NEC5 Test Drive

I have a long to-do list for my station. It reflects a lot of ambition. However, my actual pace of work is at a lower rate. Amateur radio is a hobby after all. Some items linger on the list for a long time indeed! NEC5 was one of them. I say 'was' because I've finally purchased a licence for the software and added it to EZNEC.

EZNEC makes it easy to use NEC5 as an alternative calculating engine. Considering the many advantages of NEC5 over NEC2 and NEC4, and that EZNEC is now free, it is very easy to justify US$110 for a licence. I will not bore readers with what can be learned elsewhere about NEC5 and EZNEC, which you can find elsewhere, including following links provided in this article.

These are perhaps the most relevant resources I read before diving into my initial experiments with NEC5. It helps to know the technology you are dealing with before using it and trusting the results.

• EZNEC and the EZNEC 7 manual
• AC6LA's NEC5 notes (access requires a QRZ.com account)
• NEC5 validation manual
  

Next, a brief summary of why to choose NEC5 versus NEC2. Others cover it better and more completely, but a few points are enough to get you started:

• Tapered elements, including loaded elements -- with NEC2 you need the SDC (stepped diameter correction) in EZNEC, or its equivalent in other modelling software, and also stay within its strict constraints
• Antennas with wires meeting at angles, especially acute angles -- it can be done using NEC2 with fairly complex segmentation procedures, although EZNEC and at least one other package will help you with it
• Wire segmentation is in general not at all strict -- NEC2 requires strict segment alignment between parallel conductors when the separation is small
  
• Antenna elements with loads, lumped or distributed, are handled well -- includes capacitance hats, traps and coils inline with tapered elements and more that are often handled poorly in NEC2
  
• Radials can be on the ground or in the ground, and with more accurate results -- no more having to artificially place radials a short distance above ground, and consequent issues
  

All of these have been important to me at various times. Sometimes there are modelling workarounds and other times I had to mathematically calibrate a NEC2 model with measurements of a built antenna. NEC5 promised a far better modelling experience with less opportunity for errors.

There is a cost to gaining these advantages, and I don't mean the license fee. The greatest cost is segments: you need a lot. A peculiarity of NEC5 is that the calculations converge slowly with increasing segments. That is, you need a lot more segments than with NEC2 to get accurate results. The more complex or large the antenna, the more you need.

That slows the run time and can be a bit of a bother at times. Doubling the segments is frequently inadequate so I double again. I've stopped at 4× the amount though some go further. More on this as I go through my initial modelling experiments with NEC5. 

There are other differences that must be understood. For example, NEC5 does not natively support insulated wires. EZNEC includes an algorithm to allow them when using NEC5.

Luckily for most hams NEC2 continues to be perfectly adequate, especially with the enhancements included with EZNEC. Whether to use NEC5 depends on your interests and needs. This article may help you decide.

40 meter reversible Moxon

The initial experimental model of a 40 meter reversible Moxon was the first antenna I modelled with NEC5. I did nothing more than change the calculating engine, just to see how the results would change without the segmentation and other modifications recommended for NEC5 models. Recall that the model uses constant diameter wires (25 mm) throughout; this is not a physically realistic model, only intended for computer experimentation.

The NEC2 result is at the top and those for NEC5 on the bottom. Resonance shifted downward approximately 1% (~75 kHz). Gain and F/B were similar, after adjusting for the frequency change. Doubling the segments for NEC5 had a negligible impact on the results. 

I tentatively concluded that the difference is more likely due to improved accuracy with NEC5 due to the 90° angles between wires. Even for a straight forward antenna like this we can see where NEC2 is challenged to generate accurate results. 

For those practically minded, you may have more luck getting accurate dimensions from one of the online Moxon rectangle generators (typically based on scaling working antennas) than by using NEC2. I can't guarantee that is generally true, but you ought to keep it in mind should you model a Moxon rectangle or an antenna with similar attributes.

I next tried my physical model for the reversible Moxon. This one uses tapered elements for the antenna I am currently building in my workshop. I won't detail the design in this article since it is an ongoing process. I am trying to build it using only the aluminum tubes and pipes that I have in stock, which imposes interesting constraints. I'll write an article about the antenna when it is built and tested.

Unlike the model with constant diameter wires, the initial model was far off. I doubled the segment count which, unlike for the model with constant diameter wires, did reduce model inaccuracy. For the final design I may again double the segments. That would be 950 segments! That's a lot for what seems to be a modest looking antenna, yet it is frequently necessary for accurate NEC5 models

It was necessary to make a few small changes to achieve the expected performance. One was a slight adjustment to the reflector element coil. The reappearance of short stingers on the elements is due to the material I have on hand and not to a change to my previous conclusion that stingers limit performance for this style of antenna. I am trying to keep them short without resorting to buying more aluminum.

The SWR is only slightly higher after aligning the gain and F/B frequencies with that of the earlier model. It may improve further with another doubling of segments. That may not realistically matter since environmental interactions are likely to be greater: the tower, its guys, and other antennas on the tower. 

With NEC2 the model is far from accurate, worse than the relatively small 1% inaccuracy of the model with constant diameter wires. NEC5 is worth the price if only for this one antenna.

3-element 40 meter yagi with capacitance hats

When I began designing this monstrous antenna I knew that NEC2 would be wholly inadequate. I was less concerned with the impedance than with the frequency of operation. NEC2 typically shifts the resonance downward for antennas of this type, but there is no reliable method for predicting by how much. That is why I built an experimental element to calibrate the model. 

After repeated changes to various sections of the element (position of capacitance hats, length and diameter of select tubes, length and diameter of the hats and stinger), and approximate compensation for ground effects, I trusted that the measurements were sufficient to calibrate the model. Calibration means accurately determining the differences between the NEC2 model and the real antenna. It is not practical to repeatedly raise and lower a 300 lb antenna up 150'. It was critical to get it right.

The extraordinary thing was that the antenna seemed to do pretty well once it was installed and the gamma match and driven element were adjusted. However, small doubts lingered since the calibrated model was imperfect and there is no good way to measure gain and F/B with reliable accuracy. With the NEC2 model and manual calibration, the model's behaviour from 6.55 to 6.85 MHz was calculated to match the real performance between 7.0 and 7.3 MHz.

Then I suffered the effects of a poor mechanical design of the clamps that attach the capacitance hats to the element. One arm of one hat on the reflector fractured and fell off a few months after the yagi was raised. The same later happened to the director. At first I thought it would be disastrous, yet I could not discern a performance impact on air. Even the SWR curve was slightly better.

Modelling of the missing arms using my calibrated NEC2 model suggested that the antenna had its operating frequency range increased by about 70 kHz (1% of 7 MHz). That's not good but it also isn't bad. However the F/B at 7.0 MHz should have measurably declined. That didn't seem to happen. 

Although I redesigned and built new capacitance hat clamps, I've only replaced them on the driven element. That was easily done since it is close to the tower and the tips are accessible by rotating the DE on the boom. Replacing the hats on the parasitic elements is more difficult. I haven't rushed since the antenna continues to work well, and no more capacitance hat arms have failed over the following 2-½ years.

With NEC5 installed, I ran the EZNEC model without making any adjustments to accommodate the unique requirements of the calculating engine. At first glance the results were quite good. Performance between 7.0 and 7.3 MHz was about as expected; no calibration required. Then I took a closer look.

Every yagi design is a balancing act between gain, pattern and match. That isn't easy to achieve for a high Q antenna on 40 meters due to its 4.3% bandwidth. The NEC5 calculation for the F/B at 7.3 MHz was poor. Closer inspection indicated that the optimum range of the antenna was at a slightly lower frequency, by about 50 to 75 kHz. Notice something familiar about that number?

