Elevation Pattern Nulls

Propagation prediction for most hams is a terribly inexact science. You get on the air and tune around for stations, or you click on spots. You hear the DX or you don't; sometimes they're weak and other times they're strong. But why? Well, propagation. That's as far as many hams think about the matter. 

Maybe you try another band or just turn off the radio and come back another day. And if it's a contest weekend? You understand that's the playing field for every competitor so you persevere.

The reason HF propagation is difficult is because it is a complex phenomenon, much like the weather. We understand the physics but the data to make accurate predications is sparse or not collected at all. Ionospheric propagation is rarely as simple as depicted in this diagram above. There are numerous factors to consider, some of which include:

• Polarization and Faraday rotation
• Chordal hops, within and between ionosphere layers
• Geomagnetic activity due to the sun (UV, X-rays, energetic particles and more)
• Scattering (diffuse rather than specular reflection or refraction)
• Ducting 

Our responsibility as communicators is to design and build antennas that make maximum use of the propagation paths provided by the environment. If a signal is vertically polarized, we prefer a vertically polarized antenna. If the elevation angle is large, we prefer an antenna that has a high angle lobe. If we want to work over the pole we prefer an antenna that favours the north (or south) direction. 

The important thing to remember is that the environment decides the propagation parameters, not the antenna. It can change quickly and has pronounced daily and seasonal cycles, and that's on top of solar cycles and solar activity. 

Even simple antennas can have complex patterns. This is due to their size, orientation, height, terrain, and other factors, usually with respect to signal wavelength. One antenna is never good enough for all types of propagation. We need set operating objectives and build accordingly.

The azimuth pattern of a vertically-polarized 40 meter delta loop operated on 15 meters (its third harmonic) is shown at right. You need to install it so that pattern nulls are not placed at bearing you consider important directions, and that lobes are where you want them. Compromises may be unavoidable. Rotatable antennas are less constrained but they come at a cost.

A curious situation occurred years ago when I had a much smaller station. In a now ancient article I described my initial confusion when comparing two 40 meter inverted vees. I had two so that I could cover all compass directions. Faraday rotation and polarization dependence on the azimuth angle (bearing) made for a difficult comparison since an inverted vee is vertically polarized off the ends and horizontally polarized broadside. 

They were equally effective antennas but never at the same time due to Faraday rotation. That experience highlighted how antenna comparisons can be so fraught with uncertainty. You may think you're making a fair comparison -- WSPR, A/B switching, etc. -- but in many cases all you're doing is comparing antenna patterns relative to the prevailing propagation, not performance. Assessing relative performance is never easy since propagation characteristics can make a comparison worthless or misleading.

There is a saying among many hams: you can't have too many antennas. The more antennas you have the greater the probability that one of them will best exploit the propagation to a particular station or region at any given time and band. Of course most hams don't have this option. They're left guessing how well their antennas are really performing.

My motivation to write this article came from a recent antenna selection conundrum. I was listening to the FP5KE DXpedition on 20 meters and I wanted to know which of my several 20 meter antennas was best. I was driven by curiosity, without the intention of working them, since I've worked FP countless times on 20 -- it's single-hop distance and frequently active.

I first listened on the upper 5-element yagi of the 5-over-5 stack. They were surprisingly weak, no more than S5 on the meter. This wasn't surprising since that antenna, at 40 meters height, concentrates most of its energy at low elevation angles. The lower antenna does better for high angles usually associated with shorter paths.

When I switched to the lower 5-element yagi, which is about 21 meters high, the signal was still quite weak, not much different compared to the high yagi. That seemed odd to me since it was so unexpected. I then switched the stack to BIP (both in phase) and the signal jumped to well over S9. Imagine my surprise. 

To complete the comparison, I turned the Skyhawk eas. It has 3 elements on 20 and is about the same height as the lower 5-element yagi of the stack. The signal strength was a little less than the full stack and far better than either individual yagi in the stack. 

I suspected that the differences were due to the elevation patterns of the various antennas. There are two or more lobes with nulls between lobes. The terrain is pretty flat so the lobes and nulls of antennas at similar heights but on different towers should be about the same. The patterns are likely to closely resemble those produced by modelling software that assume a homogeneous, flat ground.

This EZNEC plot contains the elevation patterns of the three selectable configurations of the 20 meter stack: upper, lower, BIP. It is taken from an earlier article, and annotated with a few lines.

