Lightning Strikes Twice

When lightning strikes twice do you blame bad luck or do you suspect a common cause? Both can be true, but they are not equally probable. The particular circumstances tell the tale. Lightning distribution on a largely homogeneous and reasonably flat expanse of geography, like mine, is highly unlikely to favour one particular location.

My station was struck by lightning a few days ago. Again. And again it struck the Beverage system. Unfortunately it is prime growing season and the fields are filled with tall hay and the bush is overgrown. I do not venture into those areas this time of year, so it may be a few months before the antennas can be physically inspected and repairs made. What I know is that the damage is almost certainly worse and the repair will be more extensive than the last time this happened.

It may seem strange that with 150' towers and a variety of high and pointy antennas that lightning would strike antennas that are low enough to be touched from the ground. Long wires can build up a substantial charge in the presence of lightning activity, and my Beverages are between 150 and 175 meters long. Lightning is an RF phenomenon and induction of charge onto a long wire is to be expected. This happens on electric utility distribution networks for the same reason.

This is a lesson I must take to heart. It would have been prudent to disconnect and isolate the Beverages during the summer storm season when they are not in use. Many do so. I haven't since this is not an area known for high lightning risk. Experience demonstrates that my station is at high risk and I will have to take steps to deal with it.

The lightning was unexpected. Although we had several storms over the past week, that morning the sky was clear and weather warnings were for later in the day. I was working on a non-ham task in the shack while monitoring the 6 meter FT8 watering hole at 50.313 MHz, waiting for a DX opening.

A small storm cell formed to the west of us and rapidly passed overhead. The unexpected thunder and lightning didn't worry me too much, and I did briefly consider whether to shut down the station. I didn't and a minute later there was the crackle of intense arcing coming from the A1500 amplifier and bright flashes visible around the edges of the band switch. The 6 meter antenna was the only antenna not grounded. A second later the thunder boomed.

Everything kept working, with FT8 signals being decoded, but WSJT-X lost CAT communication with the FTdx5000. I shut everything off and waited 10 minutes for the storm to move well to the east. The rig, amp and PC worked perfectly when powered up. When I moved on to test the HF antennas and switching systems I discovered that the Astron RS35A 13.8 VDC power supply turned on but there was no DC output. Without it I couldn't proceed to test the rest of the station.

Now I have 2 lightning damaged power supplies. The 3A Pyramid on the right used to power the antenna switches and station accessories until it was damaged by last year's lightning strike. I temporarily moved those power cables to the Astron. Temporarily turned into a year while my attention was focussed on other projects. On both power supplies the electronics have failed, likely due to semiconductor junction damage.

I guess I can't put off troubleshooting and repairing the supplies any longer! For the interim I purchased a 4A supply at a local flea market and a friend loaned me a 25A supply to test and power the second station (SO2R). Amazingly everything works, except for the Beverages. Even the receive antenna port on the FTdx5000 was undamaged despite being connected to the Beverage system.

The Beverages could not be tested because the knob on the antenna selector wouldn't move past the first position. It was physically blocked. So I opened up the antenna switching system enclosure and discovered the problem. The picture below was taken with my phone and a flashlight.

The tabs on the rotary switch deliver 12 VDC (upper left tab) over the Cat5 control cable that makes its way to the Beverage switch about 100 meters from the shack. It's buried for most of that distance. The RG6 coax for the antenna RF follows a different route. The Beverage antennas themselves are further away. A common mode transformer in the remote switch blocks DC between the Beverages and the RG6 run the shack. Of course lightning can bridge that small gap if the path looks favourable to it.

The far right (clockwise) position is off, where the switch was set at the time. The 3 middle tabs are for the current selection of 3 Beverages. The charred and melted tabs are evidence that the lightning current found ground via the power supply by arcing to the rotary conductor. The tab adjacent to the off position partially melted and physically blocked the wiper from passing underneath. There is a separate toggle switch (not visible) to power the reversing relay that delivers DC over the RG6 feed lines to each Beverage.

I hope to have the power supplies repaired in the not too distant future. As noted, the Beverage system will have to wait until well after the hay is harvested. There should be no problem getting everything back in shape by the fall contest season, despite the unwanted extra work.

I have taken modest steps to build lightning protection into my antenna farm. I admit that I need to do more. Let my mistake be a lesson to others. I'm not ashamed to admit my mistakes -- to err is human... -- when it can serve as a learning experience.

Beyond the repairs, there are steps I will take this year to reduce the risk from lightning strikes:

• Disconnect the Beverages and remote switch during the summer when I rarely operate 160 meters. Disconnect and ground cables when storms are in the area, at least as an interim measure.
  
• Investigate lightning mitigation measures for the Beverage system that may be implemented as soon as this winter.
• Install coax protection on all feed lines (4) coming into the house. There are 2 for the HF operating positions, one for VHF and one for the Beverages. I have a handful of VHF/UHF PolyPhaser protectors so the VHF feed line can be dealt with immediately.
• Complete the partial and then plan a full perimeter ground system around the house, complete with additional ground rods for the coax protectors. The best way to incorporate the station ground and electrical service ground will need to be investigated.
• Improved protection for the multitude of control cables for antenna switches and rotators. An ultimate solution is impractical so I will prioritize.
• Improve lightning protection for the 80 meter 3-element yagi. At the moment I rely on the extensive radial system, buried cables and a spark gap for the base insulated driven element (tower).

Is that enough? We can substantially lower the risk while understanding that perfection is impossible.

I am also tempted to invest in a multi-element vertical array for low band reception to avoid the lightning risk posed by the long Beverage wires. My long term plan is for a second receive array to use during multi-op contests. It may be prudent to bring the project forward and make it the primary receive array. The Beverages would only be connected for use during contests.

As I was finishing this article a message popped up when I checked the local weather. This is lightning safety awareness week in Canada. How timely.