Waterfalls: The Band at a Glance

Once upon a time, we had VFO knobs. When you wanted to explore the bands you spun the knob for a voyage of discovery. You would gradually tune in stations, usually CW or SSB, with the filters wide so that you didn't miss anything. Many of us did the same thing outside the ham bands, often before becoming licensed, finding various military and commercial communications circuits and modes, broadcasters and much more. Spinning the big knob was a gateway to the magic of radio.

Now is the age of the SDR. Instead of spinning the knob, we can view a large swathe of spectrum at a glance. See something interesting? Click the mouse and there you are. But, in most cases, you must still listen to learn what you've found. If you integrate spotting networks and skimmers with your SDR that may not be necessary since the signals can be labelled on the spectrogram. Contest software like N1MM+ has this feature when coupled with a modern transceiver.

Has something been lost with modern technology? Certainly there was the magic of discovery before we had sophisticated receivers and displays, or the global internet. As Bob Locher W9KNI wrote in his seminal work, The Complete DX'er, that there is an art to listening: care, diligence and research to know what to expect. There remains a role for this style of operating, though it is far less common than it was. 

Despite the nostalgia I don't really miss the old ways. The reality could entail hours of drudgery scouring the bands for interesting stations, finding the rare ones, calling DX for a long time on an open band because no one stumbles across you, and not knowing what was there to be found or if there was propagation at all. I appreciate modern technology for optimizing the use of my time.

Early spectrum displays were not very good. The first were manually configured with knobs and buttons, the bandwidth was whatever the narrow IF could pass, the display was instantaneous only without a progressive view (waterfall), and there was no possibility of computer integration. An example is the SM5000 add-on to the FTdx5000. I have one and it is pretty well useless for spectrum monitoring.

That changed when I purchased the Icom 7610 transceiver. The waterfall display is a tremendous operating aid; that is, once you figure out how to configure it -- the user interface could use some improvement, yet some are worse (e.g. Yaesu FTdx101). Luckily I had my 7610 configured by a guest op familiar with the rig. I was annoyed until I saw that his choices were good ones. I've kept it the same ever since.

Many hams connect their 7610 spectrum scopes to an external display or to their computers. I prefer to leave it where it is since it's works well for my purposes and I strongly dislike the addition of more displays or the additional demand for display "real estate". In this article I'll talk about how I use the 7610 spectrum display (waterfall). My preferences may differ from yours, and that's okay since my operating interests may not be the same as yours.

This waterfall is similar to the one I showed in my first article about the 7610 (link above). During a busy contest the waterfall is an excellent way to find holes where you may be able to run. However, always send "QRL?" first! Even with the time axis of a waterfall you can miss a lot of activity that you might not hear at first, such as for signals that scroll off the bottom of the display. The 7610 has a coarse scroll adjustment that could be better.

A spectrum display without the time axis -- that is, a waterfall display -- is very poor for locating clear frequencies. Yet many try, and they do it without checking for occupancy before punching the CQ key. An instantaneous display, even one with time averaging, is inferior in comparison to a waterfall. Aside from the averaging time there is the problem of noise. A momentary broadband impulse can render the averaging display useless for 5 seconds or more. On a waterfall it's an innocuous horizontal line.

My contesting has benefitted since becoming a "big gun" because I run much of the time, and finding potential run frequencies can go slowly without a waterfall.

Not all of us have clean signals. There are key clicks on CW and splatter on SSB. Examples are shown in the panels on the left (14017 kHz) and right (14250 kHz). These are easy to spot in the waterfall. When interference is heard, all it takes is a glance at the display to know who is responsible. The ability to inspect the band all at once can be occasionally depressing due to the large number of poorly adjusted transmitters. 

Not everyone is aware since they can't hear (or see) their own transmitted signals. They may be unaware since they use rigs with poor transmitter IMD or fast CW rise times, or they don't know how to adjust them, merely accepting the defaults (often terrible) or what they believe to be correct practice. In many cases the rigs are fine but their amplifiers are over-driven.

The middle panel is more interesting. That is a CW signal if you can believe it. It was raspy and wide. My guess is that it is a home brew transmitter or an ancient and misbehaving boat anchor. Decades ago this was not such an unusual signal! It is a surprise when it is heard in the 21st century.

The SSB signal at right is perfectly clean. It drew my attention because it could be made better. Notice the large peak at low audio frequencies and relatively weak higher frequencies. This is typical of an adult male voice. Unfortunately it is not great for effective radio communication. 

Most modern rigs have audio equalizers and they should be used. A few tweaks of the equalization can attenuate that non-intelligence carrying and power robbing bass resonance and enhance the critical speech frequencies between 300 Hz and 2000 Hz. Notice that I receive with a slightly narrow filter on SSB since it removes splatter from adjacent stations without loss of readability. During phone contests I narrow the filter even more.

Many have noticed the increasing dearth of signals on our HF bands. What activity there is has concentrated on narrow channels for digital communication. This has attracted the attention of non-ham actors; that is, intruders. They have always existed, and not just on the amateur bands, it's just that they seem more common than before. It could also be because of the prevalence of SDR and waterfall displays -- with a large view of spectrum the intruders stick out more than they do with a VFO.

On the right is one example. It appears to be a dense digital signal of some kind. This type of intruder is quite common, both in our bands and just outside the band boundaries. They tend to avoid our spectrum during contest weekends, probably because the "interference" affects their operations. The intruders may be government actors, criminals or ordinary citizens.

Other common examples include OTH radar, SSB and AM commercial and personal communications, narrow band data modes and non-standard modulation. That only touches on the problem. HF still has value to many despite the global availability of the internet. Interfering with hams carries lower risk than operating elsewhere.

Waterfall displays on a relatively empty portion of an HF band can be disturbing when they show many intruders that you might not otherwise notice. Yet they're there and it's better to know about it than not. In most cases you'll have to work around them, unfortunately, and waterfalls help with that. I've used the 7610 waterfall to do just that.

There are many mystery signals to be found on our HF bands that may be intruders but are more likely electronic noise, test equipment, unintentional interference from conventional users (e.g. science experiments). The waterfall sees them all. Examples include an antenna analyzer or VNA sweeping an operational antenna, electronic sensors, RFI from devices in our homes (my heat pump does that when set to cooling), and so much more. I could not easily capture screenshots of them before publishing this article.

Other signals captured by the waterfall.are all kinds of "swishers" that quickly sweep across the band leaving only a momentary sound in the headphones. There are slowly drifting electronic signals (likely RFI), harmonics or spurious emissions from unknown transmitters. You can watch (mostly digital) signals gradually drift due to oscillator instability, especially on the higher bands like 6 meters. Again, I took no pictures for this article but you'll surely recognize these if you use a waterfall display.

In contrast to the disheartening information that waterfalls bring to our attention, there are many benefits, and not just for finding run frequencies. These are a few of the ways I've used the waterfall display:

• Propagation at a glance. I tune to a band, flip through the antennas pointed in various directions, and I can instantly learn the state of the propagation. That is, if there is any activity. 
• Locate and resolve noise and interfering signals.
• Discover the onset of aurora when signals experience Doppler spreading.
• Navigate a DX pile up by sight and not just by listening. I can see the holes where no one is transmitting, and those can be good places to drop my call.

