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.

Sunday, April 30, 2017

Gift Basket

When you do regular business with a company a bond of mutual trust often develops. We do a lot of buying from fellow hams, retail outlets catering to our hobby and other companies that have the hardware and services we need to build and maintain our stations.

A good vendor will be more responsive to your needs when you offer them returning business and you can rest easy knowing that you are getting good value for your money. Occasionally the vendor will go the extra distance to show their appreciation for your business. On your part you need to be a good customer by being reasonable with your expectations and, yes, settling your account promptly.

The local tower service company doing the foundation work for my big tower surprised me recently with a box of hardware. This is scrap from commercial towers and antenna installations. Since for safety and engineering reasons it is common nowadays that new material must be used in building projects used but still good material often ends up as scrap metal or goes to the landfill.


The quality of most of the hardware is first rate: hardened steel (grade 5) and well galvanized for durability in a harsh environment. Fasteners are almost all ⅜" and ½" sizes, which I often need. I took the picture after sorting.

Some of the hardware is lesser quality and some that was discarded due to damage. You can usually spot the lower grade steel hardware by the evidence of bends, tears and dimples from use. Shiny hardware is typically plated rather than hot dip galvanized. You can see examples of both in the group of nuts at the bottom centre of the photo.

Those large size u-bolts (4-½" opening) are especially valuable for one large antenna project I am currently considering: a full size 40 meter yagi. The smaller u-bolts will most likely be used as element clamps on HF yagis.

If you investigate the pricing for hardware of this size and quality you'll find that the total adds up quickly. Any hardware I don't need can always be re-gifted to other hams.

The gesture from the company is appreciated. If I have to spend money I prefer to spend it with people who treat me well. It's worth searching them out and to treat them well in return.

Scrounging

Since we cannot count on gifts it helps to be a good scrounger. I'm sure you've met hams like this, or perhaps you are one. They have an instinct for reaching out to people and businesses that might have surplus material and products that can be turned to good use by an ingenious ham.

A scrounger needs to be outgoing. You have to cold call people and build personal relationships. Scroungers (like the best sales professionals I've worked with) are very protective of the relationships they build so you cannot often ride their coattails. Scrounging is something you must learn do yourself.

Quite a few big guns built their stations scrounging coax, towers, hardware, electronic parts and much more, saving countless thousands of dollars along the way. They are to be commended. I am not as good at scrounging as I'd like to be so the occasional gift basket is very welcome.

Friday, April 21, 2017

Asymmetric Copy in Contests

It stands to reason that except in superb conditions that one side of the QSO copies better than the other. Indeed it would be remarkable if copy was equally good (or bad) since each station has a unique set of antennas, noise, QRM and propagation. This can make for some curious exchanges during contests.

Even when SNR (signal to noise ratio) is high there can be asymmetries in copying. On SSB this may be due to language and accent for the majority of hams who are not using their native languages, or simply by poor enunciation by those who fail to realize that a communication channel with limited band width and dynamic range makes copy more challenging than talking in person. There is also the all too common practice of poorly adjusted audio. On CW it may be poor sending, deviations from standard code element length and spacing, or sending faster than the other ham can comfortably copy.

Putting those situations aside I want to focus on QSOs between operators who are doing their utmost to get the message across: in this case call signs and contest exchanges. I'll focus on CW and SSB since I don't have sufficient experience to discuss digital modes.

Run versus S & P

Let's imagine we are tuning across the band and run across two adjacent signals, one strong and one weak. Which one do you tune in first? Even if you are disciplined enough to focus on the weak one I bet that you are still strongly drawn to the strong one. This is perfectly natural since it is less work to copy the stronger station well. Struggling with a weak signal costs time and time costs points. We are more inclined to do the hard work late in a contest when all the strong ones are already in the log.

However, it is not quite so straightforward. When you tune in a strong signal in the clear you will most likely copy the call sign the first time it is sent. You will most likely easily copy the exchange. The same is often not the case on the other side of the QSO. You may be running less power and a smaller antenna; they may be experiencing strong QRM from other callers and adjacent signals near to you that you don't hear because they are in the skip zone or off the side of the beam.

It should therefore be no surprise that for stations you copy perfectly while you S & P that less than 100% of them will copy you as well. Some of the time or much of the time, depending on many variables, they will ask for repeats or you'll have to correct their copying error. During the two years my contesting was exclusively QRP the percentage of running stations that could copy my call sign and exchange the first time was not high. On the low bands it was often no better than 25%.

