[TowerTalk] RF Surge Suppressor at Base of Tower or Shack SPG or Both ?

[Lux, Jim]

On 10/13/21 3:31 PM, Jim Brown wrote:
>
> 5) As to buried coax, the skin depth of soil can be pretty great. I've 
> seen estimates from W8JI on the order of 60 ft at 2 MHz, probably a 
> bit less at higher frequencies, and highly variable with soil types. I 
> wouldn't count on burial a few feet to provide shielding from 
> lightning induced currents, which can be monstrous. 


Certainly, lightning currents will be induced on the *outside* of the 
coax that's buried.  And if you've got multiple conductors buried, 
they'll wind up with different currents and voltages. Skin depth in 
copper (i.e. the coax shield) is about 2.5 mils (0.06 mm) at 1 MHz.  
RG-213 shield is about 15 mils thick, so you've got more than the 
traditional 5 skin depths, but, well, it's not a copper pipe, after all.