Lifting the 10 Meter Yagis

Lifting the newly built 10 meter yagis onto the tower was done by tram line in a fashion no different than I've done before. However, I feel that it is worthwhile to review how it was done and to mention a few noteworthy points about the lift and antenna behaviour. A full assessment of their performance will have to wait until I gain more experience with them which, as you'll see, is not yet possible. 

Both of the 10 meter yagis were tuned using the same rope tram line used to lift the TH6 to its new rotatable side mount at around the 75' level of the 150' tower. The tram line and haul rope were then raised 40' and used to lift the lower yagi to its perch at 110' (on left). The side mounted lower yagi is fixed to Europe. 

The lift of the lower yagi was done without helpers. It was not difficult to achieve good balance and orientation for a small yagi and it is light enough to be raised by one fit individual. The lift was incident free so up I went and bolted it to the side mount bracket. That was the easy one of the pair.

To lower the antennas that were up top and to raise the upper yagi a steel tram line was anchored to a large and healthy tree in the bush at the opposite end of the hay field. I previously mentioned clearing a path to the chosen tree. Although not needed for raising this yagi, or for the preceding lowering of the TH7 and 40 meter dipole, using the tree was a trial run of the basic setup that I plan to use for raising the 3 element 40 meter yagi that is currently under construction. That's a big healthy tree, and a hefty chain to match.

As I briefly mentioned in a previous article, the TH7 and 40 meter dipole at the top of the tower were taken down earlier in October. Several friends came over to help on the ground and, as usual, I did the work on the tower. Only one friend (VE3KAE) was needed to raise the upper 10 meter yagi on the same tram line. For these higher jobs I prefer a helper even though in this case the upper 10 meter yagi is lighter than the lower yagi that I lifted on my own.

Notice the rope around the big tree? It is a safety line from the tree to the tram line cable termination. Winches are mechanical devices that can fail due to excess use and defects. Nothing is forever. When the tram line is at the desired tension, the rope is pulled tight and serves as a backup in case a problem arises. It does happen, as I can assure you from personal experience. No injury resulted in that incident (people or antennas) but it easily could have. Use a safety line.

Just because I like it, I included a shot of the upper yagi from the top of the 150' tower when it was less than 100' feet away (the tram line is 350' long, or 110 meters). Later I describe how I handled it when it arrived. The rigging for the tram ride is not always ideal for an easy connection to the mast.

The bracket for the lower yagi previously supported the TH6 that is now on a rotatable side mount further down the tower. I took the opportunity to improve the bracket and replace clamps that were showing their age. Although there are 5 elements squeezed onto a 24' boom, the wide director spacing of the optimized design allows the 10 meter yagi to comfortably fit on the bracket in any orientation without any element getting overly close to the tower.

There are nevertheless interactions, as I fully expected. For example, the SWR is not what it was when tuned. There are guys off the rear sides and one in front, towards Europe. Per my guy wire interaction model the interaction is likely to be primarily with the rear guys. I have not yet confirmed this in a model.

Although the guys are not terribly close (the picture is deceiving) and largely orthogonal to the antenna elements it takes little to disturb the pattern of a 10 meter antenna. The segments of the broken up guys are non-resonant on 10 meters but are large enough to couple regardless. I had a similar effect with the side mount 15 meter yagi but not the side mount 20 meter yagi. Size matters. I expect the antenna to perform well regardless since the impedance excursion is small and I know from other hams with similar installations and my own experience that gain remains very good.

I am unconcerned about a few minor lobes in the pattern since my interest is contests and a little radiation in various directions can pay dividends, and modest interactions don't reduce the forward gain by much. The minor lobes attract more callers without allowing too much QRM. Others with different operating interests might be more concerned. The only practical way to achieve a perfect pattern for side mounted 10 meter yagis (and for 6 meters and other VHF bands) is to use non-conductive guys.

Unlike the upper 10 meter yagi the SWR on the lower yagi is not what it was after the gamma match was adjusted at a lower height. I don't yet know how much of the change is due to tower and guy interactions and how much is due to me. The human body couples poorly but noticably on 10 meters. Antenna behaviour is affected by the proximity of my body (notice the reflection in the left panel).

The effect is reduced by standing vertically below the boom and by standing farther away. The good SWR of the upper yagi was not so good when I measured it the same way as I measured the lower yagi. The coax from the boom to the analyzer was only 2 meters long. The SWR on the right was measured when the antenna was at the top of the mast and I was at the bottom of the mast.

Now let's turn back to the raising of the upper yagi. Alan VE3KAE took a picture of me (on the left) as I took possession of the yagi at the top of the tram line. With the tram line slackened we lowered the antenna until the boom-to-mast clamp rested on the top plate of the tower. This was necessary so that I could move the chains and shackles for the tram pulley and haul rope onto the far side of the clamp plate.

The geometry of this rigging doesn't always make it easy to do the whole job with the same rigging. The large plate and integrated boom truss support made the transition mandatory. I was able to get one saddle clamp attached in this awkward orientation so there was no risk of an accident while I did the rigging. To save time I tossed no longer required chains and attachments to the ground. 

Always make sure to get your ground crew out of the way when you do this and only if you can comfortably send the material clear of guys and the antennas below. Stuff like this easily survives the 150' fall and it saves me the time and effort of carrying the rigging down with me. The steel strikes the ground fast enough that it is partially buried. On this climb I somehow knocked loose the little radio I used to talk to the ground crew and down it went. Unbelievably it survived the fall and still works!

With the antenna firmly clamped to the mast I rotated the boom so the elements were perfectly horizontal. I then adjusted the truss turnbuckles to level the boom. The turnbuckles are out of reach when the antenna is raised to the top of the mast. The next step was to remove the anchor plate (for the tram line and haul line pulley) from the mast, step the mast and hook a pulley to the top of the mast. The haul rope is threaded through this pulley down to the antenna.

It's a tedious process because I must then remove the steps to slide the antenna up the mast. Everything must be done with safety foremost, and that what takes the time. The procedure of the lift itself isn't difficult. I am deliberately avoiding details of mast stepping and mast climbing so that I don't give any ideas to overly enthusiastic readers. This is not a job for the tower novice.

With the rope pulled tight I loosen the mast clamps. While my friend pulls the rope I push the antenna upward. I again step the mast and follow it to the top. It's faster to remove the clamps and let the antenna climb freely, but it is not so easy to do the fine mechanical work of inserting the clamps (and not dropping hardware!) while perched at the top of the mast. So I do it the slower way.

To get the antenna to the very top requires rigging the haul rope to the bottom of the antenna. Otherwise you can't lift to the very top of the mast. Even so the rope jammed within inches of the top so we called it a day and I tightened the clamps, removed the rigging and climbed down.

I dress the cables accounting for the arbitrary direction the antenna ended up pointing. My home brew prop pitch motor controller allows infinite adjustment, and the direction pot on the tower has a 10:1 drive ratio, so that also allows essentially infinite adjustment. Calibration in the shack took 5 seconds.

The antenna works and it is ready for action. The lower side mount yagi will be without a coax connection until I build a 10 meter stack switch. It will make a triplet with the L-network 20 meter and 15 meter stack switches I built.

I'll close with a pretty picture. We are looking along the boom of the upper yagi towards Japan. The solar flux is high enough to work Japan on 15 meters and it won't be long before they are booming in on 10 meters. It is no accident that the 10 meter yagi project occurred this year: the solar cycle allowed me to delay until now, but no longer. 2022 is going to be a very good year for HF propagation.

Headset Woes

I operate SSB from time to time even though it is not my favourite mode. My usual forays to phone are contests and DXpeditions. I periodically use my big signal to run DX stations on phone, for fun and a change of pace. Microphones are otherwise pushed aside or unplugged to tidy the operating desk.

