Tuesday, January 31, 2017

40 Meters 3-element Wide-band Wire Yagi

As I look forward to having a tall tower later this year I am talking to others while reviewing my objectives to make a final determination on what antennas to focus on first. This brought me back to 40 meters and wire yagis. I wrote several articles on this topic in 2015 and these remain among the most popular according to web site statistics and referrals from other sites.

This popularity is not too surprising to me since 40 meters is the first band for which an antenna with gain requires more effort than buying a small bundle of aluminum and tossing it up on a tower or roof. Whether you contest, DX and just want a reliable band for rag chewing through the downside of this solar cycle 40 meter antennas with gain are an asset.

Where I am and where I'm going

The XM240 currently up 21 meters atop the free-standing tower is adequate for short paths, including Europe and the US. The bandwidth is poor with respect to gain, F/B and match. Regarding the latter two the deficiency is readily apparent. Gain is not easy to assess without the ability to A-B test against another antenna of know characteristics. Nevertheless this is a perfectly fine antenna, even with its limitations, and I am happy with it.

A full size 3-element rotatable yagi up 43 meters, should the plan come to fruition, will do wonders for longer path DX and contesting, especially to snag rare multipliers and grab those rare and distant DXpeditions. For the high volume contest paths to the US and Europe it will help very little since those are well addressed by an antenna at half that height due to the typically higher radiation angle associated with those paths.

My tentative plan was to move the XM240 to the guyed tower when the tower is finally raised later this year, side mount it at a height of around 25 meters and make it fully rotatable (300°). However this introduces a problem. The US and Europe are in roughly opposite directions and the paths are frequently open at the same time. Rotation is impractical for switching between working those two paths during a contest.

This brought me back to the idea of a fixed, reversible yagi pointing northeast and southwest. If made of wire it can be built at low cost and would provide excellent diversity for contest and everyday operating. One disadvantage of that antenna is its narrow SWR bandwidth, although better than a short 2-element yagi like the XM240. If I were only interested in CW and digital modes that would be no problem. SSB coverage without matching and switching complications is desirable for contests.

The time had come to do some modelling.

Improving the 3-element wire yagi: coupled resonator

I will take the reversible 3-element yagi with inverted vee wire elements and try to improve it to meet my current needs. This is what I want to accomplish:
  • Keep the gain as high as possible, especially in the CW band segment
  • Low SWR across the band -- 7.0 to 7.3 MHz -- without switching or tuning
  • Instant switching between directions
  • Similar performance -- gain, F/B, match -- in both directions
This is a tall order. Per my earlier models on rotatable 40 meter yagis there are really only three methods of extending bandwidth:
  • Switched matching network, which adds complexity and operating inconvenience
  • Parasitically coupled resonator or a dual-driven element, both which add a fourth element
  • Spreading the resonance of the reflector and director, which lowers gain
I chose to go with the simplest solution: the parasitically coupled resonator. This is a popular technique for achieving a wideband 50 Ω match on multi-element HF yagis, such as the OWA series of designs by WA3FET. I previously used on to achieve a full band match on a 3-element yagi.

There is a substantial cost for the additional element -- money, wind load, weight -- on a 40 meter rotatable yagi, a cost that is almost entirely avoided with a fixed wire yagi. It was worth a shot. Let's review how I did.

Modelling procedure

To begin I used the exact dimensions of the director and reflector from earlier 3-element design. Recall that it is these elements, not the driven element, that determines gain and F/B and SWR bandwidth in a 3-element yagi. Eventually some change became necessary, which I will come to shortly.

The driven element and coupled resonator were initially separated by 1 meter per my modelling results from the full size yagi design with a coupled resonator. That antenna covered the entire 300 kHz of the 40 meter band with impressively low SWR. Rather than borrow one of WA3FET's designs I based mine on seeing them and combining that with what I know of yagis. I must have done something right!

I placed these two elements -- which together comprise the driven element system -- symmetrically around the centre of the boom to best preserve equal performance in the forward and reverse directions. True symmetry is however only possible if the driven element and coupled resonator are reversed along with the director and reflector, and I chose not to do this to keep the design relatively uncomplicated. There is therefore some asymmetry in performance.

Modelling a coupled resonator requires some care since it is only a short distance from the driven element with respected to wavelength: 1 meter = 0.024λ. Segment lengths in both elements must be made as equal as possible, even as the lengths are adjusted during modelling, or there will be significant errors. A short 1 segment centre 10 cm long wire is inserted in all elements to minimize NEC2 inaccuracy due to the angle between element legs and to facilitate insertion of source and loads.

When I started modelling this antenna I expected that it would be more difficult to achieve a broadband match as easily as with the full-size yagi. This is indeed what occurred. The reasons include:
  • Thinner conductors make for inherently higher Q antennas
  • Bending dipole elements into a vee lowers the radiation resistance, both increasing loss and constraining the current range in the driven element and couple resonator, which in turn affects the feed point impedance
Without a firm theoretical knowledge of what should happen I ran a series of modelling experiments to see how far I could push and prod the antenna towards my performance objectives. I used the current and net reactance to adjust each subsequent run. Ultimately I had a reasonable design with a great SWR and acceptable gain and F/B.

As it turned out that model was wrong. Checking the antenna with the average gain test in EZNEC I discovered that I needed to double the number of segments to coax NEC2 to generate more realistic results. The final model has about 40 segments per half leg, with some variation to equalize segment lengths in all elements.

The net gain is reduced by approximately -0.3 db due to copper conductor loss (AWG 12). The driven element and coupled resonator separation finally settled at 1 meter, exactly where I started. As far as I could discover this distance, while not overly critical, seemed to give the best results. Unfortunately this turned out to be large enough to make performance asymmetrical between forward and reverse directions.

Achieving nearly full band matching with an SWR below 2 required spreading the tuning of the director and reflector. To do this the director was shortened a small amount and the inductor load on the reflector was increased. The reduction in gain of about -0.2 to -0.3 db was, in my judgment, a good trade off. See the above EZNEC SWR chart of the yagi in the forward direction.

However performance is worse in the reverse direction so if you build this antenna you would have to pick your favourite direction and orient your driven element and coupled resonator accordingly. SWR bandwidth is reduced by ~30 to 50 kHz. A static or switchable L-network can help to improve the match, in both directions. I experimented with this but I am not prepared to make a firm recommendation on which is best. There is enough doubt in the quality of the modelled impedance that I would first build and tune the antenna, and only then measure the feed point impedance and build an L-network to transform it to 50 Ω with, hopefully, a far improved SWR.

Calibrating reality to the model

Wire gauge, insulation and other modelling inaccuracies make it vital to calibrate construction of the yagi. You cannot simply cut wires to the lengths found in the model and expect to achieve the modelled behaviour. For a simple dipole or vertical making an adjustment after construction is easy. Not so in this antenna unless you have a great deal of time on your hands.

Perhaps the simplest method of calibration is to build and tune one element so that its resonant frequency is identical to that in the model. In this wire yagi the best element for doing this is the director/reflector elements (excluding the reflector coil) since its tuning is critical to gain and F/B performance and any matching issues can be dealt with in the driven element and coupled resonator which are within reach of the tower.

To do that the modelled resonant frequency must be known. I deleted all of the wires from model other than the director and measured its impedance in free space and at several heights. In free space it is 56 Ω at 7.375 MHz. At the reference 25 meter height it is 48 Ω, also at 7.375 MHz. However at other heights the resonant frequency is different: 7.425 MHz at 20 meters and 7.350 MHz at 30 meters. For other heights you should run a model first. Remember to put the element under enough tension to remove sag that would reduce the interior angle and raise its resonant frequency.

Once the element is built and tuned to the corresponding modelled resonant frequency the other elements can be scaled accordingly. In my model the total element lengths are as follows:
  • Director and reflector: 19.56 meters, with a 1.95 μH centre coil switched in for the reflector
  • Driven element: 20.72 meters
  • Coupled resonator: 20.79 meters
The interior angle of the inverted vee elements is 120°, just as it was in all the other 40 meter wire yagis I've modelled on this blog.

The angle can be reduced if that's desirable or necessary in smaller areas. Should that be done the above measurements are no longer valid. The revised antenna would need to modelled, not simply scaled. It is not a trivial task to come up with a optimized design for these variations. So be prepared to do some work. Do not expect that you can go ahead and build the antenna per my measurements and then merely cut and trim to get similar performance.

Comparison to other yagis

I took several yagis from previous design articles to compare these wide band wire inverted vee yagis.
  • XM240 (proxy design since NEC2 cannot accurately model this antenna)
  • 3-element reversible inverted vee wire yagi
  • 3-element full-size yagi
  • 3-element full-size yagi with a coupled resonator
All antennas were modelled at an apex height of 25 meters over medium EZNEC ground [0.005, 13], including conductor loss. All the models were improved from their original appearance in this blog to ensure that gain errors due to segmentation problems are correct to ±0.2 db.
I plotted the actual maximum forward gain without regard to elevation angle rather than the 10° I used previously for general DX usage. From my QTH Europe and the US paths are typically associated with higher elevation angles. Since the antenna apex heights are the same (average height of inverted vee elements is lower) the maximum gain is within a narrow range of elevation angles -- 21° to 24° -- tending lower as frequency increases, as expected.

