Snipe on a Tower

There is a limited ability to achieving mechanical leverage when you are working on a tower. You can only "push" against the tower, directly or via your positioning lanyards. As I like to say: an ordinary task on a tower is three times as difficult as it is on the ground.

A good example is one I wrote about several months ago: adjusting the direction of a large yagi. I had to rig my positioning gear to maximize how far I could lean out from the tower to plant my legs and pull on the boom or driven element to overcome the antenna's inertia. Then I had to do it again to stop the rotation. There's a lot of angular momentum in a 300 lb antenna with a 46' boom and 65' long elements!

There are many other examples in tower work. The most common is tightening and loosening the bolts that hold a tower together. On large towers those bolts have a wide diameter and high tensile strength. The required torque can be difficult to achieve on the ground, let alone at the top of the tower you're erecting or taking down.

The bolts in the above picture are examples of what I've dealt with recently. On the left is a ½" grade 8 bolt used to join the horizontal flanges of mated tower section (see the picture below right). Unlike the typical round or V-shaped tower legs familiar to hams, you'll find that many commercial towers are built this way. They're far easier to work with when the tower sections are long, wide and very heavy. On the right is a galvanized ⅝" A325 bolt that is designed for the high shear forces found in V- or L-shaped tower legs.

The specified torque for these bolts is high. Achieving a torque of 100 ft-lb or more is no easy feat when you're on a tower. It can take even more force to loosen fasteners that have corroded or attracted dirt over the years. On the left bolt you can see what was lurking under the nuts.

For the tower I was taking down, those ½" grade 8 bolts had been properly torqued when it was erected years ago. Each section joint has 6 bolts, with two per flange on 3 legs, and there were 5 of these 11' sections. 

Pulling hard on my long ¾" wrench wasn't good enough to loosen the nuts. The nuts either didn't budge or, in a few cases, the bolt and nut moved in unison. I needed more torque.

Since it took longer than expected to remove the antennas and cables, tower removal was deferred to a later date. That gave me time to fashion a solution. In essence, I needed a longer lever arm to increase the torque at the wrench head. 

There are "breaker bars" made for this very purpose but they're heavy and expensive, and if you're a typical ham you probably won't get much use out of it. Also, they usually take sockets and that can make it difficult to firmly hold the nut because you apply force to the tool arm that is necessarily offset from the work surface by up to 2".

The traditional way it's done is to slip a steel pipe over the wrench and use that for added leverage. It's simple, easy and works well when the wrench is forged steel and designed to take the abuse. My ¾" offset box wrench is very robust (40 years of reliable service!). However, it is extremely awkward to manipulate a large pipe slipped over it when perched on a tower. You'll inevitably drop the wrench, pipe or both. Ask me how I know!

A common name for a pipe used in this way is a snipe. It's a term that seems to vary by country and industry, so you may know it by a different name. I'll stick with the term I know.

Note about safety. Careless use of a snipe can destroy the fastener or the tool. If you find that you're applying far more torque than the job should require, stop immediately. The problem may not be simply the lack of torque. Inspect the fastener for signs of rust, debris, metal distortion and other anomalies. Shearing a tower bolt, if it's the last one holding the sections together, invites disaster. The shrapnel from a shattered wrench or snipe can easily injure you and the debris can strike those on the ground. Hardhats and eye protection are recommended.

When we returned several days later to take down the tower I brought along the snipe I purposely built for the job. I keep a lot of scrap material around for reasons just like this. Here's what I whipped together after 30 minutes in my workshop.

The wrench has two box ends. The 25/32" end is inside the pipe and held in place by a ⅜" grade 5 bolt. The wrench cannot slip out of the pipe. To keep the weight low I used a short length of thin wall 1.5" diameter pipe. It looks like it was once part of a mast for a TV antenna. There's a PVC coupler jammed into one end that I remember once trying and failing to remove. So I drilled a hole through it and tied on a short length of rope. On the other end of the rope is a large spring-loaded carabiner. A length of stranded wire is less flexible but you may find it more reliable than rope. Don't use solid wire since it can fatigue and break.

Because the pipe wall is thin, the edge of the wrench can bend and perhaps break the pipe under high torque. A rusty muffler clamp strengthens this high stress point. The snipe is far lighter than one made from a thick wall pipe. The carabiner clips to a ring on my climbing gear or onto a tower strut. You would have to be exceptionally clumsy to drop this tool.

Notice that the total length is only about twice that of the wrench along. As a general rule, use the shortest snipe that accomplishes what's required. There's less risk of accidents due to application of excess force. With the tool as constructed you can likely achieve more than twice the torque of the wrench alone because the round pipe is more comfortable in the hand than the wrench narrow side profile. Breaker bars are round but are comparatively thin.

The purpose of the snipe is to "crack" the nut, not to remove it. For properly torqued bolts of this size and quality there is a satisfying crack when the nut first moves. You can probably set the snipe aside at that point and use ordinary and less awkward wrenches. 

If the bolt turns, have your tower partner put a wrench on the bolt head to hold it. You typically need less torque to hold the bolt head than to turn the nut due to friction between the tower steel and the bolt head. The snipe should always be applied to the nut, not the bolt head. We passed the snipe back and forth depending on which of us was best positioned to crack each nut.

When all the nuts are cracked, proceed with fastener removal and lowering the tower section. The snipe was clipped onto the lower section while we did this. Pick a place that won't interfere with the delicate job of shifting and lowering the tower section with the gin pole.

This little snipe worked so well that after removing the carabiner and wrench I kept it intact. I don't know when or if I'll use it again but I'd like to have it ready just in case.

Preparing for Fall Antenna Work

This is what I call transition season. The 6 meter sporadic E season is effectively over and the fall tower and antenna season is a few weeks away. I have little appetite for summer contests and there are few DXpeditions at the moment. This is the perfect time to go QRT, tear the shack apart and get organized for tower work and the fall/winter contest season.

Beginning late in July, I gradually disassembled the shack until there was nothing left. First I removed the second operating position, then the SO2R gear the remaining amplifier and other peripheral equipment. Soon the desk was empty and even that was disassembled. You can see that nothing was left.

This is temporary. If all goes well I'll be active again within days. I wasn't happy with the shack desk that I built last year so I am rebuilding it. The new one should be ready to install shortly. It is designed for a more ergonomic SO2R operating position while allowing rapid reconfiguration for a two-position multi-op. I'll say more about it when it's fully built. That could be a while since I'll be reconstructing the shack in stages.

There are no new towers planned this year. There may never be. Acquiring towers at a good price is no problem, and I certainly have the space to put them. I remain very fit and I do a lot of tower work for myself and others, but time is unkind to all of us and one day that will no longer be the case. I don't want to create a maintenance nightmare in my sunset years, or at least nothing worse than what I now face.

My 2023 plan was written 9 months ago and an update is necessary. I will not get it all done, and indeed that happens every year. I like to aim high and make compromises along the way as I determine my true priorities versus what might only be nice to have.

For those keeping track (which, I'm sure, is no one except me), you can compare the current outlook with my plan for 2023. I'll do well if I get all these jobs done (coloured in red).

The trap tri-banders -- TH6 and TH7 -- are going away. I decide a while ago to migrate away from trap yagis due the inevitable loss in the traps. They have been helpful until now by filling an immediate need. Now I am in a position to move on, mostly.

The Hy-Gain Explorer 14 sat idle for a long time until I sold it last year. The TH7 was recently sold to a friend. It did its job when I had fewer antennas but it, too, is now surplus. The TH6 will come down and be set aside while I contemplate whether to sell it or put it elsewhere. It might be useful fixed south for rapid multiplier hunting. The resale value of this 50 year old antenna is pitifully low so I'm tempted to find a use for it.

Per my plan, I purchased a trap-less tri-band yagi for a multiplier antenna. It is a Bencher Skyhawk tri-band yagi (now manufactured and sold by DX Engineering). I jumped at the opportunity since it is faster and easier than designing and building an equivalent antenna. The antenna is well regarded and the performance is quite good.

