ARRL DX CW Contest (2022)

I occasionally recap my contest experience to relate events and to discuss topics that may interest others and not just me. The 2022 running of the ARRL DX CW contest is one of those. I'll try to keep it concise to avoid boring readers who have not been bitten by the contest bug.

Choosing a category

It has to be said up front: I have no illusions about winning. These days I am up against the big guns, often with even bigger stations, better propagation and better operating skill. When I choose a category I try to balance testing the station, testing myself and having fun.

Due to technical problems I was at first reluctant to operate in an all bands category. One temptation was 40 meters single band, assisted, to put the new antenna to the test. I could also rest during the day and avoid the drag of a 48 hour marathon. This worked well for in CQ WW SSB last fall when I entered the 15 meter assisted category.

With conditions good and a positive attitude I decided to see what I could do with an all band effort. I demurred going assisted to focus on improving my running skills and test the potential of the new 40 meter yagi. I believe I made a good choice, although it's likely I'd have been happy regardless of my choice.

Run versus hunting multipliers

I have a tendency to linger too long when attempting to work multipliers since I'm a passionate DX'er. This is where the logging software helps to give you perspective. I use N1MM+. On the score summary window there is a statistic at the bottom that tells you the incremental value of a multiplier. For example, it might say "1 Mult = 5.5 Q's". That is, the score will increase the same amount by working one new multiplier or 5.5 QSO's (of average point value).

If you are a big gun it can pay to keep running and not hunt multipliers. It takes time and effort, even if you are assisted. The potential value of hunting multipliers is reduced by the fact that a big signal attracts many callers, including new multipliers. When the running is good it is often best to keep at it.

Big guns benefit from hunting, and the experienced operators know it. When there is a brief opening to a difficult area of the world to work -- for us, that is always true of southeast Asia -- taking time to sweep for those multipliers or to call CQ while pointed in that direction pays dividends. When the bands are closed to Europe -- for us, that is mid-afternoon at this point of the solar cycle -- the runs slow considerably and the time may be better spent multiplier hunting.

For whose doing SO2R, it is possible to hunt while running. Indeed, that may be preferable early in the contest when running on two bands (2BSIQ) can be difficult because of the size of the pile ups.

For those with low power or small antennas the choice more often favours multiplier hunting. Every situation is different and you have to continually assess whether to stop and run rather than keep hunting. When I had a small station I would try to run at intervals and stick with it if the rate was acceptably high. Otherwise I'd return to spinning the VFO. Now I am far more likely to keep running when conditions are favourable.

2BSIQ

Running concurrently on two bands is a difficult skill to learn. Most SO2R operators run on one band and S & P on another. However when it's done well and you get into the "flow" it can be tremendous fun and your score will grow at an impressive rate. I have had SO2R success in contests like NAQP but not the major international contests. The reason is interesting.

In NAQP a large majority of stations run 100 watts. That narrows the range of signal strengths of callers, and signals are usually not exceptionally weak. When I run a kilowatt on a band with QRN and QRM there are many weak callers. The "rhythm" of 2BSIQ is lost and bedlam ensues. 

For example, the late night opening on 40 and 80 meters (after their sunrise) only lasts 1 or 2 hours, so it is very productive for 2BSIQ. Unfortunately, the many callers and their low SNR requires concentration to separate one signal from among many and to copy them well. I ultimately failed at the attempt. It would go well for a while and then I'd get a large burst of callers on one or both bands and I'd lose control of the timing and end up with pile ups raging in both ears. Half the time I'd abandon one of the run frequencies to regain control of the situation.

Saturday on the high bands the rate of European callers is high. My full attention is required to run on one frequency. Running on two bands is beyond my ability, so the second radio is only used for S & P if at all. On Sunday when the rate is lower it is a little easier to do 2BSIQ on 15 and 20 meters. But for me it is remains difficult. All I can do is keep practicing.

Automation and equipment woes

The bigger the station the greater the number of things that can go wrong. There is always something that needs repair or maintenance, or there are projects still incomplete. My rush to get the 3-element 40 meter yagi finished before severe winter weather arrived put many other jobs on hold.

Here is a selection of the equipment challenges I faced during the contest:

• The prop pitch motor turning the upper 20 and 15 meter yagis does not work well or at all in cold weather. By that I mean below 0° C. In our climate that's a huge issue. Since the weather during the contest was typical for February I parked the yagis to 330°, at east Asia, and used the lower yagis to work Europe. The stacks were never in play during the contest.
• The rotator for the side-mounted TH6 was stuck. I had parked it at its west stop to protect it from wind storms and it appears that the Ham-M brake wedge would not retract. On Saturday it freed itself, much to my relief. Due to the prop pitch problem, the TH6 was the only antenna for 15 and 20 that I could turn to the west and south. 
• Lack of automation causes a "fear and loathing" of  band changes. Each band change requires switching antennas, switching the BPF, switching the amp and tuning the amp. There are no rapid band changes to sweep for multipliers or to check propagation. For quick band changes I left the amp offline and operated without the amps.
  
• Lack of good visual indicators such as LEDs caused antenna selection errors. For example, I inadvertently used the low XM240 rather than the 3-element yagi on 40 meters to run Europe Saturday evening. I was struggling but didn't discover my mistake for 2 hours.
  
• Despite the BPF, the FT950 receiver cannot deal with a few band and antenna combinations. There is enough RF from the other radio and amp to cause excess noise and make SO2R difficult. Turning off the pre-amp helped but on the high bands that affected copy of weak stations.
• A series of unexpected strong wind gusts on Sunday turned the 3-element 40 meter yagi by 10° on the mast. I believe this was caused by an unfortunate mistake during installation. It is easy to repair. The storm also damaged one element, and that repair will be more difficult. However the antenna continues to work very well so it's more of an inconvenience for now.
  

Once the warm weather arrives I have a long list of maintenance tasks to deal with. I no longer have the excuse of major antenna projects to distract me so I'll just have to get down to work. The same goes for progress on station automation. I expect to be in far better shape for the next contest season.

40 meters

The new 3-element yagi worked well. One glitch was due to my poor switching system, whereby I was on the low XM240 for a couple of hours by mistake. I wondered why my rate wasn't what it ought to be during the European opening!

Over the pole it brought in welcome multipliers from Asia. I even managed a brief JA run after our sunrise. This experience bodes well for the future. One dark spot is that the antenna suffered minor mechanical damage during house-shacking wind bursts Sunday afternoon.

Remedial work will be done when the weather warms up. For now the antenna continues to work well despite the problems. Details will be left for a future article.

QRL?

In the heat of competition many contesters searching for a run frequency on a crowded band fail to first ask "QRL?" or even to listen for a few seconds. Only a few of these are deliberately attempting to steal the frequency. It is too easy to be trigger happy in a fast paced contest: you listen for a second or two and start up the CQ machine. Others see a hole on the SDR spectrum display, click and punch the CQ button. 

Almost all will QSY when I announce my presence. The reason for the silence that entices them is usually that I'm listening to a weak or slow station, probably one within their skip zone that they cannot hear. This is mostly a high bands problem since the crowding is less and the skip zones smaller or non-existent on 80 and 160 meters.

A related problem is for stations within my skip zone. That includes a populous region of the United States. Unless we hear each others' callers it is easy to believe the frequency is open.  We can't hear each other so we don't copy the "QRL?" We may not realize what happened until we hear the confusion of callers. The frequency isn't big enough for the two of us so one of us must go.

Propagation

Experienced contesters check propagation paths a day or two before a major event. Admittedly I don't often do it but this time I did. It helped me to plan and to ultimately select my category. 

RBN (reverse beacon network) is a valuable tool since listening for stations and calling CQ are not enough. Outside of contests few hams appear for these brief and unusual openings. I call CQ hoping for a reply, but I will settle for data from the RBN. Unfortunately there are few nodes in Asia, Africa and Oceania, and those are critical to propagation research. Despite that lack the exercise is valuable.

One example is the path to northeast Asia during our early evening and their post-sunrise morning on 15 and 20 meters. The prospects for good openings were promising and indeed there were productive JA runs during the contest at the predicted hours which had been rare during the solar minimum.

Another propagation path that is particularly valuable in the ARRL DX contests is Europe on 80 and 40 meters after their sunrise. When the geomagnetic field is quiet the opening can extend 2 hours or more  after sunrise on 80 meters. Hundreds of contacts were logged during those openings. The path is less valuable in contests like CQ WW since Europeans are more inclined to move to the high bands in the morning since they are not only looking to North America for contacts.

