20 Meter 2-element Yagi With Bent Reflector: First Models

More than a few times I've mentioned that I am not happy with the TH6. Since I have it I use it but now only as a "multiplier antenna" pointing south. Yet it still has and causes problems. These include: narrow bandwidth and loss due to the traps; interaction with the 40 meter yagi beneath it; high SWR when wet; and, high coupling to the Europe pointing 15 and 20 meter stacks. And, it's very old, leading to questions about its future durability. But after 40 years I've certainly gotten my money's worth!

Its replacement doesn't need to be a tri-band yagi, nor does it need to have high gain. A group of several small yagis for each of 10, 15 and 20 meters could suffice, and might offer more flexibility than one tri-band yagi that either can't be shared, or can be shared at high expense (high power triplexer and filters). I see no need to spend a lot for what is really just a multiplier antenna. It only has to perform well enough to punch through the pile ups.

I've temporarily set aside 10 and 15 meters since, being smaller, those are easier yagis to design and build. A 20 meter yagi can be quite large, with 3 elements typically placed on an 8 or 9 meter boom. While that will easily give me more than 8 dbi across the band, considering its size I decided to look at smaller antennas. I can live with 7 dbi and perhaps even 6 dbi if it has other positive attributes.

These are the criteria I came up with:

• Lightweight: I'd like it to be reasonably small and light. Since it won't be rotated, I want to see how little aluminum I can do this with.
• Simple: The design and construction should be straight forward.
• Performance: Low SWR across the band (better for solid state amps); good but not great F/B and F/S; and (per above) within 1 to 2 db of a full-size 3-element yagi.
• Isolated element: By insulating the elements from the boom the interaction with the nearby 40 meter yagi can be eliminated. 

My first attempts focussed on 2-element yagis. This category includes Moxon rectangles, hex beams, and other element configurations. Each has its advantages and disadvantages. The following are the configurations considered in this study:

From the right are a conventional yagi, Moxon rectangle, "spider" beam style yagi and a yagi with a half-bent reflector. All of these yagis are unidirectional to the right. The latter two use wire for the bent bits, and indeed the reflector for the vee-shaped reflector is all wire.

A conventional 2-element yagi has poor F/B, good F/S, reasonable gain and SWR with a matching network. The bandwidth over which these metrics are best is narrow, perhaps 100 kHz on 40 meter. Outside of that it quickly gets worse. This is not a popular style of yagi for the low bands.

When we double the frequency to 20 meters that's still barely half the 350 kHz band. If you operate CW or SSB, but not both, perhaps that's sufficient. But not for me. We can do better with one of the other designs, so I'll say nothing more about the conventional 2-element yagi in this study except as a baseline for comparison.

The Moxon rectangle has excellent SWR and F/B across 20 meters, and even on 40 meters where it has to stretch farther due to the much larger bandwidth (by percent). I put this to good effect on my 40 meter reversible Moxon. However a Moxon's peak gain is worse than a conventional yagi due to a portion of the elements turned inward. 

As with all four of these 2-element designs, peak gain occurs at or below the band of interest. That's simply the nature of 2-element yagis due to the phase relationship between the elements. With more adjustable yagis of 3 or more elements there is more latitude on where to place peak gain and F/B. Not infinite latitude since, due to the nature of passive, close-spaced parasitic elements, there are constraints on the phase and amplitude relationships.

The Moxon rectangle, while not overly large on 20 meters, requires tubing for all element components. The designs on the left use less aluminum by using wire for the element tips. Cost, weight and wind/ice load are reduced. On the other side of the equation, tuning these designs for optimum performance requires precision in the tip spacing and interior angle. NEC2 does poorly at this so I used NEC5 for my models. 

I chose wire tip angles that allow a cord or rigid insulation to fasten the wire to the more rigid tip of the driven element. That required multiple iterations to optimize performance and mechanical layout. While I can't claim that I achieved the best possible performance, I believe I've come close. Close enough, that is, to evaluate and compare these designs.

