3-element 15 Meter Yagi

The 3-element 20 meter yagi that I recently built now has a sibling for 15 meters. As previously related, both are meant to replace the TH6 pointing south. The tower work is planned for completion before CQ WW SSB at the end of October.

This antenna is not simply a scaled version of the 20 meter antenna. There are differences that are worth a discussion. Nothing was purchased for this antenna since all parts come from my stock, just like for the 20 meter yagi. Other than ⅝" and ½" tubes, all of the aluminum tubes and plates come from discarded yagis that are decades old. 

Limiting myself to what I had in stock imposed constraints on the mechanical design, which in turn affected the electrical design. There are asymmetries that made it difficult to use NEC2 for the model, which I prefer to NEC5 for conventional yagis. With some work I was able to achieve good agreement between both calculating engines for the gain and pattern, but not quite for the impedance. The last isn't surprising and is not critical since the matching network at the feed point is adjustable. As for the 20 meter yagi, the model uses a hairpin (beta) match since it easier to model than the gamma match that is actually being used.

Element taper

From my stock I selected 3 centre pieces that consist of a 1-⅛" tube pierced by a 1" tube. The faded marks were there originally and indicate that at least two of these came from a 15 meter yagi. One of the centre sections is longer so I used it for the reflector, the longest element. Dimples rather than hardware prevent movement of the 1" within the larger one. That's unusual but I've seen it used several times in very old antennas. There were no defects to speak of so I left them as is. 

The ends of the 1" tubes came with slits, stainless hose clamps and self-tapping screws to secure the nested ⅞" tube. I removed the screws, drilled through that small hole and out the other side of the tube for #8 stainless screws and nylocs. I reused the hose clamps rather than replace them with #8 hardware.

The ¾" tubes were already secured to the ⅞" tubes with the metal strapping described in the construction article for the 20 meter yagi. I cut those off for the DE since the combined ¾" & ⅞" sections were of unequal length. Swapping tubes resulted is nearly equal length sections. This kept the DE centre of gravity at element centre (over the boom) and enabled EZNEC's SDC (stepped diameter correction) in the NEC2 engine which requires element symmetry. NEC5 doesn't have this sensitivity, requiring neither symmetry nor SDC.

For the tips, a 1' length of new ⅝" tube is inserted into the end of the ¾" tube. The tip are ½" tubes. The first picture in this article shows the assembled elements without the tips. I avoided adding tips until the design met my objectives. The equivalent diameter of the element-to-boom clamps is 2.7" using the W6NL equation for a tube resting on a plate. The boom and hardware have a effect small enough to be ignored during design and construction.

Unlike for the 20 meter yagi the elements are not isolated from the boom. There are no destructive interactions with the antennas near where I plan to place it on the tower.

The final taper schedule of the half elements is as follows, skipping over the element-to-boom clamps. Dimensions are distance from element centre, not the lengths of the tubes:

• 1-⅛": 6" (D and DE), 9"(R)
• 1": 24.5" (D), 25 (DE), 26" (R)
• ⅞": 64.5" (D), 76.5" and 65" (DE), 77.5" (R)
• ¾": 104.5" (D), 116.5" (DE), 128.9" (R)
• ⅝": 113.5" (D), 125.5" (DE), 138" (R)
• ½": 127.5" (D), 130.1" (DE), 146.4" (R)

This is obviously not what an antenna builder would choose when using new tubes. I simply worked with what I had. Aluminum isn't cheap. The lengths of the ½" tips are for my final design, which is discussed in the next section. There were many iterations to get what I wanted.

Design and model

As you may recall from the 3-element 20 meter yagi design, I tried to keep the "spread" between the director and reflector as small as possible to maximize gain. That is, the square root of the ratio of their self-resonant frequencies. High gain increases antenna Q so there is a trade off with the SWR bandwidth. To keep solid state amplifiers happy the SWR should be below 2 across the band, and preferably better than 1.5.

To achieve this across the 350 kHz of the 20 meter band for the selected boom length and element taper schedule I eventually had to settle on a spread of 8%; that is, the director and reflector self-resonant frequencies are approximately 8% above and below the design centre frequency, respectively (see above). It is possible to do better on 15 meters since, although the band is 450 kHz wide, there is a smaller proportionate range due to the higher frequency. 450 kHz at 21 MHz is 2% while 350 kHz at 14 MHz is 2.5%. That seemingly smaller bandwidth permits a tighter spread, and thus higher gain, for the same SWR bandwidth.

After iterations with a 15 mm constant diameter wires on a 15.5' (4.7 m) boom it was possible to achieve the SWR bandwidth objective for a 7% spread. The raw boom length of 16' is proportional to the 24' boom on 20 meters, with several inches on each side reserved for the width of the element-to-boom clamps. The SWR bandwidth was about the same for a model with the above element taper schedule using NEC5. That's the plot shown here, using a beta match and a 7% spread.

Then I had a boom problem. Although I have lots of 2" boom material, the tubes were all 9' or longer. I hate waste so I didn't want to cut any of them. Since 16' isn't very long I decided to make an 18' boom. That increases the boom from 0.33λ to 0.37λ, measured from reflector to director. Since gain is in proportion to boom length the gain also increases. It isn't a lot but every fraction of a decibel counts, in this case from 0.2 to 0.3 db.

After tuning the elements in the model the SWR bandwidth was preserved and the gain increased across the 15 meter band. The only downside is less F/B, losing between 3 and 5 db. That did not surprise me since, unlike gain, F/B tends to have a cyclical pattern as the boom lengthens. For those who cherish F/B it is important to choose boom length with care. 

F/B rarely concerns me as a contester since I want to work stations off the back of the beam. Less F/B means that more stations hear me. It's to my advantage. For an occasionally used yagi fixed south to work contest multipliers it's even less of a concern. Look at a map of my location and you'll see that there is little likelihood of QRM off the back (north).

For the final design the placement of the elements on the boom, with the reflector position at 0, the DE is at 93" (236 cm) and the director at 210" (533 cm). Moving the DE a few inches could improve the pattern or gain, but only slightly. Therefore I didn't both to optimize further. Had this been a more important antenna I would have taken the time.

The SWR has barely changed with the longer boom, with a just a small increase at 21.45 MHz. This plot was done with NEC2 and EZNEC's SDC after making the elements symmetric in the model. The NEC5 plot is the same but due to the differences in the engines the modelled impedances are not quite equal. For the purpose of the plot it wasn't worthwhile to adjust the model's beta match to compensate. The small impedance difference is not important since the range of the gamma match can accommodate it. 

NEC5 typically needs many more segments for the impedance to converge to its true value. I did not test to determine whether that was the cause of the difference in this model.

My final caution with modelling and building yagis is that you should trust the tools. I am frequently amazed (and amused) by how many hams like to denigrate modelling software and would rather stumble along with their antenna projects, trying to convince themselves (and others) how great their antennas are. It's nonsense. 

NEC5 in particular and NEC2 when coupled with SDC are remarkably accurate. Believe the results and build your yagi exactly as in the model. Every fraction of inch makes a difference, even at HF. Don't guess! Measure and cut per the model, and when you can't (as for some of the tubes in this model), enter the model data exactly to the tube measurements. For HF yagis each tube should match the model to within ¼". At the very least ensure that the half element lengths are within that tolerance.

For example, my initial design had 6" lengths of ⅝" (3" nested and 3" projecting). That was to conserve my dwindling stock of ⅝" × 0.058" tubes. I later went with 12" lengths (9" projecting) and reduced the ½" tips by the same amount. The frequency shift of the yagi was significant. You might not notice it in practice since gain is very difficult to measure. But it makes a difference so you should strive to get it right. All the element half lengths had to change by about ½" (1" total per element) to return the model to where I wanted it.

