Topband: Computer noise

[GGLL]

Cheap power supplies lack mains input filtering at the PCB, that is, at
least one mixed or common mode inductor, three or four capacitors, a
couple of resistors.

The best ones also add a similar filter between mains chassis socket and
the PCB.

These cheap power supplies run the mains straight through to the fuse,
the inrush ntc, then to the rectifier bridge. Some times they add a 2n2
disc capacitor at the HV DC output.

That's why even if you turn off (well, standby) the computer, it is
still generating noise, using your cable and mains wiring as antenna.

Even if you fix  your power supply adding these missing components,
what's going on with your neighbor's computers?.

Regards
Guillermo - LU5WE.

El 26/11/19 a las 08:41, Rodman, David escribió:
> A few ideas might be helpful here.  I was at the station over the weekend and found a significant amount of noise coming from one of two computers in the station.  Significant noise S5 at 1820.  One computer runs the cluster and 2m connection.  That was clean.  The other handles most of the remote chores and has about 15 USB serial devices attached.  Everything was off, except a battery operated transceiver attached to the receive antenna feed, the modem for the cable and my router.  One can definitely see that operating the computer, closing windows or plugging in USB devices causes the modulation on the signal to change, this isolating the source to the computer alone and possible connections to peripherals (they were all turned off by the way).  I did have few chokes available but attaching them to the USB wires out of the computer to their various devices made no improvement.  I could get more specific but need to leave for my office now.  Any ideas might be helpful and appreciat
>  ed.
> 
> 
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> David J Rodman MD
> Assistant Clinical Professor
> Department of Ophthalmology
> SUNY/Buffalo
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