With the high solar flux and still good low band conditions, quite a few station were worked on 6 bands. This was rare during the solar minimum other than the occasional Caribbean station.

W/VE callers

Many casual operators participate in major contests. Sometimes their willingness to hand out points isn't helpful. For W/VE stations in the ARRL DX contests, contacts with W/VE stations are worth zero points. Yet they keep calling. W call W, W call VE and VE call VE. No one wants to be rude but it becomes annoying when I have multiple DX callers that are covered up by one or two strong zero-pointers.

Sometimes I politely tell them "sri dx dx only pse". Half the time they keep calling regardless. Other times I work them to clear the frequency but don't log them. I know that other contesters do the same, while some are more rude and others shrug while working and logging them.

Many casual operators don't read the rules, know the exchange and have little understanding of each contest's unique rules and procedures. I am happy they are always there when I need them, so I keep it polite. It is more difficult to explain the situation on CW than on SSB.

Live and let live

Do you believe that everything goes in a contest? I don't but many do. When I operate in contests I avoid narrow channels of activity devoted to non-contest operating. Examples include FT8, beacons and a few SSB frequencies used to monitor for emergencies. I avoid running or calling stations on those frequencies. A few times I've violated the rule to work a juicy multiplier so I am not blameless.

Too many jump on those frequencies and run and ignore requests (or demands) to QSY. Those with a big enough signal may get away with the transgression. Their reputations is another matter.

Future

I have never been enthusiastic about operating a weekend-long contest by myself. It was true when I was a teenager in the 1970s and it's true now. I need to get my station into a state where I can invite others to join in a multi-op team now that the pandemic is abating.

My objective is to have fun and share in the energy that a team operation generates. It is an experience I have only rarely enjoyed since returning to the hobby and contests not many years ago. At first it was nice to do what I wanted when I wanted, which is sensible with a small station and QRP. But with a bigger station the demands of a contest weekend are far greater.

There is much work yet to be done, work that I've deferred during the pandemic. Major tasks include the shack desk, equipment and automation. Getting the antennas and rotators in good shape is important but is of lesser priority. This is the year to get it done.

Final note

It feels surreal to be discussing a topic as mundane as a radio contest in light of current world events. Had the contest taken place a few days later everything would have been different. In a way it both surprises and doesn't surprise me that few hams talk about the war on the air or in personal conversations. Life goes on. My family has history in that part of the world and I know many hams with close ties to the region. Conversations on bulletin boards are lagging and so are the page views on my blog while all of us are preoccupied by world events. 

73 to all.

Farmers and Hunter-Gatherers

Let's roll the calendar back several thousand years, before humans developed civilizations and cities. The major preoccupation was survival. That required growing or finding food. Tribes that learned how to farm continued to hunt game and gather plants and fruits necessary for a healthy diet. Whether a child grew to become a farmer, hunter or gatherer was determined by ability, family and culture.

Mechanized farming in our highly developed civilization is done by a small fraction of the population. Today's farmers produce what our ancient ancestors farmed, hunted and gathered, and do it so well that the rest of us can barely comprehend how our ancient forebears lived. A better understanding can help increase our contest scores -- really! So let's push the analogy.

If you know anything of contests you will have made the connection by now. Farmers run and hunter-gatherers S & P (search and pounce). Little pistols can only do well as primarily hunter-gatherers, and will farm (run) when they can. Big guns are farmers, but will occasionally forage (or concurrently using SO2R) for multipliers. Those with stations between the extremes, or in assisted classes (including multi-ops), more equally balance their tactics.

Farming, hunting and gathering are hard work, just as they were in the distant past. A farmer is forever worrying about the weather (propagation), terrain (geography) and predators (frequency "theft"). Seed must be kept, stored and planted, the fields irrigated, weeds picked, predators dissuaded and the crop efficiently planted, harvested and processed. 

Runners must find and protect their frequency on prime spectrum (fertile land), have a signal and tactics that withstand or overcome external forces, attract hunter-gatherers, and periodically abandon the farm to hunt and gather multipliers. Since game will cross the farm from time to time or be attracted to the crop there is opportunistic hunting as recompense for staying put.

Hunter-gatherers are always on the move. You must move or you die since food sources are scattered, those with legs move around, and once you deplete an area you must find another. The old and infirm who cannot follow the tribe fare poorly. So, too, the S & P operator must keep moving. You may not die when you stop moving but your score will plateau. A seer among the tribe (DX cluster or skimmer) may tell you what and where but you must go forth to seek and take what you need.

Early farming societies were often prone to poor nutrition due to the reduced food variety. Early civilizations dependent on agriculture were vulnerable to more mobile invaders because they had to defend their land and crops. For example, the Mongols needed to keep moving as their herds (temporarily) exhausted what the fields could provide. No matter the strategy, survival was difficult and risky.

Contest operators who exclusively run or S & P will plateau and fail to achieve the top of the contest rankings. I know contest enthusiasts who are uncomfortable running because it is difficult for them to deal with multiple callers or their signals are too small to hold a run frequency for long. Others love to sit on a frequency all weekend and let the hordes, including multipliers, come to them. They enjoy being sought and the attention a big signal attracts and may dislike the work of spinning the dial and hunting.

Runners (farmers) rarely work other runners since neither moves around much. The S & P operator (hunter-gatherer) will never work other S & P operators since they can only call runners. Specialization reduces score potential. Expanding skills and pushing ourselves out of our comfort zone requires effort and, at least at first, may not be enjoyable. Many mistakes will be made before significant improvement is achieved. SO2R multiplies the discomfort and effort.

An alternative is to join a multi-op team. Those who prefer running get to run and those who prefer S & P get to hunt and gather QSOs and multipliers. Both are needed. Early in my contesting career I preferred S & P. Operating from VE3PCA in the early 1980s I liked to man the station overnight when the pickings were slim and scouring the bands to eke out whatever I could -- we were approaching the solar minimum and spotting nets didn't exist. When the high bands opened at sunrise, I ceded the station to the runners and get a few hours of sleep. Our small group included both farmers and hunter-gatherers.

I expect that most readers have by now decided that I've pushed the analogy too far! I'll switch gears and close the article with a related topic that is too small for an article of its own.

Chasing DX and hunting multipliers in a contest require similar tactics. It is a challenge to be heard in the pile ups so that you can quickly log the entity or multiplier and move on to the next. Consider the following quote from the 3830 comment by V47UM in this weekend's ARRL DX CW contest:

"successful callers were mostly about 50-100Hz up or down"

CW signals that are near zero beat with each other are difficult to distinguish. Although calling high or low can be an effective tactic, it can backfire. When too many call high or low they will zero beat each other and the tactic can fail. The reason is that you can't offset too much or you'll be outside the other station's receive filter. However, keep in mind that what you really want is to call where others are not. When the majority call high or low, calling on frequency makes you distinctive. Listen to what others are doing, find the hole, wherever it is, and call there.

Since my transition from QRP with small antennas to my present big signal, tactical calling has less value. I usually do better by zero beating or calling on the frequency of the last successful caller. Big guns have the advantage of brute force. 

In the coming days I will describe my experience in the ARRL DX CW contest. There were high and low moments, and there were lessons learned. A few are worth sharing.

Hy-Gain Rotator Mast Slippage

As the temperature crept above freezing this week I made my first tower climb of 2022. It was to re-align the antennas (yagis for 6 and 40 meters) on the 21 meter high Trylon. The rotator is a Hy-Gain T2X (Tailtwister). This is periodic maintenance that is needed due to mast slippage in the rotator mast clamp. It happens approximately once per year. It has already happened once on the TH6 side mount and Ham-M rotator with the nearly identical mast clamp.

My story is familiar to owners of Hy-Gain rotators turning medium and large antenna arrays. The mast clamp has never been improved over the decades of production by Hy-Gain (now MFJ). After all, why would they incur the cost of risk of a major product change when there is no impact on their business? Hams keep buying them despite the flaws.

The number of rotators on the market is small and at least Hy-Gain is a known quantity despite the products' flaws. There are few cost-effective alternatives. I use them but I never buy them new. They are only worth the far lower price they command on the used market.

Here's a question about these rotators that is worth pondering: When the mast slips in the clamp, is it a sign that the clamp is deficient, improperly adjusted or that the the load exceeds the capacity of the rotator?