Assembly and various supports

Unlike the 3-element 20 meter yagi, the boom is shorter and lighter and therefore amenable to a simpler solution for joining the two 9' section of 2" × 1/16" tubes. Digging through my junk box I found a spare Hy-Gain boom coupler. Although the aluminum alloy is thin wall it has served well on their large line of HF yagis over many decades. I don't know where this one came from.

The coupler is 10" (25 cm) long and is designed for 2" tubes. I've used these Hy-Gain clamps in the past on 1.9" OD pipes so it can handle a small range of sizes, provided both tubes are the same diameter. There are 2 through bolts and 4 clamp bolts, all sized for 5/16" hardware. The other 4 holes are for Hy-Gain two-piece mast clamp. I didn't have one of those handy so I made a mating plate from 3/16" steel.

The 4 inner holes for the mast clamp are arranged in a 3" square. The through-holes for the tubes are 4" apart and centered on the square. I drilled ⅝" holes for the projecting through-bolts. I could have made cutouts around those holes but drilling holes is easier and leaves a little material on the sides for added strength. The plate could be made a little wider than the 5" seen here. The antenna is small and light enough that I deemed this to be sufficient. 

The reason that I used steel was that I was running low on aluminum plate of suitable size and thickness. Steel is cheap and strong so I picked up a 6" × 3/16" remnant I saw while waiting for other steel stock to be cut to size for other projects. The downsides are that it is more difficult to machine than aluminum and it requires a rust protection coating. It's routine for me from my long time building towers and antennas. I plan to make a similar plate for the recently completed 20 meter yagi.

The holes for the galvanized saddle clamps are also 5/16". The 6" height leaves ⅞" on top and bottom, to leave enough space between the mast clamps and the Hy-Gain boom clamp, which is 4-½" high. The holes for the u-bolts were set after selecting the saddle clamps. Be careful because there is no reliable standard for u-bolts and saddle clamps for the same size tubes or pipes. Don't guess, measure.

When making custom antenna hardware it is important to carefully consider the placement of all hardware before cutting the metal and drilling the holes. It helps to be able to think in 3-dimensions. Loosely lay all the parts per the design to find any conflicts. You could end up saving a lot of time and material!

Which direction you orient the bolts can matter. I placed the heads of all the 5/16" bolts on the plate side of the assembly to avoid interference with the clamps. Also, lock washers should always be on a flat surface, not a round one. If you must place the nut on a round surface it is better to use a nyloc or jam nut. Most of the bolts are stainless for easier maintenance should it be required.

The motley selection of element-to-boom clamps are due to what I had available in my junk box. I couldn't be bothered to go to the trouble of making better clamps for this lightweight yagi.

The u-bolts for the director and DE (top two in the picture) use formed threaded rod. I've seen this construction method on antennas made 40 or more years ago. That's useful for custom sizing but otherwise a really bad idea. Tempered steel is weakened by bending and milder steel that can be formed in this fashion may not be of sufficient tensile strength. It is also difficult to get a consistent radius of curvature. But, again, the antenna is small and they were in my junk box so I used them. For the longer reflector I selected an element clamp with conventional galvanized and plated saddle clamps.

The gamma match comes from an ancient 15 meter yagi so it has suitable dimensions. The 7/16" gamma rod is 5" from the DE (centre-to-centre). I cut the insulated support bar from an ABS pipe. The coax connector is on a 1" aluminum bar, the wire from which is bonded to a short piece of the same ABS. The RG213 centre conductor for the gamma capacitor is not present in the picture. It will be cut to size during testing and tuning then soldered to the wire and sealed. The 3 u-bolts on the DE are from my stock of stainless hardware.

It looks nice when assembled in the hay field. Its measured weight is 27 lb (12 kg). The boom truss will be dacron rope to be tensioned by hand rather than turnbuckles. I prefer to avoid steel truss cables for side mounted yagis to avoid unpredictable resonances of the total system that might destructively interact with nearby rotatable yagis.

Next steps

There is as yet no tower bracket for this antenna. That is nearing completion in my workshop. Since the testing of the 3-element 20 meter yagi went so well and this one is similar I skipped doing a separate test and tuning of the yagi. I'll install the new bracket, tram the yagi onto it and then test and tune it. The gamma match is easily accessed from the tower since the DE on a 3-element yagi is near the centre of the antenna.

There will also be a need for antenna switching since there are no spare ports on the 2 × 8 switch. An auxiliary switch is being made to switch the transmission line for the 15 meter stack to the 3-element south yagi. Antennas for the same band to not need to be simultaneously accessible. I considered putting the relay and port on the 15 meter stack switch but it is already crowded inside. The switch will be installed on the tower close to the upper end of the Heliax transmission line.

The new yagi will be raised by early October, and then the switch built and installed. I will have more to say about these when the job is done.

Lessons From the WRTC Adjudication Report

The September 1 release of the WRTC report on final adjudication of the results cannot be ignored. Many have read it and been dismayed. Even more haven't read it but use its existence to publicly lash out at contests, contesters and whatever else irritates them. People are like that.

As a contester, my reaction to the report is mostly disappointment. I would like to say that I was surprised, but not really. Cheating occurs in every human endeavour and radiosport is no different. When they're caught they may or may not acknowledge what they've done and accept the consequences. Some plead innocence forevermore. I took on faith that the extra multipliers won by the original top team were acquired properly. I was wrong.

I am particularly discouraged that a fellow club member (Contest Club Ontario) and someone I know and have spoken to numerous times and won WRTC twice has been exposed as a cheater. Worse, from the interviews summarized in the report he prevaricated when presented with the evidence (more on that later). His disqualification hits close to home.

That of course is Yuri VE3DZ. His and 3 other teams were disqualified. The medals have now been awarded to the true winners of WRTC. It is possible that the 2023 results from Italy may eventually be redone since the same or similar patterns were discovered. If left as is those awards now carry a stain, or at least an asterisk.

As I already said, public comments on public discussions of the report are widespread, ranging from surprise and disappointment to calls for extreme sanctions against the individuals disqualified and against radiosport in general. There is considerably more heat than light. I am not impressed by all the faux outrage. Those in the game have been more guarded in their public comments, perhaps too guarded considering the enormity of what transpired.

There will be consequences though perhaps not what the pitchfork carrying tar and feather crowds are calling for. As bad as it looks I am happy that it was done. Daylight is the best disinfectant and we now have an opportunity to improve radiosport. Despite the naysayers, contests are not going away and are going to grow as a proportion of total activity on HF. Listen to the bands when there isn't a contest and you'll be forced to agree. The silence on the dial between the modest number of QSOs demonstrates non-contest activity is in decline and has been for many years.

To draw a comparison, look at what has happened to cycling. Although doping had been going on for decades it was only more recently that medical science raised the potential imbalance between dopers and non-dopers. There was also a culture that fostered cheating at all levels, including coaching (from youth to elite) and team and sport management as the spectacle of athletes doing the impossible drew audiences and money to the sport. Too few dared say anything since they too had unclean hands and the potential for retribution was high. They risked their careers, livelihoods and reputations by speaking out.

Radiosport has fortunately never fared as badly since there's little money in it, just prestige within a relatively small community. Even so many cheated, and still do, though perhaps not on so big a stage as WRTC. The lack of money and the nature of radio make can make it more difficult to discover cheating than in traditional sports. Many contest sponsors won't or can't take the trouble beyond basic QSO matching. Instead, they've reduce the burden by loosening rules to make certain widespread rules-breaking practices legal, and therefore almost mandatory. For example, we've seen a reduction of unassisted categories and prohibitions against self spotting.

