I ended up wiring in some CorCom line filters that I had around the house
and it completely removed the noise. I've used these supplies for years
including being used on a number of different DX-peditions....they are
light and fairly small. This fix worked just great.
I can't understand why throwing some ferrite beads at a problem, or changing
the supply, are the only two solutions.
Many times, if not most times, a few .01 uF line voltage rated bypass
capacitors are significantly better than a sting of cores, or a winding
through cores.
In the first place, we can add cores over power cords or other
multi-conductor cables until the cows come home, and it won't change
differential mode suppression. Differential excitation can be as bad as
common mode excitation, because lines are always unbalanced some small
distance away from the noise source.
There was a computer about a mile or two from me, perhaps further, and it
was exciting the telco and power lines in differential mode. The lines acted
like transmission lines with fairly low loss, and the noise went for miles.
I bought the lady a lighting protection outlet strip with internal bypass
capacitors, no series beads added, and the problem vanished.
There are two excitation modes that cause problems, and beads across
multiple conductors don't do a thing for differential mode. Beads also have
a varying effect on common mode, because the common mode impedance of the
system has to be very LOW in comparison to bead series impedance in order
for beads (or any series impedance) to have a large effect. A high CM or DM
system impedance, or an uncontrolled impedance, is what causes us to have
poor results, or what makes a system require astronomical and/or impractical
choking impedances.
I solved all my computer issues 15 years ago. I built a line filter box that
has individual series chokes on each power mains lead, and bypasses the
line source side of the lines to the safety ground and box ground. The
computer side ground pin floats from the chassis by a high current RF choke,
and the socket is bypassed only to the cord's safety ground on that side.
In conjunction with proper shack wiring, enclosures, and RF cables, I can
use any supply or computer I like.
A few hours proper work saved me years of problems.
Some line filters, by the way, are not built correctly. Some fail to address
the common mode, others fail to address the differential mode. But the
poorest and most unreliable system of all is the system that just throws
beads at a problem.
73 Tom
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Topband Reflector
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