Coax Internet Cable: If I have to build one, what am I looking for exactly?

Call or email this company and ask if this filter will work with your setup. Link to follow.

I'm now using a Brickwall surge protector with RFI/EMI filtering and have  my router and desktop plugged in.

The lines from the cable, sat, etc companies carry a high amount of RFI. Even if your new coax provides improved sound, the same amount of noise is being carried to your system. Add an RFI filter to your hookup. I use a RFI/EMI filter on my router which lowered the noise-floor in my streaming.

@oldhvymec  No, I didn't hear noise. But I used an RF "sniffer" which indicated high levels of RF at the coax entry point to the house, on the coax line along the floor, and at the router. After filtering, testing indicated no RF anywhere. When listening to Qobuz via Bluesound Node2i I noticed more clarity and detail, very audible. Also using CAT8 from Verizon router to Node.

Could be the connection from the FIOS box. I shouldn't have said "where the coax enters the house," I forgot about the Verizon hookup. I detect RFI in the coax line as it travels from basement to first floor.

I'm using a small RFI detector with an antenna and sensitivity control. It's also used to sniff out hidden cameras and bugs. I lent it to a friend, he had the same results of RF detected in coax and router.

Coax may be well insulated and shielded, but these cable companies manage to send noise thru the lines.

I can tell you there are a breaks along the way from the head end. And cable installers who kluge parts on the pole. Of course a pure signal is generated from the plant. I don't know exactly where it gets picked up, like you said, from loose or unterminated connections.

And how do you know there aren't. So you worked in cable, I worked in broadcast. Noise enters the signal path in some way. I'm not saying every dwelling in the country has an issue.

Interesting. As I stated I used a consumer device and all I was hoping for was a close measurement of RFI. The fact that my friend in a different city had RF on his coax line and router indicates interference is finding an entry point somewhere, somehow. With all the RFI around us, some cables have the potential to act like an antenna and I've never seen evidence that coax is capable of this. 

I live in a city rowhome in an old neighborhood where some houses aren't even grounded. Now we have FIOS, new transformers on the block, but my electrician tells me these homes with old wiring can be polluting the mains for each neighbor. I'm giving you some background on the level of noise possible in our mains. I'm only guessing that being in a large city there's some way RFI is entering the cable feed.