The frequency shift is very close to the higher operating range due to those missing capacitance hat arms. That could explain why the antenna is performing so well. I must quickly add that it is only a hypothesis at this point. It will be necessary to increase the segment count and make other adjustments to ensure that the NEC5 calculations are accurate. It is important not to stop the analysis just because the first hint of an insight conforms with one's subjective experience with an antenna. 

I will do that deeper analysis later, and likely with a lot more segments. For this test drive of NEC5 it is enough to achieve these inklings of enlightenment. I look forward to doing a full NEC5 analysis of this important antenna. I may decide to alter the antenna slightly when I install the new capacitance hats so that it works at its best.

5-element 15 meter yagi

The final model I tested was this long boom yagi for 15 meters. I chose it for two reasons. The first is that I've heard that multi-element yagis are challenging to accurately model with NEC5. The second is that several months ago I sent the model file (including a gamma match) to a ham who requested to see how I modelled the gamma match. He then passed it to someone who ran the model with NEC5. The resulting SWR curve was far from what I measured and successfully modelled with NEC2.

This is a complicated antenna simply because it has so many elements and each element is tapered with telescoping tubes. EZNEC with NEC2 and its SDC algorithm produced a model that matched the actual antenna with exceptionally good accuracy. However, when I added a gamma match to the DE it was necessary to replace the DE with a constant diameter wire since the SDC algorithm can't deal with the gamma match. This is not ideal since the current distribution on a stepped diameter element is not the same as on the equivalent constant diameter element calculated by the SDC algorithm, even though both exhibit the same net reactance.

When I modelled the antenna with the gamma match using NEC5 the SWR curve closely resembled what the other ham got with NEC5. I then returned to the version with a tapered DE and no gamma match and, again, the SWR curve was far off the one calculated by NEC2 (including SDC) and as measured on the actual antenna. That's the upper of the two charts above.

When I doubled the segments of every wire the SWR curve (bottom) improved, though still not very accurate. This result implies that the person who ran my model on NEC5 did not increase the segment count in my NEC2 model.

I suspect that I'd have to double the segments again to do better. That's not a pleasant job because there are so many wires in the model. There may be a convenient method to do it that I have not yet discovered.

I might yet do it just to satisfy my curiosity. I also did not revise the model to include the gamma match with the tapered DE since there would be little point until the antenna itself si accurately modelled with NEC5.

I then produced the antenna patterns at several frequencies across the band and found that the gain was similar but the F/B exhibited more variation. The deviation was worst at the bottom of the band. The pattern at 21.0 MHz has a F/B that is about 5 to 6 db lower than the NEC2 model. Since high F/B figures demand accurate and precise calculations of each element's current amplitude and phase it might again be a matter of increasing the segment count.

Other than my curiosity regarding accurate modelling of the gamma match on a tapered element, it would appear that what I've heard about multi-element yagis and NEC5 might indeed be true. I won't pursue this topic further for now since it's not a priority and NEC2 handles these antennas well.

Wrap-up

From what I've seen so far, I am pleased with my purchase of NEC5. It integrates easily with EZNEC and it can far more accurately model a variety of antennas that NEC2 handles poorly. Neither calculation engine is a perfect solution. Every antenna model requires a few moments of thought to decide which engine is most suitable. It is interesting to try both even when you know one of them will do poorly.

Now that I've done my initial experimentation, I will begin applying it to the construction and testing of actual antennas. The obvious first case is the reversible 40 meter Moxon. Unlike for the big 3-element yagi, it appears that I can develop an accurate model using NEC5 without resorting to building a sample element and calibrating the model with field measurements. Once I have more experience with NEC5 so that I can confidently trust the calculations it will save a lot of time and effort, and wondering whether the calibration procedure is sufficiently reliable and accurate.

If you enjoy playing with antennas you should consider purchasing a license for NEC5. It's a tool that I can see becoming indispensable for design and building antennas for my station.

Digital Mode Filters and Courtesy

What do we owe our fellow hams? When we have different ideas about who to have a QSO with, whose wishes should prevail? Should one ham's preference impose an obligation on others?

These are not easy questions to answer in social activity like our, yet many have strong opinions. Indeed, ask around and you will find that some have strong opinions of one kind or another, while others may express indifference and some are uneasy with the question.

It's a question of courtesy, or discourtesy if you prefer. Consider the following scenario. You call CQ DX and a decidedly non-DX station replies to you. You ignore the caller and repeat your CQ DX. There are 4 possible ways to evaluate discourtesy in this scenario:

1. You are discourteous for not accepting the call and having a QSO.
2. The other station is discourteous for replying to a CQ DX.
3. You are both discourteous: the other station for replying and you for not accepting the call.
4. Neither of you are discourteous. The caller tried and failed, you both shrug and move on.

I suspect that many of you have an opinion, perhaps a strong one about who, if anyone, is being discourteous. I don't know which of the four categories your opinion falls into and I don't really care. I also don't care which might be the most popular opinion. I would not be greatly swayed to fall in line with the majority, though some might. 

Were I to alter the scenario, opinions would shift. For example, imagine a DXpedition asking for only stations that need them for an ATNO (all time new one), yet those not among their number continue to call.

Now I'll add an additional wrinkle: the mode. I suspect that for traditional modes like CW and SSB, when you receive a caller from out of area (e.g. non-DX responding to your CQ DX) you are less likely to ignore them than for digital modes like FT8. I respond to them even though I'd rather not. They "feel" more personal to me, and probably for most hams. Usually they just want a signal report, which can be quickly accomplished.

By contrast, on digital modes I regularly ignore non-DX callers when I send a CQ DX. They can take some time, more than on CW and SSB, and time is precious during a 6 meter opening. Am I being discourteous? You be the judge. As I've already shown, there will be a diversity of opinions. I make no apology for my choice.

My use of the digital modes helps to explain my behaviour. It is limited to the following operating activities, in chronological order of my gradual migration to digital mode operation:

1. 6 meters: My primary interest is DXing and digital modes are very effective for the propagation found on the magic band, and sporadic E in particular. I regularly work non-DX on 6 meters but when I do so I send a simple CQ to solicit calls.
   
2. 160 meters: As the amount of CW activity declines outside of contests, I increasingly resort to FT8 to work DX. When I CQ it is always CQ DX, and I mean it.
3. Rare DX: An increasing number of resident operators and DXpeditions to rare entities include no CW operators. A recent examples is FT4GL (Glorioso). So I worked them on FT8. I also worked FT8WW (Crozet) on FT8 as "insurance" in case I was unable to work him on CW.

I have not yet taken to routine use of FT8 and other digital modes. I may change my mind if CW activity outside of contests continues to decline. However that won't happen soon. I can't say how I'll handle non-DX callers in that future world.

As you can see, my digital CQ'ing on 6 and 160 meters is almost exclusively for chasing DX. Anything that interferes with that is cause for annoyance and, where feasible, mitigation. Until recently I avoided using filters so I was not inconvenienced by the lack of filters in WSJT-X.

Instead of switching to JTDX, which has long had filter features, I chose a different option: WSJT-X Improved by DG2YCB. He includes a variety of features not in WSJT-X and that may never be included. One of those is filters. By choosing his "bleeding edge" version of WSJT-X I retain the familiarity of the original and can select from among the additional features. It is exceptionally easy to do the migration since it installs like any version of WSJT-X and keeps the settings common to both and the log file.

After installing the software and experimenting with its novel features, I looked more closely at its filtering capabilities.

