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Re: Presumed RF Interference

  • From: Peter Dambier
  • Date: Sun Mar 05 17:36:19 2006

David Lesher wrote:


We have a client site that is driving us nuts...


I should also add some other points:
-- We have observed failures when the building had zero power, except for the UPS .....
-- The building only operates 0600 to 1800, so many failures are occurring after hours.
-- There are no RF sources in the building.
-- We are not near an airport.
-- The building is steel framed and sided -- and a pretty good RF shield --....
Given what I have described, would you think this is an RF interference problem?

Unless you have a Gigawatt radar parked next door, I'm highly dubious
that it's RF-instigated.

3 DSL routers (cisco 8x7)
1 edge router (cisco 28xx)
1 FR router (cisco 36xx)
1 patch panel
1 telco smart jack (ATM/FR circuit)
1 PBX T1 card 1 patch panel (all jacks went open on the same pair)
	Make that Terawatt...

6+ NICs

A) All these things say grounding issues. I have to wonder if
the building is fed from more than one power entrance. The blown
patch panel especially makes me think the router on one end of
the Cat5 was being fed from a different power source than the
one on the other. (Which pair was blown?) Given the UPS mention,
maybe there's a ground differential issue with it.

B) The other, less likely, path into equipment is telco. Those
mile-long pieces of copper from the CO are also called "antennas"
and they covet static. I have no idea where this location is --
are there thunderstorms around?

C) One more possibility; perhaps some piece of equipment in-house
is putting large spikes on the internal distribution. Twenty years
ago, I read of a building where large [50 HP HVAC] and small
[fridges] motors would regularly die. The high-tech gadgets of
that era, Texas Instruments calculators, would reset themselves
seemingly spontaneously. After MUCH work, they found the BIG
copier was putting nasty spikes back on the grid.

I vote A) 75% B) 20% C) 5%

You do need an EE, one prepared to look at the building wiring/grounding

That is already half of a solution:

Go for fiber. That is imune to both ground and RF problems. Avoid
ground connections between the equipment.

Replace ethernet with fiber. Break serial lines with optical isolators.

Cut the ground wire in your power cords but ground the equipment directly
to a metal frame.

Avoid ground loops: Between two computers you have a ground connection
via the powerline ground. Connect them via RS-232 and you have a second
connection via the RS-232 ground. If your power ground is bad then you
might run amperes through the RS-232 ground that results in Volts, more
than your signal level, maybe.

Peter and Karin Dambier

Peter and Karin Dambier
The Public-Root Consortium
Graeffstrasse 14
D-64646 Heppenheim
+49(6252)671-788 (Telekom)
+49(179)108-3978 (O2 Genion)
+49(6252)750-308 (VoIP:
mail: [email protected]
mail: [email protected]