The red line at 30° elevation highlights a null common to each configuration. That can occasionally pose a problem when the propagation path favours that elevation angle. If there is real difficulty due to that null I can switch to one of the tri-band yagis.

The dark red (brownish) lines highlight elevation angles where there are two traces with nulls. That is, there is one antenna selection that will work better than the others. The chart is quite busy so I hope that readers can successfully read the critical data it contains.

Despite the generally excellent performance of the stack, it is those many nulls that occasionally render it impotent. You can get better elevation angle coverage in a stack with 3 yagis, whether of similar size or smaller.

Assuming that the plot accurately resembles that of my stack can we determine what happened when I was listening to FP5KE? We are looking for an elevation angle where each individual yagi has a null and the combined stack does not. However, there isn't one!

A reasonable conclusion is that the elevation plot produced by the model does not accurately match the real stack. That isn't too surprising. Only a small deviation from perfect terrain can move those nulls. That's because a null requires an exact cancellation of fields from the space and ground reflected waves of one or both yagis -- the requirement is equal amplitude and opposite phase when the fields are summed. The major lobes of the antennas may be close to those in the model even when the nulls are significantly different since the sums of the fields can be less critically aligned

My wild guess is that the propagation path's elevation angle is close to 30° (red line) and that one of the minor lobes of the stack on opposite sides of that angle is really much larger. But it's just a guess. It also must have been the case that the signal was constrained to a narrow range of elevation angles. Otherwise pattern nulls would not have such a prominent effect. That is often not the case, with signals appearing at a range of elevation angles due to various scatter phenomena.

A ray tracing tools such as HFTA combined with an accurate terrain profile for my QTH might deliver better insight. Or it might not. As I said, null positions are very sensitive to small deviations. Those deviations can quite easily be larger than the accuracy of the terrain data fed into HFTA.

I'm not so curious about those nulls that I'm willing to go the trouble of using HFTA. I have enough antennas that I can "navigate" around pattern nulls to work what I need to work. I am not going to rearrange my towers and antennas for dubious improvements, nor will I take the trouble to add BOP (both out of phase) to my stack switches. There are many serious contesters that would never build a station without first consulting HFTA.

I'll say it again: you can't have too many antennas.

One Screw Defeats Two Antennas

When we left the 30 meter delta loop I mentioned that it had to be disconnected for the time being. The reason is that it did not have a feed line. Instead I used the one for the 160 meter antenna (shunt fed tower). To conserve Heliax my intent was to have them share the same transmission line. That required a way to switch between antennas at the tower base. It's an economical arrangement since those antennas are never used at the same time; 30 meters is not a contest band.

Switching up to a kilowatt in a low impedance (50 Ω) system is conveniently done with an 8 to 10 amp modular relay. I keep them in stock for applications such as this. I selected a 12 amp SPDT relay, the same device I use in many of my home built antenna switches. "Dead bug" style construction is ugly but it works fine in this application. No one will see it with the enclosure cover in place.

The enclosure at the tower base was previously drilled for 2 auxiliary antenna ports (UHF chassis connectors), so I removed the tape from one of them and installed the connector, relay and flyback diode (1N4007).

The default path is the 160 meter antenna. There is no external connector for it since the enclosure includes the gamma capacitor and connections to the gamma rod and ground. When the relay is energized the RF path switches to the 30 meter delta loop. 

When (if) I add another antenna port, a second SPDT relay will be added. The relays would be chained by taking the wire to the 30 meter connector to the second relay, which would switch between the two auxiliary ports. That is, to select 30 meters the first relay is energized and to select the other auxiliary port, both relays are energized. There is negligible impedance "bump" at HF from this circuit.

The configuration of the antenna selection software was changed to select the delta loop on 30 meters and manage contention in case two radios (SO2R or multi-op) attempt to select more than one of the antennas on the transmission line.

If you've read this far you may be thinking that this is routine and hardly worth writing about. What's interesting about relays switching RF? It's done all the time. Despite hinting that I would write an article about the 30 meter antenna switching I had no real intent of doing so. What changed my mind was what happened a couple of weeks later.

The antennas and switch had been working well. Then one morning they weren't. Both antennas showed high SWR and poor receive signal strength. On a warm and sunny weekday morning I grabbed a few tools and my antenna analyzer and walked across the hay stubble to discover what was going on.

There were no obvious problems. The antenna analyzer confirmed that the transmission line was okay and that the trouble lay inside the enclosure. There were no visible faults when I opened it. The DMM confirmed that the relay was operating and the RF paths were fine. This had become very puzzling indeed.

