[TowerTalk] Re: getting coax into shack thru wall

[Tom Rauch]

> Date:          Thu, 28 May 1998 17:18:08 -0600
> From:          Dave D'Epagnier <DAVED@ctilidar.com>

> Shouldn't this be prevented from happening if a ground wire (or better
> yet, low inductance flat ground strap) is run from the tower base along
> side (and burried below) the antenna cables and is terminated at the
> ground rod outside the shack wall, which is then connected to the
> bulkhead?

A nice low impedance path from the tower to the house won't ground 
anything, a nice wide surface area connection to earth 
will. 

> Doesn't the lightning surge current basically get shunted to
> ground if this arrangement is used?

Only with a very good ground. It's a series-impedance shunt-
impedance problem. You want the series impedance from the tower to 
the house as high as possible, and the shunt (to earth) impedances 
as low as possible and isolated a the tower and house if possible, 
and everything in the house (power, telco, etc) to rise together with 
no in the house ground loops.

> Did you have your entry panel grounded outside the shack to a ground
> rod?

A single ground rod is next to meaningless compared to the low 
impedance of the attractive wires in the house! The lightning does 
need "ground" per se, it just needs a large conductive electrical 
"mass" to dump charges into or pull charges out of to create a lot 
of current. 

73, Tom W8JI
w8ji.tom@MCIONE.com

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