Mike,
My bet says it is power supply related, but either way you have to narrow
down the exact source of the problem.
Start with everything up and running. Power down printer, monitor, etc one
at a time noting what makes the interference go away. Then start pulling
cables one at a time. Mouse, keyboard, monitor etc. By this time you will
have a good idea of which subsystem is causing the problem. Try adjusting
brightness and contrast controls on the monitor as these will affect video
noise being created in the monitor. Switching power supply noise and video
are the number one culprits.
Power supply noise has a low raspy sound which may also have an AC hum to
it. It will repeat at multiples of the switching frequency which is usually
around 100 kHz but can be higher or lower depending on the design.
Video noise usually sounds like a high pitched AC hum. Sort of like a
police whistle. It will vary in tone as the screen refreshes, mouse moves,
or windows are opened and closed. It will be repetitive in frequency but
that will depend on resolution and video clocking. A blank DOS screen will
be the most quiet.
Once isolated you can begin to apply the ferrite beads on the proper cables.
There are also commercial filters for AC receptacles, I/O ports, etc.
Remember to place the beads on the cable at the source end of the problem,
they won't do a lot for video noise generated in the monitor if you place
them at the computer end of the cable.
These add on fixes are the most convenient. There are other fixes that can
be applied that are more effective but will require some internal work to
the computer which I do not recommend if you are not comfortable with
surface mount and voiding your warranty.
Earl
N5TU
At 06:20 PM 5/5/98 +0100, you wrote:
>Hi and thanks for reading this.
> I have a problem with computer noies on the low bands her in just
> certain
>portions of the band.I am running a p100 here and it real bad on 40
>meters.It peeks at every 25 kz of the band.Is ther anyway to stop this
>besides turning the computer off?Thanks again Mike K5QF
>
>
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