I believe that a lot of cheating in radiosport can be cleaned up just as in cycling and other sports, and without the onerous regime and cost of doping controls in those sports. Technology and techniques now exist that automate a lot of the effort so that more contest sponsors can effectively and quickly identify cheaters. Whether they want to is another matter; many don't appreciate the ugly truth coming to light.

Consider: if you were a contest sponsor would you want to attract the ire of cheaters and their supporters when you publicly expose them? There is risk, to themselves, and others if they mistakenly name the innocent. No method can be foolproof. Some willingly accept the risk but many would rather avoid the matter entirely. They just want everyone to have a few hours of fun on the weekend. I understand that.

Retribution really happens: look at the repeated DQRM and pirating of his calls endured by Bud AA3B because of his good works making CQ WPX a better and cleaner contest. A few don't like clean contests or those that do the cleaning if it means they can't win or are exposed as cheaters. It's an often thankless task.

There will be consequences for contesting from the WRTC rescoring and disqualifications. Although, as the saying goes, daylight is the best disinfectant, the rot is now out in the open and it may be even worse than what the WRTC report details. Despite the stink I believe this can be good for radiosport. Cheaters should know that they are in jeopardy. The vast majority of contesters that compete fairly will, over time, become more confident that competitions are fair.

Backing up, I debated with myself whether to write this article immediately after reading the WRTC report. The content was rich enough that I then reread it, and reread it again. I decided to delay this article and I'm glad that I did. The two weeks that have passed allowed me to more thoroughly digest the report and its implications, and thus refine my views. 

It has also been enlightening to read commentary about the debacle, and then comments on the commentary! People have opinions and want you to know what they think. However there were few gems to be found within the deluge. Hopefully my words add to rather than pollute the discussion.

After these 2 weeks of reflection I have several reactions. Over time I expect to modify, add or subtract so don't take these as my final words on the subject. This is to be expected since there is a lot going on and there are certain to be further developments. I tend not to trust those that have immutable opinions.

• Reputation of radiosport: The many hams that don't love contests or contesters have been handed a weapon, at least in the short term. Ultimately I believe the complaints will subside; a lot of noise signifying nothing. They don't really care about radiosport and will soon move on to FT8 or another subject to vent about.
• Stain by association: Some contesters cheat therefore all contesters cheat. Generalization of this kind mostly comes from the group mentioned in the previous point. Cheating is not a passive infection, and in fact there are few cheaters. Assigning guilt by vague association without evidence is lazy thinking and unfair.
• Burden on hosts: Prospective WRTC hosts, which are already challenging to conduct, may balk at the additional burden of dealing with cheating.
• People talk too much: It's both irritating and amusing that so many with strong opinions about the adjudication have clearly not read the report or failed to understand what it contains. For example, teams were not disqualified for working the suspected pirate(s), yet many believe that they were. Their scores were recalculated after removing those contacts. If this surprises you, you have not read the report.

As you might infer from the tone of my reactions I don't believe that radiosport is in any danger. However, it will be uncomfortable for a while. It will take time and reflection to absorb what happened in Wyboston and to collectively build a better future based on the lessons learned. It's important that we do that. 

This is an opportunity to make radiosport and WRTC better so that competitors and those who cheer for them are assured that competitions are largely fair and that cheaters will be quickly discovered and exposed. WRTC hosts will also need more than the ad hoc individual assistance given to the Wyboston organizing committee this year. It can be done, and I have a few modest suggestions which I'll come to.

I will now turn to the report itself to comment on a few passages that gave me pause. These are cases where I believe the report stopped short, failing to delve into root causes. I am being deliberately unfair since that wasn't the purpose of the report, yet these are important considerations.

"Listening to the recordings of even the disqualified stations shows that they exhibited admirable skill in handling pile-ups and efficiently working stations. Had there been no dubious operation by some participants and outsiders, their results would have been impressive."

This is true but signals a misunderstanding of who cheats and why. Let me give a cycling analogy since there are parallels to be drawn. I am a cyclist though I've never been a competitive athlete, let alone an elite athlete. I have ridden, not raced, with elite athletes, both current (at the time) and retired. Anyone that has taken to the field with elite athletes in a sport that they perform well in will understand what I am about to say.

There is a wide gulf of native physical talent, learned skills and mental fortitude between the good amateur and elite athletes. Watch them at a distance and who among us has not thought at one time or other, "hey, I think I could do that." No, you can't. Really, you just can't. The difference is that great.

Had I to juiced myself to the gills with EPO and steroids I could never have bridged that gap. Cheating would not have done me any good whatsoever. I would have done better among the local cycling heroes but that's about it. Any elite cyclist would still have left me in their dust. It is just that stark. I never would have stood a chance.

It was among the elite cyclists that cheating occurred. At the pinnacle of any sport the differences among the elite competitors are surprisingly small -- you can also see this in the WRTC scores. They're all pushing the limit of human physiology, training and a steely resolve to push themselves to the maximum to outperform or outsmart their fellow competitors. Then the question they or their handlers ask is: what more can I do to win?

So they dope. Since that is seen to work, more do it. Soon almost all are doing it because they must to stay in the game. Their sponsors, trainers and medical teams develop doping into a science and arrange matters, legally or otherwise, that the athletes will not be caught when they are tested. Considering the breadth and depth of the cheating it is surprisingly that the truth took so long to come out, or at least for the truth to be believed.

Contesters may take supplements and do other questionable things to their bodies, but we don't pay attention to that. Maybe it works, though perhaps not to any great degree. It helps to be young of course when it comes to physical stamina and mental agility whether the contest is 4 hours or 48. Cheating then takes a different form. It can be done individually (claiming unworked contacts, excess power or remote receivers) or with the help of others (pirate multipliers, cheerleading, back channel spotting).

As with cycling, I'm a pretty good contester but I'll never be at an elite level. I could do better if I trained more but that wouldn't help. Neither would cheating. It would have to be so extreme to make up for my mediocre ability that any log adjudication software would easily spot it. Cheating, like doping in sports, will never push me to the top of radiosport. Again, it's the elite that gain from cheating, just like what we saw at WRTC.

"MB1I (E77DX and DJ4MX) — Both of its starting frequencies were held by stations connected to its operators."

No cyclist starts their sporting career as a doper. Someone steers them in that direction. In sport it is often the coaches that play that pivotal role. Their first job is to convince the aspiring athlete that they need to dope if they hope to achieve their aspirations. Their young charges are talented, ambitious and impressionable so they come to believe that it is both necessary and acceptable. 

Adult supervision is critical since it is no trivial task to learn dosages, timing, control avoidance and acquire drugs that may require special handling (e.g. refrigeration). The coach benefits since the athlete is their ticket to the big leagues as well.

Several notorious examples come to mind. Since there are few cycling enthusiasts reading this I won't digress to cover that. It is just my way to introduce a discussion about the equivalent to doping in radiosport. Young and talented contesters don't just suddenly begin cheating. They learn from watching others or being schooled by more experienced hands. They are taught how to cheat. 

In the case I excerpted from the report it is easy to guess which of the two is the student and which is the teacher. Braco E77DX is a talented contester of long experience with many successes to his credit. Sven DJ4MX is young and also talented. Of course I could be wrong so I'll leave you to your own thoughts on the matter. 

My concern is that it appears we have the analogous situation to doping in sport: the coach and the aspiring young talent. They are being taught the wrong lesson. I believe that blame should accrue more to one of those parties than the other.

"The operators of all three teams were asked to explain these events. MB1I's two operators admitted what happened and accepted responsibility for the Rule 12.2 violation and the consequences of it. No operator of MB2M or MB2A has admitted any arrangement. Their answers say nothing about why the holding stations acted as they did. One operator said he was unaware of any pre-existing arrangement, but would accept his team's disqualification if a violation were found."

