Monday, June 18, 2018

Wind vs. Tailtwister Rotation Lockup

I find it unconscionable that a company can ignore a serious design flaw in a widely used product that has been in production for decades. Namely, the Hy-Gain Tailtwister rotator (T2X). If you have a T2X you have likely encountered this flaw. I'll briefly describe the flaw and how I recovered from one time in an unconventional way.

The flaw is simply this: occasionally the rotator locks up, able to turn in one direction but not the other. The usual method of dealing with this is to briefly turn it in the operational direction, after which it will once again turn in both directions. It is annoying but not a deal breaker. Since the T2X tends to be reasonably priced on the used market the flaw elicits grumbles but rarely more. I got mine for a good price and overhauled it.

I would never buy a new T2X since it is extravagantly overpriced for its features, load ratings and quality. The manufacturer gets away with it since hams keep buying them despite poor reviews and continuing problems. None of this is the direct fault of the current owner of the product line -- MFJ -- since the T2X and its woes go farther back decades. They just keep churning them out to feed the market's appetite. Obviously I decided to accept the good and the bad with this rotator.

Although the picture at right looks perfectly innocent it is not. The antennas are pointed south and, at the time, were not able to point elsewhere. This is the case where the flaw is far more than an occasional annoyance.

When the rotator locks at the clockwise or counterclockwise stop you cannot use the trick to briefly turn it in the operational direction since it stopped in that direction by the limit switches that prevent over-rotation.

Often the only solution is to climb the tower. A helper in the shack releases the brake and you grab a yagi boom and manually jiggle the mast to free the brake. Since this is not a desirable thing to do one tries to avoid the situation by being careful to never let the T2X rotate right up against the stops.

In the heat of an opening or contest it is easy to forget. Other times wind and rotational momentum will put the rotator into the danger zone despite your best intentions.

In this instance I was chasing South American DX on 6 meters and was trying to catch a new one before the fickle propagation could turn against me. My full attention was not on the rotator position. After trying (and failing) to work the DX I discovered that the rotator was locked against the south stop. Until I could unlock the rotator there would be no west coast or European openings for me!

T2X going nowhere fast

I was not pleased. Over the next few hours I would try the rotator, hoping for a miracle. Absent a miracle help was arranged for ground assistance, but not for that day. Meanwhile I fretted. At least the HF bands were available to me with my other antennas and tower.

Later that day a weather front moved through and moderate winds of up to 50 kph were with us for a few hours. I noticed the antennas rocking on the mast as they usually do with Hy-Gain rotators. This due to the play of the brake wedge in the teeth of the outer housing. As I watched I got an idea.

Back in the shack I released the brake and waited a few seconds. I tried turning the rotator. It didn't move. After a brief pause I tried again and this time the rotator resumed working as it should. What I was trying to do, and succeeded at, was letting the small and random rotation due to the wind force do the mast jiggling for me without having to climb the tower. I had never tried this before and was pleased to see that it could work.

With the antennas back towards Europe I phoned to inform my helper that the problem was resolved. He had a good laugh when I related what I'd done. In future I'll have to be more cautious when operating the rotator.

If you have a T2X or are considering one perhaps my story will someday be of use to you.

Thursday, June 14, 2018

Do Animals Climb Towers?

You have undoubtedly read about or seen the raccoon that recently climbed a 25-storey building in Minnesota. To a human it seems kind of cute and interesting, along with some worry about the welfare of the animal. To the raccoon it would have been more about survival and not much fun at all.

Being a ham this immediately brings to mind the question of whether animals climb towers. Yes, they do. This I know from direct experience. Like the raccoon in the story animals don't usually climb for fun (or to work on antennas!) but rather to accomplish some goal related to survival such as shelter or food. I have seen squirrels climb for no discernible reason at all, but that's about what we expect of squirrels.

The only regular animal climbers I have seen on my towers are raccoons and squirrels. The why and how of it are interesting. At my Ottawa QTH where I had two small towers I had frequent opportunities to witness these climbers.

Unfortunately I have to relate the rest of the story without pictures since they never waited for me to find a camera and then pose, and in any case would disappear fast when they caught sight of me sneaking up on them with camera in hand.

Instead I'll include pictures of the towers and explain the rest in words. The tower pictures are taken from blog articles back in 2014.

How?

Rodents rely on their claws to climb. On trees this works well; on steel the claws are useless. Larger animals can grip tower braces with their paws.

The first time I caught a squirrel climbing was on my DMX tower -- this tower is now the driven element of my 80 meter vertical yagi.

The first few times I noticed that the squirrel would hop onto a bottom brace and sit there. Then it would hop off and continue on doing whatever it is that squirrels do. Days later I saw one (the same one?) jump from the lower brace to the next higher one on another faces. Finally one of the brighter ones realized that this thing could be climbed and made it up to about 20' in this fashion, then immediately come down again. It was interested to observe their learning process.

During one of these episodes a second squirrel on the ground watched the one that was climbing and decided to try it. Its first attempts failed, seemingly unable to catch on to the trick of it. When it finally succeeded the two squirrels chased each other up and down the tower the same way you see them playing on trees. After 30 seconds of this they were back to chasing each other on the ground.

I never caught a raccoon climbing the DMX tower. Perhaps they didn't, however it is very exposed and raccoons are shy and mostly nocturnal. I never saw a squirrel climbing in winter. Whether it was a behavioural thing or the tower steel was too cold for comfort I can't say.

Why?

Apart from play animals can find towers useful. Actually play is useful for improving and demonstrating fitness and is common behaviour among most animals, humans included.

Perhaps the most common use of towers by animals is getting from A to B; that is, it's a kind of road. The location of the tower is therefore of utmost relevance to whether it will be attractive for climbing.

In the case of the DMX tower it was eyed by the squirrels as a bridge between trees. Not visible in the earlier picture is an huge though diseased willow tree on the left since it had just been cut down by my neighbours to prevent it falling down. The reach of its branches was ideal for squirrels, allowing them to jump to or from the branches of other trees.

With the willow gone the tower was being eyed as a replacement to cross my yard without touching the ground. It didn't work out, though they did try. One day I watched a squirrel climb to over 30' on the DMX tower and attempt to jump to the spruce on the left. Since the squirrel could not dig in its claws it had to attempt the jump from a sitting position on the brace rather than its preferred method of digging in its hind claws, leaning outward and pushing. It couldn't get enough purchase on the steel to make it work. Luckily it only fell partway, landing on a lower and longer branch.

The bracketed tower was far more useful for animal transportation. With no trees overhanging the house the tower was an easy path to the roof and from there to the overhead telephone and power lines. Utility poles and lines form a transportation network for rodents. Indeed this tower was in use long before they learned to climb the DMX since it is so obviously useful and its braces are comfortably horizontal.

This is where the raccoon comes in. One morning I walked into my home office -- a converted bedroom whose window you see in the picture -- and came face to face with a raccoon. It was heading down the tower and its head was level with mine. Both of us were caught by surprise. After staring at each other for a moment it reversed direction and hopped back onto the roof and sped away.

That's one picture I most regret missing and I never again caught a raccoon in the act of climbing. The only trouble it appeared to have with the tower was its size as it squirmed between and around the tower legs and braces.

The only other animal of note, other than birds, was a lone groundhog that stood up with its front paws on the lowest brace of the DMX tower to have a look around. Like many rodents groundhogs can climb, though not very well and may resort to it only when they have no other means of escaping a predator.

Not here

At my current QTH none of my towers is useful to animals and I have not seen any attempt climbing. This is not unexpected. The bracketed tower only gives access to the roof, which is steel and unfriendly to claws. There are no trees to jump to. The Trylon likewise has little utility since the adjacent trees are short and isolated from other trees. The big tower is in the middle of the hay field is even less useful to animals.

Though unlikely perhaps one day I'll catch a squirrel climbing a tower if only for play. But with so many trees compared to suburban lots I doubt that towers hold the slightest attraction for them.

Monday, June 11, 2018

Tuning Up Tower Guys

Adjusting tower guys is a methodical process. You start at the bottom and work your way to top, guy set by guy set, making the tower vertical and setting the tension. This is done during construction and again once or twice in the following days or weeks after the guys, grips (or clips) and other linkages deform under tension until they reach their final shape.

