Re: automatic via grid (Re: gEDA-user: cc2420 (ZigBee) board)

["James Cotton" <peabody124@xxxxxxxxx>]

I'm not sure, in one case (floating) you have two series capacitors.
In the case of a single via connecting a short leg of some copper to
ground you have a capacitor then (inductor || capacitor) to your
lines.  Probably the former is worse since the later has much lower
impedance.   Either way the best solution is to lose the copper
island.
James

On 6/2/06, Hans Nieuwenhuis <hans@xxxxxxxxxxx> wrote:
> On Fri, 2 Jun 2006 18:46:07 -0500
> "James Cotton" <peabody124@xxxxxxxxx> wrote:
>
> > I think the problem with such an automatic approach would be that
> > right now there isn't a good way to clear off unused copper islands
> > from polygons, so that would reconnect them and make lots of little
> > antennas all over your board.
> >
>
> Leaving them floating as it is now would cause more problems IMHO. If you have an unconnected copper island next to a high frequency switching trace it would cause a capacitive coupling between the trace and the floating island. If that island has a natural resonance that lies near the switching frequency of the trace beneath it, then I have no idea what is going to happen. If that island is connected to ground I can treat it as a transmission line and calculate how big the gap between them needs to be to not being affected by the capacitive coupling.
>
> Please correct me if I am wrong...
>
> Regards,
>
> Hans