Bandwidth for 2:1 SWR ranges from approximately 150 kHz for the XM240 proxy, 200 kHz for the 3-element yagis, 250 kHz for the inverted vee yagi with a coupled resonator and more than 300 kHz for the full-size yagi with a coupled resonator.

There are a few things that jump out of these charts. One is the different behaviour of 2 and 3-element yagis. This was expected and is typical. The other is how the varieties of 3-element yagi behave at the upper end of their usable range. What is different is how their performance diverges.

Some of that performance can be recaptured by shifting the frequency range of the array upward, at the expense of some gain and F/B at the bottom of the band. Since I'm primarily a CW enthusiast I choose not to make that compromise. You might choose differently.

The wire yagis have lower gain, which is expected. This is due to conductor losses and the vee shape (typically -0.3 db) and the lower average height. Yet for most of the range the gain difference is quite small, coming in at around 0.5 db. The gain loss is greater at the top of the band. As already mentioned this can be corrected, with trade-off at the bottom of the band.

In every case the 2-element yagi is a poor performer in comparison to the simplest 3-element yagi. That does not make the XM240 a bad antenna, just one with the inherent limitations for any antenna of this type. It is still far superior to a rotatable dipole or fixed inverted vee, and without excess requirements for a rotator and tower.

Will it be built?

Short answer: I don't know. First the tower must be built and something put up at the top, 43 meters up and more. It is possible that if I feel the pressure of time I will instead do something different on 40 meters for at least the rest of 2017. In this same my fallback option for the top of the guyed tower is the XM240, if I run into difficulty putting up a full size yagi this year.

Even if I build a wire yagi it may be the 3-element design I based this one on, just for the symmetry and easier construction and tuning. Unlike in that article, since I will only have the one tall tower this wire antenna will require a more conventional, although it will not be a continuous conductor to avoid interactions with other yagis on the tower. There are a few ways to accomplish this feat despite its great length (48' or 14.5 meters).

Stacking with the top yagi is on the agenda. Again, that will depend on time. Once the top antenna is selected I will model the antennas to determine whether stacking can be beneficial. It often isn't for yagis this close together -- 18 meters or 0.4λ.

Not matter what I need diversity on 40 meters and that calls for more than one antenna.

Thursday, January 19, 2017

Winter 80 Meter Inverted Vee

I need an antenna for 80 meters. With the declining solar cycle the MUF easily falls below 7 MHz, reducing the opportunities for evening operation. There is also the matter of contests where one cannot possibly compete without 80 meters. With the North American QSO Party CW rapidly approaching I moved quickly. Yes, 160 matters as well, but one step at a time. I had a kludge prepared for 160 meters.

With the only the one tower as an easily available support my options were limited.The taller trees in the vicinity would certainly support a wire vertical or an inverted-L the time and effort required was not justified. Since radials are out of the question with this tower I decided to keep it simple and put up an inverted vee.

I toyed with the idea of modifying my multi-band inverted vee to extend the 40 meter element. That would remove interaction with the XM240, get me on 80 and on 30 and 17 meters with a resonant antenna. I stretched out the antenna to consider how to do it and decided that the mechanical changes would make the project difficult. Doable, certainly, just not quickly.

I instead decided to roll out some fresh wire and put up a monoband inverted vee for 80 meters. The antenna could be left where it is or deployed on another tower later in the year to complement the planned vertical array. A moderately low horizontal antenna for 80 meters usually does better for the short paths needed to draw in QSOs with the northeast US, and can sometimes outperform a vertical on select DX paths at sunrise and sunset.

I oriented the legs north-south to avoid the house. It is therefore primarily horizontally polarized in the east and west directions and vertically polarized to the north and south. The adjacent EZNEC view of the antenna gives an idea of how it's situated.

The apex of the vee is 2.5 meters below the XM240 boom, which is 18.5 meters high. Since an 80 meter λ/2 wire is not resonant on 40 meters I anticipated little interaction. I reasoned that even if there was some it would have to be tolerated for the time being.

A coax coil for a common mode choke is difficult on 80 meters. It takes a lot of cable wound as a single layer coil on a rigid form, all of exacting dimensions, to get a high impedance at 3.5 MHz. A scramble wound coil of indeterminate size will not work the way it can on higher bands. A few months ago I purchased several 1:1 toroidal baluns from another ham, and this was the first opportunity to put one of them to use. I tested them first on the work bench with an antenna analyzer and a few non-inductive resistors.

The construction of the feed point is mechanically robust, taking advantage of the Balun Designs backing plate and integrated hose clamps. They are designed for a boom mount. A 3' length of Schedule 40 ABS pipe serves as a boom proxy and as the centre insulator. The back end of the pipe (not visible) is secured to the tower with a u-bolt. Scrap dacron rope ties the forward end to the tower. The pipe level is just above the Tailtwister.

I installed the antenna on the same climb that I recalibrated the mast after a wind storm. I even dragged a 40 meter length of RG213 up with me. This was the old coax that previously showed a DC short. A new connector solved that problem. The repaired cable tested good with the analyzer. The vee legs and coax twirled together when hauled up by rope. I untangled what I could on the way down as I taped the coax to the tower, then puzzled out the rest when I back on the ground.

One nice thing about having a lot of land is you can do things with antennas you would never do on an urban lot. I paced out one side of the inverted vee and found myself in an empty expanse of grass. I marked the spot in the snow and went looking for a suitable rock: not too heavy to carry yet heavy enough to take the tension needed to remove wire sag. The other end was conveniently right where I stored the LR20 tower and could simply be tied to a section.

I connected the analyzer to the coax and found that resonance was around 3.650 MHz. The SWR at 3.5 MHz was too high. I moved to a wider set of anchor points (dragging the rock and tying the other end to a further tower section) to lower the resonant frequency. That pulled resonance down to just below 3.600 MHz which lowered the SWR at 3.5 MHz below 2. The larger interior angle increases risk of yagi interaction but that was easier than lengthening the antenna. Presumably the insulation had a higher velocity fact that I had included in the software model.

On the air

The wait to test the antenna was brief since I finished the work an hour before sunset. The band was good and soon after sunset the log filled with Europeans plus A45XR. The antenna clearly worked, possibly better than the tower vertical I had in Ottawa. However that's difficult to tell.

An inverted vee with an apex not quite λ/4 high is a poor radiator at low elevation angles. On the other hand a vertical with a poor radial system and surrounded by metal-rich suburban houses has higher ground loss and other environmental loss. A proper comparison is of course not possible so I can only speculate based on educated guesses of the prevailing factors in each case.

The antenna performed well in the NAQP contest. There was really nothing I could hear that I could not work. Calling CQ generated modest runs. The antenna meets my expectations for contest and DX operation. It'll do fine as an expedient solution for the duration of the winter.


To my surprise and dismay the inverted vee interfered with the behaviour of the XM240. This is despite its non-resonance on 40 meters. The yagi's SWR would swing depending on direction (orientation to the fixed inverted vee) and the F/B declined on some paths. The F/B is already poor as expected for a 2-element yagi so the degradation was unwelcome. Looking west toward the Pacific the F/B was especially bad. It takes little disturbance to upset the fine balance of phase and amplitude between the driven element and reflector to get the best F/B.

I ran variations of the software model shown at the top of this article with different separations and orientations. The modelled performance was very good. There was only a slight distortion when the yagi's elements were parallel to the inverted vee. Measurement with an analyzer showed no resonance near 40 meters on the inverted vee.

Although the inverted vee alone is non-resonant I reran the model with a 40 meter long transmission line equivalent to RG213, with either a short or open at the shack end. Still nothing. Perhaps there is some effect due to the balun that is exciting a resonance that the analyzer does not see.

For now the interaction remains a mystery. Opening up the vee to tune it may have been partly responsible for a non-resonant coupling effect. Even so it is not evident in the model. Although he problem isn't so serious that I absolutely must track it down I want to understand what is happening. I may experiment with it a little to see what I can learn.

Looking ahead

After the contest I resumed DXing on 80 meters. This is when I was able to better discern the antenna's limitations. Operation on the low bands is primarily noise limited, both at your end and the other end. I find there are a large number of signals just riding within the receive noise level. Those I call tend to find the same with my signal. Only a few decibels would make a world of difference.It is particularly galling when a fairly rare DX station copies me fine while I struggle to pull him through.

While a higher horizontal antenna or a vertical with a large radial system will go some way in solving these problems that is only a partial solution. I need a directive, low noise receiving antenna for 80 and 160. That is in my plan for 2017, and perhaps soon. The other need is power.

