10BASET Environmentals

[Carlo Milono]

There is a property called reciprocity which says if something
radiates emissions in a certain way, it also receives similarly.
Thus devices that fail FCC compliance likely are also susceptible
to external interference.

10BASE-T requires an immunity to a field strength of 2 volts per meter.
(the RF voltage measured by a standard signal test antenna)
Test sites to make this test are few and far between.
I doubt you will find any vendor beside AT&T that actually measures
this; they are very picky about such things.  I know that they tested
their HUB in an environment with ALL ports occupied at a field strength
of 20 volts/meter from 0.5 Mhz to 1,000 Mhz with no bit errors.
In addition they have installed at a radar site in a field strength of
113 volts/meter with no bit errors.

They owe this performance to taking FCC compliance seriously.

On each port they provide filtering with greater than 60 dB attenuation
to all frequencies above 30 Mhz (both common mode and differential filtering).
The result is their HUB pass FCC with more than 10dB margin.  One of the racks
tested failed by 8dB with ony two plug-ins.  

You will find that non-rack architected multi-port repeaters will most likely
survive in harsh field strenghts, as there are very few areas where emissions
can escape, therefore very few areas where emissions can enter.
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|                   Carlo Milono                                           |
|    Personal:    netcom!cmilono at apple.com   or   apple!netcom!cmilono     |
|"Sometimes I think the surest sign that intelligent life exists elsewhere |
| in the universe is that none of it has tried to contact us." B.Watterson |
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