Shallow Dead Man Anchor

Our antenna towers need help to stand upright. Gravity alone can't provide stability since it can only pull them against the ground but cannot provide lateral stability. Ground anchors are what give the tower stability to withstand the forces they must face: vertical, horizontal and torque. One big anchor if it's self supported and several if it's guyed.

In most cases the anchor is a solid mass of reinforced concrete. There is one directly under the tower. A guyed tower has several additional anchors. 

Anchor specifications depend on tower load and soil conditions. To get a building permit for a tower you may be required to have a soil test done by a professional. Those without the need to acquire a permit should not skimp on the anchors or a thorough soil inspection or test. Nature and the laws of physics pay no attention to pieces of paper, or hope.

There are articles in this blog that go into some detail of the anchors for my several towers. They require siting, excavation, reinforced concrete and alignment. I used heavy equipment and hired skilled labour when it made sense to do so.

Anchors are not only for towers. Sometimes we use trees or a convenient rock to hold the ends of wire antennas. A house bracket can anchor a light duty tower. The demands on anchors for non-tower use are often less strenuous. 

I ran into a case recently that I believe is worth an article. It wasn't for a tower but for my overhead run of cables from the hay field trenches to the switching system and cable connections at the base of the Trylon tower near the house. 

Looking back in the blog I find that I never really discussed that feature of my station. That's a gap I'd like to fill. However, right now I'll leave that and focus on the ground anchor that supports the overhead messenger cable and the multitude of coax and control cables that hang from it.

The weight of all those cables is substantial. There is also the tension to reduce sag and allow people to walk safely underneath. The existing messenger cable from the tower to a 10' aluminum post at the edge of the hay field is ~60' of ⅛" aircraft cable. Two intermediate posts take up much of the sag without requiring the higher tension required for an uninterrupted span. Tension on the messenger cable is perhaps a few hundred pounds,. That's less demanding than for a tower but should not be treated lightly.

A leg of the Trylon tower base section anchors the cable at one. At the other end is a screw anchor and diagonal guy to the top of the post. A wide wood base and steel peg pounded into the ground keeps the post from leaning sideways. It's ugly but it works. Or at least it has worked until now. 

An accidental collision with the mower several weeks ago exposed a weakness with the screw anchor. Despite no damage from the mower, the screw anchor was dislodged a few inches. Over the past several years I've occasionally had to screw the screw anchor back in a few inches as it pulled from the soil and the turnbuckle bottomed out. It has become too unreliable to ignore. 

The post that supports the messenger cable (a salvaged 10' long Hy-Gain boom section) is creeping and the cables are creeping down the sagging messenger cable. The bend in the post was there all along, due to high impact with the ground when the tower it was on failed. That was over 30 years ago and this is the first use I've found for it!

Although not in immediate danger of collapse, the time has come to rebuild. I had intended the overhead run to be a temporary measure until I could trench the cables to the Trylon. Due to the constant addition of cables and the horizontal roots sprouting from the surrounding birch trees the overhead run will have to be permanent. So I need to do it right. I stabilized the post with a long rope back to the tower and proceeded to design and install a better ground anchor.

Let's review basic facts about ground anchors. The mass of the anchor does not support the tension load. The load is supported by the resistance of the soil on the anchor. The larger the surface area of the anchor and the deeper it is placed the greater the mass of soil that must be displaced by the load. Undisturbed soil can withstand a greater load than top soil. 

The anchors for my large guyed tower are 2' × 2' × 8' blocks of reinforced concrete sitting 6' below grade. That provides ample resistance for the 4000 lb static load and 3× that amount of dynamic load. The attributes are responsible for the "dead man" moniker. Concrete forms for the anchors are often called coffins. Aside from this little joke I'll stick with calling them ground anchors.

The concrete is reinforced with steel rebar so that the anchor behaves as a rigid block. There is tension across the forward and upper faces as the rod is pulled towards the load (red arrows). Tension is greatest at the rod and diminishes as you move outward. Without reinforcing the anchor will eventually crack from the tension. Reinforcing rods across the front and top faces (large black dots on the left) give the anchor strength in tension. Unlike a large tower anchor, there is little shear force in a small anchor so that there is little benefit from constructing a rebar "cage".

The requirements for the anchor to support the overhead cable run are not severe. The tension is unlikely to ever exceed 500 lb. The wind load is not a large factor since the mass of cables are low to the ground and sheltered by trees. A small and relatively shallow reinforced concrete anchor is sufficient, and it will be superior to the screw anchor it replaces.

The main problems with the screw anchor are that screwing it in disturbs the undisturbed soil and it may not penetrate deep enough for the relatively small area of the anchor plate. Proper installation requires a tractor with an auger driving attachment. This is the preferred method since it disturbs the soil far less than doing it manually and you can power through dense subsoil and stones. That is, if the anchor has the strength to withstand the forces involved.

The 2' screw anchor that held the overhead run also shows how the auger end (which doubles as the anchor surface) is bent from screwing past rocks in the soil. The steel grade of these farm oriented anchors is not great. It is cheaper to use more steel than to make the steel higher strength.

The screw anchors I manually installed for the 80 meter yagi's small tower are holding well but they are longer and penetrate deeper than the one above. They were very difficult to install and the newly disturbed soil had to "rest" over the winter and spring thaw before they were safely set in the soil. They, too, will be replaced when I rebuild the 80 meter yagi tower. That job is scheduled for 2023.

The new overhead run will have a stronger messenger cable and the post will be a 10' steel pipe. The pipe is visible above, alongside the aluminum post it will be replacing. The top of the post is guyed to the new anchor. 

The anchor is placed a few feet behind where the screw anchor was located so that there is more headroom underneath. People are less likely to walk into it. The excavation fit neatly between the two trenches to the 150' tower. The roots of the nearby spruce trees go down rather than spread horizontally and were not in the way.

The rod is 4.5' of ⅛" × 1.5" bare angle steel. I have 3 identical lengths set aside for the future work on the 80 meter yagi. I cleaned the loose rust, drilled a hole for the guy attachment and coated the steel with rust paint. The few inches to be encased in concrete are not painted since many coatings don't bond well to concrete and even rusty steel will bond. 

