[TowerTalk] Arrestor placement

[Jim Thomson]

Date: Sat, 27 Dec 2014 18:48:41 +0000 (UTC)
From: David Gallatin via TowerTalk <towertalk at contesting.com>
To: "TowerTalk at contesting.com" <TowerTalk at contesting.com>
Subject: [TowerTalk] Arrestor placement


Hello all,Somehow I have gotten the idea that one's lightning arrestors are best placed at the bottom of the tower. This seems logical to me. Then I came across another piece that said, no, arrestors are to be placed at the shack entrance panel. Which is it? Or does it matter???73,
David, AA9G

ex W5DCG and KC9EEV

##  Install one at the base of the tower AND also where the coax enters the home.  In my case, the two arrestors  are 65 feet apart. 
The one at the base of the tower is aprx 4  feet above ground.   Base of tower is earth grounded via  3 x 8 foot deep  copper clad 
ground rods..all cadwelded.   2 ga bare cu wire to each leg of the tower.  Another 65 foot of bare 2 ga cu wire, C clamped to 
basement entrance + SPG...where a 4th ground rod is installed...and also cadwelded.   The HOFFI brand lightning arrestor at the
base of the tower serves other functions.  It’s the interface between the rigid coax from the shack to the base of the tower. 
Flexible coax from tower lightning arrestor  going up the side of the HDX-689 crank up tower.  Lightning arrestor in mounted to the
spg is the 2nd hoffi brand arrestor.   Remote coax switch box is mounted to the mast.  All braids from each yagi coax is bonded to the
mast via the remote switch box.   The  lightning arrestor at the base of the tower bonds the coax braid to the base of the tower... via the
casing of the lightning arrestor. 

##  Like K1TTT  points out,  you need a 2nd arrestor where the coax  enters the home.  Now if the tower base is close to where the 
coax  enters the home, then you could get away with only the one arrestor.   If hairpin or beta matches are used on the yagis, the center conductor
will be bonded to the braid of the coax anyway..right at the feedpoint..via the hairpin or beta match.  In the case of the beta match, both the center
conductor and braid are bonded to the boom.   Either way, the center conductor is bonded to the braid..which is then bonded to the top of the tower. 

##  If it gets past all of that, the  arrestor at the base of the tower should do the trick.   If it gets past that, then it has to get past the arrestor at the SPG.
If you have a OWA  yagi, the center conductor is not bonded to anything... and the arrestor is def required.   You could always install a 15-50 uh coil
across the feedpoint of the OWA... which may not be effective for lightning hitting the center conductor side of the DE.   A 3rd arrestor at the top of the
tower would also work with any OWA yagi. 

##  A  35 uh coil  or 12 ga magnet wire wound on a torroid like ICE uses.... at the spg  will also dc ground the center conductor.   ICE uses the back emf
across the coil to fire the  gas discharge tube that is in parallel with it.   

Jim   VE7RF