The way I bought the Skyhawk is funny. Earlier this summer I was helping to dismantle an old friend's station. He hasn't been active for a while and decided to exit the hobby. The Skyhawk was on the smaller of his towers. I had a good look while rigging it for lowering and I liked what I saw. Once we had it on the ground I asked him, from 50' up the tower, how much he was asking for it. We proceed to negotiate by shouting back and forth and settled on a price. There was much laughter from the others helping that day.

After a few days of work the towers and antennas were down and the towers trucked to their new owners. One more trip with the help of a friend and his truck brought the Skyhawk home along with hundreds of pounds of aluminum and steel he'd accumulated over the years. Some of it I recognized from my youth decades earlier when I worked on his towers.

In the picture you can see the Skyhawk boom reassembled and many of the elements. At right is a small portion of the gifted aluminum. One picture can't do justice to how much aluminum there really is. Some of it has already gone to another ham with his own fall antenna plans. That will still leave me plenty of pipes and tubes to build several antennas that I have planned. But perhaps not this year.

When the Skyhawk replaces the XM240 on the Trylon tower I'll have a fully rotatable tri-bander up 21 meters that performs well and can be turned more quickly than the upper yagis of the 20, 15 and 10 meter stacks that are rotated with slower prop pitch motors. Speed counts in a contest. The Skyhawk replace the TH6, which is side mounted with limited rotation.

Putting the XM240 where the TH6 presently resides will reduce my capability on 40 meters since it will only be rotatable between southeast (South America) and west (W7/VE7/Pacific). This is temporary. My plan is for a 2-element reversible Moxon that will be more efficient, have improved F/B and SWR, instant switching between Europe and the US, and 270° of compass coverage. If I get ambitious I'll stack it with the big 3-element yagi at the top of the tower (150').

I considered a W6NL Moxon conversion of the XM240, but that's no longer necessary with all the aluminum in my possession. In any case that would have been only a partial job since I want to make it reversible. A reversible yagi makes the best use of the side mount, and I really want to avoid the mechanical challenge of a swing gate and rotator that can handle the torque from an antenna of that size offset on a swing gate. The ancient Ham-M on the side mount should have no difficulty with the 40 meter Moxon, despite its long elements, since the wind area will be lower than the TH6.

I have preliminary computer models for the reversible Moxon but I doubt I'll be able to build and test it this year. Hopefully I'll be able to replace the XM240 with the new antenna in 2024. I could do a conversion of the XM240 but it is actually easier to build a reversible Moxon from scratch with the aluminum I recently acquired and sell the XM240 if I choose to do that.

That will have to suffice for 40 meter antenna work this year since I must consider the work to repair the capacitance hats of the 3-element 40 meter yagi. That's a major repair job that I have planned this fall. The new design that I installed earlier this year is performing well so I've gone ahead and made replacements for the director and reflector elements. 

I recently designed a 2-element yagi for 17 and 12 meters. There are published designs out there but I preferred try to do it myself. This antenna is in my 2023 plan. The priority isn't high and I will delay the project if necessary. There is also the challenge of where to put it since I am running out of tower space! 

My plan for 160 meters is modest compared to my stated ambitions. I will improve performance of the shunt-fed tower, and that may be it. The radials will be doubled from 8 to 16. I have been accumulating scrap wire over the past year to make up the 240 meters of wire for the additional 8 radials. Small gauge wire isn't so expensive that I need to scrounge but it's more fun this way. Once a scrounger always a scrounger.

The other problem I want to address is the small SWR bandwidth of the antenna. As ON4UN documented in detail in his book Low Band DXing, electrically long verticals have a narrow matching range. For daily operating it is not a problem since activity is concentrated between 1810 and 1843 kHz. The narrow bandwidth becomes a problem during contests when activity spreads from 1800 to beyond 1900 kHz.

The solution is a wider gamma rod. A wire cage is lightweight and cheap and is as effective as a large diameter "wire". I have been considering alternatives mechanical designs, one of which you can see above on my indoor tower jig. Before settling on a design I'll model several configurations. Work on the 160 meter vertical will have to wait until at least late September.

At the right of the picture you can see a lot of LDF4 Heliax. This is ancient cable that I first used in 1985. It has seen some rough handling over the years and is now little better than scrap. The impedance "bumps" on the three 40 meter lengths begin to emerge as low as 4 to 5 MHz. So what can be done with it other than disposing of it as trash? Answer: Beverage!

I don't really need another Beverage for more directions. The 6 directions I now have serve me well. What I'm missing is a directional antenna for the second station for use in multi-op contests. The Beverage switching system is not designed to be sharable and schemes for doing it all have shortcomings. A separate receive antenna can help when both stations are on the low bands at night. Most of the time these will be 80 and 160 meters, but sometimes 40 meters when a little extra noise reduction is needed to dig out a weak station.

My intent is to run it east-west and make it reversible like my other coax Beverage made from RG6. It will run along the fence line that I used for a temporary 90 meter long west Beverage a few years ago. If its 120 meter length makes it too directive I can shorten it. This is a project for late fall when the snow flies and tower projects are wrapped up for the season.

I have several work items to pursue this fall on 80 meters. The easiest is to improve the anchors for the 80 meter inverted vee that I re-installed this year. Most of what I'll need has been prepared for some time but I delayed the work due to the growing hay and the arrival of tick season. 

The central tower of the 80 meter vertical yagi has to be replaced before I can make antenna improvements. That involves planting improved guy anchors. These will be identical to what I made for the overhead cable run. It is a physical job that is best delayed until the weather cools, but must be completed before the ground freezes. The new anchors can be built without disturbing the tower and antenna. However, I'll have to move quickly should I decide to replace the tower this fall because the antenna is needed for the coming major contests.

There are several half-completed projects on the back workbench that you can't make out in the above picture. I'll talk about those another time. This is, as usual, a busy time of year.

Inside the shack, the new operating desk is slowly coming together. The desktop's final coat of polyurethane is drying and the multitude of cables is being organized. This project, too, will progress in stages. I want to get the station minimally operational soon even though I have little motivation to operate in August. I don't want to rush later since that will result in a sloppy job. I'm a poor carpenter but I wasn't satisfied with the suitability of the numerous commercial products I looked at.

Other indoor projects include: rotator controllers, improved performance and new features for the station automation system, lightning protection and computer networking. Outdoors maintenance items include clearing of summer growth around the Beverage antennas, removing tree limbs near overhead cables, checking and replacing cable ties, and much more. Maintenance is the curse of a big station.

There's no end to all the work and that's fine. Amateur radio is a great hobby to learn new things and see immediate results when you put your station to the test. Sharing what I learn in this blog is one way I give back the hobby.

Contest Flare

This will be a short article about a short subject: dealing with solar flares in a contest. The goal is to briefly describe the effects of solar flares on contest strategy. 

When I've written before about contesting in poor conditions, I emphasized how everyone is in the same situation so it is imperative to carry on. For those unfortunate cases where the effects are not the same for everyone, you can still measure yourself against others in your geographic region. It's relative performance that matters, not the absolute value of your score.

Those articles were written when solar activity was low. Solar maxima are different because flares are more frequent. For the observant ham, it is possible to gain a competitive advantage when a flare occurs. The X-class flare on August 6 during the NAQP (North American QSO Party) illustrates the point.

A solar flare temporarily boosts the ionization level in the ionosphere. While this may seem like a good thing, it is too much of a good thing since signals that would be refracted are instead absorbed. The result is a radio blackout at HF. 

Notice in this map of the estimated effects of Saturday's flare (screenshot from SolarHam) that the intensity of the blackout depends on the solar declination (angle of the sun above the horizon). The tropics are hit harder than the polar regions and where it's midday. There is no increased absorption where it's nighttime. Signal attenuation declines with increasing frequency.

