First, the background of broadband common cable monitoring

When it comes to monitoring, everyone should be familiar with it. Monitoring probes can be seen everywhere on the road, in banks, in supermarkets, and in factories. It can be said that monitoring has penetrated into all levels of society, and it is no longer a unique prevention and management system for state organs. . As the monitoring system has penetrated into thousands of industries, the transmission environment has become extremely complex, and it has exceeded the single and pure corporate environment and has been applied to high voltage, high magnetic and other electromagnetic environments. In recent years, radio technology has become more popular with people, and there are many radio stations, mobile communications, and radio equipment, which have further deteriorated the space electromagnetic environment. This also puts forward higher requirements on the anti-interference performance of the monitoring transmission system. With the popularization of monitoring applications, the transmission scale has also grown from three or five points to dozens or even hundreds of points. The traditional spider-web star wiring method can no longer meet current engineering requirements. Broadband common cable "one-line communication" TV monitoring and transmission system has emerged in response to such practical needs. It has been widely used in various monitoring systems due to its simple wiring, good integration, strong anti-interference, flexible expansion, and high cost performance. In the project, it solved various problems encountered by the engineering companies in the transmission process, completely changed the wiring method of "one video and one line", and was dubbed as a new monitoring transmission pattern of "one road leads to Rome".

Second, the characteristics of the broadband common cable monitoring system

The expansion of video application areas, the expansion of system scale, and the increase in transmission distance have promoted the transformation of surveillance transmission methods, from the original video baseband transmission to video baseband, broadband common cable (RF carrier), network, microwave, optical cable, CDMA And twisted pair diversified transmission coexistence mode. Beijing Hengxing Ketong ST-6000 broadband common cable "one line" TV monitoring transmission system aims to avoid monitoring transmission interference and realize the remote transmission of monitoring signal bus system. It not only pays attention to the transmission quality of images and control signals, but also guarantees the system. The stability, reliability and practicability have completely changed the traditional cumbersome wiring method, improved the anti-interference performance of the system, and solved the difficult problem of monitoring transmission.

Simplified wiring: In practical applications, the system can realize forty-way monitoring signals (including video, audio and control signals) through a coaxial cable for two-way transmission of 0 to 3 kilometers, so that the monitoring signal realizes intensive bus system transmission.

Broadband integration: The frequency bandwidth of the coaxial cable is 0 ～ 1000MHz. Because the broadband frequency only uses 550MHz of the space when monitoring the transmission signal, so it also reserves the expansion space for the alarm and broadcasting system while transmitting the monitoring signal. Make multi-system multi-channel signal transmission aggregate into one cable transmission.

Bidirectional transmission: during signal transmission, 5 ～ 65MHz is used to transmit downstream control data signals to the front-end gimbal and lens, and 110 ～ 550MHz is used to upstream transmit surveillance video signals and audio signals, while 65 ～ 87 are used for bidirectional signal transmission Isolation zone, in which uplink and downlink signals are transmitted in all directions without collision.

Long-distance anti-jamming: move the audio and video and control signals to high frequency, only attenuate the carrier signal during transmission, and not attenuate the video signal, as long as the carrier-to-noise ratio is satisfied, and allow 6 series amplifiers to be connected in series during transmission The transmission distance breaks through the bottleneck of 500 meters and can reach 3000 meters at the farthest. This greatly extends the transmission distance of the monitoring signal and avoids common interference frequencies.

Judging from the above four characteristics of the common cable monitoring system, the broadband common cable monitoring system is very in line with the actual needs and technical requirements of the monitoring engineering company. In the future, it will be a "large system, long distance, anti-interference" monitoring system Preferred transmission method.

3. Application technology and working principle of broadband common cable monitoring

CATV cable TV technology has a history of more than 30 years since its introduction in China. At present, many cities and rural areas in China have installed cable TV systems. The technology is very mature and the equipment performance is stable and reliable. The ST-6000 broadband common cable monitoring system is the reverse application of cable TV technology. It uses mature and stable high-frequency transmission technologies such as frequency division multiplexing (FDM) and FSK data modulation and demodulation to achieve New pattern of monitoring and transmission.

1) First, the coaxial cable is divided into different transmission channels according to the transmission characteristics of the coaxial cable and China's cable TV standard PAL D / K (ie: each full TV signal occupies 8MHz bandwidth, of which the image amplitude modulation carrier occupies 6MHz, audio The FM carrier is on the 6.5MHz sub-carrier of the image carrier, which can be divided into more than 40 channels from 112.25 to 550MHz in accordance with China's broadcast and television standards). Different surveillance video signals are input to the broadband common cable modulator ST-201 (or 202D) of different channels, and are subjected to double conversion modulation and spiral filtering, and the image frequency spectrum and phase are strictly controlled, and then moved to a high frequency carrier of a channel On, the output is multiplexed into the coaxial cable network; after that, the multi-channel video carrier (RF carrier) signals of different channels that are modulated pass through the signal coupler and are collected on a coaxial cable and pass through the coaxial cable network and The signal amplification equipment is transmitted to the monitoring center.

2) After the radio frequency signal is transmitted to the monitoring center, it enters the two-way data splitter, through which the high-pass filter module filters out the downstream control signal, and only allows the video high-frequency carrier above 87MHz to pass through, and is distributed to ST-3008AV / ST 3016AV multi-channel video demodulator (or video demodulation equipment of other specifications) performs multi-channel demodulation on the monitoring signal in the coaxial cable to restore it to standard video baseband and audio signals, and finally sends it to the monitor, hard disk recorder or other video Processing equipment. (Multi-channel video demodulator has the characteristics of manual / automatic control channel demodulation, agile adjustment by touch button, high isolation, clear demodulation quality, etc., easy operation and easy installation.)

3) The RS232 / RS485 control signals from hard disk recorders, control keyboards and other equipment are subjected to data packaging and modulation via the ST-4200 FSK data modulator and modulated onto the radio frequency (38 ～ 40MHz) carrier, and enter the data divider low pass filter for downstream transmission . After being transmitted to each broadband common cable modulator through the coaxial cable network, the FSK demodulation module of the broadband common cable modulator demodulates the control data signal into a standard industrial RS-485 control signal. It is sent to the decoder to output the pan / tilt and lens control level, so as to drive the pan / tilt up, down, left, right or automatically rotate to push the lens aperture, focus and zoom action. (The FSK data modulation method has the advantages of easy implementation, low bit error rate, stable transmission, and reliable control.)