[CQ-Contest] Computer RFI

Mark Beckwith n5ot at n5ot.com
Wed Dec 28 12:39:18 EST 2005

Various comments about shack RFI and computer monitors:

> I found that switching video modes, even just
> the refresh rates, can make a big difference.


> The best fix is to use an LCD monitor
> instead of a CRT.


> changed it out for a LCD monitor this fall
> and all the interference went away!

For some reason, when I switched to flat screens I noticed an improvement 
too, but lately the RFI grunge is creeping back.  I believe the problem is 
lack of line filtering in the rectangular black switching power supplies 
that come with the flat screens.

To start, tho, I cleaned up a BUNCH of computer RF CRAP in my shack by 
adding commercial AC line filters to the computers themselves, at the 
recommendation of W0UN et al.  Go look at eBay auction # 7575746113 to see 
what I'm talking about - these come in various current ratings, but all 
pretty much look the same.  They come up on eBay all the time and are pretty 
cheap and easy to install.  You basically open up the power supply and 
de-install the standard 120VAC jack and stick this in its place (hopefully 
it fits) and button it up and your AC is now filtered.

Anyway, I had also noticed the sound of the RFI changed with the colors 
being projected on the monitor (I never tried changing refresh rates). 
Naturally, switching the monitor off and on and hearing the noise go away 
and come back can prove it's the monitor.

Which brings me to my most interesting latest bugaboo - the noise with the 
LCD monitors - the noise wouldn't go away when I switched off the monitor, 
but it would change in sound and frequency.  It WOULD go away when I 
unplugged the rectangular black outboard switching power supply.

So anyway now I'm trying to figure out how to get these little eBay filters 
in-line with the rectangular black outboard switching power supplies. 
Klooging is always an option but elegant is preferable.  Does anyone know if 
you can buy computer power cords with line filters built into them?

Mark, N5OT

PS I have a large pile of these filters - I think I bought a lot of 38 of 
them on eBay and have used about 6.  I could part with some of them for $2 
each plus shipping.  Details on request. 

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