The 3 designs are primarily evaluated for SWR (direct feed, no matching network) and gain. F/B and F/S are not major objectives considering its intended use as a fixed direction multiplier antenna -- work the mult and move on, no running or rag chewing.

Before diving into the modelling results, here are my motivations for looking at these particular 2-element yagi designs:

• Conventional yagi: Simple and well understood, with the maximum gain but relatively poor F/B and SWR bandwidth. It also uses the most aluminum.
• Moxon rectangle: Again, a well understood yagi design with relatively good F/B and excellent SWR bandwidth. But it's an awkward antenna to build and raise. Recall what I went through with raising the 40 meter reversible Moxon. 
• Vee-shaped reflector: It is, in a way, half of a Spiderbeam 3-element yagi. It is lightweight, but at the cost of gain and F/S, with SWR not as good as a Moxon rectangle.
• Reflector with bent tips: It is intermediate between the conventional yagi and the one with a vee-shaped reflector with respect to weight and cost. It is also intermediate with respect to gain and F/B, with still good F/S and excellent SWR bandwidth.

Although I knew all of this before the modelling study, there is value in confirmation and spending time to optimize performance; there is no need for hasty reasoning. After presenting the results of the modelling I'll come back to explaining why they perform as they do.

First, the free space azimuth patterns in 100 kHz steps from 14.0 to 14.3 MHz. I skipped the upper 50 kHz since I rarely operate there and performance is little different from that at 14.3 MHz. Rather than tables (as I've often done in the past), I'll present the data as overlaid traces. Pay attention to the outer ring gain on each chart since those differ for each antenna.

It is no surprise that the conventional yagi has the most gain. The greater the parallel portion at the centre of the elements the greater the sum of the currents. However, inter-element coupling is poor in a conventional yagi so that the gain bandwidth is not great. That said, the gain bandwidth isn't all that different for the others, except for the relatively poor gain performance of the yagi with a vee-shaped reflector. Gain is pretty good across 20 meters for 3 of the 4 designs.

F/B is not very good for the conventional yagi and for the vee-shaped reflector. Surprisingly, the Moxon rectangle is not as good as the yagi with the bent wire tips reflector. At least it was a surprise to me. 

F/S is relatively poor for the yagis with full or partial wire reflectors. This is expected. You can gain an insight by imagining yourself in space some distance directly off the side of each yagi. When you look at the conventional yagi you see almost nothing since the elements are pointing at you; an ideal dipole has no collinear radiation. For the other antennas, the amount of reflector that you can see is non-zero, with the least for the Moxon rectangle and the most for the vee-shaped reflector. Hence the relatively poor F/S.

Again, these are not fully optimized designs. It is likely possible to squeeze out a little more performance, in particular the yagis with a vee-shaped or bent wire tips reflector. The distance to and angle with the driven element are critical since small differences cause large performance changes. Critical coupling is called critical for a reason!

Next, let's look at the SWR across the 20 meter band. The conventional yagi uses a beta (or hairpin) match and the others are directly fed at the centre of the driven element.

The Moxon SWR could be improved with more fussing. I didn't bother since small changes will have little effect on the pattern. The same is likely true for the vee-shaped reflector. That said, the SWR at the band edges will be almost the same when the SWR is optimized to dip 1 at one mid-band frequency. 

All designs other than the conventional yagi do very well. Few transmitters would complain. Keep in mind that environmental factors (interactions with the tower, guys and other antennas) will in most cases cause deviations from perfection more than what you see on these plots.

At this point it was time to stop. I have time over winter to mull over the possibilities. At the moment the reflector with bent wire tips looks attractive: <1 db gain below that of a conventional 2-element yagi with good F/B, F/S and SWR bandwidth. Other than the conventional yagi these antennas are a little complicated to raise onto a tower, just as it was for the 40 meter reversible Moxon.

A 3-element design would be better, especially mechanically since the driven element will be pulled equally from both sides; the wire tips and cords of the parasitic elements "guy" the DE. But the antenna is larger, more complex and with only modest performance improvement. But only about 1 to 1.5 db gain improvement can be expected.

