Tech tip for open-wire lightning protection

[W7TFO]

I thought I'd mention this old trick I've used over the years.

Secure a piece of 1/8" or 1/4" copper bar about 1" wide and 5" to 7" long.

Drill two holes near the ends.

Drill & tap two holes for 13mm spark plug threads at the approximate conductor distance of your feeders.  Insert two non-resistor plugs of your brand choice.

I use Champions.  

Put it adjacent to your incoming feeders by means of two standoff insulators in those end holes.  Mount the assembly with the plug tips facing towards you, or use some 90 degree stock to point the plugs upright so you can see the gaps working.   

Run a good-sized wire from your station ground to the copper bar.

Tie each feeder lead in turn to one of the plug tips via short jumpers.

Adjust gap according to modulation and power levels used.

You now have pretty good surge protection from something that was designed to take a lot of sparks in stride!

73DG

[WA1GFZ]

AC stands for Albert Champion

[W3SLK]

Relative humidity is going to play a big part in how you set up that gap for power out. I wish I had a few of the plugs that we used for ESWL. This would have satisfied that gap uncertainty and served to discharge the voltage developed during a lightning event. However, they were designed to spark at 18KV.

[W2VW]

That idea might be OK for one band but everything changes when band switching happens.

Also spark plugs are designed to have gaps which will fire under engine compression. The required voltage to jump that gap in plain air will be a lot more. Actual firing voltages in an engine could be anywhere from 5 kv to 15 kv. Feed a halfwave antenna with a halfwave feeder and the voltage can be way over 5 kv right at the maxima. 

The current capability of a spark plug will not do anything to shunt a strike and most near strikes. It will bleed off a charge though.

I'll stick to keeping the entire antenna at DC ground here. My dipole is the highest thing in the neighborhood and has not been hit while a lot of lower things have.

[KL7OF]

Use aircraft spark plugs...They are designed to fire under low compression and have 4 spark gap electrodes...

[WA1HZK]

Used this years ago for a cheap lightning protector. Works pissa. Just adjust the gap for your amount of RF under the worst condition. Don't worry about the gap being too big. Lightning doesn't care. I hope the smell of ozone does not disturb you.
HZK

[The Slab Bacon]

AC stands for Albert Champion

Not many people know that!! Or the whole story behind it...............................

[WBear2GCR]

What is this "13mm" thing?

I don't think that is American or patriotic. Some sort of Euro scourge no doubt!

                           _-_-bear

[KL7OF]

AC stands for Albert Champion

Not many people know that!! Or the whole story behind it...............................

I would like to know the story behind it!!  I

[W7TFO]

Bear,  spark plugs (at least the "normal" ones) used and sold in the US have always been sized in metric measurement.

13mm is most common, and Ford used a lot of the 18mm size.

BTW, which is used more? 75m or 3885KC? 

Metric or Imperial, neither is domestic.

Anyways, cheap plugs from the auto parts store always worked just fine to keep HV from going too high on feedlines.  I tried Neon lamps, but they blew out from the potential during our monsoons. 

73DG

[kg8lb]

AC stands for Albert Champion

Not many people know that!! Or the whole story behind it...............................

I would like to know the story behind it!!  I

  Some people are under the mistaken impression that Albert Champion invented the sparking plug. That honor actually belongs to Oliver Lodge. In the early days France was the major manufacturer of spark plugs. Being the French were using the Metric measure, spark plugs are primarily sized in Metric units . (BTW 14 not 13 is the most common size in current use...14mm x 1.25mm pitch).
  The role of Albert played was originally as an importer of electric ignition parts. He later undertook manufacturing of plugs and related parts using his "Champion" nameplate. At some point Albert lost control of Champion and a little later formed the AC company in Flint Michigan.

IIRC:  The role of "Lightning Arrestors" Is to bleed off static charges that may build up on the antenna. This can minimize the risk of a strike or an extreme voltage buildup. There is little that can protect from a direct strike. The spark plug's working end need not be exposed. They can remain closed and protected within a blind bore.

 BTW, If you prefer fractional inch sizing the 14mm works out to about 70/127".

[Opcom]

If using spark plugs, should they be the non-resistor kind?

If going to the trouble of drilling holes big enough for spark plugs, why not just use the grounded diamond-shaped piece of aluminum metal where the pointy ends are the low side of the gaps and a triangular piece is the high side on each wire? It's in the handbook. looks sort of like

> <=> <
1 gnd 2

and if you have insulators at the entrance, the L1 and L2 pieces can be bolted right on them.

I like the spark plug idea for compactness and durability but the high voltage there from RF with a mismatch or using a tuner would seem a lot. 384V peak at 50 Ohms, 2425V peak at 2000 Ohms. Maybe more depending on the so-called SWR and how close to a voltage node the gap is. Gap 'em wide!

I just use a big knife switch to ground the antenna when not in use. It may still be a good idea to add a gap on the floating 'radio' side of the switch, regardless if the antenna is grounded as the switch center pole is still only 3" from the 'radio' side of the switch's contacts and lighting may decide to arc a bit regardless of what is supposedly grounded.  A #6 and ground rod probably don't look like a dead short with 10,000 amps.. The RF chokes to ground ought to also be used. Lightning is so powerful it really does not matter, all you can do is put as much protection as possible there and pray the intrusion is minimized.