You can likely think of other examples that you've used since acquiring a rig with a spectrum scope and waterfall feature. Now that I have one I can't imagine living without it.

Superfox and DXing

The Superfox name is not unique to WSJT-X. I didn't know that until I did an internet search for sites and images related to it. Although it isn't true that there's nothing new under the sun, this is so obvious a name for many reasons that I should not have been surprised by its commonality. 

I included an appealing image that my search uncovered. Considering the public availability of AI image generators it is surprising that these tools aren't used more often by hams as a way to create icons for our increasing software-centric hobby. If nothing else, it adds levity to discussions about new technology entering our hobby.

After I used the FT8 Superfox mode for the first time it spurred a few thoughts that I'd like to share. In this case it was to work N5J on 80 meters.

Although I prefer to work new DXCC countries on CW, that isn't always easy or convenient since most DXpeditions now devote more time to digital modes. Whatever you might think of it, digital has become more popular for HF DXing than CW and SSB. DXpeditions quite sensibly devote time to the modes and bands where there is demand. Digital is also beneficial to lightweight DXpeditions such as N5J, and to the majority that have small stations and are chasing them.

One night last week I happened to wake up before dawn. Instead of going back to sleep I padded down to the shack to see if N5J was active on CW on the low bands. With my 160 meter antenna unavailable during the summer, my objective was 80. But they were on FT8 instead. I got up to leave and then thought, what the heck. So I sat down and gave superfox mode a shot.

It was a simple matter to activate superfox since my version of WSJT-X supports it. I tuned to 3567 kHz and saw this:

On the spectrogram/waterfall their signal makes very little impression. If you listen, it sounds like the soundtrack of a 1950s sci-fi movie with its staccato series of seemingly random tones. The software decoded N5J, the superfox, however, the mode seemed vulnerable to noise. When it couldn't decode it couldn't decode any of the multitude of messages transmitted. That's unlike multi-stream FT8 where each stream is independently decoded.

I waited a minute for the noise to disappear -- probably software misconfigured by a caller -- and they were quickly logged. The 3-element vertical helped even though I limited myself to 100 watts. A friend with a smaller station was calling at the same time and got through a few minutes later.

It was easy. Was it too easy? Have DXing awards become a participation pin for just showing up rather than a sign of skill and achievement? With superfox, "verified" foxes will also reduce the risk of working pirates, something that often happens on FT8 and CW.

I don't know how to answer those questions, and I doubt the glib answers of the self righteous. But consider the progression we've made in the DXing art in the past 10 or 20 years:

• Local and then global DX spotting networks
• Real time communication by DXpeditions of their operating frequencies
• Real time log confirmations
  
• Large, well-financed DXpeditions that exceed 100,000 contacts
• Digital modes to level the playing field: pile-up opportunities for smaller stations
• Multi-stream and superfox for high digital rates
  

These advancements call into question the value of a QSL or DXCC certificate. After all, if everyone can work 'em, does the value of a DX award decline? Superfox mode accelerates the trend in two ways: more stations can be worked within the same time and resource budget, faster than CW or SSB, and getting those coveted band slots requires only a modest station investment and a few clicks of the mouse. FT8 ain't so slow any more.

I am not a curmudgeon: superfox is a marvel of logistics and technology. I applaud the technological advancements in our hobby. It's inevitable and will only continue. But I have to wonder whether DXing and station building are skills that have reached an inflection point. When reaching the stratosphere of DX achievement is far less difficult than it once was, is it a worthwhile endeavour?

Many (most?) hams enjoy working DX yet have no desire to build a big station or to devote a lifetime to reach DXCC Honor Roll. Technology brings it within reach. Does it matter that it takes far less time and effort than in years past? Probably not if the participants are enjoying themselves. It appears that they are.

One old timer of long acquaintance is using digital modes to close the gap to earn the 2500 endorsement for the DXCC Challenge award. Working N5J on FT8 superfox brought him a little closer. Most older DXers that I know have adapted very well to digital modes, often with enthusiasm. Digital modes are not being shunned by older hams, it is just that a hostile minority speaks loudly.

I've become a reluctant superhound.

U-bolt Threads and Strength

This is a topic that is not one of the most exciting that I've written about in this blog. Yet it is important since fasteners of all kinds are found in our stations. Even if you never build your own towers and antennas, a little knowledge can go a long way. That said, I'll proceed to bore most of you.

Cutting threads onto a blank bolt shaft weakens the bolt by removing material. The effective cross-sectional area has been reduced approximately in proportion to the new minimum diameter measured at the bottom of the threads. The amount of material removed depends on the bolt size and thread standard. Since a bolt without threads isn't too useful, we need to learn how to take their effect into account when choosing bolts.

A chain is only as strong as its weakest link...

...is an old saying that we use for subjects as diverse as industrial supply chains, military forces and marriages. It can also be applied to threaded bolts.

The weakening of the bolt due to the threads is not a problem in itself since you must calculate the required fastener strength (cross section and material grade) for your application. In our case the most common applications are towers and antennas. Since few of us design and construct the towers in our stations (we only assemble and erect them) that leaves us with antennas. A far larger number of hams design and build yagis, and that entails selection of many kinds of fasteners.

The style of bolt pictured above is very common. For shear applications, such as the bolts for splicing (joining) tower sections, the load is carried by the short blank shaft under the head. The threaded shaft carries no load other than that needed to keep the nut in place. Threads are more important for axial loads.

There are many styles of specialty hardware where the thread size is greater than the shaft size. For example, the guy yokes for my large towers have ½" shafts and 9/16" threads. This keeps the fastener strength that of the ½" shaft throughout since the diameter across the thread bottoms is approximately ½".

I was reminded of u-bolt specs when I was recently shopping for small stainless u-bolts for my latest antenna project: a 40 meter reversible Moxon. I ordered online from a vendor I hadn't dealt with before. The company was reputable and the specifications and price looked good. I had a close look at them when they arrived, as one should when dealing with a new supplier.

Compare the photos of the hex-head bolt and u-bolt. In the former, notice that the shaft tapers down towards the threads. For the u-bolt the opposite occurs. The reason is that on the u-bolt the threads are raised. On these u-bolts the threads are ¼"-20 (UNC) and the unthreaded shaft is less, measuring roughly 3/16".

The axial tensile strength of the u-bolt is largely determined by the diameters of the unthreaded shaft and the inner thread diameter. Although the threads are ¼", the minimum cross-sectional area is determined by the minimum diameter, which is that from thread valley to thread valley. The table (extracted from this source) contains data for most of the UNC thread sizes we are likely to encounter.

The effective cross section (Tensile Stress Area) for ¼-20 bolts is 0.032 in². We can rearrange the well-known equation A = πr² and solve for the diameter (2r). That equates to a diameter of 0.2", in agreement with the Minor Diameter in the table. That's slightly more than the 3/16" I got from my quick measurement. The shaft diameter is therefore appropriately sized. A larger shaft does not increase the axial strength of the bolt.

