OK, here's a weird one - This weekend, I suddenly had severe RFI from 4
MHz to at least 21 MHz, which took the form of a buzz-saw noise with
narrow, sharp peaks every 48 Hz. It was audible regardless of antenna
or receiver, AC or battery-powered, and was very clearly visible on the
panoramic display of my QS1R.
After a little floundering around, I discovered that my 7-year-old Dell
Dimension 2400, which has always been RF-quiet before this, had
developed a problem. At first, I suspected a failure in the line filter
in the power supply, because the noise went away when I shut down the
computer. Then I discovered that it was directly related to my video
card, an NVidia 5200. I use this card to drive two monitors, in place
of the on-board video, which was disabled. When I booted up the PC, the
noise peaks began at about 32 KHz apart, then switched to 48 KHz, and
when the displays blanked because of monitor timeout, the interference
went away.
To test the hypothesis, I switched back to the on-board video, moved one
monitor over to it, and reset the Device Manager. Noise gone. So then
I returned things to their normal places - both monitors on the nVidia
card - and the RFI went away! I can only surmise that I had a loose
monitor cable that somehow allowed sync signals to leak. Very strange,
anyway, but I thought it might be worth noting here, in case someone
else runs into it.
--
73, Pete N4ZR
The World Contest Station Database, updated daily atwww.conteststations.com
The Reverse Beacon Network athttp://reversebeacon.net, blog at
reversebeacon.blogspot.com,
spots at telnet.reversebeacon.net, port 7000
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