My needs are simple so there was very little that I needed to do. I may never use filters other than the blacklist. Obviously I obfuscated the call signs.

It can be occasionally useful to temporarily disable the filters to get the full picture of what stations are being received. The "BP" checkbox does that. I don't use the "Ignore" feature so I'll say no more about it. You can read about all the additional features of WSJT-X Improved in the documentation.

At this point you might be wondering why I filter stations. I ignore callers manually, which only requires that I do nothing. I don't often program the software to auto-respond to callers, and when I do I can easily click the CQ message button.

The blacklist would grow large indeed were I do enter every non-DX caller that replies to my CQ DX. Besides, I might want to work them, just not when I am hunting DX.

I am not even inclined to put many suspected robots in the blacklist. In most cases they don't really bother me. Again, I ignore them. To repeat a point that I made earlier:

A station's desire for a QSO, whether by human or robot, does not create an obligation on my part.

In the past I would occasionally work a robot just so that they would never again bother me. In a few cases I did not log them. I now believe that it's more honest not to work them than not to log them. Filters help me to do what I believe is the right thing, in accord with my needs and interests.

Well then, who goes into my blacklist? I am not driven by anger, to "get back" at anyone or to smugly deal with stations that operate in a manner that I disapprove of, or stations that splatter or QRM others. I do not engage in vendettas or pointless battles. My true reasons are more mundane.

The stations I typically want to eliminate are those that I'll describe as digital mode spam. Those are stations that flood my screen with endless CQing (often an hour or more), that respond to everyone whether they've worked them before or not, hound stations that obviously don't want to work them, and that are sufficiently local that I can't avoid them. Not all are robots though many are. I am rarely annoyed enough to filter a station that is only heard when propagation is favourable to their location.

Of the 4 calls in the filter screen above, 3 of them are local to me (VE2 or VE3 regions) and one is a nearby US station. This time of year I monitor 6 meters whenever I am not doing anything else with the station. I'll leave it monitoring when I'm out of the house and sometimes overnight. Having the monitor screen overflow with their "spam" means that I can easily miss the occasional message from a distant station, either because it scrolled off the screen or, during periods of heavy activity, it is difficult to spot amongst the clutter.

When I put those stations on the blacklist, my band monitoring experience is more pleasant and effective. The monitor window stays empty while the endless CQ's scroll down the waterfall. This is not about hate, disapproval or philosophical differences. I just don't want the screen filled with their clutter. 

I use the blacklist like an email spam filter. I am not even too bothered by distant "spam" since those stations at least inform me that there is propagation in that direction. I only filter the local spam.

I have only ever blacklisted stations heard on 6 meters. For my limited digital mode operating on other bands, I've never had cause to filter anyone else.

The bottom line is that if I don't respond to you it is almost certainly not because you're blacklisted. Either I'm ignoring you or simply not copying your signal. If you wish, you can judge me as being discourteous. I won't care.

I expect my blacklist to remain short. I might even delete entries since people's habits change. Perhaps I'll do that each spring at the start of 6 meter season. I can always add them back if their bad behaviour persists.

Your reasons to filter stations may differ from mine. Indeed, filters are used by few stations: they either don't use them or they stick with WSJT-X which does not support filters.

Many fervent 6 meter DXers use area filters to silence all callers out of the area they are interested in. For example, European DXers that filter all callers from Europe. There is no need to blacklist every station. I have yet to use one of those filters despite the temptation, since I consider it discourteous for a station in Canada or the US, unless they are very far away, to call me when I send CQ DX. 

Sometimes nearby friends answer my CQ DX. I usually reply to them when no DX calls me. I don't blacklist friends! With the limited message diversity on digital modes this is their way of saying hello. Custom messages are a bit of a bother and I've never used them.

I was averse to the use of filters for a long time. Times change. Perhaps the reasoning I've provided in this article can be food for thought as you consider whether and what to filter. I don't expect everyone to agree with my choices.

With the increasing number of hams attracted to 6 meter digital modes -- generally a good thing -- some bring behaviours antithetical to those of us DXing on 6 meter. The small step I've taken with selective filtering is helping to restore my 6 meter summertime experience to what it once was. Now if only propagation were better!

Between a Rock and a Hard Place

I am accustomed to sharing the towers with wasps early in the fall. Their job is done and most are doing little more than waiting to die. For some reason they are attracted to the cool steel of the towers. They are not a danger since they have no hive to protect. Leave them alone and they leave you alone, even when you're nose to nose with them. Above 10 meters their numbers rapidly diminish.

July is not that time of year. Wasps are now very active and several species are easy to antagonize if you do nothing worse than walk beneath their hives in the tree branches overhead. The occasional sting is painful but usually nothing to worry about. Then one day about 25 years ago, while mowing the lawn, a few stings from wasps protecting a nearly invisible hive 5 meters overhead sent me to emergency room. 

Doctors informed me afterward that I had developed an allergy to wasp venom. I learned that isn't unusual. The risk increases after repeated assaults because the immune system learns the wrong lesson and eventually reacts inappropriately, with a risk of anaphylactic shock. I was fortunate not to become a statistic.

There is immunotherapy available for a variety of allergens. I never got it for wasp and bee venom since it can be unpleasant. Instead I carried an Epi-pen. Years later I had successful immunotherapy for an unrelated allergen that gifted me with a side benefit in that it also reduced, possibly eliminated, my sensitivity to wasp venom. The immune system pathways are largely identical, with small differences for each allergen. 

I was surprised by this in the following year when wasp stings only elicited what can be called a normal response: pain and swelling for a couple of days. However the risk remains and living in a sparsely populated rural area there are daily encounters with wildlife in all of its variety. I am not fearful of the wildlife, even wasps, but it helps to be observant and not take due care. Several days ago I was not observant and I paid the price.

As mentioned in the previous article, I have a lot of outstanding maintenance and new construction to catch up on. One of those tasks is to diagnose and repair an intermittent in the coax going to the upper 5-element yagi of the 20 meter stack. It was a fine warm morning so I gathered my tools and gear and headed over to the 140' tower sitting amidst the growing hay. I mow narrow paths to the big tower and around the bases to ease access during late spring and early summer.

I did my usual rapid visual inspection of the tower and antennas and started up. I didn't get far. I should have taken the warning of an unusually dense cloud of flying insects at the tower base. 

During the several weeks since my last climb up this tower the wasps had built a large and growing nest about 15' above ground. It wasn't visible during my brief inspection of the tower because it was inside one of the wide girts on the climbing face of the tower. It would have been difficult to spot regardless since it's gray and shadowed by the girt in the bright sunshhine.

The density of rapidly flying insects increased until my hands unknowingly almost directly contacted the hidden hive. That's when they attacked.

Which brings me to the title of this article. On the one hand, I'm allergic to wasp venom and the stings were adding up fast. On the other hand, I'm on a tower where the only immediate escape is to jump. I'll leave you to choose which of those options is the rock and which is the hard place.

What would you do? There really is only one correct answer: climb down. Whenever you get into a tight situation there is the risk of panic and the classic fight or flight response. But you can't fight the wasps nor can you fly (literally or otherwise). Besides, if you do jump, the wasps will follow and you will suffer from both the fall and the stings. So start descending and endure the attack as well as you can. It'll feel like forever even though it may only be seconds. Luckily the local wasps don't build their hives very high.

I started running when I hit the ground, burdened as I was with my climbing gear, tools and heavy boots. Many of the wasps pursued and continued stinging me. They let off when I was about 200' (60 m) from the tower. The immediate threat had abated but it wasn't over. From experience I knew that it could be 10 minutes or more until the severity of the venom reaction could be assessed.

