Sunday, August 28, 2016

Perils of Chasing Yagi Performance: A50-6

Ever since a friend loaned me a 6 meter rig in the mid-1970s I've been intrigued with the magic band. That brief experience led to construction of a simple yagi and the addition of the FT-650B transverter for my FT-101E. When I had the opportunity to build a proper tower and station in 1985 I purchased an FT-726R and a Cushcraft A50-6 yagi. With a 150 watt amplifier I worked hundreds of grids, 6 continents and 70 countries, well before 6 meters was as popular as today and before many countries had a 6 meter band.

By the time I tore down my station in 1992 I knew that the A50-6 as originally designed is a poor performer. Computer modelling was just then going mainstream in the ham community and helped the vast majority without the means to range test antennas to evaluate antenna designs. I did the same, purchasing the MiniNEC-based ELNEC, the forerunner of today's EZNEC product from W7EL.

That was a long time ago and my model is long lost on a forgotten floppy disk. But I do remember that the antenna gain fell short by several decibels from what was theoretically achievable with 6 elements on a 1λ boom. Getting the model right, I recall, was difficult because of the long run times on a 16 MHz 386 processor without a math co-processor. Not only that but the lack of stepped diameter correction (SDC) resulted in telescoping tubing elements to have an incorrect resonance.

As I consider what antenna I will use for 6 in my next station I am revisiting this antenna. The boom is being reconstituted from its component pieces, from what had been its interim usage as a mast or for fishing wires through my backyard foliage. One section of boom needs to be replaced due to damage it suffered. All the elements are in excellent condition. A couple of them were used in the 2-element yagi I constructed for use in 2015.

Computer modelling has come a long way over the past 30 years. There really is no excuse for poor antenna design nowadays. What design best fits my operating objectives? To this end I have come back to the A50-6 to see what I can do with it. After all, I have the components of a high-performance antenna, if only I can decide how to best use them.

The original A50-6

VE3VN tower and antennas in 1985
Unfortunately I cannot easily redo a model for this old antenna. I dug up the manual for this antenna (see cover above) and discovered it had no information on element length. There isn't even a dedicated manual for it: it rates only a set of errata in the manual for the A50-3 and A50-5. It simply instructs you to insert the tubes for the tips up to the black marks painted on them, order them from longest to shortest and space them 47" on the boom. Since those marks are long since faded away and the elements difficult to retrieve from storage I have no dimension data at hand.

No matter. Other than curiosity there is no good reason to model this antenna. I know that its deficiencies.

The equal spacing may seem odd yet it is not a dreadful idea.  W2PV in his studies during the 1970s (documented in his book Yagi Antenna Design) used equal spacing, using which he created excellent designs. That is not the problem with the A50-6; rather, it is the element tuning.

For your interest I've included a picture of my tower in 1985 just as antenna construction is being completed. At the bottom is a TH6 (19 meters high), with the A50-6 at the top (22 meters high) and a Cushcraft long-boom yagi for 2 meters in between. You can see the equal spacing on the A50-6, so different from a modern yagi. You can also see that I did not use a common mode choke, which while not uncommon back then is surely a bad idea. Each yagi was fed with 40 meters of brand new LDF4-50A Heliax. The attenuation is -0.6 db at 50 MHz. That small loss was confirmed; it was not responsible for the poor performance.

Today's A50-6S

Performance of the current antenna of this name is nothing like the original. The design has been rigourously optimized, by, as I understand it, W1JR. Yet the boom length is the same (with a different taper schedule) and the elements similarly constructed. The improved performance is easily verified in EZNEC or YW, including the Leeson SDC for tapered tubing elements. I used EZNEC to model the antenna. Since the manual has the measurement details if you are interested so I won't list them here.

A50-6S wire model with the current profile at 50.5 MHz

How not to model a yagi

My first attempt to model the A50-6S did not go well. I wrote the following paragraph before realizing just how badly I messed it up.
When tuned for the range 50 to 51 MHz (per the manual) the free space gain is 13.1 dbi at 50 MHz and peaks at just over 13.5 dbi at 51.5 MHz. F/B is best toward the higher end of this range, consistently better than 20 db. Feed point resistance between 50 and 51 MHz is approximately in the range of 16 Ω to 18 Ω and the reactance is similarly stable. I didn't need to model the matching network to know that SWR would be very good and within reach of the supplied gamma match.
If you are an experienced antenna modeller you may be able to make some good guesses at what went wrong. But first I'll discuss a few points that gave me pause, evidence that led me to the answer. There are lessons here for anyone contemplating antenna modelling, and especially for yagis.

Ultimate gain

I knew that 13.5 dbi gain is high, and maybe too high. I was lulled by the Cushcraft manual that claims a gain for the antenna of 11.6 dbd, which is equivalent to 13.7 dbi. But this is 2 db more than the theoretical maximum gain for a 1λ boom.

The A50-6S gain would therefore be ~2 db better than the similar design in the ARRL Antenna Book (and other respected reference designs) and up to 2 db even better over equal spaced elements like the original A50-6 I purchased.