Now let's return to the weak station you earlier skipped over. More S & P operators than you might imagine won't pay any attention to the ones that are hard to copy. I'll assume you're not one of those, since as a contester you should never overlook potential points (and multipliers).

So you listen and listen, perhaps taking a little time to completely copy the call sign and perhaps you'll also note the exchange being sent. For many it is only at that point you make your call.

Consider what's going on here. You spent time to copy the full call and ensure it is not a dupe. You have already had one or two opportunities to copy the exchange. Even if it's a serial number you know what number comes next and you'll be ready for it!

The running station has not had that opportunity. Their probability of correct copy on the first try is perhaps, on average, no better than yours. Yet you've already gotten past that obstacle. Now it's their turn. The weak running station is even less likely to copy your call and exchange on the first try.

The lesson here is that when you S & P you should not be surprised that the running station will need repeats of your information. For the running station many callers will not be readily copied and you'll have to spend time to correctly solicit their information.

Example: Ontario QSO Party

As an experiment I did 100% running in the recent Ontario QSO Party. That is, sitting on a frequency calling CQ and never hunting other stations. The contest has light activity and I wasn't concerned about my score, only giving out QSOs to others. This is not a bad way to make it easy for non-VE3 participants to find me, and my perhaps uncommon county multiplier. Many of the active VE3 stations spent much of their time running as well, perhaps for the same reason.

The objective of my experiment was to see just how often the callers were difficult to copy. Well, it was surprisingly often. While a sample of n=1 is not statistically significant my results do fit well with my thesis and my recollection of past years of contest experience at larger stations.

My springtime QRN levels on the low bands was quite high during the contest, with several electrically active rainstorms passing through or nearby. That could have contributed to asymmetrical listening ability. Asymmetrical power wasn't a problem since I kept to the low power limit of 150 watts, which is on par or less than the majority of callers.

On 80 meters I found I had to use the Beverage all the time even though it favours Europe and almost all callers were off the side or back of the Beverage. The SNR was almost always better than the inverted vee. This worked less well on 40 meters, partly due to the Beverage's sharper pattern on that band. The 2-element yagi's directivity is not very good, which is typical of this type of antenna.

There were many callers I could not copy at all, while with other I would only catch a letter or two of the call. It seemed surprising they were copying me. Perhaps they had lower atmospheric QRN, more directive antennas or there was power asymmetry.

One obvious problem was looking west on 40 meters soon after my sunset. At that time the other station's band noise will be lower than mine. This is typical of the low bands. As soon as propagation is enhanced by the arrival of darkness the noise level rises along with the signals from the dark hemisphere.

Stations west of the terminator hear me fine while I struggle with the atmospheric QRN accompanying that of signals from the east and south. This is the same phenomenon responsible for the difficulty of working clearly heard Europeans before sunset on this side of the Atlantic Ocean.

In many cases I could not come up with a good explanation of why copy would be difficult. QRN would be low and QRM absent. Obviously I can't know what is going on at the other side of the QSO. Maybe they were driven there by a spot (or skimmer) or maybe they had already spent some time copying me before calling. All I can know for sure is that copying asymmetry was common.

Lessons 

Let's face it, for the upwardly mobile contester it is necessary to run a lot to improve scores. That guarantees you'll be struggling with many callers that are difficult to copy. Since you must do it there are things you can do to be best prepared to deal with it to your (and their) benefit. Scores will improve and frustration levels will decline as abandonned QSOs are reduced in number.
  • Directive antennas: One sure way to improve copy on the low bands, and even on the higher bands, is with highly directive receive antennas. This can be as simple as a small loop, or can be a Beverage or phased vertical array. Transmit antennas are typically not highly directive on 80 and 160 meters so a more directive receive antenna is a good addition. The results can be surprisingly profitable. Since directive antennas are directive you'll need more than one, or at least an antenna with 2 or more selectable directions.
  • F/B: Antennas for all bands should have strong suppression off the back and sides, preferably with minor lobes that are no more than -15 db than the main lobe, and preferably much better. On the low bands phased vertical arrays are often the best at this, while on the high bands a Moxon rectangle or similar critically-coupled 2-element yagi, or optimized yagi with 3 or more elements.
  • Hunt down noise sources: Any noise source -- power line, Ethernet, USB, appliance, electric fence, etc. -- is a potential killer of QSOs, especially on an otherwise quiet band. Do everything you can to locate and silence noise. If you can you should place your antennas as far away from buildings and power lines as possible, or where productive directions for QSOs are over quiet zones.
  • Filters: Learn how to alter your filter settings quickly so that you waste little time asking for repeats. This include bandwidth, centre frequency, noise reduction, notch, and RIT. The last is important since you are less likely to hear a weak caller unless you tune above and below your frequency. You don't want to overlook them just because they failed to zero beat properly.
  • Partial call database: This one can be controversial. Many contest loggers will search for calls that are similar to the partial or full calls that you type in. This can help you to deduce that the caller is one of those, either a known contester or a call you've worked before in this or a previous contest. The technology exists and it's your choice whether to us it. Whatever you do, confirm the call with the caller. Never assume.
Effective running requires good listening habits and supporting technology.