Due to interactions that I am likely to encounter in my station I did not attempt to make this a multi-band antenna. It is likely that I'll have a 20 meter mono-band yagi and a separate 10 & 15 meter yagi to replace the TH6. The latter may very well be a multi-element two-band conventional yagi with interlaced elements. Again, these are early thoughts not a definite plan. I'll develop models when the time comes.

Note: Dimensions are not shown for any of the modelled antennas since I used constant diameter tubing and bare wires rather than tapered tubing and insulated wires. These can be adjusted when and if it comes time to build the antenna that I settle on. Dimensions were selected to be approximately average element diameters. Booms are between 3 and 3.2 meters (~0.15λ), with variations made to make the wires fit the space while being connected to the DE tips.

Acom 1500: Intermittent Faults & Other Problems

Intermittent faults are the worst problems to find and repair. Unless there is a clear set of steps to reproduce the problem it can remain elusive. It is equally true of hardware and software. There is a lot of both in a modern ham shack.

Several months ago my 4-year old Acom 1500 amplifier began to periodically trip the protection circuits. There was no unique cause or consistent pattern in the protection code data. In a few case there was the soft "pop" sound near the front of the amplifier cabinet. A reset and all was well again. Then the faults became more frequent, whether transmitting or not, and whether online or in standby. It was perplexing.

A cursory inspection inside showed nothing obvious, no carbon tracks or other physical signs of distress. With close to 3000 volts in the B+ supply there are many potential paths to failure, whether a weak capacitor, dust or loose connection. Typical suspects such as the tube (4CX1000) and vacuum relay did not appear to be to blame.

Since I have a spare amplifier (3 in total) I set the 1500 aside until I could decide how to proceed. There are no factory authorized Acom service centres in Canada and it is inconvenient, to say the least, to ship heavy and fragile equipment to the US or overseas. Inquiries among friends generated no useful insights. It was a puzzle and concerning but there was also no urgency. I fretted having an expensive piece of equipment forcibly idled.

When I returned to the amp some time later I got my first clue to what might be happening. At times during normal operation the plate current (Ip) would read 0 ma. That's a very odd reading when there's a kilowatt of RF being transmitted. The same would happen when idling or transmitting without input. But again, only sporadically. There was no pattern, and a fault still occurred from time to time. I had no good ideas on how to proceed so I set it aside again until about two weeks ago.

This is a recent picture taken after I appeared to have resolved the problem. Once I narrowed the cause to measurement and protection, specifically Ip, (or one of the causes) and did my best to deal with it, I installed a physical meter in the Ip measurement circuit. Since the digital display on the amp cannot show instantaneous deviations of Ip, I hoped to spy any instantaneous anomalies by putting the meter where I could see it while operating. The microammeter only lightly loads the circuit and was calibrated with a series trimmer pot.

Unfortunately this circuit assumes that the current pickup in the B+ is working. There is no good or really safe way to splice in my own. Ip is indirectly measured by detecting the voltage across a precision low value resistor that is in series with the B+ line. The resistor is indicated by the arrow in the picture of the mains PCB and rectifier/filter assembly; The resistor is on the latter. Only low voltage DC is presented to the Mains PCB.

There are two stages of processing of the detected voltage. There is one op amp on the Mains PCB and another on the Control PCB. A 3-pin cable runs from the detector to the Mains PCB and a 5-pin cable runs from there to the Control PCB. All are circled. The physical meter taps into the Ip pin on the 5-pin cable, which is between the Mains and Control PCBs.

One immediate suspect was the connectors. It is not uncommon for oxidation or other flaws to creep in that degrade continuity. That can result in a 0 reading or a spike when it makes and breaks connection. I pulled and cleaned every connector of this type throughout the amplifier, and there are a lot of them. It has to be done carefully since moderate and evenly applied force across the connector is needed. It is easy to cause unintended damage on those with many pins. The pins are approximately the same dimensions as Dupont connectors, both in pin size and 0.1" spacing.

There is no good way to know whether the connector work made a difference. All one can do is run the amp and see if the intermittent fault returns. I did that but I then also took another step. 

