160 Meter Vertical Ground Disconnection

When the 160 meter shunt fed tower was completed I discussed the need to connect the tower to the radials so that the path was through wire. Allowing the current to flow through the ground greatly reduces antenna efficiency because of its high loss. 

The loss, although greatly reduced, is not eliminated because the tower is connected to the lightning ground rod. Lightning protection should never be viewed as optional! Therefore I accepted the small amount of remaining ground loss. Transitioning to a shunt fed tower from the previous wire vertical was driven by the desire to minimize loss via the tower ground due to the high mutual coupling of the nearby wire onto the non-resonant tower. On 160 meters "far away" can be quite close electrically.

It is also the case that ground rods should be avoided on a ground mounted vertical. The objective of the radials is to reduce -- as much as the budget for wire, time and money allow -- the antenna's near field penetration of the ground, and the consequent loss. A ground rod (resistance) in parallel with the radial field is never a good idea, even when there are only a couple of short radials, because it routes a portion of the antenna current through the ground.

But it's winter. In this climate lightning is very rare during the coldest months of the year. It is also peak 160 meter season. As I pondered the upcoming Stew Perry Top Band Distance Challenge and my intention to once again operate QRP, I ran to the computer and quickly modelled a few options to squeeze a little more out of the antenna. With QRP on top band even a little boost can help a lot.

In the articles referenced in the first two of the above links you will see how even non-resonant towers can have a substantial mutual impedance with a vertical antenna. They are not as far away as they may seem when you consider a wavelength of 160 meters. Part of the induced current distorts the vertical's pattern -- which can be good or bad depending on your needs -- and part is dissipated in the ground via the ground rod and, if the tower is connected to the steel within the concrete base, via the Ufer ground.

My tall guyed towers are not connected to the rebar. They sit flush to the concrete surface of the base pillar and over a pier pin that is also not connected to the rebar. It is therefore possible to lift the tower off ground by disconnecting the lightning ground. So I did. It was a 5 minute job. I moved quickly because it was cold and raining.

This is obviously a hack job. The black wire is the ground connection to the tower and the green wire goes to the radial hub under the gamma match. The 68 kΩ resistor drains static charge on the tower. The resistor value is not critical and although carbon composition is the best choice, at 1.8 MHz a 2 watt metal film or other non-wire wound resistor will serve for temporary use. As I said, lightning is very rare during our long and cold winters.

Although there is no direct electrical connection between the tower and rotating mast, measurement with an analyzer indicates that the mast and the yagis it supports are indeed connected and extending the electrical length of the tower. I will correct this lack when the warm weather returns.

Now I must back up and explain my technical motivation. Before venturing out into the rain with my toolbox I modelled the effect of the revised ground configuration. 

Ground loss is dependent on the effective resistance of the ground rod(s). Close to 0 Ω is good because there is no loss. Unless you are on salt water it will never come near that low value. Very high resistance is also good because current won't flow through ground. It's in between where the concern lies.

From the earlier articles you will find that I estimated the ESR of the ground rod to be in the vicinity of 35 Ω, which is well within that intermediate range of concern. That's the value I used in the model. 

The 68 kΩ resistor I placed between the tower and ground rod is effectively infinite in a low impedance system like this one. That pushes the direct loss due to the ground rod to near 0. The high resistance makes it safe to put a kilowatt into the antenna and not damage the resistor.

The ground loss reduction is quite small. The modelled efficiency improvement is about 0.4 db, which is close to negligible. But as I often tell people that when you add up those decibel fractions pretty soon you have a significant effect. Other fractions may come from improving the SWR, using better coax or increasing the Q of coils in matching networks.

Since I'd be using only 5 watts in the contest I shrugged and figured, why not do the experiment. I'll never know but maybe it made a difference. Conditions were not good and perhaps a quarter of my 200 QSOs required repeats of my call or the exchange. Only 3 Europeans were worked, and those were all very difficult. There is no reliable method to do an A-B comparison to confirm this small of an effect.

Notice that there is a 1 db deficit on one side of the antenna. That is roughly in the direction of Europe, where the other big tower is located. The tower is electrically long and non-resonant so its behaviour as a parasitic reflector is modest. 

I ran a model with the ground on the other tower similarly modified and the pattern became almost perfectly circular. The gain difference in the favoured direction was less than 0.1 db, and that is truly negligible. Well, as I said it was cold and raining, so I didn't take the trouble to do it before the contest. Maybe I should have. While we can quibble over 0.4 db there is really no doubt that 1 db does make a difference in the weak signal conditions that generally apply on 160 meters.

I will improve the modified ground so that it is protected from the weather. Perhaps I'll do the other tower as well to get that extra boost towards Europe. It is probably safe until early April when the risk of lightning returns. By May the radials will have to be rolled up anyway for haying season.

Correcting Phase Error in Stacked Yagis

The best laid plans go awry. No matter how hard we work, how careful we check and double check every step things will still go wrong. Such is the case with my recently completed stacks of 5-element yagis for 15 and 20 meters. The difficulty is only with one of the 4 antennas: the upper 20 meter yagi. This was briefly mentioned in the article about tuning and raising the yagi, and now we'll delve deeper.

Somehow along the way from successful tuning to mechanical completion, weatherproofing and tramming to the top of the tower the gamma match shifted. This was confirmed via measurements and software. For most antennas I would mutter profanities for a minute or two and then proceed to lower the antenna for repair. 

Unfortunately this antenna is a monster and winter has arrived. With all attachments it weighs about 120 lb (55 kg). Lowering, re-tuning and raising are difficult jobs in good weather and definitely will not be done before spring.

A solution has now been found by means of software modelling. Although the problem has not been implemented the 20 meter stack does work, just not optimally.

In this article I'll walk through the steps from initial diagnosis to evaluation of alternative corrective measures and final design. Although few readers have stacked HF yagis there are lessons that can be applied to more common antenna projects. RF circuits are not so mysterious when you challenge yourself to take a peek under the hood.

