Tower Alignment With a Transit

For structural integrity a guyed tower must be vertical and straight. Although perfection isn't required it is highly recommended to get as close as practical. Doing this job without proper tools is prone to error; you cannot rely on your eyeballs alone! Take the extra effort to do it right.

When I put up my first guyed tower I used what I called my poor man's transit. I later improved the usability of this technique by mounting the straightest pipe I could find in my bicycle repair stand. When carefully made vertical with a long level it held its alignment quite well. Or it did if the wind wasn't too strong! In this way I roughly aligned my 150' tower and my new tower up to the 120' level (it will be 140' when complete).

Standing (or, better, sitting) back from the pipe and sighting along the length of the tower is not as easy as it sounds. Freezing your body in one position is more difficult than you might guess. Go ahead and try it by keeping a close and a distant object in optical alignment. It's made harder by the distance difference for eyes that need corrective lenses and cannot focus on both objects at the same time.

I knew that the alignment of the towers was less than what it could or should be. One tell was that the towers were not parallel to each other. The error was no more 2" or 3" (5 or 8 cm) from top to bottom, which while not large and not a significant safety risk does offend my sensibility. A few of my ham friends call me a perfectionist, and that is not necessarily intended as a compliment.

A local tower pro after asking me how I aligned the towers offered to loan me his transit. It was an offer I could not refuse. When I was ready to do the job he handed me the instrument and suggested I search on YouTube for videos on how to use the thing.

A transit is a type of theodolite used in the building trades. Other than YouTube there are many resources on the internet that explain a transit's function, features and use. Here is one that is straight-forward and easy to follow.

I took the transit home, fiddled with it a bit and read the dreadfully poor manual. But that was enough to put it to use. Most of the features are not needed to align a tower, but can be useful to survey a plot of land for a new tower. It wasn't even necessary to turn on the power except to play with the advanced features in the comfort of my shack. Setting up the transit for tower alignment involves the following steps:

1. Plunk the transit down in the field far from the tower.
2. Level the transit.
3. Point the telescope at the tower base centre and lock its horizontal motion.
4. Rotate the telescope up and down to track deviation from a vertical line.

Sound simple? Well, not quite. Let's look at the process in more detail.

Levelling

This is the most critical step in setting up transit for use. It absolutely must be level. The method I was taught and that works well for me is as follows:

• Extend the tripod to working height, but not so high that you can't easily see the levels. Point one leg towards the tower so that you have unencumbered access to the telescope.
• Roughly level the tripod top by eye then firmly push the leg spikes into the ground (assuming you're not on bare rock).
• Mount the transit to the tripod. Adjust tripod legs until the bubble level (bottom) is approximately centred.
• Rotate the transit so that two adjustment knurls are at either side. Adjust the knurls to level the transit using the the linear level (top). Do it for each of the 3 positions, then repeat until the transit is level in all directions. You can usually get away with only being precise about the level for the one position where the telescope points at the tower if the only purpose is tower alignment. But don't get sloppy: get it level in all other directions as best you can.

You should periodically check the level as you work. Unfortunately you must repeat the process every time you move the transit, and that must be done many times during alignment. It goes faster as you become accustomed to the process.

Pick a spot

The best spot is directly opposite a guy anchor, and farther from the tower than its height. The first is to ease sighting of the tower and for left-right symmetry. The second is to keep the maximum telescope angle below 45° elevation for ease of use. Farther is better than nearer, although it requires more walking to and from the turnbuckles after each adjustment.

The best spot is not always available because of obstacles such as buildings and bush. Or the sun is behind the tower from that vantage point which makes sighting the tower difficult and dangerous for your eyes. An alternative is the place the transit behind a guy anchor, slightly offset so that the guys don't block sighting the near tower leg. This is shown in the adjacent picture.

When you do offset in this fashion be aware that your view of the tower is slightly rotated. The difference may be less than 1" but it will loom large in the telescope. Also, the pier pin will not be vertically aligned with the nearest tower leg. Keep that in mind as you read the section below on the alignment process.

Preparing the tower

The guys are under a lot of tension. When you adjust one turnbuckle the tension of other guys at that level and especially those higher can distort the tower in unexpected ways. It is advisable to loosen all the guys equally before starting. Obviously this should not be done when the tower is heavily loaded and a storm is imminent.

The guys should not be so loose as to be slack. In my case with 5/16" EHS guys the pre-load tension is a little over 1000 lb I reduce the tension to no more than 500 lb. Do it for all guys above the lowest guy set. Leave the full pre-load tension on the lowest guys. As alignment proceeds we want the guys above the set being adjusted slack enough that they cannot distort the tower due to excess downward force. Similarly we want the guys below the set being adjusted to be at full pre-load tension.

All that said, if alignment is for periodic maintenance and not the initial alignment of the tower you likely don't need to loosen the guys. This is because the expected lateral shift required ought to be small. For new towers I find that the initial eyeballing rough alignment can be out by several inches. With experience more than one guy level can be adjusted at a time and tension becomes less of a concern. Don't overestimate your ability and you won't make any mistakes.

Aligning the tower

Guyed towers are aligned from bottom to top. You start by aligning the lowest guy set and move upward until the top. Starting at the top or middle will only make the job more difficult so avoid the temptation. This point was impressed on me by several experts. Loosening guy tension before you begin, as recommended above, greatly aids this process.

With the transit in position and levelled aim and focus the telescope at the tower's pier pin or suitable centre mark at the base. The telescope includes a reticle to do this accurately. On my transit the reticle looks somewhat like the image at left. I found the double vertical lines useful for bracketing bolt holes and leg ridges.

There is a knob to lock the horizontal motion, so lock it when your aim is close. There will be another knob for fine adjustment (concentric with the lock control on mine). Swing the telescope up and check for deviation from vertical at the lowest guy station.

Estimate the lateral correction required. Loosen the turnbuckle on the side the tower leans towards, then tighten the turnbuckle on the other side the same amount. You can make a good guess at how many turns of the turnbuckle it'll take by noting the tpi (turns per inch) and doubling it (since there are two screws) and reducing the travel a bit due to the angle of the guys -- lateral motion per turn is less the higher up the tower the guy attaches; this is basic trigonometry.

For large offsets do it in steps rather than all at once. This is also good advice if you've never done an alignment before. A bit of lubrication on the turnbuckle screws helps. Turning a balky turnbuckle carrying 1000 lb of tension generates a lot of heat (and loud screeching) that can damage the threads.

When you're satisfied with the alignment do the same for the other two positions around the tower. You'll likely need to repeat the circuit once and possibly more for towers badly out of alignment. After aligning the guys at each level tighten the three turnbuckles an equal number of turns until you reach the required tension (approximately 10% of breaking strength). Use a suitable gauge that is calibrated for the guy cable you are using. If all is in order the tension should be approximately equal on all 3 guys.

Repeat the process for each higher guy set until done. You should check the alignment at lower guy stations as you go along since as each higher guy set is tightened it will place additional load on the tower that can accentuate any imperfections. Be on the watch for significant deviations since this can indicate a weak tower section or guy component.

Common difficulties

The alignment process is straight-forward but tedious. Having friends to help makes the job go much faster. I find I spend a lot of time walking between guy anchors and transit, time which can be eliminated by asking your friends to tighten/loosen turnbuckles while you operate the transit.