There are several styles of microphone with which we are all familiar:

• Handheld
• Desktop
• Boom
  
• Headset

Handhelds are fine for the occasional use at the operating desk, but are more appropriate for mobile operators. Having to hold a PTT button is tiresome for long operating sessions and contribute to transmitted noise due to hand pressure and movement. For my style of operating a hand mic is purely for emergencies when my preferred mic fails. Most rigs include one so I have quite the collection.

Many HF operators love desktop mics. Quality is often excellent and they are suitable for both PTT and VOX. I don't like them because you have to hold your head still, as if it was in a virtual vice. That makes it difficult to fiddle with the computer and rig while talking and it is uncomfortable for long transmissions and operating sessions. It blocks keyboard access, takes up valuable desk space and blocks my view of the rig.

Boom mics share many of the characteristics of desktop mics but allow your head to remain upright because they can be positioned more conveniently. Decades ago, my friends and I used to tape small mics on swivel stands repurposed from desk lamps for contest operating. PTT is a foot switch or VOX. I gave up on them after my first experience with a headset.

Headsets are worn on the head and include headphones and a microphone in a single unit. Like many contesters, this is what I prefer. Headsets have significant advantages:

• Do not impair vision and access to the keyboard and equipment
• Consistent audio level and quality since no matter how your head or body moves the mic is always in the same position relative to the mouth
  

It is no surprise that there are a variety of headset options that are of interest or concern to hams:

• Comfort when worn for long periods (typical for contesters and DXpeditioners)
• 3.5 mm or USB connectors
• Wired or wireless
• Electret or dynamic mic element
  
• Flat or voice communication audio response
  
• Enclosed or open ear enclosures for the headphones
  
• Servicability
  
• Quality: longevity; resistance to abuse; reliability
  

Once the domain of hams and professional communicators, headsets are now used for e-games, video and voice internet communications, and call centres. Supply serves the demand, so the market offers an abundance of choices for those applications. 

Unfortunately the quality is often poor and price is an unreliable indicator of quality. Since most products are targets at internet and computer use, those of good quality may score low on our requirements. Products specifically made for hams and other communicators also have deficiencies. There are more choices than ever but few that are great.

Let's look more deeply at several of the options that are pertinent to HF operating.

Comfort

Let's face it, most headphones and headsets are uncomfortable after several hours. For a contester that's a problem. When my head and ears are throbbing in discomfort, and sometimes pain, it is difficult to continue. There are very expensive headsets that are uncomfortable and there are cheap ones that are comfortable. Sometimes it helps to take my glasses off since it reduces a critical pressure point and my vision is adequate to operate the computer and radios.

One of the most comfortable and reasonably priced headsets with full ear enclosures is the Yamaha CM500 (pictured above). Many contesters agree. Unfortunately it has been discontinued and there is a dwindling supply. Although it is reputed to be robust that is relative. The mic on mine quit and it is pretty well impossible to service.

Many similar looking headsets are not as comfortable. The headband of some, but not all headsets can be spread to lessen the pressure. 

If the plastics used for the band or the ear enclosures are stiff or thin there is very little that can be done to make them comfortable. The comfortable plastic covers on many headsets wear out quickly because they are soft and pliable. This happened to my Koss SB45 headset, along with a broken wire in the cord (see picture at right).

Don't expect to be allowed to try on a pair in a store. Your best bet may be to ask your friends with similar operating habits for recommendations. Only ask those with fewer opinions and more operating experience.

Personally, I have always favoured open air headsets and headphones that sit on the ear without an enclosure. My ancient Heil headset is like that, and if the cord hadn't failed I might have continued using it. Most hams need ear enclosures to eliminate household noise, but if you can close the door of the shack that may be good enough unless you have amplifiers with big fan noise.

Connectors

You will find that many headsets have a USB cable for direct connection to a computer. You can use these if your logging software or other application can route the audio to the rig mic and headphone connectors via the sound card ports. Contesters often do this since it simplifies station cabling, mutes the mic while playing voice messages, recording messages on the fly and support audio routing for SO2R. For example, the N1MM contest logging application. That may be difficult to do outside of contests and without specialized software.

There are adapters available to convert USB to 3.5 mm stereo for both headphone and mic audio. Otherwise you may prefer to choose headset with 3.5 mm plugs. Many older radios, and a few new ones, have unique mic connectors for which you'll need adapters.

The choice will depend on your station and your operating preferences. Be very careful to read the fine print before ordering or you'll waste your money.

Wireless

Headset cords are a common failure point, and they often get in the way. It is inconvenient to be "tethered". Only some of the most expensive headsets allow cord replacement. You can try to replace or repair cords on other products if you have endless patience and you are prepared to employ destructive measures to pry them open, and try to reseal them afterwards.

Wireless headsets would seem to be desirable since there is no cord. The problem is that battery life is measured in hours, and that is insufficient for operating a contest. For some, the battery pack goes has to be placed in a shirt pocket. The other end of the wireless link is typically only for connection to a computer, and that may not work for you.

Mic element

The vast majority of headsets have a flat response. For "talk power" hams prefer a strong mid-range peak that accentuates communications at the expense of fidelity. Long ago the only good option was to select a mic element designed to do this. I had one of those elements for my first Heil headset. Special elements are no longer necessary since most high end rigs include a programmable equalizer. 

When combined with a speech processor the improvement in average power, and therefore being copied by others, can be quite impressive. There is no need to over-amplify or over-process the audio. If you do expect excess distortion and splatter.

What you never want to do is use one of those voice accentuating mic elements and an equalizer that does the same. Use one or the other. I prefer a flat electret mic for my headsets. Swapping headsets has no effect on audio processing and you have a far greater choice of commercial headsets. Leave the equalization to the rig.

You also need to consider the type of mic element. There are really only two that are of interest to us: dynamic and electret. There are still transceivers that only support dynamic mics, yet the majority of mics have an electret element. There are a few modern transceivers that have insufficient gain for the lower output dynamic mic, and for those you must use an electret element. 

Apart from gain, an important difference is that the electret mic requires DC power. Pretty well every computer sound card has this feature, as do many modern transceivers. For rigs that don't you'll need to buy or build an adapter that AC couples the audio and supplies DC bias to the element. The Yamaha CM500 includes a battery-operated adapter. I customized an adapter than connect a 3.5 mm stereo plug to the 8-pin front panel jack of Yaesu rigs, and taps the DC pin to bias an electret element and a capacitor to block the DC from the audio signal path.

Reliability and servicability

Perhaps the least reliable part of a headset is the cord. Every movement of your head makes it shake and it bends when you take them off, so that over time the thin wire fatigues. Thicker insulation and strain relievers help but do not cure the problem. Very few headsets allow cord replacement, or of any other part for that matter. Not even the plastic ear pads can be replaced when they inevitably wear out.

I have found that the cheaper headsets are not up to heavy use day after day. The cord becomes intermittent, the mic element fails or the plastic tears or crumbles. They are sealed units that cannot be opened without damaging them to a lesser or greater extent. There are expensive headsets that are easy to repair and replacement parts can be ordered. Unless you really like those headsets it is poor economy since several cheaper and often more comfortable headsets can be purchased for the same price.

I have looked around and canvassed fellow contesters and my reluctant conclusion is that headsets have a limited lifetime. They are perishable items, like batteries. When they fail, you discard them and buy another headset. There just doesn't appear to be a sensible alternative. There are contesters who have stockpiled several of their favourite headsets in case they need them fast and when they are no longer manufactured.

Since I have a strong preference for headsets in contests, my intention moving forward is to only use those headsets for contests. The rest of the time I will use other headsets, or headphones for non-voice modes like CW. Swapping headsets and headphones before and after contests is annoying but a practical way to extend their service life.

CQ WW is on the horizon

We are days away from the largest phone contest of the year: CQ WW. Since I have not been able to pick up the replacement CM500 a friend bought for me (we live far apart) I purchased another Koss 45 headset. It is less comfortable and the cord is flimsy, but from my experience they are acceptable for an 48 hour contest.