I won't bore you with the excruciating details. One picture of my hand will suffice. My face and arms looked about the same. It was a warm day so I was only wearing a tee shirt and a small cap to protect my head and eyes from the sunshine. There were few stings below my chest. The greatest worry was having to breathe through my mouth for an hour because the swelling completely blocked the air passages in my nose.

I recovered remarkably well.  When I attended a social gathering two days later, the swelling had diminished enough that few remarked on my appearance. But it did give me a story to tell!

In the end, the wasps fared worse than I did. Although difficult to reach, I went out at night when the wasps huddled inside the hive and drenched them with a high pressure insecticide canister. I always keep a couple of them in the house. 

When the survivors returned the next day, I made a 20' pole out of antenna tubing and wrecked the hive. That drove them off for good. It is to be expected that I may be slightly nervous when I resume tower work after I've fully healed.

Perhaps you found this story amusing, frightening or instructive, or a little of all three. It can happen to any ham doing tower and antenna work. In warmer climates the danger can be worse. What an unpleasant surprise it would be when wasps swarm from a hive hiding behind a rotator 50' up the tower!

What lessons can we learn from this experience? That assumes that I haven't frightened you so much that you've taken a vow to never climb a tower again!

• Know the risks: Mid-summer is prime time for insects building nests. While there isn't much shelter on a tower, competition among the critters for the best spots can lead some to choose your tower.
  
• Inspect: Inspect the tower, from all sides. That probably wouldn't have helped me in this case because the hive was well shaded. But I should have paid closer attention to the insect activity at the tower base. The danger signs were there. I typically only inspect for structural anomalies before each climb.
• Don't panic: Jumping will leave you disabled on the ground and at the mercy of the merciless wasps. Panic almost always leads to poor choices. As difficult as it may be in the moment, think clearly and act appropriately. Mitigate the attack if possible and then get out of there, but safely. The attack may continue but you will survive. 
• Get help: Seek out family or neighbours immediately if you are working alone, or whoever happens to be nearby. Get medical help in case the worst happens.
• Prevention: Build your towers and antennas away from trees and foliage. It is safer for the tower and for you. This year I worked on a repeater tower where the site owner allowed adjacent trees to grow to a large size. I had to climb through the branches. Insects blend into their surroundings and when the leaves are in bloom it is likely you'll spot the hive too late.
  

There are towers that are less likely to host hives. The wide C-channel girts on the LR20 towers that are used by many large Canadian ham stations provide more shelter than I'd have guessed. Thin tubular legs and struts like those on Rohn towers commonly used in the US provide little protective cover for hives. The underside of rotator and bearing plates on all makes of tower often host hives but you'll see them in time, if you're paying attention.

My hand grip is not yet back to full strength so I haven't resumed tower work. Another couple of days should so it, and in any case we're about to be drenched by the remnants of hurricane Beryl. Better to fall behind schedule than to take unnecessary risks.

Yagi on a Swing

Repairing yagis on the tower is not always easy. The parts you need to access may be far out of reach. With some well thought out choreography it is sometimes possible to twist and turn the yagi to bring the problem area within reach of the tower. In most cases you'll need to lower the antenna to the ground to work on it. That is often simpler and safer, at the expense of a larger time investment.

I decided to experiment with an alternative. It's one that few hams would ever need since it involves towers with multiple side mounted yagis. In this instance the purpose was to repair the XM240 40 meter yagi. Last fall the antenna was moved to one of the large towers and mounted on the rotatable side mount at ~75'. It replaced the TH6 which was raised a little higher and fixed to the south.

A mistake was made when the XM240 was reassembled for the tram ride to its new home and not noticed until a few weeks had passed. The boom clamp for the reflector element wasn't properly tightened. In high winds the element would rotate on the boom. 

A small amount of rotation is not a problem but a large rotation would not only affect its performance, it would not be rotatable since the element would collide with the TH6 above it. Damage would result since element tips are fragile. 

After an ice storm in early winter the element rotated so far that the tip was above the plane of the TH6 elements. Luckily there was no contact due to the direction the XM240 was pointed at the time. A week later a strong wind levelled it again! However I couldn't risk rotating the XM240 without first glancing out the window. That's difficult to do at night when 40 meters is open!

The XM240 boom cannot be tilted to access the reflector because of the TH6 above it. To access the reflector the yagi must be slid horizontally almost 10' (3 m). That's actually possible because there's a lot of tower above the two yagis. What I did was to build a "swing" for the yagi. The diagram shows the general idea. It is suspended from an anchor almost 40' further up the tower.

It isn't quite as simple as shown in the diagram for the following reasons:

• 
  The anchor should be at least 3× the height above the yagi as the horizontal swing distance. Otherwise the large swing angle will lift the antenna into an upward arc and the force needed to swing the yagi will be excessive.
• There can be no elements between the tower and the element being accessed since it will be blocked by the tower.
• The elements of the yagis between the anchor and the swinging yagi must be approximately parallel to the boom of the swinging yagi or the swing will strike the elements of those yagis.
• The swing can only work in one direction so it must be positioned on the side of the tower where the yagi will be swung outward.

I was fortunate that all of these constraints could be dealt with for the XM240. Pointing it west let the swing move between the elements of the TH6 and the lower yagi of the 10 meter stack. This orientation also reduced the swing distance to less than 8' (2.5 m) since the reflector is on the "back" side of the tower from the rotator and short mast. The support strut and legs of the 80 meter inverted vee legs are behind the swing and therefore not in the way.

In the picture you can see the TH6 above the XM240 and the 5-element 10 meter yagi up higher. A rope is dropped from an anchor a little above the 10 meter yagi to the driven element side of the XM240 mast clamp. My intent was for the boom to tilt down slightly on the backside to ease the repair and to help avoid bumping the TH6. The rope runs over obstacles on the side of the tower where the swing will occur. It is vital to avoid tangling the swing rope in any obstructions.

There are several precautions to keep in mind:

• 
  Do not tie the rope to the tower directly since the tower steel will cut into the softer rope material. The risk of failure is low for a rope in good condition but must still be avoided since failure can be catastrophic. I use a large shackle that has a smooth round surface for the rope to bear on. Loop the rope on the shackle several times to reduce tension on the knot. It will be much easier to remove later.
• Consider using steel cable instead of rope. Rope can be very elastic and it can stretch a lot over a long distance, making it difficult to tension properly. It can relax further while under load. Having the yagi come to rest below the mast and rotator can be a problem during the swing operation and when the time comes to remount the yagi on the mast. I used a large turnbuckle to add tension after tying off the rope and it wasn't enough. More on this later.
• Use a second method to support the antenna. Redundancy reduces risk and prevents the boom from tilting up or down too far when the rope is not attached at exactly the centre of gravity.

I installed the swing in late February when we had a period of unusually warm weather. Life then became messy for me and I abandoned most projects for several months. In mid-June I checked the swing and made adjustments in preparation for the operation. 

The boom truss was removed in February. There were high winds over the next 4 months but no ice storms. Boom trusses are partly aesthetic and partly structural support. For many medium size yagis like this don't fret over a brief absence. This XM240 is 10 pounds heavier than the original since the boom and elements were structurally upgraded by the previous owner.

We are looking toward to the reflector end of the antenna, the end I needed to access. A tow strap and shackle are loosely fit over the boom as the second restraint and to help guide the boom as the yagi is swung. The boom truss cable runs over, not within, the restraint.