Forensics

The problem was discovered several days after the yagi was raised. The SWR was very close to 2 across the band. Other than the high SWR an impedance analysis indicated that the yagi was performing properly. 

My first step to diagnose the problem was to measure the R and X components of the impedance across the band. This was done with 22' of LMR400 coming from the feed point and a further 4' from there to the analyzer. The latter length is the equivalent length of LMR400 (VF 0.85) of a shorter length of RG58 (VF 0.66).

The measurements were transformed (using software rather than a paper Smith chart) over the 26' of LMR400 to get the impedance at the feed point. Both are plotted above. It must be done this way since the yagi has a long boom and the feed point and gamma match are well out of reach

Notice that other than about 35 Ω of inductive reactance the the feed point resistance is similar to that obtained after tuning the gamma match near the ground. It is not really that simple since R is not constant when X is changed by the gamma match capacitor.

Diagnosis

This narrow range of the inductive reactance at the feed point is strong evidence that the capacitor value changed after weatherproofing the gamma match and feed point and installing the coax choke. The coax choke was swept before I installed it to ensure it was still in good shape. It was.

For the value of the capacitor when properly tuned the 35 Ω of excess reactance is equivalent to a few inches of the RG213 inner conductor capacitor inside the gamma rod (2.1 pf/inch). All dimensions of the gamma match were recorded after adjustment and checked during weatherproofing. At least that's my recollection. It is possible my memory of what transpired is imperfect.

After installing the stack switches and phasing harnesses I was able to sweep the yagi combinations from the shack. This is more comfortable than on a tower in winter.

Before being installed each segment of coax was tested and tested again when they were connected together. Some deviation from a perfect 50 Ω is normal and not a cause for concern. You just need to be aware of it when doing remote measurements. In this case the SWR dropped from 2 to 1.5. Sometimes the deviation is in your favour.

As previously reported the upper yagi is clearly working, as part of the stack or alone. The feed point impedance of a yagi has only a small or negligible relationship to the yagi's performance. On the basis of the evidence I am convinced that the gamma match capacitor value changed from the value it had when the yagi was tuned at a lower height.

Modelling and Implications

I developed a model of the antennas using EZNEC. First I modified the design to include a gamma match. This can be tricky although it works well when done correctly. For instructions on how to do so read my article on gamma match modelling.

Unlike other matches I used in the original model the gamma match gives a lower SWR across the band. I have not explored why that is -- there are several potential explanations. As a result the impedance at the feed point is different from that of the real antenna. 

Although the modelled impedance differs from the real antenna this is only of concern to me, not you. I will deal with the actual impedance of my antenna when the time comes. The process is universal so the benefit to readers is remains valid. So let's proceed with the gamma match in the model.

I adjusted the gamma capacitor in the model to give the upper yagi about the same excess feed point reactance as the real antenna. That's as good a proxy as I can easily develop unless I can find why the gamma match model is different. I then combined the antennas with transmission lines of the actual physical length and VF into an L-network using the same design as in the actual stack switch.

It is no surprise that the SWR is intermediate between that of the matched lower yagi and mismatched upper yagi. In fact it looks quite good. However, looks can be deceiving. There are two problems present, both of which degrade stack performance:

• 
  The excess reactance at the upper yagi feed point causes a phase shift. It is 20° at 14.000 MHz and declines to 10° at 14.350 MHz.
• Power division is unequal due to the unequal impedance. For the model's currents in the two yagis there is approximately twice as much power delivered to the lower yagi as to the upper yagi (65% vs. 35%). That is easily visible in the current plot to the right.
  

Recall that in a stack optimum gain requires that the yagis have equal power and are fed in phase. Despite the large power imbalance the stack gain reduction is only -0.4 db, with the main lobe reduced from 18.1 to 17.7 dbi. The phase shift is responsible for less than -0.05 db, in proportion to the phase shift across the band as described above. 

While not a dreadful impact, and certainly less than I expected, it is worth dealing with. At the very least a low and equal SWR for the 3 modes -- upper, lower, both -- has benefits, including optimum transmission line loss and no need to fine tune amplifier tuning when switching between modes.

Impedance matching

Correcting the mismatch of the upper yagi is straight-forward. A simple L-network suffices to restore the SWR to what it ought to be. Network design depends on where it is placed in the transmission line since the impedance, not the SWR, is determined by the electrical distance from the feed point, and networks transform impedance, not SWR. To repeat: networks transform impedance and not SWR.

For convenience my preference is to place the L-network at the connection to the stack switch. Other natural breaks in the coax are between the boom run and the rotation loop, and between the rotation loop and the tower run to the stack switch. The network must be placed between the antenna and the stack switch port.

For an equivalent 66' of LMR400 from the modelled antenna (which is at the stack switch port) the calculated impedance plotted is to the right. Using TLW and the design match frequency of 14.1 MHz the L-network design follows:

The L-network for the modelled yagi is different that that required for the real antenna because of the aforementioned difference between the modelled and real gamma match. We'll continue with the model and the L-network required to match the upper yagi at the same electrical distance from the feed point. The upper yagi's SWR is greatly improved.

Modelling confirms that power division is equal and that the SWR is as expected for the stack. Unfortunately that is not good enough. The L-network creates a new problem: phase shift.

Phase correction

The plot shows the elevation pattern of the impedance corrected stack. A visual inspection alone shows that something is amiss. The gain between lobes has markedly increased. The gain of the main lobe is -0.9 db lower than it should be. Note: the gain is actually 17.2 dbi, not 14 as calculated, due to NEC2 error for the close spacing due to the gamma match models; this has been discussed previously.

Stack SWR is near perfect. Power division is almost equal, disturbed no more than 10% by the relative impact of ground and mutual coupling due to their different heights. Power loss in the L-network is not included in the model since, from the TLW tuner design (above) with a relatively poor coil Q, it is much smaller than the power imbalance.

The pattern deterioration is due to the phase shift introduced by the L-network for the upper yagi. By their nature, networks shift phase and the shift is typically greater for larger impedance transformations. Although phase shift is unimportant for an individual antenna it is critical in a stack.