Of course one can always watch and wait for a rare 3 minute opening to a far country that comes only once or twice a year and so make incremental progress toward 300 countries over the years. Many have done so with surprisingly modest suburban stations. That does not suit my particular objectives. When the DX is there I want to work it. When the contest is on there is no possibility of watchful waiting. Note how this is very different than how I operated for several years with QRP and small antennas. But then I always did poorly on 80 and 160, with some notable exceptions.

The next significant test for the inverted vee will be the ARRL DX contest coming up in February. I am keeping my expectations for 80 meters very modest. My expectations for 160 are worse: unlike CQ WW we cannot work Americans for points.

Third harmonic

I still have no antenna for 30 meters. I hoped that this antenna would serve as a stopgap until I could put up a proper antenna for that band. Much like a 40 meter dipole can perform well on 15 meter, at its third harmonic, the 80 meter inverted vee has a third harmonic near 30 meters. The model and the measurement agreed closely on this score, delivery a resonance at 10.8 MHz.

Unfortunately while that may seem close it really isn't. The SWR at 10.1 MHz is high. The rig's internal antenna tuner cannot deal with it. An external tuner is required. There is no convenient way of switching the tuners I own in and out of line. They lack that feature. I did experience one fortunate instance of freezing rain this week that lowered the resonant frequency enough for the rig's tuner to bite, allowing me to work a VK2.

I did a manual insertion of a tuner during NAQP to use this antenna on 160, with the coax shield disconnected. The tuner was adjusted prior to the contest, bringing the SWR within range of the rig's tuner. It did surprisingly well on 160 for what is in reality a dreadful antenna. But as in the parable of the dancing elephant you should not criticize its dancing but rather be amazed that it can dance at all.

Sunday, January 15, 2017

Hope and Wind Are 4-letter Words

Last week we had a wind storm that provided the first test of the survivability of the new tower and antennas. While everything did survive there was an effect that calls attention to the danger of assumptions and the best laid plans. Worse is relying on hope alone, which is all too common in the amateur ranks.

I didn't do this yet I did fall victim to my assumptions and a "sensible" risk assessment. As with hope, wind is also a 4-letter word. (For those outside the North American English language culture, many of the common obscene/swear words are 4-letters long.) There are no pictures of the antennas in this article. It would not be informative since a picture would only show the tower and antennas standing there as usual. A picture would not show what happened.

The wind

This was not a severe weather event. For many it was welcome since it brought a strong southerly air flow that quickly raised the temperature to a near record high. The winds were sustained at and above 50 to 60 kph for almost 12 hours with gusts up to and possibly exceeding 90 kph. A better estimate isn't possible since I am not near a weather station and the darkness did not allow for direct observation. Instead I slept, reasonably secure in the confidence of my planning.

The wind was within my survivability threshold even with the relatively large wind load I have temporarily placed atop the Trylon. Since the wind area is at its lowest with the yagis broadside to the wind I turned the yagis northwest at the start of the storm. The wind was from the southwest. In the morning I discovered that they were pointing northeast, with the booms aligned with the wind. That is, the mast slipped within the Tailtwister mast clamp until the maximum wind area was exposed to the storm wind.

Precautions taken

When I installed the mast and rotator I deliberately avoided pinning the mast to the rotator. I didn't even excessively torque the u-bolts of the clamp. In consideration of the antenna wind area my preference is that if the yagis want to move I'll let them. I'd rather that than have the peak torque transferred to the tower. Climbing the tower and turning the mast is preferable to risking the integrity of the tower.

Some hams don't like the idea of climbing, or depending on others to do it for them, and prefer to pin the mast. A safer approach is to wind balance the yagis, whether home brew or commercial product. There are software tools available to do this, or one can follow the construction details of yagis that have been wind balanced, such as those in the ARRL Antenna Book. My yagis are moderately well balanced, however I have not confirmed that.

Calculation of antenna wind area

Calculating the wind area of elements can be time consuming and prone to error. There are many factors: taper schedule, boom-to-element clamps, tubing clamps, coils, traps, capacity hats, linear loading, matching networks, etc. Most just go by what the manufacturer claims in the product specification. This can be misleading since some report the highest wind area (dependent on antenna orientation to the wind), lowest wind area or something in between.

Booms are more easily calculated. There's just the aluminum tubing, clamps and a small protrusions such as beta matches, baluns and trusses. However it is more typical that the elements have a greater area than the boom so we need to know that area. It is also helpful to know that the maximum wind area is when either the boom or the elements point directly into the wind, not at some point in between. I refer you to the excellent work of K5IU and the cross flow principle in Spring 1993 Communications Quarterly (I can't locate a link right now). Yagi design tools such as YagiStress now include this work.

I finally decided to buckle down and do the calculation with a calculator in one hand and the XM240 and Explorer 14 manuals in the other. I'll spare you the messy details. Even with all the calculation there will be some error in the true wind force since antenna elements with many diameter transitions are imperfectly modelled by the long cylinder wind load coefficient.
  • XM240 boom: 5.5 ft², including estimates for the balun, boom-to-mast clamp and boom truss.
  • XM240 elements: 3.7 ft², including an allowance for element-to-boom clamps, tubing clamps and the capacity hats.
  • Explorer 14 boom: 3.5 ft², including estimates for the boom-to-mast clamp, beta match and coaxial choke.
  • Explorer 14 elements: 10.2 ft², including an allowance for element-to-boom clamps and tubing clamps.
The wind area of the tri-bander elements is higher than I expected and is more than the 7.5 ft² I found in my copy of the Hy-gain manual. They appear to be using the average of the boom and elements. That is misleading and potentially dangerous. Cushcraft does better, specifying 5.5 ft² which agrees with the maximum value that I calculated.

Many hams who stack yagis are aware that tri-bander elements have a large wind area and choose to mount those close to the tower top plate and an XM240 or similar antenna above it. I know it as well but chose to do the opposite for expediency considering the weather difficulties of winter antenna work. Getting the heavier antenna higher and the even higher boom truss is not easy in our winter weather.

I performed my survivability calculations accordingly, but with the published wind load value. That was a mistake even though I know to turn the booms broadside to the wind. Recalculating for the yagis pointed into the wind the mast survivability dips to below 100 kph. That's quite poor, although I was conservative in choosing the steel strength estimate for the mast. In fact the range of wind survivability is 30+ kph, depending on the wind direction.


As wind speed increases there is increased shadowing for close spaced element. This is due to the time it takes for the airflow to recombine after being diverted around an antenna element. Laminar flow is not immediately reestablished, instead resulting in turbulence.

The only likely location of shadowing in my installation involved the so-called para-sleeve (coupled resonator) surrounding the Explorer 14 driven element. If there is shadowing the wind area reduction in high winds is probably no more than 1 ft². That isn't helpful.


The tower survivability remains sufficient even with the revised wind area calculation. The mast however is more of a concern than expected. All I can do for the time being is to lower the yagis a small amount and gain 10 kph of wind survivability. The XM240 can go down 6" so the Explorer 14 could go down a foot or more and only risk added 15 meter pattern distortion. With 15 meters so poor at this point in the solar cycle that may be the right thing to do. It's only until spring.

I could also increase the mast clamping force to reduce the chance of the mast turning in a high wind since weather vaning seems to be a problem. Or the clamp could have an added insert that bites into the metal rather than solely rely on friction. But pinning the mast is a step too far in my opinion. A few days after the storm I reoriented the yagis, put a little more torque on the rotator mast clamp bolts and tightened some other fasteners I had suspicions about.

While I am not terribly concerned about the mast it would be inconvenient if it were to bend. Hopefully statistics and bolt torque are enough protection. Otherwise I'll need to take action or accept a higher risk until spring.

Friday, January 13, 2017

2017: The Adventure Begins

What a year 2016 turned out to be at VE3VN. What was a strong possibility at the beginning of the year became a reality. I am now committed and facing 2017 with a mix of hope, trepidation and a sense of accomplishment. As seems to have become a tradition for me in this blog, every January I write a retrospective of the past year and look forward to the new year. In particular what plans I have and why.

Onward with the 2017 edition. You can read the 2016 edition to form your own impression of how well I did. I scored close to 100% by my estimate. That's a pretty good prediction. I doubt I'll score so high in 2017 but then what's the point of objectives that are not ambitious? So let's get into it.

Where I stand

The first tower is up and decorated with aluminum. My hope to at least get started on the 150' guyed tower got squashed by the weather. The concrete work ran into problems and I was only able to plant two guy anchors. The remaining anchor and the base were ready for concrete, and was in fact ordered, when things went south (as we say).

It could have turned into a financial disaster. Although that was averted the consequence was that work had to stop for the winter. I'll have more to say on the topic later. As of now the work is planned to resume in early spring when the weather warms up and the ground is still frozen. If nothing else the delay gives me time to better approach the work involved in a project of this size.

To get by for winter operating I put up an inverted vee for 80 meters -- more on this in a future article. Its apex is only 19 meters to keep it out of the way of the yagi rotation loops and reduce the potential for interaction (yagi pattern disturbance). Although not an ideal performer it does pretty well. What it does very well is to get me on the band. Without it my operating would be too limited due to the short days for high band operating and the early closing of 40 meters. Yes, the MUF easily falls below 7 MHz on many paths with the solar flux hovering in the 70s during the long winter nights.

