[ADXA] Switching PS / wall warts

[w5zn at w5zn.org]

I accidently hit send before I pasted the link to K9YC’s paper. Here it is:

 

http://audiosystemsgroup.com/K9YC/K9YC-old.htm

 

73 Joel W5ZN / ZF2ZN

 

From: adxa-bounces at mailman.qth.net <adxa-bounces at mailman.qth.net> On Behalf Of w5zn at w5zn.org
Sent: Monday, November 17, 2025 5:13 PM
To: 'Jussi Eloranta' <eloranta at aa6kj.hopto.org>; 'ADXA' <adxa at mailman.qth.net>
Subject: Re: [ADXA] Switching PS / wall warts

 

Jussi,

 

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>  <adxa-bounces at mailman.qth.net <mailto:adxa-bounces at mailman.qth.net> > On Behalf Of Jussi Eloranta
Sent: Monday, November 17, 2025 4:24 PM
To: 'ADXA' <adxa at mailman.qth.net <mailto: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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