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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: Thu, 20 Feb 2025 12:33:45 -0500
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"Christopher Howard" <christopher@librehacker.com> wrote in message news:8734g9qzgu.fsf@librehacker.com...
> John Larkin <jjlarkin@highlandtechnology.com> writes:
>
>> I assume that your "leads" are a coax.
>
> Yes, the loads something my co-worker threw together from old cable
> laying around. One one side is BNC that plugs into the signal generator.
> After than is a thin coax about 3mm thick. At the other end, he split
> the inner conductor and the shield into two leads, one with a pin at the
> end, and one with an alligator lead.
>>
>> How are you measuring that noise? It's more likely to be ground loop
>> noise than coax shield leakage.
>
> I have a project I'm doing building my own analog computer - which
> currently does not have any filtering installed on it, other than some
> 100 nF bypass caps. I can see this heavy noise - about .6 mV p-p - on
> all signal output, regardless of what op amp I tap into. If I remove the
> analog computer and just tie the signal generator to the scope, I see
> the same noise.

See my other post in reply to Bill Sloman.
If the noise is not being generated by the analog computer but is causing issues for it then a metal box and some feedthrough 
capacitors might be the solution.
This assumes that your analog computer will fit in a sensibly sized metal box, doesn't have so many connections to make it 
impractical, and is a one-time design rather than volume production.

>
> If I turn the computers off around my workbench, the noise becomes less,
> proportional to the percentage of computers I turn off. If I take the
> signal generator and the computer into another room with no computers,
> the noise almost vanishes.
>
>>
>> Common-mode chokes, ferrites or toroids, can help. Just plugging the
>> generator and the scope into the same outlet may help.
>>
>
> I am planning to go that route, with the chokes and such, once some
> parts come in. But I was also wondering about the single leads
> themselves, which feed from the signal generator into analog computer
> inputs.
>
> -- 
> Christopher Howard