I may yet do something for 30 and 17 meters, but I don't want to clutter the tower too much. The XM240 loads well enough on 17, but none of the antennas loads well on 30 meters.

For the present I have no shack. The coax and rotator cable route to the upstairs balcony door and into the master bedroom. There is no operating desk. It's uncomfortable. This arrangement is necessary until renovation on the house reaches the point that I can make better arrangements without risking contractor damage to the installation.

Riding out the winter

I had hoped to have the LR20 planted so that I could slowly raise the 150' tower over the winter as the weather allowed. Since that won't happen I have extra time on my hands. What it means is adjusting my priorities rather than doing nothing.

My objectives for the winter are modest:
  • Do something to get on 160 meters. This is needed in contests to add multipliers and whatever QSOs I can garner. Shunt feeding the tower is a possibility, however it was not designed to allow for radials: there just isn't the room. But then a few meandering radials is better than nothing. Other alternatives are more difficult or problematic for a short-term solution. For example, inverted L or planting a vertical in a field somewhere.
  • Try a directive receive antenna for the low bands. I have what I need to put up a Beverage antenna. All I need to get out there and run some wire towards Europe and run some small coax back to the shack. It can be removed in the spring before it becomes a navigation problem.
  • Build the first shack. I intend to build two shacks: one for everyday operation in my main floor office and another in the basement for multi-op contesting. The main floor shack is the priority. The downstairs shack needs to be located, framed and wired. That work will begin this winter. Finishing it may be put off to the autumn.
  • Plan out the important tasks of automating antenna switching and filtering necessary to SO2R and multi-op contests. I don't need to build much right now. The critical part is having a detailed plan to which I can gradually work towards. One decision I need to make is how much to buy and how much to build. The former can be expensive but is expedient.
  • Contest! There are contests to enter and I plan to get in there with what I have. Despite just having the one tower what I have is pretty good. It only seems poor in comparison to what I am working towards.
There is lots of ongoing house renovation work. Some I am doing myself. By the spring I expect the house to be far more livable. I also need things I didn't need in the city. For example just this week I acquired a garden tractor. In addition to its ordinary uses it will play a role in tower work.

With snow on the ground I am also able to explore my 50 acres better than before. With snowshoes I was able to get out into the swamp and cross overgrown and bush areas. I do this to become acquainted with what I own and to inspect potential sites for low band receive antennas.

Categorization of tasks for the year ahead

Before I delve into specifics I'll list the categories of tasks I've set for myself in 2017. I don't really expect that all my plans will come to fruition because, well, life happens. From the categories you will gain some insight into my approach to building out the station. In any large project it is advantageous to break it down into pieces, otherwise it may be too complex to attack.
  • Structures: this includes towers and other antenna supports
  • Mounts: mechanical design and construction to affix antennas and rotators to structures
  • Antenna design: software model evaluation for target usage, before committing to building
  • Antenna selection and construction
  • Interaction: necessary for contests and important for achieving modelled performance.
  • Switching systems for direction control: start with mechanical switching and gradually automate
  • Switching systems for antennas and operating positions/shacks
  • User interfaces (software and hardware) for selection of antennas, direction and operating position
  • Low band receive antennas: choose sites, designs and get them built
  • Transmission lines and control lines: selection, burial, connectors, etc.
  • Rigs: The FT-950 with be supplemented with a better transceiver suited to my new objectives
  • Amplifier: It's time to return to QRO operating, at least some of the time
Spring plans

I can't mention spring without talking about the Dayton Hamvention. While plans are not final it appears I will be attending this year for the first time since around 1991. For me it is an opportunity to become reacquainted with the broader contesting community and to do some shopping. Well, actually it'll be a lot of shopping. There is a great deal of small parts and equipment I need that are inconvenient to gather piecemeal by mail order.

The first order of business in station building is to finish concrete work on the guyed tower and get it raised. By the fall I intend to have several yagis on that tower including two 40 meter yagis. What I can't say for the moment is whether the high yagi at 43 meters will be 2 or 3 elements, at least this year. Joining it up top will be a tri-band yagi or a 20 meter monoband yagi. They will be turned with a prop pitch rotator. These high antennas are for the difficult long distance DX paths for general DXing and acquiring precious DX multipliers and contacts necessary to contest scores.

The antennas on the Trylon tower will all come down. The likely candidates to replace them will be a TH7 I have in storage and the redesigned A50-6. The old multi-band inverted vee may join them to get me on 40, 30, and 17 meters until I can do something better for the latter two bands and to allow 40 meter operation while the tower work is ongoing.

Transmission lines and control cables will be buried. The Heliax will finally be put to use. I will run LDF7 up the Trylon for 6 meters and perhaps other VHF bands with remote switching. The workhorse for the guyed tower(s) will be LDF5. I mayy need more to get through 2017 than what I current have on hand. LDF4 will be used for HF on the Trylon and for some low band antennas with long runs. This work will stretch well into the summer.


Once the basics are completed in spring I have some difficult decisions to make. My objective is a modestly competitive station for SO2R and small multi-op (multi-single or multi-two). The antennas must support that. The waning solar cycle is a helpful constraint since it allows me to defer major antenna effort for 10 and 15 meters.

I have 3 tri-banders in my stock: Explorer 14, TH6 and TH7. One of these may go on top of the big tower, as I mentioned. As already mentioned the Trylon probably gets the TH7. The remaining one will be side mounted on the guyed tower. Whether it is fixed, rotatable over 120° or 300° will depend on my progress on other projects.

A one acre plot will be selected for an 80 meter array. I am seriously considering the 3-element switchable vertical yagi I described previously. Of course a 4-square is a more typical choice but there are advantages of physical simplicity, cost and the opportunity to experiment. After all, my objectives are not limited to operating or having a big signal but to learn and try new things.

For 160 meters I will most likely choose a vertical integrated with the 80 meter array. Anything better will almost certainly be deferred to future years.

Once I decide on my tower configuration for the year I will build yagis to suit. I'd rather build than buy and yagis are really not difficult to construct. The two 32' booms I have in stock will either become 5-element yagis for 15 meters or 4-element yagis for 20 meters. Or perhaps one of each is more sensible. If I build one for 20 meters it may go on top of the 40 meter yagi, with tri-banders fixed or rotatable at a lower height or on a separate tower. When used for 20 meters the boom may require strengthening.


A stretch objective for the autumn is a second guyed tower of similar height to be placed on the south side of the house. That tower will allow excellent separation and diversity for contests and also remove clutter on a single tall tower. Stacks for 20 and 15 meters are possible.

With that second tower I am giving serious thought to a 3-element wire yagi for the first guyed tower, switchable between Europe and USA, at an apex of around 30 meters. Any higher and there would be interactions with the 40 meter on top of the tower, be too close for future stacking and too high for those productive paths. This antenna becomes possible by reducing clutter and interactions by putting 15 and 20 meter antennas on the second guyed tower.

Next winter

I will probably back off the outdoors work since I've had enough of miserable winter tower and antenna work this year. Perhaps I will play with low band receive antennas, but little else. The shack is where I plan to spend most of my time, improving the operating positions for comfort and with increased automation. I may get far enough along that I can organize the first multi-op for my station.


My plan for 2017 is ambitious. This retrospective and looking forward article is like none of its predecessors in January of the past few years.

No matter how far I progress I intend to have a decent station for the fall contest season. With large and competitive antennas for 80, 40 and 20 meters there is every chance of doing well at this point in the solar cycle. For the remaining bands -- 160, 15 and 10 meters -- I can get by with merely adequate antennas. For general operating and DXing I will come up with something simple for 30 and 17 meters.

How much I can accomplish depends on many factors, including those outside of the hobby. My life is more than amateur radio, notwithstanding the intensity of activity these past several months.

One year hence I am looking forward to sitting in a new comfortable shack with the world at my fingertips with a better class of antennas and supporting hardware and software. You will hear me on the bands. Is this a great hobby or what?

Comments and contact address

Comments on articles are moderated. My intent isn't to prevent criticism or for other nefarious reasons. It's a matter of practicality. Spam is a problem. Google is pretty good at filtering out the majority yet a lot gets through. When those show up in the moderation queue they are summarily deleted. Everything else gets published.

The other problem is dealing with Google's identification system which makes commenting a hassle, often depending on your choice of browser. I get around this by allowing anonymous commenters; you'll even see comments signed by me that are identified as anonymous. By invoking moderation I make it easy for you to comment while also making it easy for me to kill spam. The downside is a delay until comments are published. Usually the delay is no more than a few hours.

To contact me by email you should address messages to my call sign in front of the rac.ca domain name. That will forward to my gmail account reserved for amateur radio use. If we've communicated by email last year or earlier you should not use any other email address since it may silently vanish into the aether. I will never see it. My previous ISP does not reliably issue bounce messages to senders.

