Jasen Betts wrote:

["Followup-To:" header set to sci.electronics.basics.]
On 2005-11-26, Paul Hovnanian P.E. wrote:

Twisting wires helps reduce noise induced from ambient H fields. If you
have a high ambient E field, you can still get common mode noise coupled
to a bare twisted pair. Particularly on a high impedance circuit. This
becomes a problem at low signal levels, where a CMRR sufficient to
reject the noise may be impractical. Low signal level circuits are where
one finds high impedances as well. In this case, carefully designed
shielding can help.

transformers typically have very a high CMRR. this may be whay they are used
in network cards.

Yes. But some circuits must be DC coupled.

--
Paul Hovnanian
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