Computer Power Supply Noise

[W4RLS]

In looking at the screen-shots in this and the other forums, I've noticed how clean most of them look. This is in stark contrast to my situation, where I have essentially an unusable amount of noise. For the past several weeks, I've been seeking out sources of noise and working to eliminate or ameliorate them. (Handy tip - wireless phone chargers are the devil!) I've swapped out my noisy UPS with a nice pure-sine-wave one that is quiet. I'm down to two major sources of interference - my Ethernet switches and my PC power supply. My Ethernet switches pulse at various parts of the band, but they are manageable. But my PC power supply pretty much renders any of my SDRs pointless.

For those who have recently built a new PC, what kind of power supply did you use? Or, in general, is one type or brand of PC power supply better at suppressing noise? While all PC power supplies are switching and thus inherently problematic, it certainly seems that some are better than others.

Here's an example of the noise problem that I have. While some CW, FT8, and SSB is getting through, my SDRs are just filled with noise from the PC power supply every few kHz. I know that I'm down the the PC power supply in this case for when I turn the PC off and use an old notebook, the noise disappears. And when the PC is on, the old notebook immediately sees the noise too. I've done my best with chokes, toroid cores, etc. You can see the Ethernet issue at 6.920 kHz and 6.930 kHz. That's my next step.



If you have a reasonably quiet power supply, what do you use?

Thanks.

Bob, W4RLS

[Max]

Hi Bob

I think PC power supplies are usually pretty good. What makes you think it is the PSU and not some other part of the PC? For example, a pain I know, but have you tried opening up the PC, disconnecting all of the power cables from the PSU (five minute job) then "jump start" the power supply (sorry, can't remember which wire it is to ground but lots of information online on how to do it) so the PSU is on but not connected to anything, then scan again with the laptop SDR. Of course the issue may only appear under load. So many parts inside the PC that could be the actual source.

Also, did you try disconnecting all of the USB cables, or maybe initially just de-powering all peripherals from the PC then starting it up? USB can be responsible for regular noise spikes. Sorry, again I forget the exact frequency interval, but seem to remember something like every 8 kHz. It's well documented. I had something very similar to you that appeared out of nowhere, then suddenly realised it was that I had my printer turned on (it's usually off) and sure enough noise spikes (like yours - actually a lot worse) all over the place. Connected by long USB cable. Turned it off, all gone (well most). I ust did it now and I attach two shots to see the difference. Even with printer off you can still see some SM PSU interference from somewhere. It's ever present in most homes!

Regarding PSUs, I think any "name brand" will generally be good. I think with all PC parts that to some extent you "get what you pay for". In a cheap or unbranded PSU of any type (including switched-mode wall warts....... aren't they all these days?) probably some of the first parts to be skimped on will be filter caps and inductors. For what it's worth I just recently replaced PC power supply (I had a weird intermittent switch-on problem..... or rather a "non-switch on" problem) and went for RM750x Gold by Corsair. It seems fine. No noise problems that I am aware of or have noticed. I previously had Seasonic but did a swap out for a friends identical (10 year old) unit to try and clear my switch-on issue. Same fault which had me fooled for quite a while. Needless to say I won't be buying Seasonic again, and that is supposed to be a good brand so it's not always easy!

Hope it helps.

73

Max

[KA1GJU]

My 'power house' desktop in my mancave/operating station makes QRM via the DVI cable. I used to use the HDMI cable, but lightning hit took out that input of the monitor, so I am stuck with using DVI. The QRM is up in VHF/UHF from that source, and only when I use that computer.

I found the Ethernet cables exiting my switch in the repeater shed to be essentially be cured of RFI with numerous wraps around an FT240 31 mix toroid:
https://palomar-engineers.com/tech-support/tech-topics/ferrite-tutorials/FT240-3I-ID-1-4-AC-DC-Coax-Noise-Filter-RFI-Range-1-300-MHz-p74369778
This QRM was throughout the HF bands.