Monday, April 17, 2017

Bracketed Tower (again)

I purchased a 29' (9 meter) light duty television tower 4 years ago soon after I returned to the hobby. After starting off using house eaves trough for an antenna I wanted something better since it seemed I wasn't going to wander away from amateur radio for another 20 years.

At first the tower was deployed as a guyed tower supporting a multi-band dipole and a 40 meter delta loop. When I replaced that with a stronger tower suitable for a rotatable yagi I bracketed the small tower to the house, installed a tall mast onto it and used that to support a fan dipole.

A small tower such as this is not part of my current more ambitious antenna farm planning. Even so the tower is up once again. Again it is bracketed to the house. Its intended use is LTE terrestrial wireless internet access. My current obsolete wireless service was a special order so that I could get connected quickly when I moved in last fall. The ISP wants to move me to the new, faster service and I am eager to oblige.

So while not a tower for amateur radio purposes I thought it might be of interest to any readers who want to press one of these inexpensive light duty towers into use to see how I did it. Bracketing a tower to a building, while convenient, must be properly done to avoid compromising the tower, personal safety and the structure of the building.

Base

This particular tower -- Golden Nugget -- is very common in Canada. Other countries have similar products on the market. This tower has three 10' sections (top section is 9' 6") made from 1" OD 18 gauge tubular steel pipes and horizontal cross members of formed sheet metal. The welds are a bronze-gold colour, hence the name. Load capacity is modest, perhaps 2 ft² when bracketed no more than 10' (3 meters) below the top.

A flat plate with flanges is designed for ground mounting the tower. The flanges bolt to the bottom section and holes in the plate are meant for driving stakes into the soil. I prefer a more engineered base so I fashioned one out of 4x4 preserved wood. I kept the one I had previously built.

I just had a garage built next to the house, which was my cue to begin the grading/drainage work between the buildings, including setting the new grade and then the base for this tower. Until now I wasn't quite sure at what level to set the base.

Choosing the location

Without considering other factors the ideal location for a bracketed tower is where the bracket can be placed at the maximum height. On a typical bungalow this would centred on one the side of the house with the bracket nestled near the roof ridge. There are more options on a two-story house since many points allow bracketing quite high.

Of course there are other factors. One is aesthetics and another is safety. My previous house allowed for several options with some being unsightly and others not allowing good placement of antennas (e.g. near the property edge). On my current dwelling there is really only one good place for the tower even though it is not the best for bracket height. All the higher options are in front of large windows or in the middle of a deck or balcony.

However my chosen location is not bad, allowing the bracket to be just under 16' (5 meters) above grade, which is more than halfway up. Since the only antenna will be a compact dish I do not have to worry about where HF wire antennas would go. This is good since the roof of the house is steel, which is less than ideal for HF purposes.

Selecting the anchor points

To be effective the brackets must tie into the frame of the house. On a typical North American wood frame house this is usually not a problem, if one is careful. Unfortunately from the outside it is not always clear where the studs, headers and trusses are located.


Being a country house with a deliberately rustic design the exterior is clad with batten board and striping. There are no indications on close inspection of where the frame members are located. However I do know that the frame is sheathed with chip board, on top of which are wood straps to which the cladding is nailed. None of those is acceptable for a tower bracket since they offer little resistance to tension.

The fascia is no better. Typical attachment of wood fascia is nailing into the ends of rafters or, in this case, short studs that bridge the distance from the outermost truss to provide an overhang. Again, those nails offer little tensile strength. Worse, the fascia and soffit block access to the top of the truss, which would be a good anchor for the bracket.