The phase difference is approximately 55° at 14.2 MHz, and varies between 53° and 61° across the band. Note that these figures include the 10° to 20° phase shift imparted by the mismatched gamma match determined earlier. The upper yagi lags the lower yagi.

The phase shift is trivially corrected. The equivalent phase shift lag is placed into the phasing line coax to the lower yagi with an extra length of coax. Since the average phase shift is 55° the required additional length of LMR400 (VF 0.85) at the 14.175 MHz centre frequency is 9' (2.75 m). Inserted this into the model restores the stack pattern. The NEC2 corrected gain is 18.1 dbi.

The extra length of coax has no effect when the lower or upper yagis is individually selected, other than a negligible loss in the power delivered to the lower yagi. 

With that addition the solution is complete: an L-network to correct the upper yagi mismatch and a delay line to the lower yagi to correct the phase shift due to the L-network plus that of the upper yagi's gamma match. 

The design of both requires determining the phase shift in software since it cannot be measured with the tools hams typically have at their disposal and is in any case difficult to do on the tower. 

For phase shifts of opposite sign the delay line goes on the other port. It is better to add coax than to cut since it is easier done and can be undone later.

Pros, cons and implementation options

Despite the mismatch the stack loses less than 1 decibel of gain. I was surprised. It goes to show how resilient yagis can be. Modest errors of phasing and power division have a small impact since gain is roughly determined by quasi-cosine functions. Look at a cosine curve near zero and you'll see what I mean (I won't get into the mathematical weeds here). In contrast, the RDF of an antenna is very sensitive to phase and current imbalance because for maximum field cancellation amplitudes must be equal and phase exactly opposite (180°).

Since my model of the gamma match doesn't match the real antenna, despite my success doing so with the 15 meter yagi, software tools other than EZNEC are required. There is little point in simply going with an L-network designed by TLW until the total phase error is quantified. Otherwise the solution will be less than optimal, and that is hardly sensible.

Besides, it's winter and it's cold up the tower. It would take a significant array deficit to motivate me to do that much tower work before spring. On the basis of my analysis of the mismatch and correction options I am not sufficiently motivated. One look out the window convinces me that tweaking of the amplifier knobs from time to time isn't an onerous task.

I'll decide on next steps when the warm weather returns. Either to correct the phase error as described here or to take the antenna down and redo the gamma match. The latter is the ideal solution. However, the cost of the less difficult corrective procedure is relatively modest at 14 MHz:

• The L-network has loss but that loss is a small fraction of a decibel. The modelled coil Q of 200 is lower than can be easily constructed so the loss can be kept even lower than that in the TLW window shown above. Of course a good quality capacitor is needed. That is easy with an air variable capacitor with modest plate spacing since in this application the voltage on the plates is only a few hundred volts with legal limit power.
• An SWR of 2 on the coax to the upper yagi has additional loss, but again it is quite low with LMR400 and not a concern. The additional loss on the 100 meters of LDF5 Heliax is more of a concern, though again the increase is quite small for an SWR of 2. Were the SWR higher I'd be concerned. When in stack mode the loss is lower since the mismatched parallel impedance results in a lower SWR of about 1.5.
  

Hopefully you will never have this problem should you build a large HF stack. Mistakes happen, and with all the towers and antennas I have it is inevitable that problems will arise, either when first built or later as material weathers and degrades. Perfection would be nice but never count on it!

Note: There may be one more non-technical article before 2020 closes. Regardless, I'll take this opportunity to wish everyone reading the blog a happy new year and I hope to work you on the bands in 2021. For top band enthusiasts, you can try to dig my QRP signal out of the noise in the Stew Perry contest coming up in a few days.

ARRL 160 Contest: Battle Of Attrition

Last weekend's ARRL 160 contest is a bit of an oddball. Every single band contest has its quirks. The main one is that you can only work each station once, which is a little like ARRL Sweepstakes despite that one utilizing multiple bands. Also, like most ARRL contests, they are more like QSO parties where those outside the US and Canada work each other but others can only work the US and Canada. As a consequence these contests spark only modest global interest.

Of course any DX on top band is attractive and there is interest in that. But as a competition it is of little interest to me. ARRL tends to monomania on tradition founded in the world that existed in the middle of the twentieth century. That is their choice. For true 160 meter aficionados the CQ 160 contest in January is the one that matters.

That is a problem because with little global interest there is a pretty hard upper limit on the number of stations and multipliers you can work. Unless you have a good 160 meter station you will work little DX and indeed there is not a lot to work in this contest unless you are a big gun. The focus for most is on working each other and the farthest ARRL section multipliers. 

Geography is always important in contests and in this one it is those in the US midwest with the advantage, able to reach more of the participating stations than those on the coasts. It is worse on the west coast due to the larger population on the east coast. On 160 meters there is no skip zone to speak of so that linear distance matters far more than on the HF bands. 

For the same reason the east coast has an advantage working the small number of participating European stations, able to add those multipliers and points to their score in lieu of those far west multipliers. For example, I have similar success working W6 and western Europe. When DX conditions are good the country multipliers can really add up.

With limited DX possibilities and the prospect of a long grind through two consecutive nights I do not take the contest too seriously. I've done this contest a couple of times with a multi-op group at VE2OJ, but for various reasons I now prefer to do these 160 meter contests from home. In any case that operation did not go ahead this year due to the pandemic.

Although less of a marathon than the 48 straight hours of CQ WW this one is right up there. Nights are 15 hours long in December so the serious competitor should plan on up to 30 hours of operating and sleep during daylight. I operated 20 hours and that was plenty. That lack of dedication by itself guaranteed that I would not win. This is a contest that favours endurance over tactics.

My ~1000 contacts (dupes included) works out to an average hourly rate of 50. That doesn't look bad but this is not CQ WW. The QSOs are heavily front loaded, just as they are in Sweepstakes. In the first hour I had over 120 QSOs with a mixture of S & P and running. When I quit for the night after about 9 hours of operation my total was around 640. This is ⅔ of my weekend total for less than ½ the hours I operated. As you can conclude the rate falls rapidly after the first few hours of the contest. This applies to everyone and not just me.

