The Porcupine

An ElectroStatic Discharge Device, Static Discharger, Static Brush or Static Wick

In the early 1980's I got tired of the tower being hit by lightning so often. My long time friend, Dale Heatherington - WA4DSY, and I decided to apply a little physics and try to discharge the static as it built up to reduce the liklihood of lightning strike. This is the basic principle of Ben Franklin's lightning rod. The idea we had was to use as many discharge probes as possible. We used stainless hose clamps to clamp wires on a mast to form a discharge brush. Later, I came up with the scheme shown below for building the porcupine.

Disclaimer: Prior to installing the porcupine, my tower was being hit by lightning several times a year. After installing this device, my tower has been hit by lightning only about 3 times in over 15 years. There are times when you just can't bleed off the static charge fast enough to prevent a strike but I have noticed a marked improvement here. Dale has experienced several significant lightning strikes causing damage at his location. There is significant disagreement in the scientific community about the true worth of such a device as this. I'm not making any claim for its usefulness in your situation. Furthermore, I don't claim any scientific evidence as to the effectiveness of these devices. As usual, build your own at your own risk and draw your own conclusions. I would be interested in hearing from you regarding your results.
Electrostatic Receiver Noise - Cause and prevention of static discharge problems to receiver operation.
Fulgurites - When lightning strikes the ground it heats the soil and fuses it into a glass like formation.
  Van - KF4LEX contributed this great photo of a fulgurite he dug out himself
Another interesting fulgurite photo
Tower Guard - You can buy a static discharger from the Tower Jack folks.
This is a classic example of what happens when lightning strikes a fiberglass encased antenna. This was a Diamond F23 two meter antenna.
My Porcupine
This is the home made porcupine on top of the mast. The repeater antenna is on the left. I also have a porcupine on top of the small tower the HF beam is located.
First a word about safety... This is a dangerous project from the standpoint that you have 60 sharp wires sticking out in all directions which can easily put your eye out or puncture your skin. I highly suggest you wear safety glasses, long sleeves and leather gloves. This is NOT a construction article. This is how we made our porcupines, you may wish to do the same thing. If any of this information helps you that makes us happy. If you get hurt making a porcupine, we're sorry, but we warned you.

Start with a ten foot length of rigid aluminum electrical conduit (okay Henry, use steel if you must) which is threaded on each end and provided with one coupling when purchased (or the mast you have in the top of your tower). Also obtain six yellow tab guy grips (sometimes called dead ends) and three stainless hose clamps large enough to go around the coupling and the grips. This will work just as well on the end of a mast without a coupling, just assemble and clamp directly to the mast.

(click the small pictures to see a larger picture in a new browser window)
Clamp the loop end of each grip in a vice and bend the two legs to about a 45 degree angle as shown here.
You will end up with the loop end of each grip looking like this.
Clamp all six of the grips to the conduit coupling or your mast using stainless hose clamps. Overlap the loops to obtain a symmetrical layout. The bent loops should extend beyond the end of the coupling as shown. Note: If you are using an existing mast that isn't threaded on the end you still need to bend the ends of the grips to allow them to lay flat against the mast where you can clamp them.
View of the coupling with the grips clamped in place. Note that the bend in the loops allows the mast to reach into the coupling. Without the bend, you wouldn't be able to insert the mast.
The grips are now aligned and ready to be unraveled and spread.
Another view of the grips and the coupling.
Here, Henry - KM4O (now W4HK), is unwinding the grips and spreading the wires for his porcupine.
The wires are spread here enough to separate them. Final spreading will be done just before sending the porcupine up the tower.
The detail of the grips after spreading showing the clamps on the coupling.
This is a good time to re-tighten the clamps.
Using electricians pliers to cut a very sharp angle on the ends of each wire will insure a needle point which discharges static much easier. This is an optional step as the ends of most of the wires are pretty sharp as it is. You may want to wait until you are outside and ready to hoist the porcupine before doing this. The ends are VERY sharp. Be careful to NOT poke your eye!
Henry is holding his porcupine with the quills all pulled together and tied with a string or tape. It would be tough to get the thing out of the house otherwise.
This is the porcupine mounted on the end of Henry's mast. Final spreading of the wires will be done when the mast is installed.
This is the porcupine mounted at the top of one of my towers above the Mosley TA-33.
When installing the porcupine, fan out the wires to form a broad brush to bleed off the static charge. Use the third hose clamp to clamp around the lower end of the mast. Solder a piece of heavy copper braid to the hose clamp tail end and to a piece of insulated heavy (at least number 8) copper wire which runs all the way to the base of the tower, clamps with a ground clamp to the base and then continues off the base to a long copper plated ground rod. Do the best you can to provide a low impedance ground for your tower. Never ground THROUGH the concrete base structure. Always run a heavy copper ground wire to the top of your tower. Never depend on the tower for your conductor. Some people disagree with running a ground wire up the tower. Use your own judgement here. Personally, the insulated #8 wire running to the porcupine from ground makes me feel better. The insulation on the wire helps prevent galvanic action between the copper wire and the galvanized tower.

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Last update was on March 16, 2008 11:32