Modem performance and modem selection.

Yes I did mean a cable modem.  Thank you for the responses.  However, with these responses being in conflict with each other...I am not sure which way to go.  I will keep the Cable modem outside of the clean power zone.  Thank you again.

jeff

you are suggesting the OP get something that he might not even need.

True, but so many ground loop issues end up being related to the incoming coax. I’m unusually concerned because I’ve seen a number of charts suggesting that ground loops can occur with digital devices, causing jitter instead of hum, so it’s a tweak I like for myself and recommend.

something like this could also cause issues with the return path.

What??  If you mean power ground return path, there shouldn't be any through delicate signal wire. That's an invitation for a fire. 100% of a power fault's path to ground should be dealt with by ground wiring in the AC cables.

When I mentioned the return path, I was referring to the cable return .
Often pieces will allow signal in but will not let things out and will cause issues that the customer would not be aware of UNLESS he has the proper tools to troubleshoot.   

These ground loop coax isolators are pretty smiple. Either a transformer or capacitor.

So long as the bandwidth is correct, they are bidirectional.

I use a Jensen VRD-1FF isolator at the input of my cable modem.  I don't remember what the symptoms were which prompted me to purchase it, as it was many years ago.  But whatever the issue was, the isolator resolved it, with no downside other than the cost.

Regards,
-- Al