Disconnect the coax, if necessary. I had enough looped up that it wasn't necessary, which saved me the trouble of removing the weatherproofing. All I had to do was cut the tape and cable ties securing it to the tower. The boom truss must be removed from the mast. Place both where they will not interfere with the swing or become entangled. I left the truss cables attached to the mast plate and let the whole thing dangle below the antenna. If the cables must be separated, first tie them together so that you don't drop one accidentally and leave you with a truss cable dangling far out of reach.

With all the preparation done it was time to pull the bolt from the boom-to-mast clamp. I preferred to remove the mast bolts (saddle clamps) rather than those for the boom saddle so that the clamp plate remained on the boom. That made it easier to me to operate the swing. With the clamps removed, the boom came to rest several inches lower as the long swing rope stretched under tension. It leaned slightly on the reflector side just as I had planned. The boom restraint easily held it.

My original plan was to attach a long rope to the boom to be pulled by a helper on the ground. I scrapped that because the season is well advanced and the hay is high. It isn't fair to ask someone to risk the ticks by wading through the tall plants. I decided to do the job myself.

A lightweight rope is used to pull the boom. The swing is long so the force needed to move the boom is very managable by hand. The nylon rope is loosely looped several times around the boom and knotted. This is a common technique in tower work since it can be used to lift heavy pipe and perform other tasks where there is no available tie point. The rope can be easily slid along the boom in short steps as the antenna swings outward. You never have to reach out more than a foot or two during the entire operation.

Since I was doing this myself, I wrapped the pull rope around the mast for friction. It's like having a third hand as I manipulating the rope and boom and when I periodically tied the rope to the tower. I pulled the boom with one hand and the rope with the other. I would hold the boom while I slipped the knot backward as the swing progressed. The only serious obstacles were the splice bolts connecting boom sections. To get the knot past the bolts I held the boom with one hand to reduce tension on the rope while I lifted each loop of rope over the bolt heads and nuts.

This is what it looks like when the swing is at its maximum extension. It looks impressive from the ground (and on the tower!) since this is, after all, a 40 meter yagi that weighs 75 pounds with a 22' boom and 43' elements. The antenna isn't sitting flat due to the swing attachment point on the boom-to-mast clamp plate. The element tips are well out of the way of the TH6 elements above.

Once the reflector is accessible from the tower the pull rope is tied off. Only a minute was needed to tighten the element clamp bolts; they were really loose! I took another minute to move the boom truss clamp a few inches since it wasn't where it ought to be. At the time the antenna was raised last fall it was easier to add a second mast clamp than to tram the antenna back down to remedy the error. I knew exactly where to place it since there are small indentations on the boom from when it was properly positioned.

When swinging the antenna back to its usual position, take care not to let out the pull rope too quickly. You must do it in small steps, just as before, or the knot will end up out of reach. You will only be able to retrieve it by swinging the antenna out again. Avoid the temptation to rush the job. As the boom plays out, slide the knot backward, always keeping it within reach, easing it over the boom splice bolts as before.

As I hinted earlier, the rope had stretched several inches from the tension of supporting the antenna. That doesn't hurt the rope but it made the antenna difficult to remount on the mast. It wasn't possible to lift it the extra distance with one hand and install the bolts with the other. By then I was hungry so I added another rope to hold it in place and descended. An hour later I returned with a hand winch and attachments. Within minutes I had the boom winched upward and the bolts were reinstalled.

I cleaned the antenna of all the swing hardware and hung all of it on my climbing harness. The boom truss was installed and the antenna levelled, and then the coax rotation loop was returned to its previous state. I temporarily loosened the rotator mast clamp to confirm that the coax was properly dressed by turning the antenna through its full rotation. That done, I climbed up to retrieve the swing rope and anchor and, with the aid of gravity, brought all of the equipment down with me. I'm lucky that despite my age I remain strong enough to do this style of brute force work.

After stowing my gear I tested the antenna and rotator and put a check mark next to one more item on my long to-do list. There is much more to be accomplished this year.

In a way this was an unnecessary job. With contest season over and progress on my planned replacement for the XM240, it won't see much use for the next few months. I did it since the rigging was already in place and I wanted to confirm that the procedure would work as planned. I had also promised the station to a guest operator for one of the summer contests and I didn't want to disappoint him with antennas out of service or of limited utility.

I'll close this article with a cute picture. After climbing the tower I looked down and noticed that I had a visitor. A young fawn was hidden in the tall hay and calmly feeding. It wasn't at all disturbed by all the steel on steel racket I was making. I guess it didn't see me on the ground, or realized that I couldn't see it, and deer are not in the habit of looking to the sky for predators. It happily grazed less than 40' from the tower base. Clicking on the picture should bring up a higher resolution version of it.

My recent blog output is less than my usual pace and that is likely to continue throughout the summer. There are many demands on my time at the moment. Enjoy the summer weather as you work on your antenna projects.

12 and 17 Meter Dual Band 2-element Yagi

I have no antennas for the WARC bands: 30, 17 and 12 meters. They've been low priority since I began building this station in 2016 because they are not contest bands. However, I also love DXing so I have never lost sight on this objective. I have been reasonably successful on those bands by using antennas for other bands, judiciously selected for their performance rather than match. You can do well with compromised antennas when they're up high, really high.

For 30 meters, I will be happy with a single element antenna, as long as it's resonant with a reasonably omni-directional pattern and does not interact with contest band antennas. I have a plan but I won't talk about that in this article. Yagis for 17 and 12 meters are desirable for their gain. That's the subject of this article.

My objectives:

• Efficient: no coils or other loading devices
• Gain and pattern: "good enough" performance across both bands
• Small and uncomplicated: I don't need or want to deal with of large and complex antennas for non-contest bands
  
• Match: low SWR without an elaborate matching network

A dual band 2-element yagi seems to meet my objectives. Although the gain bandwidth for any 2-element yagi (and that includes Moxons) is narrow, so are these 100 kHz wide bands. F/B is similarly adequate since high performance on that metric is not that important to me. Gain and match matter more to me, though you may have different requirements. Cebik noted how a 2-element yagi is suited for the WARC bands. There are commercial 2-element yagis -- examples one and two -- for those that prefer to buy rather than build.

Developing a model of the antenna is quite easy. I began with constant diameter elements since I was not yet decided on the physical design. I used EZNEC, as I usually do. The included NEC2 engine is adequate to model the antenna, and its built-in SDC (stepped diameter correction) will be useful when I settle on the physical element design. Since the DE (driven elements) will be close together, the segment alignment guidance in the EZNEC manual should be carefully studied.

There were several decisions that needed to be made even for a small antenna like this:

• Dual driven elements versus one driven element (coupled resonator for the other DE)
• 12 meter DE on the inside or outside of the 17 meter DE
• Matching network, if any

Yagis are peculiar antennas when you stop to think about it. They rely on opportunistic coupling to create beneficial currents (phase and amplitude) in parasitic elements to create the antenna pattern. Beyond a few elements the relationships are so complex that they defy analytic solutions. Optimized designs had to wait for fast computers and algorithms to power numerical analysis and optimization. Even with just two elements there is much insight to be gained by playing with computer models.

The parasitic elements of a yagi determine the performance and frequency range of operation. It may surprise some to learn that the DE doesn't play a significant role in that. The role of the DE is to effectively couple energy to (and from) the parasites and to set the feed point impedance. 

For a 2-element yagi we therefore need to first focus on the one parasitic element. It is usually chosen to be a reflector since that typically makes for a better antenna. However, the difference between it and the director version is modest. 

As an aside, it should be evident that since the parasite determines the pattern that in a 2-element yagi there is a "mirror image" frequency range where the reflector behaves as a director. For example, for the 12 meter 2-element yagi, the gain and F/B peak in the reverse direction at 23.85 MHz (shown above). That attribute can be ignored since that occurs outside of any amateur band and a DE designed for 12 meters won't be provide a good match at the lower frequency.

