Poul-Henning,
[email protected] wrote on 01/07/2009 05:56:19 PM: > In message <OF56303512.93B049A7-ON85257537.0079CDE3-85257537. > [email protected] > y.com>, Joseph M Gwinn writes: > > >Could be a differential TX and RX. I recall that they send a RS422 signal. > > Depending on the speed, RS422 works fine with transformers. Yes. It would be 10 MHz or 20 MHz, depending on coding. Or 5 MHz, so the transitions are at 10 MHz. I don't recall, or never knew. > >I imagine that the shield is grounded at both ends, if only for > >safety reasons. > > That is actually a very unsafe practice, unless there is another > much thicker and reliable ground connection between the two domains. There is a very heavy grounding grid, and such systems almost always ground the (outer) shields at every connector. > But you should never let the screen float in the far end, you should > terminate it with a 10M resistor and a sparkgap in parallel to the > local ground. > > The resistor takes care of static electricity and the sparkgap will > do lightnings. I've done such things, but with a 100 ohm resistor (and a safety ground to ensure that the voltage doesn't get too large. But this was a lab lashup. > >If I had it to do over, I might well use multimode fiber. > > Yes, never roll copper more than 100m or between buildings if you > can get away with installing fiber. > > >The solution was to use triax. The > >outer shield was grounded at both ends. The inner shield and center > >conductor together formed the ethernet media. The inner shield was > >connected to the outer shield in exactly one place. > > That's technically speaking not triax, that's double shield. Triax > would have the conductors and one shield. No, I think that's twinax: <http://en.wikipedia.org/wiki/Twinax_cable>. Triax is a center plus two concentric shields: <http://en.wikipedia.org/wiki/Triaxial_cable>. The terms are very similar. > But yes, double shielding works great, provided you don't have morons > with screwdrivers around. > > Poul-Henning > > (Who once lost all ethernet interfaces, the access control system > and a few minor computers when a moron first created and then cut > a 600+ A ground loop). Was there a big bang? What was the source of the 600 amps? Joe _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