If you have a quick answer to the question, I suggest that you think again. Let's consider the capacity specification for the T2X for the common case where the rotator is largely isolated from bending stress by one or two thrust bearings. From the Hy-Gain documentation, as extracted above:

• Braking strength: 750 ft-lb (9000 in-lb)
  
• Antenna wind area: 20 ft²
  
• Maximum effective moment: 3400 ft-lb
  

It is interesting that the several manuals of Hy-Gain rotators I perused for this article do not mention braking strength or vertical dead load. It is shown on the MFJ product page. The vertical load capacity is sometimes quoted as ~700 lb, but I can't confirm that value.

The precise values are somewhat tangential to the main thrust of this article. However, note that the braking strength is less than 25% of the MEM. Is the brake deficient or are the specs less than enlightening? It's the latter, and I have more to say about it further below.

Many hams worry more about the dead load weight than the braking torque limit. So much so that, in my experience, they insist that the thrust bearing take the weight of the mast and antennas to protect the rotator beneath! This is despite the facts that the rotator is designed to support the vertical load and the widely used thrust bearings are incapable of supporting any vertical load. The most common explanation I've heard is that the rotator is expensive and must be "protected". It is a peculiar belief with no basis in fact.

This may seem to be an irrelevant observation in the context of the present article. It is relevant since most hams are not as mechanically adept as they believe and the same lack of understanding appears in discussions about mast slippage.

For example, assuming the 9000 in-lb braking strength is valid, it can be reached by applying 75 lb of force to a 10' long lever attached to the mast, such as the antenna boom of a yagi. Failure would be catastrophic should the bell housing fracture. In practice it is more common for the ridges in the lower bell housing to wear or for the solenoid to bend or break, both of which will allow the mast to spin freely. The reduction gear train of a Hy-Gain rotator has little braking resistance on its own.

For the sake of discussion, let's assume that we install an absurdly large antenna on the mast. One so large that we are certain the braking strength will be exceeded in a moderate wind. If the mast clamp is perfect (no slippage possible) the brake or bell housing will fail. That would be an expensive failure. There is the immediate risk to the tower, antenna and property below, and the cost of a new rotator. You never want this to occur.

When the mast clamp is imperfect the mast will slip and the rotator will not suffer a catastrophic failure. The torque at which slippage occurs is far too difficult and imprecise to calculate. We can only hope that slippage occurs well below the threshold for catastrophic failure. Absent clamp or bell housing failure it is also important that the mast slip before there is sufficient force to damage the bell housing "teeth" and brake solenoid. Under the stress of continuous assaults of a too large antenna array the brake will eventually fail.

What I've described is a mechanical fuse. The slippage, although annoying, reduces the risk of catastrophic failure. Unfortunately that slippage often occurs with torque that is well below the braking strength of the rotator. Hy-Gain recommends pinning the mast to the rotator clamp (part 136, above). They helpfully mark a blank for the hole on the bell housing and provide a hole on the clamp plate. Following that advice can be a costly mistake.

With a pin through the mast and clamp there is no give. When a sufficiently large force occurs, and it will occur, something will break. In a typical installation the weakest link in the chain is the bell housing. The mast, pin, u-bolts and the exterior mast clamp plate are stronger. You can choose a bolt grade of lower tensile strength for the pin, however there is no good way to calibrate it to break at just the right amount of mast torque to protect the rotator. It will almost certainly break at too low a torque or not break when it should. A weak bolt will fatigue and fracture over time and it will then break at a low torque.

There is also a maintenance issue with pins. To insert or remove the pin the holes in the mast and clamp halves must be perfectly aligned. That can prove very difficult unless the holes for the pin are punched with the mast fully seated in the rotator clamp and when the wind is calm. Otherwise the weight of the mast and antennas must be precisely manipulated to align the holes to remove or insert the pin. One instance of removing and re-installing the rotator can make you regret using a pin.

There are less extreme methods to increase resistance to slippage. A few common ones are:

• Increase contact area between the clamp and the mast
• Teeth or grit to penetrate the surfaces of the mast and clamp
  
• Set screw

Like many universal clamping systems the surfaces have a V shape. A range of mast diameters can be accommodated at the price of a low contact surface area. The ridges on the bell housing side of the clamp reduce the contact area and provide no sharp striations to penetrate the mast. The other surface is smooth. Even that might be enough if the clamping material was steel. Unfortunately, the clamp plate relaxes over time no matter how much the nuts are tightened, and aluminum striations will not penetrate a steel mast.

Last year I inserted a thin galvanized mesh to see if it would be gritty enough to bite the aluminum and reduce slippage. It made no noticable improvement.

The clamp hole for the pin can be threaded for a large set screw to penetrate the mast at one point. I doubt that would work because the flex in the clamp would relax the hold of the set screw as it already does for the u-bolts. I've seen it done but I have never bothered.

One thing you should not do is over-tighten the nuts on the u-bolts. The clamp will relax regardless and you risk breaking or galling the stainless bolts or, worse, cracking the bell housing.

It is possible to machine a one or two piece mast shim with an inner surface that conforms to the mast and an outer surface that conforms to the V shaped clamp surfaces. The increased surface area will increase the mast torque required for the mast to slip. I've never seen one but I have heard of it being done. I doubt that it worth the effort.

I earlier put aside the "maximum antenna size" specs and it's time to delve deeper. How did Hy-Gain arrive at the maximum square footage and MEM limit and what do they mean? This is less than obvious. For example, 20 ft² of antenna surface area tells us little without a great deal of context. Let's provide some.

For the 135 kph (85 mph) wind zone which is most common, at that wind velocity the lateral force on a cylindrical 1 ft² of projected area the static load is 20 lb. For the listed 20 ft² the lateral force is 400 lb. That's a lot, however none of it is seen by the rotator when the mast, tower and thrust bearing(s) are doing their job. The rotator will only be sensitive to torque. 

Torque is roughly in linear proportion to both antenna surface area and MEM. That tells us little since yagis are balanced by weight (CoG is at the boom-to-mast clamp), and by the cross-wind principle the torque should be zero. It isn't zero because the boom and elements are not in a laminar wind stream. At high wind velocities the air flow and mechanical oscillations are non-linear, 3-dimensional and can create brief periods of high torque. The 6° of motion the T2X brake allows adds to the peak strength of oscillations and mast torque. It is the peak torque that the rotator and mast clamp need to resist.

The MEM spec is no more than an heuristic tool to guess at what the rotator can deal with. As mentioned earlier, that the MEM is so much greater than the T2X braking strength makes it clear that the weight of the antenna is never applied to a lever equal to the length of the turning radius. The spec is little more than a rough guide, and that guide is of little value without more precise conditions where it applies. The lack of those conditions in the specs is telling: don't trust MEM!

There is no simple or straight-forward calculation, and two balanced yagis with the same surface area and turning radius will give different answers. Tube diameters, alloy and wall thickness, along with taper schedule, truss and element placement are all factors that make for the difference. So how do we interpret and what are we to do with Hy-Gain's specs?

MEM is defined by Hy-Gain as the product of antenna weight (lb) and turning radius (ft). This is a rough analogue for the expected torque under undocumented conditions. For example, a Hy-Gain TH7 has a cylindrical surface area (elements broadside) of 12 ft², weight of 75 lb and a 19' to 20' turning radius. 

MEM of the TH7 is 75 × 20 = 1500 ft-lb. This is less than half of the specified braking strength of the T2X rotator. Is this reliable? Can the T2X handle an antenna of the same size but twice the surface area (40 ft²)?

Certainly my recently installed 3-element 40 meter yagi is too much for a T2X with its MEM of ~8000 ft-lb. The wind load is 27 ft² but the weight is 4× that of the TH7. Doubling antenna size typically requires 2² the weight to be structurally sound.

My T2X survived moderately high winds with a TH7 and 6 meter yagi on the mast (total MEM of 1700 lb-ft), but that is hardly definitive. It's like proclaiming that I plan to live forever -- so far, so good! Tomorrow the T2X could shatter in a wind storm. There will always be a storm that will destroy any installation. It's a matter of probability: is that storm likely to occur once a year or once a century? We can only estimate, build and hope that century storm doesn't happen during the life of the installation. Building for a century storm may be unjustifiably costly for the ham budget.