A second example is this large galvanized u-bolt with ⅝"-11 threads. The calipers show that the shaft is about 9/16". This is approximately the minor diameter so the shaft diameter is, again, appropriately sized. This is typical of the all the u-bolts (including muffler and saddle clamps) you are likely to encounter.

All of this is very interesting (well, I think so) but how does it help us to select hardware? There is no simple answer and there can be no simple answer. Shear strength is in some respects easier to calculate, which I did when I custom built guy hardware for one of my big towers. However, u-bolts are typically placed under axial load; that is, load along the direction of the shaft/threads axis. 

The axial load for typical antenna applications is the sum of the dead and live loads on the antenna section being supported and that from tightening of the nut against a rigid plate and tube/pipe. Use of a saddle distributes the load over more of the tube surface so that the tube is less likely to be crushed (e.g. excessive nut torque) or rotate.

Consider the following two methods for using u-bolts to support the large capacitance hats on the element tips of the reversible 40 meter Moxon that I am currently building. They may look alike until you take into account what sits on or hangs from what. In both cases the element takes the load of the capacitance hat.

In the top picture, the capacitance hat is underneath the element. The hat hangs from and is held by two u-bolts. The weight of the capacitance hat loads the u-bolts. The hat and plate both place an axial load on the u-bolts hanging from the element.

In the bottom picture, the capacitance hat is on top of the plate and the plate sits on the element. The load of the hat on the element is the same (as it must be) but the u-bolts have a lower axial load for the same nut torque. (Note that for this fitting work that I omitted lock washers or nylocs.) The u-bolts hold the tubes in place, but the only axial load is from the torque on the nuts.

Does that matter? Yes, but not by a lot. I find that hams that design and build yagis tend to stick to one method of connecting yagi elements to booms, either sitting or top or hanging below. Despite the axial load difference, I haven't heard many good arguments about which is superior. 

In a marginal case with u-bolts that are of minimum size it might make a difference. However, bolt grade, material and durability are more important in most cases. Axial and sheer strength of u-bolts become increasingly important for high load applications such as boom-to-mast clamps and rotator mast clamps. 

A failure under unanticipated stress is something you really want to avoid if you can. Size your u-bolts  by the application and fundamentals if you can, or do your best to mimic the size and grade in similar applications that have proven durable in commercial products. That is, lean on the engineering done by an engineer.

My Labrador Adventure

Blog activity has been below average due to other priorities and activities. In particular, I was travelling. But what a wonderful trip! This was my first visit to Labrador. The purpose of the trip was directly related to amateur radio and contesting. Vlad VE3JM and I drove to Happy Valley-Goose Bay (FO93) with Chris VO2AC/VE3FU to help him prepare his new remote station.

One of the astonishing aspects of the trip was that it could be driven. It wasn't so long ago that the vast expanse of land was only accessible by canoe or float plane. Once you head north from the St. Lawrence River the population density falls precipitously. There is no cell service; those that work in the vast spaces between towns rely on satellite services. Settlements in the northern interior exist to support mining and hydroelectric power generation. There are few roads; railroads and transmission lines carry the land's bounty south.

That's me standing at the western end of the Trans-Labrador Highway, between Fermont (QC) and Labrador City (NL). The more than 500 km to Happy Valley-Goose Bay is paved. There is still about 150 km of road on the Quebec side that isn't. That expensive job is an ongoing multi-year project. Chris regaled us with stories of the bumpy unpaved road his family had to navigate when he was young.

This is the hydro-electric dam at Manic 5, one of the largest of its kind in the world. It's a lot bigger than it looks in the picture, which you only appreciate when you drive close to the dam. Chris gave us a closer view of the installation at Churchill Falls, Labrador where he once lived and worked. Even from the outside the scale is impressive, as you'd expect from a facility that generates more than 5000 MW of power. That'll drive a few amplifiers.

We also had the opportunity to watch, from a distance, mining of iron ore and other minerals in the vicinity of Fermont, Quebec (Fermont translates to iron mountain). I have pictures but I'll spare you those and return to amateur radio.

Our trip was delayed for a week due to the wildfires that came within a few kilometers of Labrador City and nearby Wabush. Both communities were evacuated, with many temporarily sheltered in Happy Valley-Goose Bay. Happily both communities were unharmed and the evacuees returned. During the drive we saw the effects of previous fires and recently constructed firebreaks.

One of the evacuees was Naz VO2NS. I took this picture of him at the Labrador City club station when we passed through after everyone moved back. Driving around town everything looked so ordinary that it was hard to believe it was empty a few day earlier. There are fewer than 30,000 people living in Labrador so there are not many hams. Only a few of them are active on HF. Naz is one.

We continued east to Happy Valley-Goose Bay. Chris's parents and family friends hosted us during our stay. Labrador (and Newfoundland) hospitality is really something. All I can say is that we were treated very well and fed sumptuously. We had to watch ourselves not to overdo it -- that would have impacted our ability to work and climb.

When we arrived the new tower was nearly complete. He transported and planted the Trylon tower on two previous trips. We topped the tower, constructed and tuned the yagis then raised them. Low band wires and 40 meter vertical were raised, tested and tuned. By the time we left he had antennas for 160 through 6 meters. His remote station with SO2R capability was previously built and installed, and only needed reconfiguration to use the new antennas.

There were numerous difficulties along the way. With three experienced hams and tower climbers we resolved almost all of them. We had to be self-sufficient with parts and tools since only ordinary construction material and hardware could be bought locally.

With just the one tower there are inevitable interactions to be dealt with. We did the best we could when faced with space constraints. The picture shows the installation partially constructed, with Chris working to the left of the tower.

There were two difficulties more difficult to overcome: heat and flies. The temperature was far in excess of the normal 21° C for late July. The first day broke records with 33°, and a couple of later days were nearly as hot. The black flies for which Labrador is infamous were constantly swarming. Bug dope helps but is unpleasant. I chose to cover up as much as the heat allowed. 

The carnivorous pests soon covered our exposed skin with tiny scabs from their innumerable bites. I've always liked this song which expresses the experience pretty well:

And the black flies, the little black flies

Always the black fly, no matter where you go

I'll die with the black fly a-picking my bones

In North On-tar-i-o-i-o, in North On-tar-i-o

An eastern view with the JK tri-bander raised but not yet attached to the mast shows a little of the town and the Churchill River in the near distance. The 6 meter yagi was placed on the mast before it was raised to its final height and the rotator installed. Although the mast is strong it is not suitable for climbing, and therefore unsuitable for raising yagis to the top after the mast is in place, which I typically do for my own large towers and antennas.

Acting as tour guide, Chris showed us the numerous points of interest in and around town. On the adjacent Goose Bay AFB is one site of the SuperDARN network for ionospheric research. I counted 16 LPDA in the array. The photo of a section of the array shows Vlad VE3JM (left) and Chris VO2AC.

In the end...

...was it worth it? It was a week and a half of my time, working up to 10 hours a day and a grueling 4000 km on the road. I'm not young anymore. 

