Electronics > Metrology

CM noise problems with ethernet connected instruments

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temperance:
Hi,

perhaps not a metrology question but I think people in here might have some experience with this.

The problem:
all my instruments are equipped with Ethernet. Very practical. But with all the equipment connected onto a router I start to have some problems with common mode noise to the extend that even a simple scope measurement is problematic.

What I tried:
-replaced the router with a transformer power supply powered router from way back. It did help a bit it's still but not good enough.

I noticed that it must be one specific power supply which is responsible for most of the CM noise. Investigating further, it turns out to be the siglent signal generator. With the signal gen disconnected from the router the noise is much lower. But, still not good enough. Now I'm seeing random stuff from all the other instruments and the computer attached to that same router.

I'm wondering, pondering how to solve this. Anyone with some experience in here?

jonpaul:
insert transformer isolation, depending on the CAT and rate.

See "Ethernet Transformer" from Coilcraft, Renco, Pulse Engineering


Jon

langwadt:

--- Quote from: jonpaul on May 16, 2023, 01:19:27 pm ---insert transformer isolation, depending on the CAT and rate.

See "Ethernet Transformer" from Coilcraft, Renco, Pulse Engineering


Jon

--- End quote ---

ethernet is already transformer isolated...

temperance:
Indeed, Ethernet is isolated with transformers. Or did you mean something different when you said to use transformers?

dobsonr741:
You might have conducted EMI creeping along the cable. Did you try shielded eth cable? Not for permanently, but for testing a ferrite clamp-on?

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