With this in mind, is pinning the mast all that bad? We eliminate slippage and assuming our antennas are within the rotator's specs the rotator will survive. There is also the matter of the tower. Even if the rotator can survive the torque with a pinned mast the tower must also survive the torque. I have personally witnessed a tower twist and break in a strong wind, and the Ham II rotator survived. In that case both the tower and rotator were overloaded, and the mast was not pinned.

If we don't pin the mast, the rotator and tower can survive many severe wind storms. But we must climb the tower after those storms to realign the antennas. It would be nice to avoid this maintenance chore since I have so many others with my large antenna farm. I have already been up once to realign the side mounted TH6 after a wind storm. That is likely to be a regular chore since the antenna is not centred on the mast.

In the face of the several uncertainties I choose not to pin the mast. I prefer the maintenance over the relatively low risk of rotator or tower failure. I'll continue to grumble about mast slippage despite my choice. For those who must hire a tower rigger to do the job the balance may shift in the other direction. 

Alternatively, buy a rotator that is less prone to slippage and that has no brake mechanism. For example, one with a worm gear drive and a better mast clamp (e.g. AlfaSpid). Of course there are the matters of cost and the trading of one set of issues for another since every product has shortcomings.

There is no universal answer. But that is no reason to shrug and be complacent. Make a sensible choice based on calculations and facts. If you live in a hurricane zone or you have doubts about your tower, your choice should take that those facts into account. Rotator and tower failures are costly, and there is the risk of high liability for those living in a densely populated urban or suburban area.

Life in the Slow Lane: FT8

[Note: I've been busy so I have no well-developed technical articles in the pipeline. Instead I am going to start February slow. Real slow.]

Slowness is a notable characteristic of FT8 communications. That is an objective fact, no matter your opinion of digital modes and your operating habits -- casual, technical or competitive. The fastest QSO takes 1 minute and 2 minutes or more is not uncommon with QRM and QSB in the mix. That a long time to exchange call signs and signal reports! Although FT4 is twice as fast it is used far less. The few decibels of relative merit doesn't appear to be the reason.

I may be an outlier of my generation since I still like to drive fast, send and copy CW fast, eat fast, maximize my QSO rate during contests and not dwell too long on any one thing. I don't like speed because I'm a contester but it may be that I remain a contester because it's fast and exciting. Slow contests often bore me. Watching FT8 activity during a digital or VHF contest is as exciting to me as watching paint dry.

Occasionally I ask my non-contesting friends if they find FT8 too slow. From their surprised reactions the question appears to be unexpected. It's as if they're thinking: faster than what? Or: what's the rush? Those underlying questions seem to be ever present even as their answers touch on other issues, including the small stations that make digital modes so attractive to them.

I should not have been surprised. I am in the minority in my age group with my "need for speed". People my age tend to drive within the speed limit and prefer to savour their QSOs. Speed is more alluring to the young.

Most hams are growing old and are inclined to slow down the pace of their lives. They aren't contesters and they are not interested in rate. FT8's 15 second regimented periods are no impediment for the casual operator. It is not too slow to irritate and not so fast that it requires rapid reactions. The "Call 1st" feature provides additional relaxation by eliminating the need to make a decision about which caller to answer. Digital modes welcome and may encourage passive behaviour.

I use FT8. It is my go-to mode for DXing on 6 meters. I like what it can accomplish and so I tolerate its slowness. Attempting to spur activity on 50.318 MHz FT4 by calling lots of CQs has been unproductive. Few are listening.

I also use FT8 on 160 meters when the DX is lacking on CW, which is almost always true outside of contest weekends and the rare DXpedition. Mostly I just monitor to see what DX paths are open. I do not use FT8 on HF because there is plenty of DX on SSB and CW. At least, so far.

Digital is not my preference even though I love the technology for its ability to scrape a QSO from the merest wisp of a signal. FT8 is a mode you like or don't like, use or don't us. It's a personal choice. An increasing number of hams choose it and accept its fixed and pondering pace. That is not a problem for them. I am happy to use it to monitor 6 meters for transitory openings that are so difficult to exploit with the traditional modes.

My preference for CW and SSB is typical for hams of my generation. Younger hams feel differently. Many have never learned CW and have no intention of doing so. For many of them, their entry into ham radio was technology. For me and my peers it was communications. In the 1970s, ham radio was just about the only way for an ordinary person to reach out and talk to someone across the globe. Modern communication services have made our passion for HF and DXing look quaint to most people. 

Why does the speed of the mode matter? I'm a contester, but that's not why it matters to me. Indeed, when QRP was all I had I was not frustrated by the slowness of getting through to another station. I used it as an opportunity to hone my operating skills. I know many hams who use amplifiers so that they can rapidly log the QSO and move on. QRP is an undesirable handicap in their pursuit of speed.

Enticing more hams into contesting or FT4 is a losing cause. They like their slow CW and casual phone QSOs, and they're perfectly fine with the speed of FT8. It makes perfect sense to me when seen from their perspective.

Tedium of Single Band Contests

As I write this, the 2022 CQ WW 160 Meter contest is not over. But it's over for me, and has been since Saturday evening. The endless tedium wore me down. Better DX conditions would have helped, since without that the prospect for contacts is severely limited.

Some people like that and will work with whatever the propagation gods (or devils) provide. I can live with that in most contests. You make do since you know that everyone else is in the same situation. Skill and technology are what make winners.

In a single band contest the application of skill is narrower. When the DX isn't there on top band you have two things you can do: call CQ endlessly and trawl the bands (and cluster/skimmer spots) for fresh meat. I can maintain my enthusiasm for a while. Eventually the tedium gets me down. I have regularly bailed early from contests such as these. This isn't a new problem for me, since it was the same when I first got into contesting as a teenager in the 1970s.

My strategies for countering the tedium have been to operate with a handicap like QRP or as a member of a multi-op team. With an inferior signal every QSO is an accomplishment. There are always more stations to work and challenges to overcome. With a kilowatt and a full size vertical on top band the QSOs are not so difficult. After the first 600 to 700 QSOs you have milked at least 80% of the available stations and the rate falls off a cliff.

I had over 700 QSOs in the log when I shut down in the wee hours of the first night of the contest. I worked every available state/province multiplier and over 50 countries, despite the mediocre conditions. Many other countries were heard but they did not hear as well as the hordes calling them. Productivity suffered and the long tedium had begun.

When I resumed Saturday evening the rate improved as many stations made their first foray into the contest. Very soon that pool dried up and the tedium resumed, worse than before. Many contesters love the challenge of scrapping for every contact. The best operators scan the bands or jump on spots with one receiver while listening to answers to their CQ machines on another receiver. A few have sophisticated equipment to allow them to do both concurrently. The rest of us can only listen on the second receiver when the CQ machine isn't transmitting.

I am not happy with that style of operating. DX conditions were worse the second night and that accentuated the tedium. So I quit the contest. I never had the inclination of winning in any category and, frankly, my station, good as it is, is inferior to many others. There is added frustration from the Beverages which allow me to copy too many stations that cannot hear me. Oftentimes a kilowatt is no more productive than QRP. At least the amp keeps the shack warm during winter weekends.

I can sustain my enthusiasm in a multi-op because off times break the tedium. Every time I sit down to do a shift I am refreshed and able to dig in and get the job done. As a single op the tedium is unremitting and it wears me down. I admire the operators who deal with it better than I can.

This problem is common to most single band contests. It also occurs in contests with limited participation. I place ARRL Sweepstakes in a similar category since you can only work stations once regardless of band. The outcome is much the same, but with more spectrum to cover.

For the contests I most enjoy you respond to conditions and ever-changing activity levels by band and mode changes, alternating CQ and S & P, SO2R, watching signal strengths and spectrum scopes, among other strategies. Building and operating a multi-faceted station that permits these tactics sustains my interest and enthusiasm before, during and after the contest. In many respects I enjoy that more than operating in contests.

Single band contests rarely suit my desires. There are exceptions. Examples in 2021 include my 15 meter single band assisted entry in the CQ WW SSB contest and my (unofficial) 20 meter assisted entry in the ARRL DX SSB contest. I had fun putting to the test the recently completed stacks for 15 and 20 meters. I may do the same on 40 meters in one of the upcoming ARRL DX contest weekends to see what I can do with the recently completed 3-element yagi.

I will continue to operate the ARRL and CQ 160 contests but probably never with the objective of winning. To become competitively oriented I would need to make it a multi-op operation. As a single op, it's mostly an opportunity to work DX that is otherwise sparse on top band and to compare my antenna and station capabilities to those of others. The latter spurs my technical side to improve my station. 