Although I don't intend to put in an all-band full-time effort, the rapid approach of CQ WW motivated me to act. So I went to a popular on-line site and put in my order. The headset arrived the next day and is now in use. If only the rest of my station was as ready!

I have been tardy with blog articles because I am exceptionally busy with tower and antenna work, and the weather isn't getting any warmer. I want the work done by mid-November. Expect more about those projects in upcoming articles.

Critter Protection for the 80 Meter Array

This is not the first time I've talked about critter damage to my 80 meter vertical yagi. The cables, wires and enclosures are close to the ground and, for some reason I don't understand, deer appear to enjoy chewing on all of it. At least, I think it's the deer, going from the marks of mastication on plastic components. Maybe they're curious or bored. Regardless of the reason, the unwanted repair work is aggravating.

The bouts of damage this fall motivated me to take preventive measures that I've been avoiding. There are temporary and permanent fixes, with the temporary ones to be changed to permanent when I have more time. I am very busy this month with other projects.

I'll step through the work I've done to give an idea of what I'm dealing with. Although one item is for safety and not critter protection, I'll mention it anyway. Let's cover it first.

All turnbuckles should have safety cables. The cables tie the guy to the ground anchor. If the turnbuckle fails the cable prevents the tower from collapsing. The tower in the 80 meter array is the driven element and it supports the parasitic wire elements. 

The guy tension is quite low, just enough to keep the tower stable for climbing. I've been meaning to get this job done, and after 3 years its time has come.

One disadvantage of safeties is that the turnbuckle cannot be adjusted without temporarily removing the safety. This is difficult on the big towers since the safeties are ¼" EHS. It is a struggle to route the tough, springy stuff through the eyelets and bodies of the 4 turnbuckles without kinking the cable. It is also a potentially dangerous task. Bent EHS that slips out of your grip springs back forcefully and can do serious injury. The ⅛" aircraft cable used for the 80 meter tower turnbuckles is far easier to work with.

The parasitic elements are sloped T-shaped wires per the original K3LR design. Both ends of the sloping wire (top of the T) are supported by ropes: one to the top of the driven element and one to the ground anchor. Tension on the ropes keeps the element in place.

Deer enjoy chewing rope. That was a surprise to me, but I'm no expert on deer behaviour. Cutting a support rope disables two directions of the array. The other two directions are impaired since all the parasitic elements will sag when one rope is cut. It is an easy repair, but an aggravating one to have to do (again).

The solution is the same as it is for towers guyed with non-metallic cable such as Phillystran. The bottom of the guy is steel and connects to the main guy at a height that is sufficient to avoid accidental damage from mowers, walkers, tractors and critters. Due to the slope of the element the steel cable needs to be at least 10' (3 m) long to be safe from curious deer.

The cables are 3/16" aircraft cable since it was loitering in my junk box with no other obvious use. In this specific application almost any size of steel will do. I did not cut the ropes to size after installing the steel cables in case I need them in the future. The deer are free to chew these trailing ends if they want. The dangling extra rope was attached to the steel cable after the picture was taken.

Protecting the exposed control cables, antenna wires and enclosures at the 5 elements requires cages. The cages must be non-conductive, anchored to the ground, allow rain and snow to drain, not encourage insects to shelter there and, finally, discourage curious animals. I have a few candidate designs in mind that I can build with material on hand.

The project is not difficult except that time is needed, and right now that is in short supply. As a temporary measure I did something that was fast, cheap and ugly. I wrapped all 5 elements in plastic sheet (yes, that includes the tower base!).  The black plastic is resistant to UV from my experience using it in other temporary weatherproofing jobs.

It is obviously a poor physical barrier since any animal can easily tear through it. What I am betting on is a visual deterrent since deer are not too smart. If they see a large black blob they will likely leave it alone. What they can't see probably won't attract their attention.

Hopefully this will suffice a few months until I can build a permanent solution. The plastic wrap is easy to remove should antenna repairs be required. It is held together with black electrical tape that is easy to peel off and then back on. If it tears, well, I have an endless supply of plastic sheet.

They have never chewed on exposed Heliax, which is exposed in numerous places and is much thicker than the cables and wires they have damaged. Apparently size matters, and that is why I am guessing the "big black blob" solution might work.

Speaking of Heliax, there is one more job to be done. Although no animal has attacked the many runs of Heliax exposed at ground level, in my enthusiasm I decided to protect the exposed Heliax to the 80 meter array. The underground run of LDF4 from the electronics at the tower base is only to the edge of the radial field. It connects to a long run of LDF5 that is mostly buried but overground near the junction due to trees roots and rocks.

I wrapped the exposed junction in chicken wire. Steel discourages critters, so even though the plastic outer layer can be touched through the mesh it is unlikely to suffer bites or chewing. Rodents might but they have yet to touch any wires and cables that are on the ground or shallowly buried.

Now I cross my fingers and hope that these measures will provide lasting protection. Clearly there is more work to be done, and it is a good project during winter when tower work is suspended. 

As an aside, here is a hint of where my time is being spent. Notice that the 150' tower has no antennas on top. The TH7 and experimental 40 meter dipole were taken down last week with the assistance of several friends. 

The TH7 will remain on the ground this winter and may be permanently retired. The 40 meter dipole was inspected to see that it suffered no stress fractures or other problems. It passed inspection so I am continuing with the element design to make the director and reflector for the 3-element yagi I am building.

The 40 meter yagi in particular is responsible for my lack of time for smaller projects this fall. I will soon be raising the 10 meter yagis onto this tower (one fixed, one rotatable) in preparation for the big 40 meter lift. More about these and other projects in future articles.

6 Meter DXing Using the Buddy System

In my 6 meter season wrap-up I mentioned that I and a couple of friends all passed the 100 country DXCC mark (confirmations) on 6 meters this year, and that called for a celebration. With the gradual rollback of pandemic restrictions that became possible and we had our get-together in late August. 

Sharing the accomplishment with friends, when all have the same accomplishment to celebrate, is particularly enjoyable. It is not really coincidental that the three of us passed the DXCC milestone in the same year. As I've said on multiple occasions, the digital modes changed the DX game forever on 6 meters. Despite my strong preference for the "traditional" modes, FT8 in particular is well suited to the brief and elusive nature of most long DX paths via sporadic E propagation on 6 meters, and its occasional tie-up with TEP to reach across the equator. 

We are shown at the QTH of Cezar VE3LYC (on the left) having a BBQ, complete with a variety of Romanian treats. The latter was particularly welcome since my family comes from Romania and with the passing of my parents it brought back many pleasant memories. The picture was taken by Lucy, Cezar's wife, who is to be thanked for the wonderful meal we shared.

Paul VA3LX is in the centre and I am on the right. Both Paul and Cezar are in FN14 and I'm in FN24. Both of them live near the city of Kingston on the shore of Lake Ontario. Cezar and Lucy's home in on the very picturesque lakefront, just upstream of the city and the Thousand Islands. This is a rare photograph of yours truly since I rarely show pictures of myself. Readers and more interested in what I'm doing, and not on me.

In that light I want to turn my attention to the DX buddy system. It has slid in importance over the years as DX spotting networks, RBN, PSK Reporter and other online systems tells us where and when to find the DX. These remove a lot of the drudgery of finding rare DX. However, many DXers prefer to do the work on their own, to find the DX without outside assistance. Regardless of approach, you still have to work them.

In the buddy system, when one of the group's members notes the DX station or path opening, they spread the news to their DX buddies. This can be done in many ways, and for the three of us it has mostly been via email. Email is fast and it is not especially "pushy" in comparison to many alerting services. It suits us.

For our small group, the buddy system worked very well. All of us are at least partially retired, which gives us time to monitor 6 meters and react to pings from each other. There is also friendly competition among us regarding our successes, stations and operating styles. We are effectively egging each other on. The enthusiasm for our common pursuit rises from the positive feedback. At the BBQ we discussed the ways in which we can improve our results next year: remote operation, amplifiers and antennas.

