There are a few options now to get a HD signal over coaxial cable, so people wanting to upgrade a old analog system can often reuse their old wiring and just put up new cameras and change to a DVR supporting these new ways of doing things.
My friends and mine new 4 channel Dahua NVRs have been pretty plug and play, unlike my old Dahua 4 channel NVR that was no way near that, at least not with non Dahua cameras.
But the new boxes have been all P&P even with cheapo china IP cameras, so that's pretty nice as that network stuff are not a favorite field of me to work in.
You off course get use of the full functionality with same brand cameras and recorder, with the cheap cameras thats not always a given fact that you can get camera and NVR to play ball 100%, but the ordinary features like providing a feed and the box recording it so far have seemed to work fine for us.
My little NVR also run on 12V input, and if you like to use the POE it also support you just have to plug in the 48V PSU too ( i dont use POE )