[RFI] Fwd: Alarm Systems and EMI/EMC

[Roger (K8RI)]

Dennis Vernacchia wrote:
> ---------- Forwarded message ----------
> From: Art McBride <kc6uqh at cox.net>
> Date: Sat, May 9, 2009 at 11:23 PM
> Subject: RE: [RFI] Alarm Systems and EMI/EMC
> To: Dennis Vernacchia <n6ki73 at gmail.com>, John Kuivinen <wb6iqs at att.net>,
> Kerry Banke <kbanke at sbcglobal.net>
>
>
>  Sensors typically operate on 315, 319.5, 345, 418 and 433.92 MHz. Each hour
> they send a supervisory transmission to say they are in service.
So a simple carrier at the wrong time could/would put the enter system 
out of commission for up to an hour?
>  Only the
> 433.92 frequency falls in the Amateur Radio band.
>
>   
My take on a lot of these systems is they could easily be 
overloaded/blocked with medium to strong signals well out from the 
amateur band due to the low level signals they normally use. 
> Expected points of entry for HF operation are at the panel, the Phone Line
> and the Power line. No surprises here and no wires to sensors hence less
> pickup of EMI. Should be much better than the wired type, and the phone and
> power line are in one place and easy to filter using standard components.
>
>   
I agree they should be better than the wired type, particularly when or 
where HF is concerned, but the VHF/UHF comes with a different set of 
problems. There is an old one about a mile from me that is right in the 
440 band. I've never paid much attention to the actual frequency as it 
just shows up as a "pop" ever 30 seconds to a minute. It can also be 
heard on the 2-meter band.
>
> Digital encoding with CRC check of serial data all but eliminate a false
> signal. (1/16 e6 chance)
>
>
>   
I would think overloading of the new units would most likely produce no 
signal from a true positive.

73

Roger (K8RI)