When a couple of contesters in the area expressed concern about the poor weekend propagation forecast, I joked that if there's a solar flare all they need to do is to step out of the shack for 30 minutes. That may seem an odd thing to say and perhaps my joke went astray. It is important to understand that the various solar and geomagnetic indices we follow are not all alike. Geomagnetic disturbances, proton storms and flares have unique effects. The effect of flares is more predictable than most and typically of short duration.

Most flares are brief and the HF blackout can recede in as little as 30 minutes. Less common long duration flares have similarly longer blackouts. The intensity of the flare (M or X class) determines the amount of signal absorption and frequency breadth. The X1.6 flare during the contest (the above X-ray flux graph is from the GOES web site) was of moderate length and the worst of the blackout would have lasted perhaps about an hour -- I was unable to monitor the bands so I'm going by the reports of others.

Contests don't have a timeout when there's an HF blackout! As a participant you have to decide what to do. First, however you need to know that a flare occurred. When the bands suddenly empty of stations you should suspect a flare. Check the solar and geomagnetic indices. Some are updated within minutes, and the rise in X-ray flux due to a flare is very rapid. By the time you notice the blackout it is probable that the online X-ray flux data will show the leading edge of the flare.

Let's assume that you are an observant contester and you quickly discover that a flare has occurred. What should you do? Is there a way to take advantage? The answer depends on the contest. In many cases there is nothing you can do except take a short rest so that you're in better physical condition when conditions improve. In select cases you can use the flare to your competitive advantage.

Flares do not affect propagation on the night side of the Earth. There's about a 50% chance that the flare does not directly affect you. You might only notice that you cannot work stations in the daylight hemisphere. There may be no reason to change what you're doing. You can continue to do well on the low bands, which are certainly better at night. By the time the sun rises it will be business as usual. During times of low solar flux you may be totally unaware of the flare since the high bands are dead at night, and that is where you work most of the stations located in the flare-affected half of the globe.

That was not the case during last weekend's NAQP. All of North America was effected. Even stations in the eastern fringe where sunset was approaching would have found few stations to work on either the low or high bands. Going to 10 meters where attenuation is lower was not an option for most since the prevailing conditions were poor on that band.

NAQP is a contest where single op stations are restricted to operating less than the full contest duration: 10 out of 12 hours. There are other contests like this, including CQ WPX where single ops can operate 36 out of 48 hours, or 24 out of 30 hours in ARRL Sweepstakes. The best strategy in these contests may be to take time off when the flare occurs. The sooner you recognize the HF blackout and confirm the rise of the X-ray flux, the sooner you can pull the switch.

The minimum off time is typically 30 minutes. That may be enough to escape the worst of the blackout. Stations that continue to operate will see their rate and score potential decline. They will have no choice but to take their off times when conditions have recovered. A strategic off time can improve your competitive position relative to them. Check the X-ray flux to see if the worst as over -- that does not count as assistance for unassisted operators -- since listening time counts as operating time according to the rules of most contests.

Let's look at a slightly different situation. Imagine that the flare had occurred 2 hours later. Most of eastern North America would have been in darkness and not directly affected the blackout. Stations where it is nighttime have a different strategic option available to them. 

The high bands in NAQP favour those in the western half of the continent because they are relatively few compared to the major population of the eastern seaboard and US mid-west. Their run rates can be very high on the high bands. In the east, the low bands are the most productive since that is where the bulk of contacts can be made.

It can be very smart for those in darkness to concentrate on 40 and 80 meters while the HF blackout lasts. Check 20 meters occasionally for signs of recovery from the blackout -- this is where SO2R or a separate SDR spectrum monitor can help. Less time is wasted on the unproductive high bands. Since many eastern stations operate 40 meters during daylight in NAQP and Sweepstakes there are ample stations to work, including those that may be less aware of the flare's effects. The flare can alter the relative competitiveness of eastern and western competitors.

HF blackouts due to flares lower everybody's score potential. But the objective in a contest is to score better than competitors, not to achieve the highest possible score. Strategic reaction to solar flares can improve a station's prospects. It is good to keep this in mind since solar maxima bring more and stronger flares, and they will be with us for at least the next 2 years.

Unclear on the Concept: DX Spotting

In the beginning, when we heard a rare DX station we would pick up the telephone and call our friends. They would get on the air and work the DX, and then they might call their friends. These telephone trees were always shallow with few beneficiaries. But there were many of these small trees spread across the globe. They relied on those with the time to spin the dial and find stations, and a smaller number that globally networked with other DXers. This was how groups of DXers found stations and, importantly, knew when and where stations were likely to appear.

The internet changed everything. Now we have a large number of DX spotting clusters networked together so that when a stranger on the other side of the world spots a station we learn about it almost instantly. We click on the spot and our transceiver interfaced PC instantly jumps to the DX station and might even set the correct mode and frequency split. 

It has never been easier to chase DXCC and other operating awards. I've benefitted and it's likely that you have as well. Some laud the technology, exploiting it to the maximum. Others sneer at the ease and simplicity and mourn the loss of the traditional skills of research, tuning and listening. I'll set that debate aside to focus on a different and modern problem: poor and improper use of spotting networks.

First, what is the proper way to spot DX? We can debate which stations to spot, but that's pointless since we will never all agree. It can be rare DX, but it can also be anyone and everyone during a contest, or simply a kind note about a non-rare station who was a pleasant conversationalist. Regardless of your thoughts on this I think we can agree that spots should ideally include the following information:

• Frequency
• Call sign
• Whether the station is operating split, and optionally the offset
• The location of the station if it is not obvious from the call sign; e.g. IOTA, grid square, state/oblast/county/zone, POTA/SOTA, etc.
  

Only the first two are mandatory. The rest depends on how helpful you want to be. It isn't unreasonable to avoid including optional information so that others must do their part by listening. I'm a minimalist when I spot a station.

The list of poor spotting etiquette is long. We can roughly categorize those as careless, inappropriate or malicious. I'll talk about the ones I've encountered that aggravate, surprise and amuse me. And why not? The height of summer is a great time to relax and have some fun. I'll leave the technical topics for another day.

Above are a few examples that I randomly selected for the purpose of this article. They are assembled from screenshots collected from a web-based spot aggregator. In these screenshots I am redacted personal identification even if the spotters are not shy about what they're doing.

Careless

We all make mistakes. The proper way to deal with it is to correct the error. Few do for their bad spots. In the example above, I'm not sure if the correction was distributed out of sequence or whether the error "corrected" the correct call sign.

Careless mistakes that I often see include:

• Automatic spotting while running: Many logging applications include a feature to spot every call sign you type in or log while spinning the VFO. If you forget to tell the software that you're running (CQing on a frequency) the spots will continue to be generated. This is of course irritating for those who click on the spot and find that the station isn't there or not workable because it's the spotter's frequency. A few hams do it deliberately (bragging about their big signal?) though most often it's just a mistake.
• Call sign error: Mistyping a call sign can cause confusion. It can be a dropped letter, transposed letter, changing "0" to "O", or just a typo. Most logging software will let you make the mistake. If I click on the spot, work the station and log it, I should not expect a confirmation! These mistakes are common, so listen carefully.
  
• Propagating an error: I know this one well. Someone copies my call during a contest as "VE3UN" and spots it. Many hams miscount dits when the CW speed is very high in a contest, and this error is very common for my call. The mistake is propagated when callers, drawn in to work a new station, fail to listen and also spot the erroneous call.
• Spotting the wrong frequency: This is common for split operation in a DX pile up. Rather than spot their receive frequency (where the DX station is transmitting) they spot their own transmit frequency. This is worse than simply unhelpful since most logging software give precedence to the most recent spot. You click on the spot and find yourself listening to the pile up instead of the DX station. You either hunt for the DX or manually locate an old spot with the correct frequency.
  