When done properly there is really nothing more to do except for regular maintenance. Once or twice a year guy tension should be measured and all parts of the guys should be inspected, remotely by binoculars if necessary. Trouble signs include tension differences, fraying, rust, fretting, deformation, and stress fractures.

In this article I'll talk about some of these in the context of maintenance I did this spring. It isn't a lot of work but it must be done to ensure a safe installation. Maintenance is certainly easier than constructing the steel guys and attaching them to the tower! What is needed now is finesse rather than brute strength.

Measuring tension

The tension in each set of (3) guys will be equal unless something is amiss. Problems are typically one of asymmetry of anchor placement, gauge error or tower misalignment.

The first of those should be addressed when the tower is sited, before construction begins. The levelness of the site is easy to overlook but it can result in anchors at different heights and therefore unequal angles between the guys and tower at every guy station.


Measurement error is common with the gauges many hams use. For example, the Loos PT-3 gauge I use (as do many hams) is calibrated for 1 x 19 stainless steel marine cable. For 1 x 7 EHS guy cable the measurement is low by perhaps 10% due to the greater stiffness of EHS. This is easy to deal with by applying a correction factor. What is more difficult is that the larger strands of EHS affect the lay of cable in the gauge guides so that the measurement varies with where the gauge is placed. In my experience with the 5/16" EHS the variation can be 100 lb.

For best accuracy with this gauge I take multiple measurements and shift the position of the gauge a small amount for each measurement. Then I record either the average or the majority measurement.


I strongly recommend recording the measurements. Not only will you instantly spot problems that you might miss if you solely rely on your memory you will easily notice changes over time. I put the measurements in a spreadsheet. I do not replace the old data when new measurements are made. Looking at the trends over time can be valuable to keeping your tower in good condition.

Notice that I record the raw figures from the gauge, not the conversion to real units. This keeps the data evergreen should you discover at some point that the gauge is off by, say, 15% rather than 10%. This way you never have to guess which correction value you used in the past, and measurements are more easily compared.

Weather impacts measurements. In extreme climates tension can increase 10% or more in January from July due to temperature induced contraction. Record the date or temperature to avoid surprises. Although light wind is no impediment to tension measurement you should not do so in high winds. The wind load of the tower and antennas will raise the tension in the windward guy(s) and lower it in the others. The tension will also change second by second. Out of interest I tried this in a wind storm (80 to 90 kph plus gusts) and found the tension rose 100 to 200 lb in the windward guys and dropped up to 300 lb in the two leeward guys.

Add notes for anomalous observations you can refer back to later. Examples include suspected distortions from perfect vertical alignment by height and tower face and rust spots that need attention.

Rust

Turnbuckles, thimbles, EHS guy cable and other hardware rusts. Galvanizing can delay rust for many years but will not do so forever. Surplus parts will rust sooner due to their previous exposure to the elements. Rust on the surface of large diameter steel is not immediately urgent since it is so thick and, if specified for this application, often has more strength than needed. No matter the degree of urgency it is strongly advised that rust be repaired so that a negligible problem does not grow into a serious one.

If you're going to paint over the rust it is necessary to first remove the loose material. Some coatings are designed for rusty steel while others are not. In the latter case all the rust must be removed. A steel brush or sandpaper may suffice while in difficult cases a rotary steel brush mounted on a drill speeds the work. With power equipment be sure not to be so enthusiastic that you weaken the base metal or remove more galvanizing than absolutely necessary.

Galvanized steel often requires a special primer before the finish coats. That is how I refinished the LR20 tower sections before raising the tower.

For the turnbuckles and attached hardware I followed the advice of a tower pro to thoroughly clean them once they're installed and adjusted and liberally spray them with cold galvanizing paint. Two coats recommended, then again in future should any rust appear. All parts are hot dip galvanized but the turnbuckles and some of the other hardware are used and needed some refinishing to protect against rust.

In Canada as in many countries the quality of consumer grade oil based (alkyd) paints is often not what it once was due to environmental regulations that severely limit VOC (volatile organic compound) content. Better quality high VOC coating are still available here but are only sold to professionals with safety certifications. When you hire professionals to do your tower work there is a good chance they'll use the better products.

Deformation and stress

Guys and the towers they support are under tremendous and continuous stress.  Each guy on my big tower has a pre-load of at least 1,000 lb (450 kg). That not only stresses the guy cable and every insulator, grip, thimble, shackle and turnbuckle the tower and anchors experience the stress due to the sum total of the attached guys. Then there's the live load due to wind and ice. Deformation (metal yield) and stress risers are risks to tower safety.

At each guy station on the tower there are three guys attached. The tension is trying to pull apart the tower while also putting a vertical force on the tower and the base. I have seen tower guy stations deformed by excessive force, whether due to wind, poor design, poor maintenance or fatigue. This is subject all its own which I won't cover here. Suffice to say that regular inspection is mandatory, never optional.

As an example of what can be done with problem areas I inserted thick, wide washers under the nuts holding the guy yokes to the tower girt. The purpose is to distribute the load over a greater area of the girt which avoids stress risers due to the nuts alone since the design is such that the nuts are not flush to the girt for low and high guy angles. I omit the details since this problem is unique to the (now obsolete) LR20 tower. The point is that there may be potential problem areas in your choice of tower that should be dealt with before it goes up, especially if the tower has previously been in service.

When a suspected problem is noticed deal with it immediately. If you're not sure of what you've found a useful technique is to take pictures of the area and email them to an expert. Cracks, fractures, metal bowing, fraying and similarly highly visible flaws are evidence of serious problems. Other flaws may be less visible. For example, some hams expose the top couple of feet of anchor rods every year or two to check for rust and other below ground damage.

Turnbuckle safety and redundancy

For an installation as major as a guyed tower it is good engineering practice to reduce or eliminate single points of failure (SPOF). That complete redundancy is impractical is no excuse to not do all we can to protect our towers from component failures. Guys are also popular targets for vandalism which, unfortunately, does happen to some hams as it does commercial towers.


The simplest and most effective protection for guys is to install safety loops at the turnbuckles. A typical method is show in the diagram produced by Rohn. The loop has two functions:
  • Prevent unscrewing of the turnbuckle. Despite the high tension constant vibration and cycling of wind and temperature can and does loosen turnbuckles.
  • Turnbuckles can be weakened when they are adjusted under tension due to thread wear, torque on the body and infiltration of moisture and rust. The EHS loop mechanically couples the guy and anchor should a turnbuckle fail. It can keep a tower standing when disaster strikes.
There is more than one way to do this, depending on the anchor design. Many hams use back-to-back L-angle or U-channel steel (¼" thick or more) rather than rounds for the anchor rods since they can be built in a home shop without welding. However round rod is more robust when the anchor is not perfectly aligned, horizontally and vertically, with the tower, as often occurs.

The safety loop is run through the gap between the steel members to additionally protect against equalizer plate failures which could develop stress fractures at the upper sides of the turnbuckle attachment holes. With round rods this may not be possible so the loop is run through the lower attachments, as shown.


On my anchors the equalizer plates are welded to the rods. This leaves the lower hole in the equalizer plate unused. (Welding the plates is not uncommon for large commercial towers, which requires careful engineering and construction to correctly set the rod angle.) I therefore used this hole to provide protection for the equalizer plate.

It only takes an hour to install the safeties on all 3 anchors. Only a few things are needed: ¼" EHS cable, bolt cutters and a wrench to tighten the clips.

Notice the uniform gray colour due to the liberal coating with cold galvanizing paint, discussed earlier. The unequal threading of the four turnbuckles wouldn't happen in a commercial installation because the tower alignment and guy tension are set before the bottom grips are attached to the guys. This is not so easy for a ham to accomplish with simple and limited tools.

The safeties must be removed to adjust the guys. To avoid the extra work I delayed installing them until I was satisfied that the tower was about as perfect as I could make it. The 10M rebar on the right was used as temporary though imperfect protection while the tower was aligned and guys adjusted.

Sunday, June 3, 2018

Going Underground: Burying Wire and Cable

There is rarely any reason to bother with burial of coax and other cable in most ham stations. Towers (if any) and other supports are of modest size and close enough to the dwelling to allow direct entry to the building wall. The one or two antennas that may be further away can usually be services with overhead runs from the support to the building.