It is good practice to have the turnbuckle screws approximately half inside the turnbuckle to allow adequate room for future adjustment in either direction. I found that with each new tower my initial rough alignment when corrected resulted in turnbuckles at one anchor with too much screw and with too little at another anchor. Don't shirk correcting these problems.

If there is too little screw thread inside the turnbuckle or the turnbuckle bottoms out during alignment you'll need to detach the guy to reposition the screws. Use a winch or cable puller of sufficient capacity to relax tension on the turnbuckle, unwrap the guy grip, adjust the screws and reattach the guy grip. Tighten the turnbuckle until the tension on the winch relaxes and remove the winch.

Use a tensiometer to return the tension to what it was before. Then align the tower only adjusting that one turnbuckle. This is a good time to note that when you cut the guy cable be sure to leave a longer tail in case you need it after alignment and repositioning a turnbuckle. You can cut it closer after the alignment is complete.

If you are uncertain whether the grip is safe to reuse replace it; they aren't expensive. I will reuse them once, but not twice, and only when the strands are not distorted and there is lots of grit remaining. From my own experience and those I've spoken to in the business no one can recall a grip failing on its second use. Guy grips are tougher than they look. However none of this guarantees that a reuse failure cannot happen.

Between guy stations the tower sections may not track in a straight line. Assuming that this is not due to damage (corrosion, metal fatigue, failed weld, etc.) and the deviation is large enough it is worthwhile to correct it. The problem is typically due to a section splice in which the bolt holes on one or more legs were not properly aligned when bolted.

Correction involves slightly loosening the bolts so that the vertical force seats all the splice bolts in the same position. Unfortunately the opposite can occur in some cases. I've done it though I'll admit it makes me nervous. Just be very certain the deviation is not due to damage. Better, call in an expert to do or supervise the work. In a guyed tower damage or deviations are more dangerous the lower they are on the tower, which is opposite to the expectations of many hams.

Finishing the guying

Guy components will relax when first put under full tension. For example, grips conforming to the shape of insulators and thimbles. The tower will drift out of alignment within days. For this reason professionals return to a tower a few days or weeks later to redo the alignment. We should do the same. It is worth the trouble even if money must be spent to rent a transit.

When you are satisfied that the tower is properly aligned and the steel has settled into its final shape you should add safety cables to the turnbuckles at each anchor to prevent them from turning under load and keeping the tower upright if a turnbuckle breaks. Clean and paint them to keep them in good working order.

As part of station general maintenance check alignment at least once each year. Do not rely on adjusting guy tension alone since, while indicative of potential trouble, tension changes don't tell you what has specifically happened.

Stacking Scenarios for the New Tower: 15 and 20 M

As I grind my way towards completion of my stacks of 5 element yagis for 15 and 20 meters it is time to decide what goes where. The objective is to maximize performance, when used as a stack and when used individually. The major decisions on placement: height and separation.

There is also the matter of interactions with yagis for the other bands and with the guy wires. For the present exercise I will ignore those interactions since the way I broke up the guys to be non-resonant and with sufficient yagi separation the pattern impact will be small.

In addition to electrical considerations there are physical constraints:

• The yagis atop the tower cannot be separated by more than 3 meters (10') to keep mast stress within reason. Similarly the smaller yagi for 15 meters will go at the top of the mast and the 20 meter yagi at the bottom of the mast.
• Lower yagis must be above a guy set, but not too far above to avoid tangling with the guys further up. The constraint is tighter if those yagis are rotatable rather than fixed. At least t his year they will be fixed towards Europe.

When completed the tower for these antennas will stand approximately 133' tall (40.5 meters) and the mast will rise another 10' (43.5 meters). Guy stations are nominally at 30', 65', 100' and 135', however due to section overlap the heights are more like 28', 61', 93' and 128'.

To recap the yagi dimensions:

• 15 meters: 5 elements on a 32' boom (10 meters). This antenna has low SWR across the full band and has been optimized for best gain while having a good match and F/B. Design details can be found in an earlier article.
• 20 meters: 5 elements on a 40' boom (12 meters). This antenna is a minor optimization of the yagi having the same dimension in recent versions of the ARRL Antenna Book.

Modeling is done with EZNEC. I use dual sources for in-phase stacking rather than phasing harnesses to make the modelling exercise easier. This does not materially affect the pattern but does affect the impedance, and the latter is not the focus of this article. SDC (stepped diameter correction) is used for all elements per my tapering schedule. Construction detail will appear in a future article.

If you're new to stacking you may want to review my article on the basics of stacking. There are of course many other resources on the topic of stacking around the internet and in the amateur literature.

20 Meters

I'll look at 20 meters first since the stack is more constrained; that is, there are fewer viable options for placement of the yagis. The upper yagi is at the bottom of the mast, which I waffled on with regard to the precise height, as you can see in the plot traces. The 2' (0.6 m) different is negligible. The lower yagi is in the vicinity of guy stations, ideally slightly above as discussed earlier.

Height of the upper yagi is ~2λ. Height of the lower yagi is at either 1λ or 1.35λ. The modest difference in height of the lower yagi has a significant impact on the stack behaviour.

The respective separations are 41' (12.5 m or 0.6λ) and 67' (20.5 m or 1λ). The first is equal to the boom length, usually considered the minimum separation for good performance; this is discussed in more detail below. The second is well separated at the cost of placing the lower yagi relatively close to ground (1λ).

The lowest lobe of the upper yagi is 7°, and 11° or 15° for the lower yagi. Lowest lobe of the stack is 8° and 9°, respectively.

Gain of the stack and individual yagis varies by less than 0.4 db for the two scenarios. This is indicative of low interaction, and that is confirmed in the EZNEC model. Although not confirmed in this exercise the low interaction (mutual impedance) between yagis promises low pattern distortion when they are pointed in different directions.

Stacking gain over the individual yagis varies from 1.5 to 2.5 db, which is quite good for 20 meters at these heights. The nominal 3 db stacking gain is just that: nominal. There are many variables that determine this performance metric.

Notice that the patterns of the lower yagis differs quite a bit due to their different height, and this affects the pattern of their respective stacks.

• Vertical radiation is higher for the lower yagi at 92' since that is the only position that is not a multiple of λ/2.
• Inter-lobe nulls coincide more closely when the stack separation is smaller, as expected. Better elevation angle diversity is achieved with greater separation. That is desirable for paths with an elevation angle close to a null so that we can avoid dead spots. 
• The major lobe of the lower yagi is significantly higher at the lower height. This, too, is desirable for path diversity. When fixed to Europe with its wide range of probable elevation angles the lower yagi becomes more useful.
• High angle minor lobes are attenuated with the lower yagi at 1λ height.

The choice for 20 meters is quite easy. The lower yagi will go directly above the second guy station. When (if) the lower yagi becomes rotatable it will also perform well on paths to Africa, Caribbean and North America.

15 Meters

With the upper yagi at the top of the mast and the shorter wavelength it is easier to achieve low interaction between yagis on 15 meters in comparison to 20 meters. The shorter boom length is also helpful in this respect.

The maximum height possible for the lower yagi is below 120', otherwise the elements get dangerously close to the top guys. I therefore chose this height for the first test case since while not physically practical it highlights a too small stack height of 20' (6 m or 0.42λ), which is less than the boom length.