Inappropriate

There is a fine line between careless and inappropriate spots. My criterion is that the inappropriate spot is one whose purpose is not that of informing about a station's call sign and frequency. That is, using the spotting system for communication of other kinds of messages is inappropriate. 

Examples are legion, but here are a few that I regularly encounter:

• No copy: These are variation of "nope, I hear nothing". If that's the case, what is being spotted? Your failure to copy a station not only doesn't justify a spot but also misleads others to believe that you have heard the station. Few hams notice the added comments and solely rely on their band maps and spectrum maps that just plot the call sign at the frequency.
• ESP attempts: The DX station is working a pile up, not reading spots. You cannot effectively communicate with them this way. Pilot stations for the especially rare DXpeditions may, but that's about it, and it still won't help you. Cries of "you got my call wrong!" are not only pointless but non-radio attempts to correct the DX station's log is inappropriate. Do what the rest of us do: work them again. The same goes for spot messages such as: "turn to NA", "I need you on 160 SSB" or "upload your log!".
• Shaming: We all make mistakes. Using the spotting network to publicly shame other hams is inappropriate no matter the reason. Naming the alleged guilty party with a call sign and a message like "UP UP", "20 khz splatter", or "DQRMer" is very rude. Your impatience or frustration are not a valid excuse for your inappropriate behaviour.
• Help me: "Where is he listening?", "did he QSY?" and so forth are inappropriate. Spots are not a chat line. There are venues where assistance can be requested.
• Complaints: There are an awful of spots of this variety. Examples include: "they only work EU", "too much $$$ for a QSL", "he's deaf" and insults for a host of perceived affronts. Public tantrums are not cute after you've passed the age of 3.
• Brag: "DXCC300", "worked with qrp and dipole", "human to human" and so much more. We should be proud of our accomplishments, but not in this way. The implication with some of these messages is that those who operate differently from them or have accomplished less are lesser hams. Bragging is almost always impolite, and it is certainly inappropriate in a spot.
• Skimmers: There are always a few hams who connect their personal skimmers to spotting networks rather than to the RBN.
  

Many of these inappropriate spots should not be sent at all or should be fodder for the announcement feature of the cluster network. But few hams pay attention to announcements -- for good reasons that I won't get into here -- and these are people who want to be heard. But that's a poor excuse to misuse the spotting network.

Malicious

Human beings continue to be human when they sit in front of a radio. Hams are not angels. Those with malice in their hearts or who harbour grudges don't always set them aside when they operate. When these individuals are sufficiently uninhibited they will use the spotting network to expose their inner demons.

I won't give examples of malicious messages since this is intended as a lighthearted article. Consider the following:

• Political and hate speech
• Impersonation of others to post inappropriate messages
• Deliberate frequency and call sign errors to misdirect or confuse

You've probably seen examples of all of these types of malicious message. I suggest that you ignore them and use a cluster that actively monitors for and filters abusers of the network. Which brings me to the next topic.

Filters

Cluster operators do not act independently. They share tools and filters and discuss ways to minimize improper use of the network. They not only filter users but also clusters that permit or encourage bad actors. It is to our benefit that they do. I don't believe enough hams are aware of their efforts on our behalf.

In addition to the filters applied by the cluster operators you can have your own filters. Filter features are provided by most of the cluster software applications. You can configure those with applications such as CC User by VE7CC. 

You can also create filters in your logging software. I have done this for several hams that persistently make careless and inappropriate spots. Don't overdo it since most hams eventually correct their behaviour.

In truth, I'm rarely annoyed by poor cluster etiquette. Most of the time I find it quite funny. For example, when a busted call is posted and others echo the mistake rather than listening. Their carelessness is mostly undermining their own award chasing and contest scores. I just shrug, smile and move on.

Is the above example of spotting behaviour inappropriate? Sure. Funny? Very. Sometimes you get the right result by doing the wrong thing. Relax, laugh and don't take poor cluster etiquette too seriously.

Note to readers: You may have noticed a longer than usual gap since my last article. Nothing has happened except summer weather and too many projects. It isn't easy to sit in front of a computer and bang on the keyboard when the weather is fine. I'll soon get back to regular blogging to talk about some of those projects.

Musing on a RadioInfo Standard

Standards are peculiar beasts. They typically come about from the collaboration of competitors, whether at their own behest, pressure from regulators or, importantly, pressure from their customers. Standards can permit interconnection of equipment from different manufacturers and connection of third party equipment to any manufacturer's products.

I spent several years of my life, over 30 years ago, working on North American telecommunications standards. It was interesting at first, especially working with competitors and customers in a common forum. The objectives were good, and the work attracted idealists. 

My attitude soon soured. Typical of many companies, my employer saw the work as necessary but a distraction and a nuisance from the more important objective of building and selling products. Unless you loved the work, it did little for one's career prospects. I moved on.

Standards development can be fast or slow. It goes slowly when the products affected are not in production or when customers are uninterested. With strong commercial pressure standards can be developed very rapidly. For example, when the products can't be sold unless they interoperate. Too much of my work was of the former type, hence my dissatisfaction.

We don't often think about standards for amateur radio equipment. Nevertheless, the presence or absence of standards has an important impact on us and our shacks. I use the term "standard" loosely since in many cases there is informal agreement rather than a formal standard. Formal standards require a recognized accreditation authority which does not exist for amateur radio products.

• Connectors and signals: mics, PC audio and control; rotators; band data; and much more
  
• CAT (computer aided transceiver) protocols
• Remote operation
• Computer logging and control software API
  
• Digital modes: FTx; digital audio; PSK etc.
• Peripheral equipment: SO2R; spectrum displays; and more

That is far from an exhaustive list. It is the rare ham who hasn't fussed over connectors and software configurations after purchasing new equipment. We habitually accept these annoyances with hardly a thought. But think how much easier life would be you could plug in all the existing cables and software applications to use a new transceiver.

We don't always get what we want. The lack of standards dooms us to constantly deal with each vendor's proprietary hardware and software interfaces. Manufacturers have little incentive to collaborate, and indeed see value in putting up barriers to interconnection. On the other hand, it give them freedom to develop new products features with a minimum of external dependencies.

Some of these challenges are diminishing as we increasingly interconnect our equipment with standard PC interfaces, including wireless connections. But that only addresses a subset of diverse physical connectors. Software interfaces are another matter, and is what brings me to the point of this article after a long introduction. Setting the context is worth a few minutes of extra reading (and writing).

Longtime readers may recall that I use the RadioInfo UDP broadcasts from N1MM Logger+ in my station automation software. With it I can select antennas, antenna modes and directions, avoid contention between operators, switch BPF, and more. The API frees me from dealing with the diversity of non-standard CAT and band data interfaces of transceivers. N1MM abstracts the functionality so that the RadioInfo UDP messages are almost all I need.

The downside is that I've made myself dependent on N1MM software. My station automation software is now the only practical way to select antenna. It helps that I use N1MM for contests and for daily operating. It is possible to operate the UI in manual mode for when N1MM isn't available, such as when I use WSJT-X or a different logging application.

What if I no longer wish to use N1MM? I am happy with it now but I know that can change -- nothing is forever. The team may disband, become hostile to user input or fail to accommodate future changes to the equipment we rely on. It is also possible that a better or more preferred contest logger arrives on the scene. 

My thoughts on this were driven by a couple of recent events. One was learning that among WRTC competitors, DXLog has rapidly grown in popularity. I know contesters that have switched to DXLog and I'm sure there will be others. It is not my intent in this article to compare them, and indeed I can't because I have never used DXLog. From what contesters are saying and a quick review of its features I can see why it's acceptance is rising.

The other event is that hams I know are trying to working through how to change or replace their station automation to be compatible with DXLog. This led me to wonder whether DXLog has a similar feature to N1MM's RadioInfo broadcasts. It does. While I have no immediate interest or need to migrate to DXLog it is worthwhile to consider how I might use this feature. That is, can it be done and with how much effort? Can I make my software compatible with both N1MM and DXLog?