I opened, inspected and vacuumed dust of all compartments in the amplifier. I then blew high pressure air through the inaccessible areas to remove more dust. It's a useful step though not without risks. These include contact damage, air pressure damage and static discharge. The latter is a greater risk this time of year when the relative humidity is low.

Nothing was damaged by the cleaning. That was a relief despite my confidence in proceeding. I was as careful as I could be, especially around microprocessor circuits. I also disassembled the front of the amp and exposed the Control PCB. With care, and magnifying glasses, I inspected the measurement components and connectors. No flaws were found. All the PCBs are now very clean.

I went through the RF deck with lights and mirrors to see under and behind components. I did the same for the tube compartment, top and bottom. There was dust inside the chimney so I cleaned it and the air filter. The antenna selector board was also inspected and subjected to air pressure to blow out any hidden dust.

When all was done and the amplifier reassembled, it worked. That is, there have been no faults since, other than a power on fault that detected a connector I had forgotten to push back on. Oops. Since then I've worked many stations, SSB and CW. CW can be a better test due to the repeated on-off "spikes" of a high power carrier. This weekend I used it and the Acom 1200S to make over 1000 QSOs during the LZ DX contest. So far so good. 

Is it truly fixed? Of course I can't know that without identifying the ultimate cause. Perhaps after 4 years it was simply time to clean the inside of the amp, any amp. All that I'd done until now was to periodically clean the air filter.

Repair work came to many hours. I doubt it would have been more economical to ship it to another country since an intermittent problem takes time to find, and they of course charge by the hour. If they recommend board or component replacement, assuming they also fail at finding the fault, it would be even more expensive. Since working around the high voltages inside a tube amplifier requires care and skill, it is not recommended for the inexperienced. Every ham has to make the judgment call for themselves. 

Solid state amps only appear to be safer since there are no high voltages beyond the mains supply. However the power supply and circuits deal with the same power level. No kilowatt-class amplifier is a safe space. Be careful if you choose to do as I have done. I'm no expert but I do have experience working on amplifiers.

I hope that if nothing else you enjoyed pictures of the inside of the amplifier. As I understand it, the Acom 1500 is no longer being manufactured. The industry migration to solid state continues. A well designed and maintained tube amplifier can last a lifetime. With few new ones on the market, they have to. 

DXing in 2025

There was a time in this blog when DXing featured more often. Other than in the context of 6 meters I've said little about it the past few years. The change was not intentional, it just happened. On reflection I realize the reasons why. I've changed. That is worth a short article.

DXCC is easy to achieve, far easier than ever before. Here is a partial list of why that is:

• DXpeditions are announced well in advance, with schedules and operating plan.
• Human and skimmer spots are rapid and have alerting services, so you are always one click away from working them.
• Remote shacks mean you can work them from anywhere, anytime.
• DXpeditions have multiple stations which divides the pile ups, making them easier to penetrate for even the smaller stations.
• FT4/8 levels the playing field. It really doesn't matter where you transmit and how strong you are as long as the DX station decodes you. Hunting and timing (skill) mean very little.

In days of yore, DXing was not so easy. Here are some of the reasons why:

• Discovering that there exists a ham in a distant, rare country was difficult. Often we would only learn of activity after the fact. A lot of listening and luck (and personal networking) were required to learn of their existence. 
• Time is precious. Yet a lot of it was needed to regularly scan the bands.
• Travel was far more difficult that it is today so DXpeditions were not routine. Not all were announced in advance. Many were "surprises" due to work assignments, scientific expeditions, or simply hams enjoying the surprises they created.
• Split operation was less common since equipment often didn't support it, especially the ability to listen to two frequencies at the same time to quickly find where the DX is listening.
• With no spotting networks or just a small circle of DXing friends (if any) to alert us of an activity, rare DX was easy to miss.

Those are examples that quickly came to mind. There are certainly others. However, that isn't my point; rather it's that it is much easier than it once was. Nowadays you would have to be living under a rock to miss the activation of a rare DX entity.

Therein lies the problem, if it can be regarded as a problem: DXCC is easy with a small station and routine for the rest of us. In this fall's CQ WW SSB we logged more than 100 countries on 4 bands. It wasn't so very long ago that an achievement like that was uncommon. Now it's routine.

