[Elecraft] Computer-noise

[rrkrr]

Martin,
Filtering the power line is the right thing to do.  The broadband 
switching noise from the power supply  gets onto the power mains and 
radiates from them.  (It seems there's been a similar discussion about 
BPL lately....).  However, all the ferrite clip-on does is try to force 
the high frequency transients to be differential on the power line.  
This reduces the radiation some, but doesn't really reduce the noise 
power on the line much.  Corcom makes power line filters that will 
help.  You can get their products from Digi-Key or Newark Electronics.  
Another option is to replace your computer power supply with an 
"Instrument Grade" unit. This will cost  more than an odd integral 
multiple of the price of the average low budget computer power supply, 
but you will be amazed at the reduction in noise.  I've had good luck 
with the brand "Enermax".  There are others. ( I have no personal 
interest in either Corcom or Enermax)

I work at Georgia Tech Research Institute, where just about every 
employee has a computer on their desk, and where there are network and 
email servers, routers, uninterruptible power suppplies, etc. 
everywhere.  The noise from all the switching supplies radiating from 
the power lines in the buildings has gotten so bad that we have had to 
build screen rooms with power line filters in order to prevent 
corruption of critical signal measurements by power line noise!  Our 
office building is within metro Atlanta, but it is just about impossible 
to listen to any local AM broadcast radio station in any of our 
buildings because of this power line noise problem.

I learned by disassembling several  low cost computer power supplies 
that the foreign manufacturers simply do not install the filtering 
components required to keep the power lines clean.  Looking at the 
circuit board of one of these cheap supplies, you'll usually find 
several silkscreened input circuit component locations marked "L" 
bypassed with a wire, and items marked "C" left open.  While the 
original design included these filter items in order to get US FCC type 
acceptance, they are left out of the mass produced product to save a few 
cents per supply, and no one ever checks when thousands of these come on 
shore in shipping containers..

Bob
WB4TGG

Martin wrote:

>Hello elecrafters,
>today i wandered through the house carrying the battery-powered K2
>with a vhf antenna connected to ŽsniffŽ for the noise i have on 80 &
>160m. On 160m, snap-on ferrites on 2 network-cables completely
>removed the carriers. On 80m the problem seems to be more
>difficult: The noise is produced by one of 3 Computers in my buro,
>even when it is switched off. The other computers are quiet, also the
>one in the shack.
>The noise becomes a lot stronger when the computer is on, but only
>completely disappears when it is disconnected from the mains.
>Its a raspy carrier slowly sweeping up and down the band.
>
>Any ideas where to start? A snap-on ferrite on the power-cord
>helps a little, but not much.
>
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