I began by comparing the RadioInfo message content of both DXLog and N1MM. My comparison is rudimentary since the documentation for DXLog left me puzzled in some instances, and of course I haven't used it. Both broadcast RadioInfo messages using UDP and XML encoding.

If the text in the diagram is difficult to read, click on the image or widen your browser window.

Dots are for data with no correspondence between DXLog and N1MM. Black dots are for data I do not need or use in my automation software; green dots are for N1MM data that I do use. Arrows are for data with correspondence between the applications, although there may be differences that my brief analysis did not uncover. Green arrows are for N1MM data that I use in my software; red arrows are for N1MM data that I don't use.

Some data that N1MM provides, and that I don't use in my software, are needed for SO2R. Equivalent data is provided over a separate interface using the OTRSP protocol. It is used to communicate with the SO2R-Mini in my station, and which I can control with N1MM keyboard commands.

Most of what I need would appear to be available from DXLog's RadioInfo messages. However it is not that simple. A protocol is more than messages and data: there are semantics (meaning) and the process logic that dictates when RadioInfo messages are broadcast. I can adjust how my software behaves but I have little leverage over the behaviour of the logging app.

Questions that occurred to me while reading about DXLog's RadioInfo messages include:

• When a RadioInfo message is sent and why.
• DXLog's focus behaviour in Windows is quite different because there is one window visible to Windows rather than the multiple windows used by N1MM. Returning Windows focus to DXLog is likely easier than I've found for N1MM.
  
• The internal automation hooks for antenna selection, rotator control and other items are likely dissimilar. That doesn't concern me since my software doesn't use those features of N1MM. Station automation software produced by others may be affected.
• I have to wonder whether the difference in data labels in several cases reflects different functionality. For example, <app> vs. <logger>, or <StationName> vs. <Station>.
  

Many of my questions likely have answers in the DXLog documentation, sparse as it is. I have yet to bother since I have no immediate interest in switching to DXLog. There are features of DXLog that appeal to contesters and may one day appeal to me. These seem to include:

• Navigation within a single window can be easier than with multiple windows. For example, to edit the log. This can be quite a problem with N1MM when focus changes erratically when, for example, you try to edit the log while continuing to operate. It's worse with SO2R and two keyboards.
• Extensive scripting support for customization and extension of functionality. Many contesters have their own peripherals and tools that can be difficult to integrate with N1MM using its existing APIs. Large multi-op stations in particular have been receptive to what DXLog offers.
  

I like to keep an open mind on the matter, so I need to consider what it would take to have my software work with DXLog. It may seem straight forward but it never is, as I hinted above. What might push me over the edge is if two keyboard SO2R works better in DXLog. There are anomalies with N1MM's implementation that the developers have shown little interest in addressing. It's critical to my style of operating contests.

What would be ideal is a standard for RadioInfo messages. That would permit station automation software, including my own, to more easily support N1MM, DXLog and perhaps other applications that choose to implement the standard. Agreeing on a standard, and a process to get there, could prove difficult, and perhaps impossible. 

Both applications are free so any customer pressure for a standard will be social rather than financial. But once in place it could encourage other application developers to participate. Of course there are other contest loggers, but they seem to have low or dwindling use. That is true for paid and free applications.

A RadioInfo standardization process led by N1MM and DXLog is not impossible. I am in no position to say whether the parties would be willing. The amateur radio universe has certainly done it with OTRSP, ADIF, Cabrillo, APRS and others. I doubt that there are significant technical barriers even though logging applications are in some respects more complex than other software applications developed for our hobby. 

There would have to be compromises on some points and agreed disagreements on others. Unresolved differences can be managed with permitting proprietary data items in RadioInfo message as is done for ADIF and other protocols. We did the same for the telecommunications standards I once worked on. While regrettable it is occasionally necessary for progress to be made.

Without an early effort to unify the content and behaviour of RadioInfo messages it will become more difficult. As third parties, such as me and my custom software, become dependent on N1MM or DXLog's unique RadioInfo implementations, the contest loggers will get push back if they make changes to make them work the same. 

Perhaps there is more flexibility on the DXLog team since N1MM's implementation of RadioInfo is more established and therefore has more dependent third party users. This, too, is not uncommon in the commercial world I am familiar with. There is an incentive for latecomers to exactly emulate the first movers. But it would be unwise to rely on the hope that it happens in this case.

As much as I'd like a RadioInfo standard, it is not the most likely outcome. The only solution then is to be application sensitive in third party code, and all the work that entails. I am already thinking ahead to do that in my station automation software. I am hopeful that it will not be difficult.

Reflections on IARU HF World Championship

I didn't operate in the IARU contest last weekend. However, my station was active with a guest in the operating chair: Vlad VE3TM. I didn't take a picture of him during the contest so I'll direct you to his QRZ page.

Since I'm not a fan of summer contests, it was an opportunity for Vlad to play with a bigger station than his small one in Ottawa. His station is also plagued with noise, a common occurrence in urban and suburban settings. 

I benefitted since this was the first time someone else operated my station in a contest. It was useful to learn how the station automation, operating desk layout and equipment performed for another contester. My job during the contest was to answer questions and fix any problems that might arise. Luckily, none did. I kept the coffee flowing and otherwise kept out of his way.

I designed my station automation to be intuitive but that is no guarantee that it will make sense to others who sit down to use it the first time. I directed Vlad to my description of it on the blog and that proved to be sufficient. I explained how the SO2R system worked and how to use the many rotators. There's a lot to learn and it can be overwhelming. I'm not the best judge of the learning required because I'm familiar with the station.

Aside from 2BSIQ, which Vlad has never done, the best way to exploit a large station is to always be running on one band and hunting for stations and multipliers on other bands. That takes practice. Propagation was such that only 15 meters delivered consistently strong runs, mainly to Europe. For the most part he kept the stack pointed northeast. Runs were limited on 20 and 40 meters to times when conditions were favourable. Part of that is due to stations migrating to the higher bands to take advantage of the high MUF.

Marginal conditions on the other bands -- 10, 80 and 160 -- proved difficult since he was in the low power category (100 watts). Vlad usually operates low power in contests and that's what he did in this one. Since my amps are manual tune (A1500 and L7) he avoided another point of complexity while operating an unfamiliar station.

At the end of the contest he had a respectable claimed score of over 700K points and more than 1200 contacts. Had he operated the full 24 hours and better able to exploit SO2R he could very well have had the top score in VE/W. Nevertheless, he enjoyed himself and I learned a few things about the station. That's a win for both of us.

Now I'd like to say a few words about the WRTC competition in Italy. It of course is run in concert with the IARU contest. Many participants make a point of working the competitors with their special call signs. There was a live scoreboard so that everyone could follow the competition, but with the operator identities hidden until after the contest.

The format and location of team statistics on the official web site keep changing so I don't know what you'll see when you click on the link. Before the final tally the claimed scores were shown. Those disappeared when the final scores became available a day or two later. First they were in a PDF file and then an HTML table, so who knows. You may have to take my word on a few points since you may find it difficult to check.

The final standings may be a surprise. Operators that consistently place high in major contests have mediocre results in WRTC, and vice versa. There are known and speculative reasons for this. The ones that occur to me include:

• Big scores in major contests most often are done with big stations, from stations that everyone needs for a multiplier, or from favourable geographic locations. Run fast and you'll do well.
  
• Skills to exploit the above benefits are not necessarily the skills needed to do well in WRTC. However, it does require many well-honed skills to do well with a big station, and a mediocre operator won't do well when dropped into the chair at the world's best station. The former include: SO2R; 2BSIQ; knowing where to point antennas, and when; picking complete calls from a pile up, correctly and on the first try; a recognizable call that is easy to copy; etc.
• WRTC rules reduce the value of many big gun skills. Many contesters love to find and call WRTC competitors, but aside from that they are little pistols in this contest. I'll just include one link (out of many) from my blog that enumerates skills you need to do well with a small station. Those accustomed to being a big gun may have rusty little pistol skills that they need in WRTC. You cannot simply point the antennas, cue the CQ machine and keep at it for 24 hours to place well.
  
