Ed,
I can extend the theory of unexplained attraction to other areas.
when the screened room door has a brass surround with finger stock mounted
within, then
a) people will stand on the door frame even when you tell them not to.
b) people need to poke at the finger stock to check how springy it is!
When entering the screened room during an emission test using an active 1m
vertical rod - they need to touch the rod and blow up the Hi-Z amplifier.
When using that receiver with the 1.5mm square holes across the whole surface
- an engineer will take out the terminal screwdriver and drop the blade
through the holes - even though he has no idea what voltages the blade might
encounter!
and the list goes on...
Regards
Tim
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Tim Haynes A1N10
Electromagnetic Engineering Specialist
SELEX Sensors and Airborne Systems
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________________________________
From: [email protected] [mailto:[email protected]] On Behalf Of Price, Edward
Sent: Wednesday, December 10, 2008 1:45 AM
To: [email protected]
Subject: Cables On The Floor
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________________________________
From: [email protected] [mailto:[email protected]] On Behalf Of Gert
Gremmen
Sent: Tuesday, December 09, 2008 12:23 PM
To: Pettit, Ghery; Luke Turnbull; [email protected]
Subject: RE: Mobile Phones in EMC Labs
Of course once your gold-plated coaxial connectors wear out, and your
cables
became flat from standing on it,
you will see all kind of spurious outdoor signals in your result.
Gert Gremmen
Although I am naturally pessimistic, I am not superstitious. However, how else
to explain the near magical capabilities of a cable laying on the floor to
attract human feet?
If I lay a BNC or SMA cable (assuming 1/4" cross section by 10 foot exposure
length) onto the working area (about 16' by 12'), the cable occupies only
30/27,468, or only about 0.11% of the floor area. The typical human feet cover
4" by 12" by 2, or 96 square inches. So there are 27,468/48, or 286, places
where you can step in the room.
You would think that the odds of stepping on the cable would be 285 to 1. But
>from experience, as you talk with a visitor in the chamber, how many times
have you looked down to see one of their feet planted squarely across a cable?
Indeed, it's not all that remarkable for a visitor to managed coverage with
both feet. Or to amble along the cable as if it were some kind of guidance
wire!
Some programs attract a disproportionate amount of official (management)
visitors, and it was during one of those that I implemented my experiment with
sacrificial cables. After walking each visitor into my chamber, while
repeating the mantra of "please be careful not to step on a cable" and
pointing at a cable so that they understand what a cable looks like, I began
to notice the mathematical anomaly of non-random foot placement.
I decided to test my suspicions, so, as we moved into conducted susceptibility
testing, I laid four BNC cables around the chamber working area. (These were
cables accumulated during the radiated emission test; cables which had endured
numerous verified foot stomps.) Then I began watching the visitor pattern.
I wish I had kept accurate data, for I'm sure that I could have produced a
very important and controversial paper (that could have given me a decent
vacation for its presentation). However, I am left with only the subjective
memory of those trials. I concluded that cables have some kind of unexplained
power to strongly direct the human mind to place a foot over a cable whenever
the physical opportunity is available.
Although I never conducted further trials, I have speculated as to the
attractive mechanism that causes this. I wonder if it may somehow be related
to the technique by which cows are kept off of a roadway (cows will not cross
a couple of parallel painted stripes on the ground). True, this would be an
inverse relationship, as cables attract the foot, but I think I'm really onto
something important here.
BTW, the test cables were all later found to be in acceptable condition, and
were returned to service. I must assume that either I am being too alarmist
about the dangers of stepping on a cable, or, my management just leaves no
lasting impression on physical reality. More studies are needed!
Ed Price
[email protected] <blocked::mailto:[email protected]> WB6WSN
NARTE Certified EMC Engineer
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA USA
858-505-2780
Military & Avionics EMC Is Our Specialty
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