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Re: [RFI] Smoke and CO alarms

To: RFI@contesting.com
Subject: Re: [RFI] Smoke and CO alarms
From: Ed Richardson <ed_richardson@shaw.ca>
Date: Mon, 01 Oct 2007 20:19:43 -0500
List-post: <mailto:rfi@contesting.com>
I was plagued by a similar problem, setting off the hardwired, monitored
smoke alarm when operating on 80m and 15m. Too solve the problem, I had
to follow a couple steps. 

First attempt was to install ferrite chokes on the smoke detector power
and sensor lines as they entered the alarm panel. This helped a lot but
did not totally cure the problem.

Second step, with the assistance of the alarm company technician, I
installed a couple .01 uF caps across the end of line resistors. It
appeared that the RF was strong enough that with the long leads, a
significant voltage drop was being seen across these resistors. The
alarm panel sees the voltage drop as an alarm and sets off the siren and
calls the alarm company etc. 

Together these two procedures have eliminated the problem. 

For the simple battery powered devices, I am not sure where to begin. A
schematic would be my first thought. There must be some component that
could benefit from some bypassing. 

As a word of caution, modifying a smoke or CO2 detector could cause
problems in terms if liability or insurance if something terrible was to
happen in the future. If the insurance company learned that you tampered
with a device and it failed to produce an alarm, I am sure they would
try to put the blame on you and claim the insurance void...

For that very reason I had the alarm technician test the system before
and after the modification and put it in writing that the system was
tested and found to be working.

Hopefully someone on here knows a product line that has better RFI


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