• It has been said that contesting from Europe requires a local focus. There are more stations to work than, say, from within North America, and you must exploit that by working as many other Europeans as possible, despite the lower point value compared to DX contacts. I failed to understand that for a long time because I've never operated from Europe.
  

There is one point well worth noting from comparing the raw and final scores of the competitors: accuracy matters. The ranking of the top teams did not change but the margins did. After log checking the spread between first and second place dropped from 6% to 1%. They were very close to changing positions.

There are other notable points in the published statistics that I will not bother with. Have a close look and you will learn a few things, both good and bad. I'm sure it will be more interesting when the logs become public. I'll leave that job to others since I'm not that curious!

I have no WRTC ambitions. I enjoy watching many of the world's best contest operators do their utmost in these tests of skill and knowledge, and that's enough. Contest is recreation for me and an incentive to build a big station. That's all. 

My other great passion outside of amateur radio is cycling, and my attitude toward it is the same: it's recreation, and an incentive to hone what talents I may have. But I leave the racing to others. I didn't watch the WRTC but I do watch the Tour de France online. It was particularly enjoyable to cheer on home boy Michael Woods as he won a stage of the great race in grand style atop Puy du Dome that same weekend.

I don't know any Tour de France competitors but I do know several of the WRTC operators. It'll be interesting to hear the stories they have to tell when we next meet.

Re-boxing the Balun Designs 1113s

I repaired and reinstalled the common mode choke (balun) on the TH6. As readers may recall, the PVC enclosure for the Balun Designs 1113s shattered in several places. It was a valuable lesson on the limits of PVC and, of course, became blog fodder. In this article I'll describe how I went about the repair. The same balun on the TH7 was in good condition when I sold the pair this summer.

My first decision was how to mount the balun. The PVC enclosure is not mandatory and, indeed, many hams leave their ferrite toroid baluns unboxed so that they are well ventilated. No balun is perfectly efficient and there is heat dissipation, though small for well designed devices. Without an enclosure the balun is exposed to the elements, and that entails other risks.

My first thought was to mount the balun directly to resin backing plate. Mounted below the yagi boom it is shielded from most precipitation and is fully ventilated. 

I reconsidered when I inspected the balun and found that it does not match the device depicted on the manufacturer's web site. A picture of the currently marketed balun is on the right.

The ferrite is wound with small diameter coax. This is teflon dielectric coax that can handle far higher power than you might guess from its size. It's expensive but you need very little of it to wind baluns. Unlike RG213 and similarly sized coax, many turns can fit on a 2.4" toroid and the turns can be tightly wound (small minimum bend radius). This keeps the size of the balun small and able to fit in a standard 4" × 4" × 2" PVC electrical box. The downside is that the loss is high compared to larger coax, but that is not typically a problem at HF if the choking resistance is high (thousands of Ω).

You can see that the 1113s I have is not wound with coax. At some point the manufacturer switched from a wire-wound transmission line balun to coax without changing the product number. In my opinion the change in design is more than enough to require a product number change. Both designs can be perfectly fine but they are not the same. For example, their behaviour when subjected to high SWR or a highly unbalanced antenna (e.g. end fed wire). But let's move on.

As can be seen, instead of leaving the balun unboxed I opted for a replacement PVC electrical box. I had a spare on the shelf so it was a convenient choice that also eliminated my concerns about the weather implications of leaving it exposed. The non-coax design weighed on my decision because water, snow and ice on the bare wires is a concern.

To my surprise, the new box and the old were identical, right down to the manufacturer (Carlon) details embossed on the insides. I measured the positions of the several holes and drilled them in the same places on the new box. Not even a wire had to be bent for a perfect fit. The black cable ties with screw flanges provide support for the ferrite toroid to keep it suspended within the box.

The new box did not easily mount on the resin backing plate. The 4 mounting screws had to be forced through because they were ⅛" farther apart than the enclosure's screw tabs can accommodate. To compare the boxes I positioned the broken off tabs and old enclosure on the plate to check alignment. They were also not aligned to the backing plate holes. 

That made me wonder whether the lateral tension of the forced mounting screws played a role in the breakage. There's no good way to test that possibility. I reamed the holes on the backing plate so that the mounting screws dropped in without resistance.

Before taking it up the tower I did a quick bench test. I swept the SWR from 1 to 29 MHz with two 30 Ω resistors in series across the balun binding posts. The impedance is almost exactly 60 + j0 Ω at the lowest frequency (SWR 1.2) and it degrades, as expected, with increasing frequency. The inductance of the balun output pig tails and resistor leads is to blame.

The test was successful and also demonstrates an important lesson. Where does the balun end and the antenna begin? It's worth a few moments of thought.

The answer should be obvious: the antenna begins where the wires diverge on exiting the toroid (top centre). That must be the case since there is reduced field cancellation when the wires are not parallel, and approaches zero cancellation when they diverge as in a dipole. That is, the wires no longer form a transmission line.

The leads to the studs and from the studs to the physical antenna element are part of the radiating structure. Antenna manufacturers like Hy-Gain (I'm using this balun on a TH6) specify an exact length for the leads from the driven element clamps to the balun terminals for this very reason -- in this case the length is 6". Depending on the internal wiring of the balun the length of the driven element may need to be adjusted. Usually the effect is minor when the leads are short. For this balun that is 2" per side since the box width is 4". That's a small enough effect that I can ignore.

To reduce the risk of PVC breakage, this time I mounted the balun above the boom. It's more exposed but if the mounting tabs break there is less risk of catastrophic failure. I anticipate no weather-related trouble since the seal on the box is quite good. Sealing the coax connector is easier when it is on top so that should also do well despite being more exposed to the weather.

An accurate SWR measurement is difficult because my body was close to the driven element. On 10 meters the SWR was high with my body less than 1 meter from the driven element. The distance was limited by the short coax jumper to the analyzer and how far away I could stand without adjusting my harness. I figured it was good enough under the circumstances, and indeed the SWR measured in the shack was as it should be. Mission accomplished.

It'll be interesting to see how well the new PVC enclosure withstands the weather. It's an exact replacement for the original and we saw how that did after years of exposure in my station and, before that, in the station of its original owner.

I'll make one last observation before I close. Notice how the frequency range of the balun is specified by the manufacturer. The power rating is for 160 through 10 meters while its effective range is less. This is not surprising but can mislead if not read carefully. Also, the usable frequency in the text is 40 to 10 meters, not 40 to 6 meters as shown in the table. Is it carelessness or something more?

I have another of these baluns on the 80 meters inverted vee. I did not read the fine print before installing it or I would have reconsidered. However, although it may not be very effective on 80 that does not mean it is ineffective. For a non-directive antenna far from the house, even a common mode impedance of less than 1000 Ω can be sufficient. I haven't experienced any interaction problems when operating SO2R.

Common mode baluns have a frequency range determined by the ferrite mix, the transmission line and how it's wound. Unfortunately, measuring common mode rejection (impedance) is very difficult and experts often fail to agree on how to measure it and how to interpret the measurements. Be very careful whether you build or buy a common mode choke. The ferrite mix used by Balun Designs is supposedly custom which makes it difficult to judge without an independent measurement.

If you'd like to build your own common mode choke there are many resources. Perhaps one of the best places to learn is provided by K9YC.

High-voltage Antenna Length Relay

There are many ways to design a multi-band antenna. Each has its good and bad points, and all have been discussed on this blog multiple times. Common deficiencies of multi-band antennas are SWR bandwidth on the lowest bands, loss in the loading elements and pattern peculiarities on one or more bands (multiple lobes and nulls).