Some learn from their misdeeds and some don't. I am encouraged by the acceptance of responsibility by E77DX and DJ4MX. They were wrong to do what they did but I see a path forward for them. Who among us is without sin? You pay your dues to the community and are then given another chance. Although I don't know either of them I believe they deserve that chance. Calls by some for lifetime bans are extreme and unjustified.

I am less impressed by the reported reactions of the other 4 operators. They have not accepted responsibility for their actions. I therefore believe that they deserve greater sanction. I can't say what that should be, but I think it should be nothing less than disqualification from WRTC 2030. It hurts me to say it since, as already mentioned, I know one of those operators and I have long admired his operating skill and cheered him on.

I need to explain my position, how I can so readily treat the disqualified operators differently. Admission of wrongdoing has long been a requirement for rehabilitation in our societies. For example, the criminal justice system is kinder to those that deal with what the harm they've done or enabled than those who remain in denial. While it is true that some that deny are truly innocent the evidence in these specific WRTC cases is strong.

It is not just about admission of fault. I see two further requirements. One is to explain how the cheating was done, in detail, whether or not they name those that assisted them. The second is to publicly take a stand against cheating and to facilitate procedures to check their future contest entries. Some public discourse from them could serve to discourage others from cheating. Is that enough? I don't know.

As for the others, I really don't care what happens to them. Time alone won't remedy the harm. Their co-conspirators, unknown as they may be, can remain in the shadows but must never believe that they are out of jeopardy. It is likely that their identities will come to be known, even if that is years away.

Enough of the past. It is now time to look to the future. How can we make contesting and WRTC fairer for everyone involved? I have known contesters that have contemplated vying for a spot in a future WRTC and are discouraged by the cheating. They at least need to be reassured that their investment of time and effort would be worthwhile.

But this is not a professional sport like cycling. There is no money to enforce biological passports and other measures to ensure that athletes aren't doping. That's expensive and we have only volunteers to rely on. We need measures that achieve a lot with a modest investment. While I don't have the answers, I do have a few ideas on how we (the broader radiosport community) might go about it. These ideas are not new but bear repeating.

First, cheating in any activity is nigh impossible to eradicate. There will always exist those that will try to game the system to win. Prestige and recognition mean more to them than winning on their own merits. They may also have a network of helpers, as we saw in WRTC. When one person cheats others are sure to follow since they learn that that's how one wins.

Cheaters and the adjudicators are in an arms race, just as in computer security and so many other areas. When one side catches up the other side has to find a new way forward, and they usually do. The trick, I believe, is to outgun the cheaters by enabling innovative methods of scrutinizing contest entries. Particularly those with the highest claimed scores and every WRTC team.

Treat the following recommendations (suggestions?) with caution. I did not attempt to fully evaluate their effectiveness or implications. That is also why the descriptions avoid detail. Caveat emptor.

1) Public logs

All contests should have public logs. Not all will do so for any number of administrative and other reasons, which may be justified. However, non-complying contests should not be used for WRTC qualification. With rapid deadlines for log submittal and rapid public access to the logs anyone can scrutinize the entries, not just the official adjudicators. 

With so many eyes and opportunities for innovative algorithms (most hams are technically adept) cheaters will be outgunned. The challenge will be for the contest sponsors to filter a potentially large number of low quality reports. Experience scrutinizers, which we saw get involved after WRTC 2026, should be favoured.

2) Recordings

Several contests require high scoring entrants to record the contest as heard in their headphones. While those are rarely requested by adjudicators they can be the deciding factor when questions arise. It is a bother but no longer very difficult with several recording applications that can integrated with popular contest loggers.

I've never recorded a contest. I don't place that highly so I've never taken the trouble. For that reason it is no surprise that no adjudicator has ever asked me for one. SDR recordings of all on-air activity exist though not always accessible to the adjudicator or that capture what they need to verify. Too much depends on the SDR owner's station and location and willingness to cooperate. Luckily those were available to those scrutinizing the results from WRTC 2026.

For WRTC candidates in all qualifying contests recordings ought to be mandatory.

3) Pooling of expertise

For good reasons many algorithms and the programs that implement them are kept private. The reason is that having them widely available could reduce their effectiveness. Even among adjudicators for major contest there may be some reticence to share and pool what they have. That can reduce the chance to catch cheaters in contests where the adjudicators can't access the best tools to do so.

Of course this does take place on a limited scale already, though to what extent I'm in no position to say. Doing all we can to catch cheaters early, long before they reach WRTC, will discourage cheating and eliminating from contention those that persist.

Okay, I'm done

I wonder how many have persevered to get this far into the article! There are a lot of words and no pictures to break up the wall of text. If you are still here I have to assume that radiosport is important to you. 

Thank you for reading, and have fun in your next contest no matter how serious or not you choose to be. Above all, don't let the WRTC fracas detract from your own enjoyment of contesting.

6 Meter Recap: July Fireworks

This year's sporadic E season started poorly. It was easy to become discouraged by the time the season was to supposedly peak at the summer solstice in late June. DX openings were few and weak. That said, by then I had worked at least two new countries -- OD and A7. Yet the overall conditions continued to be surprisingly poor. I lowered my expectations accordingly. This would make 2 years in a row with poor sporadic E on 6 meters. I didn't even bother with a year end recap in 2025. Why report nothing? 

Then July happened.

Before getting into that, let's back up to earlier in the spring. The first DX arrived on schedule in early May with opening to northeast Africa, a little South America and the west coast of NA (W6, W7, VE7). It was another 2 weeks before the first workable European signals arrived. Propagation continued nicely to the west with many openings to the coast and I worked a couple of KH6 stations. Nothing new, except grids which I don't really collect except by chance.

The same story continued throughout June. Perhaps I shouldn't be so negative since there were two or three widespread openings to Europe and west Asia, including several near misses of new DXCC countries. However, the openings were weak and short lived on most days, and I added no more new countries. I am accustomed to Asian openings being more common after the solstice, so I wasn't as yet too alarmed at my prospects for the 2026 season.

July was different. I don't know how to characterize what I (and everybody else) experienced but I'll try by giving you an overview of what I heard and worked:

• There were almost daily openings to the west coast (W6, W7, VE7)
• Almost every early morning there were at least a few signals deep to the northeast, including the Arabian peninsula, central Asia, Russia and the more common eastern Europe and Scandinavia
• On several days I heard 5Z4VJ, an area in Africa I've rarely heard
• Dozens of Japanese stations were worked, perhaps as many as 100, when last year I can't recall working even one, and only hearing a few very briefly
• East Asia stations were heard as never before, including HL, BY, VR2 and others, with several entering my log
• European openings were so common there were days when I questioned whether to even bother announcing them to our local 6 meter DX group
• Many openings lasted far into the night, up to 06Z, for us and for others, including Europe where the opening to NA lasted until almost their dawn
• On at least two days there were concurrent openings to Europe and east Asia; some have reported working WAC in a single day
• One evening ZL1RS was heard here for an hour, which is remarkable since the winter sporadic E season down south is not great for carrying our signals across the equator other than TEP to South America

As momentous as the season was for me and my friends, stations to the east and south of us did better, as they usually do. Propagation weakens as you travel north (or south in the southern hemisphere) despite the signals travelling through the Arctic and sub-Arctic latitudes. Ionization can be just enough to carry the signals but not enough to refract them to the surface. 