Since the enclosure is non-conducting I moved on to test the ground wiring.  Unlike in a metal enclosure those wires are necessary. 

When I measured the resistance from the ground lug (bottom centre on the right panel above) to the transmission line connector flange there was an open circuit. How was that possible? The trouble spot is pointed out by the blue arrows.

The picture above shows what it looked like after the repair. At right is the #4 screw that I replaced.

There is rust on the screw head, top and bottom, and the first couple of threads. The rust acted as an insulating layer between the screw and connector flange, both it's outer surface and the screw hole interior walls. I used plated screws since they were handy at the time. But I did not replace them with 304 stainless screws that I bought this summer for this very purpose. I forgot.

As already mention, for a plastic enclosure there is no automatic ground path from the connector flange. It must be explicitly wired. The flange screws are critical since the solder lug, which is wired to the earth (and tower) grounding lug, must have a solid electrical connection to the flange. 

I opened the box of stainless screws and replaced the rusty one. That fixed the fault. I'll have to do the rest, just in case. Although not all are used for ground connections, it's sensible to replace them all. Stainless should not be used everywhere but when you need it, you need it. The corrosion deposited on the silver plated N-connector flange was removed by light buffing with steel wool. 

Even the biggest antennas can be defeated by a tiny screw. Don't overlook their importance.

Sanity Checking an Antenna

It is no simple matter to raise a large antenna onto a guyed tower. I've done far more than most hams and I still have to carefully plan and execute every step. From small yagis to the truly gargantuan, I've lifted them onto free-standing and guyed towers. I am well aware of the dangers so that the risks to property and people are always at the forefront of my attention.

It is aggravating when I and my friends make the effort to raise a beautiful big yagi onto the tower and find that it does not work. What can you do? Some problems can be fixed in place while in many cases, especially the largest antennas, it has to come down for inspection and repair. It should be obvious that the risks of raising and lowering antennas multiple times are greater than doing it once. Not to mention the annoyance of the friends taking time out of their lives to help.

Since antennas need to be well off the ground to work properly, testing and repairing large yagis on the ground might seem unlikely. While true there are still many tests that can be done on the ground. These include mechanical and electrical inspections. In the latter category are continuity tests, coil and trap tests, matching network tests, among others. You do what you can and then up it goes, hoping for the best.

Commercial antennas are easier to deal with than those you design and build. If you build a commercial product according to the instructions the antenna ought to work. They've done the hard work for you ahead of time. For home brew antennas you must deal with both construction issues and electrical design issues. There are more trouble areas to contend with.

However, what I driving toward is that testing an antenna is different from adjusting an antenna. What I am about to propose is the former, not the latter. For the moment let's assume that the antenna is properly adjusted, whether by following the instructions that come with a commercial product or a home built antenna that has been previously adjusted but is now on the ground.

I have previously described the design and construction of this symmetrical and reversible 40 meter Moxon yagi. Although the antenna worked and its performance closely matched the NEC5 design, the reversing function did not work. I had tested the individual components before assembly but did not do a full antenna test before raising it. I was in a hurry at the time to get it out of the growing hay. Better to raise and use it rather than disassemble the antenna and try again after the harvest. I got a few months of use out of it so the effort was worthwhile.

I gathered a crew and lowered the antenna in mid-August before heading to Manitoba. When I returned I diagnosed several electrical and mechanical issues and made repairs. This time I took the time to do a full antenna test before gathering my friends for an antenna raising.

But how can you do a full system test with the antenna on the ground? This is where we need to clearly differentiate testing and tuning: the antenna is already tuned (adjusted) so we just need to test it. The antenna has to be high (relative to wavelength) to be tuned, but not a test as a basic sanity check.

As pictured and tested, the Moxon is about 50 cm off the ground, with capacitance hat tips even lower. Even so it can be tested -- sanity checked. Although its behaviour will be very different than what you will measure when it on the tower, it will still "work".

First, the resonant frequency will be lower, perhaps much lower, due to ground coupling. In a sense, near fields are slowed due to the VF (velocity factor) of the soil. The amount is unpredictable but not too important for this type of test. Hook up your antenna analyzer and sweep through a large spectrum below its design range.

Second, the impedance at resonance will not be 50 Ω. Expect a higher SWR. In most cases the SWR will be moderate so that its ground-proximity impedance curve will remain recognizable.