Returning to the practical design of a 2-element dual-band yagi, the necessary element arrangement imposes constraints. The first is that the two DE must be adjacent. This is because they are either driven by one transmission line or one of the DE (the smaller) is excited by coupling from the other DE. That adjacency determines the placement of the two reflector elements.

Spacing between the 17 meters elements is 2.8 meters (0.17 λ). The 12 meter reflector is 0.7 meters inboard of the 17 meter reflector. For this configuration -- there are alternatives that we'll discuss -- the 12 meter element spacing is 2.3 meters (0.19 λ). Boom length is 3 meters (10'). DE spacing is 20 cm.

The few commercial designs I've looked at place the 12 meter DE on the outside and make it a coupled resonator. It seems reasonable to me to shorten the boom by putting it on the inside and to slide the 12 meter reflector back a little to compensate. Dual driven elements, connected by a short transmission line, are not difficult and would seem to remove the problem of fine tuning the DE spacing and length for proper excitation on 12 meters; coupled resonators (they go by other names as well) can be finicky.

When I placed the 12 meter DE inside the 17 meter DE, although the gain and F/B were fine it was difficult to achieve a good 50 Ω SWR on 12 meters. This was true with both dual driven DE or the 12 meter DE as a coupled resonator. When placed on the outside of the 17 meter DE, a good match was easy to achieve with either feed method.  As already mentioned, the "found" attributes of yagis have to be worked with or worked around as determined by the mutual coupling of elements in any particular design.

When dual driven, a short transmission line connects one DE to the other. While it doesn't matter which is connected to the feed line there are two differences to consider. One is tuning. The short transmission line inductively loads the second DE because its nominal impedance is typically 150 Ω to 300 Ω. The DE at the far end of the line must be shortened to compensate. The second is that it is mechanically and electrically awkward to connect coax to the outer DE. You can see his in the Bencher (DXE) Skyhawk yagi where the coax has to loop backward to connect to the outer DE.

Since the coupled resonator version of the antenna works so well it is no surprise that the commercial designs chose a coupled resonator. Only one DE needs to be isolated from the boom, simplifying construction. I recommend spacers on each side of the DE to prevent the close-spaced DE from touching in windy conditions.

Achieving the excellent SWR in the model required careful adjustment of the DE spacing and the length of the 12 meter DE. In practice it will be necessary to make physical adjustments during construction and tuning. Although I achieved the best 12 meter SWR with a DE spacing of 20 cm, I strongly suspect that they will be closer after tuning.

I have deliberately avoided reporting the element lengths since that depends on tube diameters, lengths and steps, and the method of mounting them to the boom. If you are not comfortable with computer modelling you may be able to adjust lengths during initial tuning since the antenna isn't complex. However, modelling is strongly recommended since it can be extraordinarily accurate using EZNEC with NEC2, its built-in SDC, W6NL boom coupling adjustment and segment alignment of the close spaced DE as documented in the EZNEC manual. If and when I build this antenna, I will create a precise model of my chosen physical design.

It is worth noting that the SDC algorithm in EZNEC can only be applied with a narrow frequency range. When setting the frequency in the model to one band, the SDC cannot be done for elements of the other band. That restriction does not apply for the NEC4 and NEC5 engines. However, the SDC constraint has little effect on a dual-band yagi design of this type in which the non-resonant element lengths of the other 2 elements have a limited role. But be aware of the restriction when you model a multi-band antenna.

6.6 dbi free space gain for both bands is quite good. Although the theoretical maximum gain of a 2-element yagi exceeds 7 dbi it is very difficult to achieve in practice. It is more difficult for a dual-band design. F/B is not great but that is not unusual for a 2-element yagi since the frequencies of maximum gain and F/B do not coincide. Improved F/B is possible with nested Moxon rectangles at the cost of greater complexity. I don't require a high F/B so I am happy with these azimuth patterns.

I didn't bother to plot gain and F/B across the 100 kHz of both bands since there is so little variation. F/B varies about 2 db and gain less than 0.2 db. Tune these antennas at the centre of the bands and they will work well over the full bands. The same is true of the 30 meter band which is twice the wavelength but half the size (50 kHz).

Now we come to the big question: will I build it? My difficulty is less with the construction than where to put it. My towers are crowded and I want to avoid destruction interactions with my large contest band antennas. Side mounting is not an option since this directional antenna has to rotate. It will be necessary to develop models of it next to my other antennas to see where they may be problems. I am no willing to build and maintain another tower for this antenna.

Even without a placement plan I may still go ahead and build it. It's a small project and offers an opportunity to compare it to the model and see how it tunes and performs. Until then, I will continue to use my non-WARC band antennas on the WARC bands

Age and Delayed Gratification

One of the measures of maturity is the ability to delay gratification. When a small child wants something, he or she typically wants it immediately. Denial can lead to tantrums, sulking and similar behaviour that we label childish. As we mature into adults we learn to accept delay while never losing sight of our objectives. Adults plan.

As the amateur radio population ages, I've seen how delayed gratification can work against us. Children have their whole lives ahead of them so they can afford to wait for what they desire. Yet they often won't. On the other side of life, when we're old, waiting can too easily result in permanently lost opportunities; delayed gratification, which once served us well, becomes a curse.

Pink Floyd said it well in their song "Time":

The sun is the same in a relative way, but you're older
Shorter of breath and one day closer to death

If you're an older ham, are you putting off replacing that old rig with a far better new one? How about that Windows 7 computer, or with an even older operating system? When that ancient yagi is missing elements, hardware is rusting and the coax became water contaminated years ago, do you hesitate to replace it?

Why?

I see this a lot since I do tower work for others and visit many of their shacks. Whether they are hams I've known for decades or they are recent acquaintances, they have a ready excuse. Here are a few of them:

• "Well, it's kind of okay. I jump into the pile ups and I get through eventually with the amp."
• "You get used to all that noise (or distortion or ringing). It doesn't bother me much any more."
• "I don't want to bother anybody to climb the tower (or up to the roof)."
• "I don't keep up with all the new technology and products so I never know what to buy." 
• "It seems like a lot of money. Can it really worth it? I'll think about it some more."
• "Yeah, there's lots of DX on the digital modes, but I'm too old to learn that computer stuff."
  
• "Why bother? I could drop dead tomorrow."

I bet that many of you could easily extend the list. I've heard so many spurious justifications for delay. I've used a few of them myself!

There is a modern saying that provides the antidote: YOLO -- you only live once.

No matter how much time you have left, why deprive yourself? Except in rare situations, none of us can know how long we have, whether you're 20 or 80. There is no advantage is deciding that it's all over and engage in acts of self-deprivation. There is always something new to learn or experience. Don't forgo the many available opportunities.

Indeed, I argue that the older you are the more you must pursue your dreams. Make a ham radio bucket list and get started. Do it today. The young have time to delay gratification. The old no longer have that luxury. The urgency should be escalated.

Dispose of the ancient and dusty stuff now -- don't saddle your heirs with it. Buy new and better equipment. There really is a difference!. As much as we complain about prices and complexity, the quality and performance of electronics and antennas is superior to what fills so many shacks. Nostalgia is nice but it doesn't do much for us on the air when we dive into the pile ups. The shack will be tidier, the operating more enjoyable, and the new equipment will fetch a good price for the estate when the time comes.

Yet there are obstacles. Just make sure they are approached as obstacles and not as excuses. 

