Bob,
I assume that the radio RRC is located where the new cable modem is.
You must configure the new modem/router with the port forwards that the RRC use, i.e. the three UDP ports and
the TCP port if forwarding the web browser port. If you don't know how to do that again, just drop me a mail to
dj0qn (at) darc.de and I will send you my networking checklist.
73,
Mitch DJ0QN / K7DX