by Steve Walker
31. July 2009 14:21
If your like me and have to operate an HF radio near a PC (or PCs) you are always on the look out for things that make noise, either in your shack or around it.
I had noticed a noise that was pretty wideband from 12Mhz up to about 40Mhz which came and went in severity. First off this looked like it was external to me. I had a wonder about the local area with a hand held radio when it was at its peak.
Now this was a 24/7 noise so it was pretty easy to DF ... After a while it seemed to be me causing this to myself - I could not find anything external to the shack so I decided matters needed to be resolved and I was on a mission!
After turning off all non radio devices it was still there, so I moved to the shack - tuned my hand held to 24.650 AM (which was very strong) and moved about the room slowly unplugging things using walwart style mains adaptors - still no change - good!
So deciding it *must* be one of the computers I shut the PCs down one at a time - BINGO! the last machine to power down and unplug stopped the QRN.
Now I thought I would remove all external connections and power it back up - the moment it rang thou the BIOS the noise returns - ok, then it must be this PC and something inside it.
Armed now with the machine and my hand held I probed the antenna about the case - as it neared the PSU the buzz grew, after removing the case and trying again - it was confirmed the PSU was making huge amount of HF and low VHF QRN.
Lucky for me I have a few PC parts about, so a quick change out to a cheap as chips 450w PSU and the result - 0 QRN from the shack PCs again.
Now this *noisy* PSU was not cheap, do not get me wrong it was not a value part by any stretch of the imagination, it was branded and well made and only three weeks old!
So if your being troubled by a strange modulated buzz from 12Mhz onwards every 100Khz then check to see if your PC or a PC near you have a Hyper Type R PSU - if so it may be to blame.
They are black with a silver 12cm fan and the come with CB microphone style output connectors - the old four pin screw up type - very easy to recognise. The picture above is the same as the one I have that was very noisy, it will be interesting to see if others in the same range are as bad as this one.
73
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