[ADXA] Switching PS / wall warts

[w5znjoel at gmail.com]

That’s a million $$$ question, Jon!

 

Basically, wall warts and switching power supplies generate noise hash, spurs, and a lot of goobers that float around the radio spectrum. That’s just the result of their design. The amateur radio frequencies are not unique to this as the noise is all over the radio spectrum. Other devices, such as Randy ZJ’s TV amplifier can generate noise as well. Its just the nature of these devices and even when a device is operating under FCC rules for Part 15 or other devices, they can cause issues with our detection of weak signals. Unfortunately there is a lot of crap in this country from China and countries where these are manufactured that doesn’t meet FCC rules. It is relatively easy to track down and mitigate noise generated in our own home but much more difficult, or impossible, to eliminate the source in a neighbor’s home.

 

The topic involves much more than can be covered in an email. Maybe a program during a future meeting is in order.

 

73 Joel W5ZN / ZF2ZN

 

From: adxa-bounces at mailman.qth.net <adxa-bounces at mailman.qth.net> On Behalf Of Jon W. Reynolds via ADXA
Sent: Tuesday, November 18, 2025 7:43 AM
To: adxa at mailman.qth.net
Subject: Re: [ADXA] Switching PS / wall warts

 

Layman here, where or how does the noise manifest? I suspect i have terrible noise problems due to the wall warts and powersupplies that I have laying around the house and shack and what not, but I guess I've not gotten quiet enough to notice those problems? 

 

I have seen weird things that I suspected were rf noise on WSJTX waterfall, but I was thinking the big dogs didnt FT8, (hihi). Is there an audible sound that is recognizable? And I'm guessing it "jumps" onto the antenna coax as it gets into the shack, and before the coax gets to the radio?

 

Thanks for all the informative discussion!

 

Jon

KI5UCZ 

 



-------- Original Message --------
On Tuesday, 11/18/25 at 06:05 w5znjoel at gmail.com <mailto:w5znjoel at gmail.com>  wrote:

I forgot to address your question regarding wrapping the AC power cord. That is not necessary as the noise will be propagating on the cable from the PS to the computer, so wrap as many turns of that cable as you can around the #31 toroid. The cores I mentioned are 2” ID so you can wrap several turns. The AC power cord plug won’t fit through it once you get a turn or two but again, that is not the “antenna” source of the PS.

 

73 Joel W5ZN / ZF2ZN

 

From: adxa-bounces at mailman.qth.net <mailto:adxa-bounces at mailman.qth.net>  <adxa-bounces at mailman.qth.net <mailto:adxa-bounces at mailman.qth.net> > On Behalf Of Jussi Eloranta
Sent: Monday, November 17, 2025 6:15 PM
To: 'ADXA' <adxa at mailman.qth.net <mailto:adxa at mailman.qth.net> >
Subject: Re: [ADXA] Switching PS / wall warts

 

Thank you for good advice. I will try one more power supply and then start playing with ferrites per your instructions.

Jussi (aa6kj)

On 11/17/25 5:12 PM, w5zn at w5zn.org <mailto:w5zn at w5zn.org>  wrote:

The leads from the power supply are an antenna and will radiate. For years I tried all kinds of toroids and ferrite cores, even ones that were advertised as “Excellent RFI Suppression” which was simply not true.

 

It wasn’t until Ward Silver, N0AX, was here at my station for a contest and listened to my whining to the point he directed me to Jim Brown, K9YC’s most excellent work  

 

 

Turns out I had two flaws in my effort; 1 – not using the correct ferrite mix and 2- no using enough turns to create a high enough impedance to choke off the RFI. Once I did start doing things right I eliminated ALL of the noise in my shack. I don’t recall when you were here in September 2024 if you were inside the shack but if so, you probably saw every cable wrapped around one of those #31 toroids. The photo sent in my last email was my external computer power supply lead wrapped around one.

 

Obviously you can search for a quite PS, but that is a difficult task these days. You may want to try some of these toroids and wrap as many turns around it as you can. You can purchase these from Mouser. It is a Fair-Rite # 2631803802 and here’s the link to Mouser:

https://www.mouser.com/ProductDetail/623-2631803802

 

 

 

73 Joel W5ZN / ZF2ZN

 

From: adxa-bounces at mailman.qth.net <mailto:adxa-bounces at mailman.qth.net>   <mailto:adxa-bounces at mailman.qth.net> <adxa-bounces at mailman.qth.net> On Behalf Of Jussi Eloranta
Sent: Monday, November 17, 2025 4:24 PM
To: 'ADXA'  <mailto:adxa at mailman.qth.net> <adxa at mailman.qth.net>
Subject: Re: [ADXA] Switching PS / wall warts

 

On 11/17/25 16:04, w5znjoel at gmail.com <mailto:w5znjoel at gmail.com>  wrote:

What mix of ferrite??

 

Should be a #31. See photo

 

I first tried a bunch of regular snap-ons which did very little. Then I found - must admit not sure what the specs are - a ferrite ring in my stash and tried that as well. So probably not the kind that it needs to be... I think it is just easier to find a quiet PS - but who knows!? 

Anyway, this device emits when it is just plugged in (no connection to computer).  So, the ferrites should be around the AC cord? It also radiates through the chassis as wrapping it in Al foil helped a bit. I think a hammer - as suggested earlier - is the best tool for this one.

But if anyone has suggestions for RF quiet 100W USB-C power supply, let me know (if there is any???).

Jussi (aa6kj)

 

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