From: John Woodgate [mailto:[email protected]]
Sent: Saturday, January 11, 2003 5:33 AM
To: [email protected]
Subject: Re: Fiber optic cable testing per EN 55022:1998 ?
I read in !emc-pstc that drcuthbert <[email protected]> wrote (in
<[email protected]>)
about 'Fiber optic cable testing per EN 55022:1998 ?' on Fri, 10 Jan
2003:
>
>Chris,
>some excellent points! My take on this is that a fiber optical cable has a
>cutoff frequency that is way above the "RF" frequencies we are concerned
>with. It just won't act as a waveguide for what we consider RF wavelengths.
>However, I think the optical cable certainly does leak a bit at light
>wavelengths.
That's a surprise; what evidence do you have?
Dave: Evidence for the cutoff frequency of the cable or that it can leak?
For the cutoff frequency the evidence is supplied by the formulas that
describe waveguides.
For the optical leakage my evidence is only empirical. I have noticed
leakage
when playing with optical fibers.
>It seems like one could perform light emissions and
>susceptibility testing. Now most of our light wave communications use
>cables. Sort of like if all RF communications was done in copper. With
>nothing intentionally radiated, and with the cables operating as very poor
>antennas, we might have no need for emission and susceptibility testing. On
>the other hand, the FCC does not regulate radiated optical communications.
>Maybe it's time to do so. With laser range finders, optical radar, IR
remote
>control, and other primitive devices we are accumulating pollution of this
>part of the EM spectrum. Reminds me of spark transmitters spewing RF over a
>wide frequency range.
Street lights are the spark transmitters of the visible spectrum.
>
>Shouldn't an optical cable with a metal sheath be treated just like any
>other cable? Hook it up during EMC testing?
Yes, ALL cables, of whatever sort, are to be connected during testing.
>
>And as you point out, where is the transition from RF to light? RF
>generation methods (such as gyrotrons, seem to peter out at wavelengths of
>1000 microns while visible light begins at 0.7 microns. There seems to be a
>huge no man's land in the EM spectrum.
>
Look up 'far infra-red'. This part of the spectrum is flooded with
thermal radiation from objects at normal temperatures. But sources and
detectors do exist.
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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