If you want a direct reply about any article or to get more information, such as antenna models, use email. I treat blog comments as addressed to the public, not me, and often publish them without commenting in return.

I look forward to seeing everyone on the bands in 2017.

Sunday, January 8, 2017

Squashing One Low Band Noise Source

Out in the country it is pretty quiet. I mean this in the usual sense and in regard to radio noise. The hearing has gotten increasingly difficult in urban and suburban areas, and even is some low density rural areas. Rare is the ham of my acquaintance who does not have a story of QRN woe and their efforts to track down and tame the beast.

I did my best to include a spectrum scan for every property I visited while shopping for a house last year. Even so there is noise. Here is a list of what I am dealing with:
  • Ethernet noise from the long Cat 5e cable for my terrestrial wireless internet connection. It was very bad with my temporary inverted vee propped up on the balcony and adjacent to the internet dish and cable but is now much reduced due to the distance of the yagis from the Ethernet cable. It had strongly affected 10 through 40 meters. Now it is merely a nuisance on 15 and 40, and select frequencies, depending on yagi direction.
  • The long high-voltage power line distribution is on rare occasions active during adverse weather. It is not a significant concern currently. The drop from the transformer (70 meters from the house, near the road) is underground, which helps with noise suppression.
  • Low level rapid impulse noise evident on 80 and 160 meters. Since I had not yet put up a low bands antenna it was impossible to predict whether it would become a problem. The noise does not seem strong but would cover up the weakest signals. It is managable with a noise blanker, although that is typically associated with IMD and therefore an imperfect solution. 
I originally assumed the impulse noise was coming from the electric fences to control the cows on the adjacent farms. This was even though the pulse rate is more rapid than I expected from that source. My inexperience with rural life and electric fences made me unsure of my suspicions.

There is a plan in place to reduce the Ethernet noise, so while not solved there is hope. In any case it is not hampering my activity to any significant extent since putting up the tower. It is the prospect of soon getting on the low bands that drove me to track down where where the impulse noise was coming from. So I dug around and improvised a noise detection tool.

That radio is pretty much an antique, dating back to when Pearson was our Prime Minister and I was very young. It was the very first radio that was my very own. It isn't much of a radio yet despite being a half century old works well. Or at least it did after the liberal application of contact cleaner to the volume control and the AM-FM slide switch.

What makes this radio so useful is that it is very easy to carry around and it has a ferrite rod antenna for the AM broadcast band. Ferrite rod antennas in these old radios have a strong null broadside and a strong peak on axis to the rod. It is not the ideal tool for direction finding, however I have it and it works well enough for my purpose.

I walked around the house looking for noise with the tuner set to the high end of the band, which is less than 200 kHz from the bottom end of 160 meters. This is always the best first step since it is not only convenient it is good practice to ensure that your own house is clean before seeking others to blame.

As expected there was strong fundamental induction noise when approaching house wiring and appliances, especially those with a large metal enclosure. Of greater interest was electronics of all types, including smoke and CO detectors, HRV, heat pump, LED light bulbs and so forth. These all came up mostly clean with my simple test equipment: the LED bulbs with integrated electronics are imperfect but not too awful. To be doubly sure I turned off the breakers to branch circuits servicing potential culprits and listened to 80 meters.

Finally I picked up impulse noise as I approached a bedroom that was devoid of furnishing since I was in the midst of repairing the drywall in preparation for repainting. I didn't expect that, and I only went there to be comprehensive in covering the entire house. As I entered the bedroom it was immediately evident where the noise was coming from.

For some unknown reason the ceiling light fixture was controlled by a dimmer switch. The dimmer has slider and an on-off switch. I know that dimmers are a common source of noise but assumed not in this case since there is a switch and the switch was most definitely turned to off. I cut the branch circuit and the noise on my portable radio vanished. I listened to 80 meters on the transceiver and it was perfectly quiet. Success!

I replaced the dimmer with a conventional switch and reactivated the branch circuit. All remained quiet. It was a switch I was intending to replace after painting so all I did was to advance the work by a couple of weeks.

I can now put up an 80 meter antenna with added confidence that I will not be plagued with noise. In time I have more ambitious low band plans, and antennas much further from the house and noise sources. If it had instead turned out to be one of my neighbours the solution would have proved more difficult. With a sigh of relief I can get on with antenna work.

Saturday, January 7, 2017

New Antenna Expectations

During the several years I have written this blog I wrote quite a few articles comparing antenna performance versus height. Most often this was for 40 meters, which is a particular focus of mine. However I did not neglect the higher bands. Since vertical polarization is most often used on 80 and 160 the focus is less on height than it is on efficiency, especially reducing ground loss.

Now that the Trylon tower is up and decorated with yagis this is an excellent opportunity to look forward to what I can expect. First, let's look at the antennas I have put up:
  • Hy-gain Explorer 14: 3-element tri-band yagi on a short (4 meter) boom
  • Cushcraft XM240: 2-element loaded (short) yagi
This is a temporary arrangement for the winter and spring, doing the best I can with the one completed tower and the selection of antennas in my stockpile. The temporary antennas I am planning for 80 and 160 are not horizontally polarized and therefore are outside the scope of this article.

Explorer 14 Tri-bander

This was my primary high bands antenna for 20, 15 and 10 meters at my former QTH. Its height was a little over 14 meters on my light duty guyed tower. With the antenna now at the greater height of 23 meters its low angle performance should be enhanced. The question is: by how much? That is, does the additional 9 meters make a significant improvement?

A direct comparison isn't possible so I returned to a model of a similar antenna I developed back in 2014: a 3-element tri-band trap yagi. Although not the same as the real antenna I am using it is more than sufficiently similar to compare performance versus height.

The result is shown in the adjacent elevation plot from EZNEC for 15 meters. The primary trace is the antenna at a height of 14 meters over medium ground and the secondary one is with it at 23 meters. Not surprisingly the low angle performance is improved. Also not a surprise is the appearance of additional minor lobes, and nulls in between.

With respect to DX performance I am using a median elevation angle of 5°, which is where the cursor is located. The behaviour is similar on 20 and 10 meters. At that elevation angle the gain improvement at 23 meters height is in the range of 3.5 to 4.0 db. This is significant. You won't notice it when signals are strong but when the opening is marginal it will make a large difference. This is all the more important now that the solar cycle is dying, and is in any case important for contesting where the extra signal strength will add many QSOs to the log.

After a week of use through some difficult conditions, and without the possibility of a direct A-B comparison, I am confident that I am getting the predicted performance improvement. The best test may be the first contest I enter. That is likely to be NAQP CW later this month. A better test will be ARRL DX in February.

Cushcraft XM240

According to my previous modelling of many 40 meter antennas there ought to be about 9 to 10 db low angle gain (at 10° elevation) compared to the inverted vees I used at my Ottawa QTH. Here is a summary chart of several antennas from a previous article comparing height versus gain at 10° elevation.

My XM240 is roughly equivalent to the modelled 2-element short yagi. The specific model selected includes estimated gain reduction due to coil loss and element shortening. We also need to keep in mind that the gain bandwidth for a 2-element yagi is poor, which is why I bracket the range as 9 to 10 db. Modelling and careful estimation is the best I can do short of flying a field strength meter on a drone.

Early indications are that the antenna meets my expectations. There is little that the big guns can hear that I cannot, even if not at the same signal strength. That was far from true before. In particular I can hear Asians long path, work previously difficult paths such as UA9, and far more (and weak) European stations. However this does not mean I crack every pile up. That 10 db is with respect to my low inverted vee whereas many others have wire antennas better than that, plus 10 db or more courtesy of an amplifier.

Models and feedback from other users of the XM240 that it works on 17 meters with a modest SWR. This is useful since at least for the time being I have no 17 meter antenna. The measured SWR is a little under 2.5, which my rig happily loads without a tuner. The few stations I've called hear me fine. Of course a proper antenna would work far better but that's off in the future. It is not a priority since 17 is not a contest band.

One task I plan over the next week is to profile the F/B across 40 meters to get an idea of where the reflector is tuned. The SWR which is lowest at 7.125 MHz is not a indicator of where the gain and F/B curves fall. In a 2-element yagi it is the parasite and the parasite alone that determines the gain and F/B curves. Tuning the driven element only adjusts the match, provided its self resonance is in the near vicinity of that of the reflector.

There are reports on the internet that it can be dangerous to drive the tower plus XM240 (as a top hat) as a low band vertical. The explanation is that the Cushcraft matching network (balun) cannot withstand the high voltage between the balun input (capacitively coupled to the tower and boom) and the driven element when running high power. Since I do not intend to put radials on this tower in any case I will not risk the XM240 balun by shunt feeding the tower on 80 or 160.


The 6.5' (2 meter) spacing between the yagis is an absolute minimum to avoid deleterious interaction on 15 meters. Even better would be 3 meters. Unfortunately that would be unwise since the mast and tower wind survival would be dangerously poor (see below).

