Re: signal leads that pick up less ambient noise?

On 19/02/2025 23:36, Christopher Howard wrote:

John Larkin <jjlarkin@highlandtechnology.com> writes:
 

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.

Are you sure that it isn't a part of your analogue computer squegging?

 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.

That isn't a good sign. Scope leads don't usually let a lot of interference in. Try shortening the length on the earthing clip.

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.

If you make your signals balanced differential drive then you can withstand a lot of ambient common mode noise without problems. The way that instrumentation amplifiers do it.
https://en.wikipedia.org/wiki/Instrumentation_amplifier
IOW rather than coax you have two signal lines v+ and v- inside a passive conductive outer shield that plays no part in the signal transmission. It is there only as a Faraday shield against external interference.
I think there is something funny going on with your setup.
--
Martin Brown