Topband: Desktop Power Supply Brand/Noise Question

[Tom W8JI]

> 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