On Tue,1/27/2015 4:08 PM, Tom W8JI wrote:
The flaw in this system is that differential voltages between current
carrying wires are not measured, and anything on the safety ground
isn't measured. Noise voltage is only measured from individual
current carrying conductors to ground, and the safety ground is
grounded and not measured.
Exactly right, Tom. A common design/manufacturing defect is that the
green wire fails to make contact with the shielding enclosure, but
instead goes to common on a circuit board, which may or may not ever
find the chassis. This defect, which is the power system equivalent of a
Pin One Problem, puts noise on the green wire. You may remember that we
corresponded several years ago about Astron power supplies, in which a
very common defect is that the green wire is soldered to the mounting
lug of a terminal strip, which is insulated from the chassis by paint.
The same mounting lug is the point where V- is bonded, so it never finds
the chassis either. AND, wiring for both V- and the green wire act as
antennas for both TX and RX.
I have long suspected that similar defects are at least partially
responsible for noise conducted onto coax and AC lines from consumer
products of all sorts.
73, Jim K9YC
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