I find that as I age and mellow out that my urge to help others grows. It's a great feeling to see another ham smiling when their station dream is fulfilled and they begin their new journey. Chris was eager enough that he operated (remote, as usual) for an hour in NAQP CW from the hotel where we stayed overnight on the drive home. There is more work to be done, but with what was accomplished on this trip he'll be able to do the rest by himself during future trips. I think it is fair to say that you can expect a larger presence from Labrador and zone 2 in upcoming contests.

We didn't come home empty handed. Some of that Heliax followed us home. Scroungers gonna scrounge.

NEC5 Test Drive

I have a long to-do list for my station. It reflects a lot of ambition. However, my actual pace of work is at a lower rate. Amateur radio is a hobby after all. Some items linger on the list for a long time indeed! NEC5 was one of them. I say 'was' because I've finally purchased a licence for the software and added it to EZNEC.

EZNEC makes it easy to use NEC5 as an alternative calculating engine. Considering the many advantages of NEC5 over NEC2 and NEC4, and that EZNEC is now free, it is very easy to justify US$110 for a licence. I will not bore readers with what can be learned elsewhere about NEC5 and EZNEC, which you can find elsewhere, including following links provided in this article.

These are perhaps the most relevant resources I read before diving into my initial experiments with NEC5. It helps to know the technology you are dealing with before using it and trusting the results.

• EZNEC and the EZNEC 7 manual
• AC6LA's NEC5 notes (access requires a QRZ.com account)
• NEC5 validation manual
  

Next, a brief summary of why to choose NEC5 versus NEC2. Others cover it better and more completely, but a few points are enough to get you started:

• Tapered elements, including loaded elements -- with NEC2 you need the SDC (stepped diameter correction) in EZNEC, or its equivalent in other modelling software, and also stay within its strict constraints
• Antennas with wires meeting at angles, especially acute angles -- it can be done using NEC2 with fairly complex segmentation procedures, although EZNEC and at least one other package will help you with it
• Wire segmentation is in general not at all strict -- NEC2 requires strict segment alignment between parallel conductors when the separation is small
  
• Antenna elements with loads, lumped or distributed, are handled well -- includes capacitance hats, traps and coils inline with tapered elements and more that are often handled poorly in NEC2
  
• Radials can be on the ground or in the ground, and with more accurate results -- no more having to artificially place radials a short distance above ground, and consequent issues
  

All of these have been important to me at various times. Sometimes there are modelling workarounds and other times I had to mathematically calibrate a NEC2 model with measurements of a built antenna. NEC5 promised a far better modelling experience with less opportunity for errors.

There is a cost to gaining these advantages, and I don't mean the license fee. The greatest cost is segments: you need a lot. A peculiarity of NEC5 is that the calculations converge slowly with increasing segments. That is, you need a lot more segments than with NEC2 to get accurate results. The more complex or large the antenna, the more you need.

That slows the run time and can be a bit of a bother at times. Doubling the segments is frequently inadequate so I double again. I've stopped at 4× the amount though some go further. More on this as I go through my initial modelling experiments with NEC5. 

There are other differences that must be understood. For example, NEC5 does not natively support insulated wires. EZNEC includes an algorithm to allow them when using NEC5.

Luckily for most hams NEC2 continues to be perfectly adequate, especially with the enhancements included with EZNEC. Whether to use NEC5 depends on your interests and needs. This article may help you decide.

40 meter reversible Moxon

The initial experimental model of a 40 meter reversible Moxon was the first antenna I modelled with NEC5. I did nothing more than change the calculating engine, just to see how the results would change without the segmentation and other modifications recommended for NEC5 models. Recall that the model uses constant diameter wires (25 mm) throughout; this is not a physically realistic model, only intended for computer experimentation.

The NEC2 result is at the top and those for NEC5 on the bottom. Resonance shifted downward approximately 1% (~75 kHz). Gain and F/B were similar, after adjusting for the frequency change. Doubling the segments for NEC5 had a negligible impact on the results. 

I tentatively concluded that the difference is more likely due to improved accuracy with NEC5 due to the 90° angles between wires. Even for a straight forward antenna like this we can see where NEC2 is challenged to generate accurate results. 

For those practically minded, you may have more luck getting accurate dimensions from one of the online Moxon rectangle generators (typically based on scaling working antennas) than by using NEC2. I can't guarantee that is generally true, but you ought to keep it in mind should you model a Moxon rectangle or an antenna with similar attributes.

I next tried my physical model for the reversible Moxon. This one uses tapered elements for the antenna I am currently building in my workshop. I won't detail the design in this article since it is an ongoing process. I am trying to build it using only the aluminum tubes and pipes that I have in stock, which imposes interesting constraints. I'll write an article about the antenna when it is built and tested.

Unlike the model with constant diameter wires, the initial model was far off. I doubled the segment count which, unlike for the model with constant diameter wires, did reduce model inaccuracy. For the final design I may again double the segments. That would be 950 segments! That's a lot for what seems to be a modest looking antenna, yet it is frequently necessary for accurate NEC5 models

It was necessary to make a few small changes to achieve the expected performance. One was a slight adjustment to the reflector element coil. The reappearance of short stingers on the elements is due to the material I have on hand and not to a change to my previous conclusion that stingers limit performance for this style of antenna. I am trying to keep them short without resorting to buying more aluminum.

The SWR is only slightly higher after aligning the gain and F/B frequencies with that of the earlier model. It may improve further with another doubling of segments. That may not realistically matter since environmental interactions are likely to be greater: the tower, its guys, and other antennas on the tower. 

With NEC2 the model is far from accurate, worse than the relatively small 1% inaccuracy of the model with constant diameter wires. NEC5 is worth the price if only for this one antenna.

3-element 40 meter yagi with capacitance hats

When I began designing this monstrous antenna I knew that NEC2 would be wholly inadequate. I was less concerned with the impedance than with the frequency of operation. NEC2 typically shifts the resonance downward for antennas of this type, but there is no reliable method for predicting by how much. That is why I built an experimental element to calibrate the model. 

After repeated changes to various sections of the element (position of capacitance hats, length and diameter of select tubes, length and diameter of the hats and stinger), and approximate compensation for ground effects, I trusted that the measurements were sufficient to calibrate the model. Calibration means accurately determining the differences between the NEC2 model and the real antenna. It is not practical to repeatedly raise and lower a 300 lb antenna up 150'. It was critical to get it right.

The extraordinary thing was that the antenna seemed to do pretty well once it was installed and the gamma match and driven element were adjusted. However, small doubts lingered since the calibrated model was imperfect and there is no good way to measure gain and F/B with reliable accuracy. With the NEC2 model and manual calibration, the model's behaviour from 6.55 to 6.85 MHz was calculated to match the real performance between 7.0 and 7.3 MHz.

Then I suffered the effects of a poor mechanical design of the clamps that attach the capacitance hats to the element. One arm of one hat on the reflector fractured and fell off a few months after the yagi was raised. The same later happened to the director. At first I thought it would be disastrous, yet I could not discern a performance impact on air. Even the SWR curve was slightly better.

Modelling of the missing arms using my calibrated NEC2 model suggested that the antenna had its operating frequency range increased by about 70 kHz (1% of 7 MHz). That's not good but it also isn't bad. However the F/B at 7.0 MHz should have measurably declined. That didn't seem to happen. 

