[Towertalk] Grounding mast to tower

[Pete Goudreau]

n4kg@juno.com wrote:

> The HAM series rotors have ~48 bearings in the races. With the 
weight
> of the mast and beam sitting on the rotor, I expect it makes pretty
> good contact. I measured a very low resistance across a spare rotor
> with no external load on it.

OK, that's good to know.  That makes the mast have two discharge 
ground paths to the tower, one at the rotator and one at the thrust 
bearing.  The more the merrier, I figure.

> To the best of my knowledge, I've had ZERO direct hits on any of my 
7
> towers which range from 40 ft to 130 ft. in the 23 years I've been 
at
> this location.

> All towers are 'in the ground' and all feedlines go down to the 
ground
> where they are placed in shallow open trenches to the house. NO
> Polyphaser stuff anywhere.

>From what I understand, burying the feedlines directly in the earth 
creates a capacitive shunting impedance that acts to filter off the 
surge potential that arises at the point on the tower where the 
coaxes are tied off at.  Can't get a handle on how much burial length 
it takes to do the trick but it's gotta be shorter as the Kr of the 
soil goes up.  Here in the Dallas area it's supposed to be very high, 
hope it helps.

> I have seen lightning strike in a field 500 ft North of me, hit the
> power transformer next door, and split a tree across from next door.
> The only lightning damage I have experienced came in on my power
> lines.

Yikes.  I've watched the TV go zot when lightning hit the pole pig 
behind the house back when I was <mumble> years younger, quite the 
sight.  Blew that pole pig to pieces and dumped the oil over the 
yard, killing that giant rubber tree deader'n Elvis.

Speaking of power line damage, any recommendations on whole house 
suppression?  Harger sells the Joslyn stuff but I've no idea if it's 
worth the coin.

And danged if the feedlines don't have to be buried parallel to the 
incoming power lines for about 17' before they go up to the master 
ground bar on the side of the house next to the service entrance.  
I'm sure the high Kr of the soil is a detriment, causing capacitive 
coupling to go along with the inductive coupling from a surge on the 
power lines.  Can't win for losing...

> FWIW, I've NEVER read a TowerTalk post declaring "my bearings welded
> over following a lightning strike". ( Is you background in physics? 
)

I wouldn't expect them to weld in typical ham installations since the 
tower makes for such a jimdandy ground path around that constriction. 
 Giant steerable dishes should be another matter entirely since it's 
the dish that's exposed to the stepped leader and a strike would have 
to go to ground through the pedestal without being able to flash over 
to it.

And, yeah, a background in physics it is.

Thanks for the help,
Pete, AD5HD