During the exceptional 1989/1990 solar maximum, F-layer propagation frequently appeared, with shorter path DX continuing to be via sporadic E. I had just one local buddy with whom I kept in regular contact: Gord VE3KKL. F-layer propagation is more predictable but not enough to plan your operating schedule to the solar indices. 

Finding DX was also more difficult since there was no global DX spotting network and you had to spin the dial to find those CW and SSB stations. The scanning feature of VHF/UHF rigs came in very handy, provided you and your family could tolerate the constant hiss and occasional signal burst emanating from the radio shack. Gord's family tolerated it, but just barely.

The problem for me back then was my time. I was young, working full time and with a busy social calendar. The buddy system mostly went in one direction. Getting calls from Gord at work was aggravating since I could not get on the air, and I regrettably missed many openings and the possibility of new countries. Remote operation was out of the question. When I couldn't react to his alerts we could still share our passion for 6 meters by discussing openings, predicted openings, DX stations heard or rumoured to be active.

I am relating this story since I learned not long ago that Gord became a silent key earlier this year. We spoke less frequently in recent years. I was remiss in reestablishing contact with the many old friends during that 20 years of inactivity. But soon after I returned to 6 meters we bumped into each other on 6 meter SSB and later in person. However, like many, he didn't make the leap to digital. There was little left for him to work on the traditional modes.

We all need our DX buddies on 6 meters. Recruit them, celebrate milestones and remember them when they're gone.

Building the 5-element 10 Meter Yagis

The project for a 5-over-5 stack on 10 meters is progressing well. The yagis are built, tested and adjusted, and are slated for raising in October. Although they are smaller than their 5-element 20 and 15 meter cousins that I built two years ago, the performance is similar and the construction techniques and challenges are identical.

To make best use of aluminum on hand I changed the original element design to use ¾" tubes for the centre sections. The final taper schedule for each half element:

• ¾" × ⅛" : 30"
• ⅝" × 0.058" : 33" (+ 3" overlap)
• ½" × 0.065" : variable length tips

The taper schedule was modeled in EZNEC to adjust the tip lengths to resonate the elements (X = 0) at the same frequencies. Scaling is necessary to preserve performance and frequency range when you deviate from the design. For the SDC (stepped diameter correction) I calculated the effective diameter of the element-to-boom clamps using the W6NL equation. For a ¾" tube on a 4" × ¼" plate, the effective diameter is 2.4". The clamp length for each half-element is 2".

I had a challenge ordering suitable clamps for the element-to-boom clamps. Importing of the ideal fasteners from elsewhere is either prohibitively expensive or the dealers refuse to export. Canadian dealers are not as willing as they have been in the past to do special orders. Other options involved calling in favours to use non-retail suppliers, and I didn't want to do that. I resorted to online sites like eBay to find what I wanted. Once I had the parts I drilled the plates to match the hardware.

To further economize I made the booms out of pipe in my stock. The weight is higher than needed for these yagis but since it's 10 meters the overall weight increase is small. The pipes are 1-½" schedule 40 or 80 (1.9" OD), joined by sections of 2" schedule 80 pipe (2.375" OD, 1.939" ID). The fully assembled yagis weight 43 lb and 52 lb. The lighter one will be the upper yagi of the stack, that will be mounted at the top of the mast on the 150' tower above the planned 3-element 40 meter yagi.

The SWR bandwidth of the yagi is around 900 kHz. That is good enough for DXing and contests. If you operate above 29 MHz (e.g. FM) the antenna should be scaled accordingly. However, you will lose performance at the bottom of the band. 

I adjusted the design optimize to my requirements and make the best use the available bandwidth. One change was to shift the antenna up by 100 kHz to get closer to 1 MHz SWR bandwidth with negligible impact on gain and F/B performance.

The model uses a beta match (hairpin) for ease of modelling and for compatibility with SDC (stepped diameter correction). The gamma match I use is functionally the same, and so are a variety of similar "transmission line" matching networks. We'll see the proof shortly.

Construction of the element was no different than that of the 20 and 15 meter yagis so I'll point you there rather than repeat myself. Since there are two of these 5-element yagis, there were 10 elements (20 half elements) to be built. That entailed a lot of cutting, drilling, reaming and filing. I started in August and finished in mid-September. It was a lot of work.

The element-to-boom clamp plates are shorter at 4" × 4" × ¼" but otherwise the same. Due to poor planning, D2 (director 2) on one of the yagis was on a 2.375" pipe. Since the plates were already drilled, I experimented in software with D2 shifted several inches so that it would sit on a 1.9" pipe. By adjusting its length a small amount the performance was close but not the same. Since the designs are already greatly optimized any alteration has an effect. I decided to leave D1 where it was and made a new plate to fit the larger saddle clamps.

I was careful to adjust and measure the half element lengths to be within ⅛" of the modelled lengths. As the frequency increases the need for accuracy also increases. There is little sense investing a large effort to design and build a high performance yagi to then get sloppy and lose some of that performance.

The antenna is large but smaller than many of my earlier projects. It was still a challenge moving them from the driveway, where they were assembled, to the the hay field where they were to be tested and then lifted onto the tower. A friend and I had to carry the heavier one the long way around because of the difficulty of navigating trees and other obstacles. Although the antenna isn't terribly heavy it is no easy job to carry it a few hundred meters by myself, as I did for the lighter of the two.

The rigging to tune and adjust the 10 meter yagis is similar to what was done for 3 of the 15 and 20 meter yagis, except that the antenna size and required height are lower. This is the same rigging used to lower and lift the TH6 recently, which is no accident: I planned it that way to minimize the work. After raising the height of the tram line and lift pulley, the same rigging will be used to tram the side mount 10 meter yagi to 110' (actually about 33 m).

The short length of coax looks silly with the antenna analyzer hanging off it in midair. It was an expedient choice since I didn't have a ready made length of coax that would do the job. What I did have was the recently assembled delay line for the lower 20 meter yagi -- 6.9' of RG213 -- so that's what I used. I'll install the delay line when tuning the 10 meter yagis is compleete.

Despite the short bit of coax and with the help of a step ladder it was possible to adjust the gamma match and measure the impedance with the antenna as high as 15' (4.6 m or 0.43λ) which is high enough to put it in virtual free space.

The shorter gamma rod separation helped to place the coax connector at the same level. For the greater separation on the 15 and 20 meter yagis the connector was higher (closer to the boom) with a vertical wire down to the capacitor. With careful calculation and construction it is a very good fit. I prefer this approach since it improves mechanical robustness.

For initial tuning I used a temporary strap and the gamma rod and capacitor are longer than required. I have learned to distrust gamma match design software. To my surprise the calculated dimensions turned out to be quite accurate, to within 1" (3 cm) and 3 pf (4 cm of RG213 inside a ½" gamma rod) for centre-to-centre spacing of 3" from the ¾" element centre tube.

Further playing with the software suggested, if reliable, that the antenna impedance at 28.5 MHz is 30-j35 Ω versus the 30-j30 Ω predicted by EZNEC. Design and measurements are done at 28.5 MHz since that is where the SWR is predicted to be minimum (1:1), and the SWR over the band should be as designed.

Compare the measured SWR from 28 to 29 MHz at 12' height to the free space SWR predicted by EZNEC above. They are almost indistinguishable. Modern software tools are truly awesome. There is a glitch right at 28.0 MHz that isn't there in other trials. I think the coax connector to the analyzer wasn't tight enough at the time. When the antenna was raised 3' higher to 15' the gamma match required a slight tweak.