Third, don't expect a directional antenna to exhibit the same pattern as it does in the air should you attempt an on-air test. Efficiency will also suffer due to ground loss. For a sanity check these attributes are of no great interest except insofar as excessive loss will push the SWR curve higher and may not display properly on the analyzer. In my experience this is rarely a problem. 

Sanity tests can be done for many kinds of antennas. I've done the same with tri-band yagis a meter or two off the ground. When properly constructed there will be clearly identifiable SWR dips below the 3 typical band ranges. 

In another case a ham acquired an older model tri-band yagi. There were no identifying marks remaining on the traps and a visual inspection was inconclusive. I suggested some quick experimentation by random arrangement of traps, one element at a time, sitting on trestles, and do an SWR sweep. When the element shows the expected SWR dips, set it aside and move on to the next one. Testing goes faster as the pile of traps gets smaller. 

This is an SWR sweep of the Moxon on the ground in its normal (forward) direction. The impedance is pretty good despite the almost 20% lower frequency. 

Next, I hooked up a battery to the reversing terminal to test it in its reverse direction. This time it worked. The sanity check was successful.

Notice that the SWR curve is not quite the same as in the forward direction. It's ~25 kHz higher. This could be a real difference or due to different ground characteristics under each element or slight height differences. The antenna would have to be lifted at least 0.1λ to discern whether the difference is real.

I didn't do that last test. The sanity check was good enough that I called my friends over this past week to raise the antenna. This time the antenna worked as it should when it was mounted on the tower, in both directions. The small discrepancy between the forward and reverse directions was still there so this was no testing anomaly due to ground proximity. The 25 kHz shift is most likely due to the reflector coils in each switch box not being perfectly identical. It isn't enough of a difference to worry about.

The 40 meter reversible Moxon is a heavy and awkward antenna so I hope that it continues to work. I'd like to avoid lowering it again. On the first evening of use I learned quite a lot about how it performs and compares to the 3-element yagi at twice the height. Many nights will be needed since propagation elevation angles and low angle absorption change day to day and even hour to hour.

Once I have enough experience with it I'll write an article on the antenna's performance. There is enough innovation in the design that might inspire others to emulate the antenna whether for 40 meters or other bands. This has been and continues to be a very interesting project. It was also illustrative of the advantages of sanity checking a large HF yagi on the ground.

Tower Trip to VE4

A confluence of motives convinced me to load the car with my climbing gear and drive to Winnipeg in late August. I've had several polite requests to do tower work for friends back home (Winnipeg is my home town). As elsewhere, there are fewer hams willing and able to do tower work and commercial alternatives haven't worked for them for a variety of reasons. The car was also packed with items from a deceased relative to be handed off to family. This is not the first time I travelled to do tower work.

Although it's a long drive (over 2200 km), with so much to carry it was not practical to fly. A large part of the drive north of Lake Superior is rugged and very beautiful, and I wanted to do it one last time. I don't expect to take the land route again; future visits will have to be by air.

As any contester will know, there is not a lot of contest activity from VE4. There was more when I was a young man, or at least that's how it seemed to me. Aging of the ham population and slower adoption of contesting by the younger generations of hams is as true there as elsewhere. This is despite the growing population of the province and of Winnipeg in particular (approaching 800,000), and growth of the overall ham population. There are many hams but most activity is on VHF, UHF and higher, focussed on technology and data networking. HF activity has declined. Again, that is no different than elsewhere.

In this article I'll talk about towers and antennas, and about some of the hams I met with. I apologize for the lack of pictures of hams in this article. I was focussed on towers and antennas, taking pictures on the tower but not off. While I will use what I found as topics worth discussion, as a matter of privacy I will not say which station belongs to whom. Not all belong to contesters.

First, the people. I was invited to the RSM (Radiosport Manitoba) annual BBQ. There were 12 attendees, not all contesters but certainly enthusiastic and active operators.The host was Gary VE4YH. Although his call may be unfamiliar to contesters, he hosts remote operators for contests. The station is larger than most though still modest. On his tallest tower he has a JK 3-element coil loaded 40 meter yagi that works very well from what I was told.

While the burgers and dogs sizzled on the grill I gave a talk on the building of my station. It's one I've presented a few times, updated to keep in step with the continuous changes that I make.

Perhaps the best known contester who drove in for the BBQ was Todd VE5MX. Surprisingly it was our first "eyeball" QSO. We had an interesting chat. He is headed to the WRTC competition in England next year (2026). His own station (re)building pace has slowed while his crew -- daughter and son-in-law -- start their family. Todd is a proud grandfather despite the wait for his crew to return.