Alas, this was not to be. If something looks too good to be true it probably is. Take a look at the following chart from W2PV's classic book Yagi Antenna Design. There are other references that generally agree with these figures, as W2PV discusses in his book.


The maximum achievable gain for a 6 element yagi on a 1λ boom is ~11.3 dbi. More is possible with some fine tuning of the design, at the expense of difficult matching and reduced F/B. Even so the maximum gain will fall below 12 dbi. The 13.5 dbi figure I modelled is clearly impossible.

Perils of NEC2 modelling

EZNEC features will warn you about some problems in your model. The one that is proved especially useful in this case was average gain. When you do a 3D pattern plot EZNEC calculates the total field versus an isotropic radiator. The ratio between these -- average gain -- should be exactly 1. Here is what I saw:


Now we know where that extra 2 db came from! We have only to determine why. This is where close attention to detail pays dividends. The EZNEC manual has all the information you need and is an excellent resource. But if you don't know what you're looking for how can you find it?

I had a strong suspicion of the cause of the error. It turns out my suspicion was correct. But rather than jump to the answer let's look at how I diagnosed the problem. That procedure is more important than the conclusion.

The yagi's radiation resistance was quite low: ~16 to 18 Ω. While this is entirely possible it did not look right in the context of the wide spread in resonant frequencies of the elements. So I took the driven element and isolated it. At its resonant frequency the radiation resistance was 44 Ω. A dipole in free space ought to be 73 Ω. Fat elements lower the value somewhat but not even close to that degree.

Segmentation

EZNEC didn't raise any segmentation warnings (too long, too short, etc.) yet therein lay the problem. I had made the segment lengths of the main tubing sections approximately equal but perhaps fairly large for a VHF antenna. I used a 1 segment wire equivalent for the U-bolt clamp and boom crossing, 5 segments for the next 24" tube and a variable amount for the outside tube, the length of which varied with the element length. All my choices caused problems.

The biggest problem was that centre section. I had to make it 1 segment since its length is quite short at only 1" or 2", with a diameter of ~1"; I experimented with various dimensions to determine what seemed most realistic. (Note: A 1-segment wire is not unusual and serves well when a source or transmission line connects to that wire.) The impedance dramatically changed as I varied the length and diameter. At 4" long the radiation resistance got very to the proper value: 71 Ω.

It isn't sufficient to do just that. So I reduced its length to a more sensible 2" then made the segment lengths of the tubing sections equal to that, or as close as I could get. This increased the segment count in the total antenna by quite a lot which slowed calculation. However it was worth it when the average gain came in at precisely 1.000 and the yagi's feed point impedance rose to 29 Ω. The forward gain was exactly where it ought to be, between 11.1 and 11.3 dbi, and overall good performance in its specified operating band between 50 and 51 MHz.

More perils: using the Leeson SDC

Having overcome one modelling peril I came to a more subtle matter: the reliability and correct usage of SDC (stepped diameter correction). With NEC4 the correction is not necessary so you are already one step ahead in the game. But with NEC2, which the vast majority of us use, some kind of SDC is required. It is not without its pitfalls. The NEC2 model can only be as accurate as the Leeson SDC used in EZNEC. It has numerous constraints, many of which you can read about further in the EZNEC manual (circa page 64).

The references I've checked show that the SDC for telescoping tube elements is less than 0.2%, often no worse than 0.1%, compared to NEC4. Field tests seem to confirm the model results. My own small experiment worked pretty well when putting the EZNEC model into practice.

Since in the present case I am shifting the yagi down in frequency by 1% (500 kHz) even a 0.2% (100 kHz) error is perfectly acceptable. Accumulated errors from construction technique and interactions with adjacent antennas and wires almost certainly are at least of of similar magnitude. Perfection isn't possible, and you will not notice a gain difference of 0.2 db! Even a degraded F/B due to interactions can be a poor correlate to gain loss.

The next source of error in using SDC is the centre section of the element, which is where the element crosses and attaches to the boom. The boom and clamp together make for a wider electrical diameter, though one without a well-defined translation to an equivalent wire diameter. Most formulas for this purpose assume a flat plate for an element-to-boom clamp, while the A50-6 uses a U-bolt. If we get it wrong how large an error can we expect?

I experimented with the centre section in EZNEC, varying the section diameter and length to see how sensitive element resonance is to changes. Once again I used the isolated single element model and adjusted the element tips to resonate the element at 50.5 MHz. Its impedance is approximately 44 + j0 Ω. The centre section baseline is a 1" diameter wire equivalent with a length of 1". The 1" diameter seems justifiable for a U-bolt clamp across a boom tube of 1.5" to 1.75", but I could be wrong.

Estimating the equivalent diameter and length of the centre section is important since it affect both the radiation resistance (and average gain) and the resonant frequency of the full element. There may also be interactions between segment length and the SDC algorithm, though this is not so easy to determine and isolate. I didn't try.