Sometimes you get lucky such as when I worked VE8CK in DP22 and a number of stations in northern Scandinavia. Of course there are not many stations that far north in North America so it is possible that the propagation is better than it seems. For example, many evenings the VY0SNO beacon in Nunavut was heard here and elsewhere.

Despite my reluctance to operate digital modes I recognized years ago that FT8 is well suited to the types of DX openings we get on 6 meters. When a station has propagation it is noticed immediately and you can call them. This is what I call the ease of discovery. With CW and SSB you would almost never notice them; who has the time and patience to swish the VFO over a large spectrum? 

CQing attracts the attention of a large prospective population of hams that passively or actively monitor 50.313 MHz. Since so many connect to PSK Reporter I can quickly discover where my signal is being heard even if no one replies or I can't hear them. 

I don't "chat" on 6 meters, and rarely on HF either. My interest on 6 meters is almost exclusively to chase DX. Therefore my operating is and will continue to be on digital modes. I have no disrespect for the rag chewers among us, I just have no interest in that kind of operating. To each his own. You are only likely to hear me use CW and SSB on 6 during contests and aurora openings.

Now, on to the DX during this year's sporadic E season.

Once you get over the pole there is a lot of territory to cover -- those circles are 2500 km apart. It is all far away and very enticing for DXers. Openings, if you get them, are typically fleeting. There are surprisingly many such openings that are brief and only to a small area, perhaps a single grid. This is where CQing or continuous monitoring of 50.313 MHz is vital. You might only get one 2 minute opportunity per year. Whether you want to take the time required to catch these openings is up to you.

I posted screen captures of two such contacts: BG6GQE on July 29 and EX9QT on July 13. The map is easily overcrowded so I separated the messages from UK8OM on July 6. We didn't work although I heard him again another day but only one decoded message. I got lucky in all of these and other cases. 

I knew they were on since other stations scattered to the east and south of me were heard either calling or working them at various times. It was often the case that just one at a time could hear and work these over-the-pole stations. It's spotlight propagation in action. It was difficult not to get frustrated staring at a monitor pane devoid of DX signals while seeing others working them.

This contact with southern China on July 19 was interesting. The path over the pole is more than 12,000 km. A moderate but long duration solar flare was in progress at the time. Was it coincidence or cause-and-effect? Although X-ray flares are typically bad for HF propagation, unless severe (X class) there may be little effect at 50 MHz. Occasionally a moderate flare can enhance VHF propagation by temporarily raising the MUF without an excess of ionization that absorbs signals. Was this an example of that?

It is foolhardy to derive a general rule from a single data point. Some will nevertheless make the leap. In this case I suspect that it was no more than coincidence. Many stations this year experienced these brief, long distance over-the-pole openings when the X-ray flux was low. 

VR2KW, who is very close BD7IS, is seen working K1TOL in Maine. I called but failed to work him, and I didn't hear him after that message on the screen (there were a few just before that one). All I know from PSK Reporter is that he went QRT on 6 meters a few minutes later. That was a shame since we don't get many openings like that one.

He and many others were heard this year and not worked. At a similar distance but not over the pole is the Arabian peninsula with many countries I've yet to work on 6. The only new one this year was A7 (Qatar). I had two partial QSOs with HZ and I heard A6 and A9. Very enticing but that isn't enough to put them in my log.

With what appears to be expanded privileges for hams in Russia and Belarus, many stations from both were widely heard this summer. They are far enough that the openings, though numerous, are brief and unstable. I had many partial contacts with EU and R stations until finally completing one with EU1KY, a new one for me. Many of my friends had more luck with both countries.

I worked none of the many Russian stations heard this year but I have it confirmed from previous contacts with stations in occupied Crimea which count for Russia. I'd really like to at least hear a UA9 or UA0 next year. I know that UA9 was heard and possibly worked from VE1 and W1. I have yet to hear a UA0 even though Vladivostok is very close to northern Japan which is often heard here during opening in that direction.

Speaking of Japan, the openings were numerous, unlike last year. I worked many stations in JA and HL, including stations worked in previous years, and many new ones. It is likely that I worked close to 100 Japanese stations this year, in all parts of the islands, including in the Okinawa island chain. I didn't take the time to count them all. What a change a year makes.

I now turn to the DX stalwart for North American 6 meter operators: Europe. The path was open a lot during July. Openings of many hours duration became routine. Even when the easier western Europe wasn't heard there were openings on the more northerly path through Scandinavia into the Baltic states and Ukraine. The longer paths were the most unstable but also the most productive with respect to interesting DX.

Unfortunately there are few countries in Europe I have yet to work. These include 3A, T7, Z6, ZC, OJ, HV and several others. None are easy, even on HF. I've heard some of them but cannot count on working them to boost my DXCC total. The only new one was SV5DKL who I've chased for a while. We had a partial on 50.313 MHz, then made a solid contact when he QSY'd to 50.323 MHz. The QRM on 313 was too intense for reliable decoding of weak signals. A nice problem to have!

For me the more interesting aspect of Europe on 6 meters is the propagation study one can do due to the large population of hams and the many 6 meter enthusiasts who, like me, push to find the limits of what is possible. It was fascinating to hear the long openings between all parts of Europe and the west coast of North America, and then further into the Pacific. I am sure the Europeans had a lot of fun with it. I had a big smile on my face as I watched these QSOs taking place. It was delightful.

I posted this pic once before for a different reason. There is nothing remarkable about these QSO traces on Gridtracker. They are just the stations I was copying one day in early June. The map is illustrative of what 6 meter propagation is often like. First, look at the intersecting lines in the north Atlantic Ocean. That is a point of enhanced ionization. It can indeed resemble a point since the area can be exceptionally small. It is how spotlight propagation occurs. 

From my experience I have to think that the briefest and most unstable DX paths rely on exceptionally small areas of enhanced propagation, areas that seem to flicker in and out and move from side to side. You may copy just one distant DX station at a time. Later, you hear a different station. Others in a different location, although nearby, hear different stations or the same ones before or after you do. 

I track what others hear since there is a good chance that I will soon hear the same. Notice on the map that I heard a European station along a track that passed through my location (FN24) but not one in QSO with a US station on a different path that appears to utilize the same ionization patch over the Atlantic Ocean.

It's a little like the flickering of the aurorae. The ionization clouds are not themselves in motion, but the rise and fall of ionization throughout the large zone of enhancement can make it seem so. When others see the flickering of stations I pay close attention since I might very soon have an opportunity. Sometimes I will hear them and sometimes not. It's a part of the magic on 6 meters, despite the occasional frustration.

More common are the short, single hop sporadic E openings in eastern North America as shown on the map. QSOs follow a similar pattern of utilizing a single ionization patch, with lines connecting stations crossing at a small area between them. In the case shown, stations are mostly along a single line. That is deceptive since it depends on what propagation allow me to hear and because my yagi was pointed as southern Europe. As is typical for yagis, I can hear stations directly off the back pretty well but not off the sides. 

Internet activity mapping services will show a more complete picture of global propagation. Others rely on those quite heavily while I do not. I monitor the DX spotting networks to discover where in the world there's 6 meter propagation. That is easy and convenient to check without navigating websites with their many options. All I really need to know is that the band is open and some insight into who is hearing what. All that I then need to do is watch and wait, and occasionally CQ to see if I can attract attention.

There were DX openings in other directions this year, though they were less productive for DX from this part of the world. The map centred on FN24 has been deliberately cropped to highlight the circled target regions. Notice that the directions deviate only a little from an east-west line. That is about the extent of what we can hope for with sporadic E propagation. More southerly directions require F-layer (rare now that the solar cycle is waning) or an assist with TEP. Sporadic E can, at best, bridge to southern hemisphere propagation phenomena. Crossing the equator is therefore not easy except directly south to South America.

