USB cautionary tales

Mike O'Dell mo at
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 
of the
cable was tied to building ground. This was no problem at first. Then 
they extended
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, 
all the
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 
destructive power
of "ground bounce" was taken to heart and is why the original DIX 
Ethernet 10-megabit
standard required transformer-coupling, and the isolation requirement 
remains the case to this day.

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