• Money: You likely have the money, or at least enough to outfit the shack with new equipment. Perhaps you believe that you are spending the inheritance you plan will leave, or that you've developed a habit of thriftiness, and so you won't spend what you can. Reconsider. A few thousand dollars is minuscule in comparison to the large assets you will bequest, real estate in particular, and the resale value can be very good.
  
• Labour: When it comes to tower and antenna work, there are options if you are no longer able to do it on your own. Almost every club has members who will do at least small tower jobs for others -- hams helping hams. At worst, hire a rigger with experience working for hams. The expense is modest.
  
• Learning: Old dogs can learn new tricks, if you persuade them to get them off the couch. We tend to relax and let life wash over us as we age even though we are perfectly capable of mentally and physically exerting ourselves. You can learn to use a PC, digital modes, novel features of modern equipment and sophisticated test equipment, and so much more. All you have to do is, well, do it.
  
• Overreach: Indulge, yes, but don't go so far that you create a burden for yourself and others. It would be difficult to overdo by upgrading the shack, but so easy once you plant towers. You don't need to build a big station like mine to have a lot of fun and operating success. Don't alarm your family and neighbours by putting up multiple 100'+ towers and large yagis. One reasonably high tower, a multi-band yagi and low-band wires can do wonders. It will not be expensive to dismantle when the time comes. My towers will almost certainly be cut down to save the expense. My large property makes this possible.
  
• Cost-benefit analysis: A common objection to investing further in the hobby is that there may be little time to enjoy the investment. How can you know? We can die tomorrow or not for many years. The assumption of impending demise (fatalism) is merely an excuse to deny ourselves. If it's only a year, well, who cares? You won't be around to do the final sums, but you will have had a year of enjoyment. Fatalistic estimates should not unreasonably constrain your choices.
  
• Burden on survivors: I have a friend who incrementally downsized his antenna systems as he aged. When he was longer confident doing tower work he took down his tower. When he could no longer climb onto the roof, he resorted to ground mounted antennas. He went QRT when that became a maintenance difficulty. He was more comfortable doing it that way even though I offered to take down his tower when the time came. I wanted him to enjoy the hobby for as long as possible. Make a plan and you can eliminate the worry of leaving behind a burden for your survivors.
  

Have I motivated you to act? Sadly, probably not. That's been my experience from the many conversations I've had with elderly hams of my acquaintance. It can seem a major undertaking at a time of life when we increasingly spend our time looking to the past rather than ahead.

I think that's a shame. You can all too easily rationalize delaying gratification beyond the point of no return. Try this: replace that old equipment with a modern digital transceiver. It isn't all that much money. There's nothing easier you can do to appreciate the value of looking towards the future with optimism. Don't deny yourself.

CQ WPX - Making It Fun Again

I don't really like the CQ WPX contest and I've said so several times in this blog going back many years. It was one of my favourites decades ago when special prefixes were more rare. Chasing prefixes was akin to chasing countries in CQ WW, which added a lot of interest (in my opinion). These days I enter CQ WPX very casually or for contest practice, or not at all.

I was engaged in casual contest activity on Saturday morning when I noticed that my first 30 or so contacts were all multipliers. That isn't unusual: the rate of duplicate prefixes grows slowly as the QSO accumulate since there are so many available prefixes. For those that accumulate thousands of QSOs the multipliers decline to approximately one third of the total QSOs.

I decided to continue operating with the aim of only working new multipliers; that is, stations with a prefix not already logged. As noted, that's very easy in the beginning and only slowly increases in difficulty. I enjoyed it so much that I kept at it for the rest of the weekend. My operation remained casual, only sitting in the chair when chores and other diversions (such as a DX opening on 6 meters) had my attention. I eventually called a stop when I had logged 500 QSOs, and prefixes.

Why do it?

Why not do it? It isn't possible to be competitive operating this way, so it's just for fun. It's a style of contesting that is used by a minority of competitors in this this contest in others. For example, look at the line scores for ARRL Sweepstakes and you'll find a few stations that achieved a clean sweep by working exactly one station per section. 

You can't work every prefix in CQ WPX or every country in CQ WW, so another milestone must be chosen. Usually it's a round number. In my case it was 500. It wouldn't have been difficult to strive for a higher number.

When you get down to it, the reason we enter contests is because we enjoy it. A contest can be enjoyed without winning, and that's a good thing since winning is difficult and there can be only one winner (per category). The thousands of other participants each have their own objectives to make the time spent worthwhile.

Pick any contest and an objective that tweaks your interest and just do it. That could be working 100 countries or all 50 US states, or whatever else you decide. All that matters is that you enjoy it. You don't have to win to feel like a winner when you achieve your objective. Failing to meet an especially difficult objective can still be very enjoyable since the much of the enjoyment comes from the pursuit.

How to do it

Although it may just be for fun, the operating objective should be well defined. Decide in advance and stick to it; don't switch to an easier objective when you run into difficulty. You can of course operate casually with no explicit objective, but that's different from what I'm talking about. To make it fun and competitive, an objective might be defined as follows:

Maximize score while working only multipliers, either for the full contest duration on all bands, or one chosen band, with or without assistance, etc.

You get the idea. I simply chose an explicit objective similar to the one I casually pursued in CQ WPX CW this past weekend. I stopped at 500 prefixes, but for a truly competitive objective there should be no limit other than what's allowed under the formal contest rules.

Let's run through the specific tactics I used, or that I had to use while pursuing prefixes.

No running: If you hate running, as many do, this objective is perfect. The reason is that you can't control who responds when you call CQ. It would be rude to ignore callers that are not new multipliers. I therefore operated S & P (search and pounce) throughout the contest. There are so many multipliers available in this contest that my rate was close to one QSO per minute. The downside is that you can only work stations that run, and that excludes many casual operators with rare prefixes.

Assistance: Searching for just multipliers by spinning the VFO can be tedious. I enjoy unassisted operation in most contests, but I connected to the cluster to receive spots. Since it's a CW contest, I opted to receive skimmer spots in addition to spots by operators. By keeping the search relatively easy I avoided the risk of fatigue. You might choose differently.

Frequent band changes: Since the solar flux is high, activity is spread over more bands. Indeed, the solar flux is so high that during the northern spring and summer the high bands are typically better at night. When the rate slowed on one band I'd switch to another. Alternatively, I would choose or turn an antenna in another direction (e.g. Asia or South America instead of Europe). Most stations QSY'd often, including the big guns that mostly run, so that many of the spots I clicked on were no longer valid. After I shortened the spot timeout to 10 minutes, stations I clicked on were almost always there.

Difficult QSOs: Not every running station in a contest is an expert at it. As time wore on and multipliers were less common it was necessary to try and work runners who were not very efficient at it. These included operators that had difficulty copying, necessitating many repeats, waiting for them to complete with other stations, inability to pick a call out of several callers, and so forth. Had I been operating SO2R it would have worked others on another band while I waited or repeated the requested info. Early in the contest when new prefixes were plentiful I'd simply click on another spot to avoid waiting. I am not criticizing those stations: they are learning new skills and I am glad that they are active in the contest.

Power: I kept the amplifier off. It was a warm weekend and I didn't want to put up with the exhaust and noise from the amplifier. It was not needed for my style of operating since I could easily skip over stations that didn't hear me or the pile up was to deep. I'd go on to other stations and try them again later. Limiting myself to 100 watts had little impact on my success. Had I been running, the extra 10 db would have made a big difference.

Bands and propagation: Because I could work a station only once, I was not discouraged when propagation didn't allow me to work them. I could catch them on another band where the propagation was more favourable. In this way it was a lot like Sweepstakes. Nearby stations were mostly worked on 40 and 80 meters, while DX was easier on the high bands. There were of course many exceptions. The point is that I could wait until propagation was in my favor on any band. There was no point wasting time when it was difficult. Stations with new prefixes were plentiful and I would likely work the difficult one later on another band.

