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

To: jim@audiosystemsgroup.com
Subject: Re: [RFI] Apartment complex RFI associated with Fire Alarm Control Panel circuit
From: Don Kirk <wd8dsb@gmail.com>
Date: Sat, 9 Mar 2019 11:28:06 -0500
List-post: <mailto:rfi@contesting.com>
Hi Jim,

Yep, I strongly suspect the power supply, but please note that from a
liability standpoint it's very important that the owner of the
equipment/property is the one to make the decision about the solution and
if at all possible they are the ones (or one of their agents) that actually
implements the solution.

I make recommendations but always put in writing the following statement
(or something similar).
"I leave it up to you to call the shots (I am not liable for the actions
taken to solve your RFI issue since I am just some guy off the street
making suggestions to you), but always glad to provide some options to you
and let you make the decisions."

While my above statement might not hold up in court, I've been involved
with numerous residential and commercial RFI mitigation cases and am very
concerned about the liability issue.

So far in the commercial property cases I have been involved with,
commercially manufactured input power line filters have solved the RFI
problems (historically the commercial property RFI issues have been related
to variable speed drives).  I often solve residential cases using Toroid
cores based on your design notes.

P.S. Here is a fun but not really a related story.  When I was a young ham
(about 18 years old), I was causing interference to a PBX phone system in a
commercial office building right behind my parents home and I had begun
running tests with some telephone system engineers/technicians.  During
that general time period the building experienced a very large fire and
pretty much burned down to the ground, and the next thing I knew I had
insurance investigators discussing with the fire department about the
possibility that my transmissions somehow started the fire.  Fortunately I
was at my part time Zamboni driving job at the local city owned ice rink
when the fire started, so my involvement in the fire was quickly negated.

Just FYI,
Don (wd8dsb)

On Fri, Mar 8, 2019 at 4:44 PM Jim Brown <jim@audiosystemsgroup.com> wrote:

> 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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