Re: signal leads that pick up less ambient noise?

"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