It is the casual operators that make the difference. They might only come on for a few minutes or a few hours and they come and go throughout the weekend. If you aren't on at that time you will not work them, and if you don't work them you won't win. You must be there.

Some of the casuals -- which includes serious contesters who are not serious about this event -- choose to run or S & P, and often just one and not the other. Competitors must alternate between running and scouring the bands to maximize their take among the casuals. Of course those in an assisted category spend less time scouring by interrupting their running to click on and call these stations when they are spotted. This gets easier as the weekend continues because running rates get very slow indeed and there is no harm done by not CQing for 30 seconds. Of course after the contact you must race back to your run frequency before someone else grabs it.

Which brings us to the next issue. To maximize your score you must run, and in this contest that involves endless CQing later in the contest. If you are in a high power category, well, all I can say is that you don't need an outside source of heat to warm cozy in the shack on cold December nights!

That is one of the reasons I avoided turning on the amplifier and entered the low power category. It seemed wasteful for a contest that had limited interest to me. By running 150 watts I was able to give my new antenna a workout and discover how I would fare against others with good antennas in difficult top band conditions.

I would say I did pretty well. According to 3830 my placing in the low power category is #6 the last time I checked. That's good since those with a higher placing operated more hours. Had someone scored similarly with fewer hours invested I would have been spurred to see how I might have chosen better tactics. I believe that the antenna and operator performed well.

This is where I must make a negative comment about competitiveness in this contest. A contest that is won by the person with a decent station who operates the longest and CQs the most is a contest that is not a serious one. Skill and tactics should play a larger role in determining a winner.

Consider a shorter alternative with the same rules. By limiting the contest to a single night you could not win by merely nailing your butt to the chair. Tactics would be superior to endurance for stations and operators of equal caliber in the same geographic area. At its current length this contest is a battle of attrition. Stay awake longer than everyone else and you can win, even with mediocre skill and tactics. 

What kind of competition is that? Looping CQ's while you browse the internet is not a true test of ability. Yes, I know that's an exaggeration, though not by much. You do have to toggle the Beverage selector a bit and trim the RIT every CQ or two, or three. It's boring, yet boring wins this one.

In the CQ 160 contest I will be tempted to switch on the amp and try harder. For the DX if nothing else. In the meantime there is casual DXing on top band every one of our long winter nights. I was very pleased when one morning this week I worked a VK6 for the first time on 160. 

Absent a DXpedition to one of a couple French islands to the southwest of VK6 that's as far from FN24 as you can get. For me that one QSO was the equal in satisfaction to 20 hours of the ARRL 160 contest.

Lifting Yagis: 15 and 20 Meter Stacks

 

This is the first of several articles on my (mostly) complete 15 and 20 meter stacked yagis. They were first put to real use in CQ WW CW and they worked well despite not easily rotated or configured. I will now back to talk about lifting and supporting the 4 yagis. There were 3 separate lifting operations:

• The lower 15 and 20 meter side-mount yagis in January
• The upper 15 meter yagi in May
• The upper 20 meter yagi in October
  

The lifts were progressively more difficult. Before each lift the gamma matches were tuned at a lower height. The first 3 lifts were done with a rope tram line which allowed the same rigging to be used to tune and lift the yagi. The upper 20 meter yagi was tuned with a rope rig and lifted on a steel tram line. You can't tune a yagi sitting on a steel cable for reasons that should be obvious.

Related items are mostly already covered in other articles: mast, tram line basics and prop pitch motor rotator.

Lower side-mount yagis

The wintertime lift of these antennas was briefly mentioned in a January article. I'll fill in the rest now. As mentioned above the lifting rig was the same for tuning the lower 20 and 15 meter yagis, and tuning the upper 15 meter yagi. The only modification for each was to move the tower anchor point for each lift. These antennas are not too heavy so we did the lifting manually. Two people are sufficient. Getting a car into a snow covered hay field was in any case impossible and I didn't have convenient access to a tractor.

The mounting brackets for the booms use pinch clamps. These were built by me from the original engineering drawings for this vintage LR20 tower. For convenience I used ¼" 6061-T6511 plate for the boom clamp and galvanized angles to pinch the tower legs. It's stronger than it looks. Not all of the weight bears on the bracket since a substantial fraction is taken by the boom truss.

The boom trusses are attached to a tower girt using short lengths of painted steel angles I pulled from my junk pile. One complication is that the centre of gravity (CoG) of each yagi is not at the boom midpoint. Tramming requires lifting at the CoG so that after mounting the boom had to be slid a short distance to centre the antenna.

Boom counterweights can be used to move the CoG to the boom midpoint. This isn't strictly necessary when the distance between those two points is small and I didn't bother to do so for any of the 4 yagis. It is still important that however it's done that the lower and upper yagis are in the same lateral positions for optimum stacking gain, otherwise the phase shift will slightly reduce stacking gain. 

When the lower yagi is rotatable (mine are fixed to Europe) there will in any case be a phase shift since the rotation centre of the side mount yagi is inevitably offset relative to the mast mounted upper yagi. The impact scales with wavelength and is rarely a concern at HF, even on 10 meters. A swing gate incurs the greatest offset.

The SWR of the yagis mostly survived the lift, as shown below. I was less successful with one of the upper yagis, as we'll come to later.

The 15 meter yagi either suffers from guy wire interaction or a shift in the gamma match. Since it is working well and as expected on air I suspect the latter. The risk of guy interaction was modelled and a picture of the potential difficulty is exemplified by the presence of a guy to the front and left of the yagi the photo below. SWR of the 20 meter yagi didn't shift at all. I took the picture of the 20 meter SWR in the shack because it was cold up the tower that day in January and I was in a rush to descend.

