Re: signal leads that pick up less ambient noise?

John Larkin <jjlarkin@highlandtechnology.com> wrote:

On Wed, 19 Feb 2025 09:35:52 -0900, Christopher Howard
<christopher@librehacker.com> wrote:
 

Hi, I have a very noisy workbench (lots of digital computers and
computer monitors nearby) and it seems like I pick up a lot of noise on
the long leads coming out of the signal generator BNC output — around
600 mV p-p. I am wondering if there are any particular leads I could buy
that would somehow pick up less ambient noise.

 
I assume that your "leads" are a coax.
 
How are you measuring that noise? It's more likely to be ground loop
noise than coax shield leakage.
 
Common-mode chokes, ferrites or toroids, can help. Just plugging the
generator and the scope into the same outlet may help.

That would be the direction I would look first.  Remember the signal
path is a loop, so if the earth return is not through the co-ax screen,
you may pick up noise on the earth wire if it follows a different path.
Even if you have the earth solidly joined along the co-ax screen,
interference can be introduced if it is paralleled by another return
path that picks up noise.

In the 'old days' , lifting the safety earth lead off the mains plug of
one of the instruments was a way of cutting the parallel path, but that
is frowned upon (and probably illegal) these days.  Doing that meant
that when the signal earth was disconnected, a dangerous voltage could
exist between the two instrumnets because one of them wasn't properly
earthed.  With most modern instruments, which use double-insulated
construction, there is no need for a safety earth and consequently no
earth lead to lift.


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~ Liz Tuddenham ~
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