This has bred entitlement -- believing that we deserve to log the rare DX -- and impatience with reaching key DX award milestones. But if it was easy, what has actually been accomplished?

In my case the modern ease of DXing has resulted in mild lethargy and disinterest. I don't react quickly when the DX is spotted, unless it's truly rare or on a band where they are difficult to work, such as 160 meters. Filling up band slots to reach new DXCC Challenge plateaus is becoming less interesting. No matter, the numbers keep climbing on my LOTW account (Logbook of the World).

Some of this is due to the size of my station. I'm a big gun now. Quite often I crack deep pile ups with one call. Where's the fun in that? To compensate, many times I'll use lower power and a non-optimum antenna to practice my pile up skills and to make the chase more interesting. Skill development and practice was a major preoccupation of mine when I ran QRP with small antennas. Now I have to artificially recreate those conditions.

Despite the many changes making DXCC and even Honor Roll so much easier, these awards remain coveted by new and long time hams alike. I track my progress even though I have never applied for any DX award and I probably never will, no matter how stratospheric the achievement level.

That said, during a DX contest I take great pleasure in running up the country count as high as I can in the 24 or 48 hours of the event. It is a worthy accomplishment to do so while also making as many QSOs as possible. The challenge is one of deciding when and where to run while concurrently hunting for countries, whether assisted or unassisted. 

I am easily motivated to work DX in contests but the rest of the time, except for rare countries, 6 and 160 meters, and occasionally under difficult conditions, it doesn't mean all that much to me anymore. Times change and so have I. I use the available technology regardless, and I enjoy doing so. It's just that the accomplishment means little to me most of the time.

But putting rare DX in the log is far easier than it once was! There is no pride in drudgery, and to be honest that's what it once was. DXing was a game won by the well-connected, the wealthy (with their big stations) and retirees with lots of time to scour the bands. Technology levels the playing field. As much as we gripe about the price of equipment, it is not expensive hobby to build a station that allows one to work lots of rare DX.

Time is also not the impediment it once was. We can receive alerts, operate our stations remotely with widely available applications and product, or we may work from home just a few steps from the shack. These also level the field.

The main differentiators now are the willingness to pay attention (accept interruptions), following DXpedition schedules, perhaps "donations" to facilitate confirmations, and of course skill. The latter is still of significant value -- listen to most pile ups and you'll understand. Witness how many chasers are their own worst enemies.

Despite the negative tone of this article I still chase DX and I am certain to keep doing so. The allure of communicating across the globe with someone sitting on the beach of a remote island never pales, no matter the relative ease compared to years long past. It's enjoyable if not quite so exciting. Hams new to DXing are excited to work the rare ones and that is vicarious pleasure to enjoy as well. It's good to see enthusiasm in the newcomers to our great hobby. 

Will DXing eventually fade as one of the attractions of amateur radio? Perhaps. It is not easy to predict the future. By what I hear in the pile ups, that day won't arrive for many years.

To Rotate or Not To Rotate

In the lead up to CQ WW SSB, one of my challenges was rotators. I hate them. So do many hams.

These mechanical devices suffer from all manner of ills that seem to manifest just when they're needed most. I am perfectly capable of working on these beasts -- from the smallest TV rotators through to prop pitch motors -- though I'd rather not. They're finicky, full of messy grease and tend to reside at the top of towers under a large load bearing down on them where they're difficult to service. Getting them down from the tower, temporarily supporting the load and then putting them back after repair can be difficult and dangerous.

I am not the only one muttering about these pesky devices. One of the all time most popular articles on this blog is the one about refurbishing a Hy-Gain Tailtwister rotator. I doubt that readers of articles like that have affection for their rotators. Despite the availability of alternatives, which we'll come to, often the cure is worse than the disease; there are pros and cons for any approach to direction selection.

Many contesters won't put it with rotators at all, deeming them not worth the effort, or the risk of failures during major competitions. Instead they deploy a variety of fixed yagis and electrically switched directional arrays. Just click and you're pointing where you want. Sounds nice but it is rarely as simple as that.

