[RFI] Alarm Systems and EMI/EMC

WA3GIN wa3gin at comcast.net
Sun May 10 05:09:49 PDT 2009


I wonder how close one of these units would have to be...I know some U-links 
here in VA are some 25 miles from the repeater...running 10-20 watts to a 6 
ele yagi at 500ft ASL...seems that would spray a significant signal across 
miles of area that these sensitive devices might hear and block.  The 
inverse problem is interference to the U-link receivers.  Lucky for us hams 
we have PL and DCT, etc.

What a hoot,
----- Original Message ----- 
From: "Roger (K8RI)" <k8ri at rogerhalstead.com>
To: "Dennis Vernacchia" <n6ki73 at gmail.com>
Cc: <RFI at contesting.com>
Sent: Sunday, May 10, 2009 12:54 AM
Subject: Re: [RFI] Alarm Systems and EMI/EMC

> 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.
>> Most garage door operators are also AM pulse modulation and some of the
>> cheap systems still use super-regenerative receivers.  These receivers
>> are about 5 MHz wide in bandwidth for only -3dB down.   Really broad as a
>> barn door.
> Garage door openers are notorious for failing to respond to control
> signals with signals that block them and they are not much more  than an
> wide open front end.
> 73
> Roger (K8RI)
>> Sorry that there is no easy answer but "that's the way it is".
>> Ham HF or VHF operation is unlikely to cause false alarms.   For HF
>> frequencies we are far enough away that the only problem might be that 
>> their
>> EMI microprocessor noise may interfere with our receivers.  For VHF/UHF
>> operations we may jam them for a short while, but they will normally 
>> reject
>> our FM signals since they only demodulate AM pulse coded signals.
>> I have heard of a number of instances where very high power HF stations
>> caused false alarms to the panels, but that was due to so much RF 
>> saturating
>> the remote signal wires that the ICs sensed a push button or sensor 
>> signal
>> where there really was no signal.  Using some ferrite cores and wrapping
>> the sensor wires around the core at the alarm panel fixed these problems.
>> The new microprocessors are getting very fast, have more EMI output and
>> are more sensitive to outside EMI.   Every time that Microchip does a die
>> shrink to make their processors faster, cheaper and better we get bit in 
>> the
>> butt.
>> John Kuivinen, WB6IQS
>> EMI/EMC Engineer
>> Linear LLC
>> Carlsbad, CA.
>> On Sat, May 9, 2009 at 7:52 PM, Jim Brown <jim at audiosystemsgroup.com> 
>> wrote:
>>> On Sat, 09 May 2009 12:28:05 -0700, Michael Tope wrote:
>>>> Anyone know any home security equipment dealers who are hams or who
>>>> know anything about EMI/EMC?
>>> No experience with these guys, but security systems are notorious
>>> for RFI susceptibility.  FWIW -- that 300 MHz range is commonly used
>>> for garage doors and remote control of A/V systems. I don't know of
>>> instances of RFI to the RF functions, but expect problems with  RFI
>>> to other circuitry. The usual fixes are twisted pair wiring, caps
>>> across wiring from dry contacts, and chokes to kill common mode.
>>> 73,
>>> Jim K9YC
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