On Wed, 26 Dec 2007 16:17:49 +0000 (GMT), Roger Parsons wrote:
>All the supplies have an IEC connector, and I have
>found that in nearly every case, it is possible to
>replace this with one with a built-in filter.
Yes. For a line filter to be effective, there must be a very short
shield and circuit return for the filter back to the shielding
enclosure of the computer. Any exposed wiring between the filter and
the enclosure can radiate the noise.
One of the MAJOR advantages of what you recommend is that the filter
is entirely within the computer, so these leads can't radiate at
all. The disadvantage of this method is that filters built into the
IEC connector are so small that they don't usually have as much
attenuation as a larger filter. But -- the attenuation of the larger
filter can be significantly degraded by long leads between the
filter and the noise source.
Jim Brown K9YC
RFI mailing list