I connected the 20 meter yagi to the Heliax transmission line since it was in easy reach. It was for a few months until work on the stacks resumed. After initial testing the lower 15 meter yagi was left disconnected. The Heliax termination point was further away and I didn't want the bother of a temporary hookup.

Upper 15 meter yagi

We waited for spring to lift the upper 15 meter yagi. Lifting a large and heavy yagi to the top of a 40 meter tall tower and then to the top of a 3.5 meter mast is a major operation and carries risk if not done properly. Cold weather substantially increases risk because everyone is uncomfortable and uncomfortable people make mistakes.

The upper yagi of the 15 meter stack was raised in late spring just as the hay began its growth spurt and the ticks emerged. I don't like asking friends to work in those conditions. Trampling through the hay is unpleasant, makes the work difficult and risks the ticks endemic to the high vegetation. Lifting of the upper 20 meter yagi was deferred until late summer, after the harvest.

As for the side mount yagis we lifting this one manually. We added a third person to do the hauling because of the greater weight and vertical angle. I rigged the rope through a pulley so that the 3 people could work in a line and maintain COVID-19 physical distancing.

While all ended well the lift was not without drama. Despite a lot of experience with this operation I made a mistake in rigging the rope cradle for the tram pulley and haul rope. I would like to tell you what I did wrong but I don't know. The result was that the yagi gradually rotated from its carefully arranged orientation until the boom hung close to vertical rather than horizontal.

Above you see my trusty ground crew puzzling over the predicament. They are (left to right) Alan VE3KAE, John VE3NJ (holding a tag line) and Don VE3DQN, all veterans of tower work at my QTH. The lower elements in this picture are tangled in the lower 15 meter yagi. I went up the tower to wrestle with the yagi to push and pull it around the lower yagi, guys and the tower itself. Lowering it and starting over would have been no easier. It took an hour of frustrating and exhausting effort until it was finally sitting atop the tower.

Mistakes happen, unfortunately, regardless of experience. Happily no damage was done although there was some banging about, including the fragile gamma match.

I was relieved to measure a perfect SWR curve when the yagi was on the mast. It's only slightly little different than when tuned closer to the ground. Modelling agrees that the sharply inclined guys below have little effect.

After twice the time it should have taken the yagi was secured to the mast. I was pretty tired after the marathon effort, as were my friends. We had a late lunch and called it a day. A week later the yagi was lifted to the top of the mast. The tram winch was moved to the haul rope and operated by ground crew while I pushed it up the mast, moving the pulley upward in stages. 

The picture above gives you an idea how messy the rigging can get! Despite the mess it was all nicely arranged. There is also a length of Heliax visible that was raised soon after.

The design and construction of the air core coax choke for this yagi is identical to that for the lower yagis. The difference is that this time, rather than use 400UF (ultra flex) I used LMR400. I considered using RG213 (higher loss at 21 MHz) or ordering more 400UF but instead went with what I had. There are several rolls of LMR400 from 40' to 150' in my stock that I purchased as reel ends at a good price. 

Shown below are the coax choke and gamma match of the upper 20 meter yagi. A continuous 22' length of LMR400 comprises the choke and boom lead in. The choke can be built as a separate unit but I prefer to reduce the number of inaccessible coax connectors and therefore points of potential failure.

Making a choke from LMR400 requires care. The foam dielectric combined with a solid centre conductor can deform when improperly formed into a small diameter coil. Read and understand the mechanical specifications of the cable before proceeding. LMR400 and its various clones do not necessarily share the same specs. These chokes use LMR400 made by Times Microwave.

The minimum bend radius depends on how the cable is used. It is smaller when bent once than when bending is repeated. That should be unsurprising. The 15 meter choke has a diameter of 6" (15 cm) for a bend radius of 3" (7.5 cm). Since 3" is less than the 4" (10 cm) value for repeated bending it is advisable to get it right the first time you wind the coax. There is risk of damage despite being well above the 1" minimum radius for a single bend event.

Damage may not show up immediately. The stress within the thick centre conductor will relax with time or it may apply pressure to and migrate into the pliable foam dielectric. Impedance and power handling will suffer in the latter case. Measure the impedance before and after making the choke. Let it sit for several days and check it again. Doing so can save you grief later when the yagi is high in the sky and the choke is inaccessible out along a long boom.

Because the yagi is perched at the top of the mast the boom truss requires a separate support. It is a pipe several feet long that is clamped to the boom-to-mast plate. For stability there are 4 large clamps holding the plate to the mast. Only two were used while pulling it up the mast to reduce "grabbing".

The truss is adjusted on the ground then fine tuned on the mast to level the boom. Only then is it lifted to the top of the mast where the turnbuckles are no longer accessible. The SWR was also checked to confirm it was good before raising it up the mast. You don't want to discover problems after it is lifted to the top of the mast. The procedure to lift it up the mast was discussed in a previous article.

Upper 20 meter yagi

The upper yagi of my new 20 meter stack has 5 elements, a boom length of 12.5 meters (41') and weighs at least 55 kg (120 lb), including mast clamp and boom truss. This is the largest antenna to date that I've raised at my station. The tram line had to be engineered for the task. Constraints included suitable anchor points, lack of a mast back stay (to counter tram tension) and a forest of guys to navigate. 

The yagi had been sitting on the ground for 2 months awaiting the completion of mechanical work, good weather and the availability of friends. As summer turned to autumn the weather turned colder and unstable.  The first order of business was to adjust the gamma match and confirm that the SWR curve was as expected.

The general approach is the same as for the first batch of yagis. The difference is that due to the proximity of its twin on the tower the tuning location had to change. Another factor is its significantly greater weight due to the more robust boom. A strong rope runs between the towers at about 21 meters height. The towers are 60 meters apart. A winch tightens the rope and the tension pulls the yagi upward. The rope harness reduces droop and stress due the antenna's weight when it is turned and pulled during repeated tuning trials.

Dimensions for the gamma match were almost exactly that of its side mounted twin. That is the ideal to strive for. Later I attached the coax choke and began work on the tram line. It required some thought to a suitable design because, including mast clamp, truss and the rigging the tram line would be under considerable stress.

