Sorry if this topic has already been covered, I am new to this site! I have seen some small (OEM) modules for injecting DC into a coax at the receive site and another module for extracting the DC at the camera. The DC rides up the cable with the video. 
  
Can anyone advise where I can get specs for these modules and suppliers in the UK or US. 
  
Thanks 
  
G   [/b]