. What we do need is the minimum to test interactions with antennas mounted at various heights, especially when side mounted, and varying orientation to the guys when the antenna uses a rotator.

My interaction model contains 3 guys of identical construction. They are broken into the selected lengths, joined at the top and angled downward. Guys are joined at the top since the first segment is tied to the tower and together they form a short inverted vee. This important factor is not addressed in some studies.

The tower itself is omitted since it is orthogonal and symmetric with respect to yagis on the tower, and other antenna types that have symmetry with respect to the tower (e.g. inverted vee), and thus has negligible interaction. The same is true of control cables and coax running up the tower. The tower appears virtually in the model by lengthening the upper guy segments to account for the tower width.

I first built the guy in a horizontal line which could then be copied and rotated into the desired orientation. Each segment after the first is full length but offset by 5 cm to simulate proximity at the egg insulator between them. For later reference the wire numbers from top to bottom of the first guy are 16 through 21. The other two guys are identical, starting with wires 22 and 28, respectively. These numbers are visible is the EZNEC plot. The test antenna is already present in the model and view, constructed from wire numbers 1 through 15.

The adjacent plots include my first test antenna. The intent is to have the guy wire model and then import and position an antenna model from my large library of EZNEC models. The antenna is easily moved up and down, either above or below the guys, the pattern and SWR generated and compared as secondary traces on one azimuth or elevation far field plot. The guys can be rotated to simulate antenna rotation (this is easier in the model than rotating the antennas!) to find best and worst case scenarios.

Antennas that are mounted below the guys simulate side mounted yagis. The baseline plot is taken with the antenna well above the guys to serve as the baseline for the comparison; that is, where the interactions are negligible.

Constraining the model

Although the tower will have 4 sets of guys only one set is in the model. This is adequate for antennas above the tower and above the next to highest guy station. Lower antennas will point through 2 sets of guys. Since I do not plan any important antennas lower than halfway up the tower this is the most that needs to be modelled.

An important consideration is the number of segments in the model which is pushing the limits of the software and my patience in waiting for each run to complete. The time needed to alter the segmentation of the guys to experiment is multiplied by doing all 12 guys rather than one set of 3. Since I can identify problem areas with just the one set I do not strictly need to model more. I can simulate that, when desirable, by lowering the antenna so that the guy set appears to be a higher set.

My initial runs fix the angle of the guys with the tower at 45°. In the actual tower the angle for the guy sets is 40°, 49°, 60° and 75° starting from the top. In fact, this is approximately true for any tower with 4 equally spaced guy stations that follows the 80% rule -- anchors located 80% of tower height from the tower base. Therefore 45° is a good proxy for the upper two guy sets. Interactions for antennas side mounted on the bottom half of the tower will see increased interactions with the lower guys since they are more horizontal. This matters but is not my immediate concern.

A peculiarity of my model is that I chose to eliminate ground and model in free space. Ground does matter, though most often only to a small degree with regard to guy interactions. As with eliminating multiple sets of guys I do this to focus on the direct contribution of the guys to antenna behaviour. Too many variables make for a big muddle from which reliable conclusions can be difficult to obtain. If you want the model to completely predict behaviour you'll need to include ground and all guys. However, that model may obscure the most important problem areas you need to address.

Because I am modelling in free space I will only show azimuth plots, and those will be at 0° elevation. This is not what we will encounter in the real world. What it does do is identify guy positions, guy segment lengths and antenna orientations that are going to cause problems. That is what I want to discover.

Test antenna

For the initial modelling runs I used a small 3-element tri-band trap yagi that I developed a few years ago. This allows convenient interaction testing on the most susceptible bands with one antenna. Once problem areas are identified I will substitute antennas that are similar to the ones I intend to put on the tower.

Preliminary results

There are in effect two variables to play with in the constrained model: antenna height and guy orientation. Here is how I approached both.


I selected four heights in this experiment, with respect to the 25 meters height, with the guy apex 50 cm below that (24.5 m): 13 meters above; 0 meters; 7 meters below; and 10 meters below. As mentioned earlier the first height is the baseline for comparison, a height that ensures negligible interactions. The second represents the yagi mounted directed above the guys, whether top or side mounted. The third case is a side mounted yagi that is tightly tucked underneath the guys. The final case is about as low a side mounted yagi could go without running up against the next lower set of guys.


I then chose three guy orientations that are representative of scenarios that I expected to be most illustrative of the spectrum of interactions: one guy directly in the yagi's forward direction (top of diagram); one guy directly to the yagi's rear direction; and one guy in a plane parallel to the yagi elements. My results seem to indicate that I chose these scenarios well.

What do you think? Before I disclose the results and my interpretations it promotes understanding to look at an unfamiliar problem to consider how it might be solved. I recommend spending a few minutes right now doing that. You're on the honour system so I'll assume you've done that and I can continue.

The second worst case scenario is the one on the far right. The rightmost guy is in a plane parallel to that of the yagi elements and so is more similarly polarized than the other guys. Not only that, the affects are asymmetrical. Pattern distortion is evident on both 10 and 15 meters.


The primary plot is for 15 meters height which is ~10 meters below the guy apex (as explained earlier). Again, all scenarios were run in free space to minimize variables; the heights are there for future use only when I may run the models over real ground.

