I simply purchased 10 Corcom filters on ebay ( I think they were $2 each +
shipping). I cut a power supply cord (universal plug type) about 6 inches
from the computer and wired the filter into a plastic electrical box with
the other end of the cord out the other end of the box. I used standard
electrical cable clamps to secure the cable to the box and added the
cheapest electrical plastic cover. The whole thing cost me about $6 each
and
I built 5 of them in a couple of hours. The boxes live behind the
computer
so the blue color appearance doesn't matter. When I purchased newer
computers, I just moved the filtered cord to the new computers.
That's OK, but be aware the corcom appears to be a typical design with
limited value for choking isolation.
See this page:
http://www.cor.com/pdf/DA.pdf
The windings appear to be linked magnetically, and the ground appears to
have no isolation. This seriously limits the effectiveness of the filter,
making it similar to beads over cords. The worse part is not having
isolation on the ground path.
The best part is the filter adds bypass capacitors, which when properly
sized either assist any added iron core cord chokes, establish a low or
controlled differential and common mode impedance, and often do a better job
than any practical choke system or core does.
I use a filter like this:
http://www.w8ji.com/images/filters/filter7.gif
It isolates and bypasses all three wires.
One of my tricks in a suburban environment was a three wire plug with two
.01 uF 250VAC UL/CSA bypass caps. No cord or anything on it. I moved that
plug around my house until I found a sweet spot that eliminated conducted
noise from the house next door. They had some battery charger that just tore
up 80 and 160 through our common sharing of a pole transformer.
73 Tom
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Topband Reflector
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