I previously wrote that I had a lightning strike this summer and that my Beverage remote switch suffered what appeared to be lightning damage. All the relays connected to Beverages blew their integrated suppressor diodes. The damage went unnoticed for several days since I rarely venture onto the low bands during the summer.
At the time I was just happy that all the equipment and antennas seemed to be okay. Of course I was eventually going to find out what had really happened. It took a few weeks for me to notice.
The season has progressed to the point that it is possible to navigate the summer growth in the Beverage field. I found where the lightning struck and the full extent of the damage.
It was a direct strike and not a secondary one as I originally thought. Lightning is funny: there are two very high towers nearby yet the strike hits an antenna that is 2.5 meters off the ground. There are many things commonly misunderstood about lightning which I will not delve into in this article. Lightning can and does frequently plague Beverage antennas (scroll down to "Why composition types?").
Discovering and resolving the faults involved several steps. The first was to repair the switch. The relays were replaced with identical devices from my stock. I always order more than needed so that I can repair the devices I build. It is inexpensive insurance.
I ought to use relays without integrated suppressor diodes so that I can use 1N4007 or similar devices with a high voltage rating. It was faster and easier to dig into my stock and I am busy this fall. Next year I will reconsider the design of the switch and, as a minimum step, replace questionable components with better ones.
After testing the relays in the Beverage switch I installed it in the field. There was some risk since the Beverages themselves had not yet been inspected for lightning damage. Each antenna head end uses two SPDT reed relays for reversing directions with the DC power supplied by the switch on the RG6 feed lines. Those reed relays use external suppressor diodes of know type. I am more confidence of their robustness. If a voltage surge is brief enough it is possible for semiconductors to survive.
To my delight the switching electronics of all 3 Beverage antennas worked. That means the relays and suppressor diodes survived. Diodes that fail in this fashion usually short, which is easily noticed when reversing current is supplied. The celebration was short because, unfortunately, the blown relays were not the only problem.
The north-south RG6 reversible Beverage worked, but the others did not. From the head end side at the edge of the bush all I could discern was that one wire of the 2-wire NE-SW Beverage was a little slack. That's where I left matters until a friend dropped by to help and we trod our way into the bush.
We discovered wire breaks in two places: one on the NE-SW Beverage and one on the E-W Beverage. The causes of the failures were quite different.
The ground wire on the E-W Beverage reflection transformer was chewed through. This is the same problem I've dealt with several times on the 80 meter array. The reflection transformer at the eastern termination of the Beverage is at the edge of the swamp (I own part of the swamp) and the local hunters know this as a good place to stalk deer. The wildlife keeps to this narrow strip of bush between the open fields and the swamp. It is also coyote country since they hunt the deer.
The shredded AWG 18 stranded wire was replaced with AWG 14 stranded wire. This time I used a slightly longer length so that it could sit close to tree and rotting log below over the path to the ground rod. In my experience, deer are more attracted to wire dangling in midair.
After this simple repair the E-W Beverage worked. Although it wasn't lightning damage the break and the repair were part of the process. Now we come to the NE-SW Beverage and what the lightning strike did to it.
The reason for the slack wire was easily found. About 100 meters along the 175 meter long antenna the wire was cut. On closer examination we saw that the aluminum wire was vapourized. It was thin as aluminum foil at the tips. Probably there was a hot spot where the current flowed and the wire melted and tore apart.
By pulling the broken ends together we determined that only a short length of wire was gone. The ends met at a dead tree (pictured at top of this article). The tree supports the Beverage wires using screw-in electric fence insulators. The now empty insulator had a carbon track on it that led to the tree trunk. It would seem that the dead tree is now a little deader.
We could not determine whether the lightning first struck the wire or the tree. Because the tree was dead it was not easy to tell what damage, if any, was caused by lightning.
One nice thing about aluminum wire is that it is easy to splice. Aluminum oxide that coats aluminum soon after exposure to the atmosphere is conductive. Aluminum electric fence wire has the tensile strength to withstand tension for fences and Beverages, and it is stiff enough to hold together when two wires are twisted together.
I used a longer than necessary length of wire to splice the ends together since the original wire may have lost its temper surrounding the break. Until the wire tension was restored I couldn't be certain how much of it had been lost from the flash heating.
I set the tension at the northeast end and returned to the southwest termination where the head end electronics are located. There I discovered a curious problem. The galvanized nails I use for an improvised rope cleat had been consumed by the tree. The growing bark rode up the nails and half covered the ropes.