The subject for this article occurred to me as I was preparing the station for CQ WW SSB. One of my many projects this year is to make the lower yagi of the 15 meter stack rotatable. It's always more complicated than anticipated. First, the rotator I had in mind had a broken direction pot. The pot I scavenged from an old rotator also turned out to be broken. So I bought a Ham-IV at a flea market.  Although the controller has a minor glitch that needs repair, the rotator itself seems fine, inside and out. I have spare controllers to pair it with.

Next, there are control cables to be run from the shack to the rotator shelf. Luckily I buried enough heavy and light gauge cable in the last trench that I dug. But it took time to run cable up the tower, do the connections and splices and then route a cable into the shack for the controller. I got that mostly done. 

Third, while up the tower completing the side mount bracket and wiring, I discovered a serious problem with the mast. So I set aside the project to fix that before the contest. Then the rain began to fall. (Sigh.) In the end the antenna remained fixed on Europe. I'll try to have it done for CQ WW CW.

It may seem intelligent and forward-looking to decide to forgo rotators entirely. Put up a few more antennas and problem solved! As you can probably guess, it isn't so simple. First, consider how many directions of coverage you need, whether for general operating, DXing or contesting.

The global bearing map centred on my QTH gives some scope of the challenge. There are 6 critical directions: Europe, Africa, South America, US south, US west and midwest and east Asia. It is coincidental and convenient that the long path for each DX path is approximately along one of those directions. Others regions of the world can't count on that.

It should be unsurprising that I have Beverage receive antennas for those 6 directions. I originally planned for two more but the returns would be minimal. I don't miss them. My 80 meter vertical yagi has 4 of those directions. The main lobe is wide enough that east and west have some gain and there is its omnidirectional mode, plus a high inverted vee for broader coverage.

The high bands are another matter. The competition is more fierce so that more gain is highly desirable. But more gain is at the expense of coverage: a narrower main lobe. I often point the yagis of my high band stacks in different directions (spray) to take advantage of multiple paths open at the same time.

Perhaps it is not as bad as that. Consider the azimuth pattern comparison (right plot) of 2, 4 and 6 element yagis. The narrowing of the main lobe is necessarily accompanied by a narrower beam width. But that a relative comparison. On an absolute basis those long boom yagis do pretty well at the edges of the main lobe, and often have a wider SWR bandwidth. Therefore fixed (non-rotated) high-gain yagis don't impair coverage by much. 

Of course you don't get something for nothing. All that energy in the main lobe comes at the expense of elevation pattern beam width (left plot). Stacked yagis can solve that restriction by enabling a variety of elevation angles lobes and nulls which the operator can choose from.

Well then, if reducing or eliminating rotators isn't as dire as it might at first appear, what must be done to achieve similar coverage? There are many possibilities for station builders to consider. Here are what may be the most common:

• Rotating tower (K0XG system, left panel): All yagis rotate together, usually pointing in the same direction, but not always. Contesters require more flexibility than this system allows. This is an expensive solution with few remaining in the business. Or you can build your own, if you dare.
• Stacked yagis on a rotating top mast: Commonly called a Christmas tree due to the usual practice of putting the largest yagi at the bottom and the smallest at the top to minimize bending stress.
• Ring rotator (TIC, right panel), swing gate (centre panel) or 120° ordinary side mount: Allows all or partial rotation. The mechanisms can be complex and expensive, and a swing gate can place significant torque and bending moment on the rotator and tower.
• Side mounted fixed direction yagis: Usually complementary to a top rotator, either as part of stacks or independent. I have several of these in my station.
• Reversible yagis, fixed or rotatable, wire or aluminum: Some of the solutions are the least expensive and simplest, such as reversible wire yagis. For example, my recently built reversible 40 meter Moxon with 260° coverage.
• Multi-direction, electrically switched arrays: These include 4-squares, vertical yagis and BSEF arrays, with the latter more often built for low band reception. They are more commonly found on the low bands where rotatable horizontal yagis are difficult and expensive.

