[TowerTalk] spark gaps & GDT's for lightning/static protection

[Grant Saviers]

I've seen pictures of all sorts of gaps,  two wires almost touching, 
interlocking rings, adjacent spheres, Jacobs ladder like rods with 
tapered spacing , etc.  One amateur radio product uses automotive spark 
plugs (non resistor) and is sold as a pair on a copper plate for open 
wire feeders.  However, a copper plumbing sweat fitting is soldered over 
the gap so it is impossible to measure the gap.  My question is, if I 
use a non resistor spark plug as a arc gap, is there any experience that 
can be shared about what the gap distance should be set to?  I plan to 
have a removable cover over the gap end for WX protection .

Are there better designs for a gap that are easy to fabricate and 
weather/bug resistant?

And a second question:  Gas discharge capsules are used in coax 
lightning protection devices.  A large variety of gas discharge 
components are stocked at Mouse, Digikey, etc in various voltages and 
Kamps.  Is there any difference in the RF properties of the tube in the 
in-line coax devices vs what I can buy a lot cheaper as a component?  eg 
Littlefuse and TDK 800v @ 10Ka around $3ea.

http://www.littelfuse.com/~/media/electronics/datasheets/gas_discharge_tubes/littelfuse_gdt_cg_cg2_datasheet.pdf.pdf

Grant KZ1W