When the towers and antennas get big they are typically further distant and burial is often needed to avoid eyesores and to reduce interactions between antennas and the the long horizontal runs of cable. Ground mounted verticals benefit from burial of radials and coax to eliminate hazards to people and lawn mowers, and to help prevent the feed line from becoming part of the radial system.

Until now I have kept cables overhead or on ground in my present station. Some was intended to be permanent while others were temporary solutions when weather prevented burial in the frozen ground. The time has come to deal with the problem.

For the present I have buried the control and transmission lines from the big tower to the rock wall surrounding the house area of my property, and the feed line, control cables and radials for the 80 meter vertical yagi array currently under construction. Once the coax and control lines are out of the hay fields they run overhead to the switching system at the base of the Trylon tower located near the house. This was done to ease maintenance and avoid dealing with tree roots and other obstacles incompatible with going underground.

Other than the radial wire all the buried cable is rated for direct burial. No conduits are used. Trenches are dug, the cable laid down and the soil replaced. Many hams swear by conduits while others swear at them. Water, moisture and condensation are always risks with conduits other than in arid climates.

Perhaps the only good reason for conduits is to avoid digging when cables must be added or removed. This can be troublesome in many cases. I have always found it best and easiest to go with direct burial. Should I ever need to add cable in future I can easily dig another trench. In this article I'll show how I've gone about it.

Radials

Radials are the simplest to put down out of the way, except that there's so much of it! My 80 meter array will have up to 2,000 meters of radial wire when complete. Since the radial field must be mowed -- haying is banned in the area since the machinery will disturb on-turf or wires pushed up by frost heaving -- burial was chosen rather than turf staples. With that much wire and uneven ground there is a near certainty of radials finding their way into mower blades from time to time.

I did initial testing of the 80 meter antenna with radials on the surface. This is done immediately after mowing to maximize the time to test the antenna and then bury the radials before the next mowing. Then I do it again to add more radials. As I write this I have 12 radials buried and 8 more on the ground for the driven element. My objective is at least 32 for the driven element and 16 for each of the four parasitic elements this year. Even that may be too much to achieve this year with all the other antenna and tower work to be done.

To bury the first 4 radials I built a manual sod cutter. This is supplemented with the sharp end of a pick axe to widen the narrow furrow. The latter is necessary since the gap in the sliced turf is so fine that it can be difficult to find in places to push the 18 AWG wire into it with a light push so as to avoid zigzagging up and down and side to side around hay roots.

The turf slicer is a length of hard wood with a couple of common steel construction straps that are filed to an edge. This is pushed into the sod alongside the radial and pulled backward. It works quite well although tight tangles of vegetation deflect the blade a small amount. Having two blades allows placing the blade on either the right or left side of the wire (used as a guide), whichever works best. There is little risk of the blade slicing the wire.

After cutting the sod the furrow is widen by dragging the pick axe through it. Even with this done it can be frustrating at times to find the furrow and insert the wire. This is so much not enjoyable that it is necessary to constantly remind myself how wonderful an antenna this will be!

Since that wasn't enough to sustain me I built a plow attachment to my lawn tractor. With it I can sit and relax while I plow a furrow. It must still be done slowly but it is much less effort.


As you can see it's very simple, merely a length of ½" threaded rod through a pre-existing hole on the left side of the mower deck. With the tractor in position and the rod alongside the radial wire the mower deck is lowered and the tractor driven forward. The rod digs into the ground after only an inch or two of forward travel. The threads must be cleaned afterwards so the nuts can be unscrewed and the rod removed.

Unfortunately the furrow made this way proved imperfect. Where the ground dips the plow doesn't dig deep or at all. Dragging the pick axe through the furrow is still necessary, after which I went along it on hands and knees to fit the wire into a furrow obscured by infalling dirt and sod that hinged back to where it was before plowing. This is the best I can do for now so I proceed a few radials at a time to avoid being driven crazy with the tediousness of it all. Tick and fly protection is strongly advised.

Coax and control cables

Radials are easy to deal with since they are largely immune to ground conditions and mostly only suffer by injudicious future digging or abuse by burrowing animals. While control cables are nearly as hardy the same cannot be said of coaxial cable. These must be handled with care if they are to survive underground for long, preferably a few decades.

Hazards include but are not limited to:
  • Ground frost bending and deforming coax
  • Water infiltration through cracks or holes in cable jackets
  • Rocks abrading cable due to motion induced by ground frost
  • Burrowing animals gnawing or exposing cable
  • Farm equipment snagging cables too near the surface
  • Tree roots which will move and grow over the years and destroy cables
To dig the long and deep trenches for the coax and control cables I rented a trench digging machine. The small one you see in the picture alongside the driven element of the 80 meter array is positioned to begin the third of four shallow trenches for the control cable to the base of the parasitic elements. These trenches are shallow (4" or 10 cm) to speed digging and ease maintenance. Deeper trenches (12" or 30 cm) are dug for the coaxial cables.


Despite being about the smallest trencher you can find the machine weighs in at 270 lb (120 kg) and must be moved manually. It's hard work for someone like me whose weight is half that of the machine. After starting the engine the cutter is lowered and begins digging. The depth lever is locked when the cutter reached its target depth. You then stand on the foot pedal which uses a cleat to pull the machine backward. A front cleat (mostly) prevents the machine from kicking forward when rocks and roots are struck.

The deeper the trench the longer it takes. One nice feature of this machine is that it will kick out rocks up to ~6" (15 cm) diameter and eat through modest sized roots. It just takes some patience and enough muscle to hold the cutter in position. The carbide bits are incredibly tough.

You'll likely notice in the pictures that the trenches are not perfectly straight. There is a torque on the machine due to the cutter not being centred so it tries to turn left (as seen from the operator position). Once I realized this a few minutes after starting it up I took to manually shoving the machine slightly to the right every few feet. That mostly solved the problem. But it doesn't shove easily.

Partial back fill over control cable & radial
Once the trench is dug prepare to get dirty. It is rarely enough to simply dump the cable in and back fill. Try to have the cables sit flat along the bottom of the trench. There's a reason you dug them to that depth. Hard line should be carefully straightened before lowering into the trench since the weight of the dirt alone won't cure rippling.

Coaxial cable in particular should be carefully inspected for nicks, abrasions and cuts. A breached jacket will result in water infiltration. If you must use a cable with jacket damage use a liberal amount of a professional grade sealing compound and then rubberized sealing tape and an outer abrasion coating of high quality electrical tape. Don't skimp! Even burial grade coax with a cut in the jacket will succumb to water within a year or two. Hard line such as Heliax with a damaged jacket will survive longer but will eventually fail as well as the copper outer conductor corrodes.

When directly buried cable must be replaced or added it is always better to dig a new trench rather than attempt to uncover previously buried cables. Mark the trench if possible so that when you dig a parallel trench years later you do not dig into the older cables.

Back filling

Putting the dirt back into the trench when you're done is mostly straight-forward and quick. For best results there are a few items to keep in mind.

The first is to keep sharp-edged and large stones away from the buried cables. Either dispose of these elsewhere or put them aside until the cables are well covered with granular material. I use a heavy gauge rake to fill the trenches which also serves to filter out stones.

Avoid voids under the cables which will fill with water and reduce the risk of section of cable rising to or above the surface where they are prone to damage from mower blades or deer hooves. Sod staples on radials can help but may not be a forever solution.

Big tower trench: cable first laid (left) then fully buried and trench back filled

Finally, you may discover that you don't have enough dirt to back fill the trenches. Usually it's the opposite, that you seem to have more dirt than the hole will hold. The reason for the latter is that without compacting the excavated dirt will occupy more volume. This is common in larger excavations such as tower bases. For low volume trenches the machine grinds the soil into smaller grains that tend to be lost in the sod beside the trench. It can be very difficult for the rake to find it all. Find soil from elsewhere to level the surface if you can't otherwise easily level the surface.

Look carefully and you'll see that the back filled dirt over the trench from the big tower is higher than the adjacent ground. It is better for the buried cables to let the rain transport to compact the dirt and transport it into voids than to aggressively compact the dirt mechanically. Soon the field will be safe for haying.

As I write this article I have back filled all but the coax and control line trench to the 80 meter array. I have to do more work before it is ready to be back filled. Once you back fill a trench it is not easy to undo so be sure to do it right!