What I did instead was a sensitivity analysis of the centre section. The simple test I performed in the model was to double the wire diameter and length, going through their allowable combinations in the model and measuring the change in resonance. I varied the wire diameter while keeping the wire length constant (2" segment length) to avoid the segmentation error discussed above.


The first case is my baseline, with the centre section being a continuation of the ¾" tube; that is, no wire diameter increase due to the U-bolt and boom crossing. Notice that the resonant frequency is more sensitive to larger diameters. At my original 1" estimate the shift is negligible. Although not shown I did some trials with a 4" centre section (with adjusted segmentation) and determined that the length was significantly less of a factor than the wire diameter.

Based on this analysis I went with the 1" wire diameter that is 2" long and 1 segment. It really isn't the equivalent of 2" long but making the length shorter reintroduced the segmentation error. The segmentation I settled on was 1, 11 for the centre 2" long section and  the ¾" section. The segments in the ⅝" section (element tip) varied from 12 to 17, selected to keep the segment length as close to 2" as possible. This brought the feed point resistance of the test dipole to ~71.5 Ω, about where it ought to be.

Lowering resonance to capture more of the available gain

The maximum gain of yagis with 3 or more elements typically falls at the high end of the usable band width, and sometimes higher. Despite the gain being close to the ultimate there is some more that could be milked from the antenna. This is in part due to the new A50-6S design is being more broadband than I require. Getting that additional gain will almost certainly narrow the SWR bandwidth due to a lower radiation resistance where the gain is maximum; that is, at the high end.

Changing the element lengths to capture this gain runs into a conundrum: I don't know the precise frequency range of the stock antenna. Modelling is not so reliable that I can assume that my model, which includes SDC and estimated centre wire parameters, is sufficiently accurate, and I don't know how reliable the manual is. I reviewed the cleaned up model and compared it to similar 6-element designs but I still cannot be certain the model is accurate. This matters since I will not only be adjusting element length but also shifting the yagi down in frequency so that the maximum gain is closer to the bottom end of the band.

Since the best performance of the antenna is skewed toward the upper end of its ~2 MHz optimum bandwidth and I am only interested in the first 500 kHz of the band a first step to optimizing the antenna to my personal interests is to lower the range. This is easily done by shifting resonance of all the elements downward by 500 kHz, or 1%. Each element half is lengthened by ½".

Gain at 50.1 MHz is improved, which is where most of my activity takes place. The difference may be small -- incremental gain of 0.2 db and F/B reduction of ~5 db -- but why not take it if we can?

One danger is that towards the upper end of the original range the feed point resistance begins a rapid rise. Another is that the gain, typical of optimized multi-element yagis, drops steeply above a critical frequency. However in this case the gain is 11.5 dbi at 51 MHz with a F/B of almost 30 db. This is excellent.

The SWR with a suitable matching network is also excellent, though it does show signs of a high end rise.
We could lower resonance even further to capture a little more gain and F/B but perhaps at the expense of an optimum match.



There is some benefit in keeping the SWR below 1.5 to satisfy the need of legal power broadband amplifiers, if that is what you want. For that reason alone it's worth the tuning effort. Gamma matches can be tedious to tune so some time must be spent to get that perfect match. Since the feed point is so far along the boom this is an ideal situation for adjusting the gamma match with the yagi in a vertical orientation.

Perils of increasing gain

We can push the gain higher if we dare. To do so will necessarily narrow the SWR bandwidth since the radiation resistance will drop, thus increasing antenna Q, and almost certainly reduce the F/B. I am willing to risk both because my target band segment is narrow and F/B is not much of an issue on 6 meters, and can be deleterious by making it less likely that you'll notice an opening in other directions. This is a personal choice, and you may feel differently.

Yagi tuning for maximum gain is in general achieved by reducing the ratio of the resonant frequencies of the reflector and director(s). Since we have 4 directors the critical one is most often the last director. In the case of the A50-6S that is director 4. Per the manual's dimensions the resonance spread of the yagi based on the two outermost elements is ±11.5%. This is quite wide. That the gain is near the theoretical maximum is evidence of how good the performance of the redesigned A50-6S is.

As with the 15 meter yagi from an earlier article I tightened the tuning by shifting the reflector resonance up and the director 4 resonance down by an equal amount. The other directors were not changed. In the A50-6S the length of director 4 is significantly less than director 3, so we have some room to play with it without ruining overall performance.

The change was made in small increments of ¼". At each step the yagi performance was checked. Where necessary the array's frequency range was shifted up or down by adjusting all elements the same amount.

As expected the gain crept upward while the F/B declined and the variability of the feed point impedance increased. When I had about as much gain as I could eke out without overly degrading the match and F/B I stopped.

My optimization quest garnered only an additional 0.3 db gain. It ranges from 11.6 dbi at 50.0 MHz to 11.65 at 50.5 MHz. This is pushing hard against the theoretical maximum. F/B degraded to no a little less than 20 db. The free space azimuth plot show how it fares at 50.2 MHz, which is the near the centre of its most useful range.


