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.