[600MRG] (Fwd) Re: [RFI] Smoke-alarm Interference - not TVI but SAI

[Edward R Cole]

I have been using twisted pair harvested from cat5e cable for dc 
hookups in the presence of RF for while.  Adds a little rejection to 
RFI thru dc contacts to sensitive ckts.  I also add a couple ferrite 
beads at the feedthru caps.

Many years ago (1964) when a student employee at college I was tasked 
with installing radiation alarms at the cyclotron building outside 
entrances to the shielded area that held the "atom smasher".  All was 
fine until they fired up the 40-MHz high-power oscillator that drove 
the electrodes of the cyclotron (with mega-watts).  ALL the generic 
alarms went off together causing a minute of panic, until it was 
realized as RFI vs ionizing radiation (one of the rooms had 300 curie 
tank of radium in it).

So the next thing I was tasked was with installing ferrites and 
bypass caps.  The alarms were powered by individual power supplies 
from ac wiring in the building (which made a nice 40-MHz antenna).

The "RF pump" oscillator was interesting as it used waveguide to 
drive the cyclotron.  Can you imagine how big waveguide is at 
40-MHz?  You can walk thru it.

73, Ed - KL7UW

At 10:21 AM 10/22/2014, Kenneth G. Gordon wrote:
>Another one...
>
>Ken W7EKB
>------- Forwarded message follows -------
>Date sent:      Wed, 22 Oct 2014 10:26:15 -0700
>To:     rfi at contesting.com
>Subject:        Re: [RFI] Smoke-alarm Interference - not TVI but SAI
>
>
>On 10/22/2014 7:47 AM, Mike Ryan wrote:
> > ANY amount of HF rf would set it off.
>
>The alarm industry is notorious for ignoring RF susceptibility. When the
>RF is coupling via wiring from dry contacts in the form of a simple
>on/off, a cap across the input of the receiver will generally fix it. If
>the interconnect is sending data, a cap will likely kill the data. Mfrs
>often tell their users to use parallel conductor wiring for
>interconnects, which makes them more susceptible to differential mode
>RFI. They SHOULD be using good twisted pair, which strongly rejects
>differential mode coupling.
>
>------- End of forwarded message -------
>
>Kenneth G. Gordon W7EKB
>
>"Courage is being scared to death but saddling up anyway."--- John   Wayne
>
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73, Ed - KL7UW
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