In initial testing there is no degradation to the 15 meter SWR/impedance. Modelling tells me that the most sensitive to interaction is F/B and other lobe distortion. Since it's winter and the solar flux is very low I have not yet had a chance to test whether there is a pattern problem. I plan to do that when I am able.

There is a potential for other interactions with wire antennas attached to the tower. My main concern is with 40 meters and 15 meters interaction with the XM240. I am less concerned with interactions with the Explorer 14 since it is higher up and therefore further from wire antennas. There will need to be at least one wire antenna for diversity in this winter's contests and to have something for 80 and 30 meters. I may do a model to predict interactions.


Within the first 72 hours of completion we were hit with snow, freezing rain and wind gusts of 80 kph. This brings the importance of survivability solidly to the fore. This is as applicable to a permanent installation, a short term one such as mine or for a Field Day weekend. All that changes is the probability of destructive weather events declines over shorter time periods.

Yet since anything can happy anytime it is a matter of how much risk you can tolerate versus your investment. In this respect I have made my choices for this initial phase of my new antenna farm.

There are several aspects to consider in the failure modes of this installation. Although it is temporary, perhaps only until May, I will not accept excess risk. However I deliberately increased the risk I will tolerate in comparison to a more permanent installation. I'll walk through those points and my thoughts. Not all would agree with my choices.

Mast: The mast is just the sort that professionals warn you against: water pipe. Specifically 19' (6 meters) of 1.5" (nominal) Schedule 40 galvanized water pipe. This is the same pipe that served as a mast for stacking VHF yagis above a TH6 in my previous stations from 1985 to 1992. Almost 12' projects above the tower although I am not using all of it, nor was that my intent. In its previous use 10' projected above the tower and I did use all of it.

For now I only need enough mast to minimize interactions between the tri-bander and the 40 meter yagi. For that I need no more than 8'. The additional length is intended to be used when the 40 meter yagi is moved to the guyed tower later this year and the mast is freed up for VHF, 6 meters in particular. If that had not been my plan I would have cut the mast shorter.

As built the XM240 is 1' above the top bearing and the Explorer 14 is 6.5' above that. Therefore only 7.5' of the available 12' is being used.  When plugged into AC8Y's mast stress spreadsheet (based on the ARRL Antenna Book) and choosing a conservative strength of 30,000 psi for the water pipe the wind survivability of the mast is ~115 kph. This is poor but acceptable for the next several months. I live in a 135 kph (85 mph) wind zone and I have only seen such winds twice in the past 3 decades.

The maximum wind speed that can be survived is improved by turning the yagis so that they are broadside to the wind since the booms have a smaller area than the elements for both of my antennas. That is, if you trust yourself to do so when the wind comes up, and you happen to be at home. Our worst winds tend to cluster in the summer and early fall so I feel the risk is acceptable for the next several months even if I fail to turn the antennas.

Tower: Trylon frequently updated the load limits for the Titan series over the years. It is not that the tower changed. Instead they appear to have reacted to how their customers are using their towers. Hams in particular tend to look at the wind load capacity in the most benign case and, unsurprisingly, come to grief. Then they blame Trylon, which is unfair. To gain a deeper understanding of what the tower can support I needed to delve into my archive of old Trylon engineering data that they no longer publish in their catalogues.

From those old sources the T400 can handle 240 of lateral wind load for an antenna mounted within 3' of the top plate. At 135 kph this translates to approximately 12 ft² of cylindrical surface. With ice the wind that can be survived can be greatly reduced due to the increased surface area of the antennas and tower. Do keep in mind that the capacity figures include the surface area of the tower so that ice on the tower also reduces the antenna load.

As for the mast there is a bit of a gamble involved since I am counting on the weather to keep my tower load within the limit for the next several months. The major concern is the multi-element Explorer 14 that is 7.5' above the top plate and therefore reduces the survivable load. Unfortunately a calculation is difficult to perform due to the many factors involved: gust and wind duration; presence of ice; construction quality; etc.

In my estimation the tower has a wind survivability similar to that of the mast.

Rotator: The bending stress of the wind acting on the antennas and mast are transferred to the tower and then to ground -- all earth bound buildings transfer load to ground. Rotators generally have a lower tolerance to radial loads than to axial loads. This is the case with the Tailtwister.

The main contributor to radial load is the Explorer 14 located approximately the same distance above the tower top as the rotator is below it. For the moment let's assume the that the tower top bearing is a perfect fulcrum (it isn't). Therefore the wind load on the yagi translates to an equal radial load on the rotator, but in the opposite direction (windward).

If we again assume 6 ft for the wind area, at 135 kph (85 mph) the wind force is 120 lb. The radial thrust is well within the capacity of the Tailtwister. Although the rotator will survive it may have difficulty turning and braking in a high wind. The solution is to not operate the rotator in a wind storm or to reduce the radial thrust. Actually doing both is wise.

The presence of a second thrust bearing on the second plate of the top section substantially reduces radial thrust on the rotator. It does so by transferring the radial thrust to the tower. The cost is that the tower takes additional bending stress since the load transfer occurs ~2 meters higher than when the second bearing is omitted. Although the proper engineering calculation is beyond my ability I suspect that the trade off is a sensible one.

One intermittent problem I am experiencing is that occasionally the rotator will not rotate. Sometimes if I keep the motor energized it eventually gets going and other times it does so on a later attempt. Thinking that it was a wiring issue I went up the tower to remove all flexing of the wiring near the connector and terminal strip. Now I suspect a failing phasing capacitor or something else. When I overhauled the rotator nothing appeared amiss with the motor or reduction drive.

Back to antennas?

Something odd happened over the past several months. This blog was supposed to contain articles about antennas perhaps more than any other. Yet this is the first one since early August, 5 months ago! Antennas had to take a back seat since I had little time for them during the process of buying and selling property, taking down and putting up towers, and of course dealing with the crush of tasks responsibilities that come from a change in residence.

Although there is much that is still going on behind the scenes to occupy my time I expect antennas to return to the fore. If not immediately, at least in the coming weeks and months. After all, the primary reason I moved was to have the freedom to do much more with antennas, and especially high performance antennas for contests and DXing.

Thursday, January 5, 2017

Trylon Gin Pole: Review

As with everything there are things that work and things that do not. The gin pole I constructed for the Trylon tower did the job though not without some problems. I like to be open about what goes wrong since it is almost always a valuable learning experience. Refer to the earlier article on the construction of the gin pole and the objectives I set for it to better understand what follows.

The good

We might as well begin on a positive note. The primary one being that it worked quite well. Here are the main points:
  • Capacity: The gin pole easily handled weights up to 150 lb. It was also rigid and secure enough to allow some lateral force, needed when tugging on the tag line to free tower sections when they tangled with the tower or protrusions on the gin pole itself.
  • Smooth action: Operating the winch to lift large and bulky loads was surprisingly easy. The 4:1 advantage of the winch still required some sweat to lift the heaviest items yet could still be done with one arm. One time I accidentally lost my grip on the handle, allowing the load to drop and the winch to unwind. Even so the drop was slow and was easily stopped by grabbing the handle. That's another benefit of the 4:1 ratio. Adjusting the load up and down for final positioning also worked well.
  • Economics: It was really cheap. The pipe was free, and even if bought is not expensive. The hardware can be found in any hardware store. The most expensive part was the winch. For that I went with quality rather than cost. It's an investment since it will have other uses.
  • Easy to build: The machining only required a drill, hacksaw and file. No special tools or techniques were needed other than attention to detail.
The bad

Despite all of its positive points there were a variety of problems. These were all managed without undue danger or effort. Well, there was one uncomfortable moment which I will describe.

Tower hooks: I'll mention the worst problem first. The hooks I constructed worked well but did have a few important negatives. First was some difficulty in attaching the gin pole to the tower. There is a narrow gap between the keeper plate and support plate into which the tower leg must be inserted, and there are two of them that must be done at the same time. When I was holding the gin pole from the bottom, supporting its weight and striving to keep it vertical, that act was not easy. However the pole could be temporarily set on the tower diagonals so that a rest could be taken.

For about half the sections there was a small gap between one support plate and the diagonal due to the tower design. I mentioned this in the construction article. Since the kick out due to the gap was typically small I usually ignored it. That is until the time the bottom hook disengaged completely when the tower section being lifted was swung over the tower into position for splicing. The only reason the gin pole didn't swing out of control was the loaded weight of the support plate on the diagonal. But I could not lift the gin pole plus tower section to reset it in place. Instead I kicked it a few times to push into place, again gripping the tower leg. From then on I always used tie-down straps to secure the gin pole to the tower.

Weight: At 2.7 lb/ft the Schedule 40 water pipe gin pole comes in at about 35 lb (16 kg), including pulley, hooks and hardward. This can be handled by one person of ordinary ability. Anything heavier becomes unwieldy since not only must the weight be lifted and maneuvered on the tower, it must also be kept vertical or it will "get away" and cause a serious incident. It becomes a two man job.