In the second case the lower yagi is at the more practical height of 100', a little above the second highest guy station. This maximizes the distance from the outermost elements to the upper guys. The stack height is 40' (12m or 0.85λ). This is much better spacing.

When modelled the difference in performance is readily apparent. As with the 20 meter stack the greater stack height there is better distribution of the elevation nulls, reduced high angle radiation and greater stack gain.

If I had a tower dedicated to each band I could exploit the height to add a third yagi to the stack. This is not practical in my case where 15 and 20 meter yagis present since optimum and equal spacing would have yagis tangling with the guys or parked too close to a yagi for the adjacent band. A friend of mine who does manage to have a 15 meter 3 stack shared with 20 meters uses a taller tower than mine.

My next test case was to move the lower yagi even lower, though not too close to the lower 20 meter yagi at approximately 68'. The chosen height of 80' is, like 120', risky since it places the outermost elements close to the next highest set of guys.

The result is a mixed bag. Rearward lobes are small but there is an increase in radiation at high angles. Differences in gain of the stack and individual yagis compared to 100' are negligible at less than 0.3 db.

My tentative choice is to place the lower yagi at 100' or a little lower to increase distance to the upper guys while not getting too cozy with the set of guys immediately below.

Other antennas on or near the tower

Interactions limit further use of the tower. I plan to use my TH6 and TH7, possibly stacked, at lower heights for short paths such as the US and Caribbean. There is no good place for these tri-band yagis on the tower that would not impact performance due to interactions with at least the lower 20 meter yagi in the stacks. The tri-band yagis will therefore go on the other big tower, well below the 40 meter and 10 meter yagis.

I would like to leave open the possibility of a wire 40 meter yagi pointed at Europe, strung on a catenary between the big towers. With 5 elements the wire yagi would be 30 meters longs, which is about half the distance between the towers. Interaction with 20 meter yagis should be managable. Impacts on the performance of the 15 meter yagis could be more severe. The same is true of the tri-band yagis which are, of course, resonant on 15 meters.

I am looking at alternative placements of the wire yagi to best advantage. There is modelling work to be done.

Vertical antennas for 160 meters are less concerning due to the polarization difference. However the T-top of my current 160 meter antenna will require a close look to confirm that it will not causing any problems with the yagis on both towers.

Yagi separation vs. boom length

There exists a rule of thumb that two yagis in a stack should not be closer together than the yagis' boom length (for identical yagis). This is good guidance even if it obscures the reason for why it is a useful rule. Without delving into excruciating detail we can dig a little deeper for some insight.

But first let's review how a stack develops gain. For two identical yagis fed in phase, in free space and far enough apart that the mutual impedance is negligible, the stacking gain is exactly 3 db. This fact alone is a curiosity since we are dividing the power so that each yagi get half of it and the yagis' far field patterns sum in the far field. Fortunately I wrote an article on how this is possible if it seems paradoxical.

In the real world the yagis interact with real ground and there will always be some mutual impedance between the yagis. The closer together the greater the mutual impedance since the various elements will have near field coupling to those in the other yagi.

It is possible to have stacking gain greater than 3 db with carefully engineered close spacing. However this is only advisable if the yagis always point in the same direction, whether fixed or rotatable. Otherwise when one of them is turned the high mutual impedance will distort the patterns of both yagis. In general it is a poor idea.

Ground reflections for the two yagis place their lobes and nulls at different elevation angles which affects stacking gain. By closely spacing the yagis the lobes, especially the lowest main lobes, will reinforce each other and give close to the theoretical but nominal 3 db gain. This is at the price of a reduced ability to sidestep elevation angle nulls since these, too, will coincide, as we saw in the discussion earlier in the article.

With the preliminaries out of the way let's return to yagi separation and coupling. Yagi gain increases with boom length. Gain comes from a narrowing of the main lobe. As the lobe narrows the mutual impedance to a vertically separated identical yagi decreases. This is due to field cancellation away from the main lobe, directions which would intersect elements of the other yagi. Note that for this purpose we are primarily concerned with the free space elevation pattern (shown on the right).

However the lobe narrowing happens in concert with a longer boom length. Therefore the angle of, say, the -6 db point is lower but will still interact with the outermost elements of the other yagi because they are further out. The relationship is not exactly proportional but close enough that the rule of thumb is justified: increase the separation as the boom length increases to achieve approximately the same amount of element coupling (interaction).

Keep in mind this is a minimum distance not an optimum distance. When you allow the yagis to point in different directions more separation reduces pattern distortion. This is usually a better choice than trying for maximum stack gain.


Refinement

I have ample time before winter to refine the stacking arrangements. This can be done in parallel with the construction and tuning of the four yagis. Although I had hoped to be further along by now I am getting closer. It's been a learning experience, one with unexpected stumbling blocks.

You can see from the picture of aluminum shavings (the dark patches are steel) filling most of a 5 gallon pail that I have not been idle! Construction of the yagis is a story unto itself and will be covered in future articles.

6 Meter Season Wrap-up for 2019

We are now into 6 meter withdrawal season. This is the time of year when Es (sporadic E) openings rapidly decline in number and distance yet aficionados cannot quite let go. All I hear now on FT8 is endless CQing from those within direct or tropospheric propagation (within ~500 km). Although there is still some DX to be found if you are patient the season is effectively at an end.

This is a good time to reflect on my accomplishments this season and what I've learned. I did a similar season end report last year.

DX

Purple is my favourite colour

I ended last year with 56 DXCC countries on 6 meters using FT8. I tally countries separately from other modes to track my progress. Official counting methods mean little to me since I do not chase DXCC awards. As I write this I have worked 15 more countries this season for a total of 71 DXCC countries on 6 meter FT8. I don't believe there are any countries I've worked the last few years on CW and SSB but not on FT8.

I heard many more countries than I worked. That's the nature of 6 meter propagation. Of note I worked Japan for the very first time on 6 meters, using any mode. These QSOs were my first with Asia. With respects to continents only Oceania still eludes me. I heard several Hawaii call signs this year but all were in the continental US. American call sign practices can be frustrating to the DXer. I know the path exists since several hams in this corner of the continent worked Hawaii this year.

In my season's end article last year I noted that I worked 40 European stations on August 4 during an amazing multi-hour opening. Perhaps more amazing is that I broke that mark this year, working 43 Europeans on July 20. My European distance record now extends to Ukraine. Even so I have heard but failed to work many European countries such as OH, LX, 9H, LZ, YO among others.

I was unlucky with African openings apart from adding CN and EA9. I heard 5T5PA a few times, though very weakly and never workable. Better was 6W1TA who had a fine strong signal for almost 2 hours one day. In this instance I caught the opening near its end and failed to make it through the large North American pile up.

Looking south I worked HC5VF for a new one. CP1GJ was heard but not worked. Many stations were worked in northern South American and Caribbean. One that was active but not snagged was P41E.

My final country for the season was CY9C. In this case I got lucky since many others in this region had difficulty despite the relatively easy single hop path. You win some and you lose some. It would be no fun if every station heard is worked.

50.323 MHz

What seemed to be a great idea to move intercontinental DX activity to its own FT8 window is not working out. There was little to be found there this year. I did QSY to the DX window when domestic contest activity crowded me away from 50.313 MHz but with no success. The DXers, here and abroad, wouldn't move even when the QRM became overwhelming.