Although I redesigned and built new capacitance hat clamps, I've only replaced them on the driven element. That was easily done since it is close to the tower and the tips are accessible by rotating the DE on the boom. Replacing the hats on the parasitic elements is more difficult. I haven't rushed since the antenna continues to work well, and no more capacitance hat arms have failed over the following 2-½ years.

With NEC5 installed, I ran the EZNEC model without making any adjustments to accommodate the unique requirements of the calculating engine. At first glance the results were quite good. Performance between 7.0 and 7.3 MHz was about as expected; no calibration required. Then I took a closer look.

Every yagi design is a balancing act between gain, pattern and match. That isn't easy to achieve for a high Q antenna on 40 meters due to its 4.3% bandwidth. The NEC5 calculation for the F/B at 7.3 MHz was poor. Closer inspection indicated that the optimum range of the antenna was at a slightly lower frequency, by about 50 to 75 kHz. Notice something familiar about that number?

The frequency shift is very close to the higher operating range due to those missing capacitance hat arms. That could explain why the antenna is performing so well. I must quickly add that it is only a hypothesis at this point. It will be necessary to increase the segment count and make other adjustments to ensure that the NEC5 calculations are accurate. It is important not to stop the analysis just because the first hint of an insight conforms with one's subjective experience with an antenna. 

I will do that deeper analysis later, and likely with a lot more segments. For this test drive of NEC5 it is enough to achieve these inklings of enlightenment. I look forward to doing a full NEC5 analysis of this important antenna. I may decide to alter the antenna slightly when I install the new capacitance hats so that it works at its best.

5-element 15 meter yagi

The final model I tested was this long boom yagi for 15 meters. I chose it for two reasons. The first is that I've heard that multi-element yagis are challenging to accurately model with NEC5. The second is that several months ago I sent the model file (including a gamma match) to a ham who requested to see how I modelled the gamma match. He then passed it to someone who ran the model with NEC5. The resulting SWR curve was far from what I measured and successfully modelled with NEC2.

This is a complicated antenna simply because it has so many elements and each element is tapered with telescoping tubes. EZNEC with NEC2 and its SDC algorithm produced a model that matched the actual antenna with exceptionally good accuracy. However, when I added a gamma match to the DE it was necessary to replace the DE with a constant diameter wire since the SDC algorithm can't deal with the gamma match. This is not ideal since the current distribution on a stepped diameter element is not the same as on the equivalent constant diameter element calculated by the SDC algorithm, even though both exhibit the same net reactance.

When I modelled the antenna with the gamma match using NEC5 the SWR curve closely resembled what the other ham got with NEC5. I then returned to the version with a tapered DE and no gamma match and, again, the SWR curve was far off the one calculated by NEC2 (including SDC) and as measured on the actual antenna. That's the upper of the two charts above.

When I doubled the segments of every wire the SWR curve (bottom) improved, though still not very accurate. This result implies that the person who ran my model on NEC5 did not increase the segment count in my NEC2 model.

I suspect that I'd have to double the segments again to do better. That's not a pleasant job because there are so many wires in the model. There may be a convenient method to do it that I have not yet discovered.

I might yet do it just to satisfy my curiosity. I also did not revise the model to include the gamma match with the tapered DE since there would be little point until the antenna itself si accurately modelled with NEC5.

I then produced the antenna patterns at several frequencies across the band and found that the gain was similar but the F/B exhibited more variation. The deviation was worst at the bottom of the band. The pattern at 21.0 MHz has a F/B that is about 5 to 6 db lower than the NEC2 model. Since high F/B figures demand accurate and precise calculations of each element's current amplitude and phase it might again be a matter of increasing the segment count.

Other than my curiosity regarding accurate modelling of the gamma match on a tapered element, it would appear that what I've heard about multi-element yagis and NEC5 might indeed be true. I won't pursue this topic further for now since it's not a priority and NEC2 handles these antennas well.

Wrap-up

From what I've seen so far, I am pleased with my purchase of NEC5. It integrates easily with EZNEC and it can far more accurately model a variety of antennas that NEC2 handles poorly. Neither calculation engine is a perfect solution. Every antenna model requires a few moments of thought to decide which engine is most suitable. It is interesting to try both even when you know one of them will do poorly.

Now that I've done my initial experimentation, I will begin applying it to the construction and testing of actual antennas. The obvious first case is the reversible 40 meter Moxon. Unlike for the big 3-element yagi, it appears that I can develop an accurate model using NEC5 without resorting to building a sample element and calibrating the model with field measurements. Once I have more experience with NEC5 so that I can confidently trust the calculations it will save a lot of time and effort, and wondering whether the calibration procedure is sufficiently reliable and accurate.

If you enjoy playing with antennas you should consider purchasing a license for NEC5. It's a tool that I can see becoming indispensable for design and building antennas for my station.

Digital Mode Filters and Courtesy

What do we owe our fellow hams? When we have different ideas about who to have a QSO with, whose wishes should prevail? Should one ham's preference impose an obligation on others?

These are not easy questions to answer in social activity like our, yet many have strong opinions. Indeed, ask around and you will find that some have strong opinions of one kind or another, while others may express indifference and some are uneasy with the question.

It's a question of courtesy, or discourtesy if you prefer. Consider the following scenario. You call CQ DX and a decidedly non-DX station replies to you. You ignore the caller and repeat your CQ DX. There are 4 possible ways to evaluate discourtesy in this scenario:

1. You are discourteous for not accepting the call and having a QSO.
2. The other station is discourteous for replying to a CQ DX.
3. You are both discourteous: the other station for replying and you for not accepting the call.
4. Neither of you are discourteous. The caller tried and failed, you both shrug and move on.

I suspect that many of you have an opinion, perhaps a strong one about who, if anyone, is being discourteous. I don't know which of the four categories your opinion falls into and I don't really care. I also don't care which might be the most popular opinion. I would not be greatly swayed to fall in line with the majority, though some might. 

Were I to alter the scenario, opinions would shift. For example, imagine a DXpedition asking for only stations that need them for an ATNO (all time new one), yet those not among their number continue to call.

Now I'll add an additional wrinkle: the mode. I suspect that for traditional modes like CW and SSB, when you receive a caller from out of area (e.g. non-DX responding to your CQ DX) you are less likely to ignore them than for digital modes like FT8. I respond to them even though I'd rather not. They "feel" more personal to me, and probably for most hams. Usually they just want a signal report, which can be quickly accomplished.

By contrast, on digital modes I regularly ignore non-DX callers when I send a CQ DX. They can take some time, more than on CW and SSB, and time is precious during a 6 meter opening. Am I being discourteous? You be the judge. As I've already shown, there will be a diversity of opinions. I make no apology for my choice.

My use of the digital modes helps to explain my behaviour. It is limited to the following operating activities, in chronological order of my gradual migration to digital mode operation:

1. 6 meters: My primary interest is DXing and digital modes are very effective for the propagation found on the magic band, and sporadic E in particular. I regularly work non-DX on 6 meters but when I do so I send a simple CQ to solicit calls.
   
