What is Video Termination?
Termination in video is a terminology that refers to a resistor of a particular value (usually 75 Ohms in video) that is connected to both ends of a transmission cable. When the recorded footage from a CCTV camera is being sent down the cable, it may reflect back from its unterminated end which as a result causes two or more “ghosts” of the original image to appear on the monitor. This ghost effect mostly appears on top of the original footage and is also referred as terms ‘edge enhancement’ or ‘ringing’.
The video termination problem is minimized or non-existent when the cable transmitting video signals from camera to DVR is short enough, so you will see ‘crisper’ quality footage. It also depends on the quality of CCTV camera as they are properly source-terminated. Video termination results in a loss of picture quality. And as the length of the transmitting cables gets larger and larger, this issue becomes noticeable and is very undesirable.
Why Does Video Termination Happen?
The video transmission line or cable has an energy stored in it. So, when there is a resistance at the end of the cable, that stored energy gets absorbed by the resistor. If the terminating resistor is either too low or too high, a portion of the received energy will be reflected onto the transmission line that will then travel back to the source (camera) and then sent to the monitor, which you will see in the form of ghosting. So the ‘ghosts’ you see on the monitor actually make two trips down the length of the cable and if your CCTV camera is properly source-terminated, then that specific portion of energy (ghost) will be absorbed there and won’t return to the monitor. And as mentioned above, it also depends on the length of the transmission cable.
Which CCTV Cameras Have Video Termination?
Most of the quality CCTV cameras available on the market nowadays don’t have this issue because they are accurately source-terminated with 75 Ohms. However, some inexpensive, low quality surveillance cameras on the market are not properly source-terminated and they are the ones that usually have ghosting issue as well as other host of problems. Some of the other problems with those cameras may include improper operation of different types of interfacing equipment such as pan and tilt control, etc. Inaccurate source-termination at Ohm shorts out these control signals.
How to Test CCTV Cameras for Video Termination?
Sorting out cameras with video termination from others is quite easy. All you need to do is connect the cameras one by one to be tested to any unterminated Oscilloscope or Video Voltmeter. Monitor the Peak-to-Peak voltage and then terminate the metering device with a 75 Ohm terminator. After that, notice the Peak-to-Peak voltage. The voltage will drop to one-half the value when the device is terminated, providing that the camera is correctly source-terminated. And if the camera is not properly source-terminated and has video termination problems, then the voltage will drop only 1-5 percent when the metering device is terminated.