[RFI] M&S Systems intercom RFI where to start

EDWARDS, EDDIE J eedwards@oppd.com
Tue, 4 Jun 2002 11:31:19 -0500

> -----Original Message-----
> From:	Rob Atkinson, K5UJ 
> These get rid of (or attenuate) rf travelling on the audio 
> wires and also ac lines gg into the units.  Of course if something is 
> rectifying your sig. inside the intercoms these won't help.
	Rob, I'll have to disagree with a slight disclaimer:  If RF is coming into the unit VIA the external cabling and then getting rectified or "detected" internally, then the ferrite chokes will probably work fine.  If there is some other cabling internal that is picking up the signal, put chokes on them as well, if there's enough spare wiring/cable and they're placed as close to the detecting P-N junction(s) as possible.  If it's picked up by the PC board (fairly unlikely) then it's simply due to poor design of the board or circuits--not much to do except by a good one.

	Most of the time the audio rectification problem is caused by external cabling picking up the signal in a common-mode manner then the device can detect the signal once it's found a P-N junction in an amp or whatever.

	de ed -K0iL