On Mon, Aug 20, 2012 at 9:15 AM, Jim Brown <jim@audiosystemsgroup.com> wrote:
> On 8/20/2012 8:53 AM, iain macdonnell - N6ML wrote:
>> How do you "ground" the coax shield at the top of the tower? What do
>> you connect it to??
>
> Not a dumb question at all, and it arises because "ground" is the wrong
> word, although we commonly use it. The right word is "bond," and the
> connection point is the tower. The intent is to limit the potential
> difference between the coax and the tower, both of which are conductors.
> This matters both for RF and ligntning (and lightning is RF, not DC).
That was my point - there is no "ground" at the top of the tower
(under normal circumstances anyway!).
I think the original topic included feeding the tower itself (as a
low-band TX antenna, I assume). Does it really help to bond the
shields of other coax runs to the tower if it's being used as a
radiator? I have never actually studied loading towers as antennas,
but imagined it involves insulating the tower from the ground at the
base, which means it's definitely NOT "ground" at either end!. I could
see how the (other) coax could be grounded (really) at the base of the
tower (but not bonded to the tower). Instinctively, it seems that
bonding the other coax to a tower that's being used as a radiator
would be worse (RFI-wise), but these things are not always instinctive
(to me).
73,
~iain / N6ML
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