The feed point impedance was difficult to tame. It can be kept below 1.5 between 50 and 50.5 MHz, but rises to 2 before again dipping above 51 MHz. The antenna's gamma match should be able to deliver the above SWR curve with careful adjustment.

The dimensions of the half element (boom centre to element tip) are as follows, using the A50-6S hardware without other modification:
  • Reflector: 59 ½"
  • Driven: 55 ¼"
  • Director 1: 54 ¾"
  • Director 2: 53 ¾"
  • Director 3: 54 ¼"
  • Director 4: 51 ¾"
The frequency spread between the reflector and director 4 has been reduced to ±7.2%.

Was it all worthwhile?

When I began writing this article I intended to exclude my errors and false starts to exclusively focus on the A50-6S performance. Since that turned out to be the least interesting aspect of my experiment I changed the primary focus to modelling challenges and gave the results less prominence. I believe this is more useful to you and to me.

My final judgment on whether I ended up with a better design for my A50-6 than the already excellent A50-6S remains open. An interesting point is that I got more incremental gain by shifting the antenna down in frequency than I did by tightening up the tuning for more gain. That is, even at the lower frequency range in the Cushcraft manual the gain peaks too high in the band to be useful for my operating preferences. Your situation might or might not mirror my own. Perhaps all I ought to do is lengthen the elements by ½" and not risk the F/B and SWR performance

My hope for this article is that the lessons learned can be applied to any antenna project, whether the antenna is designed from scratch or a modification of a commercial product. W7EL has done a good job of documenting common errors in modelling with the NEC2 engine, and the tools to diagnose those errors. You need only learn to understand NEC2's peculiarities and EZNEC's model testing features.

Don't hesitate to play with commercial products! Be reasonable in your expectations and proceed with caution.

Tuesday, August 16, 2016

The Best Tower Climb

I first became aware of amateur radio before I was a teenager, before I had any understanding of the technology and science of wireless communication. To me an antenna was rabbit ears on the family television. Gradually I became aware of loop antennas inside AM (MF) radios and telescoping rods on FM broadcast receivers car radios. Height only entered my awareness when my parents opted for a rooftop antenna so that we could watch US television from stations in northern North Dakota and Minnesota.

Fatal attraction? (Wikimedia Commons)
I was aware there were big towers some distance outside the city. I did not immediately connect them to coverage area and performance of television and radio broadcasts.

As my knowledge of amateur radio increased I began to notice backyard towers, usually small ones, supporting curious contraptions that I soon learned were called yagis. Apparently these were superior to bits of wire in the same manner of the television antenna (yagi or LPDA). But to me the towers were simply convenient supports; my awareness of height as a performance factor came later, after I got my ticket and absorbed the knowledge of more experienced hams.

It didn't take a genius to realize that towers are dangerous. An older high school friend suggested I try to climb his small tower to see what it was like. I did it ladder-style, with bare hands and no safety equipment. I still remember the fright I felt when I reached 20', about roof level, and looked down at him. That's as far as I got; I quickly retreated to the safety of the patio. He laughed and explained how it was the same for him until he got over the natural fear of climbing. Soon enough I had my own tower, on which I learned to climb safely and without undue fear.

Why do we have towers?

There are good reasons and bad ones for having towers, especially big towers. After all, we would never need to climb towers if we didn't benefit from them.
  • Performance: Height improves performance by lowering elevation angles for our horizontal yagis. At least up to a point. Tall towers also permit stacking and room for multiple, side-mounted antennas. How much performance you insist on will depend on your budget and objectives. More towers may be more suitable than a single tall tower.
  • Support: Antennas need to be supported at some height. Trees and buildings may be unavailable or difficult to use. Towers can be engineered to support the antenna load and place them above obstructions, decouple from the environment and turn freely.
Apart from sensible or at least justifiable objectives there are others. Like big boats, big houses and big cars a big tower is often an ego booster. It can also be a giant phallic symbol that is attractive to a certain mindset. Although there is nothing necessarily wrong with putting up a big tower for these reasons (it's your money and your risk) we ought to honestly reflect on our true motivations. All I would ask these hams is whether they want to risk their lives climbing a status symbol?

Benefit vs. risk

We each have our perspectives on measuring benefits and risks of towers. Some are based on science (mutual coupling and far-field pattern production) and others on local circumstances (regulations, insurance, personal health, budget). The decision to put up a tower and what type of tower and antennas will not be the same for everyone. Apart from the science what we do have in common is human physiology and gravity: if you fall you will die or be severely injured.
From: Simplified Safety blog article

Safety equipment is no panacea. All types of fall arrest systems encumber our movements, are easy to use incorrectly, can be costly and require careful maintenance. When they do come into play you will still be injured. The most common fall arrest systems are the tower-attached cable with cable grab and hand-placed fall-arrest lanyards. Both require a full body harness that is properly adjusted and used.