Overlay contest?

This style of competition is easy to formalize as an overlay category, officially or unofficially. A few minutes of thought was enough to come up with several rules to make the competition fair and interesting to participants. However, I am not convinced that it would receive broad acceptance. I don't even know whether I'd want do it as a competitive effort. 

It was still a lot of fun and I might do it again. There is nothing to stop you or anyone from inventing novel pursuits in a contest and have fun doing it. Other contest participants won't know what you're doing, but they will appreciate putting you in their logs.

MFJ-1896: 6 Meter Moxon

It may seem surprising that I have an MFJ antenna. The story behind it is interesting. While chatting with a friend last year I mentioned that I would like to have a second 6 meter antenna. It would be used to check for DX in directions other than the one the main antenna is being used for. Turning antennas to find openings is tedious and during those minutes I can miss stations from all directions.

He mentioned that he had a small 6 meter yagi that he bought at a flea market but would never use because he had no room for it. When he brought it over I was surprised to find that the carton was unopened; it was a new antenna. It turns out that the fellow that sold it to him for a few dollars had the same problem: no room for it. So I found myself with a free and brand new MFJ-1896 6 meter Moxon.

It languished for a year. The 6 meter season was drawing to a close at the time and I had more urgent projects. I felt a little guilty with the carton standing there over the winter since a gift ought to be enjoyed. This month, with the 6 meter season started, I finally made the effort. It's a small project that I could tackle despite the family issues that are occupying so much of my time at present. Assembly and tuning took just 2 hours spread over a couple of days.

I opened the carton and found most of the parts loosely packed. The hardware was bagged and a there was a bit of bubble wrap around the tubes. There were two assembly guides, a large one inside and a smaller version stuffed in a fold of the carton. I don't know why. I didn't bother to compare them in detail, though they appeared to have the same content.

The instructions were skimpy, as noted by others in the small number of eHam reviews. All the listed parts were located, including a few spare lock washers. The heads of the #10 hex bolts were smaller than standard size. I think all the hardware is stainless. A little time spent outdoors will soon confirm that.

As noted in the reviews, finish quality was lacking. A couple of the corner pieces were not bent to right angles, tube slots had hazardous burrs and the coax pigtail wasn't wide enough to fit onto the driven element studs.

I filed the burrs, bent the corner tubes and slit the coax a bit to fit the studs. A bolt hole on one side of the driven element was askew, which made it difficult to push the #10 bolt through it. 

Let's talk about the aluminum tubes. The extraordinary light weight of the antenna offers a hint. They are thin, very thin at 0.03". The same goes for the 1.5" diameter boom. This is half the wall thickness of the usual aerospace 0.58" wall used for telescoping yagi elements in better antennas. Even that isn't the entire story.

For proper telescoping the step is 1/16" rather than the usual ⅛". The main tubes are ⅜" diameter and that of the corner pieces is 7/16". This by itself isn't worrisome for a fairly small VHF antenna. The problem lies with the aluminum alloy.

This is not high tensile strength aluminum alloy. It crushes all too easily. There is almost no resistance to the pressure from screwing on an ordinary #10 nut. No matter how careful you are, the tube will crush before the hardware is properly torqued. Eventually the tube will further yield under wind load and weaken the mechanical and electrical bonds.

The situation is less dire for the joints with the elbows and element tip insulators. The distributed pressure of hose clamps avoids the risk of crushing the tubes. The driven element in particular needs support inside the tube to reliably secure the low tensile strength aluminum tubes. I did not attempt to "fix" the antenna's design woes.

I put my concerns aside and completed assembly of the antenna. I followed the dimensions printed in the manual. The critical element coupling inherent to the Moxon's operation requires more care in measurements than for a conventional yagi.

The picture shows how I modified the feed point to reach the studs and used silicone caulk to seal the unprotected open end of the RG58. RG58 of any length at VHF is a bad idea but I had no compelling reason to upgrade it. It's only a few feet and I doubt that I'll be tempted to put a kilowatt into it. I can replace the supplied coax if I'm even so inclined.

The other end of the short coax has crimp UHF female connector. I taped the coax to the boom and attached a (tested) length of RG213 to allow the analyzer to be connected from a distance where ground and a human body would have no significant impact on antenna tuning. The absolute minimum height should be ¼λ (1.5 m) and more is better. Happily that's easy to manage for a VHF antenna.

This was my testing setup. The antenna is approximately ½λ above ground (3 meters), which is more than sufficient to stabilize the feed point impedance. The SWR should remain unaltered at greater heights, assuming there are no interactions to contend with. It is easy to tune a VHF yagi this way in comparison to tuning HF yagis. I crouched down and moved around during testing to confirm that my body didn't have an effect on the measured impedance.

The initial SWR measurement was out of bounds, with the minimum SWR found at 49.5 MHz. It is almost exactly 1, which was promising. One of the critical dimensions to get a 50 Ω match on a Moxon is the distance between the element tips and the quality of the insulator connecting them. 

I was careful to get that distance exactly right during assembly (3-¾"). The plastic rods supplied with the antenna are of unknown material but at first blush appear to be adequate.

I remeasured the element dimensions and found a few small errors. Mistakes are easy because the rounded corner complicates the measurement from the outside of elements to the boom centre. After correcting those dimensions the minimum SWR rose to 49.7 MHz. That's still far too low.

The elements were shortened to raise the frequency of minimum SWR. The elements must be adjusted in concert to maintain the frequency relationship between the driven and reflector elements. I therefore chose to slide the inside end of the elbows into the element tubes to shorten the elements. I did it in ¼" steps until I achieved the SWR curve I wanted.

The minimum SWR is now slightly above 1. There is no advantage in fussing with the antenna to make it exactly 1. In any 2-element yagi, which includes Moxon rectangles, the frequency for maximum gain is below that of minimum SWR. My chosen SWR curve is a compromise that should provide good performance from the low end of the band (CW and SSB) up through the digital windows above 50.3 MHz.

Mission accomplished, I leaned the antenna against a wall of the garage until I am ready to raise it. I hope to do so in the coming weeks and use it during most of this year's sporadic E season. I will probably feed it with LMR400, since that is cheap and convenient, and the run will be less than 50' (15 m). There is no compelling reason to fuss with Heliax to reduce loss over this short distance.

Is this antenna worth paying the retail price? Obviously I paid nothing for it but it is a valid question for almost everyone else. A 6 meter Moxon is an easy and inexpensive antenna to construct from raw materials. But that would require an investment of time to create a mechanical and electrical design and to find, purchase, machine and assemble the components. The driven element insulator might make an interesting 3D printing project. 

Not many hams would want to do this, preferring to invest their limited time on other projects or on operating. MFJ has made a business of meeting the needs of hams on a budget for many decades. I wonder what if anything will take their place now that the business is shutting down.

All I can do is shrug. If an antenna like this inspires more hams to enjoy what the magic band has to offer, it serves a purpose. Don't expect it to last many years in fierce winds and winter weather. Hopefully by the time that happens the owner will have become a 6 meter enthusiast and will be ready to make a larger investment in their next 6 meter antenna.

I have a place for this antenna, at a modest height on a tower currently unused. I had intended that small tower to put up the radio/antenna for my wireless internet service. Since that had to be higher for a reliable connection from my isolated QTH it has only been used for climbing onto the roof of the house. I'll have to dig up a small TV antenna rotator to turn it. If I get a couple of years out of the antenna it'll be worth the effort.