> -----Original Message-----
> From: towertalk-bounces@contesting.com [mailto:towertalk-
> bounces@contesting.com] On Behalf Of Donald Chester
> Sent: Thursday, January 04, 2007 1:55 PM
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] Antenna/Tower Grounding (Lightning Protection)
>
> I use my tower as a quarter-wave vertical on 160. It is on a base
> insulator
> salvaged from a damaged AM broadcast tower, and I use 120 quarter-wave
> radials, each about 133' of #12 bare copper wire.
>
>
> I have never felt any need for ground rods near the tower. I do use them
> at
> the guy anchor points, per the Rohn catalogue/manual. Because of its
> short
> pulse cycle, I believe that lightning should be treated more like RF than
> DC
> or low-frequency a.c., so IMO radials should be more effective than ground
> rods, although I have heard claims to the contrary (without any
> explanation). I seem to recall from somewhere that the dominant energy in
> a
> lightning pulse tends to be in the vicinity of 10 mHz, so if you are
> installing a lightning protection system, radial and conductor lengths
> etc.
> should be chosen that would minimise rf at that frequency.
>
> Don, k4kyv
Hi Don,
Lightning peaks around 1 MHz but extends well into VHF. A 160 meter ground
system will take care of the bulk of it.
In some types of soils placing ground rods on the radials has shown some
improvement in lightning dissipation over just a radial system as broadcast
stations use. The idea of the ground rods on the radials is to cause arcing
deeper in the soil to increase conduction. This is most effective with very
dry soil in the area as I recall. The ground rods will also help with
conduction of the near DC component in lightning with difficult soil types
also.
73
Gary K4FMX
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