The nails could not be easily removed so new nails were hammered in. It took some pulling to pry the rope out of the bark on the old cleat.
When I tested the Beverage after sunset I discovered that this time I was not so lucky with the repair. The Beverage worked after a fashion: the reversing relays worked, but the directivity was poor.
Summer growth had to be cleared along the 175 meter length of the wire, and there was a lot of it! It had to be done anyway and there was a chance that the work would restore the antenna. It took three hours for two of us to cut and prune tree limbs. Bare Beverage wires touching trees limbs are not often a problem since the impedance is high and the contact points with foliage are not very conductive.
With the physical damage dealt with and the problem unresolved it was time to troubleshoot the electronics and transformers. These include the head end and the far end reflection transformer. Opening the enclosures showed nothing amiss other than insect litter.
I disconnected both enclosures and the ground wires and took them indoors for further testing. Before proceeding I cleaned them of the insect litter. A spider living alongside the reflection transformer was evicted. I plugged the weep holes of both boxes since they seem to cause more problems than they prevent.
Testing is no different from what I did while building them. The only difficulty was that to individually test components they must be de-soldered. I didn't bother with that.
Ohmmeter and through-the-box impedance tests strongly indicated that they were working as they should.
The impedance transformations were as expected, the relays switched and the physical Beverage wires were repaired, yet the Beverage had poor directivity. The next suspect was grounding.
Inspection of the grounds bore fruit. Below is the ground wire lug that connects to the head end stud. It is badly corroded on both sides and rust stains coated the stainless washers. I must have made a mistake when I selected the lug from my stock since I believed it was tinned.
I replaced the ground wires on both ends of the Beverage with tinned insulated wire. For a simple and reliable connection I tinned the stud ends of the wires to make them rigid and formed them into a J for wrapping around the stud. I no longer trust my stock of studs. Short copper strips of copper were soldered to the other ends for a copper-to-copper electrical connection to the copper-plated ground rods. I now have this style of ground rod connection to all the Beverage grounds.
I chose pink wire as an experiment. All the wires the deer chewed are black. Perhaps a brighter colour will be less attractive to them. The experiment is cheap, so why not.
Epilogue
Re-installation of the Beverage boxes was completed a little before sunset. A few hours later I was relieved that the antenna was working. The full Beverage system is now back online.
It is interesting how much of the damage had nothing to do with lightning. Nature doesn't rest during the summer months when the majority of hams abandon top band. The faults that were not caused by lightning would have been discovered anyway and the repairs made regardless of whether there hadn't been a lightning strike.
Beverage antennas are simple to build and maintain since they are so low. That low height makes them susceptible to frequent animal and vegetation damage. Their length makes them susceptible to lightning induced surges.
Repairs are usually easy but their regularity is annoying. Vertical arrays are easier to maintain and typically perform better, but they are complex and are beyond the ability of most hams to design and build. Commercial products are expensive. I'll stick with Beverages for now.
It is deer hunting season. Considering how much damage deer have done to my antennas this is welcome. I say that despite my love of wildlife. They can be pests and a danger, and they draw coyotes that extend their gaze to the local farmers' livestock. I mention this because I raced to complete the repairs before hunters arrive on my property. They requested access and I happily agreed. They're responsible people but I prefer not to be in the bush when they're present.
Lightning is funny (weird)
To repeat what I said at the start of this tale: "lightning is funny." It doesn't particularly care for tall conductive structures and it jumps on and off metal conductors seemingly at random. It may seem strange that it would vapourize a wire, draw an arc from a rotary switch 250 meters away, blow a string of relay suppressor diodes and leave everything else undamaged.
What did survive? Transceivers, relay coils and contacts, electronics, tiny transformers wound with thin enamel coated wire and so much more. I can't say whether the multitude of ground rods in the Beverage system, buried coax and control cables, and more robust ground rods at the towers and house entrance did any good or were merely bystanders during the event.
Coincident thunder and lightning are never a good sign. Check everything, no matter how good your grounding system and protective devices and procedures. Lightning has a mind of its own. It can devastate the best protected station and leave an unprotected station unhurt. Don't gamble. Employ the best lightning protection system you can afford and you are far more likely to survive the inevitable.
Ron, perhaps a few plastic shopping bags tied to vulnerable sections of the Beverages would deter the deer. They don't like anything that moves unpredictably and the bags would flutter in even a slight breeze. I have heard of other Hams using this trick successfully, especially at the ends of a Beverage where it slopes to the termination point. Very interesting stuff .. thanks for sharing. - Michael VE3WMB
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