Going overhead

Trenches are nice but not always possible or desirable. I only use trenches over open ground. When I get near large trees and other obstacles I run the cables overhead. Doing so avoids a lot of work, reduces future risk due to root damage and eases maintenance. When convenient I place connectors on cables at either end of the trench to make it easier to isolate problems and to replace buried cable that has deteriorated.

There are a few places that are currently overhead that I plan to bury in future. One example is the short distance between the Trylon tower and the house entry point. All antenna switching and control cable terminations are at the base of the Trylon. Burial must wait until I have a permanent switching system design in place.

The coax from the Beverage antenna remains on the ground along the tree line from the feed point to a point near the yard where it proceeds overhead to the tower. Eventually I will raise it off the ground where it is easier to maintain and to reduce the risk of animal damage.

Wednesday, May 23, 2018

NIL, Again: Contests and DXing

Getting a NIL (not in log) penalty in a contest can be exasperating. It's one of those things that cannot be entirely eliminated since it is mostly dependent on the other end of the QSO. As I perused the final LCR (log check report) from the CQ WW CW contest last fall I felt some frustration since I thought that I'd been making progress reducing these errors.

Consider the ways in which a NIL can occur and you'll understand the difficulty avoiding them:
  • The QSO was logged with your call incorrect and the log checker software failed to match the erroneous record with that in your log. Software isn't perfect so this will happen. There is little you can do about it other than to be certain the other station has your call correct.
  • You are running on the same frequency as someone else who you cannot hear and you think you have worked someone who instead worked the other station. Yes, this really happens and you may not notice what's going on for several minutes. All you can do is QSY and hope for the best.
  • User error results in your QSO not being entered into the other station's log. Every contester makes mistakes so this will happen occasionally. I know I've done it myself and unless caught instantly there is no recovery possible, and indeed you may be unaware of the mistake.
  • The other station gives up on you because you're too difficult to copy -- happens a lot when you run QRP -- but instead of telling you sends "TU XX9YYY" and continues onward. You think the QSO is good and log it. In my opinion this is unsportsmanlike behaviour.
When you make thousands of QSOs in a contest you should expect a number of NIL penalties. While it is possible to reduce their number with care if you want to get to zero you will also need very good luck! As one contest director once told me: don't worry about it too much, it happens to everyone. Yet it still bothers me.

I was surprised to find that I could remember a few of those NILs in this most recent LCR. A couple of them I was sure were good. But as noted above the log checker may have gotten it wrong. Although I didn't bother this time a couple of years ago the CQ WW contest director at the time suggested looking in the public logs for these NILs. It was both enlightening and perplexing. By comparing logs you can sometimes see where the software may have mismatched records but you can not see into the other operator's mind if your QSO is absent.

Learn what you can, do your best to ensure your future logs are accurate and hope for the best. Since many of your competitors are seeing similar penalties the score reduction is only a problem if you are especially negligent, in which case their lower error rate will hurt you. Perfection may be impossible but you will surely not attain it if you don't try. Accurate logging is a valuable skill for contesters to practice. I can do better.

But what if you're not a contester? Are you a DXer? The possibility of NIL still applies to you. Let's examine this with a real situation I encountered, but without revealing call signs.

A few weeks ago there was a DXpedition from a moderately rare country, one I've worked many times before. When they showed up on 40 meter CW I jumped in if only to practice my pile up skills.

After just one minute I got through -- having a yagi up high helps! The band was noisy here and presumably there as well (warm weather in both places) with the usual QRM from poor operators who keep calling regardless of the station being answered. As a result he took a few tries to correctly copy my call. Then without having ever sent my correct call (one letter was wrong) he sent "TU UP" and moved on to the next QSO.

I may have been in their log with my call correct, my call incorrect or perhaps he gave up and erased the QSO. There was no way for me to be sure. What would you do in this case? In a contest I would most likely have logged the QSO, risking a NIL, and perhaps duped him later if it was a needed multiplier.

However this was not a contest. If you are a DXer you'll have been in this situation many times and faced the question of whether to log the QSO. From my experience I know that many would log the QSO and either hope for the best or check the DXpedition's online log and try again if the QSO doesn't appear.

What would you do? Be honest. Think about it for a moment before you continue reading to discover what I did.

I erased the QSO from my log. To me that was the ethical choice since I did not hear him send my call correctly. In effect I assumed NIL or copying error, making the QSO invalid. Had this been a new country or band-country I admit I would have been tempted to log it and hope. When I hit "delete" I was motivated by the disgust I felt at the poor operating practice that left me in doubt.

A day or two later I was talking to a friend who congratulated me on working this station on 40 meters -- we tend to check up on each other in DXpedition online logs so that we know when to call each other when we hear them on. I had to tell him that, no, I didn't log the QSO and proceeded to explain why. He had a good chuckle over that one.

All of this leaves us with an ethical viewpoint on the NIL problem. During contests we expect to hear our call correctly before logging the QSO, although some don't care because it's the other guy's score that will suffer, not theirs. Indeed when you're running it is common for callers to never send your call so you can never know if you're in their log or logged incorrectly. Some always send the running station's call to remove doubt, which annoys some operators due to the two seconds it consumes.

For DXing both stations do try to ensure correct copying of our call since the penalty for a NIL is arguably greater for the rare ones. We all notice the sloppy DXpedition operators who do not strive for accuracy, leaving us in doubt and annoyed. We also notice the sloppy callers who pay little attention to whether their call is being correctly sent in their enthusiasm to work the DX.

In DXing as in contesting it pays to be accurate and to confirm or correct what has been copied.

Friday, May 11, 2018

Radials: Resonant to Non-resonant

We all know -- or should know by now -- that for ground-mounted vertical antennas the more radials the better. Specifically, more and longer radials reduce the near field ground losses by confining antenna return currents to the highly-conductive radials rather than the lossy ground below. That is, a good radial system forms a low loss ground plane.

This is highly desirable since ground loss can be substantial. This is a shame since vertical antennas can be excellent radiators at the low elevation angles needed for effective DXing on the lower HF bands which is difficult to achieve with horizontally polarized antennas. A lot of wire and ground area is required to construct a good radial system which is impractical for most hams, and so they must compromise. That compromise may be short radials, few radials or avoid vertical antennas entirely.

But for this exercise let's assume you are building a ground-mounted vertical and radial system. I'll do this for 80 meters since that's the antenna currently of interest to me. The data can be scaled to other bands if that's your interest. I will further assume that you are comfortable with the data and theory regarding near field and far field ground loss associated with verticals and vertically polarized antennas. If not there are ample and excellent resources available to you. Perhaps some of the best can be found on N6LF's web site and in ON4UN's book Low-Band Dxing. I addressed a few of these elementary items in my own small way, such as here and here.

In this article I want to focus on the effect of radials on the resonance of a ground-mounted vertical. The reason is that I am currently dealing with this issue and I have not found any easily digestible material out there that describes just what happens. In particular what it means when we say that radials tend to "resonant" when there are few and "non-resonant" when there are many.

Developing a model

Modelling a ground-mounted vertical with the NEC2 engine has drawbacks. In case this is unfamiliar to you here are some of the issues to be aware of:
  • Even with the real ground models used in EZNEC there are ground loss and velocity factor inaccuracies with on-ground radials. As the radial count increases the effects will diminish but are still difficult to quantify.
  • Ground is not homogeneous yet the model must assume that it is. At low frequencies the antennas fields can penetrate many meters into the ground, so what you can't see can hurt you.
  • Radials cannot touch the ground or be placed below the surface. They must be placed a small distance above ground for the model to work, which contribute to inaccurate calculation of ground loss and radial velocity factor.
  • Monopoles constructed with an open lattice tower cannot be directly modelled and must rely on a substitute "effective diameter". Determining the effective diameter is difficult and is more difficult yet for tapered towers, such as the one I am using in my 80 meter array, where a stepped diameter correction is impractical. It almost inevitably requires post-construction measurements and adjustments to the height to achieve the desired resonance.
  • The feed point of a real tower vertical is located within the tower base. Since the model can't deal with that there will a difference in effective lengths of the radials and monopole.
Despite these challenges a NEC2 model will still deliver excellent insights into vertical antenna design when developed with care. Although there will certainly be inaccuracies in the results the general trends and behaviours can be correct and useful.