Outside of contests, there is now far more top band DX to be worked on FT8, and I do make regular appearances. That's a story I'll defer to a future article.

Yagi Side Resonance

RF is very sociable: it happily interacts with everything in the universe. A few interactions are significant, some are minor and the vast majority are negligible. As hams we discover or predict interactions, then deal with the problematic ones and ignore the rest. Often, interactions are unknown or dismissed, and only addressed when they are too severe to be ignored. 

As deliberately radiating devices, antennas are especially prone to interactions, as the perpetrator or as the victim, or both. As the victim, an antenna's pattern and efficiency can be degraded by interactions. Those interactions can be with structures, utilities, trees, ground other antennas within a couple of wavelengths.

When I designed my 3-element 40 meter yagi I paid particular attention to its interaction as the perpetrator and the 15 meter stack as the victim. It is big and high enough that it is not particularly prone to be a victim. This is helped by the vertical polarization of the 80 and 160 meter antennas: orthogonal antennas interact little.

Here you see a simple 80 meter dipole excited at 3.6 MHz. It is positioned 200' (60 m) laterally from the centre of the 40 meter yagi and 50' (15 m) lower. The 40 meter yagi has a substantial mutual impedance and is happily interacting. How is this possible? 

It is no surprise that the pattern of the 80 meter dipole is distorted. For an 80 meter yagi with 2 or more elements the pattern degradation would be substantial. This is of particular interest to me since I am considering a wire yagi for 80 meters suspended between my two tall towers, including the one supporting the 40 meter yagi.

A ham in the distant past had the interesting idea of making a yagi into a dipole for the next lower band. Viewed from the side a yagi is a short dipole with large capacitance hats. A typical 3-element yagi resonates at about half that of the design frequency. That is, a 3-element 20 meter yagi is resonant within or near the 40 meter band, and the same is true of a 3-element 40 meter yagi on 80 meters.

The trick is with the feed point. You must excite the boom and not the driven element. Although they are mechanically and electrically connected the 40 meter feed is neutral with respect to the boom. As is common knowledge, the elements of a yagi are electrically independent of an orthogonal boom that crosses their centres.

Yagis with elements insulated from the boom do not have this attribute. At least the outermost parasitic elements -- reflector and last director -- must be electrically connected to the boom. 

Since the boom is a continuous conductor a similar feed system is required as for a yagi with a continuous driven element. A gamma match may work. More often an omega match must be used since the yagi cannot be adjusted to be compatible with a gamma match. In an earlier article I referenced a couple of construction articles by those who have done this.

Were the elements of the yagi insulated from the boom, its 46' (14 m) length would serve pretty well as a dipole on 30 meters.  

For those modelling these effects it will be necessary to add the boom to the model. It is ordinarily omitted from the model because, other than the element-to-boom clamp, the boom is neutral. To model the boom dipole I had to split the centre wire of each element to allow connection of the wires that comprise the boom. SDC (stepped diameter correction) and other NEC2 limitations that confound accurate yagi modelling are a relatively minor source of inaccuracy when the elements are employed as capacitance hats.

Both matching networks are difficult to retrofit to an existing 40 meter yagi due to its size. For example, the calculated gamma rod length for the impedance at 3.6 MHz is 13' (4 m) long. There is no good way to do that without a crane and basket. More capacitive reactance can reduce the length by several feet but that requires rebuilding the 40 meter yagi! Perhaps a "long enough" but short gamma rod and an L-network will get you to 50 Ω.

Notice that there are other resonances, which is not unusual for an antenna with many protuberances. There is a resonance at 14.4 MHz that, due to model inaccuracies, might actually fall within the 20 meter band. I have not done the modelling to determine the magnitude of the 20 meter interaction.

Although the antenna can have a DE feed point for 40 and a boom feed point for 80 meters, it is not advisable to operate both bands concurrently without band pass filters that are up to the challenge. However this is usually only a concern for multi-op and SO2R contesters. Everyone else can utilize two transmission lines (one terminated) or a switch at the antenna.

There are pros and cons in this situation. The major benefit is the possibility of a high dipole on a band where one might otherwise only be able to deploy a wire antenna like an inverted vee at a lower height. The major disadvantage is that a yagi can interact with a horizontal antenna for the lower band when the boom is broadside to that antenna. There is no one solution since every station is different with respect to operating objectives and favoured beam directions.

That lower resonance is there whether you feed the boom or not. Putting that lower band resonance to use as a dipole may involve significant effort. The boom resonance can be defeated in the same manner as for a tower. However I've never heard of someone taking the trouble to do so. Interactions are silent so that their impact is easily mistaken for other things and therefore may never be addressed.

Out of interest I created a boom model for my 5-element 20 meter yagis. The resonance is lower than half of 14 MHz because, with 5 elements, the boom is electrically longer. The boom resonance surprisingly falls right inside the 60 meter band. Of course it almost certainly doesn't but it should be nearby. But I have no interest in that band and the interaction isn't important since it isn't a contest band.

Notice how the elements adjacent to the feed point at the boom centre are very active (directors 1 and 2), but not so for the other 3 elements. There isn't much current flowing at the extremities since the most active elements introduce a current distribution discontinuity. That is in the nature of capacitance hats. There is a similar effect with loading coils. That is why they are effective at their job of shortening an antenna.

More can be said of unusual yagi resonances, how to positively exploit them and the downside of interactions with other antennas. But I won't. Every antenna and station is unique so it's enough to raise awareness of this little understood issue. Look around your antenna farm, whether it is big or small, and consider what might be at play. Most will shrug it off since characterizing the scope of the problem and taking mitigation measures is neither easy nor straight-forward.

If I build the 80 meter wire yagi that I have tentatively inserted into my 2022 plan there are factors that lessen my worry. First, most of the time the boom of the 40 meter yagi will not be parallel to the 80 meter elements. Second, yagis have enough directivity to reduce interaction when they are at different heights. Third, I still have the 80 meter vertical yagi should a problem arise when the 40 meter yagi is pointing in a direction that increases the interaction.

When I get serious about building an 80 meter wire yagi I will develop models to explore the matter in more depth. I have no plan to convert any of my yagis as lower band dipoles since I have enough antennas to meet my needs. My concern is interactions.

Gamma Match Peculiarities & Challenges

After a brief struggle with the gamma match on the newly installed 3-element 40 meter yagi I thought to myself that there has to be a better way of doing this. Unlike many other ways of feeding yagis, the gamma match remains an enigma. Calculating its dimensions is at best an estimate and it can be off by quite a lot. 

We can get by despite this because the gamma match will match a wide range of feed point impedances. A bit of trial and error usually does the trick. It is interesting that it can be so difficult to analyze and accurately predict its behaviour!

The most common style of gamma match is shown below. A reference diagram will help to avoid the possibility of confusion even though most hams have encountered the gamma match.

Unfortunately I do not have the relevant education to dive too deep into the transmission line and antenna theory to properly understand the gamma match. I can get through partway and then I will inevitably hit a wall. I have not been successful, so far, with published material on the gamma match since they tend to touch lightly on important theoretical points, make assumptions that overlook the general case, or crunch through the complex number equations and hyperbolic trigonometry without explaining what is being done and why.

The basic behaviour of a gamma match is as follows. I am paraphrasing an article that like by Healey W3PG in April 1969 QST. His figure 4 is reproduced above. ARRL members can pull the article from the QST archive.

1. As a short or partial folded dipole, the current split on the DE (driven element) and gamma rod multiplies the feed point impedance (both R and X components) by a step-up ratio. The ratio is determined by the tube diameters and spacing. 
2. The impedance is raised before being stepped up because the DE tap point (gamma rod strap) is off centre. This occurs due to the current and voltage gradient along the element, with voltage rising and current declining as you move toward the element tips. The increase isn't large -- a typical value is 5% -- but well worth taking into account.
   
3. The shorted stub formed by the gamma rod and element adds parallel inductive reactance Xp to the stepped up impedance Z₂ at the DE tap point and also transforms the net impedance since it is a transmission line. 
4. In a typical gamma match, the reactance at the feed point is inductive. The series gamma capacitor -Xp cancels that reactance at the design frequency.