I intend to search out lighter and stronger pipe, either aluminum or thinner wall steel with a wider diameter, for lifting the LR20 sections since the sections are 10' and so require a taller gin pole.

Height and offset: As constructed the height of the pipe up to the pulley is ~10.5'. With the amount of pipe that straddles the tower section and pipe that extends above the pulley and below the bottom hook the distance between the top of the tower and the pulley is 6.5'. Since a section is 8' the grab point is about 2' below the top of the lifted section. This is adequate and serves to reduce gin pole height and weight and therefore increase safety when handling it on the tower and pulling on the tag line.

With this design a few precautions are recommended. Because the lifted section will lean more as its centre of gravity is approached heavy sections require more effort to swing into position for splicing. This was discussed in the earlier article (link at the top of this article). Two workers up the tower is best.

A more subtle problem is that the pulley can jam against the section or lifting hook when it is pulled into position for splicing. The problem is exacerbated when the gin pole is strapped to tower for additional security since there is less play. The solution is to build an offset into the gin pole at the upper hook so that it leans back a bit from the tower rather than following the contour of the leg or tower face. I didn't do that for this gin pole and I should have. The problem did occur on 3 lifts requiring extra effort to perform the splice. I took a shortcut thinking I could get away with it on this tower and I was wrong. It could have been achieved as simply as an extra nut between the pipe and the keeper plate on the upper hook.

Winch misalignment: I carefully squared the winch to the ground so that the cable would be normal to the winch during lifting. The intent is to avoid lateral force on the winch and tower mount and to ensure the cable winds onto the spool across its full width. This is the correct procedure for straight sections that are the norm for guyed towers. However this does not work for tapered self-supporting towers.

Since a photo does not show the problem very well I drew a diagram to make it clearly evident. Notice how the cable extending upward from the winch leans left. As a result the cable naturally tries to wind onto the spool from right to left. But we want it to alternate left and right when the cable reaches the side of the spool. The problem is always present to the same degree (the angle is constant with height) although it becomes more evident (worse) as the tower rises due to the amount of cable that is spooled.

Especially for heavy loads it is necessary to manually reverse the winding towards the right by pulling the cable sideways while cranking. This is tedious and tiring. The solution is to mount the winch so that it is normal to the tower leg rather than to the ground. My tower mount system did not allow for adjustment of the winch orientation.

Winch spool capacity and cable tension: From shopping around the size of winch spools is roughly proportional to the working load rating. This appears to reflect the size (cross section) of cable for that working load. Unfortunately this limits the amount of cable that the spool can hold. For tower this is a problem since so much cable must be used, more than twice the height of the tower.

Using 3/16" aircraft cable for the lower sections the spool on my winch could only hold enough cable to get me up to 5 sections of tower. I tried using rope at that point, without the winch, but the sections were too still too heavy for me to do alone. Since I needed lots of smaller cable anyway I bought a 500' reel of ⅛" aircraft cable and cut 200' for the winch. That worked. However, note that while tidying up I wound the full length of cable onto the winch and found that was all that would fit.

Although a higher capacity winch isn't needed for the loads being lifted in future it may be needed simply for the larger amount of cable that can be held.

The other problem is one of cable tension. When taking up slack the cable does not compress on the spool. This becomes a problem when the slack is taken up and tension develops. The underlying cable on the spool is compressed by the cable, causing kinks and crushing. This must be carefully managed to avoid damage and weakening of the cable.

Tag line: I quickly relearned that all lifts require a tag line (or lines) where a fixed overhead pulley is used. This includes gin poles.

The purpose of the tag line is to avoid tangling of the load being lifted with the structure it is being hoisted along. It is natural that the load will strive to rest against the structure (tower) since that's where the pulley is affixed. There are many opportunities for tangling due to the many protrusions and opening in the tower, gin pole and load. If the load has a tendency to rotate in the wind, especially yagis, two tag lines may be needed.

Little tension is needed on the tag line, just enough to avoid unwanted contact, or any contact at all if abrasion is a concern. For example, the soft zince galvanizing coating. Too much tension is usually a bad idea with a gin pole since it does not have the lateral strength of a tower or mast. An experienced hand on the tag line is helpful to get it just right. When I was doing the work alone I allowed the load to brush against the tower and only touched the tag line when something caught. Most often it was the underside of the gin pole.

You can see the presence of a tag line in the previous article on topping the Trylon.

Abrasion: When rope is used the concern with abrasion is on the rope rather than the tower. With steel cable the concern is with the tower. Aircraft cable is very strong and substantially harder than the structural steel use in towers and far harder than the tower coating, whether it is paint or zinc galvanizing. The harder substance always abrades the softer one.

My design of the Trylon gin pole involves some abrasion of the cable on the tower, mostly at the top where there is a slight angle change in the cable from the pulley over the top member of the tower, both towards the load and the winch. There isn't a lot of abrasion but it is less than ideal. Abraded areas are prone to rusting sooner than undisturbed surfaces.

The solution is to offset the pulley from the gin pole, and even use a second pulley so that both sides of the cable clear the tower completely. This requires more fabrication and additional gin pole strength, which comes down to cost and weight. Some designs see the cable thread the interior of the gin pole which can eliminate most, though not all points of abrasion.

For the future

Gin poles are pretty simple machines. The challenges are mainly in their construction and use. I have chosen construction techniques that do not require welding or machining with tools I do not own. That may have to change if I want to avoid problems in the future.

The local tower service company offered me the free use of one of their many gin poles. While very kind of them none were suitable for Trylon towers. First, all of them were heavy, with the lightest among them almost 80 lb. Second, the hooks seemed to be designed for towers with round members, which is more common for commercial products that the formed sheet metal used by Trylon and others. They would have deformed the L-shaped diagonals.

Most recommended gin poles use L-shaped hooked where the horizontal part rests on the tower cross-member and the vertical part keeps it  from sliding out. For towers with symmetrical cross-members on each side of the legs each hook has two parts, allowing the gin pole to straddle the leg and hold its position that way rather than rely on gravity to pull it down one diagonal to rest against the leg.

This is what I attempted to accomplish in the gin pole I built for the DMX tower I put up at my Ottawa QTH. Unfortunately this is not easy to do with standard hardware. The hooks need to be formed from steel stock and welded to the gin pole. Alternatively the hooks are welded to short pipe sections that slip over the gin pole proper and bolted in place at the desired position, determined by the tower type.

The same article I link to immediately above has a diagram of a manufacturer recommended gin pole that places the pulley a few inches outboard of the pole. Its purpose is to reduce contact (abrasion and tangling) between the tower and load, perhaps obviating the need for a tag line. Of course the gin pole must be strong enough to handle the lateral forces of an offset load. In some cases the arm will pivot on the pole to ease positioning the lifted section over the tower.

I will shop for a lightweight, strong pipe as a basis for a gin pole and spend some money with a welder to build proper hooks for the tower types I have or might have in future. Considering the amount of tower construction I am planning this will be a good investment. No more improvising.

Tuesday, January 3, 2017

Topping the Trylon

VE3VN has finally returned to the air with a substantial set of antennas. The Trylon tower is complete, the mast and rotator are in place, as are a couple of yagis. It's nice to be back, and with antennas such as I haven't had for 25 years. There's a smile on my face.

In this article I'll recount the key points in the construction and what I learned along the way. At least some of this should be useful to others.

Help arrives

I demurred on continuing with the tower project alone when I had 7 sections raised and 2 more to go. Doing it alone necessarily involves at least 3 trips up and down the tower. The risk multiplies as the tower rises: there is more opportunity to make mistakes and the additional physical effort makes one tired and more prone to mistakes.

Luckily an experienced tower climber was willing and able to drive out to help me with the project. So I waited for him to be available. That ham was Vlad VE3JM, a dedicated contester with his own substantial antenna farm and contest station east of Ottawa.

-4° C and a north wind: a perfect day for tower work
With everything prepared it was several hours work to raise the final two sections and the mast. The mast was no simple matter since it is 19' (6 meters) long, 11' of which stands proud of the tower. Vlad did the bulk of the tower work with me crewing on the ground, most of the time.

Unconventional lift

The penultimate section (#5) went up without an issue, just like all those that preceded it. The only thing different about it is that at the top was a plate recently drilled for the Tailtwister rotator. It was the next section that presented a challenge.

Over tea Vlad and I reviewed several alternatives:
  • Raise the 4T in the usual way, then add an extension to the gin pole to lift the mast above the tower and drop it in.
  • Add an extension to the gin pole and lift the 4T with two bearings and the mast installed in its intended position.
  • Use the gin pole as is and lift the 4T and mast together but with the mast projected below the section so that the centre of gravity is below the highest point the gin pole can attach: 6.5', or 2 meters above the section the gin pole is sitting on.
We decided to go with the third option. Our concern was that the extended gin pole, which would be almost 15' tall would be too heavy to safely manage and that the pipe splice for the extension was an unknown factor. I had all the hardware on hand for the splice and the pipe sections were pre-drilled.
VE3JM preparing to grab the 4T+mast assembly

The mast was inserted through the 4T on the ground and moved down until the centre of gravity was far enough below where the winch cable attached that the assembly would reliably hang somewhat vertically. When we did this the mast protruded 3' (1 meter) below the bottom of the 4T. The mast was locked in place with a muffler clamp so that it could not slide down.

