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From: "Edward Rawde" <invalid@invalid.invalid>
Newsgroups: sci.electronics.design
Subject: Re: signal leads that pick up less ambient noise?
Date: Fri, 21 Feb 2025 10:53:01 -0500
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"piglet" <erichpwagner@hotmail.com> wrote in message news:vp9uol$3diav$1@dont-email.me...
> Christopher Howard <christopher@librehacker.com> wrote:
>>> Frequency??
>>
>> I'm not sure exactly, but when I zoom in to it on the scope, the noise
>> appeared to have a regular ebb and flow of about 40 Khz.
>>
>
> That seems very likely to be from some power supply, either wall wart or
> built into some equipment.
>
> A great EMI sniffer to sleuth out is an old school $5 pocket AM broadcast
> radio (the kind slightly larger than a cigarette pack and powered by 2 AA
> or 9v block battery).

Ah yes thanks for reminding me. I've used that method many times.
Waving a problem detector around and then demonstrating that it goes silent when you put it in a closed metal box can be an 
excellent way of demonstrating that a metal box may be needed in some cases.
You don't even need to read any text books by anyone at all.

>
> -- 
> piglet