We've got an existing c. 10 year old analog coax door entry system made by Elvox. From what i can see the outdoor door entry camera video signal is sent over coax to the control box and then the control box links to the internal monitor. The control (eg. door release) seems to be controlled by some twisted pair cables or a flex. We're also putting in a Hikvision IP system using a DS-7608NI-K2/8P NVR. Would it be possible to branch the video from the coax of the door entry monitor and then put it into some sort of modulator / transformer / so that we could run the signal over cat6 and put it as an input into the NVR ? If so what kit would be required ?