[RFI] Apartment complex RFI associated with Fire Alarm Control Panel circuit

Jim Brown jim at audiosystemsgroup.com
Fri Mar 8 16:44:03 EST 2019

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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