Presumed RF Interference

David Lesher wb8foz at nrk.com
Sun Mar 5 22:03:56 UTC 2006




> Greetings:
> 
> 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? 

No...

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
grid.










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