Rather than rope I opted for a steel tram line and rigging that is more rugged and less prone to the type of mistakes that can happen with ropes and knots, as it did with the upper 15 meter yagi. Steel has the advantage of a small MoE (modulus of elasticity) so that less tension is needed to support the antenna for an equal amount of sag in a rope tram line. That can be very helpful to keep yagi elements from snagging guy wires and other obstructions.

I purchased snatch blocks designed for steel cable rather than ever again risk failure of a rope pulley. This is not a place to skimp as I discovered to my dismay. Although not the ideal choice I have thousands of feet of guy strand on hand so I chose a 200' coil of ¼" EHS as the tram line. Aircraft cable or wire rope are better choices for their flexibility since the stiffer EHS can weaken from the stress of a large load at a single point as in this application. 

Use of multiple pulleys or snatch blocks spreads the load for safe lifts of even heavier antennas using EHS. However, under no circumstances use EHS for hauling. The turning radius around any pulley will be too small for EHS, and that will damage the pulleys and cable. For that job I use rope.

The initial test of the EHS tram was successful. The snatch block I seslected is large enough to ride the guy grips at the mast and ground terminations. That is important to put the yagi close to the mast.

The other tower base is the tram line anchor. A winch tightens the tram line and a guy grip is fitted to a coupled length of EHS to support the load during the lift; the grip is wrapped when correct tension is reached. The upper end is a tow strap looped around the base of the mast and tied to the thimble on the tram line with a shackle. 

Once wrapped the winch is left in line for backup and to take up the tension later when the tram line is disconnected. A second backup is a rope that doubles as an aid to guiding the steel tram line around the lower yagis both before and after the lifting procedure.

I did not anchor the tram line high on the mast since there is no convenient anchor on the opposite side of the tower to support a temporary back stay. With a tension of several hundred pounds I wanted to avoid stressing the mast. My trusty tension meter was used to monitor tension on the tram line and the upper set of tower guys.

Tension on the tram line with the yagi off the ground is less than 400 lb. Tower deflection was slight and not a problem at all. The tension on the two opposite top guys each rose about 100 lb.

At right is the pulley arm at the top of the tower, shown after the antenna was raised and most of the rigging removed. The shackles provide freedom of rotation so that tension on the haul rope aligns the pulley with the ground anchor and the lower pulley. The tower face does not quite point in the needed direction. The pulley at the base of the tower enables a vehicle to provide lifting power with horizontal travel.

For additional safety I put keepers on the pulleys. These short loops of chain protect against falling yagis and tram line should a pulley suffer a catastrophic failure. At this height the heavy weight would destroy the lower yagis and can damage or even sever a guy. The latter would be catastrophic. The precaution is well worth the trouble.

When the big day finally came -- warm and sunny for early October -- my friends gathered for the lift. Unfortunately we were cursed when the wind speed rose too high for a safe lift. The yagi remained grounded and we instead undertook other important jobs on my list. 

The wind load on a 5-element 20 meter yagi makes it too unwieldy to steer and stabilize when the ground wind speed rises above 40 kph. The wind is almost always stronger 40 meters or more above ground. It isn't worth the risk. Had there been two of us up the tower we might have proceeded. 

Two weeks later we tried again, this time successfully. A shorter delay would have been better if only I could coordinate my friends' time with the weather forecast! As the saying goes: beggars can't be choosers.

Once it's all rigged the lift goes smoothly. The challenge is getting to the point where it looks easy! The driver (VE3DQN) is just beginning the haul in the picture. I am always begging cars from friends for these pulls since an automatic transmission is strongly recommended for smooth torque control and the ability to quickly "feel" and react to snags. Any vehicle has sufficient power since it is rare that a tower section or antenna weighs more than one adult.

There are a couple of attachments near boom centre. The turnbuckles for the boom truss are tied together and to the boom. The bit of rope tying the two turnbuckles is very important. If you accidentally let go of one while attaching them to the mast it can't fall out of reach. Mistakes happen, so plan for them. The other item is a come-along and tow strap. They are for lifting the antenna into position once it was at the top of the tram line. Doing it this way was easier than climbing encumbered with the awkward weight.

The elements are level in this pull and that was a mistake. Usually I tilt them upward, perhaps as much as 30° to better clear guys. Since the upper 15 meter yagi is already attached to the mast and the elements tend to tilt further upward near the top of the tram when the haul rope takes all the weight I wanted to avoid tangling the elements of the two antennas. My improved rigging kept the elements from tilting and due to the droop in the long 20 meter elements directors 1 and 2 (the ones on either side of centre) did slide underneath the upper set of guys.

When I saw it happen we lowered the antenna (easy to do with a car providing the muscle) and I adjusted the rigging and attached a tag line for steering. This got us past one guy but not the other. Up the tower I could not swing the element out of harm's way since the antenna is too bulky. Instead I leaned out and removed the element. I hung it on the tower until later. With that last tangle corrected the yagi was lifted to the side of the tower.

At this point things get complicated. However it's a complication that I planned. To avoid bending stress on the mast by anchoring the tram line a few feet above the tower (discussed earlier) the tram line is anchored below the top of the tower. I attached the come-along between the boom truss clamp and the boom. A cable and shackle to attach the come-along was installed a few days earlier. It is visible in the picture above.

Once I took up the weight the tram line was detached at the ground anchor and walked in to the tower. Next, I removed the snatch block, detached the cable from the mast and tied it off to a previously positioned shackle located on the tower below the mast. The space above the yagi was now free of obstacles.

With the 1 ton come-along I pulled the yagi the 2' or so to the side of the mast where it was to be mounted. The only difficulty was that the bolts on the boom-to-mast clamp hooked under the top tower girt and the boom hooked under the pulley arm (see picture above). I had to push the boom outward with one hand while stretching my other arm to crank the lever on the come-along. Other than the muscle required the lift was quick.

