[TenTec] RFI update

[Dave Kamp, KW0D]

Al wrote:
> He brought his clone computer home that they had bought for him last fall
when he went off to school and started using it here. I have checked from
their QTH and the RFI seems to disappear completely with unplugging it --
now I need to get on the landline with him and check from my QTH. I had him
unplug it as a secondary test because when it was on it _completely_ wiped
out the AM radio in the hall outside his room with broadband noise! (BTW
the computer is an "Alaska" brand: PS says "Made in China" as to be expecte!

Hi Al!

Since I assemble all my computers (and usually they're made from
leftover-old-junque), I've run into many China switching PC supplies that
do exactly what you describe.  I've found that these supplies typically
lack bypass capacitors between line and neutral, and from both leads to
ground.  I've noticed that hard-drives in said machines also great
substantial amounts of noise-  unhooking the drive's power leads kills lots
of noise.  What I think is happening... is that they're generating enough
noise so that the power-supply re-radiates it (perhaps the noise is being
amplified through the voltage-feedback circuit), and passing it out over
the line.  Installing bypass caps at the supply's AC in socket solves most
of the problem.

There are a few other points-of-radiation... I've had some modems that
transmitted noise onto the telephone line... I use trash-cans to fix these
modems.

I've experienced neighbors who have the fancy (non-approved-by-anybody)
cases which have cool "peek-in" windows and neon bulbs for a nice
'cool-blue' glow... these windows are excellent portals for escaping RF of
every imaginable frequency, and the neon bulbs just add RF hash to the RFI
orgy.

I have six or seven (can't remember) machines in my shack, and none of 'em
generate noticeable RF on 160, 80, 40, 6, 2, or 440 (my primary op bands).
To keep some of 'em clean, I even resorted to using aluminum duct-tape to
seal up the edges, but I've improved internal grounding, sanding paint off
contact points in the case, and adding shielding to open-plastic drive bays
to minimize escaping RF.

DK  :-)
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73's from KW0D Dave in LeClaire, Iowa