Having witnessed firsthand what lightning can do to a completely unprotected station, I decided to do things differently when the time came to rebuild the Excalibur Site.
The following photo is from a lightning strike that entered the shack five years ago via a balanced feedline. There was no grounding system in place, so the lightning energy flowed through a wall stud and an ARRL Antenna Handbook on the book shelf on its way to ground. The wall stud burned almost completely through, and the thick handbook was turned to fine ash. The building was subsequently dismantled.
How many of us have thought our equipment was safe just because we disconnected the feed line(s) from the ATU and/or radio?
The lightning protection plan currently being implemented at WQ4RP is based on several months of research and consultation with experts on the subject of mitigating the damage to radio stations resulting from either nearby or direct lightning strikes.
The sobering news is that a serious level of lightning protection necessitates the need for a comprehensive grounding system–unless you really think that a few feet of ground wire and one, or two, or a hand full of ground rods are going to provide an effective energy sink for several hundred (or possibly thousands ) of amps of lightning energy.
I contend that while it may not be possible to guarantee 100% immunity from a direct lightning strike to one’s tower, tower mounted antennas, typical backyard dipole, or associated feedline(s), it is entirely possible to substantially increase the odds that such a strike will have most of its energy dissipated in a protective ground system well before it has a chance to get into your shack or radio equipment.
This post is not intended to be an in depth treatise on the why and how of lightning protection for amateur radio stations, but rather a description of what steps the KnightLites at the WQ4RP Excalibur Site are taking to minimize the risk to people, the shack, and the antenna system.
Interested readers are encouraged to study the following links:
For the Single Point Ground Entrance Panel WQ4RP, a panel was purchased from KF7P (http://www.kf7p.com/KF7P/Welcome.html) Chris, KF7P is providing a valuable service to the amateur radio community with his functional, beautifully crafted entrance panels and associated components.
The RG8x feed line from the big 160M vertical is connected to an Alpha Delta TT3G5O Surge Suppressor. The coax shield is connected to the large copper plate (thru a large bolt on the surge suppressor), which in turn provides a low inductance path through the ground strap to the ground rod. The TT3G50’s patented gas discharge chamber will shunt potentially damaging lightning energy from the coax’s center conductor to ground.
Thanks to Alex KC4PHJ for his generous donation of four additional surge suppressors which will soon be installed on this panel.
The ground strap from the entrance panel above terminates at the ground rod below. The ground rod clamps for the copper strap are also manufactured by KF7P.
This grounding strap will be removed from this ground rod within the next few weeks and connected to a comprehensive grounding system.
Several hundred feet of trenching was done the weekend of July 4th, using a rental trencher that could dig down to 36″. The going was slow but steady, taking about nine hours to complete all the coarse work. This included time to extricate the beast three times from soft dirt and rookie maneuvering on my part. Thanks to a 4WD vehicle and a strong chain, the trencher was persuaded to rejoin terra firma all three times.
The goal of the trenching was to create three ground circles, or halos–one around the shack, one around the tower, and one around the 160M vertical. Additionally, two long feed line/control line trenches were dug–one from the shack to the tower and the other from the shack to the 160M vertical. The goal is to have all three halos bonded together to the single point entry panel at the shack so all three halos and associated feed line trenches are at the same potential during a lightning strike. There will be no isolated grounds in this system.
Below is a photo of the ground halo around the tower. The trench at 2 o’clock is for the feedlines, control, and power lines to the tower.
A number of 8′ long copper clad ground rods (30) will be driven vertically 2′ below grade into the trenches, spaced 16 feet apart and bonded together (using cadwelds) with #4AWG solid copper ground wire. This process will be highlighted in the next blog, as most of the cadwelds are on backorder for another week.
Below is a picture of the ground halo around the shack. The intersecting trench at 7 o’clock is 16′ long will provide additional grounding with an additional ground rod.
I decided to invest in a used heavy duty hammer drill to drive the thirty ground rods. The first test has been a complete success, as it took 30 seconds to drive this 8′ rod down three feet into rocky clay soil. I then hit a big rock and leaned on the drill for 1 minute until the rock fractured and the rod easily completed its descent into the trench.
In case you are wondering which drill I’m using, it’s a Bosch Model 11311EVS with an SDS MAX 5/8″ ground rod driver bit. This bit does not deform the top of the rod as it’s being hammered in. Incidentally, the hammer drill absorbs most of the pounding, so the process is not too hard on my 64 year old bones.
Here’s the rod driven about 12″ below grade, with the original conical head undistorted. I challenge anyone to do that with a sledge hammer.
Mid Summer is usually a dry period in central North Carolina, but numerous thunderstorms have visited this area over the past few weeks, with the trenches now filled with tadpoles.
At least the clay is thick enough that it is not flowing back into the trenches. It will be a happy day when the trenches are filled with ground rods, ground wire, and coax!
Stay tuned for part 2, where we will be installing the ground rods and firing off the cadwelds.
72, Paul AA4XX