[TowerTalk] Ground System

[Gary Schafer]

> -----Original Message-----
> From: towertalk-bounces at contesting.com [mailto:towertalk-
> bounces at contesting.com] On Behalf Of Dick Green WC1M
> Sent: Monday, August 13, 2007 10:32 PM
> To: 'K4SAV'; towertalk at contesting.com
> Subject: Re: [TowerTalk] Ground System
> 
> > Coax shields won't take very much current before they melt. A large
> ground
> > wire will lower the impedance between the tower and the common point
> > ground, as well as reduce the voltage drop for these low frequency
> > components.
> 
> RG-8 style coax shields won't take much current before they melt, but as I
> mentioned, I have two runs of 1-5/8" heliax running between the tower and
> shack, connected to the tower ground system at one end and the SPG at the
> other end. For those not familiar with this type of cable, the outer
> conductor of each run is nearly 2" in diameter -- basically a big,
> flexible
> copper pipe with a lot of surface area. I don't have a spec on the
> thickness
> of the copper, but it's probably on the order of 1/64". The resistance per
> foot is .14 ohm/1000 feet. I don't know the current handling capacity, but
> the power rating is 310 KW. Although the heliax is jacketed, and therefore
> won't conduct a surge to ground like a bare wire in the trench, it seems
> to
> me that the two large copper tubes present a much more inviting path to
> the
> SPG than the bare wire. True or false?
> 
> 73, Dick WC1M
> 

There will be a great amount of capacitive coupling to ground provided by
those long cables even being insulated. A great deal of lightning energy is
connected to earth by capacitance in any ground system. Yes a DC (bare wire)
connection would be better and help more with the low frequency energy
coupling.

73
Gary  K4FMX