CW and SSB

The digi-averse die hards are still on conventional modes. The only significant operating I did on CW and SSB was to use those modes exclusively during the ARRL June VHF contest. Unlike my experience in 2018 this year I had far better success. With only a little effort I managed well over 100 contacts, reaching as far as the west coast. There are still signs of life at the low end of the band!

Despite my almost 100% focus on FT8 for DXing I have not used it in a contest. Perhaps I never will, but you never know. It's too slow and mechanical to hold my interest.

FT4

I have yet to use FT4, restricting myself to occasional monitoring. The 6 meter window is 50.318 MHz. It is certainly fast enough to interest me but I don't know if it'll catch on for DX work. Certainly it has promising attributes for 6 meter DXing. Maybe I'll try it next year.

Decoding sensitivity

There is an ongoing debate regarding FT8 decoding success rate between WSJT-X and alternative software branches, in particular JTDX. This may very well be true. What gives me pause is a few of the methods JTDX uses: correlation to known or expected messages and correlation to a data base of known active calls.

I am still thinking about whether this is a good idea. There is a fuzzy line between viable decoding and guessing, and I am ethically opposed to the latter. Even when I use Super Check Partial (SCP) during contests I always request a repeat or confirmation of the call.

Until now I have been happy to do no more than tweak upward the aggressiveness of WSJT-X decoding, yet even it does a bit of guessing. Where should the line be drawn? I don't know. As time permits I will download and experiment with JTDX on HF, listening only, to learn what it can do and how I feel about it. In the 2020 sporadic E season I will likely run higher power and I can expect more weak callers and therefore have greater need for decoding sensitivity.

Improvement is possible beyond the software. I have altered how I set up my rig and computer to better match the dynamic range of the receiver and sound card ADC. While preliminary results are ambiguous it looks promising. I may have more to say about this if I learn something of substance.

It is unfortunate that WSJT-X calculation of signal reports is not usable for determining signal levels, SNR or receive performance since it is relative to other signals and noise within the pass band. I only learned this recently. It explains some bizarre disparities between received and sent signal reports that I've witnessed.

Transmit quality

There is more activity on 50.313 MHz than ever before. Getting on is easy since every modern transceiver has 6 meters and many HF amplifiers include 6 meters. If you use RTTY or other data modes (or you do SSB contesting, like I do) you already have the required audio connections to your computer.

The trend may continue for the next two years until the solar flux edges upward and thoughts return to HF. I may be responsible in my own small way by encouraging local activity (FN25 and adjacent grids) during several talks I gave to local clubs last winter.

Unfortunately it is all too easy to transmit a dirty FT8 signal and its incidence is increasing in proportion to rising activity. Monitoring your own signal quality isn't easy and few bother to make the effort to do so. Most rely on recommended practices but without feedback don't realize when they've done it wrong.

I got more serious about it this year. With the help of a buddy we transmitted back and forth while tweaking our rigs to see what works best. I am now reasonably confident that my signal is clean. Over the winter I will build a test system so that I can monitor and make adjustments on my own. Perhaps I'll write it up if it looks to be useful to others.

The adjacent screen capture shows an FT8 signal with adjacent images that are often decoded. These are not harmonics. The DSP and equalization circuits in modern transmitters create novel difficulties. These images are present on far more FT8 signals than is good for peaceful coexistence. I get them on my own signal under some conditions and I want to make further improvements.

W9MDB has written a document on setting up your transmitter that looks quite good to me and explains a few peculiarities I've run into. Some surely need the lesson since there are too many signals far worse than is seen in the spectrogram above.

Improving QSO throughput

One of my objectives this year was to improve the number of QSOs I can squeeze into a shorter time. The key to this is understanding the software in greater depth and making liberal use of auto sequence features. The difficulty is understanding what auto sequence does in the critical crossover between one QSO and the next.

I have had good success once I let the software free to do what it thinks is best. It does always work out, and in those instances you simply need to be paying close attention and quickly alter the message or the station you are responding to. In short DX openings, with all their QSB, it is possible to interleave QSOs when one is interrupted by propagation or QRM yet be able to complete it a minute or two later.

There is much more to be said on the subject so I won't dwell on the topic now. I believe it is worthy of its own article. There is always more to learn about the subject and it is possible that many readers will benefit from knowing more, even veterans of digital modes.

Looking forward

As I've said before it is very likely that I'll have a 6 meter capable kilowatt amplifier next year. That is perhaps the biggest change I am planning for the near future. Once my HF antenna farming matures I will pay more attention to VHF. This includes an improved antenna of some kind and antennas for 2 meters and 70 cm. That's the upper limit of my interest.

With regard to other digital modes I have ventured back into MSK144 for the Perseid meteors. I haven't worked much, just playing with it to get more experience. Meteor scatter is something that interests me more for 2 meter use; on 6 meters the distance is easily spanned using more common ionospheric propagation modes.

Of more immediate interest is HF. Now that the peak sporadic E season is over there are antennas and towers to build and get operational for the fall and winter season. It also severs an inconvenient and invisible tether to the shack that keeps me from antenna work.

Draining Tower Static

We are all familiar with lightning, in which charge moves between ground and the atmosphere. There is less familiarity with the role that static plays on our towers and antennas. Charge doesn't move until the potential is large enough to bridge the distance from a location with a different charge. This static discharge can play havoc with reception. It is better to continuously bleed the charge so that its potential remains low. The best place to move that charge is to ground.

Let's begin with a story. Many years ago I visited a friend who was doing work on his modest suburban tower and antenna system. As is quite common during autumn in this climate there was light snow falling. As we were chatting we could hear a periodic snap sound coming from the doorway to the basement shack. We walked over to see what it might be.

Lying on the desk was the disconnected coax for his VHF yagi located about 15 meters up the tower. As we were looking around for the source of the sound a spark jumped across the coax connector. The snow was depositing a charge on the antenna which increased until the potential was enough to jump the gap and the charge would flow to ground via the coax shield. We could reproduce the spark at will with a screwdriver to reduce the gap with a wait of perhaps 15 seconds. At the time I was surprised this could occur with such a small antenna at a modest height.

Ordinarily the charge would be constantly bled through the receiver front end or a grounding style coax switch. When drained in this fashion the potential cannot rise high enough to cause any damage. But it would be unwise to plug the coax into the rig when there is a static charge present. Better to wait for the weather to settle.

A tower has a static charge on it due to its height despite being grounded. The ability to bleed the charge to ground can be difficult due to the potential gradient and the potential of the ground surrounding the ground rod. Although you cannot directly experience it there is a charge gradient along the tower, and indeed right up through the atmosphere. Just as there is no absolute protection from lightning the same is true of static charge, but the risk can be reduced. Our main concern is with reception. In extreme environments (high and very dry) transmission can be a problem but rarely at amateur power levels.

The Cushcraft XM240 40 meter yagi has a couple of inherent challenges with respects to static charge:

• Elements insulated from the boom
• Small diameter rods in the capacity hats

The former impedes the flow of charge to the boom and from there to the tower and ground. The latter increases the risk of corona and therefore more energetic discharges. Many hams connect the reflector element to the boom to permit charge flow. This has negligible effect on the resonance of the element. Although the driven element cannot be connected to the boom there is at least a long path to ground via the coax and into the shack.

