Digital Transformation and Application of Yuncheng Microwave Transmission System

Digital Transformation and Application of Yuncheng Microwave Transmission System

The Yuncheng microwave transmission system is responsible for the transmission of multiple signals such as Shanxi TV Station, Yellow River TV Station, Yuncheng TV Station, Yuncheng People's Broadcasting Station and Yuncheng News. Before the digital transformation of the system, the WSF8-03 analog microwave transmission equipment produced by the Xi'an Microwave Factory in the 1980s was used. With the rapid development of digital technology, backward analog images and sound broadcasting can no longer meet the ever-changing requirements of electronic technology . Under the unified arrangement and deployment of the Shanxi Provincial Radio and Television Bureau, the Yuncheng microwave transmission system completed its digital transformation in December 2006 and May 2007, respectively, and carried out a 1 + 1 system backup. After one year of system operation, the transmission quality of broadcast and television signals has been greatly improved; after one year of use and maintenance, our technicians have also learned some digital microwave transmission knowledge and mastered some related equipment maintenance experience.

Introduction to the Digital Microwave System of Yiyun City

Yuncheng Station is a terminal station in the southernmost part of Shanxi Province. The original station was located in the Yuncheng City Committee Building. In December 2006, it was moved to the Yudu launch station during the digital transformation. The station is at 35 ° 03′27.29 ″ north latitude, 111 ° 0′52.49 ″ east longitude, the site is 369 meters high, the antenna is 40 meters high, the magnetic declination angle is 3.77, the magnetic communication azimuth angle is 359.85 degrees, and the antenna elevation angle is 1.32 degrees. Jiwang Mountain on the station 36.17 kilometers. The point-to-point microwave transmission system between Yuncheng Station and Jiwangshan Station adopts PDH transmission method for corresponding digital transformation. The PDH digital microwave capacity is 45MB, which can provide 21 2MB interfaces. The transmission frequency of Yuncheng Station is 7925.60MHz, and the reception frequency is 8236.92MHz. At the same time, it receives two digital TV signals, returns two sets of digital TV signals, and two digital broadcast signals. The signal flow of Yuncheng Station is shown in Figure 1.

Two microwave digital equipment functions and features

1. 45MB PDH digital microwave communication equipment

The Yuncheng microwave transmission system uses the SMART-2000 45MB PDH digital microwave transmission system designed and manufactured by Guilin Southern Communication Equipment Engineering Co., Ltd. by introducing internationally renowned companies such as NEC, using the latest integrated circuits and FPGA technology. This system is specially designed for digital microwave transmission of integrated services such as television, radio, voice, and data, and is specially developed for the digital transformation of radio and television transmission systems. It is mainly composed of microwave transmitter, QPSK modem, 45MB multiplexer, service, monitoring and power supply. The system combines the high efficiency of radio and television transmission and the flexibility of telecom digital transmission, which can simultaneously transmit 7 digital TV Signal and 30 channel 2Mbps interface voice. The equipment has advanced technology, flexible networking, easy installation and maintenance, and large transmission capacity, which provides a good platform for transmitting more services in the future.

2. SMART-2000 channel machine hanging box

SMART-2000 type channel machine hanging box includes six plug-in parts. Instant plug-in, sending plug-in, modem plug-in, power plug-in, monitoring plug-in and 1 + 1 switching plug-in. They are all installed in public units, called channel hanging boxes. There are two channel machines and a monitoring plug-in in a hanging box. At the terminal station, two sets of channel machines are one main and one standby. When one channel machine is faulty, it can automatically switch to another channel machine to work; at the relay station, the two sets of channel machines face up and down respectively. The microwave port and the intermediate frequency port of the channel machine are in front of the hanging box, and the various data interfaces are on the motherboard behind the hanging box. These data include the modulated 45M input, the demodulated two 45M outputs, and the official channel input Output and input and output of two RS232 data (the second channel is monitoring channel). In addition, a 45M second distributor is built into the motherboard for 1 + 1 switching system.

(1) Channel machine plug-in

Both receiving and sending use 70MHz IF interface, the working principle is as follows:

The sending end converts the 70MHz modulated intermediate frequency signal and the local oscillator signal into a microwave signal, filters the unwanted signal through a three-cavity filter, sends it to the power amplifier input terminal, and amplifies it to a specified level. Sent by the antenna. as shown in picture 2.

At the receiving end, the received weak microwave signal is split by the splitter and sent to the low-noise amplifier for amplification. The amplified signal is mixed with the local oscillator signal and mixed to 70MHz intermediate frequency; and the image signal is filtered by the three-cavity filter. , 70MHz IF signal is time-delay equalized by time-delay equalizer. The equalized IF signal is sent to AGC IF amplifier for amplification. After AGC automatic level control, the final output level is kept constant odBm, and then sent to demodulator for solution Tune. As shown in Figure 3.

