[TowerTalk] lighting protection setup

[David Gilbert]

That is all good and valid info, but the problem Jorge described is 
static buildup on the wire dipole itself, resulting in a spark jumping 
across the end of the coax connector (from pin to shield) inside the 
shack.  That isn't a common-mode problem, it's a differential one, and 
grounding the coax shields won't help.  A good quality lightning 
arrestor with a DC ground (like the ICE units) would fix the arcing, but 
other people have also used high inductance coils across the feedpoint 
at the antenna, or even resistors, to accomplish the same thing.

I've had that same thing happen several times on "temporary" antennas 
that I hadn't bothered to DC shunt at the antenna, although I was always 
careful to keep them disconnected from the rig when they weren't in use 
and I usually shorted the end of the coax at the shack to bleed off the 
charge.  When I neglected to short the ends of the connectors, I'd often 
get a nice large arc snapping about every three to five seconds as a 
storm approached.

On one occasion about a year ago, I had an 80m dipole up with the coax 
running into the shack but disconnected.  I was working outside and saw 
a summer storm developing, and even though there hadn't been any 
lightning yet I decided I should go inside and short the end of the 
coax.  The end of the coax was just laying on the concrete floor, and as 
I leaned down to reach for the cable (not the connector) with my other 
(right) hand touching the concrete, a thick bright blue 2" long arc 
jumped from the connector to my left hand.  It zapped me pretty hard, 
and the biceps muscles of both arms were sore for about three days.  A 
good portion of that voltage was probably common-mode since it otherwise 
would have been jumping across the connector, but I'm pretty sure it was 
still just static buildup ... there were no nearby lightning strikes at 
the time.

Nasty stuff ... and yes, I've done the calculation to see how much 
voltage it takes to jump two inches across reasonably dry air.

For my new, more permanent setup, I ground the shields of all coax at 
the top of the tower, the bottom of the tower, and at the entrance to 
the shack.  I also have coax lightning/EMP arrestors 
(center-conductor-to-shield) at the shack for each coax line, and surge 
suppressors on each rotator or relay control line (line-to-ground), both 
at the top of the tower and at the entrance to the shack.  Finally, for 
extra margin I made up several shorted PL-259's to connect to the coax 
lines in the shack during the summer months when we get lots of 
thunderstorms and I'm less active, since the bands are in generally poor 
shape then anyway.

73,
Dave   AB7E



Rick Stealey wrote:
> Greetings Jorge,
> Good practical info is available on W8JI's website.  http://www.w8ji.com/station_ground.htm
>
> I try to not repeat the info you have been reading in those good publications.  So in summary what you should do is bond the coax shields at the top and bottom of the tower to the tower, and of course the tower is grounded.  Then do the same where the cables enter the house.  Tom does not use lightning arrestors (Polyphasers).  The tower ground and all other grounds need to be bonded together (include the telephone, cable tv, POWER !!!!).  This should keep surges outside your house.
> Then at your shack, each piece of equipment should be connected to a point called a single point ground (SGP).  The SGP is also the point where you can install surge suppressors for coax cables.  The SGP should then be connected to a good earth ground as close as possible.  And guess what?  THAT ground rod has to be connected to the other one.  It would be nice if your ham shack was close to where all your cables enter the house.  Then the SGP ground and the entrance ground (along with the electrical power, tc, etc) can all be one and the same.
>
> Maybe I will email you a photo of my SGP (and any other readers who merely send me a one liner and ask for it).  It will help to see something real.
>
> Rick  K2XT
>
>
>
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