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.

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:

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.

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.

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.