[RFI] CO Detector

Roger Parsons ve3zi at yahoo.com
Thu Feb 15 20:35:07 EST 2007

I appreciate the various comments received directly
and through the reflector.

It appears that the Kidde CO monitors affected by
VE3WO's transmission are all of the kind that are
linked together. I could not find any technical
information on the Kidde website, but it appears that
the only conductor between the monitors is the power
cable. Therefore, some form of 'radio' transmission is
being used, possibly UHF, but more likely some form of
poor man's BPL :-) This would probably account for the
increased susceptibility to 160m and 80m

A rf filter on the power cable would be likely to
greatly improve the rfi situation, but depending on
the transmission method, it would also be likely to
kill the inter-unit communications. 

I presume that there is some way of fitting a filter
that meets code, but the filter would have to have (at
least) the same current rating as the breaker
(probably 15A), and be approved for fitting into
household wiring, and that is likely to be expensive.
It would also have to be mounted right by each
detector to be effective. 

I am of the opinion that the only realistic form of
filtering is a toroid through which the power cable
passes close to each detector. That would provide some
choking of the rf, and might be enough to fix the
problem without impacting electrical safety.

We are still trying to get a definitive response from
Kidde - so far all their messages have been of the
'B** off, it's your transmitter's fault' variety which
is not helpful.

73 Roger

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