My oldest ham radio buddy and fellow contester is Rob VE4GV. You'll hear him most often from PJ2T, portable /6Y, and occasionally from his own suburban station. He has quite a story to tell, which is related in great detail on his QRZ.com page. My original call (VE4OY, since reissued) shows up a few times.

Jessy VE4JBB/VE4DX is relatively young compared to most contesters. He has a tower and wires at his father-in-law's farm outside of Winnipeg. We can expect to hear more from him in the future. For now he is busy raising a family and his job in the IT sector. He gave me a few ideas for accelerating software development for my station projects by using AI tools. I'll have to explore that, but I admit to having doubts.

Barry VE4MA has long been a pioneer in EME and the microwave bands, with his exploits and record attempts published widely. I got my first and only experience of EME by listening to echoes of him pinging 432 MHz signals off the moon. That was in the late 1970s while I was in university. He continues to be very active locally and at his winter home in Arizona.

Cary VE4EA organized my tower work schedule while I was in town. My trip came about when I reached out to him to find a local tower climber who could help an elderly ham in Winnipeg. One thing led to another and off I went. Cary operates contests remotely since he lost his tower in a storm several years ago. During winter he occasionally joins multi-op teams at various stations in the US southwest.

Cary also arranged a visit and tour of Winnipeg Seniors Amateur Radio Club: VE4WSC. It is in an old fire station that was gifted to RAM (Radio Amateurs of Manitoba) for their use. There is a lot of space for meetings, stations (VHF, UHF and HF), workshops and a variety of radio and networking equipment. It's on a prime strip of real estate on a major thoroughfare and bordering the Red River. I imagine that any club would drool over this extraordinary facility. A picture of the fire station and its complement of antennas can be found using the above link.

The main purpose of my visit was to discuss HF antennas, specifically what might be possible. Since it's a city owned building any towers or other building attachments must meet their standards. The fire hall brick tower is in poor condition (the building is old!). The roof and masonry had to be reinforced just to support the Hy-Gain Explorer 14 yagi and other antennas. There are wires for the lower HF bands.

They will likely need to install a tower higher than the building (70'+) adjacent to the building to improve their HF capability. They can't make that decision on their own since the installation will have to be done by professionals approved by the city. Perhaps the bigger problem is lack of interest in HF by most of the local hams. They have a modern and sophisticated station that sits idle most of the time. It's available should an emergency arise but it could be used for so much more.

Now let's talk about towers. 

After my recent tirade against the excess enthusiasm hams have for nylocs I will now address another obsession: stainless steel. It is a myth that stainless hardware is always superior to more prosaic steel fasteners.

There are 3 critical questions to ask before selecting stainless fasteners:

• Alloy
• Strength and toughness
• Galvanic corrosion when in contact with other popular metals, especially aluminum 

At right is a thrust bearing where the steel set bolts were replaced with stainless. F593C was stamped on the bolt heads, which is not very specific with respect to alloy and grade. They were seized within the thick cast aluminum bearing housing. They were too tight to the mast to jack up the mast and antennas (400 lb) to access the rotator.

After liberal dosing with penetrating oil, two of the bolts heads still sheered off when forced with a long wrench. The third reluctantly turned. That was enough to jack the mast. There was an ample coating of "white dust" on the embedded bolt threads due to galvanic corrosion. It is almost always the case with most stainless alloys in contact with aluminum. Choose suitable alloys and lubricate stainless hardware. Otherwise prepare for future trouble. 

I replaced the bolt with a fully threaded grade 5 bolt. Also, those locking nuts really ought to be outside the housing, not inside. Those, at least, all turned with the help of penetrating oil.

While we're on the subject of thrust bearings, let me counter another popular myth that I've mentioned more than once on this blog: do not support the mast and antennas dead load with the thrust bearing. These devices are almost universally designed for radial loads only. 

Too many have their lifetimes cut short due to this persistent myth. I've seen this happen more times than I can count. Don't let yours end up like the one at right. They are not easy to remove and replace!

There are industrial bearings rated for both axial and radial load, but those are not the ones typically marketed to hams as tower thrust bearings. I have several of those bearings to support massive antenna systems to protect the prop pitch motors (rotators) from radial and axial loads.