The purpose of the paint is to slow, not prevent, corrosion due to soil, water and moisture. The rod can be uncovered occasionally to check for corrosion. The anchor is not affected by removing soil from around the rod.

The hole was dug with a small shovel and garden trowel to keep it from becoming too large and consuming more concrete than needed. A concrete brick serves as a chair for the rod. Hole depth is 30" (75 cm), which is well into undisturbed soil. If you live in a cold climate you should place the anchor below the frost line to prevent shifting due to frost heave.

The rod is aimed at the tower. You can see a large concrete block being used as an emergency repair to the existing screw anchor. The angle of the rod is low because it is further back of the steel post than the post's height. That lowers the rod's angle so that the rod must be longer than usual to rise above grade. A string pulled tight from the top of the steel post is used to align the rod's direction and vertical angle. This ensures that the rod does not twist or bend under tension.

Mixing concrete is a lot like baking. Make a well in the centre of the dry ingredients, add just the right amount of water and mix it until you have a consistent viscous goo. I used two 30 kg bags of pre-mixed concrete (cement, sand and stone). I've used electric or tractor driven mixers for large jobs where concrete delivery was impractical or expensive. For a small job like this a wheelbarrow and shovel will do the job. The total volume of concrete was slightly more than 1³ ft, which is enough to make an anchor 8" × 8" × 27". There is enough room to encase the rebar by the recommended 3" (7.5 cm) of concrete.

At left is the coated rod sitting on the chair. It is loosely pierced by a few inches of rebar to fix the rod in the anchor. Digging a narrow and deep hole is sloppy work. I used stones to fill unwanted cavities to preserve the anchor's shape and avoid the need for a third bag of concrete.

In the middle panel the anchor is half done. I have just laid an 18" length of 10M rebar to reinforce the upper face of the anchor. Its twin is more forward and buried below the rod to reinforce the front face of the anchor. See the diagram further above. At right all the concrete is in place. A small trowel was used to smooth the surface. Although a buried anchor doesn't need to be pretty it is good practice to eliminate gaps and cavities where water can collect and freeze. Over the years the concrete will crack from repeated freeze and thaw cycles.

Before walking away I rechecked rod alignment. After several days the hole was ready to be back filled.

Notice how the 1ft³ of soil displaced by the concrete has miraculously vanished! Of course it's all there but has been used to level the uneven ground at the edge of the hay field. Small stones were buried in the excavation so they didn't need to be carted away. The sledgehammer was used to compact the loose soil as it was shovelled into the excavation. No further subsidence is expected. There was a lot of displaced soil and rock from the excavations of the big towers. The backhoe moved it out of the hay field.

I will wait at least another week before putting tension of the anchor. Concrete is typically rated by its strength after 28 days of curing. In this case that's 3000 lb, and of course strengthened by the rebar. I am happy to start work on a tower after only a few days since the concrete is strong enough in compression to build upward. It is better to wait for the concrete to cure more completely when it is to be placed in tension.

More on the winter prep work keeping me busy is still to come. But now my focus is shifting to the CQ WW SSB contest this weekend.

Prop Pitch Motor Direction Indicator Using Op Amps

The PPM (prop pitch motors) I purchased in advance of building my current station included a home brew controller. In addition to motor control it has electronics to display the direction on a scavenged meter from a Hy-Gain rotator (appears to be from a Ham-M). It relies on a 10-turn 10 kΩ pot on the tower that turns with the mast. It was up to me to figure out how to do that.

The direction control is really very simple. There are a couple of op amps, pots, resistors and regulated ±12 VDC power supplies.

The first stage employs a 741 op amp as a differential amplifier. The tower pot connect to one input and the same pot type in the connects connects to the other input to zero the meter. Both pots are linear 10-turn 10 kΩ.There is no need to physically align the tower pot since the indicator can be zeroed at any position over its 10 kΩ range. The only requirement is that the tower pot not hit the end of its range. 

Over-rotation beyond 360° is supported provided the coax rotation loops can reach that far. The physical or electronic display must also support bearings greater than 360° and less than 0° in some fashion. A soft limit switch would be useful the operator avoid damaging the rotation loop.

The second stage uses another 741 op amp as a DC amplifier with variable gain -- dual op amp devices are available. The unlabelled resistor and pot are selected to set the gain range. The variable gain has two purposes. The first is to allow for different pot rotation ranges depending how the mast is physically coupled to the rotation system. The second is to set the voltage range to drive a meter or electronic bearing display. 

Alternatively, if the maximum voltage from the differential amplifier is directly usable, the second stage can be replaced by a variable voltage divider (pot) or software parameters in a computer controller and display. The value of the unlabelled resistor at the op amp output is selected to limit current to the meter movement. Meters are tolerant of modest and brief out of range conditions, but beyond that they can sustain irreversible damage.

There are many variations possible on the same theme. A few of these include:

• Variable supply voltages instead of a gain stage
• Add variable gain to the differential amplifier, taking care to preserve linearity across the rotation range
• Single power supply op amps to limit the output voltage range between 0 and Vcc to be compatible with an Arduino or other analogue input (ADC GPIO) of a computer controller such as an Arduino
• Centre, left or right movements of physical meters

With a little thought I am sure that readers can come up with other and perhaps better circuit variations. My plan is to begin with a physical meter and later transition to a software application for direction control and display. By using a physical meter I can get the display built and working faster, and right now my time is at a premium.

Everything I've written so far is elementary to many hams. It isn't to me. While I have many technical skills, circuit design is not one of them! I struggle with semiconductors. I still write about it since when I learn something since I know that there are others who will benefit. In that spirit of mutual learning we can proceed.

The controller I purchased along with the PPM was old and home brewed by the ham I bought them from. They were built so long ago that his memory of the design had faded. But his electronics knowledge is superior to mine and he made an effort to reconstruct the design from memory, filling in the blanks from his understanding of circuit fundamentals. That was helpful when I first installed the PPM and the controller.

