HOW TO SEND VIDEO & POWER ON THE SAME WIRES

DCSI SIGNAL INJECTOR

HOW TO SEND VIDEO & POWER ON THE SAME WIRES

 HOW TO SEND VIDEO & POWER ON THE SAME WIRES

By: Don McClatchie

                Have you ever gone out to a jobsite to install video cameras only to find out that the contractor forgot to run coax cable for the camera or put in enough wires to run an unshielded twisted pair to get the job done? Or how about those times when the customer changes their mind and wants to add extra cameras and there just isn’t enough wires to put them in. This is no problem when you can just run more wires or add additional coax cable, but what if the wires are buried in walls or in the ground or it is otherwise cost prohibitive to pull new wires, then what do you do?

          To solve these kinds of problems it is important to know that it is possible to run a video signal over the same twisted pair wires that you are using to run power for the camera. Of course, you cannot just twist those two types of signals together to make it work because the power wires would short out the video signal and the power supply would certainly burn out the video camera or DVR electronics. Putting DC or AC power directly into a cameras BNC output connector will permanently damage the camera.

          So, what must to be done to get the video camera signal onto an active power wire pair and take it off at the other end? The first thing to know is that the power wire impedance is in the low Ohm range of one or two Ohms and the video is driving a signal with a 75 Ohm impedance so the video is going to see nearly a dead short circuit to its signal. It is necessary to change the impedance of the power supply above a certain frequency to allow the video signal to exist on the power wires.

         Then you must raise the frequency band that the video normally operates in from (DC – 10 Mhz) up into the 15 Mhz to 25 Mhz band. This allows you to use band splitting filters at each end of the power wires to isolate the 75 Ohm impedance of the video separate from the low impedance of the power supply. Use this method when running extra wires is cost prohibitive or too labor intensive.

          Here is what you need to get the video onto the power supply wires. At the camera, you install a device called a DCSI -2 Signal Injector filter to band split the power wire then also install a TVP-20, this unit is normally used to put two video signals onto a single coax cable but in this application, it is used to raise the frequency band of a single video channel so a filter can be used to isolate the video from the power supply. The TVP-20 takes the video signal in and modulates it up to the 20 Mhz band and that signal is connected to the DCSI filter’s BNC input connector at the camera.

 

DCSI SIGNAL INJECTOR

DCSI SIGNAL INJECTOR

                                                                                                                      DCSI Band Split Filters

TVP-20 Transmitter Video Plexer

                                                                                                          TVP/RVP-20 VIDEO Up-Converters

          At the other end of the power wire you install a second DCSI filter to isolate the power wire run and then connect the RVP-20 to the DCSI’s BNC output connector that receives and demodulates the 20 Mhz signal and outputs the video signal without any loss or distortion caused by long power wire runs. The DCSI splits the frequency band used by the power wire and the TVP-20 / RVP-20 up-converts the video into a band that will pass on the power wire without interfering with the power supply and the power supply will not affect the video signal. Each DCSI filter has two screw terminals one for the power input and one for the power output. It also has a BNC connector to insert high frequency signals to pass down the power wires. They are used in sets, one at the camera and one at the DVR to combine and then split the power and video to ride on one power wire pair. By the same method, you can put RS422 PTZ camera control on the same power wires using the DLT/DLR-1. This application is a neat trick to keep in mind for those times when you are up against a difficult installation.

DCSIblock1

Power up to 4 Amps AC or DC can be connected to the DCSI units and it will pass through to power the camera. Connect the video up-converters to the NC signal input and output on the DCSI units and the video signal will be inserted onto the power wires without interference from either the power or the video. They will both co-exist on the power wires to get your video signal connected.

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