When properly configured the feed point impedance is 50 + j0 Ω, at one selected frequency, usually near the centre of frequency range of interest. The SWR curve across the band should be similar to that of other antenna feed systems. As Cebik W4RNL points out in "Some Preliminary Notes on the Gamma Match", and I found with my new 40 meter yagi, getting the gamma match to do that is not as straight-forward as for other common feed systems. The mathematics are more difficult, the physical dimensions are critical and the (dipole) feed point impedance we seek to transform may be impossible to measure. (Search for the Cebik article in a search engine to locate an extant archive.)

I would like to better understand the gamma match. I have most of the mathematical training required but not enough of the electromagnetic physics and engineering. I sometimes joke that I've forgotten more mathematics than most people have ever learned. There is a thin layer of rust coating my neurons. However I never formally studied electromagnetism. 

Bear with me as I plow through what I can of the subject without delving deep into aspects that I am not yet qualified to comment on. After designing a number of yagis and gamma matches, and then modelling, measuring and adjusting them, there are several challenges about gamma matches that I've been contemplating:

• Achieving a perfect 50 + j0 Ω match at one frequency is not difficult. Since a yagi is a high Q antenna its impedance changes rapidly with frequency. There is no gamma match design process that I'm aware of that optimizes the SWR across an amateur band. Is there a best set of driven element length (pre-match R + jX Ω) and gamma dimensions that maximizes the SWR bandwidth? If there is one, how large an improvement is possible?
  
• For a yagi like the one I built for 40 meters that cannot be accurately modelled with NEC2, it would be helpful to reverse the calculations. That is, knowing all the dimensions and the impedance at the gamma match feed point, what is the dipole feed point impedance? Since the element is continuous rather than split there is no good way to measure it directly; I used a split centre for my early experiments. We most often rely on models and heuristics to estimate the impedance to be matched. But I have no accurate model of the antenna impedance and I need to know the actual impedance across the band to fully understand the antenna's behaviour.
  
• Reliability of the gamma match calculations is sensitive to several mechanical design parameters that are difficult to control in practice:

• The "open stub" between the gamma rod beyond the shorting strap and the driven element
• Tube diameter steps along the driven element and gamma rod that are typical of large yagis
• Asymmetric lengths (imbalance) between the coax connector and the connections to the DE and gamma capacitor
• Transmission line effects of a long, thin tubular gamma capacitor versus a fixed capacitor (lumped constant)
• What is the best gamma match topology to allow a minimum number of supplemental switched reactance elements to improve the SWR at the high end of the 40 meter band? The gain and directivity are very good high in the band but the rapidly declining radiation resistance prevents achievement of a low SWR across the full band with a static matching network. Yes, an OWA design with a coupled resonator does far better but that is not the problem I'm trying to solve.
  

The challenge is greater for the 40 meter yagi than I experienced with my yagis for 20, 15 and 10 meters because of the increased mechanical complexity, physical size and the greater bandwidth of the band. For example, there are 4 dimension steps along the gamma match, and the 300 kHz bandwidth of the band is equivalent to 600 kHz at 14 MHz and 900 kHz at 21 MHz.

Restricting ourselves to the bottom 200 kHz of the band helps to manage the SWR bandwidth but it is still a greater matching challenge compared to yagis for the higher bands, especially since having more than 3 elements makes it easier to achieve a wider SWR bandwidth. 

I ran into issues with the gamma match on the 40 meter yagi that were not as easy to deal with as they were for the higher band yagis I constructed over the past few years. The greater bandwidth requirement is one of the reasons. Since it's cold and snowy this time of winter I am taking the opportunity to better understand the gamma match and plan for improvements. When warmer weather arrives and I can comfortably climb the tower those steps can be taken.

Instrument choice

Let's assume you measure a perfect 50 + j0 Ω with your antenna analyzer connected to the gamma match feed point using a variable capacitor for the gamma capacitor. Now swing the capacitor back and forth until you get, say, -100 Ω and +100 Ω reactance. You will notice that the R value also changes.

There are two potential causes for the varying R. One is that the mismatch causes standing waves through the components of the gamma match and antenna. In practice this is really not an issue for a typical antenna utilizing a gamma match.

The other cause is the measuring instrument. Measuring antennas is usually done with a handheld single port analyzer. These common instruments run the gamut from horrendously inaccurate to very good accuracy. The Rig Experts AA54 I use is middle of the pack in expense and quite accurate for the price. That is, to a point. Every antenna analyzer and VNA will exhibit decreasing accuracy as R and X depart from their nominal port impedance of 50 + j0 Ω.

In the case of the AA54, when I achieved a 50 + j0 Ω match at about 7.085 MHz with 290 pf of series capacitance, I swung the 500 pf variable capacitor from one extreme to the other. R varied by a few ohms, in the range 46 Ω to 54 Ω. 

One investigator who I will not name noticed a far greater range of R when using an inferior instrument and concluded that the various mathematical models of gamma matches were unreliable! I was amused since it was obvious that he was really measuring the poor accuracy of his antenna analyzer and not the antenna. That did not appear to occur to him since he questioned none of the measurements.

Since the antenna analyzer has that inherent inaccuracy it is better in most cases to adjust the capacitor to get X = 0, measure the capacitor's value and calculate the capacitive reactance. The R value, if it's not too far from 50 Ω, will be quite accurate even on poor instruments.

You should invest in an instrument that is equal to the task you require of it or you should modify your use of it to mitigate its limitations. Compared to the problems you'll run into with a poor instrument the modest expense is worthwhile. I know far too many hams, some of whom have reached out to me after reading my blog, that use poor antenna analyzers and then make excuses when they see nonsense readings rather than invest in a better instrument. Please don't be one of those hams.

Gamma section stepped tubing

The DE and gamma rod dimension steps along the gamma match length, and the Z₀ of the 2-wire transmission line they form, are:

• [4"] 7.5" element-to-boom plate & 0.84" rod: Z₀ = ~270 Ω & step-up of ~13
• [26"] 2.375" DE & 0.84" rod: Z₀ = 340 Ω & step-up of 6.0
• [18"] 1.9" DE & 0.84" rod: Z₀ = 350 Ω & step-up of 5.4
• [variable] 1.9" DE & 0.625" rod: Z₀ = 370 Ω & step-up of 5.9

This is mathematically messy. Aside from the boom clamp, most HF gamma matches do not have steps on the DE and gamma rod. Perhaps a weighted average is a good enough estimate for those critical parameters. I hope so since that's what I've been doing.

You can certainly find a match by combining a naive estimate with trial-and-error adjustments. For the majority of cases that is good enough. However, it's a problem if you would like to reverse the gamma match equations to find the dipole impedance of the unmodified antenna. As already said, "plumber's delight" construction of the DE does not allow a direct measurement of the dipole impedance.

Gamma capacitor

There are two common types of series gamma capacitor: lumped constant (fixed or variable capacitor) and cylindrical (insulated wire or tube inside the gamma rod). They are only roughly equivalent, yet few hams consider the inherent peculiarities of cylindrical gamma capacitors. I have run across a few cautionary notes about the cylindrical capacitor, like that by W8JI, but nothing specific. The linked page is long so here's the relevant paragraph:

The above example of decreased power rating is especially important to Amateurs using coaxial cables as capacitors. Voltage is NOT constant along the length of a long coaxial capacitor. Maximum voltage in the component is always HIGHER than the actual voltage across the terminals of the "capacitor", and it is higher than the voltage calculated by the current through the capacitor! Coaxial capacitors or linear stubs used as reactive elements always have significantly lower operating Q, higher power loss, and operate under more electrical stress than a well-designed lumped component. Stubs and linear loading does have the advantage of spreading heat out. You won't notice the heat as much, even though there is a lot more heat energy! Just don't let the smaller temperature rise fool you into thinking the system has less power loss.

Without worrying about the theory, let's look at a few measurements I took. I used the best instrument I have: the VNWA3 by DG8SAQ. The calibration point is at the end of the short cable terminated with a male BNC (on the right). The calibration error due to the barrel connector, binding posts and short wires to the capacitor is small at 7 MHz. Despite the calibration it will be seen that the 13" from the VNA port to the gamma capacitor is significant.

Before doing the measurement I tested the capacitance read by the VNA with two different high Q capacitors designed for moderate to high RF current. They read almost exactly flat up to 30 MHz, with a gradual rise up to 100 MHz. They are boring charts so I omitted them from this article.