It became more urgent recently when the indicator malfunctioned. I suspected lightning damage to the op amps. However, I was late noticing the problem since the tower pot was succumbing to the elements and obscuring the true cause. When I replaced the pot on the tower, along with a redesigned mast coupling system (more on this in a future article) it continued to misbehave. Since the pot checks out perfectly when measured in the shack with an ohmmeter it must be the controller.

This was a further spur to set about a redesign of the direction indicator. The basic op amp design is a good one so I stuck with it. What I didn't like was the need for dual power supplies and the voltage level. It is perfectly good for a physical meter movement. I know hams who do it with discarded Hy-Gain rotator controllers that are frequently found at flea markets from rotators that have expired. I am tempted to do the same, however I also want to prepare for computer integration and control.

With my tenuous understanding of op amps I researched alternative devices. I wanted an op amp that would operate from a single DC supply and would work well at 5 VDC. This is ideal for connection to the ADC GPIO pins of an Arduino. Risk of damage to the microprocessor is reduced when the voltage is unable to swing negative or above 5 volts, and therefore doesn't require a more complicated circuit to prevent out of range voltage presented to the analogue GPIO pin. 

I also wanted to maximize the gain to use as much of the voltage range as possible. The 10-bit ADC of Arduino and some other microprocessors can resolve 1024 points. With a 10:1 pot and no gain a full rotation only utilizes 10% of the voltage range. That leaves only 100 points, or a position resolution no better than 3°. That's acceptable for HF yagis but is often inadequate at VHF and UHF.

I settled on the LM358 dual op amp and purchased a small quantity. Like most electronic components they are inexpensive and encourage experimentation. The output range is from 0 to Vcc - 1.5 volts, which in this case is 0 to 3.5 volts. It seemed a perfect choice. Unfortunately it is not so simple. 

Rail-to-rail operation of an op amp is constrained by its design and by operating conditions. It was the lower rail limit of 0 volts that caused me grief. I didn't fully understand this and I ran into difficulties adjusting the inputs to get the range and linearity I needed. I got close but with parameters that would be difficult to maintain in practice. In particular it required precise setting of the tower pot. That is not reasonable when working 40 meters up the tower.

For computer integration the non-linearity can be compensated in software though not easily and it, too, is susceptible to the pot setting. I gave up the experiment with the LM358 and dove into my bag of 741 op amps. This approach was far more successful despite the seeming chaos of the breadboard prototype.

Tower pot rotation is emulated by the pot on the left. Degree of rotation can be eyeballed from the knob indicator. The 10 kΩ pots zero the direction pot (left) and set the gain of the second stage (right). All the resistors are 10 kΩ except the 33 kΩ current limiting resistor in series with the meter. 

The meter pulled from my junk box has a centre zero so that 0 volts output from the circuit represents due north. Negative and positive differential voltage pull the meter toward south counter-clockwise and clockwise, respectively. The batteries supply ±9 VDC.

In the picture the bearing is about 60°. That the stage 2 output voltage (that's what the DMM is measuring) bears a striking resemblance to that value is a coincidence. All that matters is linearity, gain and a suitably marked meter face. The last two can be implemented in software when the circuit delivers the signal to a computer ADC port.

Meter movement can be reversed by switching the tower pot connections at the controller or by switching the V+ and V- inputs to the second op amp. The same can be done with a DPDT switch. I probably won't bother since it's easy to switch the wires and reversal only happens by swapping wires during maintenance. Little mistakes like that are easy to make.

As built, the circuit gain is suitable for a the 1:1 rotation ratio of the chain drive PPM on the tower with the 40 and 10 meter yagi. For the upside down PPM on the other tower the rotation ratio is closer to 3:1. That is, the resistance range of the 10 kΩ pot on the first PPM is 1000 Ω and perhaps 3000 Ω on the second PPM. I will alter the design so that the circuit is compatible with both. More components will be needed for a computer interface to strictly limit the output within 0 and 5 volts.

This is the design I'll proceed with. For the first version I'll tap the ±12 VDC regulated supply in the old home brew controller and adjust the gain stage accordingly. Physical meters with a linear scale (the scale units on the face plate don't matter) will be used for the display. I will do it for both PPM rotators since diagnosing and repairing the malfunctioning circuit is more difficult due to its accessibility. 

For the next version I may, as others have, use Hy-Gain control units for both direction indication and motor control. DC power for the motors will be taken from the existing control unit's power supply. Once this is done the old control unit can be moved off the desktop.

Of more immediate concern is the pot wiper for the pot on the 15-20 stack PPM rotator. I grounded it with the expectation that I'd use the LM358. The ground wire will be disconnected on my next trip up that tower. The ugly rope I first put on for the pulley belt has already been replaced and tested.

Nothing especially novel has been introduced in this article. The circuit is simple and its usage straight forward. Nevertheless, even basic concepts are worth communicating since they are often unfamiliar to new and longtime hams. Experimenting and prototyping with a breadboard is a valuable technique to learn.

New Towers at VE3KG

Despite the scale of my own station I also do tower work for friends. When I was young it seemed that I was on someone's tower nearly every weekend. I enjoyed helping other hams with their tower work, no matter the size. The accumulated knowledge and experience came in handy when building my current large station.

This has never been a business for me. I have never charged any ham in need and there are many times that I refused offers to pay me. That said, I rarely turned down a meal after the job! I was a hungry lad, unmarried and new to the city. Home cooking was an irresistible attraction.

These days there isn't a lot of tower work to be done. The average age of hams is quite high it is far more common for hams to downsize than to build upward. Many elderly hams have taken down their towers down or have gotten out of the hobby entirely. That's unfortunate but understandable. Therefore I take some joy in seeing hams that are putting up towers.

An old friend of mine, Dave VE3KG, recently moved back to this area after retiring. Most recently he was VE9CB and at various times he has had call signs in VE2, VE3 and VO1, and he has DXed and contested from locales as far flung as BY, 6W, ZL7 and VO2. He now has a few acres 20 km north of my QTH. Several of us helped him to build his new station.

