[SI-LIST] HF return currents + RF energy to EGND = "Hot-box"

Hello All,

Yet another EGND vs Logic GND question.


Is it true that HF/RF energy can be injected directly
onto the Chassis if you tie Logic GND to EGND back at
one point on a PCB card? And that this energy makes
the chassis a "HOT-BOX" making the system more
susceptible to noise and high freq radiation?  Also is
it true that it makes the Logic ground more
susceptible to lightning strikes potentially causing
damage to circuit devices?

*  If one ties Logic GND to EGND at a single point on
a card, do you tie it directly or do you use a
filtering circuit between Logic GND and Earth ground?


My problem with isolating or floating Logic ground is
that, it does not have a good reference to a near zero
volt potential.  Logic ground should be forced to a
zero volt potential for signals to have the
appropriate zero (GND) volt reference. I would
appreciate any comments on this issue, please let me
know if I am wrong and should go with isolated or
floating ground.

I will continue to browse through the archives to see
if I can find something relevant and useful.

Thanks,

-- Sal Aguinaga
-- 3Com
-- Rolling Meadows, IL




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