The gamma capacitor is 43" (1.1 m) of PVC jacketed RG213 inside a 6' length of ⅝" × 0.058" tube. I previously measured this capacitor as ~340 pf (8 pf per inch) with a lower quality RLC meter that uses a low frequency signal to measure coils and capacitors. I replaced it with LMR400 in the gamma match of the 40 meter yagi since PE is a superior dielectric material compared to PVC (lower loss).

The gamma capacitor is far from an ideal flat line! I placed markers at points of interest. The RL (return loss) plot hints at the loss due to the PVC dielectric.

At very low frequencies the capacitor value is about what it should be. However, notice the loss shown by the RL. The loss peaks at ~8 MHz before moderating, and then becoming extreme between 80 MHz and 120 MHz. I did not compare a length of LMR400. The test RF capacitors have negligible RL.

The first capacitance peak at 26 MHz is near where I estimated the frequency at which the gamma capacitor is an ¼λ open transmission line stub. The VF within the capacitor is difficult to estimate, and I didn't bother trying to measure it since it requires subtracting out the VF of the VNA coax and connections to the capacitor. The stub begins at the VNA port, not at the gamma capacitor, so it is 56" (43" + 13"), with VF changing at cable junctions. Although I did not verify the source of the high loss 100 MHz resonance, there is one candidate that I strongly suspect.

The ¼λ stub frequency will be different when installed on an antenna. It is far enough from 7 MHz that it is probably not a problem. However, notice how the capacitance rises dramatically at half the stub frequency. That may be noticable.

Open stub beyond the shorting strap

Most analyses of gamma matches ignore the open stub formed by the gamma rod and DE outside the shorting strap. After many trials of building and adjusting gamma matches I feel the same. My model of gamma matches also indicated little effect. I thought it still worth a calculation.

For the 23" of ⅝" gamma rod beyond the strap on the 40 meter yagi DE the calculated parallel reactance is approximately -3700 Ω at 7.1 MHz, for a capacitance of 6 pf. Since the magnitude of the reactance is much larger than the stepped up antenna impedance the effect should be small. It is also swamped by the larger reactances of the gamma match's shorted stub and series capacitor.

That said, it is best to keep the length of the rod only long enough for the gamma match to have a moderate amount of adjustment room. That minimizes any potential effect and reduces wind load.

Lumped reactance vs. transmission line sections

Unlike the cylindrical gamma capacitor, a lumped constant (fixed or variable capacitor) should provide a better all-band match. It's simply more predictable. One factor that may have played a role in my matching woes is that the length of LMR400 is just shy of 60". That would lower the ¼λ stub resonance of the cylindrical capacitor, perhaps as low as 20 MHz, and the capacitance gradient would begin its rise at a proportionately lower frequency. 

There is a slope to the capacitance curve at 7 MHz with the shorter RG213 gamma capacitor. That is in part due to transmission line effects that worsen as the ¼λ stub resonance is approached. The higher capacitance lowers the reactance of the series capacitor. The reactance of any capacitor decreases as the frequency increases since Xc = 1/(2πfC). 

I would like to measure the series capacitance needed to cancel the inductive reactance at several spots across the 40 meter band. Then I can tell whether the sign of the decreasing reactance of a fixed capacitance is the same or opposite to that of the inductive reactance. The first makes the SWR worse and the second makes the SWR better. However, I won't climb the tower in winter to do the measurement.

The deviation of the capacitive reactance across the 40 meter band is likely to be smaller than ±10 Ω from the mean value of ~75 Ω. That's significant but not disastrous. Until I take those measurements I don't know for sure if this effects are responsible for the worse SWR curve with the cylindrical capacitor versus the variable capacitor I used for the initial adjustment.

There may be other effects that a measurement would uncover. There are certainly several quirks shown by the VNA measurement.

There is another curious effect of the cylindrical capacitor we need to consider. When the capacitance is reduced by sliding the gamma rod outward the lead in wire from the feed point is lengthened by the same amount. We are therefore increasing XL while increasing Xc. If the magnitudes are similar the adjustment does not go as expected.

For the capacitor on the 40 meter yagi gamma match we have the following. For a capacitor value of 300 pf, a 1" movement of the gamma rod changes the reactance 1.5 Ω. The inductive reactance of the lead in wire is ~0.7 Ω per inch. The former is pretty exact but the latter is estimated from coil forming equations. Therefore sliding the gamma rod will have about half the expected effect.

The rate of change of capacitive reactance depends on gamma capacitor construction, frequency and length relative to wavelength. I have run into adjustment trouble with a couple of yagis due to the magnitudes of XL and Xc being too close. One solution is to alter the DE length so that a different capacitance is needed. The rate of change of a capacitor's reactance is inversely proportional to its value, and in that way the rates of change can be made to diverge.

Methods to reverse the gamma match calculations

The best way to determine the dipole feed point impedance of yagi is to temporarily substitute a split centre to the DE. That is how I conducted my experiments in 2020 with the 40 meter dipole. That isn't always possible or effective use of time and materials, especially for the size of a 40 meter yagi element.

With exact measurements of the feed point impedance and gamma match dimensions there are several methods to calculate the dipole impedance of the antenna:

• Reverse the gamma match design equations and solve for the feed point: Z₀ = R + jX
• Build equations from the fundamentals to calculate the dipole impedance Z₀
• Using an existing gamma match calculator, manually enter R and X values until the design parameters match the dimensions of the built gamma match; alternatively, automate the process with a software algorithm

I gave up on the gamma match calculator distributed with the ARRL Antenna Book because it is difficult to use. Each iteration requires re-entry of all the parameters, which is absurd. It is also not possible to inspect the algorithm. For my most recent calculations I used the TNL (Tolles, Nelson, Leeson) algorithm programmed by Cebik in an Excel spreadsheet. 

Cebik is gone but his articles and files have been archived in several places. I won't give any URLs because they likely have a short lifetime. Use a search engine to locate copies extant at the time of your search. After all, you could be reading this article years after it was written.

I converted the Excel spreadsheet to Open Office and plugged in the dimensions of the gamma match. I hoped to see the best fit with the NEC2 model of the yagi's dipole impedance. That didn't happen.

I manually adjusted the dipole Ra and Xa values in the spreadsheet until it churned out the measurements of the matched antenna to within a few percent. The final values of Ra and Xa that resulted in the actual gamma match dimensions do not look realistic (see the screenshot below). Even so, the TNL algorithm's estimate based on the modelled impedance was a pretty good starting point to build and adjust the yagi's gamma match.

As previously discussed, there are anomalies introduced by the cylindrical gamma capacitor and other components of the built antenna and match. For example, the precise location of the feed point (coax connector and wire leads) and using 2" as the average DE diameter. I found that small changes to Ra and Xa cause relatively large changes to the gamma rod length Lgr and gamma capacitor Cs.

The values of Ra and Xa are not correct. Ra ought to be closer to 20 Ω and Xa nearly twice as large. But I don't really know, and that's why I want the ability, with reasonable accuracy, to reverse the gamma match equations. I copied out the equations from the spreadsheet cells to see how difficult it would be to reverse them. I successfully reversed the less complex of the equations but without better fundamental knowledge of RF network theory I am unlikely to be successful. Besides, the manually discovered Ra and Xa diverge from reality enough that I doubt the work would be worthwhile.

I heard that there are improvements to the version of the TNL equations encapsulated in Cebik's now old spreadsheet. Unfortunately I don't have them and a cursory search didn't turn them up. The sensitivity of the equations to diverse physical parameters are also a concern. I don't plan to pursue the reversing project further at this time.

Next steps

Gamma matches are fun, if you like that sort of thing. They are useful, simple and terribly enigmatic. The opacity of their behaviour may delight the many hams of the trial-and-error brigade while horrifying those of us who prefer exact specifications and predictable behaviour. I keep making them even though they frustrate me to no end. I wish there was a more accurate design procedure.

When warm weather returns I will climb the tower and take a host of measurements at the feed point of the 40 meter yagi. I have two purposes. One is to improve the SWR bandwidth. The second is to determine the dipole impedance across the band so that I can verify my model of the antenna. The latter is not particularly necessary since the antenna performs very well. But I'm curious.

With the measurements in hand I will redesign the gamma match to improve the SWR curve and design a switching system to extend the low SWR range to cover more of the SSB band segment. There is no rush since it works well on CW and CW is my most common mode. I rarely venture onto 40 meter phone except during a handful of contests.

If I get very ambitious I'll resume my attempt to reverse the gamma match equations.

