RE: Filtering and RF grdg of high powered coils: was: Grounding my TC

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Original poster: "Steve Conner" <steve.conner@xxxxxxxxxxx>

>this is the second time that I've had to call the alarm com-
>pany to fix my  alarm system after firing my coil at the very
>lowest possible input power to make it fire at all.

I think alarm systems are a nightmare. They have hundreds of yards of
unshielded cable that gathers up RF and funnels it into an unshielded
plastic box full of microprocessors :-o My old ham station used to set off
my neighbour's burglar alarm whenever I used RTTY and that was with only 100
watts. The only cure I found was to avoid using RTTY when he was out. And
you have a 1 megawatt (peak) spark transmitter...

You might like to try putting those clamp-on ferrite suppressors onto all
the cables that enter or leave the alarm control box. I think you can buy
them from Radio Shack in the US. (Maplin here) However this won't protect
the sensors. PIR motion detectors have very sensitive electronics inside.

It might also be worthwhile checking your toroid and breakout to make sure
all the metalwork is solidly connected together. Little sparks jumping
between pieces of metal generate lots of high-frequency crud. (Your garage
door might have a fair voltage induced on it so check the garage door is not
sparking to the frame)

Or you could get rid of your alarm system and get a guard dog- they'll stand
any amount of RF short of a direct hit :-D


Steve Conner