2. 160 meters: As the amount of CW activity declines outside of contests, I increasingly resort to FT8 to work DX. When I CQ it is always CQ DX, and I mean it.
3. Rare DX: An increasing number of resident operators and DXpeditions to rare entities include no CW operators. A recent examples is FT4GL (Glorioso). So I worked them on FT8. I also worked FT8WW (Crozet) on FT8 as "insurance" in case I was unable to work him on CW.

I have not yet taken to routine use of FT8 and other digital modes. I may change my mind if CW activity outside of contests continues to decline. However that won't happen soon. I can't say how I'll handle non-DX callers in that future world.

As you can see, my digital CQ'ing on 6 and 160 meters is almost exclusively for chasing DX. Anything that interferes with that is cause for annoyance and, where feasible, mitigation. Until recently I avoided using filters so I was not inconvenienced by the lack of filters in WSJT-X.

Instead of switching to JTDX, which has long had filter features, I chose a different option: WSJT-X Improved by DG2YCB. He includes a variety of features not in WSJT-X and that may never be included. One of those is filters. By choosing his "bleeding edge" version of WSJT-X I retain the familiarity of the original and can select from among the additional features. It is exceptionally easy to do the migration since it installs like any version of WSJT-X and keeps the settings common to both and the log file.

After installing the software and experimenting with its novel features, I looked more closely at its filtering capabilities.

My needs are simple so there was very little that I needed to do. I may never use filters other than the blacklist. Obviously I obfuscated the call signs.

It can be occasionally useful to temporarily disable the filters to get the full picture of what stations are being received. The "BP" checkbox does that. I don't use the "Ignore" feature so I'll say no more about it. You can read about all the additional features of WSJT-X Improved in the documentation.

At this point you might be wondering why I filter stations. I ignore callers manually, which only requires that I do nothing. I don't often program the software to auto-respond to callers, and when I do I can easily click the CQ message button.

The blacklist would grow large indeed were I do enter every non-DX caller that replies to my CQ DX. Besides, I might want to work them, just not when I am hunting DX.

I am not even inclined to put many suspected robots in the blacklist. In most cases they don't really bother me. Again, I ignore them. To repeat a point that I made earlier:

A station's desire for a QSO, whether by human or robot, does not create an obligation on my part.

In the past I would occasionally work a robot just so that they would never again bother me. In a few cases I did not log them. I now believe that it's more honest not to work them than not to log them. Filters help me to do what I believe is the right thing, in accord with my needs and interests.

Well then, who goes into my blacklist? I am not driven by anger, to "get back" at anyone or to smugly deal with stations that operate in a manner that I disapprove of, or stations that splatter or QRM others. I do not engage in vendettas or pointless battles. My true reasons are more mundane.

The stations I typically want to eliminate are those that I'll describe as digital mode spam. Those are stations that flood my screen with endless CQing (often an hour or more), that respond to everyone whether they've worked them before or not, hound stations that obviously don't want to work them, and that are sufficiently local that I can't avoid them. Not all are robots though many are. I am rarely annoyed enough to filter a station that is only heard when propagation is favourable to their location.

Of the 4 calls in the filter screen above, 3 of them are local to me (VE2 or VE3 regions) and one is a nearby US station. This time of year I monitor 6 meters whenever I am not doing anything else with the station. I'll leave it monitoring when I'm out of the house and sometimes overnight. Having the monitor screen overflow with their "spam" means that I can easily miss the occasional message from a distant station, either because it scrolled off the screen or, during periods of heavy activity, it is difficult to spot amongst the clutter.

When I put those stations on the blacklist, my band monitoring experience is more pleasant and effective. The monitor window stays empty while the endless CQ's scroll down the waterfall. This is not about hate, disapproval or philosophical differences. I just don't want the screen filled with their clutter. 

I use the blacklist like an email spam filter. I am not even too bothered by distant "spam" since those stations at least inform me that there is propagation in that direction. I only filter the local spam.

I have only ever blacklisted stations heard on 6 meters. For my limited digital mode operating on other bands, I've never had cause to filter anyone else.

The bottom line is that if I don't respond to you it is almost certainly not because you're blacklisted. Either I'm ignoring you or simply not copying your signal. If you wish, you can judge me as being discourteous. I won't care.

I expect my blacklist to remain short. I might even delete entries since people's habits change. Perhaps I'll do that each spring at the start of 6 meter season. I can always add them back if their bad behaviour persists.

Your reasons to filter stations may differ from mine. Indeed, filters are used by few stations: they either don't use them or they stick with WSJT-X which does not support filters.

Many fervent 6 meter DXers use area filters to silence all callers out of the area they are interested in. For example, European DXers that filter all callers from Europe. There is no need to blacklist every station. I have yet to use one of those filters despite the temptation, since I consider it discourteous for a station in Canada or the US, unless they are very far away, to call me when I send CQ DX. 

Sometimes nearby friends answer my CQ DX. I usually reply to them when no DX calls me. I don't blacklist friends! With the limited message diversity on digital modes this is their way of saying hello. Custom messages are a bit of a bother and I've never used them.

I was averse to the use of filters for a long time. Times change. Perhaps the reasoning I've provided in this article can be food for thought as you consider whether and what to filter. I don't expect everyone to agree with my choices.

With the increasing number of hams attracted to 6 meter digital modes -- generally a good thing -- some bring behaviours antithetical to those of us DXing on 6 meter. The small step I've taken with selective filtering is helping to restore my 6 meter summertime experience to what it once was. Now if only propagation were better!

Between a Rock and a Hard Place

I am accustomed to sharing the towers with wasps early in the fall. Their job is done and most are doing little more than waiting to die. For some reason they are attracted to the cool steel of the towers. They are not a danger since they have no hive to protect. Leave them alone and they leave you alone, even when you're nose to nose with them. Above 10 meters their numbers rapidly diminish.

July is not that time of year. Wasps are now very active and several species are easy to antagonize if you do nothing worse than walk beneath their hives in the tree branches overhead. The occasional sting is painful but usually nothing to worry about. Then one day about 25 years ago, while mowing the lawn, a few stings from wasps protecting a nearly invisible hive 5 meters overhead sent me to emergency room. 

Doctors informed me afterward that I had developed an allergy to wasp venom. I learned that isn't unusual. The risk increases after repeated assaults because the immune system learns the wrong lesson and eventually reacts inappropriately, with a risk of anaphylactic shock. I was fortunate not to become a statistic.

There is immunotherapy available for a variety of allergens. I never got it for wasp and bee venom since it can be unpleasant. Instead I carried an Epi-pen. Years later I had successful immunotherapy for an unrelated allergen that gifted me with a side benefit in that it also reduced, possibly eliminated, my sensitivity to wasp venom. The immune system pathways are largely identical, with small differences for each allergen. 

I was surprised by this in the following year when wasp stings only elicited what can be called a normal response: pain and swelling for a couple of days. However the risk remains and living in a sparsely populated rural area there are daily encounters with wildlife in all of its variety. I am not fearful of the wildlife, even wasps, but it helps to be observant and not take due care. Several days ago I was not observant and I paid the price.