When you fall the equipment will stop your fall, but not without slamming you against the tower after a short drop. The rapid deceleration will further injure you, even with the proper equipment. The more you weigh the worse the potential injury. You may be unable to reattach to the tower or descend without assistance and you may suffer injury from blood flow interruption from being suspended by the harness until rescue arrives.
CDC report

The higher the tower the greater the chance of falling. Climbing, descending and working at heights are acts of heavy physical labour. The higher the tower the more likely you are to become exhausted or feel the effects of the weather (cold, sun, etc.), and the less likely you can be reached in an emergency. If you are overweight, in poor physical condition and not sensible about reading and interpretting the messages your body is communicating to your brain the risk is multiplied.

These are serious risks. Are you prepared? Are you willing to learn and do it right? When you're young it is often possible to use agility and main strength to recover from stupidity. Most hams nowadays are not young. In any case relying on luck and youth is a poor strategy.

How do you calculate benefit and risk? That's for you to decide, for your own life. Be honest with yourself. It may be that a tower is a poor choice if you (or your family) judge the risk of climbing to be too great. There is nothing wrong with coming to that decision.

Perhaps just as important, consider whether you are covered in case the tower falls or a child comes to grief on your property. Taking preventive steps for your "attractive nuisance" can be as valuable as buying insurance.

Alternatives to climbing

The benefit vs. risk assessment can be improved by alternatives to you, the tower owner as tower climber. Many older hams do just that. There are several approaches available:
Versalift
  • Tilt-over or crank-up tower
  • Outsource to a friend or a professional climber
  • Man buckets: crane lift or bucket truck
All of these options are costly, though less costly than human life, and even then involve danger. Since many older hams have more money than fitness the expense is justifiable. You may not even have to limit your height ambitions since there are man buckets for cranes that will take you up 40 meters or more.

One thing to beware of with bringing in a climber, whether amateur or professional, is liability and insurance. Most hams don't worry about this too much since disasters are rare. Yet a disaster in one sense can become one in another sense. Your buddy may accept the risk of injury but if he should die working on your tower it is his family that may initiate action. Even when dealing with a professional be certain that he has suitable accreditation and is bonded and insured.

You don't have to do this if you are unwilling to accept the risk. However, avoiding the issue is not the same as consciously and conscientiously accepting risk.

The best tower climb

I have a curious confession to make. So far in 2016 I have not climbed my larger tower even once. I have been up the smaller, house bracketed tower a few times but that was only to access the roof for non-ham related tasks. I have climbed towers this year but only those of other hams.

The reason is simple: nothing of note has gone wrong on the tower and the antennas it supports and I have not added or removed any antennas this year. This brings us back to the subject of this article, the question of what is the best tower climb.
The best tower climb is the one you don't have to do.
Every time your feet leave the ground you are in mortal danger. The only way to truly avoid that danger is to avoid climbing. Of course since we want towers to gain the benefits they give us we cannot avoid all climbing, or any of the alternatives to climbing discussed above. What we can do is reduce our climbs to the minimum number possible. That is, to remove the necessity of climbing.

When is a climb necessary?

To understand how to avoid climbing we need to review the reasons for climbing. From this you'll immediately see how we ought to attack the problem.
  • Tower raising and removal: This may seem trivially obvious but it is not so simple. When I raised my towers on my own I did so knowing that I'd have to climb up and down more than if I had a crew. With a good crew you can raise a tower in pretty much one climb, going up section by section and descending when you're done.
  • Antennas: When done right you put the antenna up and it stays there, perhaps for many years, until you choose to replace or remove it. Do it wrong and the antenna, and you, will make several trips up and down. The lesson is to build them right, use good material and fasteners, and tune them before they go up to the top.
  • Connectors: Use the best connectors on all cables (coax, rotator, control lines, etc.), install them well and follow best practices for weatherproofing. By avoiding water infiltration, fatigue breaks, corrosion and intermittent or failed connections you will not have to climb the tower diagnose and repair or replace what could have been done properly the first time.
  • Quality: Buy and install the best equipment you can afford for your tower installation, and refurbish, repair or inspect everything before it is raised. This goes for rotators, supports, coax, baluns, and everything else. That special deal you got at the flea market will seem less special on the fifth trip up the tower to make repairs.
Practice safety

When you do have to climb plan it out so that there is little chance of requiring more than one trip up the tower, such as having all the tools and parts you need. Binoculars or a drone flight are your friends. They allow you to do a visual inspection of suspected problems before you get started, potentially saving one or more climbs. From the shack use an analyzer and ohmeter to identify connections that may have failed or impedances that are no longer what you recorded when antennas were first installed.

