Bring you a comprehensive understanding of the broadband common cable monitoring system

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 environment harsh places. 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 (that is: each full TV signal occupies 8MHz bandwidth, of which the image AM 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 certain 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 to the RF (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.)

4. Anti-jamming performance analysis of broadband common cable monitoring

In terms of anti-jamming, broadband common cable monitoring has unique technical advantages, which is not available in the video baseband transmission method. As mentioned in the previous narrative, the video transmission in the broadband common cable monitoring is transmitted using the frequency band of 112.25 ～ 550MHz in the coaxial cable, and the common interference frequency is completely avoided by the method of high-frequency carrier modulation, so that the interference signal Unreachable and useless land. In my awkward book "Analysis of Anti-interference Performance of Broadband Common Cable Monitoring", there are detailed descriptions of common interference phenomena and interference frequencies. The frequency of common video interference sources are all distributed below 45MHz. It can be seen that the image transmission frequency monitored by the broadband common cable and the interference frequency have a wide frequency band distance. The common interference frequency cannot interfere with the RF carrier image signal at all. This fundamentally guarantees the quality of the transmitted image, so that the monitoring and transmission of various electromagnetic environments with complex factories, communities, enterprises, coal mines, power plants and substations in high-voltage environments are no longer confused by common video interference sources. Broadband common cable monitoring is a tool for anti-interference with its unique technical characteristics, turning a new page for the expansion of monitoring applications.

5. The program capacity and expandability of the broadband common cable monitoring system

One of the characteristics of broadband common cable monitoring is that it greatly simplifies the wiring structure, breaking through the unsatisfactory bottlenecks of traditional monitoring and wiring, such as tedious, complex, time-consuming, labor-intensive, and difficult, so that multiple signals can be used by multiple systems "one cable" Two-way transmission has created a new pattern of "a road leading to Rome" with a brand-new concept.

For example, a newly established detention center needs to install a TV monitoring system to monitor the activities of detained prisoners in real time. This detention unit has 100 prisons. In order to see the panoramic view without leaving a dead end, each prison has 2 monitoring points to monitor One point, one of which has cloud mirror control function. Then, there are 200 monitoring points, including 100 static points, 100 dynamic points, and 100 monitoring points. In the case of the traditional wiring method, when no secondary control is required, 200 video cables, 40 control cables, and 100 monitoring cables are required. Except for the power cables, 200 + 40 + 100 = 340 cables are not required. It can be seen that this method has high material cost, cumbersome wiring, large construction volume, inconvenient maintenance, and time-consuming.

So what would it be like to monitor the transmission system with a broadband cable? Through the above introduction, we can know that the common cable transmission mode can transmit forty channels of monitoring signals, including 40 channels of video, 40 channels of audio, and 40 channels of control signals. Then 8 coaxial cables are enough for the above project requirements. 8 / 340≈1 / 42. From the above formula, we can get an accurate comparison. The number of cables, material cost, construction period, and maintenance difficulty required by the broadband common cable transmission method are 1/42 of the traditional monitoring transmission method. This is also the advantage of the broadband common cable monitoring, which not only saves material costs and simplifies the wiring structure, but also shortens the construction cycle, reduces auxiliary materials and construction costs for the contractor, and simplifies post-maintenance. Moreover, each cable of the common cable system can hold up to 40 to 50 channels of video signals, and it has strong scalability.

Sixth, the transmission distance of the broadband common cable monitoring system

The video baseband transmission method uses 0 ~ 6MHz of the coaxial cable to transmit the video signal. During the transmission process, not only the chroma, brightness and saturation must be differently attenuated, especially the high-frequency color components are greatly attenuated. It is difficult for general video amplifiers to achieve good linear amplification from a few Hz to a few MHz bandwidth, which makes the signal only transmit 300 meters in the SYV75-3 coaxial cable. A video amplifier needs to be added if the distance exceeds this threshold. In addition, the cable itself will generate thermal noise during transmission, which will reduce the signal-to-noise ratio. While the video amplifier amplifies the signal, it will also amplify the noise signal at the same ratio. After amplification, the transmission will greatly reduce the image quality and cannot achieve monitoring. System image standard. If there is interference signal intrusion in the cable, the signal-to-noise ratio of the system will further deteriorate and the image quality will be worse.

The broadband common cable monitoring makes full use of the one-gigabit frequency bandwidth of the coaxial cable, divides the bandwidth into different channels, and uses the broadband common cable modulator to modulate the video and audio signals onto different channel high-frequency carriers for transmission. When the signal is transmitted in the cable, only the carrier signal is attenuated, and the video signal is not attenuated, and the brightness, color, and saturation can be synchronously nested and transmitted. Carrier signal level attenuation can be added to the mains amplifier to amplify the carrier signal, as long as sufficient carrier-to-noise ratio is ensured. The amplifier only amplifies the high-frequency carrier signal, and the image spectrum, phase and other components will not be distorted, nor will there be noise intrusion. This will extend the transmission distance of the monitoring signal and the image quality.