Peeking through the screened attic vent told me little. Other than a lumber frame around the vent (not a good choice for bracketing!) I could see little. The house blueprints only provided generalities not specifics of how the wall was constructed. Density meters for locating studs, pipes and wires are inadequate to locate framing from the exterior.

When my previous house was built I took lots of pictures (film, remember that?) of the house framing before the insulation and drywall were installed so I knew where everything was located. I only needed to take some measurements, compare to the pictures and I could find suitable anchor points to within an inch. But for this house I needed to see inside.


Before purchasing the house neither I nor the inspector I hired could find an access to the attic over the bedroom wing; the rest of the house is post and beam with a cathedral ceiling so there is no attic except here. I puzzled this one through, periodically looking up as a walked around the house. That's when I spotted someone odd about the overhang in front of the house. I had one of those "aha!" moments.

Minutes later with a ladder and a few tools I was in. I took pictures of what I could see of the wall I'd selected. Coincidentally we are looking directly across the roof of the shack. I did not enter the attic since quite a lot of care is needed to cross the rafters in a modern house with engineered trusses and heavy insulation that buries all the structural bits. I've done it when necessary, and I can assure you it isn't much fun. It is very easy to damage the ceiling, and yourself.

However all I needed was the picture. All that needed to do the rest is one measurement from the outside to calibrate the scale of the picture. For me that was the width of the vent frame: 24". From that I could determine the location and size of all the dimension lumber and how it all ties together.

I chose the 2x6 header over the vent frame for the bracket anchor. It provides a wide solid support for long lag bolts and it is suitable tied into the end truss. The sheathing, though weak on its own, adds to the lumber connections so that tower loads are distributed over the framing. For a larger tower with an HF yagi I would not recommend this choice. For my internet dish or for wire HF antennas or a small VHF yagi this anchor is perfect.

If you are going to go big with a bracketed tower I suggest you either hire an engineer or find a more secure anchor in the frame. On my previous house I was able to anchor into two layers of 2x6 header sandwiched between the rafter of the trusses and the exterior 2x6 support walls. That will take substantially more load than what I have selected here.

Installing the brackets

I kept all the hardware used to bracket the tower to my previous house. Some is custom and some is specifically made for bracketing a small tower. In the picture below is pretty much all that I needed, other than the hardware store perforated angle steel I use to make the bracket arms and the U-bolts to attach the arms to the tower legs.


The L-brackets are attached with lag bolts to the house (upper flange) and with grade 5 bolts to the arms (lower flange). I picked the two in the best condition. These L-brackets are sufficient high grade to resist bending under load or under bolt torque. I chose to use 5/16" lag bolts rather than anything larger since the tower load is small. The shorter bolts secure the base plate to my homemade preserved wood base.

With a little geometry I calculated the required distance between the L-brackets to that when positioned the tower faces would align with them. As it turns out I made an error during measurement and they were 1" off. Thus one of the bracket arms wasn't flat against the tower face. This is not a serious problem so I didn't bother moving the L-brackets, and avoided repairing unwanted holes in the siding.

Raising the tower

Several hours during a warm spring day was all it took to attach all the hardware and raise the tower. It helps to have a friend although I did this job on my own.

The L-brackets went into the header just as planned. In one case when drilling the bolt holes there was the expected gap between exterior board and sheathing, while in the other I got lucky and hit the wood strapping between those layers. In the latter case this permitted me to torque the lag bolts without undue concern. The other required me to not tighten the bolts too much since that would only bend and possibly break the exterior cladding board.

It is important that the holes through the intermediate layers permit the lag bolts to slip through; the threads should not bite into the siding or sheathing. Collars are available for lag bolts to allow the bolt to take full torque without bending the cladding. This requires carefully drilling a hole for the collar or it will sit too deep or too high and not do the intended job. I didn't bother with collars, even though I have them in my stock of parts.

The full length hole is smaller so that the lag bolt threads engage the frame lumber. Although you skip this hole, drilling a hole reduces the chance of splitting the wood and thus compromising the strength of the bracket. For my 5/16" lag bolts I used a 3/16" drill bit.


With the L-brackets installed I sat the bottom tower section on the wood platform and weighed it down with stones (I have plenty on my property!). From the ladder I lifted the next section and dropped it in place. Bungie cords, one per L-bracket temporarily hold the 20' of tower upright.

