[TowerTalk] Lightning Protection Question

[Jim Thomson]

Date: Sat, 11 Sep 2010 22:22:35 -0700
From: "Jim Brown" <jim at audiosystemsgroup.com>
Subject: Re: [TowerTalk] Lightning Protection Question


Gene,

I didn't misread or overlook it at all. The function of an arrestor is to 
protect sensitive (and expensive) electronics from a strike. ALL IT DOES IS 
SHORT THE COAX. That remote switch is neither sensitive nor expensive. 
Although, as K8RI noted, it's easy to do that with the switch, the coax isn't 
connected to the shack, so it doesn't matter. So I'm sticking with my (and 
K1TTT's) advice. Arrestors go as close as practical to the sensitive 
electronics that they protect. Anywhere else is a waste of money.

73, Jim K9YC

##  Some folks will use SPDT vac relays  for the remote coax switch. [ IMO, this makes for the
ultimate, reliable  remote coax switch, esp if a gigavac G-2 is used].   I wire those
things so when the relay is DE-energized, the center conductor is grnded to the remote switch box
which in my case, is at  the top of the tower..where it belongs. Yagi's with hairpin match's will have the 
center conductors grnded anyway. [ since the braid of the same cable is bonded to
top of tower..via the remote coax switch. ]    Now whether the super duper, type 31 cookbook
5 k+ ohm balun will impede the lightning is debatable.   OK, now we have ALL the braids
of the remote switch box grnded to top of the tower... and ditto with all the center
conductors. [ excluding OWA designs]. 

##  In this one example... there is now a single coax coming down the  side of the crank up tower. 
In my own case, that smaller cable, then has to interface into a larger cable..which heads back
to the basement [aprx 60'] .   Since the small cable has to be interfaced  into a larger cable,
I decided to install a  bulkhead lightning arrestor at base of tower.  You can now kill  3 x birds with
one stone!  [A]  interface 2 x different cable types.  [B]  grnd the shield of BOTH the small + big
coax cable.   [C]  have a lightning arrestor at the base of the well grnded tower. 

##  I install a 2nd lightning arrestor at the SPG.   I use this lightning arrestor  to [A] bond
braid to SPG.  [B] interface back to a small coax cable.  [ C] lightning arrestor.  I also run a 
2 ga Cu  wire between base of tower, and  SPG.  

## In previous tower install's, [ not crank ups] I also ran ALL coax, and control lines  down the
INSIDE of the tower, on the inside of the big V shaped legs.   Those were all big face width towers,
one was 32", top to bottom.  Other's were even bigger.  I don't think I would want to try running 7/8" heliax
up the inside of Rohn-45.  

## in this one case... since big and small coax cables have to be interfaced at base of tower, plus braids 
need to also be grnded... a  lightning arrestor, imo, is a wise choice.   It's easily accessible,  and also provides
a  demarcation point, and / or  test access point.  IE: insert test gear and either look up the tower... or look back
towards the shack.  In some cases, I can see where the 'base of tower arrestor' would take the brunt of the damage.

Later... Jim   VE7RF