Common mode rejection filtering is generally what fixes these types of
problems. The RF is induced to all of the wiring connected to the device,
then tries to find its way to ground through the power wiring with all the
control circuitry right in the middle. You have to break up the path and
the most painless, non-invasive way is with ferrite torroids.
The 'bible' on how to use these is on this link:
http://www.yccc.org/Articles/W1HIS/CommonModeChokesW1HIS2006Apr06.pdf
The large 2.4" units are Amidon FT-240-43 (www.amidoncorp.com) and the
smaller ones, 1.02" OD, .505" ID 1.125" long work very well (and are much
cheaper) if you don't have a large connector that has to thread through the
loop.
I recently fixed a nasty problem with my lawn sprinklers using this
technique that would cause the solenoid valves to "bang" on and off when I
talked on 75 meters. I wrapped all the incoming wires from the solenoids
around a 2.4" Mix 43 core where they entered the control box, and wrapped
the power wire that went to the "wall wart" on one of the small cores.
This also fixes problems with stereo systems, telephones, cable TV, garage
door openers and more!
Ron N6IE
www.N6IE.com
----- Original Message -----
From: <W4ABW@aol.com>
To: <geraldj@storm.weather.net>; <tentec@contesting.com>
Sent: Sunday, April 22, 2007 10:00 AM
Subject: Re: [TenTec] RF gets into computer (ADT Alarm System)
I use the FT-1000MP and I get RF (I think) into the ADT Security alarm
system. It sets off the alarm when its not armed. Any thought on this?
Its only
troublesome on 40m where I use a dipole that's closer to the house than my
80m
dipole and my tri-band beam. My 80m dipole is just a lil farther away and
has never caused this effect. The firemen have been out here twice now.
thanks
Al
W4ABW
Raleigh
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