[TowerTalk] Computer RFI

[W2RU - Bud Hippisley]

An alternative solution is to remove the power supply from the PC and 
take the cover off (usually four screws and a label that pretends to be 
a seal).  Inside you will find two wires from the hot and neutral sides 
of the AC line input socket to lands on a printed circuit board.  You 
need to get a foot or so of ordinary lamp cord (zip cord) and thread as 
many turns through a Type 31 or Type 43 toroid as you can -- typically 
you'll want to find one with about an inch I.D.  Replace the two 
existing wires with the zip cord / toroid assembly, and add some 0.001 
uF bypass caps from each of the two terminals on the AC line socket to 
the chassis ground at the socket.

In some cases the PCB silk-screened markings will actually show where 
the toroid and other filter components used to be located on the board!

Aren't cost improvements wonderful?

There's also a third approach.  Contact the manufacturer of the PC or 
the power supply and advise him that the unit is not meeting FCC specs 
for Type B (home) emissions.  Offer him the opportunity to send you a 
cleaned up supply before you notify the FCC of his failings....This 
sometimes works with the smaller importers of these Chinese supplies.

A couple of my PC supplies were originally so trashy I could hear them 
with a receiver out near my tower!  (I threw that in to keep this 
relevant to TowerTalk....)

Bud, W2RU

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Clive Whelan wrote:

>If you are saying that the noise does not quit when you
>switch the computer off, but DOES so when you unplug from
>the wall, then it's open and shut, and is due to the switch
>mode power supply....The cure is pretty straightforward, viz replace the PSU,
>which is a screwdriver job. You will of course need to get a
>recommendation from someone who knows a clean third party
>PSU.
>
>-----Original Message-----
>Jim Miller WB5OXQ
>
>I am getting a lot of interference on the low bands from my
>pc but from 20 meters and up there seems to be none.  The
>noise is very wideband and does not stop unless I unplug the
>computer from the ac outlet.
>  
>