The Caribbean is an easy shot for us. The challenge is activity. Several of the many countries in the region are very active while others must wait for the occasional traveller with a penchant for 6 meters during the summer season. Most vacationers from northerly latitudes travel south in our winter, which is not very helpful to 6 meter DXers. We take what we can get! One easy shot that I have yet to work is PJ7 since I was never in the right place at the right time.

All of my Caribbean contacts this season were new stations in countries I've already worked. It's possible I've overlooked one but I'm not going to the trouble of checking. My aim was to work stations in countries that are not confirmed since those earlier stations don't upload to LOTW, or not without payment. I don't do that so I go the route of working others. I'm okay with that but others are more impatient with getting contacts confirmed.

Most of Africa has low activity and few native operators, which is a shame considering its large size, number of countries and large populations. Waiting for DXpeditions is usually our only option. The situation is unlikely to change anytime soon. It's the same on HF though less acute. 

Countries with more activity, such as ZS are too far south to be reachable via sporadic E, too far east for TEP and even a challenge via F-layer propagation at solar maxima. V5, which is not too far away, is easier for us. A few hundred kilometers can make a big difference over these long paths.

This year I heard a few from east Africa, in particular stations in SU and 5Z. Several stations more centrally located were heard and worked by others but not by me. Unlike previous years I did not hear any 7Q stations that have been previously active. Perhaps those young hams are more attracted to HF. 6 meters isn't for everyone.

We have more success to ZL located in an almost mirror-edge position from south-central Africa with respect to my location. Sporadic E and F-layer propagation is not equal everywhere at the same geographic or geomagnetic latitude. There is an acute sensitivity to bearing and latitude with northern New Zealand being easier for us than the south island and the south part of the north island. One evening this July I heard Bob ZL1RS for one hour straight with a good signal working many North Americans. I just listened since I've worked him a few times already. I heard two other ZL1 stations but only briefly.

VK4 is far enough that despite a direction that is more westerly I've never worked them. I have only ever been received there (as shown on PSK Reporter) and heard them a couple of times. Australia would be a new one for me, with VK4 being our best bet due to their location. VE3's to our west, as close by as FN03, were more successful. I've heard that their power limit makes it more difficult for us to hear them than vice versa. Maybe next year or, less likely, during our winter sporadic E season which is their summer season. It's less likely since winter sporadic E is poor at our latitude.

In between there is a lot of water. We had several good openings to Hawaii but otherwise the expanse of the Pacific Ocean was a desert this summer. There were stations on 6 meters that were not heard by me.

Robots

As more stations move to 6 meters so do the robot operators. I've even seen longtime ops opt to become robots. They can do what they like as far as I'm concerned, however I don't like what they do to my operating. They pollute my monitor screen so that I have to scroll back to see if I missed any DX, they call me, relentlessly, no matter how directional my CQ messages, and they occupy spectrum with their endless CQs during DX openings.

WSJT-X improved (which I use) has a blacklist function with which I manage some of the problem. To my dismay its limit of 12 stations is no longer enough. Maybe I should put in a feature request to make the blacklist of indefinite length, which is a sad testament to what is seen on the bands. For now I replace calls when a new robot creates a major annoyance and hope that the ones I had to delete don't return. Unfortunately most do.

DXCC & VUCC and other awards.

As I've mentioned a few times in the blog, I don't chase awards. I like to count and chase DXCC entities on 6 meters as on HF yet I've never applied for DXCC. Most others that I know feel differently and will apply for DXCC and VUCC awards on 6 meters. I check what confirmations show up on LOTW (Logbook of the World) but don't otherwise care about QSLing. If I want to confirm a country and a worked station doesn't upload to LOTW I'll work another and hope that they upload.

Despite my aggressive disinterest in chasing awards my DXCC total on 6 meters now stands at 156 worked and 146 confirmed on LOTW. While I didn't bother to count at the end of the 2025 season, I'm pretty sure that I've worked 10 new ones this year. That's a larger annual increase than I've seen in the past few years. It's a combination of good conditions and more activity.

Although I barely pay attention to grids my VUCC total is now 969, which is getting close to the 1000 milestone that many strive to reach. It's likely I'll reach 1000 in 2027 if the trend in my accumulation of grids continues, even though the accumulation is mostly passive. 

I've written about FFMA (Fred Fish Memorial Award) where the objective is to work every grid in the continental US. Although I don't pursue it since I don't chase grids, a friend of mine does. I keep his needed list close by and if I hear one he needs I let him know. He's worked many new ones as a result. 

Often I'll work them as well since, if he still needs it, the grid is rare and attractive in a way. FFMA is tracked on LOTW and my count is rising as a result of helping a friends. However, I don't track what I need so I'll never reach the 488 grids required. The rare FFMA grids that I find for my friend and work myself contribute to my VUCC progress.

I occasionally receive a request to work someone that needs FN24. It usually has to be an off-air request since when I'm working DX that's all I'll work. I don't often work others in North America unless they're on the other side of the continent. Although there are other stations in FN24, Canadians and Americans alike, it appears that my signal is the best, so I'm they one they usually chase. I recall being surprised to learn that I count for FN24 in FFMA despite not being in the US.

I no longer use auto-answer on WSJT-X. It was a useful convenience feature in the first few years I operated FT8 but it has become a hindrance. So many non-DX stations, robot or not, call me when I explicitly specify CQ DX, CQ EU or other directives that I only respond to stations I manually select. It's a little more work but worth the effort. Real operators (not robots) might try once or twice before realizing that I'm serious, which I'm okay with since we all like to play the odds. However, it is not okay when robots persistently follow me around and never stop calling. That's an excellent way to be added to my blacklist.

I want to mention a trend that keeps growing: stations operating remote on 6 meters to gain a propagation advantage. This is seen most often with western US stations renting one of the super-stations in Maine. For awards like DXCC this is permitted as long as they remain in the same country. I find it odd to hear well-known west coast station signing FN64 during European openings. I don't object to the practice but it isn't something I'd do. I don't take awards as seriously as others so I am not too concerned how they go about it.

The end

There was a geomagnetic storm at the end of July that wiped out 6 meters. Propagation never recovered. I had only a handful of DX contacts in August and nothing especially interesting. I don't know whether the storm was responsible for the end of the sporadic E season or if it was merely coincidental. It was time.

I am okay with the season ending since July was so wonderfully productive. It became an opportunity to get out of the shack more often and enjoy the August weather. When the band is hopping it is difficult to wander too far away because I'm afraid I'll miss a rare opening. Nevertheless, during the season I monitor most of the day and I'll often leave the rig running overnight with the yagi pointed north just out of curiosity of what might come through.

While difficult to predict now that the solar flux is in decline, we could see a resurgence of DX on 6 meters from mid-September through October. That will mostly be to South America which, while nice to see, is unlikely to turn up any new countries for me. There are only a few that I need from that continent and they're rarely activated or without operators active on 6. 

For that reason I don't have high expectations for the fall. I don't expect to work any new countries on 6 meters until 2027. I'm fine with that since I have so many other things to do, including quite a lot of tower and antenna work, and of course the fall contest season. CQ WW SSB isn't far off. I have no excuses to get to work on those projects now that the sporadic E season is behind us.

Building & Tuning the 3-element 20 Meter Yagi

There was no rush to build the new 3-element 20 meter yagi since it can't be raised until the fall for several reasons. I worked on it over the summer as time permitted. It is now largely complete, tested and tuned. This fall I'll take down the TH6 and replace it with this antenna. I also plan a similar antenna for 15 meters. Both are to be fixed south, just like the TH6. They will be more efficient and less prone to multi-station interference than the TH6. Another for 10 meters can wait since the solar cycle is waning.

