On 8/28/2012 6:15 AM, Hardy Landskov wrote:
> Corcom filters have a common mode choke on the hot and neutral in
> their filters but not on the green wire. What is your take on that?
> 73 Hardy N7RT
Useless if the noise is common mode on all three conductors unless the
filter is effectively bonded to the noise source by a very short
conductcor. I have a bunch of their filters here, bought surplus. Used
to own their stock when they were a public company. Good company, good
products.
One root of the problem is the power systems equivalent of The Pin One
Problem -- that is, the noise source is not properly banded to its
enclosure, so the noise is common mode on all three conductors. A simple
example: I own three Astron linear supplies, all three of which have the
same fault -- the green wire and circuit common go to the chassis lug of
an old fashioned terminal strip, which is insulated from the chassis by
PAINT. A simple test with a DC ohmeter shows no continuity between the
green wire and the chassis. These products are in violation of every
building code I know of, and should not have passed final test. And such
faults are NOT unusual. If this product was a switching power supply,
the lack of that bond would cause line cord to radiate a lot of common
mode noise!
Another root cause is what WE call common mode -- all three conductors
-- is different from what the power industry calls common mode -- noise
between neutral and green.
73, Jim K9YC
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