The gamma match was subsequently altered to make the components smaller. I did this by shortening the each half of the driven element by ½" to increase the capacitive reactance. This allowed shortening the gamma capacitor, which is desirable for mechanical robustness. The capacitor length was trimmed so that the rod could be shortened while leaving room for further adjustment if needed. After adjustment the SWR curve was almost exactly the same. Perfection is not the objective since. For the side mount yagi, there are almost certain to be guy interactions that will alter the impedance and pattern a small amount

Pieces of the final version of the gamma match are shown above. Construction is similar to that of the 15 and 20 meter yagis, but with a strap that is only ¾" wide. I unsuccessfully tried to form a harder aluminum alloy for the strap but I could not easily do it with the tools I have. So I used same softer alloy as for the straps on the lower band yagis.

With the antennas built and tuned the remaining parts were the boom-to-mast clamps and boom trusses. In my junk box I found a ¼" aluminum plate with holes in exactly the positions needed for the lower, side mount yagi which uses a short length of 1.9" pipe for the mast. 

For the upper, rotatable yagi I chose a ⅜" aluminum plate from my junk box. As for the upper 15 meter yagi, there is an integrated boom truss support. This allows it to be placed at the very top of the mast, as far as possible above the planned 40 meter yagi. 

At the time the picture was taken the fittings for the clamp are incomplete. There were a few more holes to be drilled and saddle clamps selected. One of the 3" DXE clamps for the 2.875" mast is shown, while a second had to be rescued from a "temporary" use on one of the towers where it's been for 3 years.

Still to be done are the coax chokes and boom trusses. For the latter, I am using what I can find in the junk box. The current plan is for short lengths of plated chain anchored on the boom with old muffler clamps, ⅛" aircraft cable as the truss cable and galvanized turnbuckles connected to the mast. It won't be pretty but it will work and nothing has to be purchased.

Coming up is the raising of the yagis and construction of the stack switch and phasing harness. That will have to wait until the antennas at the top of the tower are removed -- TH7 and 40 meter dipole -- and the tower is rigged to lift the as-yet incomplete 40 meter 3-element yagi. Other project have intervened so it will be two weeks or more until both 10 meter yagis are raise.

Side Mount for a Limited Rotation Yagi

For the past few years I have had a Hy-Gain TH6 side mounted at ~72' (22 m) on the 150' tower, fixed south to W4/W5, the Caribbean, Central and South America. It has been used as a multiplier antenna in contests, and it has proven to be very useful in the intended application. That said, having it fixed is less than ideal. I would to use it to cover more of North America to earn more contest points working the US when my bigger antennas are pointed to more distant DX locales.

I have written previously about different methods of side mounting yagis on towers for partial compass coverage. This year I decided to do it for the TH6. A rotation of a little more than 120° allows coverage from 150° (Brazil) to 285° (VE7). That's perfect for my purposes.

I have more to say about the TH6 that will be deferred to a future article. It had to come down for reasons other than the new side mount system: to permanently repair a wire bond that could not be done on the tower, and to flip the boom to mast clamp since the rotatable side mount is on the opposite side of the tower from the fixed side mount bracket.

It is amusing to note that the antenna and rotator were manufactured not long after I was licensed almost 50 years ago. I acquired them secondhand in 1985 when I bought a house and could put up a tower after moving Ottawa as a young man several years earlier. Both went into storage when the tower came down in 1992, where they remained for over 20 years. 

The rotator, a CDE Ham-M, was refurbished and used when I returned to the hobby and put up a tower and tri-bander in 2014. In 2016 they went back into storage.

Looking around at my stock of metal and hardware I formulated a plan. I have a large stock of scavenged material that tends to find its way into projects or gets passed on to others. Nothing needed to be purchased for this project other than a few bolts. 

The tasks to be accomplished included:

• Take down the TH6 and its side mount fixture for service
• Service the rotator
• Select a mounting geometry that would achieve the desired rotation and not interfere with climbing and the numerous cables affixed to the tower
• Build a side mount system that is sturdy, servicable and meets the objectives
• Design the cabling system (about 230' long) to use the minimum amount of new cable and provide adequate current capacity
• Raise the refurbished TH6 and test the system

Getting the TH6 down was straight-forward. For simplicity I used my lawn tractor as the tram line anchor. You back up until the rope is taut, then block the wheels. I can do this for antennas up to around 70 lb, and more if the slope of the tram is low. For heavier antennas and the requisite greater tram line tension, the wheels lift off the ground. Lawn tractors aren't very heavy.

There is some difficulty rigging the antenna for proper balance since, unlike going up, you really only get one chance. The TH6 was a little unbalanced and a couple of tubing clamps snagged a guy. Jiggling was enough to free the snags. The entire job was quickly done with the help of just one friend as the ground crew. Less muscle is needed to tram antennas down, and is further helped by the shallow slope (under 25°) of the 200' long tram line and a height of 75'.

The new side mount went up the same day that the TH6 and the old fixed side mount bracket came down. It had been fabricated over the previous weeks in my workshop where I have a spare tower section to use as a jig. At 10' tall the tower section rests against a roof rafter. I use a step ladder to comfortably work at the top of it.

Laying the tower section horizontally makes it easier to for work on it in some respects. The negatives are that floor clearance is needed for tower projections, visualization is more difficult and levelling and supports can behave unexpectedly. Keeping it vertical help with visualization, and levelling and alignment are the same as when it is on the tower. I shim the wood plate under the tower section to make it level and vertical. Garage floors are sloped for drainage.

On the left is the basic structure. The angle aluminum (⅜" × 3") attaches to the tower girt with two grade 5 ½" bolts. Although A325 hardware is a better choice, the shear force in this application is well within the rating of bolt, nut and tower girt. Large fender washers provide a larger bearing surface for the bolt heads, which helps to reduce point stress on the tower girt and aluminum arm. The aluminum angle was cut to a length that is long enough to mount the rotator, and not too long for excess bending stress due to the weight of antenna, rotator and mast balanced at the end of the arm. 

Not seen in this picture is a vertical support cable for the arm, running from next to the rotator to a tower strut. You can see it below after it was installed on the tower. The cable reduces stress and the turnbuckle allows for exact levelling of the system when it is under full load. Even without the cable the support easily handles my weight when I stand where the rotator is located.

That 3" width of the aluminum angle is a tight fit for the Ham-M bolt pattern so I attached a short length of steel angle to the aluminum. The rotator is centred on the joint between the two to keep it in line with the tower face. Levels were used to keep everything aligned. On the right a pipe (mast) goes from the rotator through the upper support arm affixed to the next higher girt. Detail can be seen in the picture below.

The multitude of holes in the aluminum angle were already there. There are a couple of holes directly under the rotator that are used to fish the 8-wire cable to a terminal strip on the angle, where it is partly sheltered from the weather. The aluminum angle was rescued from a dumpster for free. I had no particular project in mind when I claimed it, but I was sure that it would find a use. There is more in my stock for future projects.

The support girt is at the 75' level, which is 5' above the second set of guys. The upper support arm is at 80'. These are nominal figures that ignore tower section overlap, and the actual values are closer to 72' (22 m) and 75' (23 m). This is a good height to minimize guy interactions and to match the elevation angles needed for the intended coverage area.

On the left you see the support cable and the level used to adjust the turnbuckle. It has to be tightened a tad when the antenna is mounted. The rotator cable and terminal strip are visible below the level.

The steel angle arm supports a mast bushing. A bearing is not really necessary for horizontal wind thrust when there is no vertical force. Also, a bushing is cheap to fabricate. For the 1.9" diameter of the mast the bushing is a short length of 2" schedule 80 aluminum pipe with an ID of 1.939". The fit is so close that the bushing must be carefully aligned. A burr present on the mast had to be filed flush to the pipe surface so that it would slide through the bushing. The mast diameter is probably closer to 1.91" due to the galvanizing for an even closer fit. 

Time will tell how the bushing wears in service; it is aluminum so that it will wear rather then the steel mast. The bushing is easy to replace if necessary.

