Noise And "Wall Warts" ?

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Robert111
Posts: 20
Joined: Wed Aug 19, 2020 10:53 am

Noise And "Wall Warts" ?

#1

Unread post by Robert111 »

Hello,

Regarding these "wall-warts" that we seem to have all over the place these days:

Before I crawl under everything removing them one by one:

Not sure how similar one brand is to another, but what are the "typical" frequencies one might
expect to be radiated as "noise" ?

And, is it a function of load ?

Ferrite clip ons found to be effective, or a waste of time ?
Should they be on the AC input line, or "dc" output , or both ?

Have significant noise in the 2-3 MHz range (AM)

Thanks,
Bob

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G0OFE
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Location: Sunny Sunny Bournemouth IO90BR
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Re: Noise And "Wall Warts" ?

#2

Unread post by G0OFE »

Depends on the wall wart. Your mileage may vary.

Some radiate crap back in to the mains, so a ferrite may not even help in some cases.
Jim, Bournemouth IO90BR
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PD3LK
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Re: Noise And "Wall Warts" ?

#3

Unread post by PD3LK »

Hello Bob, please make a FULL screenshot in SDRC of that 2-3 Mhz range (if possible wider) so we can see how the noise looks like.

Robert111
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Joined: Wed Aug 19, 2020 10:53 am

11For PD3LK et al: Re: Noise And "Wall Warts" ?

#4

Unread post by Robert111 »

Hi,

Assuming it works, here's a photo of the "noise" I am trying to peg.
Please let me know if it doesn't show (anywhere).
I'm still a bit uncertain re how to Attach or include photos.

It's pretty much exactly the same from 2 to 3 MHz, AM, all the time.

Thanks for help,
Bob
Attachments
Screenshot-2020-08-19-082619.png
Screenshot-2020-08-19-082619.png
Screenshot-2020-08-19-082619.png

Max
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Joined: Thu Aug 13, 2020 9:47 am

Re: Noise And "Wall Warts" ?

#5

Unread post by Max »

Hi Bob

At risk of sounding repetitive (I've mentioned it in quite a few interference threads) I had something very similar, at about same frequency, and it turned out to be my UPS sitting right in under the computer desk. I had not really suspected that even though I had done tracking exercises before. Surprised me as I thought all decent brand UPSs would be well filtered. Seems not. Well known brand. Belkin. So if you have a UPS try turning that off (totally, on switch and unplug from wall).

Must say that does look like a very nasty case though. Many interference sources do turn out to be in our own home, so the first thig to do is fire up a laptop (on battery of course) to run SDRC on, then shut off all circuits at the main "consumer unit" where main power enters the home. Then, turn on individual circuits one by one while monitoring the result. In my case when I have done this I have (1) yes, found some sources of RFI but (2) also been a bit disappointed that it is not all from one source, but a general raising of the noise level as each circuit goes on, but yours is so identifiable that it should be easy to trace.

Regarding "wall warts", brand is no guarantee of cleanliness. However, a good brand will be more likely to be clean than a non-descript unit bought from eBay simply because it has probably passed the test necessary for CE/FCC certification. Yes, I do mean "probably". No guarantee as many manufacturers self-certify. I was going to say Chinese/Far East but they are all manufactured there anyway, so country of manufacture is largely irrelevant. Switched mode are nearly always the main culprits at HF, but then again 95% of all supplies are SM these days, and some are extremely clean. It's just a question of if the manufacturer has decided to save a few pennies per unit by omitting filter components. I have some very clean SM supplies and some very dirty ones. I even had one that "went rogue" that had been clean but suddenly started radiating a strong signal harmonics on 14 MHz and again at double that on 28 MHz amateur band. Cap blew I guess?

So, to summarise, no quick fix. I think it's actually easier to source a good quality SM "wall wart" PSU and replace them one by one than chase around trying to silence them with ferrites and filters which can be of varying success and very time consuming. Surprising how many items run on 12 volts DC. And of course the "turn-off all" tracing exercise which sounds a pain but can quickly locate the source.

If the source of the RFI proves to be outside your own home then that's more difficult to solve of course.

Another common source of noise is from USB cables. I recently discovered my Canon printer was making a racket due to long USB cable and no ferrites. Disappeared when I turned the printer off. As I recall USB generated interreference often has an 8 kHz repeat interval (not sure why). Not the case here for you, and anyway those "spikes" are very broad (just like my UPS ones were), whereas the USB 8 kHz spikes are very narrow (in my experience).

Good luck

Max

jdow
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Joined: Mon Aug 10, 2020 8:17 pm

Re: Noise And "Wall Warts" ?

#6

Unread post by jdow »

G0OFE wrote: ↑Thu Oct 08, 2020 4:21 pm Depends on the wall wart. Your mileage may vary.

Some radiate crap back in to the mains, so a ferrite may not even help in some cases.
If they are plugged into a plug-strip then put a clip on around the incoming power wire as well as the output wire.
{o.o}

Robert111
Posts: 20
Joined: Wed Aug 19, 2020 10:53 am

Re: Noise And "Wall Warts" ?

#7

Unread post by Robert111 »

Hi All,

Thanks for thoughts on this.

Think I will look seriously into a UPS unit to feed "everything" again.
Have been thinking about one for quite a while, but have always backed off due to
the many, many, posts I have read about them bursting into flame, unexpectedly !

That big battery in the larger sizes is a real danger, apparently.

Would also have to be the "sine wave" model I guess.

Not to sure if i should get or not.

Is there any conscenous re safety ?
And, brand ? Or, what to definitely avoid ?

Regards, and stay well,
Bob

Max
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Joined: Thu Aug 13, 2020 9:47 am

Re: Noise And "Wall Warts" ?

#8

Unread post by Max »

I've got two of these. They are excellent and very RF quiet, which is why I bought a second one:

https://www.cyberpower.com/global/en/pr ... 500epfclcd

Saw it recommended on some radio forum (sorry can't remember where) and it has not disappointed, for me using mostly HF frequencies at any rate.

73

Max

Max
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Joined: Thu Aug 13, 2020 9:47 am

Re: Noise And "Wall Warts" ?

#9

Unread post by Max »

Bob. Also see here for previous discussion:

https://sdr-radio.groups.io/g/main/topic/5933968

Max

agene
Posts: 1
Joined: Wed Aug 19, 2020 9:57 pm

Re: Noise And "Wall Warts" ?

#10

Unread post by agene »

I had a desktop PC with power supply which gave terrible RFI so it is not only the wall-warts which can give problems.
Mike Simpson
South Penrith, NSW, Australia

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