Shared Knowledge

"AT&T Home Security System - Eliminating False Alarms Due to Radio Interference"

18 January 2009

This is probably only applicable to amateur radio operators (hams) who have an AT&T home security system installed but from Roger Shultz comes a solution to eliminating false, monitoring company phone calls, when operating on 80 or 40 meters. Note that if you are receiving phone calls from your monitoring company and it is a false alarm, you may want to consider taking measures as defined below.

As reported in other sections, when the CC receives a signal from any active element in the system, it decodes that signal and raises the applicable zone line to +12VDC. When the zone line goes to +12VDC, this triggers the AT&T digital communicator to dial the stored number of the monitoring company and report. Unfortunately, an amateur radio transmitter can introduce enough radio frequency interference (RFI) on a zone line as to cause the digital communicator to falsely dial the monitoring company.

The solution? Install .01 mFd capacitors on each zone line, shunting any received RFI to ground (negative side of 12VDC supplied to digital communicator).