[TowerTalk] station grounding question

[Martin, AA6E]

The complete solution is to put your station entirely in a shielded
room, with conductors on all surfaces.  All power and antenna leads
enter through surge suppressors, etc.  Lightning currents pass on the
outside of the room to ground.  Inside, there are no fields, and you
don't have to worry much about interior grounding.  This may be the
only reliable approach for complex installations.

The hard part about lightning protection is working in and around
existing residential structures.  My "tower" is 20 ft high, sitting
squarely on my roof, for example.  It is connected to our lightning
rod system, but it's clearly not the best design for lightning
protection.

73 Martin AA6E

On 11/29/05, gm3sek at ifwtech.co.uk <gm3sek at ifwtech.co.uk> wrote:
>
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> >
> >
> >> If you want the best isolation of equipment, a separate ground lead from
> >> each piece of equipment or rack of equipment would be run to the single
> >> point ground plate. That would eliminate currents being fed from one piece
> >> of equipment to another.
> >
> >Only if each lead is the same length and the same impedance/reactance.
> >The rapid rise time for the current and the wide range of frequencies means
> >only a slight difference in "electrical" length could cause large voltage
> >differences.
> >
>
> Good point. As our stations grow larger and more complex, the 'star' grounding method becomes
> less and less realistic. You wind up with connections of very different lengths running back
> to the ground plate, and the whole star design is undermined by cross-connections through
> signal cables. That is exactly the situation we're trying to avoid.
>
> The same is true of the busbar layout, because most busbars don't have a low enough inductance
> to prevent surge potentials developing along their length.
>
> At some stage, we have to step across to a method that is aiming to create one large
> groundplane. Unlike a star, the aim of a groundplane is to short-circuit all potential
> differences anywhere across its surface. That then allows you to add interconnections freely.
>
> Again this will be far from perfect, but it is practical to stand all the rigs on a really
> wide metal sheet, running the whole length of the table. Each piece of equipment is then
> bonded to the sheet with the shortest possible length of wide strap. In order to work anything
> like a groundplane, the sheet needs to be REALLY wide... I'm thinking of at least 12-18in,
> almost the full front-back depth of the rigs. If it still looks anything like a busbar, it
> isn't wide enough yet :-)
>
> Likewise the sheet should be bonded back to the single-point entry with a wide strap, ideally
> acting as a conduit for all the incoming cables.
>
> As I said, it isn't perfect, but I think it would be better than a star layout that has been
> fatally undermined by cross-connections and unequal lengths of ground leads.
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> 73 from
> Ian GM3SEK
>