The greatest danger of tower climbing is ascent and descent, not the act of working at height. Even so there is danger from remaining on the tower for a long time. Every aspect of tower work involves risk. There are ways to reduce the risk for both climbers and crew. Make safety a routine in every tower job you do.
  • Inspect all equipment: Before every climb inspect your safety equipment, ropes, fasteners, hard hats and also the tower itself. Don't become lazy about it. Hams are often surprised by the routine I follow and some find it foolish. Ignore them; do it right.
  • Know your limits: Are you fit? Are you feeling 100%? Is the weather uncomfortable? I can honestly say that I am fitter than well over 95% of all hams and I have my limits. Tower work is fatiguing and it becomes worse as the tower height increases: longer ascents and descents and longer hauls on ropes. Don't ever become overconfident. When that happens you will make mistakes.
  • Descend before you have to or call a break to rest. When the chill begins to restrict circulation, the harness causes muscle soreness or you experience tremors from standing in one spot for too long it is probably time to return to the ground. If you wait until you can no longer continue to work it is too late. You may not be able to safely descend. The taller the tower the greater the danger. Consider taking up a small snack (energy bar) and water bottle for long jobs and warm days rather than descend to eat.
  • Avoid fools and mavericks: Every member of your crew, including yourself, ought to be mature adults who appreciate the danger of tower work, do not take unnecessary risks and will not do something unexpected or inappropriate. They risk not only themselves but everyone on the team. Weed them out early. If you can't easily prevent their inclusion find suitable tasks for them that are helpful while keeping them out of the way of others.
"Experience is a dear teacher, and a fool will learn by no other"

Most of what I know about tower work I learned from more experienced hams, the safety literature and a number of professionals I've had the opportunity to work with over the years. Listen, watch and learn. There are too many hams that ignore all good advice and seem surprised when things go wrong or their tower crashes to the ground. While my own safety practices are not always perfect I always strive to apply good sense as I go about a job.

Unfortunately when I do tower work for others there are those who will not listen to advice on equipment choice or proper installation technique. For them faith in myths overrides science and evidence. This is disturbingly common among hams. Sometimes I can ignore them simply because they don't climb and can't see when I've done a job right rather per their instruction. In this way I avoid future climbs.

Yet common civility can only go so far. There comes a point when I just won't do a job, whether because of the equipment used, their insistence on unsafe practices or the quality of people they bring in to help. It can be a difficult choice.

Stay safe, do it right, and if you can't make others cooperate be prepared to walk. You may lose a friend but avoid mortal danger. That's another way to have the best tower climb: none at all.

Monday, August 8, 2016

Last Kick at a QRP Contest

For the fun of it I organized a team for NAQP CW this past weekend comprised of members of the local Ottawa Valley QRP club. On short notice we could only rustle up 4 entrants, one short of a full team. I expect we'll do better in future.

I discovered the club soon after returning to the air in 2013, while operating QRP for the first time in my ham career with my newly purchased KX3. I was invited to get involved by Bob VA3RKM, also a QRP contester, who I met at a local hamfest/flea market. The main attraction of this club for me is that the monthly meetings are held in a pizza restaurant! Seriously though, they are a fun group with a variety of operating activities and enjoyment of building small QRP kits and seeing what they can do with modest antennas. There's a lot to like about this approach to the hobby.

Nevertheless, as I've already signalled, my time as a regular QRP operator and QRP contester is coming to an end. I am more likely to be QRO when I build my next station with the objective of being more competitive in contests and all of my other operating interests, along with a more serious pursuit of high-performance antennas.

I hadn't planned to be serious about my NAQP entry so gathering a bunch of QRPers together to a joint effort was a great way to rekindle the QRP flame, if only for  a last fling.


My task before the contest was to reconnect the KX3. It has been sitting lonely and ignored on an upper shelf of the shack operating desk since it was used in several of the major contests last winter. For this contest I created a rats nest of cables to temporarily splice the KX3 into the rest of the station to minimally disrupt my usual setup with the FT950. This included the WinKeyer, antenna switching, computer interconnect, headphones and power.

One thing I did as part of this exercise was to stick labels on all the cables. All those USB and phono cables look alike and I've gotten tired of tracing them back to both ends every time I do this before and after contests.

Luckily the KX3 is small enough that I could sit it in front of the FT950 and still have plenty of room to operate. After the contest I was able to remove the rats nest and reintegrate the FT950 in under 10 minutes. The KX3, looking pretty after I carefully cleaned it with a small brush, is back to its place on the upper shelf. Which is a shame because it is such a fantastic rig. It has its deficits when pitted against the challenges of a contest and the DX pile-up, but the modern SDR design is a joy to use most of the time.

The contest itself did not produce the personal result I would have liked: 342 QSOs and 110 multipliers, before log checking. This was good enough for fourth in the QRP category as of the last time I checked the reports on 3830. Conditions were poor: 10 was dead while 15 and 160 were disappointing, and the disturbed geomagnetic field attenuated my puny signal. On top of which I became ill during the contest. By the next day I was healthy but it cost me about 2 hours of operating time. That's contesting for you.

There's always next time, though in my case it may not be QRP. Exactly what my situation will be this fall is difficult to predict at this point. Change is coming at the home of VE3VN.