Examples include:

• Traps
• Fans (parallel elements from a common feed point)
• Adjustable matching network, in the shack or at the feed point
• Frequency sensitive transmission line sections
• Relays
• Motorized, adjustable length elements
  

All can be complex to home brew due to finicky design and construction. It is no surprise that most hams that need or want a multi-band antenna choose a commercial product in which all the complexities have, hopefully, been solved by someone else.

Perfection is impossible so tradeoffs are necessary. You choose an antenna where the tradeoffs are acceptable for your operating interests and what fits within your property and support structures. Many hams make their choice by price and size. Performance claims are either believed, ignored or deemed acceptable. Yet it is possible to avoid many of the deficits of multi-band antennas. That requires careful design, an understanding of antenna and network theory and practice, and test equipment.

It has been quite a long time since I last wrote an article about antenna design. I most often write about what I'm doing, of which there's an awful lot, and for the past year I spent little time designing antennas. I was recently motivated to investigate a multi-band challenge I have in my station. Although you may not have the same type of antenna in mind, the following discussion may be useful.

One of my objectives is to make the 160 meter mode of my 3-element 80 meter vertical yagi more effective without compromising 80 meter performance. Currently I switch in a loading coil and L-network at the antenna base. On air testing suggests a deficit of -6 to -7 db compared to the 160 meter shunt fed tower.

The big shunt-fed tower, which is an excellent top band antenna, is not available year round because I must roll up the radials for several months in spring and summer while the hay is growing and then harvested. Burying the radials is an option that I am unlikely to attempt this year, if at all. It isn't an easy project.

Alternatives that I considered long before I built the 80 meter array were impractical when it came time to build them. Before going further, consider skimming that article since it introduces several issues discussed in this one.

I am planning changes to the 80 meter array that will make it mechanically easier to improve its 160 meter performance, and prepare for 80 meter yagi performance improvements. Both depend on replacing the tower with a taller one. That will allow me to get rid of the long and problematic stinger.

A new stinger at the top of the taller tower would only be used for 160 meters. The tower itself, and probably with the help of a short "tuning" pipe at the top, will be a resonant ¼λ on 80 meters. Modest loading at the base of the stinger will resonate it on 160 meters. The base coil will be removed and the L-network redesigned for the measured impedance.

With an acre of radials (almost 2000 meters of wire) under the 5 vertical elements of the 80 meter yagi, the 160 mode of the array will be far more effective with negligible impact on the 80 meter array. Because it will be shorter than a ¼λ on 160 the load cannot be loss free, the new design will likely be 2 db less effective than the shunt-fed tower, but that's a notable improvement over the present design. That will let me be competitive on top band during the summer when the shunt fed tower is unavailable.

The drawings at right show just the essential aspects of the existing (left) and proposed (right) construction. Since the new stinger cannot extend 20 meters above the tower, loading will still be required on 160 meters. Support ropes for the parasitic wire elements would attach to the top of the taller tower rather than the top of the stinger, as in currently the case. That allows the stinger to be lighter duty. If it is 8 to 10 meters long, the 160 meter vertical will be about ⅜λ, so the loading coil can be small and low loss.

The stinger will have to be switched by relay. Use of a trap or parallel (fan) vertical have been discarded due their negative effects on 80 meter yagi performance and narrow bandwidth on both 80 and 160 meters. A switched stinger is far superior in this regard. The primary challenge is with the switching between 80 and 160 meters. 80 meter impacts must also be quantified. 

The design can be done in the comfort of my shack by computer modelling. My tool of choice is EZNEC and its version of the NEC2 engine. I began by building a simple model to investigate switching methods, and refining that until I had a workable design. 

This article focusses on the simple model to investigate switching behaviour. After the tower is replaced and I can take measurements of the new array, I will refine the design.

Modelling the relay

Relays are not perfect devices. The coil requires wires for power, wires to the contacts have inductance, closed contacts have resistance and there is capacitance between open contacts. When the relay contacts are open, as they are in this application for operation on 80 meters, the voltage across the contacts can be very high, well over 1000 volts for legal limit power. This is a case where my relay phobia may be justified.

The EZNEC model ignores the wires powering the coil, assuming they are suitably routed and choked to isolate them from the high adjacent RF field. We'll return to these challenges later.

You may have to expand the picture to read the tables. There are wires for the 80 meter vertical, the 160 meter stinger and a short connecting wire containing an RLC load. The load is modelled as a pure capacitance. A small value for open relay contacts (80 meters) and a short for closed contacts (160 meters). 

Relay spec sheets may or may not show the capacitance for open contacts as measured at the terminals. The capacitance depends on relay construction, comprised of that between the contacts and the wires to the relay terminals, and the housing and other conductors if they are significant. The reactance decreases with frequency so that "leakage" is greater on the higher bands. In this instance the capacitance is only relevant on 80 meters where the contacts are open.

The SWR curves were drawn with a load capacitance of 0.01 pF. Up to 2 pf the R and X components change by no more than 2 to 3 Ω. That is negligible. With a good radial system (which I have) the impedance is low enough that a matching network may be helpful. For a poor radial system the series ground loss would improve the match at 50 Ω without need for a matching network.

I adjusted the wire lengths (all have a 40 mm diameter for simplicity in the initial models) to resonate the 80 and 160 modes where I want them. Relay lead inductance is ignored but they are almost negligible for these long wavelengths and are easy to compensate with length adjustments in the built antenna.

Conducted 80 meter current in the 160 meter stinger peaks in the centre of its length. For 1 pf of relay capacitance the peak current is 6% of that at the base of the vertical. It rises to 7% for 2 pf. That's comfortably small but may impact F/B when the array is operated in its directional modes on 80. I am deferring the exploration of that interaction to a later time.

Differences between the SWR curves and gain on both bands are negligible when compared for single-band verticals; that is, without the relay, and the stinger removed from the model on 80 meters. That is what I expected. So far so good.

Relay requirements

You don't often see antennas like this, using a relay to switch bands. Traps are far more common in this application despite their inherent loss and increasing the antenna Q on both bands. A relay has neither of those disadvantages. This is readily apparent in the EZNEC model's load data with the relay open for operation on 80 meters.

On any antenna with an open end -- which is almost all antennas other than closed loops -- the current at the ends of elements falls to almost zero and the voltage is high. Should you attempt to feed the antenna at one of these locations -- such as an EFHW (end fed half wave) -- the impedance is very high. Matching it to 50 Ω can be done, at the expense of transformer loss and difficult to control common mode current. In our case, it is only the voltage that needs to be tamed.

Relays exist that can withstand over 1500 volts of RF but they are not ones you commonly encounter. Contact flash over voltage is misleading since the spec is typically for DC or the low frequency AC found in power systems. The coil, insulators and conductors behave differently with RF flowing across the contacts. When the contacts are open, some RF current will flow due to stray capacitance or due to humid or polluted air. 

The resistance can be higher than expected when the contacts are closed, and the capacitance higher when the contacts are open. Further, the actual voltage could be higher than in the model due to voltage modelled in the wire segment rather than at the wire tip, and various environment and construction details. I would at least double the relay's voltage breakdown spec to be safe. A properly rated relay can still be destroyed by accidental hot switching. Luckily that's unlikely since a relay for changing bands is only operated when the transmitter is idle.

There are two classes of high RF voltage mitigation: use a relay designed for the application, or design the antenna so as to reduce the voltage where the relay is placed.

The preferred choice for applications like this is a vacuum relay. They are available with breakdown voltage ratings starting at 2 kV and going much higher. Unfortunately they are expensive: starting at well over $100. There is a good market for surplus and used vacuum relays to limit the expense, if you can find those with suitable specs.

There are other considerations: they can be fragile, difficult to mount and protect on a tower, detailed specs may be difficult to locate (e.g. capacitance for power and signal relays), and have inconvenient coil voltage (24 to 28 VDC is most common on the used market). Choose carefully.