For my model I am using the following parameters. You can adjust these as necessary to suit your own requirements for design and construction. Better yet, if you can afford it, use NEC4.
  • Monopole height of 19.9 meters and effective monopole diameter of 50 cm (20").
  • AWG 18 insulated wire for radials.
  • Radials and monopole raised 10 cm (0.0012λ) above EZNEC medium ground.
  • Segment length of ~1.0 meters. It is desirable to equalize the segment length of radials and monopole for model reliability.

Running the model

The model was run for a range of lengths and numbers of radials. The data collected is resonant frequency (X = 0) and feed point resistance at the resonant frequency. Radial length is varied from 10 through 25 meters, which covers lengths that are both above and below the resonant frequency. Radial counts are: 2, 4, 8, 16, 32 and 64. Doubling radials at each step is most illustrative since the effects are not proportional to the number of radials.

The only quirk I encountered was with 64 × 25 meter long radials which exceeded the1,500 segment limit in my version of EZNEC. For that one case I was compelled to use just 58 radials.


In the left chart the transition from resonance to non-resonance is plainly obvious for all radial lengths as the radial count increases. Notice how in all cases the resonant frequency regardless of whether the radials are shorter or longer than resonance. However the greater the radial length departs from resonance the more radials it takes to converge to the ultimate resonance that is approximately 3.680 MHz.

I added the 18 meter length radial data since that is the closest integral value that keeps the antenna resonance static with respect to radial count. The true value is closer to 17.5 meters, which would have required violating my rule of keeping segment length constant at 1 meter.

The implied velocity factor for the radials due to ground proximity is ~0.89 plus a further 0.02 reduction due to wire insulation. The true velocity factor is almost certainly lower when radials rest on or slightly below ground. As discussed above this cannot be fully modelled with NEC2. Expect the measured velocity factor be no higher than 0.75: radials resonant at 15 meters length or less.


The story for feed point impedance is more complicated. N6LF addresses this matter in detail so I will not delve into the topic too deeply. High feed point resistance is a indicator of excessive ground loss, which is not surprising to see for short radials even when there are many of them. Many radials can only partially compensate for short length.

For long radials the lower feed point resistance is not a reliable indication of lower radiation resistance or ground loss. As N6LF demonstrates the current peak moves outward from the feed point when the electrical length of the radial is greater than ¼λ which changes the character of the entire antenna.

By expecting a final feed point impedance for your vertical antenna or array you will be better equipped to plan ahead for a matching network, rather than merely hoping for a perfect match or stopping when one is reached despite it being a symptom of high ground loss or less than optimal radial currents. Requiring an L-network for a vertical network should be seen as a nice problem to have.

What does it all mean?

When your chosen radial length is substantially unequal to a ¼λ you should expect unusual resonant frequencies when you first attach a few radials and then large changes as you add more. Forearmed is forewarned so the charts above can help you to anticipate and to avoid surprises. Certainly this happened when I first lit up my 80 meter vertical a few days ago!

Had I chose shorter radials the effect could have been the opposite of what I measured, with resonance occurring above my design frequency and then falling lower as radials are added. To give a more concrete example, when I attached a long on-the-ground length of RG213 back to the antenna switch the resonance shifted upward to 3.5 MHz from 3.4 MHz. With only 4 radials the outer surface of the coax acts as a unreasonably long fifth radial and that disturbs the symmetry of the other 4. This resonance effect would largely disappear with a radial count of 16 or higher. However this is distinct from common mode current on the coax surface, a separate though related problem.

It was these experiences that motivated me to run the models and write this article. Nowhere that I could find was there a quantitative or visual presentation of the precise migration of vertical resonance with radial length and count. My thought is that if these models are helpful to me it may be helpful to you for the design of vertical antennas and the gradual deployment of radials. I certainly won't wait until there are 64 radials before I try an antenna. I doubt that any ham would!

Rely on those referenced resources and others to plan your vertical antennas to achieve the optimum number and length of radials for your individual circumstances and performance objectives. Models will help as well, provided that you take account of modelling software constraints and limitations. It is my hope with this article that I've provided one point of insight into the process.

Wednesday, May 9, 2018

80 Meter Array: Driven Element Construction

I am building the 3-element 80 meter vertical yagi in stages. The first stage is the driven element, the greatest part of which is a ground isolated tower. This is the very same DMX-52 tower and floating base that I used at my previous QTH to support a tri-band yagi, wires and was fed as an 80 meter top loaded vertical (yagi as top hat capacitor).

Since the tower is ~14 meters a stinger is needed to take the antenna to a full λ/4 on 80 meters (~19.7 meters in my case). The stinger is made of aluminum pipe and tubing with the structural strength to support the wire parasitic elements. To maximize the vertical height of the wire parasites (for best performance) I added one meter of PVC pipe on top. Anything longer would become unwieldy and less robust. I want this antenna to last.

Construction, tuning and testing of the array is a large enough project that one article would be impractical so it will spread over several. Even if this array is of no interest there should be aspects of interest to any ham with an interest in building antennas and towers. If nothing else this first article may be of interest to those putting up small towers and low band ground-mounted verticals.

Tower base

My first task was to choose a site. After various considerations it ended up very close to where it was in my original site plan. The location has these attributes:
  • Well spaced from power lines (50 m), Beverage antenna field (30 m) and existing towers (60m and 70 m), while not being too far from the shack (60 m). My major concern is interactions in a couple of directions. From what I have read and from other hams with similar issues I expect my choice to work pretty well, with no enhanced minor lobes (F/B, F/R) and gain to the southeast reduced well below 1 db.
  • Minimized impact on haying. Radials and support ropes preclude farm equipment and could take ~1 acres out of production. By moving closer to the tree line the radial system overlaps the perimeter bush, thus reducing tillable land impact by ~15%.
  • Ease of access for mowing and other regular maintenance.
I staked the site to place the base, parasites, anchors and radial system perimeter, then got my shovel to plant and level the floating tower base. This was the easy part. When the guy anchors went in a problem appeared (see next section). That's why I didn't proceed with the project over the winter. I did stand the first two sections (16') and tie them down so they wouldn't be buried under the snow and ice.


When the snow melted I resumed work on the base. I used a similar method as before for sitting the tower legs on the wood base but took additional step to ensure good RF isolation from ground. A thick plastic block is placed under each leg and bolted to the base. This first requires accurate siting to the guy anchors. Not visible is a ½" length of rubber tube that pierces the plastic block and L-bracket. A rubber grommet sits atop that and a screw lightly holds it all down.

The base does not prevent the tower from overturning; that's the job of the guys. The rubber allows a small amount of rocking in high winds, prevents lateral motion and electrically isolates the tower (driven element) from ground. The driven element will be directly fed between radials and tower.

Raising and guying the tower

As I've mentioned a couple of times I ran into an apparent problem with the ground anchors late last fall and decided to be prudent and stop construction until I could address the problem in the spring. That time has come, adjustments were made and construction resumed. I'll review the problem and how I decided to proceed.

Since the load on the tower and antenna array is modest I decided to use ordinary augur-style anchors. These have a bevelled blade at the bottom that acts as both a bit and as a load bearing surface. It is best to screw them in with a augur attachment on a tractor but it is possible to do it by hand with some effort. I don't have a tractor and it seemed excessive to rent one or cajole a neighbour to help so I did it by hand.

I don't include a picture of the anchors since I neglected to take one before burying them. For a ham relevant discussion of screw anchors, and pictures, I'll refer you to W8JI. The only difference is that mine are much shorter at 3' (~90 cm) long, common in farm country to anchor fence lines. That page has related information I'll come to shortly.

After carefully siting the anchors so that they are precisely 120° apart and 12 meters from the base of the 14 meter tower I broke the surface sod with a shovel. Other than hitting rock the surface is the most difficult to penetrate since vegetation roots in soil form a surprisingly solid mass. If done carefully the sod can be put back once the anchor is in place.

The tools required are quite simple: shovel, steel bar and a sledgehammer. The steel bar should be long enough for turning torque and to push down against but not so long that it hits the ground every half turn. I used my old trusty 1" cold chisel.

Quite a lot of force may be required depending on the soil type. Even if the soil is not hard you must still press down hard as the screw is turned or the soil will be ground up and weakened until time eventually heals the wound. Minimizing soil disturbance is perhaps the most important reason to use a power augur to drive in screw anchors. When a stone interfered with progress a judicious tap of the sledgehammer on the anchor pushed it aside just enough to screw past it.

