Re: Any transmission line experts?

On Thu, 02 Mar 2006 21:44:03 GMT, Geoff C <notinterestedin@xxxxxxxx>
wrote:

I have an EMI problem with a high speed system. There is a pair of wires
which are taken from a high speed driver to a high impedance electrostatic
plate which resides in a vacumm. The plate is enclosed in a metal enclosure
so does not emit, but the wires do. They are an untwisted pair about 4
inches of which is exposed, between 2 metal boxes. The signal on the wires
is about 500 volts with a 1 nanosecond rise time and about 48 khz
repetition rate. The rise time may not be compromised.

I have tried coax type shielding, but this slows down the rise time. I was
thinking the next step is a rigid conduit about 2 inch diameter, which may
have a higher impedance/lower capacitance than a coax. Also, twisted pair
is worth trying, but again I cannot afford to slow down the signal.

You could put the wires in a pipe, like Joerg suggests. Electrical
conduit, with conduit fittings on the boxes, would give pretty good
shielding too. Use some plastic disks to make separators/supports for
the wires if needed, to keep them spaced nicely relative to each other
and to the pipe. If one wire is ground, you can probably delete it and
use the conduit for the return, forming essentially a hi-Z coax...
that might actually improve risetime.

What sort of pulser makes the 1 ns, 500 volt edge? How wide is the
pulse? What's the physics?

John

.

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