[TowerTalk] Ground...and talking around it

[Gary Schafer]

Jim Jarvis wrote:
> Guys...
> 
> A few true-isms:
> 
> 1) coax braid will not handle lightning currents. It will
> evaporate before draining a strike.  Ground strap is better,
> out of the box, but after corosion, and depending on how you
> bend it...it may or may not work.

You wouldn't use a piece of #12 wire for a main lightning ground either.


> 
> 2)  Copper strap is the only answer.  And even then,  you need
> to make sure you have gentle bends.... 18" radius is about right.
> Else, you have an inductor.

You have an inductor with a straight piece of strap also.


> 
> 3)  If your house/station ground does not have a single point
> system...if telco or power come in elsewhere, and wander around
> before reaching your RF ground.... you've got a lightning problem.  
> 
> In practice, and with older homes, this is hard to do.  Still, it's
> real. Much easier to do with new-build.   
> 
> I did a single point ground at a radio studio for AM/FM/telco/power,
> audio...5 control rooms and 4 studios/announce booths...the worst 
> noise was a burble when the strobes on the 500' FM tower fired. 
> And that was at -140dBm in the audio chain (vs. signal at -30dBm) 
> 
> Imagine, for a moment, that you might live on a sailboat for a while.
> You may be the highest point for 30 miles.  How would you ground your
> mast?  A #8 wire, as the manufacturer recommends?   Coax Braid, which may
> corrode?  Or copper strap from mast to keel?  

You might use several pieces of #6. Or several pieces of copper strap. 
One run is usually not sufficient. You would also ground all the stays 
to the keel also with run of heavy wire or strap.
No one would use coax brad for that job or any other wire that small.

73
Gary  K4FMX

> 
> You know where I come down.
> 
> n2ea
> jimjarvis at ieee.org