Place the load on the rotator where it belongs. Rotators have all those bearings and large diameter races to withstand hundreds of pounds of axial load and even a substantial bending moment. A polymer sleeve/bushing is usually more than sufficient to hold a mast in place -- a bearing isn't necessary and a bushing is easy to repair or replace. But I am under no illusion that this article will extinguish thrust bearing myths. I expect that the myth will outlive me.

For some reason I've found myself repairing a number of old Moseley yagis this year. The driven elements are difficult to work on since the screws that secure the coax pigtails also provide mechanical support for the element halves. This one uses a cable tie and wire as secondary supports to ease electrical work. It's ugly but it works. I had to redo the setup to replace a cracked insulator and severely weathered coax and rotation loop.

My very first yagi was a TA33jr (same as the one above) back in 1975. I'm not nostalgic and I still don't like them for their poor mechanical design and lossy traps. But they sure have a lot of satisfied customers. Unlike so many other antenna companies, Moseley is still in business and selling many of the same antennas they did decades ago. 

Trylon self-supporting towers are very popular in Canada. They can handle smaller yagis and quite large HF stacks depending on the tower model and height. As you might expect, many hams put far too much on top. When the tower fails they blame the tower rather than themselves. Optimism is nice as long as it doesn't blind you to the realities of mechanical engineering.

The most popular Trylon self-supporting tower among hams is the Titan series -- I have one. For more demanding applications the more expensive Super Titan series is occasionally selected. Price, weight and foundation requirements must be considered before selecting any tower. A realistic assessment of wind load for your area is vital. Destructive prairie winds can rip across the landscape when you least expect it. The winds laugh at hams and their towers.

I saw a couple of Trylon Super Titan towers during my stay in Winnipeg and worked on one of them. Since the diagonals have a large slope, optional pegs are attached to one leg for climbing. Although this is an awkward way to climb a tower it is far better than dealing with the steep diagonal struts. Steel soled boots are mandatory.

Self-supporting tapered towers are stressed in predictable ways. The most common experience is bending stress due to the wind load (lateral force) of yagis at the top. When the legs yield it typically occurs about ⅓ of the tower's height from the top. Depending on the installation details, the failure point can be a little lower than that, but probably not below ½ the height.

A Trylon tower that has been stressed in this fashion may exhibit bent struts (structural members between the legs on a tower face) where a future failure is likely to occur. That's a danger sign that I've seen on far too many ham towers. The struts (or diagonals, if you prefer) can be replaced if you can find a source. If lightly bent it may be possible to bend them back into shape; any more and the tempered steel will be weakened. These measures can buy you time but that's all. I advise tower owners to reconsider the entire installation.

There are other failure modes. One is torque due to wind action on the yagis; most yagis are not symmetrical with respect to wind surface area and can build up a lot of momentum due to oscillations and wind gusts. In this case the tower usually fails at or slightly below the rotator. The struts at that location often do not show bending stress before the legs fail. 

A less common failure mode (in my experience) is due to bending stress on the top section(s) when the mast is stronger than the tower. The struts above the rotator will likely be bent. 

I've found many installations where the owner insists on the strongest chrome-molybdenum mast available and places it in a tower of far lower strength. That is guesswork, not engineering! A strong mast won't save your tower. I am speaking from experience.

The adjacent picture shows upper section bending stress on a Trylon Titan tower I inspected during my trip. The same damage was found on all three tower faces.

The tower is old and there are two large yagis on top. I'm surprised that it hadn't already failed. As you can see this is in a tightly packed suburban area where failure poses significant risks. I suspect the tower lasted this long due to wind shadowing by the many mature trees in this old neighbourhood. Trees don't grow fast in cold prairie soil.

I gave the tower owner a few ideas on how to deal with the problem but there was nothing more I could do. Any solution will be difficult and expensive. Ideally the tower be taken down and replaced with one engineered to survive. 

I'll end with a story of tower rust. Towers don't rust quickly on the cold and dry Canadian prairie. A similar badly rusted tower of the same age where I live could still be rust free in Winnipeg. 

If the rust doesn't go deep it is easy to repair. Remove the loose stuff and use one of the available paints to coat the damaged area. It can be a messy job on a tower, especially using spray paint.

I was fortunate that the wind was light and in the right direction to allow application of a cold galvanizing spray on this minor rust damage without getting any on my clothes. For my own towers I wait for favourable weather, a luxury I did not have on this busy trip.

I hope to be back to a regular schedule soon. Too much has been going on this summer. I have a lot of tower and antenna work to get done before winter and the major contests.