Mitigation measures

There are ways to reduce the stress on the relay to reduce the risk of failure, and in some cases it may be possible to use a conventional open-frame or sealed relay. These are the ones I modelled, and all work, though not necessarily very well:

• Capacitance hat below the relay
• Leakage capacitor across the relay contacts
• Large diameter wire (tower) below the relay
  

The models I developed to test these methods are solely intended for the purpose of exploration. I will make no recommendations or provide dimensions for a real antenna. NEC2 and pretty well all modelling engines are not highly reliable with respect to voltage, current and impedance at the open ends of wires. Real antennas and relay terminal voltages will never exactly match the models. But they can come close, and that makes the modelling experiment worthwhile.

The capacitance hat option (left diagram) was a disappointment. The voltage across the relay only dropped by 25% with two arms that are 5 meters long. For an antenna that is 20 meters long the effect is severe and must be corrected by shortening the vertical quite a lot. That's unacceptable since the shorter length would degrade performance of the 80 meter array. I did not bother to dig deeper to quantify the effect because a 25% voltage reduction isn't enough to eliminate the vacuum relay.

The reason I expected better from the capacitance hat is that it partially mimics a large diameter wire (as in the right diagram) which is known to reduce corona effects found with sharper antenna tips. Instead it behaved as if the voltage was measured inward of an ordinary element or T-top vertical.

To model the "fat" lower wire (right diagram) I increased the diameter of the 40 mm wire to 200 mm (8"). This is quite close to the top (#1) Delhi DMX tower section I am currently using, and will be again when two larger bottom sections are added to the tower. Tower taper can be ignored for the experimental model since we are interested in the voltage at the top of the tower and not its exact height. The model's wire containing the relay (again, a low-value series capacitance load) was made 2 mm (AWG 12), while the 160 meter stinger diameter remained at 40 mm (1.6").

This option is promising. The voltage across the simulated relay contacts dropped from 1500 to 850 volts, which is more than 40%. The resonant frequency on 80 meters barely changed. The voltage reduction is enough to consider using an inexpensive relay with contact and wiring isolation voltage of 2000 volts or more. The model is not definitive since there are factors to be considered in a physical antenna. For example, the relay is likely not close to the tower top plate because a tuning stinger may be required for height adjustment. There are also the effects of humidity, pollution (dirt particles in the air) and precipitation.

Despite the concerns, it may be worth the experiment when the antenna is rebuilt. Flea market open-frame relays are inexpensive enough to risk destroying a few! Since I am designing for high power it is highly recommended to do the experiment using an amplifier with fast-acting fault protection. Luckily I have one of those.

A capacitor across the relay contacts (middle diagram, above) may be an unusual option since until now we've been trying to minimize stray capacitance due to the relay. The trick is to increase the capacitance to pass enough current to cause the voltage to fall to a value where a conventional relay can be used. Reactance decreases with increasing capacitance.

The 80 meter resonant frequency drops since the series capacitor electrically lengthens the anteanna, and that can be a problem. There is no effect on 160 meters because the capacitor is shorted by the closed relay contacts. We need to know how much capacitance is needed to substantially lower the voltage across the relay while avoiding excess lowering of the 80 meter resonant frequency, as we saw for the capacitance hat.

The result is not good. It took 30 pf to reduce the voltage by 25%, and the resonant frequency dropped ~10% to 3.2 MHz. This is very similar to the 5 meter long capacitance hat described above. I suppose that should be expected since a capacitor and a capacitance hat are close relatives. Current in the 160 meter stinger peak at just under 25% of that in the 80 meter wire (tower). Gain of the vertical on 80 meters dropped by -0.1 db, which is negligible. However, the stinger current could be a problem in the array's yagi modes, but I have not run the model as yet.

The only promising mitigation measure is the "fat tower" option; the others have too many deficits. I may play with the model further to see if I can improve it beyond what I did for this article. It would only be for curiosity since I now know enough to proceed.

Further considerations

Whether a vacuum relay or the ordinary kind is placed atop the top, wiring it to the switching system at the base of the tower must be done with care or the wiring itself will modify the antenna's behaviour. The usual way of doing this is to run the cable inside the tower. Skin effect is our friend in since the antenna currents primarily run on the outside of the conductor. It is more complicated with a lattice tower than a solid cylinder (wire or tube) but the current flowing along the inside of the tower should be much lower than on the outside.

Spacers must be used to keep the wires several inches from the tower surfaces. The tower is not grounded so two wires are needed, one being DC ground. RF chokes should be placed on both wires at both ends of the cable and another set midway. That will detune the relay wiring on 80 and 160 meters and keep RF out of the switching electronics. The cable will have to be carefully routed around the top tower plate. Check the relay specs to ensure that the minimum voltage breakdown between the contact wires and the coil wires is at least as good as we need between the relay contacts and wires.

If the stray capacitance of the relay is very low and the loading elements on the stinger keep it far from resonance on 80 meters, there should be little enough current on the stinger to keep it from disturbing the 80 meter yagi modes. This was modelled and discussed earlier, but I have yet to model the full 80 meter yagi to confirm that the stinger current does not degrade the yagi pattern. It probably won't but it would be foolish not to check.

That said, there is reason to add a capacitor across across the relay contacts. We want a small value that does not appreciably load the 80 meter vertical. Perhaps no more than 5 pf. Its purpose is to damp corona effects at the relay that can amplify the voltage across the relay contacts when the humidity is low. A high value resistor should be added in parallel to bleed static charge on the tower and stinger when it rains or snows. Vacuum relays can't do the impossible so we should do what we can to reduce the stress on this valuable device.

The top of the tower can be made wider with a wire cage between the top plate and the base of the relay to lower the voltage across the relay's open contacts. A capacitance hat won't do that, as we've seen, because it is too thin. The cage complicates construction and may not be worth the trouble just to avoid a vacuum relay. The structure would also make working at the top of the tower awkward and possibly dangerous. Out of curiosity I may model it regardless.

Attaching the 160 meter stinger to the tower has its own challenges. It will be quite tall with substantial bending stress at the bottom. There are a couple of ways it can be done: A) inline at the top of the 80 meter vertical's short tuning pipe, or B) bracketed to the tower. The loading coil and relay should be close to the bottom of the stinger. High quality and mechanically strong insulators (red) are needed since, as we know, the voltage can be very high. 

I believe the best approach is to bracket the stinger to the tower. The mechanical demands on the insulation are far less than placing it inline, especially for a long stinger. For example, one or two layers of PVC pipe can be placed over the stinger where the tower bracket clamps to it. One layer may be enough if excess voltage due corona and static are managed as see above.

Next steps

While this article is about my particular antenna, it is applicable to other vertical multi-band antennas of the same design. The technical challenge to incorporate a relay is modest and may be well worth the effort to achieve maximum performance. This can be particularly welcome on the low HF bands where a higher Q method such as traps significantly reduces the SWR bandwidth.

I am undecided whether to begin working on the 80 meter array this year. I am behind with other projects and I am trying to take a rest from major projects this year. The earliest it will happen is this autumn after the insects die off. The project will proceed in stages to avoid finding myself without a good 80 meter antenna when contest season begins in earnest. 

The 160 meter change described in this article is more likely to be undertaken in 2024. Replacing the tower and guy anchors must be done first, and that requires taking the tower down and doing a lot of digging and concrete work. After the tower is replaced I can attach the wire elements to the top of the new tower and not have to change any of the existing switching electronics and matching networks. 

Unlike the models in this article, the physical stinger height for 160 meters will not be full size (20 meters). That will lower the SWR bandwidth on 160 but not on 80 meters. Loading is irrelevant to the characteristics of the relay and mitigation methods.

One item I'd like to revisit for the blog is a survey of the alternative methods for multi-banding vertical antennas that I listed but did not delve into at the start of the article. It may be worthwhile to compare and contrast them in more detail. I've done all this work in the past but my perspective has changed. Perhaps this winter.