The thrust arm is steel angle (⅛" × 1-½"). It pivots on the rear bolt to the girt for one degree of adjustment (there are 2 bolt holes on girt that can be selected) and another degree of adjustment is made by moving the nuts on the ⅜" threaded rod between the arm a short and heavy steel angle bolted to the girt face (not shown). The adjustment range was tested on the jig and determined to be sufficient.

Once everything is tightened the arm is very stiff. It will be periodically inspected it to check that it doesn't shift. I will add lock washers and other hardware if the need arises.

Hy-Gain rotator clamps are not very adjustable and a mast has to be about 2.1" diameter to be properly centred. The 1.9" OD pipe can be shimmed to meet that spec. I don't see the need since the distance to the bushing is far enough and the restricted rotation angle small enough that mast misalignment is unlikely to cause binding at the bushing.

After the TH6 was repaired it was trammed to the new side mount. The picture contains several items worth noting. First, notice that the mast clamp is low on the mast, close to the rotator. Although the bushing prevents bending stress on the rotator, an extreme wind can "bow" the mast. That increases bending stress and it is maximum at the midpoint of the mast. It's not a major concern but why take chances. A second benefit is that a shorter mast can be used to secure the boom truss. In this case the mast clamp for the boom truss is just below the bushing.

For a swing arm you must use thrust bearings above and below the swing arm for support and to protect the rotator. In my side mount article the diagram I drew of the swing arm is incorrect; I know better but the mistake crept in anyway.

Geometry and utilization of the tower faces dictated that the side mount would be placed on the tower's one climbing face. One of the other faces is dedicated to cables, which excluded it from consideration, and the other face was not ideal for the desired compass coverage and there is the risk of the antenna boom striking the cables. Putting it on the climbing face raised the problem of having to climb over the wide aluminum strut (see above). In practice the 3" projection from the tower face turned out not to be a problem. Not only do I not accidentally bump into it, it is comfortable to stand on when I'm working at that level.

The pulley for the haul rope is suspended directly above the mast with an arm attached to the tower. Depending on the geometry of the tram line this may be necessary to ensure the mast clamp aligns with the mast when the tram line is slacked. It is easier to bolt together the clamp halves without having to use muscle to align them to insert and secure the long bolts. Alternatively, have a friend join you on the tower. Yagi wrestling isn't fun.

The longer the side mount the further the rotator is offset from the tower. This can be tempting since you can eke a few more degrees of rotation. With my mount I have approximately 135° of rotation available. Placing the boom on the outside of the mast adds another couple of degrees. However, go too far with most antennas there will be a problem: the elements on either side of the mast can strike the tower. That's a bad idea.

Rubber cushions will be put on the boom so that it softly strikes the tower at the rotation limits. The Hy-Gain rotators have too little torque to do any damage and the motor will halt when contact is made.

Side mount rotation, whether a fixed mast or a larger-rotation swing arm, requires an antenna with elements spaced far enough from the centre so that it is the boom and not the elements that limit rotation. Smaller yagis and those for higher frequencies are more problematic. 

The Hy-Gain Explorer 14 that I recently sold is not compatible with a side mount because the driven element is close to the mast (boom centre). The TH6 has adequate space for this system (see diagram, above, copied from the TH6 manual). I opted to use the TH6 rather than the TH7 because there is inadequate space between the two driven elements of the newer antenna. The mono-band yagis I built for 10, 15 and 20 meters are compatible with rotatable side mounts, should I choose to do that in the future.

In addition to mechanical clearance there is electrical interaction of the innermost elements and the tower as they come into proximity during rotation. In most cases it is minor, and when it's the driven element the effect is mostly on the feed point impedance (SWR) and not the antenna pattern. The benefits of rotation typically far outweigh the negatives of pattern distortion. I ran several models to judge the potential magnitude of the interaction for the side mount article, and I reported my general findings. Exact determination of pattern distortion is difficult to do in a software model.

In a future article I'll say a little more about the side mount rotator and rotation. As of this writing the rotator is not wired back to the shack. Indeed, the TH6 is oriented so that the tram can remain in place to lift and adjust the 10 meter yagis that are now built. I should have everything working by early October.

Fighting Flora and Fauna

This is not the first time I've written about my troubles with wildlife. While a rural QTH is great for antenna farms, the majority of animals are not accustomed to seeing or dealing with humans. Unlike they behaviour changes they exhibit in and near urban areas, they proceed as if in the wild. 

They come close and satisfy their curiosity by chewing or walking on cables, dig in the loose soil of recent excavations and make their homes in shelters built for antenna and cable switches and junctions, and inside tubes and pipes. Deer and their predators follow the trails I make through the foliage and snow. The predators are intelligent enough to respect humans, and their firearms, and keep their distance.

Dealing with animals, vegetation and insects is an unavoidable part of regular station maintenance. Sometimes it is damage I must prevent or repair, and other times nature must be tackled in pursuit of my antenna farm projects. Read on for my latest adventures.

Many insects like dark enclosed spaces in which to build their nests and to store food and eggs over the winter. To their delight, all of my outdoors enclosures for matching networks, switching and cable junctions have weep holes to allow moisture (rain or condensation) to exit. It seems that no matter how small I make the holes there is an insect that is smaller yet. I can't make the holes too small or the surface tension of water will prevent drainage.

Even so, when I built the Beverage antenna remote switch early in 2020 (see article for pics) I made the weep holes smaller than usual and the hole for the Cat5 control cable a snug fit. In early summer the switch exhibited intermittent short behaviour (excess current to the relay coils). A few weeks later when the hay was harvested and I could safely access the switch.

As I slid the cover off after removing the screws an enormous number of ants came scurrying out. They crawled around the enclosure, over my hands and up my arms, with most jumping off when they realized they were on an animal (me). In the 30 seconds or so that it took me to pull my phone out and take a picture only about half the ants were left inside.

You can see the cocoons under the ant mass. These had to be scraped off after the the ants were cleaned out. The funny thing is that the ants were not responsible for the switch failure. After bench testing in my workshop the likely culprit is a secondary lightning strike. Long Beverage wires are notorious for building up large induced voltages from nearby strikes, and in this case the integrated suppression diodes in the relays had failed. 

Unfortunately, as I discovered in a similar case, the diodes fail to a low resistance value (not a complete short) when their PIV rating is exceeded. I was further irritated that the specs for these Littlefuse reed relays do not state the PIV rating of the suppressor diodes. I didn't notice that when I selected them. For the interim I have more of these in my stock so I will be installing them shortly, in time for the fall 160 meter season. I would like to replace them with relays that use my choice of suppressor diodes.

Despite the diagnosis the ants are not innocent. They brought a lot of moisture into the small enclosure that left its mark. Notice that all the bare copper wires are heavily corroded (green). Tinned wire and hardware is unaffected. When I rebuild the switch the bare copper will be replaced by tinned wire. Wire that than cannot be easily replaced (e.g. transformer windings) will be coated to inhibit corrosion.

It is interesting that one of the two styles of coax jacks corroded (on the left) and the other did not. Application of dielectric grease to the threads should inhibit further deterioration.

The ants were a surprise since it's earwigs I typically have to deal with. Earwigs will climb at least several feet to find a nice comfortable hole to lay their eggs in late summer. At last count there are 6 enclosures with earwig infestations (including every one in the 80 meter vertical yagi). I am not yet able to reach the Beverage antennas which each have two enclosures (head end and reflection transformer) to be inspected.

The picture shows the 80 meter yagi switch box with the largest earwig infestation. It is the one at the base of the southwest parasitic element. All the covers were removed and the units left open for a few days until the eggs dried and could be cleaned out. Try it when they're fresh and you will only smear the black goo everywhere. 

A bit of rainwater while they're uncovered won't damage the relays and coil. Neither will a water rinse. Sealed relays can put up with a lot of environmental abuse.

