[RFI] RFI to Audio System

Jim Brown jimbrown.enteract at rcn.com
Fri Nov 7 08:53:05 EST 2003

Here's a post to a pro audio list to which I subscribe.

I throught this would be of interest in view of the obvious RF
generated by the NEC plasma. The Quad cable construction mentioned is
one that uses two twisted pairs to carry balanced audio. That is, there
are four conductors inside a braid shield, with each side of the
balanced signal on a twisted pair. 

I suggested to the original poster that he replace the mic cables with
a new Belden type that has both a foil and braid shield, but also that
he contact his Canadian communications authority re: emissions from the

It should be obvious that if the NEC unit is putting out enough trash
to get into audio gear, it's probably making a much greater mess on a
nearby HF receiver

Jim Btrown  K9YC

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OK!  We have installed 11 microphones into a training center's "U"
table, with  XAP800's and everything sounds great until we turn on the
Plasma that is in the same room. We have identified that the actual
cables are
picking up the radiation from said plasma.  We are using Canare Star
cable and although this eliminates much noise compared to standard mic
the problem is additive and the noise floor jumps up with every cable
Just for fun we hooked up only 2 mics and the wrapped the cable with
"Aluminum Foil" and this killed most of the interference.

With this thought we cannot very well wrap every cable with aluminum
(well perhaps we can but looking for something more PRO looking) so we
looking for suggestions.  How about Ferrite suppression modules? Any
cable that would do the trick? Any way to trap it at the output stage
on the
XAP? Any way to filter it in the XAP DSP? HELP!!!
Any thought would be most welcomed.

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