Overly disturbed soil is what stopped me in the fall. Two of the anchors had 1" to 2" freedom of axial movement in the waterlogged soil after being screwed in. Since I couldn't tell whether this was temporary or my 3' anchors aren't long enough for the soil type I elected to wait until spring to decide whether to fit the anchors in concrete to form a larger soil bearing surface.

Once the ground frost was sufficiently thawed (tested with a soil probe) I tested the anchors and none moved under load. However I partially unscrewed and redid one that I had put in at too shallow an angle. I was aiming for ~45° since the guy station is up the same distance the anchor is from the base: ~12 meters.

Newly confident that the anchors would hold I manually stood the two pre-assembled bottom sections, completed the base (see above) and temporarily guyed the tower with ropes and turnbuckles. When I reached 4 sections (~31') I attached temporary steel guys and one-by-one shifted the load from the ropes to the steel guys. I did this by loosening the turnbuckle, slipping on the steel guy over the open hook termination of the turnbuckle screw, tightened the turnbuckle and finally removed the rope.

Do this methodically or you risk the tower toppling. It only takes a few minutes so don't become careless from impatience. The picture shows the final rope guy about to be replaced. For additional safety I placed a ~100 lb stone on a lumber cradle sitting over the bottom X-braces of the tower.

Sections went up very quickly using the same gin pole used before for this tower. Since the original aluminum angle was claimed by another project I replaced it with steel angle stock from my junk pile. The gin pole worked well despite its limitations.

There was a two week delay topping the tower due to a series of late spring snow and ice storms, the need to keep the top section at hand for constructing the stinger, and to recover from a wisdom tooth extraction. It was very frustrating. When work could resume I raised the top section with stinger attached, retracted into the section so that it was not too top heavy for lifting and splicing. Lifting and inserting the stringer separately would have been awkward and potentially dangerous due to it length.


Topped; still nested & temp guys
The stinger is made of a 7' length of schedule 40 1-½" aluminum pipe (1.9" OD, 1.61" ID) and two 7' lengths of 1.5" OD tube. The pipe and bottom tube were made snug with a wrap of aluminum flashing and secured with stainless steel bolts. A short length of PVC pipe wrapped in flashing made up a butt joint which was secured with bolts. Electrical continuity is protected by coating aluminum surfaces with a thin layer of aluminum grease (Noalox brand, but there are many others on the market).

About 1 meter of PVC pipe at the top supports a guy ring and rope catenaries for the wire parasitic elements. The ropes must be attached at this time since the top of the stinger is out of reach once it and the top tower section are raised. The ropes are lightly tied to the top section until the wire elements are installed later.

Raising the top section complete with nested stinger was more of a problem than expected. It's slightly top heavy and the improvised gin pole couldn't grab it any higher. Tag lines were used to direct it around the temporary guys and then to pull it roughly vertical so that it could be spliced. Despite all the problems the entire operation took only 2 hours.

With everything up the permanent steel guys are attached and the temporary guys removed. The guys are a combination of ⅛" and 3/16" aircraft cable salvaged from their first use on this tower. The top segment is kept very short to minimize capacitive loading. The other segments are non-resonant on 80 meters and have negligible loaded per my EZNEC model.

I originally intended to guy with the black dacron rope I bought for this purpose. Instead I went with steel to reduce deflection of the structure in high winds which could stress the base and parasitic element wires. The rope will go to one of a couple of projects tentatively planned for the future.

The tower feels very solid and survived 90 kph wind when held with the second set of temporary guys at 40'. Even the unrestrained stinger did fine. I don't anticipate a problem when complete. The anchors and guys will be regularly checked for the next few months to ensure that the anchors are not shifting, especially after heavy rainfalls which can partially liquefy the topsoil.

Radials

The radials are attached using a similar arrangement to the one I improvised for the 160 meter t-top vertical. It worked so well and is inexpensive and easy to use I couldn't resist. We'll have to see how it survives in practice.

The attachment pillar is a 3-½" plastic coupler friction fit over several screws driven into the floating base. An all stainless steel (the band and the screw) hose clamp secures the radial wires and the wire to the feed point. Gripping the copper conductors between an insulator and stainless steel greatly reduces the risk of galvanic corrosion. The large diameter pillar is helpful when the radial count is high and it minimizes the deflection when a radial has to be routed around a tower leg.

To attach a radial you simply strip 1" of wire, slightly loosen the hose clamp, slip in the wire and fold it over the band. Tighten the hose clamp and it's done! For the initial test (first light) there are 4 x 20 meter long radials. All radials are AWG 18 solid insulated wire. The price is reasonable and is more than adequate for QRO when many radials split the antenna current.

First light

As first tested with my analyzer the resonance was not as expected. Resonance is almost exactly 3.4 MHz with an impedance of 50 + j0 Ω, well below the expected resonant frequency of 3.9 to 4.0 MHz with the stinger partly nested inside the top section. (If you expand the photo above you should be able to see the SWR curve on the analyzer screen, which is centred at 3.4 MHz.)

This appears to be due to the small number of long radials currently installed and perhaps I did not properly account for the tower diameter in the model. Once the situation has been fully investigated remedial measures will be taken. The impact of the former item per EZNEC is to lower the resonant frequency by 100 to 125 kHz since the on-ground radials are longer than an electrical ¼λ and, due to the low count, greatly affect resonance

Although the SWR of 1.0 looks very nice it is not. Recall that the radiation resistance of a ground mounted ¼λ vertical is typically 35 to 37 Ω, and can be lower for a "fat" monopole such as mine. The ground loss, which is in series with the radiation resistance, is therefore approximately 15 Ω. That's quite high although entirely typical for the small number of radials currently installed. As radials are added the feed point resistance will fall.

My objective is no more than 5 Ω so that ground loss is a minor factor when the array is in full operation as a 3-element yagi, whose radiation resistance is much lower than a vertical alone. This is modelled and explained in more detail in the antenna design article.

About that stinger

The final stinger height must be firmly determined before the parasitic wire elements are designed and installed since the resulting geometry determines the structure of the t-top parasitic wire elements: lengths of the vertical leg and t-top. There are also mechanical considerations I must deal with.

The driven element does not absolutely need to be resonant. The feed point resistance will be low enough when all the radials are in place that an L-network may be desirable to lower the SWR when used in the array's omni-directional mode. Provided that the resonant frequency is roughly in band that will ensure sufficient mutual coupling with the parasitic elements for the array to perform as intended.

The final call on stinger height will come after initial testing and a little bit of modelling to verify adjustments to the design. 

Getting from here to there

With the basics done I have run coax to the the antenna so to compare the vertical to the temporary inverted vee up at 32 meters. I will write up the comparison for the blog. The comparison will help to establish baseline performance to a known antenna. Once that's done the inverted vee comes down to get it out of the field for haying season. I will almost certainly put it up again to work nearby US stations in contests, with height and location to be determined.

The permanent feed point will be constructed, the stinger redone and L-network designed. Tuning requires completion of the feed point since the temporary setup will certainly have different wire lengths from the coax termination to the radial hub and to the tower (monopole). At least 16 radials will be required to erase most of the resonance-influencing effects of the radials. Again, I'll delve into this in a coming article.

With all that out of the way the parasitic elements will be hung off the driven element stinger, tuned and radials laid. As you can see there is a logical sequence of steps to go through when building an array of this nature.

Before the switching system is fully deployed I may temporarily wire it as a fixed yagi to assess performance. I will then need to complete and deploy the direction switching system, switchable L-network and switching units for the parasitic elements. All of this is straightforward but time consuming.

Unless other projects deflect my attention over the next few months the array could be substantially complete this spring. The final objective is that it be complete in time for the fall contest and DX season. That's when I find out for sure how well it performs. Either way it is going to be interesting!

Friday, May 4, 2018

Rolling Up the Radials -- My 160 Meter Season

My 160 meter season is now at an end. The radials and coax have been rolled up and put away for at least the summer. The t-top vertical antenna itself will remain in the air for a few days until I have an opportunity to climb the tower. That'll be a multi-purpose trip since I do not like to climb 150' merely to untie a rope!

As you can see in the picture there's a lot of wire involved. That's 240 meters (8 x 30 meters) of AWG 18 insulated wire. If that seems like a large amount consider that I just picked up my order of another 1,000 meters of wire to make the radials for the 80 meter array I'm currently building. With the strength of the US dollar and the overall rise in metals prices I paid 10% more than I did 6 months ago.


