USB cautionary tales
mo at ccr.org
Fri Jun 15 09:28:39 CDT 2012
This is a pretty good intro-level article.
The pix of the crispy critters at the end of the article are worth the
price of admission.
This is germane to Hams because some of them (nobody around here, of
course - big grin)
run yer HIGH POWER, especially on the Squawk Radio long waves. If some
of that RF got loose
in the shack (radiating coax shield, high SWR, etc), USB cables could
look mighty inviting.
This also applies to Ethernet, although not quite so bad. In the early
days of Ethernet
at Xerox PARC, when they were using CATV coax and cable taps, the shield
cable was tied to building ground. This was no problem at first. Then
the cable into another building and followed the same rules. OOPS!
The local grounds in Building A and Building B were now tied together
the coax shield. When Building A took a very-near miss lightning strike,
equipment on the Ethernet in Building B exploded before the cable had time
to burn open at the entrance to Building B. That harsh lesson on the
of "ground bounce" was taken to heart and is why the original DIX
standard required transformer-coupling, and the isolation requirement
remains the case to this day.
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