I won't give a detailed account of the planning and building process since it is little different from what I've already written up for this blog. Like me, he ran into trouble with the excavations due to the slow percolation of rain and snow melt into the bedrock and the endless quantity of large rocks buried in the soil. On the bright side, we didn't hit bedrock. That's always a worry since the Canadian Shield rock lurks below ground in this area. 

In many places the bedrock rises above the surface, which makes planting towers a challenge. Many years ago I ran into that with my own station -- 1 foot of soil over shale -- and others in this area. Powered breakers are needed to penetrate the rock. Shale is unsuitable for rock anchors so it must be removed.

The water problem was solved by waiting until late summer. The rocks were broken and removed by hand tools, or lifted out with the assistance of a friendly neighbour eager to play with his new backhoe. Even so we didn't get down quite enough per the manufacturer's foundation specification. Instead the volume was increased to match. This is acceptable if you don't deviate far from the spec.

Both towers are identical to my first tower at this QTH: Trylon T400 with 9 × 8' sections, coming to just under 70' (21 m) above grade. Following my example he used the same cradle design for setting the base sections in the foundation holes. Again it worked well to hold the base sections for the concrete pour. No adjustment was necessary during the pour, and I checked often.

One of the holes was out of reach of the truck so we endured the amusing spectacle of several gray-haired hams carting an endless succession of wheelbarrow loads 30 meters across the lawn. There were minor mishaps that were fodder for laughter.

Tower sections were rapidly lifted with vehicle muscle, just as I did for raising my large guyed towers. I was joined on the tower by fellow contesters VE3JM and VE3FU to splice the sections and push the gin pole skyward. Other local hams provided critical support on the ground. Each tower took a day to raise. One advantage of using a vehicle was that masts and rotators could be attached to the tower sections on the ground. The extra weight was no problem for the vehicle or the gin pole.

The gin pole is almost the same as what I built for raising my Trylon tower. It is 2' (60 cm) taller to accommodate the 10' sections for my LR20 guyed towers. The shorter 8' Trylon sections could be lifted from the top which helped to keep the wide lower sections more vertical and managable when maneuvering them into position for bolting.

Antennas are fragile and were lifted separately to avoid damage. Tag lines kept the antennas away from the tower during each lift. None of the antennas could be lifted straight up because the bottom sections of the tower are wider than the antenna element spacing. It takes choreography to equalize the force when two people manipulate each tag line. It was clumsy but we got it done.

At right you can see me working on the hookup for the Cushcraft X7 on one of the towers. That is the only HF yagi at present. The tower will support wires for the lower bands. The other tower is currently only for VHF and UHF antennas. From top to bottom (below): 6 m, 70 cm, 1.25 m and 2 m. There is space at the bottom of the mast for a future HF antenna. 

Disciplining the rotation loops is difficult when there is no yagi near the top of the tower. The bundle of 4 lengths of RG213 naturally sag and will snag the "ears" of the tower legs. No matter how you secure the other end of the loops on the tower the descending run will not reliably clear those ears.

The top plate holding the thrust bearing on Trylon Titan towers is mounted below the splice bolt holes for the next smaller section. Even if it was easy to move the plate to the top edge of the legs there would be chafing as the rotation loops develop enough tension to scrape over the corner of the triangle.

We solved the problem by mounting a short fake boom on the mast to which the descending cables are attached. It acts as an arm to hold the rotation loop clear of the tower. You can see the upper edge of the support plate for the fake boom in the photo above.

There are other ways to clear the tower but this one is desirable since there will be a yagi in that position there. When it's installed the cable bundle can simply be transferred from the fake boom to the real one. We tested the rotation loops on both towers while I was up top so that I could make adjustments for best operation.

When there are multiple cables on the tower it is helpful to organize them. Dave colour coded the cables for each yagi. To make maintenance easier, including swapping of main coax runs, he asked me to place the connectors for the rotation loops at one level. Since the lengths did not line up on their own, the excess lengths were coiled (off the left of the picture). 

The main runs were individually tied to the tower diagonals. More cable ties and tape are required but that is only pennies spent to have a cleaner installation that is easier to maintain. The downside is that the job took longer and I was racing against sunset. Connectors were weatherproofed after each run and antenna were tested. One run failed the test and was lowered for repair.

Several carabiners threaded with long ropes were prepared beforehand and attached to the tops of the towers. This will let Dave raise and experiment with low band wire antennas with a minimum amount of tower climbing. I've done this for other hams and it works pretty well. It is important that the carabiners can't sag against the tower or twist or the rope will jam. Pulleys make pulling easier but there is greater risk of trapping small diameter ropes.

As I said, it was sunset. A final picture of the completed towers seemed appropriate, along with one of Dave VE3KG in front of the north tower (left).

Notice that the bottom section is painted blue. That section comes from the estate of Don VE3RM. I only met Don once many years ago, but several other notable local contesters knew him well. He opened his station to them for contests back in the years when I was out of amateur radio. It is appropriate that his towers are seeing new life in those contesters' stations.

With that job out of the way, it's time to get back to work on my own station. Winter is coming.

Beverage Repair and Maintenance (again)

Beverages are fantastic low band receive antennas. They're simple and inexpensive, yet they perform exceptionally well. With a little bit of simple electronics and winding small transformers they can be made reversible, giving you two directions. My first unidirectional Beverage toward Europe was installed soon after I moved to this QTH. Along with my first ever full size 160 meter antenna I had a wonderful time on top band.

The one thing Beverage antennas need that most hams don't have is lots of space. A Beverage for top band is typically from 100 to 200 meters long. I am fortunate to have the space. They are located in an area of derelict bush that hasn't been farmed for decades. The 3 reversible Beverages cover the 6 most useful compass directions. There are plans for a fourth, but the need isn't urgent so I have deferred the work in favour of other projects.