I am motivated to do what I can since the static discharge noise on 40 meters can be dreadful when it is raining and sometimes when it is snowing. It is bad enough that the static discharges can be heard on nearby antennas for other bands. The XM240 is at particular risk of static charge since it is at the top of the mast. If it were completely bonded to the mast and tower to bleed the charge the QRN ought to be greatly reduced, protecting reception with it and antenna further down the tower.

Which brings us to the next difficulty: continuity between the mast and tower. If you've never thought of it before this may seem a strange question. Most would assume there is an electrical path between the mast and tower due to all those set screws and clamps holding everything together at the bearings and rotator. The problem is that electricity is being asked to conduct through bearings, which due to surface grease on the rolling components may not have reliable metal-to-metal contact.

The routine solution is a flexible wire between the tower and mast. Think of it as an insurance policy against poor continuity through the bearing surfaces. It might not help but it might help a great deal.

During a maintenance climb up the 150' tower several days ago one of my tasks was to install just such a wire. As you can see it's very simple. I cut a 2' length of heavy gauge, multi-strand speaker wire that was handy (though unlikely to be UV safe) and fitted ⅜" tinned lugs at both ends. One end connects to the tower via a top plate bolt and the other end conveniently fits onto a galvanized muffler clamp already on the mast. I was going to use the stainless hose clamp (visible in the picture) but I saw an opportunity and took it.

Will it help? I'll find out soon enough. I will need to see how it performs during rainfalls in the coming months. Unfortunately the insulated XM240 elements could muddy my observations. In any case the XM240 will come down soon and this time around I'll remember to ground the reflector to the boom. The "to be determined" antenna that will replace it at the top of the mast (46.5 meters high) will be bonded to the mast.

If the strap works I will do the same to my other towers. The fix is simple and justified even if the data of its performance is inconclusive.

Summer (blog) Vacation

I'm still here. New blog articles are slow to appear because I am very busy with antenna and tower projects, 6 meter DXing and a large number of non-ham summer fun stuff and chores. I thought I would fill the blogging gap with a progress report of sorts so that regular readers don't think I've vanished. I haven't. Regular blogging will resume, eventually.

To give you an idea of what I am up to I've listed the most important projects below. From this you will get an idea how busy I am. All will be written up in future articles as each project is completed and I have the time. But right now the weather is too good to waste. I have not provided links to articles which discuss these projects so if interested try the search box.

• The 80 meter vertical yagi is near completion. The parasitic elements are tuned and the switching system is operational, as is the control head in the shack. What's missing is the control box containing the switching matrix, cable interconnections and switchable L-networks. It is partially built and I have all the parts.
• Options and specs for the mast and rotation system for the new 140' tower have been discussed with my local machine shop and I should have the fabrication complete in the first half of August. I will be using my spare prop pitch motor as the rotator.
• One boom left to be built for the 2 × 5-element stacks of 20 and 15 meter yagis. That one requires machining of a 20' long pipe the machinist can't handle in his shop. But it'll get done one way or another.
• I have fabricated 2 sets of 5 element-to-boom clamps for those yagis. The rest are awaiting an order of fasteners to make drilling templates.
• All the aluminum for the 20 yagi elements (4 × 5) is on hand and the bulk of the machining is complete. Once that is done the sections will be joined and yagi construction and testing should begin around mid-August. Elements have been scaled in software for the taper schedules that I settled on.
• Design of the elements for a forthcoming full size 40 meter yagi is proceeding. I hope to at least get one complete element in the air as a dipole for testing over the winter to see how it performs electrically and mechanically.
• Tower maintenance is ongoing. This includes patching surface rust, vertical alignment and checking of all hardware. Repair of malfunctioning antenna requires getting them down using the same tram line used to put them up them.

Reading the list is fatiguing enough, yet these are things I have to get done in the next few months.

Haying on my land should be complete this week and I will have more freedom to work on towers and antennas. This includes malfunctioning yagis that need to come down for repair or to be moved to a different tower.

I hope the weather is as good where you are as it is here and that you, too, are making progress on your station projects. Soon enough the weather will turn cool and the race will be on to complete work before winter settles in. Then I will have the pleasure of cold weather projects such as low-noise receive antennas and shack equipment. It'll be a while yet before I can truly relax.

Working Japan on 6 Meters

From my start on 6 meters in the mid-1970s, to the tremendous solar maximum of 1989-1990 and into the modern era of FT8 it is interesting that I had not achieved WAC (Worked All Continents) on the magic band. The one continent that confounded me was Asia. I came very close in 1989, eking out several partial CW QSOs with Japan. That was my sole shot since almost all of west Asia, like most of Europe, did not have a 6 meter band at the time.

With FT8 prospects improved, despite the lack of sunspots. Sporadic E openings to Japan and the Far East from eastern North America have been known about for a long time but due to their fleeting nature have only rewarded the most dedicated 6 meter aficionados both here and there. These openings are easier to catch with FT8 since all activity is captured by the software. This is what I've coined the discovery problem which FT8 solves so very well.

Historically it is known that the probability of an opening between Japan and northeastern North America peaks in the last week in June between 2130Z and 2300Z, our late afternoon and early morning in Japan. In fact the times between this daily window and their sunrise and our sunset are nearly equal. Although that may be nothing more than a coincidence it is nonetheless interesting.

To my chagrin I missed a fantastic opening in late June last year, the first year that I and most of the 6 meter community were on FT8. It was dinnertime and by the time I discovered what had been occurring the opening was ending. Sitting in front of the rig every day during the propagation window is not realistic, nor very enticing.

This year I was not so complacent. I really wanted a QSO with Asia, and openings to the Middle East have so far yielded no QSO. So I monitored, watched and waited for another opportunity to work Japan.

Statistically speaking I would likely have one or two chances, each lasting no more than 15 minutes. This would be terribly daunting were it not that it is early evening when I am more likely to be in the house. But this time I would have to pay close attention to activity.

During the second half of June there was no workable opening to Japan from this QTH. Others to the south, west and east had better luck. Other than a couple of decodes of very weak signals nothing was workable here in FN24. That changed in July.

The first opening arrived on July 2. Unfortunately it was only JA7QVI who was sporadically copied over a period of 10 minutes. Several other likely but very weak signals that appeared on the spectrogram did not decode. I called him without any luck. This isn't surprising since he is a big gun who typically runs QRO and his weak received signal boded ill for my 150 watts.

Success had to wait two more days. On July 4 signals were being reported by others in this part of the continent as early as 2200Z. I did not hear any QSOs being completed but clearly something was brewing. A strong opening to OX was on the wane at that time and the Nunavut beacon VY0SNO/B was widely heard. It was a challenge to monitor the band while cooking the evening meal! Happily the real fireworks waited until meal preparation was completed.

When signals began decoding I noticed that more were stations calling KL7HBK. Alaska's bearing is only 10° west of the Japan path but I never did copy him.

JE1BMJ was calling CQ NA but I couldn't get through to him as he faded in and out for several minutes. None of the other stations heard were decoded more than twice.

They say that patience is a virtue, so I made a sacrifice by eating my dinner in the shack. I watched and hoped for signals to grow stronger. Of course I was not quite that patient so I filled the silence with my own CQ JA.