2022: Chasing Loose Ends

It is time for my annual look back on the year that was and year that has begun. You'll find that this is a tradition when you look back in this blog for January of each year.

Undertaking the construction, maintenance and use of an amateur radio station of the size that mine has become does not happen by accident. Well, you might accidentally arrive at a worthy destination by directionless wandering, but I'm getting too old to waste time. So I plan.

A plan is worthless unless it has clear and measurable milestones to track your progress. That makes many people so uncomfortable that they conveniently forget their stated intentions or they "move the goalposts" and hope that no one notices. People do notice, though in most cases they will remain diplomatically silent. I am too honest with myself to engage in self-deception. Putting my plans in the blog at the start of each year helps to keep me honest.

So, how did I do in 2021? For those with time to waste and a penchant for fact checking have all the raw data at hand: my stated plan and where I ended up on December 31. I am not surprised that my success rate for the line items is not high. I like to aim high but I won't sacrifice my life to get there.

What is important is that the major projects were completed. The items in my plan are not intended to be equally weighted. The following statement from my 2021 plan remains valid:

"Beyond 2021 no major antenna projects are planned. There will continue to be refinements and improvements, and I will likely dabble with experimental antennas and related projects."

By far the largest project was designing, building and raising the 3-element 40 meter yagi. The 5-element 10 meter yagis were a lesser challenge that consumed more time than I anticipated. Difficulties getting the rotatable, side mounted TH6 working properly took time I'd have preferred to spend elsewhere. Nevertheless the year was reasonably successful.

One important change to the plan was that the rotatable side mount was done for the TH6 and not the XM240. I left the small 40 meter yagi where it was because I determined it was more productive to have it fully rotatable (360°) and the TH6 was really only needed for the shorted North American paths and as a rapid choice to work Caribbean and Central America multipliers and to work South America. By doing it this way I was able to avoid building the more complex swing arm (300° rotation) for side mounting the XM240.

Lesser projects completed in 2021 included:

• New amplifier for high power SO2R (with BPF) and 6 meter DXing
• Correcting the mismatch of the upper 5-element 20 meter yagi
• Reversible east-west 156 meter Beverage
  

Of these, the only one I have yet to discuss is the BPF (band pass filters). There is a reason for the deferral, and I hope to correct the omission in the not too distant future. Numerous repairs are omitted from the list since those are unavoidable maintenance tasks for those with large stations. There's always work to be done. 

To give examples of the maintenance that must be done, this week I repaired a Beverage that a tree fell onto. A dead limb of that tree is hung up in another tree, out of my reach, that is certain to fall in the near future. On the 15/20 meter tower the prop pitch motor has become unreliable in cold weather. It will need service (again), but I will live with the problem until warm weather returns.

2021 projects that were deleted or deferred included:

• Stack switch for the 10 meter yagis
• More radials for the 160 meter antenna
• Efficiency improvements for the 80 meter vertical yagi
• VHF antennas: longer boom 6 meter antenna, and an antenna for 2 meter DXing
• Antennas for the WARC bands: 30, 17 and 12 meters

The 10 meter yagis were raised late in the year while the 40 meter yagi was under construction. The latter was the priority so the 10 meter stack switch was put aside to the new year. All the parts are on hand and construction is straight forward since it is no different than for the 15 meter and 20 meter stack switches.

Laying more radials for the shunt-fed tower on 160 meters is easy enough, if I had the wire on hand. I didn't so it didn't happen. Eking a fraction of a decibel on 160 meter was not a priority. Of even less urgency was improvement to the 80 meter array. I have alternative ideas to mull.

The same lack of urgency applies to VHF and WARC antennas. Maybe in 2022.

I previously published an annotated version of the following photo on the blog and on my QRZ.com page. It will be interesting to compare how different the station looks a year from now. I doubt that it'll looks very different from this visual perspective. Most of the changes will be in the shack, electronics on the tower and antennas, and relatively minor antenna changes or additions.

Many hams have told me that it is impressive. I suppose it is, however I get exhausted looking at it. It was a lot of work over the past 5 years since moving to this rural QTH. What I can celebrate is that the bulk of the big projects are now done. All of it must be maintained, and that is a never ending job. 

I didn't get here with a firm plan from the outset, as long time readers will know. There were too many uncertainties in my mind about what I really wanted and what I could realistically accomplish. I wanted "big" with no clear definition of what that meant. There were too many alternatives to explore. 

Each next step was well considered but not always the step after that. This is not a commercial enterprise so I allowed myself to be influenced by whims and opportunities, and by the adventure of exploration. Every ham with a large antenna farm has their own story.

Future projects will be less arduous. I am contemplating the addition of a small tower in future to avoid interaction and mechanical challenges of antennas on the existing towers. I also want a small tower with few encumbrances for antenna experiments. The station will not reach stasis for a long time since there will be new antennas to explore and improvements made to existing ones.

With a sigh of relief that I've made it this far, let's look at what I have planned for 2022. Although the projects will be less visually impressive they will have a impact on contest competitiveness, among other advantages.

• Prop pitch rotators: I am having more difficulties with the motor that turns the 15 and 20 meter yagis. The gearbox is the problem this time. Service will wait until warm weather returns. I must also finish building the direction pot for this rotator and improve the one for the chain drive prop pitch motor on the 40/10 tower. Once those are done a new controller in the shack is needed to make them ergonomic and more reliable. The controller will be home brew, including software.
  
• 160 meters: There are two options to improve my top band signal. One is to shunt feed the other tower and feed them for switchable end-fire and broadside configurations. The second is a parasitic array using a wire driven element between the towers or adding wire elements to the existing antennas. There are pros and cons to be weighed. A large consideration is for ease of deployment each fall and removal in the spring for haying.
  
• VHF: At minimum I need a 2 meter yagi suitable for DXing and occasional contest use. It will go on the Trylon, just below the 6 meter yagi. A superior 6 meter antenna is possible this year but may be deferred to 2023. Extending my DXCC count on 6 meters will not be easy.
  
• WARC band antennas: My primary interest is chasing band-countries for general DXing on 30, 17 and 12 meters. I have no specific plan at present and there are too few major DXpeditions expected this year due to the ongoing pandemic. I use a tuner on the XM240 for 17 meters and the 80 meter vertical for 30 meters, and on 12 meters I load whatever high band antenna is broadside to the station I'm calling. While far from ideal at least it works well enough, for now.
• 40 meters: The matching system for the 3-element yagi needs work to improve the SWR and it needs a switchable network to make it more usable on SSB. It's just a matching problem since performance is excellent.
• 80 meters: I am contemplating a reversible 3-element wire yagi with a rope catenary strung between the towers. A horizontal yagi could pay dividends by being more efficient and to exploit high elevation angle DX paths. It would point northeast to Europe and southwest to cover most of the US. The main lobe of a 3-element yagi is broad enough to work well for most stations I can expect to work. A second 80 meter antenna provides a backup in case one fails before a contest.
• Station automation: I am making slow progress on the hardware and software. Some of what I need should be complete by early spring. The rest can wait until I can begin inviting others to do multi-op contests. COVID's resurgence will delay multi-ops for a while longer.
• Station modernization: A new SDR transceiver will replace the FT950 which has long overstayed its welcome. More extensive software control of equipment and antennas is planned. Other equipment changes are being contemplated.
• Receive antenna: The Beverage system is performing well, although it demands regular maintenance. Completion of the desired 8 directions with a future NW-SE reversible Beverage is doubtful because it's benefits are at best incremental. These antennas are not so directional that more than 6 directions are strictly necessary. Instead I would like a second receive system, probably a multi-direction vertical array. The benefits are diversity reception and for low band multi-op contests. Planning and design can proceed this year, and construction to follow in 2023.
  

This list is vague in comparison to those I've made in previous years. That's deliberate. From here on I will be more relaxed about my station plans. Major projects were never intended to continue forever! Speculative projects for fun and for experimentation will be undertaken when I feel the motivation and interest. 

I will spend more time this year and in subsequent years for non-ham retirement activities.

With that I will end the annual retrospective and look forward. I hope to meet more of you on the air. It's always enjoyable when a contact, during a contest or other times, tells me they read and enjoy the blog. Thank you for following along in my journey. Major contests are on the horizon, the 6 meter summer sporadic E season is only 4 months away and the sunspot count is climbing. Pandemic or not, 2022 will be a great year.