[RFI] Alarm Systems and EMI/EMC

[WA3GIN]

UHF links for repeater satellite receivers...434.000 - ????

----- Original Message ----- 
From: "Dennis Vernacchia" <n6ki73 at gmail.com>
To: "Jim Brown" <jim at audiosystemsgroup.com>
Cc: <RFI at contesting.com>
Sent: Saturday, May 09, 2009 11:36 PM
Subject: Re: [RFI] Alarm Systems and EMI/EMC


> 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.
>
> 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.
>
> Sorry that there is no easy answer but "that's the way it is".
>
> EMI/EMC:
> 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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