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Re: [RFI] Apartment complex RFI associated with Fire Alarm Control Panel

To: rfi@contesting.com
Subject: Re: [RFI] Apartment complex RFI associated with Fire Alarm Control Panel circuit
From: Jim Brown <jim@audiosystemsgroup.com>
Reply-to: jim@audiosystemsgroup.com
Date: Fri, 8 Mar 2019 13:44:03 -0800
List-post: <mailto:rfi@contesting.com>
On 3/8/2019 10:30 AM, Don Kirk wrote:
Hi Steve,

Yes, I'm very suspicious of the AC power supply (also wonder if the battery
is OK, but I would think the system would alarm if battery was sick), and
can't wait to see what we find out.

The power supply/charger is certainly the first thing to suspect, and it should be easy to rule out if the system can run on the battery -- simply pull the supply/charger from the AC line. If that's the culprit (or one of the culprits), multi-turn #31 chokes on both AC and DC cables leaving the supply should make a big dent.

I've recently added the admonition to my applications notes that, to be most effective, the turns must run through the ferrite core IN SEQUENCE -- that is, turns wound in order around the core. A turn that is out of order will cancel another turn, significantly reducing the impedance and the raising the resonant frequency. This is equally important for both toroids and clamp-ons.

73, Jim K9YC


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