Originally Posted by mm2margaret
So, if I install a POE filter between Comcast and my very first splitter, as the Cable Modem is downstream from the POE filter, can the POE filter interfere with it?
Only if you have a cable modem that has MoCA capabilities, and you are using (or intend to use) said unknown capabilities as part of your MoCA network.
Older cable modems without a built-in PoE filter can benefit by having MoCA signals blocked.
Newer cable modems tend to have a filter built-in, due to the potential issues.
A small number newer cable modems have MoCA capabilities, and would need to not be blocked, if their MoCA is going to be used.
Some will put a PoE filter on the coax-in of the cable modem, if it is one without MoCA, without a built-in filter, or the internal filter fails to work, which can cause unreliable operation (or non-operation).
What cable modem do you have?