When I opened the box housing the L-network all was perfectly clean and dry inside. The disk ceramic capacitor in the L-network looked good despite putting up with several months of 200 watts. I was also pleased to find that the galvanized framing nails I used to pin the far end of the radials did not rust through from spending a wet winter and spring buried in the soil.

In short, nothing went wrong. That kind of luck doesn't happen often enough. That's pretty good for a temporary antenna.

Why now?

With the hay beginning to grow and the rapidly increasing risk of ticks this is a good time to remove the antenna. Warm weather QRN is making DXing quite difficult and in any case there has been a sharp reduction in activity on top band over the past several weeks. I know that this tends to annoy our neighbours in the southern hemisphere since there is less DX for them to chase. You can't please everyone.

Unfortunately I will not have a 160 meter antenna for the CQ WPX CW contest coming up in a few weeks. I can live with that since CQ WPX is not my favourite contest and I have other priorities now that mild spring weather has arrived.

No DXCC

One of my operating objectives for this season was to achieve DXCC on top band. I didn't make it although I came close. My country count rose from 32 to 96 with 79 confirmed on LoTW. That's not too bad for a one season effort with a maximum of 200 watts (100 or 150 watts in most contests). I worked a surprising amount of DX using QRP, especially in the Stew Perry Top Band Challenge. The antenna obviously works.

I would have easily exceeded 100 countries had I been running a kilowatt. Many countries were nearly worked when the DX operator could not pull through my complete call, or I could not compete in the bigger pile ups. I'm okay with that. I enjoy the challenge of chasing DX on 160 meters with less than the legal limit, so some are destined to get away. If it were easy it would be less interesting and I would have less incentive to design and put up better antennas. For casual DXing the antenna is competitive, perhaps because most hams operate top band with compromise antennas.

I have little doubt I'll reach the DXCC threshold this fall soon after I have an antenna up again. Truth is that even with the power I have I could now be over 100 had I put in more effort. DXCC was a goal not an obsession.

Contests

Apart for general DXing I desperately needed more firepower on top band to add multipliers and contacts to boost my score potential. Having worked several major contests, and a few small ones, I can absolutely declare success. Although I am not in the same league as the big guns I compare very well to others in this part of North America who are in the same power category.

My one Beverage to the northeast did marvelously well towards Europe. This was especially evident after their local sunrise when they could hear my low power signal better (lower atmospheric QRN) and I could hear their attenuated signals just riding above the noise level. Switching to the transmit antenna I could not hear most of them at all. Many multipliers entered the log that way.

The lack of receiving antennas for the other directions is a problem. I failed to make sufficient progress on this item which I'd planned to do over the winter. I have most of the material needed, locations have been surveyed and marked but I ran into delays designing and building a custom remote switching system for a collection of unidirectional and reversible Beverages.

Poor listening ability in most directions hurt a little but not as much as expected. I don't believe I lost out on many QSOs during contests. Most often I was limited by the inability of other stations to hear me, either because of my power level or their lack of good (low noise, directional) reception. When I move to QRO it will be a problem. Beverages are an increasing priority, but it'll have to wait until next winter.

Future plan

Sitting here in early May I predict that I will not have the time or incentive to come up with a superior antenna for the upcoming fall/winter season. There just so much other higher priority tower and antenna work to be done. I expect that this antenna will be put back into service for at least one more winter season. That's not so bad since it does work very well indeed.

Monday, April 30, 2018

Coil Geometry, Inductance and Wire Length

If you play with HF antennas you are certain to be winding coils, perhaps more than you'd like. They are used to shorten antennas, make traps, as components of impedance matching networks, filters, coax common mode chokes and as a helix can be the antenna itself. Although deceptively simple devices they can be the source of much angst.
  • Accuracy: There are a variety of inductance calculators for coils giving different results. I usually ignore these differences since they are typically small and often are minor in comparison to construction variation that in any case requires adjustment in the field. But there are a couple of factors worth considering:
    • Coil diameter: What is the true diameter of a coil?
    • Insulation: Is there an effect?
  • Wire length: How much wire does it take to wind a coil? Of course the trivial answer is that the wire should be long enough to reach from one end to the other! Often you will want a better answer than that when you must cut the wire before winding the coil.
  • Efficiency: Diameter, length, gauge, metal, pitch, form and core all have their effects. Lots of good stuff has been written about this so I will direct you there. Excellent resources are W8JI on coil Q, N6LF on effect of wire insulation and K9YC on ferrite cores
Rather than deal with the more technical aspects of coils -- which as noted are ably dealt with by others -- in this article I'll address a few geometric parameters that while seemingly trivial are important for building coils. Reviewing elementary knowledge can be helpful.

Coil diameter

What is the diameter of a coil? A common answer is that it is the outer diameter of the coil form. This is only approximately true. As the ratio of wire diameter to the form diameter approaches zero -- thin wire, large form -- it is effectively true. However it is not true when the coil's application is high power or high Q since the wire diameter can be a large fraction of the form diameter. The diameter to use in coil inductance equations is wire centre to wire centre.

The diagram at right illustrates the problem. The form is shown as a solid tube and the wire is shown with insulation, although there may be none. I frequently use insulated wire in my antenna projects for its convenience and to remove the risk of shorted turns in my hand wound coils.

Let's assume the coil form is 2" (5 cm) since that is one I use in some of my projects. AWG 12 wire has a diameter of 0.064" (1.63 mm), which gives a wire to form ratio of 0.032, or 3.2%. This can be quite significant. If the wire is insulated the ratio increases to ~5% (depending on the insulation rating) because the insulation separates the form and wire.

For bare copper the coil diameter is 2.13" and for insulated wire the diameter is ~2.2". If this appears surprising notice that we use twice the wire radius, which is its diameter, and twice the insulation thickness, which is one side of the insulation on each wire. An easy way to do this is to measure the full wire width with calipers and add that value to the form diameter.

Consider a coil built in this fashion that has an inductance of 3 μH for a coil diameter of 2". When you account for the wire gauge and insulation (AWG 12) the true diameter is ~2.1" and the inductance grows to 3.6 μH. That's a big difference! A small difference cause a large inductance change because the inductance of a coil increases with the square of its diameter, for a fixed coil length and turns.

By calculating coil inductance with the correct diameter you won't be for an ugly surprise when you install it in a matching network, and there adjustments will be fewer and finer. For an example look at my article on the 160 meter vertical matching network I built which required no adjustment at all. Accurately measuring coil inductance can be difficult so it's nice to know we can get the inductance right by understanding the impact of coil geometry.

Wire length

Often you'll need to cut the wire before winding a coil. That's when you especially want to accurately calculate the length of wire required. Cut it too short and you run into grief, and waste; cut it too long and some wire is wasted. Copper isn't cheap! I just ordered more radial wire and the price has increased 10% over the past 6 months.

I covered coil diameter first since you need to get that right if you're to correctly calculate the amount of wire in a coil. A naive length calculation of the wire length for a single coil term in the previous example (2" coil form) is 2π = 6.28". However since the true diameter is closer to 2.1" a better estimate of the wire length is 6.59", which is 5% higher. The wire length is proportional to the diameter.

This is significant since for a 10 turn coil on a 2" form you would end up 3.1" short using the naive calculation (65.9" vs. 62.8"). Of course you should not forget to add to the total the length of the coil tails at both ends. I tend to underestimate the tails so you may want to be careful with that.

Coil pitch (turns per inch)

A coil turn is a spiral rather than a circle. It should be evident that the length of wire in a spiral is more than in a circle due to the linear displacement of the start and end points. The linear displacement due to the coil's pitch increases the length of wire required for a given coil diameter, pitch and turns count. That is: L > TπD. But how large is the difference?

We can deal with spirals using elementary topology. Notice that a cylinder, like a steel pipe, is a rectangle folded into a circle. Unfolding one turn's worth of the cylinder help to visualize the problem and to accurately determine the length of wire in a one turn spiral.


The spiral turn of wire around the cylinder becomes a diagonal line between opposite corners of a rectangle. The rectangle's height is the the turns pitch; if there are 8 turns per inch the pitch is 0.125". The rectangle's width is the circumference of the coil. Pythagoras comes to the rescue by noting that the diagonal is the hypotenuse of a triangle. The wire length is the square root of the sum of the squares of the pitch and diameter.