Beverages have their negative points:

• They are typically no higher than 3 meters. They are susceptible to damage from people, animals and vegetation. Search the blog and you'll find several articles about the construction and maintenance challenges I've dealt with since putting up my first unidirectional Beverage in early 2017. Maintenance and repair twice a year has become routine.
• Despite being so low, Beverages are highly susceptible to lightning. Their length easily induces high voltage currents from nearby strikes, and they provide a conveniently large number of junction points for strikes to reach charge reservoirs in the ground. Many hams disconnect their Beverages during the summer when lightning is common and activity on the low bands declines due to the high atmospheric noise.

It was September before I could access most of the Beverage system. The hay, insects and summer growth strongly discourage anyone venturing into the fields and bush from late spring to late summer. Over the past few weeks I've discovered that the lightning strike earlier this year did more damage than I realized. It will be some time yet before the system is back in full service.

The first job was to retrieve and repair the Beverage remote switch. It was easy to reach once the hay has been mowed. All the relays had to be replaced, and for the same reason as the previous time lightning struck. All I had in my stock was SPDT reed relays so I used those. Since I only had 3 and there are at present only 3 Beverages, I left the fourth port disconnected. An important advantage of SPDT relays is that I can ground the feed line to the Beverages when they're not in use. That provides limited protection against lightning. I'll take it.

Unlike the SPST reed relays these replaced there are no internal flyback diodes. To make the job easier I didn't put any in the switch. I will add them to the switching system in the shack. Their location is not critical, so putting them close to the electronics they are meant to protect is perfectly acceptable.

Lightning was not content to only wreck the relays this time. The pair of 0.1 μF coupling capacitors were blasted by the surge. These capacitors are only rated for 50 volts. Had they been rated for a kilovolt they still might not have survived. I'll order more robust capacitors for future repairs.

With the remote switch tested and reinstalled I proceeded to test the rest of the system. The east-west Beverage was completely dead and the northeast-southwest Beverage was bidirectional and unresponsive to reversing current. The north-south Beverage was unaffected because the electronics were taken indoors before the strike due to a switching problem. However I have yet to fix it, with the result that none of the Beverages were in service.

I brought the head ends indoors for examination. I also performed simple tests of the Beverage wires and reflection transformers and all passed. That was the only good news. I waded through the bush and confirmed there was no physical lightning damage, but there were other problems which I'll come to shortly.

Above is the head end of the east-west Beverage. The blocking capacitors and the RF choke of the bias-T for the reversing current were blasted apart. At least one transformer winding arced and melted through. Scorch marks on the plastic enclosure from arcing are obvious. Several copper traces on the underside of the PCB vanished.

Despite having done no further component tests I think it is fair to say that the head end may be a total loss. It will have to be rebuilt from scratch. The northeast-southwest head end has less damage and may be salvagable by replacing a few of the parts. I plan to order new relays and rewind the transformers for both head ends. One of the transformers of the north-south Beverages will probably also need to be replaced.

I reconfigured my Beverage test fixture as a differential mode head end and installed it on the east-west Beverage. There is a 5:2 transformer inside and a pair of 0.1 μF coupling capacitors. The impedance match is not exact but good enough. The capacitors prevent a short if reversing current is accidentally applied by the operator (me!). West is a useful direction for the Pacific opening this time of year. It's a temporary measure.

Parts need to be ordered and the head ends rebuilt. I'll do that in the coming weeks. In the meantime there was routine physical maintenance to be done to repair and prevent animal and vegetation damage. The only animal damage this year was to the northeast termination of the northeast-southwest Beverage. It was most likely caused by a deer walking into the wire running between the reflection transformer and ground rod. 

The wire was torn off the ground rod clamp and the transformer enclosure pulled off its mounting. The damage was easy to repair. To prevent a repetition, I stacked a pile of stones under the wire. There was an ample supply within a few meters since, as was typical when the land was originally broken for farming, the stones that litter the soil in this area were rolled over to the fence lines. 

What I should do is lengthen the ground wire so that it can lie on the ground out of the way of trespassing wildlife. The extra length of wire will have a negligible impact on antenna performance. Perhaps I'll do that once I have other jobs out of the way. The stones can remain to protect the ground rod.

The rest of the maintenance involved trimming vegetation. It is often quite a surprise to see how much the trees and bushes grow over the summer. Branches that were previously trimmed have grown back and in many cases tangled in the Beverage wires. New bushes sprout up where there was none before. If left uncut they will threaten the Beverages next year. It's unpleasant and tedious work, but it has to be done.

Especially problematic bushes and trees are cut down rather than just trimmed. For example, the thorny bush above was chopped down on this outing. In some respects it's a shame to have to do it, but this is wild secondary growth on an abandoned farm field that has no particular value. I am tempted to bring in a large tractor and flatten the vegetation.

Last year I had a problem with the wires of the northeast-southwest Beverage. They would oscillate in the breeze and eventually spin and short together. When I installed the original single wire Beverage I used every available tree and bush along the route as support. There were no artificial supports. 

This haphazard approach simplified construction but created a problem when I twinned the wire to make the Beverage reversible. The Beverage is not quite straight. It wanders a little one way then the other to utilize the available supports. Beverage performance isn't affected by minor deviations.

As vegetation grows the deflection and spinning tend to increase. In two instances I had to decouple the wires from the supports without installing a pole to replace them.

My interim solution was string attached to the Beverage at those two points and tying them to small bushes. It didn't work as well as I'd  hoped. During this maintenance outing we installed a PVC pipe at the most problematic location. Spinning is far less likely since both wires are firmly attached to the pipe. Over time I will have to do more of this and perhaps abandon all of the natural supports.

To ease the job this fall, I was assisted by my friend and favourite ground crew member, Alan VE3KAE, along with his trusty axe. Why suffer alone when you can share the misery.

The vegetation growth was serious enough that it took us longer than expected. There was no time afterwards to work on other projects. I have yet to lay out the radials for my big 160 meter vertical. We got a good workout and had enjoyable conversations as we inched along through the bush. I can unroll the radials on my own another day.

In light of all this complaining and frustration there is the inevitable question: are the Beverages worth all the work? It is a question worth contemplating since there are alternative low band receiving antennas.