In case you're wondering, the clamp plate was made in my workshop from ⅜" 6061-T6511 plate. The u-bolts on the boom are the big stainless ones from DX Engineering with the textured solid aluminum saddle. The u-bolts on the mast are the galvanized Cycle 24 clamps, also from DXE. The bolts are not inexpensive but this is not the place to be cheap! I prefer the Cycle 24 clamps for the mast since they are rugged, easy to work with on the tower, don't have the galling risk of stainless steel and resist motion due to wind torque better than the textured saddles and round stainless u-bolts.

By this time sunset was close and my friends had families expecting them back home. The antenna was left untested with the boom truss not yet attached and a missing director. The next day I slid the boom so that boom centre was at the mast. The truss was attached and I levelled the boom. Director #2 was attached a few days later.

Sad to say, all was not well electrically despite no mechanical problems and no antenna damage. The SWR was about 2 across the band. Although the yagi worked perfectly well as a yagi somehow the tuning of the gamma match shifted before the lift, perhaps when I installed the coax choke or when I weatherproofed the components of the gamma match. 

The season is late and this is not an easy antenna to lower, tune and lift again. Besides which, the yagi works, on its own and phased with the lower yagi. It just doesn't have a low SWR and power division between the yagis is not optimal. I took a full set of measurements and sat down to study them on the computer. There is a solution that does not involve taking the antenna down. More about this in a future article.

I'll end with a picture taken at sunset the next day after the boom was trussed and level. The fall colours are golden and sporting a missing director the yagi looks like a child grinning after scoring big with the tooth fairy. But it is pretty.

On a closing note, you may have noticed that despite the length of this article I am vague about numerous details. That is deliberate. From years of corresponding with readers of the blog, too often these articles are taken as gospel rather than a simple description of my adventures in amateur radio. That is, for some out there they feel that if I, a ham, can do these things so can they. The reality is that this is often not true.

Before embarking on a project the size of this one you need to reflect on the challenge, the danger and, yes, the cost in money, time and maintenance. These are serious considerations. Thank you for reading and, please, be careful out there.

Coming up...

Expect articles this winter on the complete stack switching system, operator control and planned integration with station automation. You can also expect to hear more about the anomalous SWR of the upper 20 meter yagi. As already noted the stacks played well in CQ WW CW so the SWR is not a deal breaker. 

The prop pitch motor suffered another failure after the bearing was repaired and that was why the stacks were not quite ready in time for the contest. The motor is working fine for now but it will need more work next year. I may have to write another article on prop pitch motor repair when that job is done.

In 2021 or later further improvements to the stacks will be investigated with the intention of improving their effectiveness during contests. There will also be a stack for 10 meters to take advantage of the rising cycle 25.

CQ WW CW - How the Antennas Played

Another CQ WW CW contest is behind us. It was quite the weekend. On a positive note my single op score is the best it's ever been. This is the result of all the antenna and tower work I and many of my friends have done over the past 4 years. I have only entered a contest with better antennas as part of a multi-op team at someone else's station. 

The raw numbers are as follows, obviously before log checking and several incorrect multipliers tagged by the software:

 Band  QSOs  Zones  Countries
------------------------------
  160:  334    12       34
   80:  740    16       54
   40:  673    24       65
   20: 1204    33       83
   15:  567    20       64
   10:  115    18       35
------------------------------
Total: 3633   123      335  Total Score = 4,220,012

Despite my success and some impressive looking numbers looked at in isolation my effort was far from competitive in the single op, high power, unassisted category. It could have gone better. At best I'll be ~30^th overall and top 5 in Canada. The winners will have much greater scores. There were several reasons for placing:

• One amplifier, and it is not quite in the same league as others in the high power category. Therefore any attempt to do SO2R was with low power on the second radio.
• No BPF (band pass filters) made SO2R very difficult except for a small number of frequency and antenna combinations. Most of the time the kilowatt made operating on the second radio impossible.
• I could not get full use of the antennas because the control systems are missing. Everything works pretty well and with improvisation not practical while operating most of the features are there.
• My skills need improvement. Despite first operating contests 45 years ago and now perhaps more active in contests than ever, I do not have the requisite experience to get the most out of my station. Another way of putting it is that the station is better than the operator. For my previous less developed stations and power level my skills were the equal of or better than the station.
  

Of these the first 3 are easy to remedy with the investment of time and money. They will get done. The last is the most difficult. I have to decide how much of my time to invest in skills improvement. It won't be easy. For example, concurrent running on two bands with unruly pile ups on both. 

I know I don't have the talent to be work my way up to the top tier of contesters, yet quite a lot of the gap can be closed with a serious effort to improve. That is my objective. Beyond that my focus will be open my station to multi-ops once the pandemic is over.

Let's put all that aside and focus on the antennas since that will be of more interest to you. I learned a lot this weekend about how the antennas played on the big stage. There were positive and negative revelations. I will use this experience to refine my antenna plans for 2021 and beyond.

160

Band conditions were poor and I suffered along with everyone else. Although there was some improvement as the weekend progressed it was still awful. I expected up to twice the country count. The new antenna works well and the amplifier was adequate, and I did get through to some of the weak DX that others didn't.

The Beverages continued to work well. The only difficulties were that I don't have enough of them and the current mechanical controller is tedious. After most CQs I have to run through 3 of the 4 available directions -- NE, SW, S -- to listen for replies. While that process is unavoidable it can be made easier. This is already on my list of winter projects.

The 160 mode of the 80 meter vertical array was not used, nor did I intend to use it. When the superior winter antenna is up it is only needed as a backup.

The coming 160 meter contests -- ARRL this weekend and CQ in January -- will be better tests for the antennas.

80

Like 160, 80 meters was poor the first night. The improvement the second night was striking. While darkness lasted in Europe my rate continued to be good. The big difference this year was that all the Europeans disappeared when the sun rose. With improved high band conditions they didn't stick around, which is smart on their part, despite continuation of the opening for another hour or so.