The assembly weighed ~100 lb (45 kg), which was well within the proven capacity of the winch, cable and gin pole. So up it went, with me on the winch and Vlad on the tag line to keep it from tangling with the tower and gin pole. It was quite a sight! When we had the behemoth dangling above the tower 70' in the air Vlad climbed up for the next step.

His task was to pull the leaning assembly inward, push the 50 lb (23 kg) mast up through the bearings and tower top, swing it over the tower and lower the mast through the empty rotator plate. Sound like fun? It turned out surprisingly well. Once that maneuver was complete I lowered the section for Vlad so that he could fit the section in for splicing.

It was only then we had some difficulty. I was prepared for a tight fit since I had spliced these sections on the ground to ensure proper section alignment after performing repair work, including replacement on one leg on both the 5 and 4T sections. The problem was exacerbated when the gin pole pulley jammed against a tower leg and wouldn't allow completion of the splice.

I joined Vlad up the tower to free the jammed gin pole and fight with the tight fit of the section splice. With the two of us working together the job was done. We descended, cleaned up and shared a tea before he returned to his family and holiday activities.

Installing the rotator and rigging for lifting the yagis

A few days later when the weather was decent I went up the tower to take care of several tasks. Considering the number of things to be done I did well in getting it all done in one climb. The work was physical enough that even though the temperature was below freezing and cloudy I stayed comfortably warm even while working without gloves.

The first task was to lift the mast several feet and hold it there so that the rotator could be slipped into place. This was more difficult than expected. Although only 50 lb and easy to pick up and carry on the ground it is another matter to stand astride the tower, reach in and lift that much weight. I had no success at all until I removed my warm gloves and gained the advantage of an improved grip. Getting cozy with that much biting cold steel is not terribly enjoyable.

When I got it above the rotator plate I covered the hole with a short length of lumber I brought up with me. This allowed me to rest before continuing the lift. I then hooked a rubber tie-down strap onto the mast, lifted again and hooked the other end of the strap onto a tower diagonal. I then hauled up the rotator and control cable by rope. This was one of two ropes I had taken up with me.

I fished the cable and connector through the plate, lifted the mast once more and slid the rotator underneath and dropped the mast into place. Unfortunately I then had to pry up the 70 lb of rotator and mast to align the rotator mounting holes with the drilled plate, slip in a spacer and drive home one bolt. With the rotator now pinned the other 5 spacers and bolts went easier.

After tightening the clamp I taped the control cable to tower, plugged it into the rotator connector and weatherproofed the connection. Climbing up I centred and tightened the two mast bearings onto the mast. With that done the mast and rotator installations were complete and it was time to set up the rigging for lifting the yagis.

I transferred the pulley from the gin pole to a mast clamp and lowered the gin pole to the ground on the rope with which I pulled up the rotator. The next step is one that many hams prefer to avoid. I stood up on top of the tower, strapped to the mast.

After surveying the landscape and enjoying the unobstructed view I got to work on the rigging. The winch pulley was raised to several feet above the tower and the clamp tightened. The winch would be used to lift the XM240 which weighs at least 70 lb. This antenna is normally 55 lb but this one has been improved for survivability (W6NL mods) by its previous owner who, interestingly, never did put up the antenna.

I retrieved another clamp and pulley from my tool pouch and reached as high as I could (~7') and tightened it onto the mast. I then threaded the second rope I brought with me through the pulley and down to the ground. This pulley is for the Explorer 14 tri-band yagi. These antennas are to be my main antennas for the next several months until serious tower work recommences in the spring.

I snapped a selfie of my feet and the ground below and started my descent. As I descended I taped the control cable to the tower at intervals. In our winters it is vital to use good quality electrical tape that can be manipulated in cold weather. Cheap tape becomes brittle and unworkable in the cold.

Down on the ground I tidied up and went inside to connect the controller to the cable and test the rotator. That was a solid day of work and excellent progress. The antennas came next. There was another delay because of the weather and time needed to complete yagi assembly and the feed systems.

Lifting the yagis

Vlad returned a week later to help with lifting the yagis. Over several days between Christmas and New Years Day I assembled the antennas, built the feed systems and tested various lengths of coax for use in the rotator/drip loops and transmission lines. I encountered several problems along the way though nothing serious.

The modified XM240 took several attempts until I had the elements and feed system correctly positioned and oriented. The cold temperatures made this challenging since fingers get clumsy and numb while kneeling in the snow and manipulating tiny screws and nuts. The capacity hats were left off until the antenna was lifted since they are too fragile to rest on the ground.

Much of my RG213 coax is 30 years old and spent many years partly buried. Although it served me well at my most recent Ottawa QTH some testing was in order. Here is what I discovered:
  • Loss was greater than spec. At 28 MHz the several 40 meter lengths had a measured loss of around -1.9 to 2.0 db. This compares to -1.5 db for new RG213. That isn't bad for old coax.
  • The characteristic impedance had dropped to around 46 to 47 Ω. This results in a slightly elevated SWR though, again, nothing worth worrying about.
  • One length of coax had a DC short. This was unexpected since it worked well just last year.
  • The coax I ran off the 1,000' reel (I still have some of the original coax unused) measures right on 50 Ω, so I assume the impedance dropped with age due to chemical or physical deterioration.
While I have lots of LDF4-A50 Heliax of similar length and age I do not want to struggle with hard line in the cold and snow. This tower configuration is temporary and I can live with an extra decibel of loss for a few months. Also, with all the renovation work going on I'd rather a contractor accidentally damage ancient RG213 than Heliax.

With everything prepared Vlad and I had to get everything done in a few hours before sunset. We didn't get everything done, but we did get both yagis lifted and mechanically attached. The tri-bander was lifted first since it goes on top. At only 45 lb this is a one man lift with a rope. However as with the mast it was made difficult by the need for gloves and the stiff and slick nylon rope. Vlad climbed up and fought for a while with the Hy-gain boom-to-mast clamp. There are lots of bolts to deal with.

After checking out the antenna with an analyzer he came down and we raised the XM240 with the winch. I had moved the gin pole pulley over to the mast several days earlier. The capacity hats went on with the yagi a few feet off the ground. With a 22' boom and 43' elements it took some effort to keep it out of the trees for the bottom portion of the lift. Tag lines were used on both yagis since there are many protrusions on the antennas that easily tangle with the tower.

One problem we discovered is that the 2" galvanized muffler clamps I had just purchased were of slightly different manufacture and did not quite fit the machining of the custom boom plate. We wasted time elongating the holes with a round file, finally opting to squeeze the u-bolts and hammer with our gloved hands! Steel is harder than aluminum so the threads were not ruined.

That's as far as we got. It was up to me the next day to go up the tower and complete the job. This involved installing and adjusting the XM240 boom truss, testing the XM240 with an analyzer, pushing the Explorer 14 to its intended height and removing all the lifting pulleys. Once that was done the transmission lines were lifted, the rotator/drip loop attached and weatherproofed, and finally, on the way down, taping the coax to the tower.

And finally...

I am back on the air. Finally. However there are difficulties which I am looking into. One of these is that the rotator has cut out a couple of times for no obvious reason. Jiggling the wires up the tower fixed the problem which, if not merely a coincidence, indicates trouble with the wiring harness or connections. This is long run of cable which has given problems in the past, but it is all I have on hand for the moment.

Another problem is that the XM240 is not resonating per the assembly instructions. At first I assumed I'd made an error until another ham mentioned having the exact same problem, with the very same measurements. So for the moment it resonates in the lower part of the SSB segment on 40 meters (~7.125 MHz) and requires a tuner at the low end of the CW segment. I was amused when we got freezing rain the next day and resonance dropped to 7.025 MHz. But I can't rely on ice storms to properly tune my antennas.

As you can see in the picture there is some misalignment in the yagis. While it looks sloppy it is inconsequential. There is only so much fussing one can do in the cold weather. It'll do. The tri-bander is a little lower than I'd planned, with only 2 meters separation between yagis; interaction on 15 meters is my concern.

At least I have something. It is a joy to effortlessly work over the pole into Asia and crack through small pile-ups. The shack is very temporary because I have to keep the cables away from the construction zone beside my house to avoid damage. I will be putting up a simple antenna for 80 meters to get me through the winter. I can use the XM240 on 17 meters even without a tuner since the SWR hovers between 2 and 2.5. However I have nothing usable on 30 meters or 160 meters unless I put up more wire.

I will have more to say about my plans for 2017 and why I've made the choices I have in my current temporary arrangement, and say more about the problems I encountered. For the present, happy new year and I hope to see all of you on the air and in the upcoming contests.