Beverage are simple and effective but vulnerable to nature. I may no longer be able to keep them connected during summer. That hasn't been a major problem because I have to disable my big vertical during the summer. That may change in the future. 

It has always been my intent to have a second low noise receive antenna system for multi-op contesting. That would be a short vertical array. They are reasonably compact, less susceptible to nature's assaults and in most cases have superior performance (RDF) in comparison to Beverages. I have enough room for Beverages and a vertical array.

Since these systems are very finicky to design, build and adjust most hams use commercial products. They can be quite expensive. Further, the amplifiers they require must be sufficiently robust to withstand a simultaneously transmitting kilowatt during contests; at other times it is not an issue. I know hams that have had to deal with pre-amp overload when using their vertical receive arrays during contests.

Another alternative is to go back to unidirectional Beverages and simply put up more of them. They're simpler and the vulnerable reversing electronics are absent. They're easier to build and repair. But do I want double the number of Beverages to maintain out in the bush? Or perhaps have several that are installed in the open fields during the fall and removed in the spring? A lot of coax must also be deployed since it is not convenient to have the feed points close together given the constraints of my property.

By laying out the pros and cons you can perhaps better appreciate the alternatives. Every low band operator must choose. It comes down to trade offs of money, ability, performance, land use and effort. Two hams can come to opposite decisions and both be right. 

I am not yet near a decision and I won't make one this winter. There's a lot to mull over.

Transformer Hum

Power transformers are everywhere: in our equipment and in our homes. They transform the utility service voltage (120 or 240 VAC in Canada) to a higher or lower voltage needed by an electrical device. Those that transfer high power are large: dimensions, weight and cost. Copper isn't cheap. Although they can be remarkably efficient there is power loss.

Heat is the most noticable attribute of power loss. Another is sound. The intense magnetic field can vibrate loose components in the transformer that are subject to the field. Those are the core and the windings. All transformers vibrate but an improperly constructed transformer or one that is old and suffering from degradation of chemical binders and insulating layers can be objectionably loud. 

The greater the power the transformer is handling the stronger the vibration. If the equipment is in the shack you'll notice it! For example, the power transformer in a kilowatt amplifier when it is transmitting.

The sound has a fundamental of 120 Hz (counting both positive and negative swings at 60 Hz) and there can be substantial harmonic content. The latter is more noticable since our ears' sensitivity rolls off at low frequencies. The transformer's enclosure and how it is mounted can amplify the sound, and those harmonics, in the same fashion as a speaker and its enclosure. In severe cases it can be quite loud and annoying. 

Headphones are not very good at blocking low frequency sounds, and other noise such as rig and amplifier fans don't cover it up very well. It is better to solve the problem at the source. Unfortunately that isn't always possible, depending on the condition of the transformer and its placement inside the equipment. 

Let's look at a few cases I've dealt with, or tried to deal with, that may give you a few ideas should you have to deal with loud transformer hum. Don't confuse this with the other kind of audio hum that can be cured with a transformer.

The sheet metal enclosure for the Drake L7 amplifier's separate power supply is prone to vibration since it is large and thin with little structural bracing. It is close to the transformer on 3 sides of the large plate transformer core. When I first set it up it was loud. The sound was amplified when I placed it on a shelf under the operating desk since the desk and wall acted as an acoustic enclosure.

The enclosure is not easy to remove so I waited until I had to open it to replace the rectifier and filter boards. The first thing I tried was to tighten the bolts that press together the laminations comprising the core. They may loosen over the years from the 60 Hz vibrations. That helped a little but not nearly enough.

The next step was to add dampening to the enclosure. Fibreglass insulation was attached to the top and sides of transformer core. The layer was just thick enough to fill the gap between the core and enclosure. This material works well since it fire and heat resistance and provides excellent soundproofing. It is important to allow adequate airflow when you do this since the transformer heat has to escape or the transformer will prematurely fail -- fibreglass insulation slows heat transfer (obviously). Use it sparingly.

The sheet metal vibration is greatly dampened by the insulation it is in contact with. The noise was sufficiently suppressed that I considered the problem solved. The hum is still audible though quiet enough that it almost completely disappears when wearing headphones.

This spring I purchased a small Astron linear power supply to replace, perhaps permanently, another that was damaged in my most recent lightning strike. Transformer hum was objectionably loud. Simple measures such as its placement on and under the operating desk were ineffective. A friend loaned me a power supply so I forgot about for a few months. About a week ago I decided to try again.

I'll tell you up front that I was not successful. Failures are interesting so I thought it would be worthwhile to show what I did, what effect it had and my final assessment of the power supply. Apart from the transformer hum the power supply works perfectly well.

The transformer is attached to the chassis with rivets. Unlike bolts and nuts, which have adjustable torque, rivets are not adjustable once installed. Transformer vibrations can be amplified and chatter if they are even slightly loose. They appeared to be tight but I removed them anyway. A drill is used to split the outer plate from the shank with a bit about the same diameter as the rivet shank.

I experimented with a more absorptive mount with the objective of attenuating the coupling of transformer vibration to the chassis. Plate steel chassis are notorious for vibrating and amplifying sound from within it. 

Screws and nuts replace the rivets, with fibre washers under the bolt head and nut. There is a thin layer of fibreglass insulation between the chassis and transformer flanges. With the enclosure still open, the level of audible hum was reduced. More insulation was loosely wrapped around the transformer to see if that would help. It didn't.

Before doing that, I tightened the 4 long screws at the corners of the transformer core. Only a little additional torque could be applied before the soft metal of the screw heads began to distort. Vibration was unaffected.

A small C-vise was applied to the vertical plates on the sides of the core to see if additional pressure would have an effect. It didn't. This was safer than torquing the screws beyond their limit. 

Had it worked I would have considered replacing the screws. This is not a good idea most of the time since the lamination and their coatings can be damaged. 

Should you try it, avoid steel screws unless the allow is designed for this application. Otherwise they may be heated by the magnetic flux. Brass or a similar non-magnetic metal can be used. The metal determines the maximum torque that can be applied. Be careful.

