On 3/25/2014 10:42 AM, Stan Labinsky Jr. wrote:
One point the instructor made was to look at your whole system setup
from a top down attitude (like you were the ceiling) and make sure
that all of the interconnections came from a common hub, like an old
wagon wheel. But, there should ONLY be spokes... NO WHEEL-RIM. No
cross connections from one spoke to another which would create a
magnetic loop capable of coupling both in and out.
It's difficult to make a rule that fits all situations, and that one
doesn't work all the time.
Every time I hear that rule I'm reminded of the time I was called in to
debug a noise problem on a piece of equipment some guys had built. It
was a combination digital plus analog system. The guys had heard that
rule and applied it. They ran separate ground wires for each on-card
ground area, off each card and back to a common point 2 ft away where
all the grounds tied together. The system was a total disaster. All
the cards had to be redesigned.
Hams also misapply this rule by running separate ground wires from each
piece of equipment back to the ground rod outside.
If you want a rule that works try this. Draw a diagram of your system,
which includes all the ground wires, and analyze where the currents go
and what the effect of those current will be.
If you generate specific rules, it has to apply to very specific
situations. That's one of the main problems people have wih grounding.
They have heard a bunch of rules but don't know when or where to apply
them or even if they are significant for the situation.
Jerry, K4SAV
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