The small sledgehammer and scrap wood you can see were needed to press the section into place since the legs were slightly ovalized. They are easily deformed when tightening the splice bolts. Separating sections can be difficult if the installer was over-enthusiastic with the wrench.

The next step was to attach the bracket arms to the L-bracket and tower legs. If you don't have the manufacturer's bracket arms you can fashion your own, as I did, from galvanized or painted steel of suitable strength. If this makes you uncomfortable I strongly recommend you only use the purpose-designed brackets from the tower manufacturer. The previous owner of this tower fabricated his own bracket arms. Although they were very poor strength the tower survived for years. I rejected them.

With the brackets holding the tower the bungies were removed and the tower made vertical with a long level. Only then is the base plate bolted to the wood base.

To lift the top section I opted to reassemble my old light duty gin pole that I had built for raising DMX tower sections. The brackets I made fit the Golden Nugget reasonably well but require securing the gin pole to the tower since with horizontal cross member the gin pole can easily slide.

Although the tower sections are light I strongly recommend a gin pole since it is harder than you might guess to lift a 10' section above you, holding it perfectly vertical, aligning all 3 legs at the same time and pushing it down into place. I know some rare individuals with the physical gifts to do it, however I am not one of them and it is  almost certain that neither are you.

The mast is easy enough to raise and slip into place without a gin pole, if you are careful to keep it nicely vertical during the procedure. Surprisingly little deviation is enough for gravity to twist it out of your grip and cause injury to you and your house. Don't hesitate to ask for help if you need it.

All done

As the sun set the tower was complete and the tools and materials put away. Now I have only to inform my friendly neighbourhood ISP to visit at their convenience to install their equipment and upgrade my wireless internet service.

Monday, April 10, 2017

Swimming Hole

We've had a lot of rain over the last week. So much that roads are flooded and some homes are threatened throughout eastern Ontario. Couple that with spring temperatures and runoff due to incompletely thawed ground and you get something like this:


Sad, isn't it? However it is not as bad as it looks. Soon enough the water level will drop and the rest will be pumped out. Then the debris in the hole will be removed. The concrete work on two holes was completed in the fall which leaves two swimming holes (this one and one more) yet to be converted into tower foundations.

Soon enough that anchor you see will hold 2,000 kg of tension, its share of holding up a big beautiful tower. For now I thought some readers might enjoy this view of my impromptu swimming hole. The full story of planting this tower will come when I've got it done. With a little bit of luck that should happen by early May.


Friday, April 7, 2017

Listening

Many years ago I bought and absorbed The Complete DX'er by W9KNI. If there one overriding lesson from that book was the importance of listening. Of course there was no global DX spotting network -- just pockets of friends who would let each other know when a rare one appeared on the band -- making listening, and lots of it, an absolute must for the DX enthusiast.

Although I had been around long enough by then to not learn much from the book it put what I was already doing into perspective , therefore enabling me to better understand the strategy of good listening. When I returned to air a few years ago after a long hiatus from ham radio I soon learned that too much listening could actually be detrimental. While I listened someone else spotted the rare one and those receiving alerts from the spotting networks got there first.

Since I was QRP at the time showing up late was often no better than not showing up at all. I updated and honed my pile up skills to overcome this handicap, and I seemed to do pretty well at it. However the value of listening is still there, if you understand how the game is now played. Listening is a way to catch the DX before the horde arrived, especially the majority who would only stir when there was a spot. The majority have, in effect, delegated the listening to others, including the skimmers.

The why of listening

There is of course the operating awards benefit of listening, that of getting there first and not having to contend with the pile ups. Modern pile ups are like the phenomenon of flash mobs, growing from nothing to a large crowd in a minute -- spotting networks are a kind of social media. Years ago it took time for the pile up to build since there was no instant communications to one and all about where the DX was located, or that a rare one was active.

That is not the only reason to listen. Listening is in itself a pleasure. When I was very young and first discovered the magic of short wave radio I liked to listen to signals coming in from all over. But I didn't have a receiver. Instead I would "borrow" the family 5-tube AM radio from the kitchen. I had learned that by unscrewing the slug in the local oscillator coil I could lift the coverage to well above the end of the broadcast band at 1,600 kHz.

There I heard AM broadcasters, commercial operations such as ship to shore and the odd pulsations of RTTY as heard through an AM detector. I also came across the rhythmic thumping of CW and the unintelligible squawk of SSB. That was how I first discovered the existence of amateur radio and hams. A ham license was still several years in the future.