Therefore the wire length of for a 10 turn coil is L = T × sqrt(P² + (πD)²). Using a pitch of 0.25" (4 tpi) and a coil diameter of 1.1" (1" form plus wire) the length of wire is 34.7". Even for this rather large pitch the spiral's length is only 0.3% (0.1") more than the 34.6" for a naive calculation assuming the a coil turn is a closed circle.

The naive calculation is perfectly adequate except for coils with an exceptionally large pitch and narrow form. The only time you are likely to encounter this is in a helical antenna. Although not really a coil (inductor) the geometry is the same.

Deformation

When you coil a wire you are often pushing the metal beyond its yield strength to get a non-elastic deformation. That is, the wire doesn't snap back into its pre-coiling shape. Deformation can occur throughout the wire diameter, being stretched into a greater length on the outside and compressed to a shorter length on the inside of the coil. However the former is more likely.

This is not a simple problem to solve, so it is lucky the that the effect is small enough in almost every case that it can be ignored. Since we improved the diameter calculation to use the centre of the conductor and the centre is approximately equidistant from the surfaces where deformation is likely to be greatest we should see little difference in the length requirement. Were the wire centre to stretch we would in fact need a tiny amount less wire to wind the coil.

Insulation adds elasticity to the wire. Bend straight lengths of identical insulated and bare wire and you'll see that the insulated wire rebounds more. The copper is still yielding on the inside but when the force is remove the elasticity of the plastic covering reverses some of that. Since it's the diameter of the conductor that concerns us we can ignore the behaviour of the insulation. It would take an extreme bend radius of a heavy gauge wire for the plastic to ripple on the inside thus increasing its effective thickness.

Toroids

Toroidal and other non-cylindrical forms add another factor for consideration. If the wire is of large enough gauge the coil will tend to follow a circular form rather than seat on the toroid's quasi-square surface. In that case with regard to wire length the diagonal cross-section distance is a good approximation to the coil's diameter, plus of course the wire itself as we saw earlier.

Smaller wire than conforms to the toroid surface can treat the coil form as a square (or rectangle), and therefore those dimension should be used as the basis for determining the length of wire required.

Getting the length right is generally more important for a toroidal coil since in almost every case the wire must be cut beforehand and wound onto a holder that can be threaded through the centre of the toroid. This is where you really don't want to underestimate the length of wire required.

Conclusion

There are several coil and wire geometric parameters than affect inductance and wire length. While some of them are quite interesting there is only one that is significant in nearly every real coil: effective diameter. As we saw, using the coil form diameter for the coil diameter can lead to significant error in the calculated inductance and required wire length.

Well, so much for this little diversion. With less bad luck than I've suffered recently I should soon be back to talking about antennas.

Tuesday, April 24, 2018

Deadwood

The killing field. The large tree on the
ground is the one that did the deed. The
other leaning deadwood is now cleared.
There's been a lack of articles recently for a variety of reasons. We had a string of springtime snow and ice storms accompanied by two days of high winds (up to 90 kph). Once that was out of the way I had to deal with an impacted wisdom tooth. This brought all antenna work to a halt for nearly two weeks.

Once I could get outside and do stuff again in the late-to-arrive mild spring weather there were many non-ham jobs that took priority. One of these tasks was to clear away fallen trees and branches due to those storms. Even so I have been able to do some antenna work, in particular making progress on the 80 meter vertical yagi. I'll have more to say on that in about a week.

What I thought would be one of the more mundane tasks was to inspect the northeast Beverage that goes through some heavy bush along its 175 meter length, with the far end at the edge of the swamp (bog). By mid-May this area will be effectively off limits since the growing vegetation will host some nasty wildlife. By this I mean that the bush and hay fields become tick heaven until at least mid-summer.

I had a suspicion this wouldn't be a normal inspection since the Beverage has not been performing well lately. When I approached the feed point my fears were confirmed. The aluminum wire was slack, evidence of a break somewhere. A month earlier all had been well. I waded through the bush along the antenna line looking for the problem.

Wire hanger bent when the tree fell on the Beverage
Approaching the termination the land slopes gently downward into the swamp. With the frost not out of the ground in sheltered areas run off pools on the surface. The ground is very squishy. The problem was discovered just 15 meters shy of the termination resistor.

Presumably during the storms a lot of the dead and dying trees met their fate. Trees in the boggy ground are prey to disease and rot. Many of the softwoods are skinny things with sparse leaves, unable to fare better in the saturated soil. Even so they pack a punch when they come down. It has happened before though without ill effect. Aluminum fence wire is surprisingly strong. However it is not invulnerable.

I counted five of these benighted trees in the space of less than 10 meters that had fallen onto the Beverage wire. One of them was large enough to sever it. Surprisingly a couple of the broken trees were still leaning against the wire which was still under some tension because the big tree was lying on top of it.

Manual splice: ugly but
it works, for now
A severed terminated Beverage becomes an unterminated Beverage. This is still a reasonably good receiving antenna except that it is bidirectional, only rejecting signals off the sides. A bidirectional Beverage has the advantage of covering two directions at once but with the serious disadvantage of poorer performance in the one direction you are most interested in.

The dead trees were pushed aside to rot in peace on the wet ground. After determining that the termination box containing the resistor and the ground rod connection were undamaged I retrieved the broken ends of the wire and manually spliced the break by wrapping 3" of the wires together. It held when I pulled on the wires to test the splice. Although this is not the proper way to splice aluminum wire it is a quick and easy way to temporarily put the antenna back in service.

I was not done since the slack had to be taken out the Beverage wire. All soft drawn wires will stretch a surprisingly large amount when put under high tension. It should be obvious that a wire that has been pushed beyond its breaking strength has also been pushed beyond its yield strength, which is typically ~70% of breaking strength. The 175 meter wire stretched ~60 cm (2').

Since I had only about half that much rope remaining at the termination I returned to the feed point, along the way lifting the wire off the foliage that trapped it while it lay slack. I removed the rest of the slack at the feed point and was pleased to find that my improvised splice held. Again I followed the wire to the termination and then back to the feed point to pull the wire free from twigs it snagged as it was lifted to its original height. Yes, this is a lot of work! Having an antenna farm is not for the lazy.

When night fell I was pleased to discover that the antenna was back to its usual awesomeness. Hopefully it'll survive the summer. In the autumn I may replace this antenna with a bidirectional Beverage although I am still loathe to tamper with an antenna that performs so well to Europe, which is the most productive contesting path.

This tree was too large to remove without assistance. Instead I
defanged the threat by cutting the branches which are long
enough to strike the Beverage wire when the rot progresses
to the point that the tree falls the rest of the way down.
The next day I went back into the bush with a saw and cleared away several dead and dying trees within reach of the Beverage. I want to avoid a repeat. Luckily it is only this area near the swamp that has sick and risky. Elsewhere they're healthy and strong and not too tall or are evergreens that do not have large overhanging branches.

Having lots of trees available as supports is nice provided you account for the risks. Everyone I know who runs Beverages through bush periodically clears deadwood, and yet still suffer breaks from time to time. This is my fate as well. Beverage maintenance will only become more onerous when I put up more of them.

Is it worth the trouble? In my experience: yes! Just keep these things in mind:
  • It's not a matter of if but when. Have a plan and material on hand to quickly and effectively repair or replace Beverage wires.
  • Splicing aluminum wire is difficult and there is likely no mains power nearby. Beverages made from coax that are spliced with connectors cannot take tension so you'll have to use messenger wires or replace the coax.
  • Inspect the full length of Beverages twice each year. Once in the spring after winter has done its worst and again in fall before the contest and low band season begins. Remove suspect trees and deadwood that can threaten the Beverage when they come down.
  • Be safe! Cutting down trees is dangerous work. It is even worse with deadwood since you will get little warning when a rotten limb or trunk you are sawing snaps. Trees will kick out, twist, break, pivot on obstacles and otherwise behave unpredictably when they are cut, chopped, pulled or pushed. They can be far heavier than you expect since deadwood is often waterlogged. Do not overestimate your ability to outmanoeuver a falling tree!
Get the help of a friend or professional is you are uncertain how to proceed. Don't improvise! As you would for tower work acquire and learn to use the proper tools. Beverage antennas are wonderful things but are not worth the risk of serious injury.

Deadwood cast aside to peacefully decompose on the wet boggy ground