[RFI] Sudden Computer Racket

Pete Smith n4zr at contesting.com
Fri Jun 25 04:31:13 PDT 2010

Yesterday afternoon I suddenly experienced a violent increase in the 
noise on my receiver.  Looking with a spectrum analyzer program and a 
broadband SDR, I can see that the noise consists of peaks at 48-KHz 
intervals, and many smaller "carriers" in between which effectively 
raise the noise floor about 20 dB.  On the lower bands the band noise 
effectively covers the "stuff", but on the higher bands it is distinctly 
audible in CW and SSB modes as a closely-spaced series of signals.

Now here's the weird part - I turned off my pain shack computer and the 
noise disappeared.  This computer has been in place for 5 years, never 
with this problem.  It continues to operate fine, in all respects - it 
just makes noise.

I am assuming that the racket is from the power supply -- although it is 
suggestive that it began shortly after I re-activated a M-Audio 
Revolution sound card to try interfacing it with my new K3.  Anyhow, I 
disavled the Revolution in Windows XP, and the noise is still there.  
Would it be worth physically uninstalling the sound card to see if 
perhaps it is a Dc-to-DC converter on the card that is making the fuss, 
and has not been turned off by the operating system?

If it isn't something involving the sound card, then I assume it's the 
power supply.  I can simply get another one and swap it in, or go 
looking for a failure in the line filtering.  Any suggestions would be 
gratefully appreciated.

73, Pete N4ZR

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