Although a 3-element yagi is a common directional antenna there are a few factors worth discussing. Those will make the article longer than you might expect. The details may prove useful to others, including how construction choices affect performance. No matter our experience and knowledge there is always more to be discovered even in antennas that we believe to be thoroughly understood.

Element taper and K-factor

The ratio of wavelength to wire diameter (λ/D) affect the SWR bandwidth of an antenna element. The higher the ratio the greater the change in reactance for a given change of frequency (dX/df). Therefore an antenna made from wire has a narrower SWR bandwidth than the same antenna made from tubes -- fat is good! The effect is greater at longer wavelengths (lower frequencies) for a given wire diameter. The effect is noticable at 20 meters, but small enough that it can usually be safely ignored.

Antenna modelling engines readily calculate the effect. It influenced my choice of a 7% spread for the parasitic elements of the 3-element yagi. For contesting I want a low SWR from 14.000 to 14.350 MHz. However, the model utilized fixed diameter elements, while the real antenna uses tapered elements. It is not obvious what the effective ratio is for tapered elements.

The steps for each half element are as follows:

• ~1.5": 3" long, calculated for the boom-to-element clamp, where director and reflector are electrically isolated from the boom; the estimated diameter for the DE (driven element) is not critical since it is accommodated by the matching network
• 1.315": 9" long for DE and director, and 21" for the reflector
• 1": 51-¼"
• ⅞": 51-¼"
• ¾: 51-½"
• ⅝: 21"
• ½": 24" (R), 13" (DE), 4" (D)

Small deviations of actual tube lengths were accommodated during construction so that the half-element lengths are 224" (R), 200" (DE) and 191" (D). The tubing from 1" to ¾" came from 20 meter yagis built by a long-gone Canadian firm almost 50 years ago and I saw no reason to take them apart to change their lengths.

When I ran the model with this taper schedule there arose a problem. The effective λ/D ratio was higher than that of the initial model with fixed diameter elements. The change of SWR at the band edges was enough that I increased the 7% spread to 8%. That achieved the same SWR bandwidth while sacrificing about 0.2 db of gain. Since this is a "multiplier" antenna pointed south the gain difference is not too concerning.

The lesson is that element taper is a significant design factor. The effective wire diameter more closely resembles that of the outermost thin tubes than the average or the large diameter found at element centre.

Boom

I was fortunate to have all the aluminum and attachments in my stock to build this antenna. That includes the boom. With the pieces I had there were several alternatives to make the boom. I finally decided to use a couple of length of 2"×1/16" tubes that came from old yagis. Hy-Gain used the same size tubes but neither of these appeared to come from a Hy-Gain yagi based on the wear marks.

To join the tubes I used a scrap 2' length of 2-⅜ OD schedule 40 6061-T6 pipe. Aluminum flashing fills the small gap since the ID of the pipe is a little more than 2". They are held  together with ¼" stainless (304) bolts and nylocs. Lock washers are not effective on round surfaces so it was nylocs or jam nuts. I've used both techniques in my various antenna projects.

One end of the longer 2" tube has a press fit galvanized tube (left picture). Clearly this was the original boom's coupler to another 2" tube. I intended to use it to join the tubes but I couldn't make it work. There has been enough oxidation over the decades that making it fit would have taken a lot of tedious preparation of the surfaces. It wasn't worth the effort. I cut the steel flush to the end of the tube. 

When I was done the boom was 282" (23'-6" or 716 cm). I reran the model with the slightly shorter boom (24' in the original model) and the performance difference was negligible, as I expected. The actual length of the yagi is several inches shorter, measured centre-to-centre from director to reflector, due to the boom-to-element clamps. One can be seen on the left being tested for its fit. The small clamp you can see on the right picture is one of the boom truss attachments. These were found in my junk box (source unknown).

Elements

Since the widest tubes of the old element sections mentioned above are 1", I slipped them inside 1.315" OD pipe. This is schedule 40 1" (IPS) pipe so the ID is a slightly over 1". For other antennas I've wrapped the 1" tube with aluminum flashing. The amount of flashing is easy to calculate since C = πD and D is 1" so the circumference is ~3.14". I rounded down to 3-⅛" so that the flashing didn't overlap itself.

It didn't work; no amount of forcing the pipe, flashing and tube would make them fit together. I measured the OD of one and the ID of the other with calipers and discovered that the ID of the pipe was a little less than expected. All of this aluminum was milled around 1980, so either the mill finish is responsible or it's a build up of aluminum oxide. Since I'm not equipped with a metal lathe I cut the flashing in half (to ~1-½") and it all fit together nicely.

Notice (top left) the obviously hand cut slits; most of the pipe ends didn't have slits. I didn't discriminate and all were joined in the same fashion as shown in the picture. The rear stainless screw head presses directly on the 1" tube for improved rigidity and electrical continuity (see the larger hole in the bottom left corner). Conductive grease was applied to all surfaces after sanding off imperfections and oxides.

The joints between tubes are peculiar. I don't think that was state-of-the-art a half-century ago! Metal strapping squeezes the slit tube onto the inner one. This would have required a special tool. Under tension the machine folds back and crimps then cuts the strap. It's a very solid if unconventional method of joining tapered yagi elements. I can only remember this method being used on shipping crates. A self-tapping screw further prevents slippage. While unusual I saw no reason to redo any of it. 

The ¾" tube was the tip of the original yagi elements and the elements were roped with ¼" polypropylene twist rope. Those were not a good choice so the rope and plugs were removed. I don't anticipate much singing in this yagi but we'll see how that goes.

The smaller tubes were attached in ways I've done before. The end of the smallest tubes (¾") of these sections and the ⅝" tubes were drilled for #8 stainless screws and secured with nylocs. The ⅝" tubes were slit for hose (gear) clamps to secure the adjustable ½" tips. All except the longer tips on the reflector were pulled from my junk pile. They have holes and other imperfections from earlier projects which don't matter as long as the tubes are structurally sound. This isn't an art project.

Notice the black marker rings on the ½" tubes. The element halves were precisely measured to match the EZNEC model. From experience I know that the SDC (stepped diameter correction) algorithm is very reliable. For a 20 meter yagi I try to match the model to within ¼" -- try to do even better on higher bands. A lot of time and effort goes into the design and construction of a yagi so this is not the place to be sloppy. Don't cheat yourself by talking yourself into believing that precision doesn't matter. 

Boom resonance

I've previously discussed how a 3-element yagi can behave as a loaded dipole at about half the yagi's design frequency, where the boom is the driven element and the outer elements are capacitance hats. The is a significant risk of interaction to an antenna on that lower that is close and orthogonal to the yagi. I have this problem with the 40 meter Moxon (and the XM240 before that) and the south-pointing TH6 above.

I reduced the interaction by raising the TH6 a little higher. When this yagi replaces the TH6 the problem must once again be dealt with. However, unlike the commercial antenna I have design options to nip the 40 meter resonance issue in the bud.

The director and reflector elements are electrically isolated from the boom. That prevents them from becoming capacitance hats with respect to the boom resonance. The stray capacitance between the 1.315" pipe and boom clamp is negligible in this application.

The insulators are cut from a flexible ABS pipe that was surplus to a property drainage project. They fit nicely and are strong enough to take the compression of the u-bolts to keep them in position. If you do something similar I will warn you that the insulators must be slipped on before the second half element is attached to the centre pipe, otherwise the tapered section joint hardware (screws, hose clamp, etc.) will block their passage. You'll would then have to cut the insulator, in one place if the insulator material is flexible or in two places if it is rigid. Those cuts can make it difficult to prevent insulator distortion and eventual failure.

