Presumed RF Interference

Jon R. Kibler Jon.Kibler at
Sun Mar 5 22:37:13 UTC 2006

David Lesher wrote:
> > 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.

> 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%

Re: C, I think (hope) the power company has already eliminated internal power spikes. The have recording monitors on both the building feed and on the distribution panels for the office area. The only thing in the building that pulls more than 20A is a couple of 4 ton A/C units and the server room UPS. 

Re: B, The "telco lines are antennas" concept is why we were thinking RF. The location is in the SE US, but no thunderstorms this time of the year.

Re: A, I don't remember which pair was blown. Since it was a new patch panel (less than a week old) we initially wrote it off as a manufacturing defect -- but now we are not so sure. Everything in the server room -- which includes PBX and all networking equipment -- is on a single UPS. The CAT6 in the building terminates at PCs. Each PC has its own separate UPS. A floating ground or ground current was among my first thoughts -- but a few things about it bugged me and made me look elsewhere:
   1) How could a bad ground cause DSL line noise that ia inaudible? Also, the noise is on the telco side, not the LAN side.
   2) Why would it be blowing DSL routers that are isolated from the LAN by a switch and another router? And, all of this equipment is in the same rack, on the same ground, and on the same UPS.

Well David, thanks for your thoughts. I guess the next step is to find an EE that want to tackle this challenge without asking for an open-ended purse!

Jon Kibler
Jon R. Kibler
Chief Technical Officer
A.S.E.T., Inc.
Charleston, SC  USA
(843) 849-8214

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