Monday, August 1, 2016

6 Meters: The Irritating Reality of the Magic Band

As the saying goes, 6 meters is the magic band. It's full of surprises since at one time or another it supports propagation by every propagation mode imaginable, and sometimes combinations of them:
  • F- layer during solar maximum
  • Sporadic E, especially around the solstices outside the tropics
  • Aurora, mostly in middle and high latitudes
  • Tropospheric, depending on weather systems
  • EME
  • Ground wave
Ever since 6 meters became standard equipment on HF transceivers more and more hams have migrated to the lowest of VHF bands for the challenges it presents and the interesting propagation phenomenon.

However, the magic is often more marketing than reality. Or perhaps it's black magic rather than white magic. According to the hype 6 meters, when it opens, allows QRP stations with a whip antennas to make QSOs with ease, and even world-wide DX when the solar flux is high.

This is not what we typically experience. I would prefer that our expectations reflect the reality than the marketing. It's a wonderful band but not easy to achieve good results.

I'll reflect on the major reasons, as I see them, now that we're nearing the end of this summer's E season. You might also read the World Above 50 MHz column in the August QST for additional insight and links, since I noticed there are overlaps with my own thoughts. I did reasonably well this year despite making do with no antenna, compared to the small yagi I had last year. Having 100 watts rather than 10 watts with the KX3 made a difference. I am now up to 19 countries since coming back to 6 meters last year.

Latitude

Propagation is, of course, not the same everywhere. Sporadic E like many propagation modes is better at lower latitudes. In particular, lower geomagnetic latitudes. Since the geomagnetic pole is located in northern Canada we are at a disadvantage.

Quite often we hear stations to the south working stations we cannot hear at all. But then this is also true for F-layer propagation due to ionospheric absorption even during minor geomagnetic storms. Where you live matters on 6 meters as much as it does on other bands.

Internet: a boon and a road to disappointment

Back in prehistory (the 1980s) spotting clusters were rarely networked. There was no convenient means to discover openings by receiving reports from the global ham community. Ardent 6 meter operators used receivers with scanners (and squelch), monitored the informal 6 meter coordination net on 28.885 MHz (10 opens before 6 meters as the MUF rises), telephone ("Hey, the band is open, get on!") or simply put a lot of time in front on the rig.

Today I can be almost anywhere and receive activity reports on my smart phone. It is also possible to program alerts for 6 meter spots from your general geographic area. There is really no excuse for missing openings.

The downside of the technology is constant interruption and consternation. Unless you are a fanatic the constant stream of information and alerts can become annoying during E season. You can ignore the interruptions but then you may worry that you're missing out. Or, if you are not at home, you will fret about what you are missing.

When you do react by heading to the shack you will often be disappointed. Openings are fleeting or limited to so small an area that you hear nothing. Disappointment can turn to frustration since this happens so often, and can be especially aggravating if you are chasing a needed grid or country.

Do you sit there for a while, listening to white noise, or do you give it up and go back to what you were doing? Don't be surprised when you do leave the shack that another report, maybe even for the same station, appears just minutes later. Rinse and repeat. I almost find myself wishing for the end of the E season.

E clouds are small and rarely well positioned

Sporadic E is not at all like F layer HF propagation. While the science behind the phenomenon is incomplete we do know that the formation, movement, size, shape and dispersal of these high-ionization regions evolves rapidly. Long-haul DX involves multiple E cloud hops (multiplying the variability) or coupling to other propagation modes, including F, TEP, aurora and perhaps even tropospheric ducting. The complexity and uncertainty makes for a lot of excitement, and operating angst.

When you have a good, clean and direct path via the E cloud between two stations signal strength can be fantastically strong. These are the times when the smallest of stations can achieve great results. Alas this is not typical. Most of the time the path may be by scatter off the cloud (not direct path) or weak. When this happens the relative strength can be -30, -40 db or worse than the direct path. QRP and a whip won't cut it.

A lot of time can be spent waiting for the ever-evolving E clouds to momentarily set up perfectly so that the wanted DX station pops up 10 db and becomes workable. Miss that window and you go back to waiting. In the meanwhile you notice all your buddies just one grid square away are all working the station you might not be able to hear at all for most of the opening. For example, in June I worked an S5 (Slovenia) who suddenly popped up with a strong CQ. By the time I finished transmitting the spot to the cluster he fading to nothing. I never heard him again, and probably did anyone that reacted to my spot.

Over my head

Multi-hop sporadic E propagation does not need to involve the ground, just as it does not need to do so for F layer propagation. It is very possible for signal paths to go right over your head to connect points on either side of you. An example is a frequently noticed path from Europe to the central US, with nothing heard in VE3 despite our being directly on the path.

