[BC] CAT5 EMI Filters?

[Harold Hallikainen]

I have an application where we're running 16 channels of AES audio (8 AES
pairs) over a pair of CAT5 cables. This has worked well for over 1,000
installations. However, at one installation, the system is behaving very
strangely. We've replaced the equipment, and the new equipment behaves the
same (a front panel light LED that has no relationship to the audio
flickers with the audio when very loud audio is present). We've tried to
duplicate the problem here with the same content, but cannot. We've had
the customer disconnect everything from the box except this incoming AES
audio and power. The problem is still there. They have something like 10
or more of these boxes, and only two exhibit the problem, one worse than
the other. The only thing unique I can see about the site is that there's
a cellular telephone tower across the street. The worse operating box is
the one that is closest to this tower. So, for lack of anything else, I'm
guessing that we're having problems with RF being conducted into the box
down these AES cables. I've tried ferrite beads, and that has not solved
the problem.

So... I'm wondering if anyone knows of a REALLY GOOD EMI filter for
Ethernet. I suspect it would be a good common mode filter on each pair
with a ground connection we'd connect (with a very short strap) to our
chassis. This should have an in and an out RJ45 (8p8c) connector for each
of our two cables (I'll probably need to use two filters, as I doubt a
dual exists).

Ideas?

THANKS!

Harold

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