The driven element is grounded to the boom. This is for the convenience of building the gamma match (see next section). Since an element near the centre of the boom does not electrically load it in the same way as the outer elements it is an acceptable choice.

I modelled this combination of element brackets to confirm that the 40 meter boom resonance was eliminated. Notice that placing the source at different places on the boom (top: near the DE; bottom: boom centre) effects its impedance at higher frequencies just as it would in any dipole. However, those are irrelevant to this scenario; you could feed the boom this way for real if you cared, but that is hardly typical! That peculiarity does not bear on the fact that the boom resonance on 40 meters is gone. Problem solved.

Gamma match

In the EZNEC model the impedance matching network is a beta (hairpin) while the built antenna uses a gamma match. The former is quite easy to model while the latter is not. In practice, the beta match is a good proxy for designing the driven element of a yagi with a gamma match. 

The reason is that both matching networks perform best when the self resonance of the DE includes -20 to -30 Ω of capacitive reactance, and both work well for the typical 20 to 30 Ω feed point resistance range typical of yagis. There is often no need to adjust the tips of the DE when a gamma match is used despite a beta being employed in the model.

The gamma match saved me the trouble of isolating the DE from the boom and splitting the DE at the centre as the beta match requires. That is, it's convenient and the gamma match works well, though often misunderstood. No, it doesn't cause the antenna pattern to be measurably asymmetric or promote common mode on the coax shield. A CMC (common mode choke) is advisable no matter the matching network.

The design of the gamma match differs in a few respects from those I built for my stacks of 10, 15 and 20 meter 5-element yagis. First, it is more rigid at the centre. A ⅛" thick aluminum bar ¾" wide is attached with a galvanized saddle clamp to the DE adjacent to the boom-to-element clamp. That is the minimum width to comfortably accommodate an SO-239 UHF panel connector. Hanging below it is a piece of rigid PVC that I pulled from my junk box. Have I ever mentioned that I'm a pack rat? I throw nothing out. Particularly astute readers will recognize that rectangle of PVC from a previous project.

The RG213 gamma capacitor is stripped of jacket and shield and inserted into the 7/16" gamma rod. The rod and shorting stub came from one of those ancient 20 meter yagis I scavenged so they are the correct dimensions for this antenna. When fully assembled the gamma match is stable and rigid, and should be up to the rigours of the elements. If not, since this is a 3-element yagi, the gamma match is easily accessed from the tower for service. 

One addition I may add before the yagi is raised is an aluminum jumper from the bar to the element to bypass any galvanic incompatibility due to the interposition of the galvanized saddle clamp. It is fine as it is to conduct initial testing and tuning.

Assembly

Once the boom and elements were built the antenna had to be assembled in the hay field. Although it is reasonably lightweight, an assembled 20 meter yagi needs a lot of room. I did this at the planned launch point for tramming it onto one of the guyed towers for testing and tuning. 

Of the alternatives for getting it high enough off the ground -- preferably λ/2, or at least 30' (10 m) -- this seemed most convenient since for a 3-element yagi the DE is adjacent to the tower. It is easy to adjust the gamma match with minimum fuss. For yagis with any other number of elements (2 or 4+) the DE is out of reach from the tower and other tuning arrangements are necessary.

Since the 2" sections of the boom are different lengths and the longer one has the steel insert that I couldn't extract, the reflector was placed on the short section, since it is heavier, to help balance the antenna. With the DE closer to the reflector than the director the final balance point was almost exactly midway along the 2-⅜" coupling pipe. That's convenient even though the halfway mark by distance is on the longer 2" section.

I used my usual method to weigh the assembled yagi by placing an ordinary scale on a flat surface, then measuring my weight and the weight while lifting the yagi off the ground. The weight is 40 lb (18 kg), which is quite light for a yagi of this size. It will be up to 10% heavier when the boom-to-mast clamp and boom truss are added. Neither is yet built nor needed for initial testing and tuning.

Test & tune

The yagi sat in the field for two weeks while I travelled to Labrador. Back home with August racing to a close I really needed to get this project moving. The bugs were fierce before the trip and they were likely to subside later in the month. Despite that hope being dashed I ploughed ahead.

Yet there was no real reason to do this test. From long experience, models built with NEC2 and the SDC correction within EZNEC are remarkably accurate. It nevertheless gives me piece of mind and confidence that when the yagi is raised to its final position on the tower that it will work correctly. A fault at that time would be more expensive to fix. I judged that a few hours of work would be time well spent.

I set up a tram line between my two big towers to tow the yagi up above the lowest set of guys. A height better than ½λ is more than enough for precise tuning. The tram is at a shallow angle since the towers are 200' (60 m) apart. That makes it an easy one man job. Both the tram line and haul line are ropes so that they don't interact with the antenna. The biggest hassle was unravelling the long lines since no matter how well I fold them after use they still like to tangle.

Tram lines have featured so frequently in this blog that I see no need to say a lot about it. Put the term in the search box if you want to read more. One point to mention is the yellow rope from the tower to the link between the tram line and the winch-driven cable. It is a safety line so that if the winch fails the tram can't collapse. Another point is the height of the anchors and haul cable pulley at around 45' (14 m). The bottom guys of the destination tower are at 35' (11 m).  That allows the element tips to clear the guys and place the yagi midway between the first and second set of guys to minimize interaction.

Hauling a 40 lb yagi at a shallow angle requires little effort. The penalty is that it takes a while due to the length of the tram line. It's a trade off I liked since it made the job easy to do myself. Once the yagi was up the tram line was slackened to bring the boom into the tower so that all parts of the gamma match could be reached from the tower. 

The gamma capacitor was purposely made long. By the time I was done it as almost a foot shorter. I'll make it a little longer for the final version and add the support insulator for the gamma rod near the feed point. Tuning went quite well as you can see on the left. The final SWR curve will be slightly different and better since I stopped when I was close enough. Recall that this is a test to ensure that the yagi is performing as expected. So far so good since it closely resembles the EZNEC model.

Note the connection of the analyzer to the feed point with a male-male UHF adaptor. Although this is less convenient than a short jumper cable it has an important advantage: no need to compensate for the impedance transformation of the coax while adjusting the gamma match. Without it I'd need to guess at each step or use a tool like TLW to transform each measurement to the impedance at the feed point. This way is awkward but saves a lot of time and frustration.

With a successful test in hand I lowered the yagi and parked it in the hay field. It can stay there until I'm ready to raise it to its final location on the tower. Mechanical work on the gamma match, boom truss and other items are ongoing. I'll probably reuse the CMC that's currently on the TH6 or I may make a coax (solenoid) choke for it as I've done for my other monoband yagis.

Next steps

Obviously the next step is to raise the yagi. That will have to wait until the fall. First, it will take planning to arrange for the removal of the TH6. The 40 meter Moxon, which is not far below it, will have to be navigated around. I have a few alternatives to get it done. Aside from that I have other projects and obligations to deal with. 

The second reason is that I'd like to have a 15 meter yagi ready to go at the same time. The TH6 covers  20, 15 and 10 meters, and although I can delay a south-pointing 10 meter yagi to the next solar cycle, 15 meters is more critical for the multiplier rich south. I have been assembling the parts but as yet I'm not far along. I will also need to bury more Heliax since I am running out of transmission line capacity. The 15 meter yagi will go on the tower with the 15 and 20 meter stacks, but low enough that it will not appreciably interact with the stack.

The 15 meter yagi will be a relatively easy project since the antenna is smaller. I will most likely keep it to 3 elements so that it can fit on a short boom while having similar or better performance than the TH6 which, although it has 4 elements on 15 meters, some use traps. I'll write about it when it's done.