As you can see in the screen shot that eventually signals did rise. A few decibels made all the difference. First in the log was JH1IFS. Then for a few short minutes I was the object of a small pile-up. I worked just 4 stations before the opening faded, but even one was enough to leave me delighted. During the fade I made a couple of partial QSOs as signals briefly rose out of the noise. Within 10 minutes they were gone for good.

It is interesting that I never heard the KL7 the JAs were calling and big guns only a few hundred kilometers from me appeared to work nothing in this opening. This is a great example of the spotlight nature of 6 meter openings. The spotlight narrows as the path length increases. All those points of intense E-layer ionization must line up in space as well as time to make the QSO possible. That's part of the attraction, working with what nature tosses our way to put the magic in the magic band.

Notice that every Japanese station calling me skipped message #1 in the standard FT8 sequence and used RR73 rather than separate RRR and 73 messages. That is an excellent practice for fleeting openings. They can be so short that the 30 seconds saved is critical to success. It also allows for more QSOs to be made by everyone during the opening.

I suspect the Japanese operators are acutely aware of this since almost all their DX QSOs on 6 meters are on paths of this type. Once you miss out on some juicy DX using the standard (and longest possible) message sequence you quickly learn. Exchange of grid squares is nice but is not necessary. The minimum required information for a valid QSO is call sign, report and confirmation of both.

Afterward I sat back and contemplated this achievement. It was one more of persistence than any particular skill. Sometimes that's all it takes. Just as in contests the one under-appreciated difference between the winners and losers is BIC: butt-in-chair. That was perhaps the most important factor that put these rare QSO into my log.

Technically I now have WAC worked on 6 meters. However I restarted my DXCC count when I returned to the air in 2013, on which basis I still need Oceania. My best shot for that is a Sporadic E openings to KH6. From here these are rare but certainly workable, perhaps no worse than Japan but with fewer active 6 meter operators. I've had a few false alarms since with US call sign portability the only KH6/AH6/WH6 stations I've heard were within the continental US. However I know that some in this region have worked Hawaii this season.

Returning to the topic of spotlight openings, these openings to Japan, Hawaii and other distant locales cannot be so unique. There must be many more similar openings to the unpopulated or lightly populated expanses of the Pacific Ocean and northwest Asia. Without active stations those openings remain undiscovered. Certainly there are other islands and UA0 is hardly empty, but the population density is low and the ham density is lower still. We need a confluence of rare conditions and a dedicated group of hams attuned to the nature of 6 meter propagation.

Calling CQ into a silent band is not a bad strategy even though there is rarely a reply. Somebody has to CQ, so why not you? It may be a rare occurrence but every so often a strong DX signal will answer. Sporadic E DX propagation has existed for many millions of years and will continue long after amateur radio is just a memory. It's up to us to appreciate this gift and put it to good use.

Resolving Amplifier Arcing

A vacuum tube high power RF amplifier is full of high voltages. The large physical size of the tubes requires high voltage between cathode and anode to function. The combination of high output impedance and high power results in a high RF voltage (by Ohm's Law). Prevention of high voltage arcs requires careful design, component selection and operation. Those arcs are potentially destructive: to the tube, power supply and your ease of mind.

Arcing is more common in older amplifiers due to chemical degradation of insulators, insulator cracks and component warping from thermal and electronic stress, and the oxidation and burning of the contacts in physical switches. Although arcing is rare in solid state amplifiers since they operate at relatively low voltages that is no panacea since they suffer from other ills. But this article is about tube amplifiers.

Not long after putting my recently acquired vintage Drake L7 to work it suffered from intermittent arcing at the high end of its power range. Because the high DC plate voltage is independent of power level the arcing was almost certainly at RF. Although the arcing has been eliminated I expect it to return because the faulty part requires replacement. It's on my very long to-do list and it'll take a while until I get around to a implementing a long term solution.

If you've never worked on a high power tube amplifier my relating of how I investigated and resolved the arcing may be of interest. Despite the large size and lethal operating voltages and currents tube amplifiers are actually quite uncomplicated. With attention to safety and the peculiarities of dealing with high voltage, current and power they are not too difficult to work on.

Locating the arcs

The case of the L7 has no opening except on the bottom and rear for forced air cooling. These are useless as windows into the amplifier's interior. The case must be removed. This is the first problem in any properly designed amplifier. There are interlocks to prevent accidental electrocution and burns to budding technicians who are out of their depth.

The Drake L7 has two interlocks: one shorts the 3000 VDC plate supply and other (well hidden) prevents the amplifier from being turned on. Both interlocks must be disabled to operate the amplifier without the case. Before you try this, or even consider doing so, you must educate yourself about what you're attempting to do. Better still, have a knowledgable friend help you out. If you get yourself killed don't say I didn't warn you.

Yes, that's really a brick! I needed something flat, heavy and non-conducting to safely disable the high voltage interlock. The mains interlock (not visible) on the bottom is disabled with a chunk of plastic wedged under it. In the picture the amp is on and idling with a plastic (non-conducting) LED desk lamp for added illumination. Arcs are so bright that no ordinary lighting will wash them out.

I mentioned my suspicion about the loading capacitor in an earlier article. I dutifully straightened the multitude of plates until they maintained a decent gap for their full rotation. Unfortunately that repair resulted in no improvement. Hence the deep dive into the amp's innards.

As I increased drive the amp arced as expected but not where I expected. The loading capacitor sat quietly when the fireworks began.

It was the plate capacitor that was arcing. Although the spacing was generally good (and much wider than the loading capacitor) a number of rotor plates didn't track well. I straightened them without needing to remove the capacitor from the amp. There is an unrelated problem that will require its eventual removal for repair but that can wait.

Straightening the plates did not fix the problem. Worse, the arc location was seemingly random. Each one occurred in a different location. The arcs were evidently due to a fault elsewhere that caused an excess voltage condition beyond the rating of the capacitor. The capacitor is working just fine.

This is interesting so let's take a detour to review the design of a tube amplifier's output network.

Amplifier pi-network

The simplified schematic below is that of a typical pi-network found in many tube amplifiers. It transforms the high impedance of the tube output to the low impedance of the antenna system. The operator adjusts the plate capacitor to resonate the plate circuit and the loading capacitor for a high efficiency match to the impedance presented by the antenna system.

The resonance condition is a typical feature of an impedance transformation network, as previously covered in this blog. The circuit also attenuates harmonics since it is a low pass filter.

The blocking capacitor keeps DC out of the antenna circuit and the choke keeps the RF out of the power supply. Band switching (not shown) alters the range of the variable capacitors and the inductor value. The T/R switch (input side not show) bypasses the amplifier during receive.

RF voltage is determined by the power and impedance in accord with Ohm's Law: E = SQRT(PZ). From the data sheet for a pair of 3-500Z tubes a little arithmetic suggests there is approximately 3000 volts across the plate capacitor at 1000 watts RF output. The recommended capacitor rating is 4.5 kV because the impedance, and therefore voltage, can be higher depending on operating parameters.

On the high bands the L7 places a fixed capacitor in series with the variable capacitor to reduce the capacitance. This also lowers the voltage across each capacitor since capacitors in series act as a voltage divider. Because of this arcing incidence is greater on the low bands. However it is not eliminated. Something more dire is going on to cause arcing when the RF voltage is low.