Before winter I plan to deer-proof the cables and support ropes in the 80 meter yagi. They do like to chew things, much to my surprise. In my station they are far worse than rodents. Squirrels, mice and their kin have molested none of the on-ground cables. Sometimes a chipmunk will dig a home along a trench line but they have not damaged anything. Perhaps they favour recently disturbed soil.

In the picture above you may be wondering what the problem might be. It is an after picture, once the problem was resolved. When I put up my first big tower in 2017 the ideal location for one of the guy anchors was behind a short spruce tree. It was not really in the way so I ignored it. Little trees grow into big trees and that's when the trouble begins. 

First it gobbled up the lowest guy. I trimmed branches to avoid contact with the guy. The tree continued to grow and soon gobbled up the second guy and was well on its way to the third. I like trees so I avoid cutting them down when possible, especially an attractive tree in a pleasant setting like this one. 

My patience was exhausted when climbing vines that infest trees grew over the guys. Vegetation in contact with steel, including galvanized steel, promotes rust. With the help of a friend the tree was dispatched and roots cut out below ground. They guys are now free and ground levelled where the tree once stood.

There is a ham I know (call withheld to protect the guilty party) who installed a guy anchor near a seedling many years ago. The tree grew and grew until the anchor and equalizer plate were embedded in the trunk of the now large tree. Neither the tree nor the anchor seemed to suffer from the experience, or at least not yet. I would have loved to take a picture but did not to avoid offending the ham in question. It would have made a great picture, and an instructive one.

Speaking of anchors and trees, there is one last item that is a little different. In this case the tree in question is very much wanted.

A few years ago I opened a path in the bush at the east end of the hay field to use a tree as an anchor for tramming yagis up and down the 150' tower. This worked well. I want to do the same this fall when I decommission the TH7 and bring down the experimental 40 meter yagi element. 

If the latter passes inspection for its mechanical soundness it will become the driven element of a 3-element 40 meter yagi. That project is proceeding and if all goes well it will be built and raised to 150' later this fall. The yagi will weight close to 300 lb (135 kg) and will require a tram line that is equal to the challenge.

There is a large and healthy tree deeper in the bush that appears to be ideal. Equally important is that it is directly opposite the guy anchor discussed earlier. The guy anchor, which has a spare eyelet for this purpose, will hold a back stay cable to the mast to balance the large force of the tram line tension and the yagi's weight.

Clearing of the bush to access the tree and make a path for the skyward pointing tram line is ongoing. The above picture shows the current progress. The tree itself is hidden in shade at the centre of the frame. I'll have more to say about it when it is ready. As a trial run the tree will be used as an anchor to lower the TH7 and 40 meter yagi.

I'll close on a more amusing note. Wild turkeys are common in the area. They roam the lawns and harvested fields almost daily this time of year. They step around guys and over radials and, so far, have done no damage. I leave them alone.

The big birds are shy and run (or fly) when they see me. This one was taken through the window. One day earlier this year there were more than 20 of them in the driveway.

Correcting the Mismatch of the Upper 20 Meter Yagi

To summarize a long story, after the upper 5-element 20 meter yagi of the stack was raised I discovered that the gamma match had somehow slipped out of adjustment after being tuned. This probably happened while weatherproofing the gamma capacitor. Since the antenna is very large and heavy I decided to correct the mismatch and not to take the antenna down for repair. Taking the antenna down, adjusting it and raising it again would take 3 full days with the help of several friends. Correction is the easier and safer alternative.

I developed models to determine the effect of a matching network. A simple L-network is all that is required, and it can be made very efficient. For convenience my plan was to mount the network at the stack switch. Since the network and the gamma mismatch both shift the phase of the upper yagi it is also necessary to bring the yagis back into phase. The existing phasing lines assume that the yagis are identical, per the design of the antennas and stack.

Although the problem I am solving is specifically for my antenna system, the techniques and tools are applicable to other antenna challenges. Since these may be of use to readers, it is worthwhile to describe the resolution in depth.

Danger of calculation versus measurement

I keep so busy with my many projects that I don't always remember what I've done and my notes may be missing or difficult to understand. I had a set of impedance values across the band for the upper yagi in my notes and I assumed they were measurements. It turned out that they were calculated for the length of the phasing line to the stack switch based on measurements at the coax joint on the boom where it connects to the rotation loop.

The impedance is determined by the electrical length of the transmission line. The phasing harness lengths were calculated from the physical lengths and the VF (velocity factor) of the coax. For the upper yagi that includes 11' of RG213 (rotation loop) and 30' of LMR400 (tower run). This is approximately equivalent to 44' of LMR400. The total length is 66' including the 22' length of LMR400 from the feed point to the tower.

Physical lengths are easy to measure and mine were done with great accuracy. Unfortunately the published VF of coax is not always exact for a variety of reasons. When the phasing harness segments are from the same coax reel the VF is usually equal. In other cases, the VF can differ and the yagis will not be properly phased.

Under the misconception that the recorded values were measurements I used TLW to design the L-network. It turned out to be a degenerate case where the network reduced to a single component: a series inductor. 

I dutifully built it (see above) and tested it with an analyzer (at right). The box must be closed since the inductance is reduced by the aluminum enclosure. To compensate, the coil is designed with a higher inductance. The required 31 μH of series inductance is what I got after adjusting the coil turns.

I discovered my mistake at 110'. Thoroughly confused and out of time that day I descended the tower.

Measurements

Several days later I went back up the tower with an antenna analyzer to measure the upper yagi impedance at the stack switch. It was a windy day so I had to visually integrate the readings as the elements wiggled and waggled above me. A few ohms either way is not a serious issue since the L-network can be fine tuned once it is installed.

Taking care not to lose the piece of paper with the numbers in the brisk wind I came down and ran them through TLW. With a bit of experimentation the measurements and calculations matched for a 40.5' physical length of LMR400. That's an error of 8%! This implies a VF of 0.78, far less than the specified 0.85. This is so surprising that I plan to take a tape measure up the tower to recheck the lengths, despite having triple-checked them on the ground.

At right are the measurements, taken at every 50 kHz across the 20 meter band. From a cursory examination of the impedance values it might appear to be impossible for a fixed network to properly transform the SWR across the band. Appearances can be deceiving.

Accounting for frequency, one network can transform a disparate set of impedances to a fixed target impedance. That is approximately true in this case where one network restores the designed SWR curve for the 5-element yagi: about 1.5 at the 20 meter band edges and 1 in the vicinity of 14.1 MHz.

Achieving a perfect 50 Ω impedance is not possible nor is it desirable. Careful design should result in a close match to the lower yagi's SWR, and therefore equal power division and near equal SWR when switching among upper, low and both yagis in the stack. There are software tools to ease the design process. Having one antenna exactly 50 Ω across the band does not achieve either objective.

Designing and testing the L-network

An L-network consists of a capacitor and a coil, one in series and the other a shunt on either the 50 Ω or the antenna port. There are two optional configurations, usually called low pass or high pass since they also behave as filters. Its filter performance is unimportant for this application so I chose a low pass network because the calculated L and C values were easy to work with. By this I mean a low value for L (small coil and low loss) and for C close to a capacitor value and power rating in my junk box.

As for the gamma match, I designed a network to transform the impedance to 50 Ω at the same frequency, a little above 14.1 MHz. For the gamma match that gave an SWR below 1.5 across the 20 meter band. It is a little more complicated for the mismatched upper yagi. Some experimentation was required.

I used a combination of TLW and SimSmith. Using the actual impedance measurements, I designed an L-network for 14.150 MHz. I plugged the network into SimSmith and checked how it performed against the measured values across the band. The SWR curve was good but not great. For the best SWR the L-network was set to match at 14.100 MHz. The result was an SWR of 1.3 at 14 MHz and 1.7 at 14.350 MHz.

I picked a vintage 100 pf transmitting mica capacitor from my junk box for the network. These capacitors are old and require testing, but I have had good success with them. A modern transmitting ceramic doorknob is a better choice. A variable capacitor can be used but you'll need a larger box and adjustment will require extra work. It really isn't worth the trouble for this application. But if you choose to use a variable capacitor, pay attention to the voltage calculated by TLW. The variable capacitor must meet the requirement for your maximum power, plus a safety margin.