As mentioned in the previous article, I have a lot of outstanding maintenance and new construction to catch up on. One of those tasks is to diagnose and repair an intermittent in the coax going to the upper 5-element yagi of the 20 meter stack. It was a fine warm morning so I gathered my tools and gear and headed over to the 140' tower sitting amidst the growing hay. I mow narrow paths to the big tower and around the bases to ease access during late spring and early summer.

I did my usual rapid visual inspection of the tower and antennas and started up. I didn't get far. I should have taken the warning of an unusually dense cloud of flying insects at the tower base. 

During the several weeks since my last climb up this tower the wasps had built a large and growing nest about 15' above ground. It wasn't visible during my brief inspection of the tower because it was inside one of the wide girts on the climbing face of the tower. It would have been difficult to spot regardless since it's gray and shadowed by the girt in the bright sunshhine.

The density of rapidly flying insects increased until my hands unknowingly almost directly contacted the hidden hive. That's when they attacked.

Which brings me to the title of this article. On the one hand, I'm allergic to wasp venom and the stings were adding up fast. On the other hand, I'm on a tower where the only immediate escape is to jump. I'll leave you to choose which of those options is the rock and which is the hard place.

What would you do? There really is only one correct answer: climb down. Whenever you get into a tight situation there is the risk of panic and the classic fight or flight response. But you can't fight the wasps nor can you fly (literally or otherwise). Besides, if you do jump, the wasps will follow and you will suffer from both the fall and the stings. So start descending and endure the attack as well as you can. It'll feel like forever even though it may only be seconds. Luckily the local wasps don't build their hives very high.

I started running when I hit the ground, burdened as I was with my climbing gear, tools and heavy boots. Many of the wasps pursued and continued stinging me. They let off when I was about 200' (60 m) from the tower. The immediate threat had abated but it wasn't over. From experience I knew that it could be 10 minutes or more until the severity of the venom reaction could be assessed.

I won't bore you with the excruciating details. One picture of my hand will suffice. My face and arms looked about the same. It was a warm day so I was only wearing a tee shirt and a small cap to protect my head and eyes from the sunshine. There were few stings below my chest. The greatest worry was having to breathe through my mouth for an hour because the swelling completely blocked the air passages in my nose.

I recovered remarkably well.  When I attended a social gathering two days later, the swelling had diminished enough that few remarked on my appearance. But it did give me a story to tell!

In the end, the wasps fared worse than I did. Although difficult to reach, I went out at night when the wasps huddled inside the hive and drenched them with a high pressure insecticide canister. I always keep a couple of them in the house. 

When the survivors returned the next day, I made a 20' pole out of antenna tubing and wrecked the hive. That drove them off for good. It is to be expected that I may be slightly nervous when I resume tower work after I've fully healed.

Perhaps you found this story amusing, frightening or instructive, or a little of all three. It can happen to any ham doing tower and antenna work. In warmer climates the danger can be worse. What an unpleasant surprise it would be when wasps swarm from a hive hiding behind a rotator 50' up the tower!

What lessons can we learn from this experience? That assumes that I haven't frightened you so much that you've taken a vow to never climb a tower again!

• Know the risks: Mid-summer is prime time for insects building nests. While there isn't much shelter on a tower, competition among the critters for the best spots can lead some to choose your tower.
  
• Inspect: Inspect the tower, from all sides. That probably wouldn't have helped me in this case because the hive was well shaded. But I should have paid closer attention to the insect activity at the tower base. The danger signs were there. I typically only inspect for structural anomalies before each climb.
• Don't panic: Jumping will leave you disabled on the ground and at the mercy of the merciless wasps. Panic almost always leads to poor choices. As difficult as it may be in the moment, think clearly and act appropriately. Mitigate the attack if possible and then get out of there, but safely. The attack may continue but you will survive. 
• Get help: Seek out family or neighbours immediately if you are working alone, or whoever happens to be nearby. Get medical help in case the worst happens.
• Prevention: Build your towers and antennas away from trees and foliage. It is safer for the tower and for you. This year I worked on a repeater tower where the site owner allowed adjacent trees to grow to a large size. I had to climb through the branches. Insects blend into their surroundings and when the leaves are in bloom it is likely you'll spot the hive too late.
  

There are towers that are less likely to host hives. The wide C-channel girts on the LR20 towers that are used by many large Canadian ham stations provide more shelter than I'd have guessed. Thin tubular legs and struts like those on Rohn towers commonly used in the US provide little protective cover for hives. The underside of rotator and bearing plates on all makes of tower often host hives but you'll see them in time, if you're paying attention.

My hand grip is not yet back to full strength so I haven't resumed tower work. Another couple of days should so it, and in any case we're about to be drenched by the remnants of hurricane Beryl. Better to fall behind schedule than to take unnecessary risks.

Yagi on a Swing

Repairing yagis on the tower is not always easy. The parts you need to access may be far out of reach. With some well thought out choreography it is sometimes possible to twist and turn the yagi to bring the problem area within reach of the tower. In most cases you'll need to lower the antenna to the ground to work on it. That is often simpler and safer, at the expense of a larger time investment.

I decided to experiment with an alternative. It's one that few hams would ever need since it involves towers with multiple side mounted yagis. In this instance the purpose was to repair the XM240 40 meter yagi. Last fall the antenna was moved to one of the large towers and mounted on the rotatable side mount at ~75'. It replaced the TH6 which was raised a little higher and fixed to the south.

A mistake was made when the XM240 was reassembled for the tram ride to its new home and not noticed until a few weeks had passed. The boom clamp for the reflector element wasn't properly tightened. In high winds the element would rotate on the boom. 

A small amount of rotation is not a problem but a large rotation would not only affect its performance, it would not be rotatable since the element would collide with the TH6 above it. Damage would result since element tips are fragile. 

After an ice storm in early winter the element rotated so far that the tip was above the plane of the TH6 elements. Luckily there was no contact due to the direction the XM240 was pointed at the time. A week later a strong wind levelled it again! However I couldn't risk rotating the XM240 without first glancing out the window. That's difficult to do at night when 40 meters is open!

The XM240 boom cannot be tilted to access the reflector because of the TH6 above it. To access the reflector the yagi must be slid horizontally almost 10' (3 m). That's actually possible because there's a lot of tower above the two yagis. What I did was to build a "swing" for the yagi. The diagram shows the general idea. It is suspended from an anchor almost 40' further up the tower.

It isn't quite as simple as shown in the diagram for the following reasons:

• 
  The anchor should be at least 3× the height above the yagi as the horizontal swing distance. Otherwise the large swing angle will lift the antenna into an upward arc and the force needed to swing the yagi will be excessive.
• There can be no elements between the tower and the element being accessed since it will be blocked by the tower.
• The elements of the yagis between the anchor and the swinging yagi must be approximately parallel to the boom of the swinging yagi or the swing will strike the elements of those yagis.
• The swing can only work in one direction so it must be positioned on the side of the tower where the yagi will be swung outward.