After my listening sessions I would screw the slug back down, making sure to calibrate the dial to a local broadcast station, and return it to the kitchen. My parents were very tolerant of my burgeoning hobby. That is, as long as there was no harm to what was to them an expensive appliance.

My listening habit carried over after I was licensed. Some of that was out of necessity since I did not have much of a station: an 807 to a dipole 3 meters high. I enjoyed it immensely nonetheless. In a way I found more pleasure in discovering DX on the bands than calling and, sometimes, working it. As time went on my DXing, and then contesting, became more intense so that my listening had an objective: I was hunting more than listening.

Why do it now

I am happy to say that I have rediscovered some of that early magic. At times I find myself tuning the bands for no other reason than to hear what is out there, having no inclination to transmit at all. With the new Beverage antenna I can listen in on far more distant DX on 80 and 160 meters than before. Without a decent transmit antenna I cannot work them, so listening to them is all I can do for now.

With the return of the equinox comes propagation over the pole from south and southeast Asia. I enjoy tuning the bands from 40 meters on up to catch the openings and hear what I can hear. Often the signals are very weak and not easily workable. Either I don't have enough power or they are hearing others far more strongly than from this part of the world.

Of course I do sometimes come across some moderately rare DX, and that's all to the good. Just this morning I tuned across V85TL calling CQ on 20 meter CW and getting no callers at all. No one had yet spotted him. I worked him without much difficulty. Then I listened as his subsequent CQs went unanswered. The band was busy, with stations all around, yet none seemed to be listening. After a couple of minutes I spotted him and that drew in callers.

Modern times

I think it's a shame that too many hams nowadays don't listen. This is not about getting there first or sharing the burden of hunting down the DX and spotting it for others. What I find unfortunate is that too many seem to have lost the simple pleasure of tuning the bands and listening, and perhaps finding the unexpected. Not for awards or points but for the thing itself.

Do newer hams feel the magic of radio? Perhaps not in the same way, and that's a shame. Some of my own generation seem to have lost the magical feeling that drew them to amateur radio in the beginning, yet others I know still have it. There are hams I know who in their single-minded pursuit of DXCC Honor Roll will only stir to turn on the rig when a new one appears on the bands. That leaves me cold -- to me amateur radio is much more than that.

This is not to be critical of anyone or to make myself out to be a curmudgeon. Radio still has magic to it and I regret that some may have lost that feeling or perhaps have never had it. All I can do is shrug it off, feeling that they are overlooking something of value. I will keep listening.

Tuesday, April 4, 2017

Building and Tuning the Remodelled A50-6

Sporadic E season is rapidly approaching. We can expect the regular appearance of propagation on 6 meters beginning in early May. Unlike the previous two seasons I plan to be active with a far better antenna. Hence my remodelling of my ancient Cushcraft A50-6 to conform with the optimized design by W1JR in the more recent A50-6S.

With resumption of serious tower work still several weeks in future this is a good time to prepare antennas for the season. I can't even get to the Beverage termination to continue experimentation with it since the fields and bush are a boggy mess. Eventually the ground will thaw and dry, but that takes a while in this climate and our soil conditions.

For 6 meters antenna preparation is a relatively easy task since I have everything I need. Most of my other antennas require more extensive modelling, tooling and parts acquisition before construction can commence. So it was time to work on the A50-6 and get it ready to go.

The modelling went quickly, requiring no more than minor adjustments to my earlier work. The final design largely conforms to the A50-6S dimension. I lengthened the reflector, driven element and first 3 director by ~¾", and the fourth director a little more. Half element lengths:
  • Reflector: 59-¾"
  • Driven element: 54-¾"
  • Director 1: 54-¼"
  • Director 2: 53-¼"
  • Director 3: 52-¾"
  • Director 4: 49"
The first change moved the best gain performance to the bottom of the band where all my operating takes place. The second change boosts the gain ~0.3 db (by tightening the resonance range of the array) while having little effect on F/B and not degrading SWR below 51 MHz.

Element spacing is identical to the A50-6S. All dimensions were measured to within ⅛".

The original A50-6 design used equal spacing between elements. This can work well -- as shown by W2PV -- but not in this antenna! The W1JR optimized designed does much better although it does introduce mechanical considerations due to the clustering of elements at the rear of the yagi.