The voltage across the loading capacitor is easier to calculate since the antenna system impedance is nominally 50 Ω. At 1000 watts the potential is a less than 300 volts. The voltage will often be higher when the SWR is greater than 1, which is very common for most hams. If the SWR is too high the loading capacitor with its smaller plate spacing can arc.

Sequencing

Since the capacitors appear to be in good shape and the output impedance is well within the acceptable range the problem must originate elsewhere. Most likely is a fault that affects the impedance at the output port. The antennas, external switches and transmission lines were ruled out by additional testing. High power can aggravate weak components and loose connections in an antenna system to create intermittent and permanent impedance changes.

By this process of elimination I focussed my attention on the T/R relay. It is common for slow or faulty amplifier relays to cause plate capacitor arcing when transmitter power appears at the amplifier input before the output relay contacts have settled. Unsettled contacts cause a momentary high impedance (open condition) at the output port. Once an arc starts it can continue after the relay stabilizes since the path to ground is always lower impedance than the antenna system.

The solution is sequencing to ensure the amplifier relays settle before power is applied to the input port. This can be coordinated with the transmitter, signal source (e.g. PTT in advance of transmit) and even with the amplifier itself by having the output port relay close faster than the input port relay.

The open frame relay in the L7 is typical of many vintage amplifiers. It iss slow at best, and with age the contacts are suspect. Replacements can be found but better solutions are available.

While arcing at turn on was occurring its incidence was less than that of arcing during a transmission. That is sufficient evidence to rule out sequencing as the cause of my problem. It does not mean sequencing isn't a concern, just that it isn't responsible for the observed behaviour.

Relay woes

I had good reason to suspect the relay. I earlier had to clean the contacts on the input and output of the bypass side due to intermittent signal attenuation on receive. With an ohmmeter connected to the centre pins of the input and output SO239 jacks you clean the contacts until you reliably read 0 Ω. Since the relay arms can shift laterally it is important to test for this by manipulating the relay arms.

The bad contact can be isolated by connecting one ohmmeter probe to the bypass bridge seen on the right. The output port is at the bottom of the picture and the input port is at the top. The centre arm applies tube cutoff bias during receive. Just my luck that both sides of the relay were corroded.

I had to resort to aggressive cleaning with an abrasive when a deoxidizing contact cleaner and non-abrasive buffing were insufficient. Do this only when absolutely necessary since abrasives can easily damage the thin contact coating, assuming there is any left (usually silver) after several decades of use. This is discussed in more detail by W8JI. I used a thin strip of 3000x sandpaper to be as gentle as possible. It worked.

Checking the through amplifier relay contacts is more difficult since an ohmmeter cannot be easily employed to measure resistance. Deoxidizing cleaner and buffing didn't resolve the arcing problem, but it did seem to reduce its frequency. Having gone that far I resorted once more to the sandpaper. After thoroughly clearing the contacts of debris I did another test. This time the arcing vanished entirely.

Permanent solution

I don't know how long the repair will last. The relay needs to be replaced. In any case it is slow and loud. Not only is that very annoying it is cause for ongoing worry. I don't want to take the risk of it failing during a contest.

Designs and even kits to replace T/R relays in vintage amplifiers are available. Some are fast enough to enable QSK operation. I don't need QSK just a solution fast, reliable and quiet.

Another problem with the existing T/R switching is the long lead lengths along the bypass path. On 6 meters it is enough (almost 0.03λ) to significantly raise the SWR. With 6 meter season in full swing I manually bypass the amplifier when I am not using it. Any T/R relay replacement will need to address this issue.

Vintage amplifiers are cost effective assuming you have the time and motivation to repair aging equipment and add modern features. My next amplifier will likely be a new purchase, one with a stiff power supply, silent operation and 6 meters. That way I can tolerate the quirks and faults of its older cousin at the secondary operating position.

80 Meter Stinger Version 2.0 (and Pipe Fitting)

You might think that because I write a blog about antennas and station building that I always do things right. I only wish! Perhaps I make fewer mistakes than some but I have my share of them. The original stinger for the driven element of my 80 meter array is one.

I was economical with the aluminum tubes and pipes I had on hand, saving the longer pieces for other projects. The stinger was 21' long, with 19' (6 m) projecting above the tower top. That was topped by over 3' (1 m) of 1" PVC pipe to get more height for the parasitic wire element support ropes. The total amount of aluminum and PVC above the tower was 7 meters long. That's a lot.

Although the stinger is guyed by the catenaries for the wire elements the tension produces a downward force (compression). It was obvious during setup that a butt joint between 1-½" x 0.095" aluminum tubes was not up to the stress. My hope was that it would last long enough that I could focus on other projects until I would have to replace it. All seemed well for a year as it survived one wind storm after another. Then the joint suffered a fatigue failure and the top half of the stinger fell down.

Stinger version 2.0

The stinger needs to be robust but not necessarily lightweight. The stinger must resist modest horizontal tension of the parasitic element catenaries. It must also be up to the compression force due to those same catenaries, especially with regard to high stress points where the yield point could be exceeded in a high wind and icing, or from tension imbalance among the 4 catenaries. It is laterally stabilized by those same catenaries which act as guys.

Being lightweight is beneficial when installing the stinger since it is long and must be lifted overhead to be dropped into the tower top. It can be assembled in pieces and raised from below at the price of more time and effort. As you will see I did a bit of both.

Rather than a butt joint between two lengths of 1-½" aluminum tubes the main improvement is a butt joint between two lengths of 1-½" aluminum pipe (1.9" OD). This allows me to use the existing 2" saddle clamps that secure the stinger to the tower plates. I also have a supply of these surplus pipes on hand and I know where I can get a few more at a good price.

Pipe fitting

My introduction to fitting pipes together for antenna construction was simply out of expediency: I had sources of cheap surplus aluminum pipe and tubes are expensive. I later came across the same idea in W6NL's book Physical Antenna Design (now out of print), which increased my confidence.

Although aluminum pipe is almost always 6061-T6 -- excellent tensile strength -- they have a seam, hard as it can be to find one on these aluminum pipes. They are theoretically weaker than seamless tubes although I have yet to see a seam failure. Indeed, some of my stock comes from commercial antennas that have survived harsh Canadian winters at great heights.

Aluminum pipe follows the same size schedules as steel pipe in the US and Canada. That's very convenient. Plastic pipe that is now in common use for water pipe and conduit -- ABS and PVC -- are similarly sized. I'll provide several examples of how pipes and tubes can be mated with respect to my 80 meter stinger, and additional ideas covered in earlier articles. There are other combinations of pipes and tubes that can work well together.

On the left are two schedule 40 pipes: a 1-½" pipe inside a 2" pipe. The inner pipe OD is 1.9" and the outer pipe ID is 2.067". The gap is 0.167", or 0.083" all around. Depending on the application the pipe can be simply bolted together. For improved rigidity a shim made of aluminum flashing can be used. An alternative is to increase the amount of overlap to reduce wobble, at the expense of greater weight.

The middle example is almost the same except that the outer pipe is schedule 80 with an ID of 1.939". That is a much better fit. Both are options to butt join two lengths of 1-½" pipe. I considered using the schedule 80 pipe until I found what is, to me, a more favourable solution. I prefer to save the schedule 80 pipes for my various yagi projects.

