[TowerTalk] LMR600 male DIN - baluns, coax and grounding

[Jim Thomson]

From: "StellarCAT" <rxdesign at ssvecnet.com>
To: <towertalk at contesting.com>
Subject: [TowerTalk] LMR600 male DIN - baluns, coax and grounding
immediately

and more than likely ANYTHING you had done to waterproof the connectors 
including water proof connectors would have failed with a direct hit. Just 
because a connector might be water proof doesn't make them a magic energy 
sink capable of thousands of joules... Grounding the shell at the top and 
bottom (and middle if over ~75') which is what I plan on doing is probably 
the best thing - and I'm sure you had that as well.

Indeed therein lies a problem - how to do this AND seal it ... at the base 
I'll have a box on the tower so that connection is inside (metal box with a 
separate connection from the inside to the tower as well). All of the 
antennas but one are hairpin matches so it will be DC grounded through that 
at the antenna and the 2 switch boxes (stacking and then antenna select) 
will accomplish two more grounding points ... the 4 element Optibeam 40 will 
need a think through.... and the rotary 80/75 dipole at the top - its 
hairpin is a coil and is not grounded ... hmmmm....

that brings up a question: Does having a balun at the antenna - assume a 
good one - allow one to ground the shield of the coax to the tower 
immediately ... i.e. say the DE is out 20' ... there is a balun there ... 
can one have another connection at the tower and have that connection shell 
grounded - does the balun make this possible? I believe I know the answer 
(and I'm trying not to get in to the QUALITY and capability of the balun) 
... but would like to hear from the experts - K9YC?

Gary
K9RX

##  yes, bond the braid /shield of the coax  at the top of the tower, middle of tower,
and bottom of tower.  Then grnd rods etc, at base of tower.  Then  bond, via  2 gauge stranded bare CU,
from base of tower, to SPG in house.   I would use a heavy duty lightning arrestor at base of tower as well. 

##  If a hairpin is used, then BOTH sides of the DE  are bonded together.... via the hairpin.  Since braid /shield of coax is
then bonded to top of tower, then  both the center conductor + braid end up   grnded to top of tower. 

##  if hit by lightning, both braid + center are bonded to top of tower..and braid is bonded to middle and also base of tower.
If lightning manages to get past all of that, it will  arc inside the lightning arrestor, from center to shield...which is then bonded to the
tower as well. Lightning arrestor bonded to tower base.  You can always install another lightning arrestor at the SPG. 

##  problems may arise, if a hairpin not used..then  only the lightning arrestor  will possibly save the center conductor..in  which case,
you may want to install the arrestor at the top of the tower....or just downstream  from the balun.  But you have to be able to get at all this
stuff. 

###  BTW, for you folks that might, by accident, TX  full power into the wrong ant,  you can always install an adjustable spark gap
across the load cap of a PI /  PI-L net, and /or the output coax connector of the amp.  I use a high swr shut down device as well.   In which case,
the adjustable spark gap is tweaked, such that it arcs slightly higher than the  2:1  or  3:1  swr shut down threshold.  The idea here was to
protect the expensive vac variable load cap in the hb amps.   IE:  set the gap so its well below the max peak V rating of the load cap used, which
is not a heck of a lot on an air variable load cap. 

##  The spark gap is just  2 x machine screws, each sharpened to a point, with one fixed, and the other moveable..and the  2 x points
facing each other.  One side to chassis, the other side to hot side of coax /hot side of load cap.   Lock nuts and angle Al used, + 
one stand off insulator required for the hot side.   The concept works good too. 

Jim   VE7RF