Since the antenna is the same as last year there is nothing noteworthy to report on its performance. It works but it could be better. I have previously discussed planned improvements and those were not looked at this year because of more important projects.

My typical strategy was to point the antenna northeast when the European rate was good. Other times I set it to omni-directional to attract callers from anywhere and I used the Beverages to pick out the weaker stations. Other directions were selected when calling specific stations in the Caribbean, Pacific and elsewhere.

I suspect that I will eventually have to complement the Beverages with another receive array for more effective SO2R and multi-op contests. Receive antennas are mandatory on 160, useful on 80 and occasionally needed on 40. Splitting the feed from the Beverage controller does not provide the needed flexibility and independence of use.

40

My most frustrating experience in this contest was 40 meters. The high dipole works great but is hopeless on its own during the contest. With a kilowatt the antenna attracts too many callers that cannot be heard. I was constantly switching in the Beverages, or the XM240, and hunting in all directions. It was not dissimilar to standard operating procedure on 160 meters. In fact it was worse because the Beverages have sharp main lobes on 40 meters and too many stations are not received well by any of the (currently 4) Beverage directions.

On example was a weak signal while I was running Europe. I expected it to be a European and I didn't hunt it out on the Beverages. It turned out to be a VK6 on the long path, probably from the southeast. Previously I would often point the XM240 east in the late afternoon to catch these opening while also working the start of the Europe opening.

On the positive side the dipole serves to work Europe and the US at the same time. A similar case is early morning opposite paths to Asia and the Caribbean. The dipole is temporary, an experiment to test its durability, to be replaced by a 3-element yagi based on the dipole's design. If that project doesn't happen as planned in 2021 I'll need to put another small yagi up at 46 meters just like when the tower first went up.

The XM240 at 21 meters continues to perform well. My mistake was to eschew its use and depend too much on the high dipole. The small yagi was typically pointed south or southwest to work the Caribbean, South America and the US. Perhaps I should have swapped their roles. To compensate for a slightly weaker signal reception would have improved, leading to improved results, more time spent on 40 and prevented listening fatigue.

20

I am behind with articles describing the state of work on the 15 and 20 meter stacks. The phasing harnesses, stack switches and control lines were completed only a few hours before the start of the contest. All that tower work in the two days leading up to the contest left me fatigued and far from my best for most of the contest. The work was worthwhile since they boosted my results.

Unfortunately the control lines into the shack had nothing to connect to. The rotator and antenna selectors worked but were not usable in the heat of the contest operation. I'll skip the details in this article and simply say that for the contest the yagis were fixed on Europe (per the photo) and set to BIP (both in phase). The tri-banders were used for all other directions on 15 and 20 meters, and for 10 meters.

The stack to Europe works very well indeed. I spent most of my time working Europe on 20 meters because the stack worked so well and the opening to Europe was longer and deeper than on 15 meters. While running I had callers from south Asia and long path from VK. That may have happened anyway with the TH7 at 43 meters, but it's impossible to know. 

The 20 meter stack is a minimum 1 S-unit improvement over the TH7 and often 2 to 3 S-units. Unfortunately these numbers are not easy to convert to decibels and I won't try other than to estimate that the improvement was never more than 10 db. Of course that's a lot: the equivalent of using 1000 watts versus 100 watts.

Combined with a kilowatt you can imagine how intense the pile ups were. Pulling out calls was difficult and too many wouldn't stop calling when I sent partial calls. I need to get better at this or the improved antenna could hurt rather than improve my score!

Back scatter to the eastern US is greatly enhanced by the antenna gain and high power. I had lots of American callers while using the stack to Europe. There were also many off the back of the stack into W5/8/9/0. The F/B is good but that's relatively to the forward gain. On an absolute scale the stack's rearward performance is also improved over the other yagis.

15

The difference between the stack and the TH7 was actually better on 15 than on 20 meters. Although I knew it would be good I wasn't fully prepared for the reality. Signals in the noise with the TH7 would come up to S4 or S5 on the stack. S9 signals would often jump up to +10 db or better. I had no difficulty attracting attention.

I could have doubled my QSOs on 15 had I been equipped to do SO2R properly and had I not overslept Sunday morning. The latter is part of the price I paid for pushing to complete the tower work right before the contest. Short daylight hours this time of year account for the abbreviated 15 meter openings on the northern paths. The lower depth of the opening garnered fewer multipliers than on 20 where the opening extended deeper into Russia and beyond on the productive northeast path.

Ideally I would split the stack to have the lower yagi pointed to Europe or other shorter paths and the upper yagi on the longer paths to Asia, the Pacific and for long path. It isn't critical yet. As cycle 25 progresses the stack's flexibility will deliver dividends. That time isn't far off.

10

Better antennas for 10 meters are in my 2021 plan. For now all I have are the TH7 at 43 meters and the TH6 fixed south at 22 meters. For the limited though very welcome openings they were good enough. 

The fixed tri-bander pointing south was the more productive of the two. With marginal openings it is the north-south path that is most reliable. It is handy to have an antenna always pointing that direction. Of course that was no accident. To work the small number of European and African stations that could be heard the TH7 was adequate though not spectacular. Those multipliers were a gift.

Next year I must have better antennas for 10 meters. A year from now 10 meters is certain to be much more productive and I need to become more competitive. The TH7 will be taken down and will most likely be side mounted on the same tower and pointed west. The new yagis will be higher up and stacked.

Winter works

Over the winter my antenna work will mostly be done on the computer. Control systems for the operating desk will be designed and built. Both are ideal activities in our cold climate and the isolation needed while the pandemic runs its course. The control systems will be a mix of hardware and firmware. Long term I expect to transition to software with selections on a touch screen, and the only hardware being relays on the control lines.

By late winter I expect to gather material and begin construction of antennas. For the next CQ WW the station should be fully operational with pretty well all the important antenna work done. That is not to say that the station will remain static! There will always be new and interesting project to pursue. For example, I have no antennas for 30, 17 and 12 meters, and then there's VHF to pursue. 

It is a certainty that there will be blogging material for a long time to come.