When this happens there is little you can do other than hope that E cloud somewhere to the northeast will increase in intensity and bend, or at least scatter, signals down to the ground. The wait may be long. I've experienced the phenomenon myself numerous times, especially years ago when I had a good antenna for 6 meters. This is one more instance where patience may be rewarded, at the cost of lots of time spent in the shack listening to white noise. It does happen, as I've exper

Beacons from nowhere

6 meters is overflowing with beacons in every imaginable corner of the globe. When conditions are good they can even QRM each other. Beacons are a great way to spot band openings that you can rely on since the beacon is absolute proof that the band is open to a particular area.

Except we may be disappointed. Some beacons are placed in areas where there is no activity at all. Or the local hams are at work. It can be frustrating when a beacon in a needed grid or country comes pounding in and no one is active just then. As the opening wanes and the beacon fades into the noise not to be heard for another year or two you might begin to wonder why you even came to 6 meters.

Weather vs. 6 meters

By weather I don't mean how weather affects 6 meter propagation. What I do mean is that peak E season is during the time of year when the weather is at its best in this part of the world. Our winters are long and cold and spring drags on interminably. When summer truly arrives everyone's thoughts turn to the outdoors. Canadians have a tendency to jump into a frenzy of vacations, sports and outings to cottages, lakes and beaches, fitting in a year's worth of fun into 3 months. I am no different.

It can be difficult to go downstairs to the shack when 6 meters is hopping. Not only is it the summer weather but also that 6 meter's diurnal cycle means that the best times are late morning and early evening when even on the hottest days it is very comfortable outside. Stations in more southerly or tropical locales might find the shack a relief from the heat, or they can wait for cooler weather since sporadic E and TEP are more common throughout the year. But not at this high geomagnetic latitude.

Balance is required. With no regrets I will often go out and enjoy the sunshine even though the band is full of signals. There is always tomorrow. Although I love this hobby I don't want it to become an obsession.

Been there, done that

Early in the sporadic E season every station you hear beckons for attention. You want to work every station you can hear. By July many of us ignore most stations to concentrate on the most interesting and rare openings. By August I get a little testy when the band opens again to the same old places and I hear all the same old stations.

This is the point when it is the time to move on. Some enjoy talking to the same folks if only to keep current the connection to fellow enthusiasts. I prefer novelty. No offense intended, but when I hear another opening to W4 (or even KP2) in this waning part of the sporadic E season I am tempted to just turn off the rig. They may feel the same way about VE3.

How do we deal with all these irritations and frustrations?

My prescription is pretty simple, though perhaps not to everyone's taste. I would summarize it as follows:
  • When the interest wanes turn off the radio or QSY back to HF. Don't obsess over 6 meters. There will be other openings to work, whether tomorrow or next year.
  • Put up a bigger antenna higher up. Small antennas down low do well for the typical single-hop sporadic E openings with their relatively strong signals and high elevation angles. For long haul DX experienced operators generally agree you need something more to increase your probability of success. Just a few db can make a big impact since most DX openings are marginal.
  • Enter a contest. This is one way refresh the enjoyment of working the same old stations again. Consider especially the ARRL June VHF and CQ WW VHF contests occur during the E season peak. You might even become enthusiastic enough to become a rover and activate a nearby rare grid square.
  • Study propagation science to understand the beast you are contending with. K9LA has some good information on VHF propagation on his web site, with links to other material. Even Wikipedia will point you to numerous scientific references.
  • Exploit services around the internet. For example, DXMAPS has near real time plots of sporadic E MUF across the globe. Real time chat can be found at ON4KST.
  • Go digital. There is an increasing amount of JT65 activity on 50.276 MHz where despite marginal openings or poor antennas successful QSOs at negative SNR are common. This is on my list of things to try sometime in the future.
Should you wish to skip all the marginal and rare propagation modes you can always sit out the next few years until the peak of solar cycle 25, sometime around 2023. When F layer propagation come to 6 meters the results can be fantastic. By the time cycle 22 was waning I accumulated 70 DXCC countries and all continents except Asia. That quite good when you consider than most of Europe and in fact much of the world did not have a 6 meter band.

If you decide to wait keep in mind that cycle 24 was a bust for 6 meter F layer propagation at this latitude. Cycle 25 might not be much better. I doubt that I will live to see another solar cycle that compares to what I experienced in 1989, based on long term predictions of solar activity. Instead I try to appreciate sporadic E, no matter how whimsical it may be.

I'm staying on 6

Don't be misled by negative points I've written in this article. Despite everything 6 meters is a lot of fun, a challenge and offers an opportunity to learn more about propagation science. Just be wary since too much of a good thing often turns bad.

6 meters is definitely planned for my next station. Initially I expect to refurbish my venerable Cushcraft A50-6 (purchased new in 1985). That will likely be the subject of a future article in which I strive to improve the antenna's performance. I initially plan to have it 20 to 25 meters high, depending on towers and placement of higher-priority HF antennas. I have a 40 meter long run of Andrews LDF7-50A Heliax ready to go.

Once I have a feel for antennas at various heights versus propagation modes I will settle on a more permanent arrangement. I expect to be on 6 meters for a long time to come. Occasional bouts of frustration can be dealt with by pressing the band switch on the rig.