Coaxial cable transmission video baseband signal is usually about the video signal, its bandwidth is 0-6MHZ, in general, the higher the signal frequency, the greater the attenuation, the general design only to ensure that the high-frequency signal amplitude can meet the system requirements , The attenuation of the video signal at 5.8MHZ is as follows: 3C2V+DC Video cable attenuation 30dB/1000m, RG6+DC cable attenuation 19dB / 1000 m, RG11+DC cable attenuation 13dB / 1000 meters; such as high quality requirements on the image around the case without interference, 3C2V cable can only transfer 100 meters,RG6 transmission 160 meters,RG11 transmission 230 meters; practical applications, there are some 3C2V can transmit 150 meters, RG6 can transmit 300 meters,RG11 can transmit 500 meters; for the transmission of longer distances (such as the long distance, , You can use video amplifier (video restorer) and other equipment, the signal amplification and compensation, can be transmitted 2-3 km; In addition, through a coaxial cable can also achieve common transmission of video signals and control signals, coaxial Visual control transmission technology, the following brief about the technology: In the monitoring system, the need to transfer the signal there are two, one is the image signal, the other is the control signal. And the control signal is from the control center to the front of the camera (including the lens), PTZ and other controlled objects; and, to the front of the control signal, in general, is the video signal to the control center of the front; Through the decoder installed in the front-end decoder and then to control the camera and PTZ and other controlled objects like. Coaxial video transmission technology is the use of a video cable can simultaneously transmit video signals from the camera and the PTZ, the lens control function, this transmission saves material and cost, construction convenience, maintenance simplicity, in the System expansion and transformation of more flexible; coaxial control method to achieve two types:
First, the use of frequency division, that is, the control signal modulated with the video signal in a different frequency range, and then combined with the video signal transmission, and then do the demodulation in the field to distinguish the two; as a result of frequency segmentation technology, in order to completely Bandpass filter and low-pass filter, low-pass filter, thus affecting the transmission of video signals; the need to control the signal modulated in the video signal Frequency, the higher the frequency, the greater the attenuation, so that the transmission distance is limited; the other method is the use of double modulation, the video signal and control signals modulated at different frequency points, and cable television, and then the former , Back-end demodulation.
The control signal is directly inserted into the blanking period of the video signal, and the blanking period portion of the video signal is not displayed on the monitor, so that the control signal is not displayed on the monitor; therefore, the video signal is blanked, Image display does not produce interference, does not affect the image transmission quality, through the front-end video signal pre-amplification and the receiving end of the signal amplification, can greatly extend the video signal transmission distance, such as RG6 video cable, you can achieve 2000 Meters, RG11 cable to achieve 3500 meters, QR500 cable 5000 meters of video transmission and reverse control. (B) transmission through the coaxial cable RF signal Video signal is the video signal modulation to a certain frequency for transmission, which is the use of cable television transmission, usually speaking of the "one line", "total cable transmission" "Broadband transmission" is the use of this technology.