Boom

Before I could assemble the boom I had to straighten one tube that had a slight bend. This goes back to when I used the boom as a wire antenna mast a few years ago. The 1-½"tube with a more pronounced bend was repairable with the pipes I had on hand. A different technique was needed for the 1-⅝" tube. Looking around my large stock of material I found a 1" solid steel rod and a large tree that suited the task.

With straight edges and careful rotation of the tube in my workshop I precisely located the peak of the bend and the section of the tube that was curved. The peak was not at the centre of that section. I marked these points on the tube and went outside to visit the tree I'd selected.

The peak point was centred within the V where the trunk branched, conveniently at shoulder height. The steel rod was measured and inserted so the end was similarly centered. A small length of pipe collared the pipe where it exited the tube in order to minimize the risk of kinking the tube.

With everything in position I proceeded to push the rod until the tube yielded. It worked quite well. I then repeated the procedure with the bend point to one side then the other of the peak to smooth out as much of the bent area as I could. Although the result wasn't perfect you can only tell by sighting along the full length of the assembled boom.

A further problem with the boom is that the centre of gravity is off-centre. The A50-6S compensates for this by using a longer length of 1-⅝" tube on the long side of the boom. The A50-6 tapers to 1-½" for the last few feet. At some point I may want to replace the boom with heavier wall tubing to increase its wind and ice survivability.

Pointing straight up

As many hams know and as I described in a previous article a convenient technique for tuning yagis is to point them straight up. The reflector can be quite close to the ground, even 0.25λ can work well. The reason is that cancellation of radiation to the rear of the antenna reduced ground interaction. Keep in mind that all we're doing is tuning for best match -- not gain -- and that F/B has to be moderately good over the desired bandwidth.

I used EZNEC to model the antenna in this position to see the effect of ground and to determine how low I could safely go. I settled on 5' (1.5 meters, or 0.25λ) for reasons of available props, modelled performance, safe handling and accessibility of the driven element. The prop is a length of schedule 40 water pipe with a 1.6" I.D. which fits reasonably snugly over the 1-½" boom (plastic end cap removed).

I didn't use the Trylon tower as the support since the tower is very wide and could interact with the antenna more than I'd like. Instead I used a log frame in my backyard. I did my best to orient the yagi so that its elements were nearly orthogonal to the 80 meter inverted vee overhead and off to one side. It seemed to work fine even though I ought to have temporarily moved the inverted vee.

Notice how the coax is routed along the boom and straight down so that it doesn't interact with the elements. A temporarily common mode choke consisting of two cylindrical ferrites reduces the effect of RF conducted onto the coax outer surface.

Tuning it up

The antenna uses a gamma match for transforming the low impedance of the antenna to 50 Ω. In EZNEC I used an L-network since it is easiest to adjust in the model. These and similar networks have almost identical matched SWR curves so they can be considered equivalent. The EZNEC model optimized SWR curve for 50 to 51 MHz is quite good. I initially setup the gamma match per the A50-6S manual. That turned out to be a good starting point despite my design changes.



The objective is to see how well I can adjust the gamma match to get the same result. This assumes the SDC (stepped diamter correction) is done properly so that the real antenna and the model have the same resonance, and therefore the same performance metrics of gain and F/B. Since I've done this before and had good results I am confident that I've got a close match to the modelled performance.

It took about 30 minutes of fiddling with the gamma match until I got what I wanted. Each adjustment required moving a step ladder into place, making the adjustment (usually in ¼" increments) then moving the ladder away.

Look at the measured SWR curve and see what you think. Perfection isn't necessary since the environment for tuning is different form that atop the tower and stacked above an HF yagi. Further tweaking can be done then, though not easily since the driven element is far from the mast.

Performance note

Tuning an antenna for a match is at best an indirect indication of good performance; at worst it is totally misleading. Optimum gain and F/B per the model can quite easily be frequency shifted in the tuned yagi.

It is the shape of the SWR curve that is of more interest since it indicates that the rate of impedance change conforms well to the model. As an example, yagis typically show a sharp decline in radiation resistance near maximum gain. The rapid impedance change will appear in the SWR curve since the matching network cannot deal with these sharp swings and the SWR will soar. Too flat a curve is similarly an indication that something is amiss.

That the measured SWR curve is so close to the model gives me some comfort that the antenna performance will be as modelled is however no guarantee. That requires field strength testing.

Packing up

Declaring success I tightened all the adjustment fasteners and took down the antenna. It has been placed out of the way and off the ground until I am ready to install it on the Trylon tower. I have high expectations for this year's sporadic E season.