[Lowfer] Computer noise

Mon, 14 Jan 2002 18:31:20 -0500

Monitors typically have a Horizontal Sweep rate of
between 31 and 69 KHz and the Multisync models can
automatically find what sweep rate your computer, or
more precisely, your video card generates.  The rate
depends, as others have said, on the screen resolution
and corresponding Sweep rates -- which can usually be
manually set from the Windows Control Panel in degrees
that depend on the individual video card.  

The sweep circuits of the monitor are quite powerful
and radiate lots of harmonic energy (Sawtooth waves -
several watts).  Sometime you can see a major drop in
the level of the interfering signal when you turn off
the monitor -- but there may be some residual from the
video card (lower power) itself.  In any case it's a
good test.

Another test to see if it's the monitor is to power up
the computer from a dead start while listening to the
receiver.  The computer usually starts up in plain old
640x480 VGA mode while it's doing startup housekeeping
and then, when windows comes up, it changes to a higher
resolution. There's a significant difference between
the sweep rates for VGA and the higher resolution
modes. If the interference isn't there during the
bootup housekeeping process, and starts when the
monitor goes into higher resolution windows mode,
you've got the problem cornered or at least identified.

Click Start>Settings>ControlPanel>Display and then
click the Settings Tab and the Advanced button on the
lower right followed by the Adapter Tab.  Hopefully you
will be able to mess with the Horizontal Refresh rate
which will rubber the monitor frequencies around a
bit.  Try a few and see what it does to the receiver.
Hopefully your monitor will be able to handle the
variations -- most modern ones can. Windows will switch
back to the previous mode in about 15 seconds if you
can't read the screen.  This kind of switching can
really mess up very old (single sync) monitors, but
they probably deserve to be smoked anyway.

You can also click Start>Settings>ControlPanel>Display
and change the resolution of the screen.  This will
make the display card change the Sweep rates and should
show up on the receiver.  Sometimes you have to reboot
the computer to fully see the results of a change, but
it's a worthwhile process.  

I managed to totally quiet down my LF machine by
following the above process'.  All of the above was
done under windows ME, but should be very similar for
other versions.  If you have a Mac, Sinclair, TRS-80 or
a CPM machine, all bets are off. 

Your mileage may vary.  I can not be held responsible
for any problems you might encounter with the above
recommendations, but will be happy to take credit for
any positive results.

And of course it could be a harmonic of the little
switching regulator in your main power supply......

Good Luck

Rye K9LCJ
Springfield, VA

[email protected] wrote:
> 
> Anyone have any luck or magical remedies to take care of RF noise from a
> computer short of turning it off? I found that I hear "signals" generated
> from my computer in signal strengths of S-9 or better...which wipes out much
> of the LOWFER band and pretty much keeps me from using any software to pick
> up the LOWFER stations.
> 
> Bob Carter
>  Operations/Engineering
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