Whether the yagis are rotatable, fixed or reversible, there are many considerations that you must be addressed for optimum performance. It would be shame to go to all that expense and work for naught:

• Interactions: Between yagis stacked on one tower, whether or not on the same bands, guy wires, antennas on other towers, interaction in some orientations and not others.
• Optimum height and direction combinations may be attainable with careful system design and layout.

If you insist on rotators, you may escape some of the above downsides at the expense of others:

• Mechanical failures and repair: If you've read my blog for a while you'll know that this is a regular feature. Indeed, one of the most popular articles is about refurbishing a Hy-Gain Tailtwister rotator. Clearly I'm not alone. Prop pitch motors, despite their many positive attributes for large antennas and turning towers (see above), are not easily serviced. I have seen similar troubles with Prosistel, Yaesu and other models. Rotators deal with a lot in a hostile environment. Maintenance and service are inescapable.
• Availability of parts and service: With the demise of MFJ and the product lines they bought from defunct companies, Hy-Gain rotators -- perhaps the most popular in North America -- will become increasingly difficult to service. Spare parts are being hoarded by non-MFJ rotator repair shops. When the part supply runs out they may become irreparable.
• Rotatable side mounts: These are mechanically challenging, especially on self-supporting towers, and in most cases entail custom builds. You are on your own. They also create their own unique kinds of interactions from and to other antennas and guys. I have one with partial rotation and another is under construction.
• 
  Cables and controllers: Copper is expensive! The taller your towers and the further they are from the shack, the greater the expense of wiring them. They are also prone to environmental woes ranging from animals to weather. Controllers also fail, and some brands are more fragile than others. Parts and service (see above) are becoming more difficult.

This trail of woes turns many hams away from rotators. There are also the many controllers required. Where do you put them and how do you manage them in a multi-op contest station? My station is small enough that I can stack them up between the operators but this does not work well in bigger stations. 

In those cases it is better to use software applications at each operating position. Of course it is to be expected that occasionally another operator will turn a yagi you're using either because it's shared (see below) or on the same rotator as the yagi they're using. Point and click can be a deceptively convenient alternative. Of course the software and network interface adds complexity and therefore another point of potential failure.

But to effectively exclude rotators is difficult. Those with small stations may not worry about it, accepting that in some directions their antennas will have deficits. However, if you are building a "big gun" station for contesting, there is much to consider when rotators are excluded:

• 
  Interactions: The more antennas, the greater the potential interactions. These can be largely avoided with careful planning, but cannot be eliminated. It is a judgment call as to whether an interaction is serious enough to matter. A popular alternative is bliss through ignorance.
• Sharing: Use of multi-band directional antennas such as tri-banders can reduce the number of antennas, if you purchase quite expensive BPF and triplexers. These will have to use non-trapped or loaded elements since two high power transmitters will very likely destroy those components.
• Towers: Fixed yagis in multiple directions, optimized for stacking and interactions, requires more towers than in big stations that utilize rotators. For scroungers, used towers are available at reasonable prices, however you need to transport them, plant and raise them and then maintain them. With big towers failure is not an option: when one comes down it can take down one or more others unless they are far apart (see next bullet).
• Land: Lots of towers and optimum placement takes land. A typical guyed tower requires ~1 acre of land, and you the space to arrange their placement to minimize interactions while also permitting installation of wire antennas and room for heavy equipment and tramming. There is inexpensive land available in this part of the world, if you can deal with the isolation and lack of civilized comforts. Otherwise prepare to pay a lot.
• Service: Working on towers with many yagis is more difficult than on those with fewer. You have to climb on and around them, avoid tangles when raising and lowering them, inspecting and replacing hardware, dealing with asymmetric load stress and many, many runs of transmission lines and control cables. The nature of maintenance changes but not the magnitude and the risk.

My final message? A big contest station entails lots of work and expense, and ongoing maintenance. That's the case whether you choose more towers and antennas or fewer of them plus rotators. The differences can be found in switching and control systems, and operating procedure. Choose your poison. Either path can lead you to success, however you define it.