At this point I was running out of ideas. The core does not appear to be the source of the vibration. I concluded that the windings are at fault. This can be due to age or poor manufacture. I hesitate to blame Astron since this hasn't been common with their power supply products in my experience. However, I've sampled only a small quantity of their products.

My final attempt was to fully stuff the enclosure with insulation. This is not a particularly wise move but I had nothing to lose. Heat isn't able to freely escape and bits of insulation can cause a mess. I don't recommend it as a permanent solution. In any case it didn't work.

Well, that's not quite true. It did work well with the top cover off. When the cover was slipped on, screwed on or not, the noise returned. It was barely attenuated at all by all that insulation. In the photo you can see what it looks like. (Note: the cover was accidentally reversed when I took the picture but that's not how I tested it!)

The enclosure is amplifying the noise and there is no easy cure. It's partly due to its design. Notice that there are only two screw holes on top where the cover attaches to tabs on the rear panel by the heat sink. The front panel is free to vibrate, as is the top of the cover. Perhaps fabricated tabs and screwing it together would help. I don't plan on doing that since it isn't worth the effort for such an inexpensive product. I've exhausted my patience.

I am left with several options.

• Use it with the cover off. While not the safest thing to do it will not be in reach of inquisitive fingers. A soft plastic cover can avoid the bulk of the electrocution risk.
• Place it where the noise doesn't disturb the operator. I can do that, except turning it on and off becomes a chore.
• Replace the transformer. That's an overkill repair and not worth the expense. Rewinding the transformer is a job for a ham braver than me, or one with far too much time on their hands.
  
• Repair the lightning damaged power supply and relegate this one to the workshop. I have tried repairing the malfunctioning Pyramid power supply but it involves replacing almost every semiconductor on the PCB. There could be one or many faulty devices. It, too, isn't worth the effort.
• Buy or build a new power supply.
  

I will use it for a while with the cover off and replace it at some point. I have two power supplies damaged by lightning and perhaps I'll get lucky getting one of them working again. The application is my station automation system which does not require a highly regulated 13.8 VDC. Relays aren't fussy. I have 5 VDC regulators to tame the power supply for the Arduino and relays.

Working on this problem was more about personal interest rather than necessity. I enjoy playing with broken things to see if I can get them working. I spent little time on it because my interest level isn't high. I've exhausted the learning experience dealing with vibrating power transformers. 

Is this report useful to readers? Perhaps it is, and that's why I took a few minutes to write it up.

Control Systems: Relays vs. Transistors

I haven't said much about revamping my automated control system since mentioning it a few months ago. A lot has happened since then. That said, progress has not been rapid because it was summer, and summer is a time for other activities. Despite the many delays the software is not far from completion. 

Well, that's the software. Where I have been more reserved is with my decisions for the hardware. Software cannot on its own do anything: it must be connected to the real world. On an Arduino and similar systems the GPIO (general purpose input output) pins are the interface between the two. 

I have waffled between solid state and relay switches to put signals on the control lines, weighing their various pros and cons. Now that I've made firm decisions and begun implementation I thought that this would be a good time to discuss my investigation and experiments, and the reasons for my choices. This could prove of interest to others, hence this blog post. 

Despite being oriented towards contesting, the presented information should be of broader interest. Our increasingly software-centric shacks enable opportunities for station automation and remote operation that we could only dream about in the past. 

I do not claim expertise. What I can do is explain the how and why of my design choices. There are many online resources that delve into greater detail, and there are commercial control solutions for the ham shack. My citing of these will be sparse since that is not the topic of this article.

Using GPIO on Arduino

pinMode(gpio#, OUTPUT);

It may seem obvious but don't forget to include the above code in your Arduino sketch. I've forgotten a few times and the result was confusing behaviour. You can perform a digitalWrite on GPIO pins that have not been so declare (the default is INPUT) except that the GPIO may only supply a few milliamps before a logic HIGH sags to become a logic LOW. I now make sure to declare all the GPIO pins as OUTPUT during initialization (reset).

GPIO output pins default to LOW. That seems sensible since we tend to think of LOW as off and HIGH as on. That is often not the case. There are good reasons to use reverse logic (LOW is on) to simplify connection to external modules.

I posted a picture of a midsize Arduino. Mine is a Mega. I need the Mega's large number of GPIO pins due to the sheer size of my antenna farm and shack equipment. Most hams can get by with less.

What I need to switch

The mosaic of switches that can be found in my station are collected below. It is partial since there is far more.

Going clockwise from the upper left, and then the centre:

• Beverage remote switch
• Head end of a reversing Beverage
• Stack switch
• 2×8 antenna switch (Hamplus)
  
• 80 meter 3-element vertical yagi
• Parasitic element (there are 4) of the aforementioned yagi
• Relay board of the 6-band low-power BPF (VA6AM)
  

As you can see there are many relays in the RF path. To reach those remote switches there are multiple DC control lines that wend their way out to and up the towers, below ground and on the ground. There is a lot for the station automation system to connect and manage. Further, the threat of lightning is ever present and therefore the risk to control system electronics in addition to its more spectacular effects.

I am not able to switch the amplifiers at present because they are manually tuned tube amps. My plan for the future is for modern amps that can be automatically switched. An alternative is RF-detection that is available in an increasing number of amplifiers. A few milliseconds of transmitted RF will switch the band and ATU setting automatically. 

Switching devices

GPIO pins can't deliver enough current to directly switch the switch the relays shown above, and if you try there is risk of damage to the Arduino. Many control lines power multiple relays so the current requirement is even higher. It is also unwise due to the risk of damage to the processor from pulses and surges from relay coils, precipitation static and induction from nearby lightning strikes. On the bright side, all of these components, including Arduino boards, are inexpensive.