Notice the degradation of F/B and F/S in these azimuth plots -- there are also distortions in the elevation patterns, which are not shown here. For the yagi directly above the guys (25 m) the pattern distortion is very slight. For this antenna and for this guy configuration there is some peril in side mounting, but it isn't dreadful.

Gain is almost unaffected (no more than 0.2 db reduction) and F/B and F/S though worse are still respectable. SWR is barely affected. When side mounting for stacking gain it should work out just fine.


The worst case is for the guy orientation in the centre of the earlier set of diagrams. Does this surprise you? It surprised me. I expected the one discussed immediately above (guy parallel to elements) to be the worst. Looking at it more closely I can see how I was perhaps misled in my expectations. I have not evaluated it in detail so I can only suggest why this is occurring.

Notice how much the F/B and F/S have deteriorated especially on 15 meters, and there is a significant gain drop at the lowest height. On 10 meters it is not so bad, and is arguably no worse than for the case with the parallel guy.

Let's first look at the leftmost orientation. You might think that for the sensitivity of interactions that determine F/B and F/S that guys behind the yagi would be problematic. Yet this isn't the case. I suspect the reason is much the same for why it is possible to tune a yagi by pointing it upward, with the reflector close to the ground. Field cancellation to the rear and sides that is typical in a yagi reduces the potential for interaction with guys in those directions. The EZNEC Current table supports this interpretation.

In the forward direction the presence of guys will interact since that is where the field is strongest. Currents in those guys will upset the balance of phase and amplitude responsible for good F/B and F/S (directivity). Again, the currents table supports this interpretation.

I not only plotted the patterns I also looked closely at the currents induced on all guy segments. In EZNEC use the Currents table; do not rely on the graphical view since small but significant currents are not visible. Where the current is negligible the interactions are of no consequence. In all cases where the patterns were distorted there are guy segments with currents of only 5% to 10% that in the yagi's director and reflector. That is enough to disturb the fine balance required for best directivity in an optimized yagi with 3 or more elements.

The short guy segments at the top were in every case not responsible for interactions. Not even the top segment that joins with its siblings via the tower fasteners. Only when the segment length grew to 19' (6 m) did significant currents appear in select orientations, heights and bands. In the case of one parallel guy it was the two 19' segments in that guy that exhibited significant current. In the other cases the 43' (13 m) segment lower down also developed significant current in the guys positioned ahead of the yagi. This appears to confirm the reasoning I described above though it is not certain.

Conclusions

Side mounting can be a problem with selected orientations and bands for guys broken into non-resonant segement. Non-resonance is no assurance of good pattern since even small currents can wreak havoc with directivity. All you can hope to do is manage the problem by careful engineering.

Yagis above the tower are largely unaffected by guy interactions. The closest guy segments are short and are far from horizontal orientation. This is even true on 10 meters.

For fixed side mounted yagis the guy (or guys) ahead of the yagis can be chopped into smaller segments to preserve the pattern. However the cost versus benefit is doubtful, especially since you might in future decide to add a rotator to that yagi.

A guy aligned with the yagi boom does not interact at all. This should not be a surprise since it is orthogonal to the elements. I expected this.

That 15 meters performance came out worst is not necessarily indicative of what will occur with long boom mono-band yagis or other antenna types. Longer booms put the outer parasitic elements closer to the guys, leading to greater coupling and guy currents. Yagis further down the tower can also be more affected by interactions since the guys below and around them are more horizontal that those higher up.

You may have noticed that I did not show the plots for 20 meters. The reason is that the pattern distortions due to interactions were small, even for the side mount cases. Gain deteriorated by no more than 0.25 db and F/B by no more than about 3 db. While these figures make for uninteresting plots the message is that my selection from the literature of guy segment lengths works well for 20 meters. At least that is the conclusion so far, in advance of more detailed modelling.

Future work

The model I've presented here and the ways in which I've exercised it is a good start though far from the complete story. I intend to perform additional modelling to evaluate at least the following:
  • Lower guys that are more horizontal and that will therefore have a higher mutual impedance.
  • Effects of looking through 2 sets of upper guys from a lower side-mounted yagi.
  • Long boom yagis, which will get closer to the guys when side mounted.
  • Fixed wire yagis where inverted vee elements will be more parallel to the guys.
  • WARC bands, which while not a great concern I'd at least like to know what to expect when an antenna for 30, 17 or 12 meters is side mounted. 
  • Adjust guy wire segment lengths hopefully to tame interactions on 10 and 15 meters.
Regrettably I have more time for modelling than I'd like. The heavy rainfall we are receiving is keeping the ground saturated, too wet for finishing the concrete work on my big tower. I have no choice but to wait for the ground to dry. Perhaps late May, but I really don't know and I can't do much about it.

I can, and have pumped the water from my swimming holes to inspect them. Repairs to the damage winter has caused will have to wait for heavy equipment to arrive. They're a mess and every rainfall refills the holes. Indeed, we are experiencing extensive flooding in this part of the country. I had a near disaster yesterday when the sump pump failed overnight and the basement began flooding. Luckily I had an emergency pump handy -- the same I used to pump the tower excavations. The loss is minor but it sure is wet down there.

Whether it's guy wire interactions or sump pumps there is lots to keep one busy building and maintaining a large station located in a sparsely populated region.