I was fortunate that all of these constraints could be dealt with for the XM240. Pointing it west let the swing move between the elements of the TH6 and the lower yagi of the 10 meter stack. This orientation also reduced the swing distance to less than 8' (2.5 m) since the reflector is on the "back" side of the tower from the rotator and short mast. The support strut and legs of the 80 meter inverted vee legs are behind the swing and therefore not in the way.

In the picture you can see the TH6 above the XM240 and the 5-element 10 meter yagi up higher. A rope is dropped from an anchor a little above the 10 meter yagi to the driven element side of the XM240 mast clamp. My intent was for the boom to tilt down slightly on the backside to ease the repair and to help avoid bumping the TH6. The rope runs over obstacles on the side of the tower where the swing will occur. It is vital to avoid tangling the swing rope in any obstructions.

There are several precautions to keep in mind:

• 
  Do not tie the rope to the tower directly since the tower steel will cut into the softer rope material. The risk of failure is low for a rope in good condition but must still be avoided since failure can be catastrophic. I use a large shackle that has a smooth round surface for the rope to bear on. Loop the rope on the shackle several times to reduce tension on the knot. It will be much easier to remove later.
• Consider using steel cable instead of rope. Rope can be very elastic and it can stretch a lot over a long distance, making it difficult to tension properly. It can relax further while under load. Having the yagi come to rest below the mast and rotator can be a problem during the swing operation and when the time comes to remount the yagi on the mast. I used a large turnbuckle to add tension after tying off the rope and it wasn't enough. More on this later.
• Use a second method to support the antenna. Redundancy reduces risk and prevents the boom from tilting up or down too far when the rope is not attached at exactly the centre of gravity.

I installed the swing in late February when we had a period of unusually warm weather. Life then became messy for me and I abandoned most projects for several months. In mid-June I checked the swing and made adjustments in preparation for the operation. 

The boom truss was removed in February. There were high winds over the next 4 months but no ice storms. Boom trusses are partly aesthetic and partly structural support. For many medium size yagis like this don't fret over a brief absence. This XM240 is 10 pounds heavier than the original since the boom and elements were structurally upgraded by the previous owner.

We are looking toward to the reflector end of the antenna, the end I needed to access. A tow strap and shackle are loosely fit over the boom as the second restraint and to help guide the boom as the yagi is swung. The boom truss cable runs over, not within, the restraint.

Disconnect the coax, if necessary. I had enough looped up that it wasn't necessary, which saved me the trouble of removing the weatherproofing. All I had to do was cut the tape and cable ties securing it to the tower. The boom truss must be removed from the mast. Place both where they will not interfere with the swing or become entangled. I left the truss cables attached to the mast plate and let the whole thing dangle below the antenna. If the cables must be separated, first tie them together so that you don't drop one accidentally and leave you with a truss cable dangling far out of reach.

With all the preparation done it was time to pull the bolt from the boom-to-mast clamp. I preferred to remove the mast bolts (saddle clamps) rather than those for the boom saddle so that the clamp plate remained on the boom. That made it easier to me to operate the swing. With the clamps removed, the boom came to rest several inches lower as the long swing rope stretched under tension. It leaned slightly on the reflector side just as I had planned. The boom restraint easily held it.

My original plan was to attach a long rope to the boom to be pulled by a helper on the ground. I scrapped that because the season is well advanced and the hay is high. It isn't fair to ask someone to risk the ticks by wading through the tall plants. I decided to do the job myself.

A lightweight rope is used to pull the boom. The swing is long so the force needed to move the boom is very managable by hand. The nylon rope is loosely looped several times around the boom and knotted. This is a common technique in tower work since it can be used to lift heavy pipe and perform other tasks where there is no available tie point. The rope can be easily slid along the boom in short steps as the antenna swings outward. You never have to reach out more than a foot or two during the entire operation.

Since I was doing this myself, I wrapped the pull rope around the mast for friction. It's like having a third hand as I manipulating the rope and boom and when I periodically tied the rope to the tower. I pulled the boom with one hand and the rope with the other. I would hold the boom while I slipped the knot backward as the swing progressed. The only serious obstacles were the splice bolts connecting boom sections. To get the knot past the bolts I held the boom with one hand to reduce tension on the rope while I lifted each loop of rope over the bolt heads and nuts.

This is what it looks like when the swing is at its maximum extension. It looks impressive from the ground (and on the tower!) since this is, after all, a 40 meter yagi that weighs 75 pounds with a 22' boom and 43' elements. The antenna isn't sitting flat due to the swing attachment point on the boom-to-mast clamp plate. The element tips are well out of the way of the TH6 elements above.

Once the reflector is accessible from the tower the pull rope is tied off. Only a minute was needed to tighten the element clamp bolts; they were really loose! I took another minute to move the boom truss clamp a few inches since it wasn't where it ought to be. At the time the antenna was raised last fall it was easier to add a second mast clamp than to tram the antenna back down to remedy the error. I knew exactly where to place it since there are small indentations on the boom from when it was properly positioned.

When swinging the antenna back to its usual position, take care not to let out the pull rope too quickly. You must do it in small steps, just as before, or the knot will end up out of reach. You will only be able to retrieve it by swinging the antenna out again. Avoid the temptation to rush the job. As the boom plays out, slide the knot backward, always keeping it within reach, easing it over the boom splice bolts as before.

As I hinted earlier, the rope had stretched several inches from the tension of supporting the antenna. That doesn't hurt the rope but it made the antenna difficult to remount on the mast. It wasn't possible to lift it the extra distance with one hand and install the bolts with the other. By then I was hungry so I added another rope to hold it in place and descended. An hour later I returned with a hand winch and attachments. Within minutes I had the boom winched upward and the bolts were reinstalled.

I cleaned the antenna of all the swing hardware and hung all of it on my climbing harness. The boom truss was installed and the antenna levelled, and then the coax rotation loop was returned to its previous state. I temporarily loosened the rotator mast clamp to confirm that the coax was properly dressed by turning the antenna through its full rotation. That done, I climbed up to retrieve the swing rope and anchor and, with the aid of gravity, brought all of the equipment down with me. I'm lucky that despite my age I remain strong enough to do this style of brute force work.

After stowing my gear I tested the antenna and rotator and put a check mark next to one more item on my long to-do list. There is much more to be accomplished this year.

In a way this was an unnecessary job. With contest season over and progress on my planned replacement for the XM240, it won't see much use for the next few months. I did it since the rigging was already in place and I wanted to confirm that the procedure would work as planned. I had also promised the station to a guest operator for one of the summer contests and I didn't want to disappoint him with antennas out of service or of limited utility.

I'll close this article with a cute picture. After climbing the tower I looked down and noticed that I had a visitor. A young fawn was hidden in the tall hay and calmly feeding. It wasn't at all disturbed by all the steel on steel racket I was making. I guess it didn't see me on the ground, or realized that I couldn't see it, and deer are not in the habit of looking to the sky for predators. It happily grazed less than 40' from the tower base. Clicking on the picture should bring up a higher resolution version of it.

My recent blog output is less than my usual pace and that is likely to continue throughout the summer. There are many demands on my time at the moment. Enjoy the summer weather as you work on your antenna projects.