________________________________
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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