Best thing I have done was to use old 75ohm cable TV hardline (such as the coax used out on the street) and run a couple hundred feet away from occupied buildings, repeater sheds, etc to feed an end fed wire of +150' long across the tree tops via a 9:1 unun that is grounded locally. Three of my five servers use this method, and users find them very QRM free for the most part.

73 Kriss KA1GJU

[W4RLS]

Very good points. I have very few USB devices, aside from the SDRs. I have indeed disconnected all my devices except for the keyboard, mouse and monitors. I have applied chokes to the HDMI and DVI cables as that's what my video card has - one HDMI, one DVI. You are correct that I need to get more granular.

I have based my view on the power supply to the results of my tinySA spectrum analyzer, which I'm using for noise detection. I have a 20dB attenuator attached to the little whip antenna, which I keep collapsed, thus making a pretty terrible receiver. When I put the tinySA with the attenuator plus poor antenna beside my power supply, it goes berserk. The tinySA is small enough that I can wave it across all parts of the tower - CPU, hard drives, fans, daughter cards, etc. It's only when I get close to the power supply that it starts to show splatter over the spectrum.

I also have a Meterk MK54 EMF tester. It too exhibits the same behavior as the tinySA. When I place it near to the power supply - it too starts beeping like Chernobyl. Of course there will be electrical and magnetic fields around a power supply. The EMF tester also lights up at points in the tower where I expect it to, like the fans.

I'll do more digging. Thanks so much for your help.

Bob, W4RLS

[ukdx]

I've settled on using Corsair PSUs for all my builds as they seem to be particularly quiet on the bands I'm interested in as well as across HF. I ditched cat5 ethernet a long time ago as the sunshielded cable radiated like crazy, the patch leads were a lot better but not perfect so now I do everything wirelessly, including mouse and keyboard just to keep cabling to a minimum. I had an issue with an Asus motherboard that seemed to have very noisy power supply issues that was impossible to cure so I replaced it with a Gigabyte and problem solved.

Some years ago I started getting horrendous QRM from 1MHz up as far as 56MHz before, I tracked it down to a neighbours new desktop he'd recently had built by the local indy PC shop. Lucky for me he let me replace the PSU (at my cost I should add) but the shop was quite stroppy with me threatening to report it to Ofcom and only reluctantly agreed for me to do it without affecting the warranty. Quite rightly they said the PSU was CE approved so I could see their point but shows what a worthless system that is!

Here's the PSU in question shortly before I took a hammer to it, spot the mains filtering!

[G0OFE]

Supposed to be in top right of the circuit board, I am guessing......

I'd have taken it to the shop in question and pointed out the missing components that were the cause of the problem.

With regard to wired networking, I installed shielded Cat 6 cable here, no sign of any radiation from it. Had short lengths of Cat 5 at each end which DID radiate, once the Cat 6 patch leads arrived, problem gone.

[G6PZZ]

Has anyone had any success in reinstating these missing components?
Following on from there I wondered if there would be point in contacting the manufacturer in the event of QRM being caused.
I realise one might need a manufacturer with a UK office to make a start and that for some models there might be a chain of sub-contractors to wade through.
Might local trading standards investigate that it might not meet CE standards?
Currently I don’t have a spare to start with.
73
Tom G6PZZ

[ukdx]

I'm not sure it's worth the bother Tom, if they're desperate enough to save a few pence on filters I can imagine they'd be happy using low quality components through out. Junk like this is probably bought via Ebay/AliExpress etc direct from a distributor in China, I doubt your concerns about QRM would get far with them and Trading Standards would likely just log it and take no action. I decided it was easier, quicker and more satisfying to batter it to death.

Interesting what you say about the shielded Cat6 Jim, I've got some S/FTP patch cables for when I want to speed up transfer through a switch and they are fine but maybe I should invest in a drum and see how quiet it is over a longer distance, unshielded cable renders 30-40MHz just about useless for DX.