[Elecraft] PC and video monitor QRM...

[Don Wilhelm]

Steve,

There are a thousand and one ways that RF noise can get out of computer
boxes, and I have seen some plastic cases that obviously don't even try to
keep it inside.

The most likely culprit is the monitor.  Try split cores on all connections
to the monitor itself, then proceed to all connections (to anything) at the
PC end.  Unless the PC power supply itself is generating a lot of noise,
split cores on the power cord will not help a lot.

Moving the computer further away and using extension cables for the monitor,
keyboard and mouse may help, but sometimes the extra cable lengths also act
as antennas - you might just try things one at a time noting which improves
things and which have no effect.  There is no single cure.

I am using a ViewSonic V90 monitor (running in 1024 x 768 screen size with
60 Hz refresh rate) that is not very bothersome ( I can switch it off when
hamming if I need lower noise level) , and I have the computer in an Enlight
case which I have found to be much better than many of the cheapy cases for
keeping the RF inside the box.

Try changing your monitor refresh rate and/or screen while listening to the
receiver to see if that makes a difference.  Even if it doesn't make the
noise disappear, you can hear if there is a significant change then you will
have more knowledge of either the potential cures or what doesn't work in
your particular case.

73,
Don W3FPR

----- Original Message ----- 

| Does anyone have any suggestions about possible ways to reduce QRM
affecting
| a K2, which is likely coming from my nearby video monitor and/or PC, which
| are both AC-operated?
|
| Awhile back I think I read a post answering a similar question, which
| suggested installation of split beads of some type for the ends of the
PC's
| AC supply cord.  It may have also recommended similar treatment for the
| video card's signal line which connects to the monitor; however, the
details
| of the post escape my memory.
|
| In my case, the K2 and PC (and its monitor) are separated by about 3 to 4
| feet without extra shielding of any sort, except for the RF case covers on
| the PC.
|
| The QRM is worst on 20m.  (Naturally, that's where I sped a lot of time.)
| It's not terribly bad, but it definitely seems that the PC and/or monitor
| are the QRM source.  The interfering signal is a bothersome audible AC
hum.
| It tapers off significantly (essentially disappears) on the bands above
and
| below 20m with the PC and monitor turned on.  When the PC and monitor are
| turned off, the noise diminishes on all bands (especially 20m) by about
one
| S-unit compared to when they are both turned on.
|