On the right is the 1" schedule 40 PVC pipe that is fit to a 1-½" aluminum tube at the top of the stinger as a non-conductive extension for the catenary attachments. The OD is 1.315" and the ID is 1.049". The 1" pine dowel purchased at a hardware store provides structural strength and fits well enough for the intended use.

This size PVC pipe will also fit well over 1" tubes. I may use PVC pipe as an insulator on the driven element 1" centre segments if I decide to use a beta match. Insulation is not needed for a gamma or T match.

Here are a few more pipe fitting ideas. When I used a 2-½" aluminum pipe to mate with 3" tubes for my first set of long yagi booms I had a machine shop turn down the pipe a few hundredths of an inch. The mast on my 150' tower is a 2-½" (2.875" OD, 0.25" wall) steel pipe slipped inside a 3" (3.068" ID, schedule 40) steel pipe used as the drive shaft for chain driven prop pitch motor. There the fit is so poor that I needed shims to prevent slippage caused by the large mechanical load. For one long yagi boom I fit 2" OD heavy wall tubes into both ends of a 2" schedule 40 pipe, which is a good fit. I bought several lengths of heavy wall 2" tubes to mate with these pipes to make booms for the 20 meter and 15 meter long boom yagis I am building.

There are other applications of pipes that I will discuss in future articles about those projects. Consult charts of pipe sizes and trawl through surplus yards for cost effective solutions in your antenna farm.

Stinger butt splice

In my junk box are Hy-Gain yagi parts that have been collected over the years. Hy-Gain booms are mostly 2" OD and spliced at the centre for the longer yagis. I have two of these surplus brackets. I tested a bracket on 1.9" OD pipes and was successful in achieving a secure fit despite the smaller size.

I butt spliced 10' and 7' pipes in the bracket. Holes were drilled through the pipes to make use of the bracket holes for that purpose in lieu of using the inner perimeter holes intended for a mast clamp.

I briefly experimented with plastic pipe as insulators to electrically isolate the pipes. I would need do this to attach a switchable coil to add 160 meters to the 80 meter array. I slit a scrap length of 2" white PVC pipe to slide over the pipe. It had to be slit since the ID is slightly less than 1.9".

At the end of the dressed pipe is a round insulator made of pressure treated lumber, cut with a hole drill, to provide mechanically robust isolation between the upper and lower pipes. The lower pipe does not need an insulating sleeve except perhaps to achieve a consistent diameter within the bracket.

I put the idea aside as not quite ready for implementation. It can be retrofit later. I first need to ensure high voltages between the pipes when the coil is active (not shorted) cannot jump the gap through the slit while maintaining high mechanical strength. It may be as simple as a wrap of thick polyethylene sheet and a seal to keep water out.

Upper stinger

Spliced to the upper pipe is a 7' (2 m) length of 1-½" x 0.095" aluminum tube. This is the only piece of the original stinger used in version 2. The 0.11" gap (the pipe ID is 1.61") is filled with a wrap of aluminum flashing coated in conductive grease. Stainless screws with nylocs hold it together. The 1" PVC pipe (1.315" OD) with its inner wood dowel are attached to the 1-½" tube (1.41" ID) in a similar fashion.

The original holes for attaching the rope catenaries are reused, and holes drilled through the wood dowel inside. The raw pine is protected by a cap of pressure treated wood, the top of which is sealed with caulk. The hose clamp adds tensile strength to the PVC and wood to better withstand the tension on the catenaries. The tension isn't high but I want to ensure years of trouble-free service.

The final stinger is ~2' (60 cm) longer than the original. This is intentional. I found that with my parasitic T-element design there is some slack on the vertical wire. The longer stinger removes the slack, and is easier than rebuilding the wire elements.

Installation

The new stinger was raised in two steps. The lower 10' pipe with Hy-Gain bracket went up first and dropped into the tower clamps until the bracket rested on the top clamp. The nice thing about aluminum pipe is high strength-to-weight ratio. The 10' of pipe with bracket attached is only ~9 lb (4 kg). It is easy to hold it vertical over my head as I fuss with inserting it through the tower clamps.

The catenary ropes are tied to the top of the stinger and detached from the wire elements in preparation for the next step. I briefly considered leaving the elements attached until I realized that the lateral tugs of those small weights would prevent safe lifting of the 17' long upper stinger.

With everything in place I lifted the upper stinger and dropped it into the Hy-Gain bracket. Once that was secured the elements were reattached. The complete stinger was then pushed up through the tower top and clamped in place.

Back on the ground I tensioned all the catenaries. The test for tension equalization was to have the stinger straight and in line with the tower. That was after the adjacent picture was taken.

Although a simple procedure it is tedious. I took an overnight break at one stage when I felt that I was too tired to do the lift with complete safety. A brief delay is preferable to an unnecessary risk.

Matching network changes

The new stinger's mechanical length is 2' longer and its electrical length is 3' longer. The reason is explained below. But having done so the new electrical properties of the driven element must be dealt with. For a λ/4 monopole on 80 meters the approximate rate-of-change (dF/dL) is10 kHz/6 cm; that's ~150 kHz lower due to the 3' extension.

There is no reason to make the driven element resonant at any particular frequency. The low impedance still requires a matching network, both as an omni-directional vertical and in yagi mode. I am using a switchable L-network.

My next task is to remeasure the antenna's impedance across the band, in both omni-directional and yagi modes. I will then use TLW to determine what changes are required. They should be small. I'll describe the details in my final article about this antenna, which will be written once it is complete and fully operational.

Catenary rope length changes

Changing the stinger height presents an interesting geometry problem: to lengthen the catenary ropes in a manner that keeps the parasitic elements vertical and preserves yagi performance. My first inclination was to ignore the problem since the change is quite minor. However it isn't difficult to check this on paper so I took that precaution.

Since the two sides of the right angle triangle are approximately equal each increment in height lengthens the full catenary (including the T-top of the wire element) by 0.7 increments; that is, 1.4' for a 2' height increase. However we only need to lengthen A to B, the distance from the top to the vertical wire, since we can freely add rope at the bottom. With A and B only 40% of the total length -- 10.5/25.5 -- we need only 40% of 1.4' or 6" (15 cm).

By not lengthening the top rope the wire element will lean towards the driven element ~4" (10 cm). As confirmed by modelling (and as you'd likely guess) this is negligible. Since I had no slack to lengthen the upper rope section I built and installed long insulators between the rope and upper end of the T shaped wire element. These are made from PVC pipe. The height of the vertical component of each wire element was increased by 0.8' (25 cm) -- 40% of 2' -- which took up all of the slack. Mission accomplished.

Returning to work

With the stinger rebuilt, better and stronger than before, work can resume on the yagi. All the parasitic switch boxes are installed and working. Tuning of the elements is partially done. Then comes the final step: the main switching system at the base of the driven element (tower).

Progress on the antenna has slowed due to more urgent projects, especially the 20 and 15 meter stacked yagis. Not to mention 6 meter DXing and otherwise simply enjoying the warm weather. With my 80 meter interest being DXing and contesting the 80 meter yagi is not urgently needed. It can wait until late summer, but may be completed earlier depending on circumstances.

In consideration of the weather and my busy schedule don't be surprised by a slowed rate of articles through the summer.