[RFI] Alarm Systems and EMI/EMC

[Michael Tope]

Roger (K8RI) wrote:

>Dennis Vernacchia wrote:
>  
>
>>Jim,
>>
>>here is  a more detailed answer from my amigo John WB6IQS who has a lot of
>>practical experience in the EMI/EMC field.
>>
>>73, Dennis N6KI
>>
>>Security Systems:
>>They are all over the place actually.  Honeywell uses 345 MHz, GE uses 319.5
>>and Linear has numerous frequencies but most of them now are on 315 MHz.
>>There are also some narrow band FM European types that are imported into the
>>US that operate on 433.92 MHz.
>>
>>The security receivers are generally superhets now, fairly broad in
>>frequency bandwidth (+/- 125 KHz) and they typically use pulse position
>>encoded AM modulation.  Older systems have super-regenerative receivers that
>>are much more susceptible to outside interference.
>>
>>Garage door operators:
>>These are all over the place.   372.5 MHz for Genie, 390 MHz for Chamberlain
>>(old frequency), 315 - 318 MHz is commonly used now for Chamberlain and
>>Linear products.
>>
>>Other systems had 288, 310, 318 MHz all the way up to 433.92 MHz.
>>
>>  
>>    
>>
>
>I would think that most in the VHF - UHF range would be easily 
>overloaded and blocked.  They may not decode due to being blocked, but 
>one being next door to a 440 system might be down most of the time. The 
>one batch of imports operates right on the section of the 440 band used 
>for repeater links.
>
>  
>

Yes, the keyless entry on my wife's camaro gets blocked up on Mt. Wilson 
above
Los Angeles where the big antenna farm  is located (all manner of 
repeaters, paging
transmitter, TV transmitters, FM radio transmitters, etc). If you don't 
have a physical
key, you are SOL to get back into the car. The keyless entry just didn't 
work at all.

I suppose a clever thief could use a transmitter to block the wireless 
sensors in a
house depending on the protocol used. If the system used a watchdog 
timer and
polled the sensors periodically it could trigger an alarm  if the 
sensors didn't respond
after some set period of time. Of course, the class of criminals who 
would be that
clever would probably be targeting a higher class of victim than me :-)

73, Mike W4EF............