Since the capacitor measured as 102 pf versus the required 96 pf it was necessary to return to SimSmith to check the network performance across the band with the larger capacitance. The capacitance may be even higher due to stray capacitance within the enclosure.

It is no surprise that a perfect SWR of 1 cannot be achieved at the design frequency. The best I got was the depicted 1.1. That is not really a problem since it has negligible effect at the band edges where the SWR is highest. This is typical since the mismatch at the band edges is dominated by deviations of R and X from 50 and 0 Ω, respectively, of the load's complex impedance rather than the small deviation due to the capacitor being off by a few percent. With this network SimSmith calculates the SWR as 1.4 at 14 MHz and 1.8 at 14.350 MHz.

The inductor was designed with Coil by K6STI. It is 7 turns of AWG 12 bare copper wire, with a diameter of around 0.8" (2 cm) and 1.25" long (3 cm). To wind the coil I used a ½" PVC pipe that has an OD of 0.84". The calculated Q is about 350, which is quite good. TLW predicts very little power will be dissipated. I took the old coil out of the enclosure and substituted the new one. A 50 Ω load was connected to the antenna port (the same setup as was shown earlier) and measured by an antenna analyzer at 14.1 MHz. 

To adjust the coil I opened the enclosure to squeeze or spread turns. The measurement must be done with the enclosure closed since the aluminum reduces the inductance. For this reason the coil design was for an inductance of a little over 0.5 μH. Once the measured inductance was 0.46 μH the shunt capacitor was installed. It's a tight fit but that's okay; the coil and capacitor can be close, or even touch, and the only effects might be slight increases of C and L. The coil can be adjusted during final turning of the network.

For tuning the network a simulated complex load is helpful. It is not really required if you enjoy doing this work 110' up the tower! My preference is to minimize the tower work by simulating the load in my workshop. For the measured impedance of 82-j9 Ω I put a 75 Ω resistor in series with a 1000 pf capacitor. Although 75-j11 is not exact it is close enough to test and coarse tune the network.

The simulated load only permits adjustment of the network at the 14.1 MHz design frequency. You would need to build loads to simulate the impedance at other frequencies to fully bench test the network. I didn't do that since it isn't strictly necessary. If the measurements are correct the software calculations for its behaviour over the rest of the band should also be correct.

Testing of the completed network is shown at right. The SWR is a little high because the enclosure is open for the purpose of taking a picture. With the enclosure closed the SWR is 1.1, which is quite good for the inexact simulated load.

The network was further examined with SimSmith by substituting the simulated load and seeing what the measured impedance would be. The impedance measured by the analyzer was within 1 Ω for both R and X. That's less than the accuracy of the analyzer so we can't expect to do any better. 

I do have a better instrument (VNWA3) but that degree of accuracy is overkill for what this project requires.

On a final note, look above at the image from TLW. Notice the RF voltage across the shunt capacitor. It is not much higher than for a matched load at a kilowatt. The transformation ratio is small so there are no high impedance points in the network and therefore no especially high voltages.

A physically smaller capacitor than the one selected is not advised. The current is high and you want a capacitor rated for high power RF so that the loss is low and within the physical heat dissipation rating of the component. 

The low risk of flash over to the aluminum enclosure permits a tight fit, and that will come in handy during installation on the stack switch. The high power test would have to wait for installation since there is no easy way to simulate a high power complex impedance load for bench testing.

The time had come to go for a climb.

Installation of the network

Through the miracle of software and bench simulation the work on the tower was brief and successful. I plugged the coax to the upper yagi into the antenna port of the network and the analyzer to the other port. Take care because the network is not symmetrical. Label the ports if that help you to remember.

I fiddled with the coil to see if I could do better. For reasons described earlier, it was not to be. The match was near perfect at 14.1 MHz and behaved as calculated by SimSmith elsewhere across the band. It is a little high at the top end of the SSB segment, a place I only venture during popular SSB contests with heavy activity. I can live with it.

The enclosure I chose for the L-network was no accident. It fits very nicely onto the stack switch antenna port with a male UHF barrel connector without striking the connector for the other (lower) antenna port. Weatherproofing is a challenge since there is little space between the upper and lower yagi ports to wind tape. I will have to improve the temporary job before autumn's cool, wet weather.

The enclosure is oriented to allow water to leak out the bottom edges. The bottom two screws were not installed to help with that. Tape placed across the top edges limits water incursion. There are better enclosures available but I used what I had on hand, and it really is good enough. It's 110' in the air and no one will see it but me.

Back in the shack the SWR of the upper yagi was nearly identical to what I measured on the tower. Some reduction of SWR can be expected and is not unusual due to the very lengthy transmission line. The LDF5 Heliax is doing its job well. 

When in lower + upper stack mode (BIP) the parallel SWR via the stack switch L-network is even better (see picture to the right). 

I tested the completed system with a kilowatt to be sure there are no weak components or poor arc tolerance. All is well.

Phase compensation

The misadjusted gamma match and the upper yagi's matching network both exhibit a phase shift. In this case they are in the same direction so they add. A delay line for the lower yagi is required. Should I ever fix the gamma match on the upper yagi the network and delay line must be removed.

Measuring the phase of the antennas is impractical, so I rely on calculation. Unfortunately, it is easier to calculate the delay line length in software than in reality. On the other hand, forward gain is not overly sensitive to modest phase error. Where we can lose is with the size of minor forward lobes, as shown in the previous article on this topic.

Phase shift in the L-network can be accurately calculated. You can see this (above) for both TLW and SimSmith. The phase shift in the mis-tuned gamma match is more difficult to ascertain. Modelling of the net reactance at the feed point is the best bet, and what I previously did with a model. That is what I will use: varying between 10° to 20° across the 20 meter band. 

The L-network phase shift (before substituting a 100 pf capacitor) is 39° at 14.1 MHz, and it, too, varies with frequency. Since this network is almost identical to that in the modelling exercise, and I have had difficulty developing a model that corresponds well with the real antenna measurements, I estimate the phase shift ranges between 49° and 58° across the band, including that of the gamma match. 

They add because both phase shifts have the same sign, which is to advance the signal to the upper yagi. Correction therefore requires a delay line of around 54° to the lower yagi. This is a almost exactly what was found for the earlier modelling exercise, and that is not surprising. Software modelling works and it can save a lot of time.

For the average phase shift of 54° the length of the delay line is 0.15λ, or 3.2 meters in free space at 14.1 MHz. That must be multiplied by the VF of the coax used for the delay line. For example, 2.1 meters (6.9') for RG213 and 2.7 meters (8.9') for LMR400. All that said, the length is not critical since the phase shift is frequency dependent. No fixed length can be a perfect solution, and an average value is good enough in this application.

My plan is to use RG213 and insert it at the tail from the lower yagi's feed point at the tower. Should I not repair the gamma match on the upper yagi and the delay line continues to be used, the RG213 will eventually do double duty as a rotation loop. I hope to make the lower yagi rotatable in the next year or two. It is currently fixed on Europe.

This is easy to implement, and yet I haven't done so yet. The degradation of the stack pattern without the delay line is small, but with careful A-B testing on the air it is noticable. The modelled deficit is about 1 db of gain and the appearance of a higher angle minor forward lobe.

Good performance without the delay line may seem odd but when you add in the larger uncertainty of terrain on the yagi patterns the phase error is not a major concern. SWR is the more important concern since amplifier tuning can be a problem when switching among the stack's 3 modes. Correcting the mismatch also restores the equal power division required for optimum stack performance.

Time is a concern now that autumn is fast approaching and my many antenna projects require my attention. Those are the priority now that the SWR of the 20 meter stack has been corrected. The delay line can wait a few more weeks.