At right are several choices for switching devices. Clockwise from left, and then the centre, are:

• 2N2222A NPN transistors
• The same devices mounted on a proto-board with base resistors and current-limiting load resistors (e.g. for LED or a second switch stage); an SPST reed relay is shown, though not connected
  
• ULN2003 NPN Darlington transistor arrays
  
• Module with high current relays and drivers suitable for direct GPIO connection
• 2N6034G PNP Darlington transistors
  

The solid state devices are cheap and easy to buy in bulk from online suppliers. They are small and quiet, which is nice for use within the shack.

Darlington transistors are important for switch voltages higher than that of the microprocessor logic. With a single transistor (Darlington transistors have two in series), there is a substantial risk of the higher switched voltage destroying the microprocessor.

During prototyping I tried all of the possibilities. In the above photo the NPN drivers are lighting LEDs that represent one side of the 2×8 antenna switch; the port for the 20 meter stack is selected. PNP Darlington transistors on the lower right and their NPN drivers light LEDs for the 10 meter stack switch. The upper yagi is shown as selected. The relay module is connected but with normal logic (see next section) none of its relays will switch on. 

The power supply PCB (upper right) with two 5 volt regulators is not being used. USB 5 volt power is the sole power source. The relay module has 5 volt coils, however the only reed relays on hand have 12 volt coils that could not be tested without a 12 volt supply connected.

Reed relays are quiet and small, and well suited to the modest demands of control line switching. The relay modules are larger and louder but they're cheap and easy to connect to the Arduino. If size and noise are a problem it is possible to locate them outside the shack with a wireless Arduino shield. That is my ultimate intent.

A benefit of using SPDT relays is that when the control line is idle it can be grounded by connecting the NC terminal to ground. That is only possible with high-side switching; with low-side switching, grounding the NC terminal energizes the circuit, which is not what we want. This brings us to the next section.

High-side and low-side switching, and switching logic

The switch (mechanical or electronic) can be placed on the low side or high side of the circuit. The diagram at right shows both. The supply voltage is applied at the high side of the load (e.g. relay coil) and a low side switch grounds the load to complete the circuit. The opposite applies for a high side switch.

You don't always get to choose. All of my home brew antenna switches are high side. The Hamplus 2×8 antenna switch requires low side switching. The same is true of almost all amplifiers, where you ground the control line to bring the amp inline when transmitting. I prefer high side switches for outdoor equipment so that the power supply is not continuously in circuit, leaving the power supply exposed to all potential occurrences of static and surge. In practice it's no big deal and I may be overreacting.

Whichever you want or require there are implications for how the GPIO are used. With a solid state switch you can use either NPN or PNP transistors. The choice is not arbitrary since they are not equivalent.

• NPN: normal logic (HIGH is on) and low power dissipation.
• PNP: reverse logic (LOW is on) and high power dissipation.
  

Vce is very low with an NPN switch so that the I²R loss is also very low. Vce is typically 0.6 to 0.8 volts with a PNP switch and the loss is higher. That is why it is common to see NPN Darlington array chips and individual PNP Darlington transistors with a heat sink option (see the picture above). With the small relays we typically use the power dissipation is modest and a heat sink is not required.

With normal logic and high voltage (12 volts is high when dealing with a microprocessor!) a high side switch requires a complementary Darlington transistor: NPN followed by a PNP. Since there are pretty well none of these devices commercially available it must be constructed from individual transistors, and the parts count is high. That adds up when you have dozens of control lines to switch. With a PNP Darlington you escape that if you use reverse logic (LOW is on).

For the typical multi-relay modules marketed to Arduino users you can directly connect them to the GPIO pins if, again,  you use reverse logic. With normal logic an NPN driver is required to invert the logic.

My choices

After looking at the effort and cost required for the various options I have settled on my final choices for switching devices.

• Indoor equipment: Darlington transistors
  
• Outdoor equipment: Relay modules

Relay modules are surprisingly inexpensive from multiple online sources. This stack of 48 relays cost me only a little more than $1 (CDN) per relay. That many relays might seem excessive at first glance until you consider that just the 2×8 switch requires 16 relays. The small PCB at the lower left is for one of the 6-band BPF. It is partially populated with PNP Darlington transistors.

By restricting myself to these two options I will use reverse logic in the Arduino. I recommend that you use similar code as that below when doing this. You can easily switch between normal and reverse logic by changing just two global variables. Mixing logic in an Arduino sketch can cause confusion during coding so I recommend sticking to one or the other.

int R_OFF = HIGH;
int R_ON = LOW;

digitalWrite(gpio#, R_OFF);
digitalWrite(gpio#, R_ON);

There are no NPN drivers required at all! The PNP Darlington transistors are driven directly by the GPIO pins with only a base resistor: 3.3 kΩ appears to work well for the 2N6034G. I have designed control boards for the BPF to support both manual and automatic band selection. Other than the transistors all it contains are bypass capacitors, base resistors and several Dupont connectors.

The relay modules connect directly to the GPIO pins. Except for the 2×8 switch (low side switched) the NC relay terminals will be grounded for lightning mitigation. The system will be large with all the relay modules stacked. It will be placed out of sight under the operating desk.

When I transition to Wi-Fi to untether the control system from the PC, it will be placed where the relay chatter can't be heard at the operating desk. Lightning protection for the station can be better when the control lines are kept out of the shack and closer to an external ground. A small 13.8 VDC power suppy can be colocated with the remote control system.

Next

Cabling is no small job. There are over 100 Dupont connectors to be assembled, most in groups, for connection to the Arduino, relay modules and BPF PCBs. A crimp tool is essential for the work to proceed smoothly and to produce reliable connections. 

There are multiple DB9 and DB25 connectors and cables to/from peripheral equipment and the control cable patch panel in the basement. It's a tedious but necessary job.

For the initial installation I might not use an enclosure for the control system. The quantity of connectors and an almost guaranteed need for future changes makes for difficult and perhaps unnecessary work. Provided there is sufficient RFI protection it can be left "open" until the design of the control system matures.

With a little luck and some hard work the full system should be ready for CQ WW SSB at the end of October. Well, that's the ideal, but with all the tower and antenna work I am doing for myself and others I might not be done in time. I'll have more to say about the full system once it is complete and it has been used in at least one contest.