Written by: G4ZTD_Gnome

EMC. RSGB and Intruder Alarms

Here is a excerpt taken from A Leaflet on the RSGB Website Entitled:


Dealing with alarm EMC problems – Advice for RSGB members (Leaflet EMC 03)

The Full Leaflet is Available on the RSGB Website

Please NOTE (READ) the Text that is underlined in red

Ham Radio and Alarm Systems

I have had years of experience dealing with Alarm Systems and here is some information

I write this article with my views to the information contained within the
This Leaflet concerns Triggering of Intruder Alarms with Ham Radio transmissions.
The leaflet states that if
RF Immune Detectors are used as stated under BS4737, then Ham
radio transmissions will not trigger the Intruder alarm system.
But as I am a Electronic Security Engineer myself, and having spent many years with large
national Intruder Alarm companies , I find the information not quite correct.
Yes it does help to have RF Immune Detectors fitted, but even so I have proven over the
years that alarms can be triggered by RF, (An acquaintance of mine use to boast that he
parked his car outside a factory to Deliberately set the alarm system off), this triggering can
be caused by other errors in the installation that were un wittingly done when the system was
For example, I have found in numerous cases that re-running a wire from say the control
panel to the detector
in question can cure the problem, this could be caused because that
particular cable run was at the correct length for the particular band of transmission causing
the activation to act a bit like an antenna and pick up the transmitted signal and cause the
problem, thus re-running the cable in a different and say longer or shorter run would cure it.
It would of course be a good idea to use screened cable too, but most systems are not
installed with screened cable due to its increased cost.
Quite a lot of the more modern up to date control panels have to use screened cable so this
does not come in to play.
I have had a Fire station triggering the alarm system on a indoor shooting club, this clearly
was a concern to the police, again, re-running the cables and even fitting suppression
capacitors and RF chokes to the DC output at the control panel and even the detectors can
cure the problem, as it did in this case (Over 20 False activation from this club inside a 2
week period before I was called to have a look, as most alarm service engineers have no
knowledge of RF at all).
Of course it goes without saying that a well designed and installed intruder alarm system,
using the best quality materials and care in the placement of the system parts would be the
best approach from the onset and hopefully will give years of false alarm free use to the
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