(2) Modem plug-in

The main task of the modem is to modulate the coded and compressed broadcast and television program signals to the 70MHz intermediate frequency band, and then to modulate the intermediate frequency signal to the microwave. The 45Mbps modulator uses QPSK modulation to shape the 45MBbps digital signal, single and double conversion , Differential coding and modulation to 70MHz intermediate frequency. The principle block diagram of the modulator is shown in 4.

The demodulator adopts the coherent demodulation method, that is, it uses two mutually orthogonal reference phase carriers for coherent detection (that is, synchronous demodulation), and outputs 45MBbps data signals through differential decoding and double-single conversion. Using QPSK phase modulation, the system has good anti-noise performance, high spectrum utilization rate, and simple equipment configuration. The principle block diagram of the demodulator is shown in Figure 5.

(3) 1 + 1 switch plugin

Configured to improve the transmission reliability of the microwave channel, distribute various input data to the main and backup modulators; at the same time, the output data of the main and backup demodulator (44.736Mbps data, official signal, two RS232 data), select the best Select, switch output. The switching basis is the working state and bit error rate of the channel machine. The switching mode is direct switching, and the switching time is less than 5ms. The switch also provides two 45Mbps data outputs.

(4) Channel power plug-in

The channel power supply is -48V input, providing + 5V, + 12V and -12V power to the channel machine.

(5) Monitor plug-in

Each monitor can manage the alarm monitoring data of up to two receivers, two transmitters, two modems and two tap multiplexers (tap), and organize and package the monitoring information into R232 The data communicates with the central (Taiyuan station) monitoring computer through the monitoring channel and data exchange. As an end station, we do not use a data switch, so the RS232 data interface of the monitoring machine plug-in is directly connected to the auxiliary data 2 interface of the modem plug-in through a network cable (crossover cable).

3. Tap multiplexer

The multiplexer integrates multiplexing and demultiplexing into one, completes the multiplexing and demultiplexing function of 45Mbps data to 21 2M data, and provides a monitoring port. This device converts the internationally used DS3 data interface into a domestic E1 data interface, which is convenient for us to use various mature terminal devices on the 2M port. It is a key device for digital transmission and transformation.

4. Business jet

It has two functions: voice terminal and official signal relay (branch). Its official signal is connected to each modem or switch, and the 20-core cable is used to connect the SC I / O port of the channel hanging box in the 1 + 0 link, and the four-core is used in the 1 + 1 link The telephone line is connected to the EOW port of the switch. Each business jet can link up to four directions of business signals

The business jets at all stations in Shanxi Province are the same and can be interchanged, but the phone number (selective call address code) is unique and is set according to uniform regulations.

5. Broadcast and TV terminal equipment

Broadcast TV terminal equipment refers to digital terminals below E1 data, namely broadcast encoders, broadcast decoders, TV encoders, TV decoders and adapters.

(1) Encoder

The encoder used at Yuncheng Station is the EN2200 digital encoder produced by Beijing Huanhuan Digital Image Technology Co., Ltd. This encoder can perform digital compression processing on both analog and digital audio and video signals. The ASI and G.703 interfaces output TS code streams. The output code rate of ASI interface is adjustable from 1.5 Mbps to 105Mbps (± 10ppm), which is in accordance with DVB standard. The RS-232 interface can be connected to the computer serial port to complete the encoder parameter configuration, working state extraction, remote state extraction, remote network management, data transmission and other functions.

(2) Decoder and adapter

The decoders and adapters used to receive signals from Shanxi TV Station and Yellow River TV Station are IRD-2900 decoder produced by Israel Scopus Company and TLK1000 adapter produced by Beijing Huanwang Technology Company, respectively. The decoder can accept MPEG-2 / DVB transport streams that comply with the G.703 standard. It has the ability of channel decoding and error correction in compliance with the DVB standard. Input TS stream at the input ASI interface, composite video, S terminal at the output end, audio output 2 analog stereo balanced output, data output interface, so that the decoder can be software upgrade or data loading. TLK1000 is an MPEG 4: 2: 0 mode adapter, which is based on MPE-2 and DVB standards, supports PAL and NTSC video formats, and has 4 E1TS stream input interfaces and 2 ASI code stream interface outputs.

6. System power

The Yuncheng digital microwave equipment system uses the POWEC high-frequency resonant power supply produced by Guangzhou Jishiyu Communication Technology Co., Ltd. using Norwegian technology. The power system consists of a control module, an alarm module or an alarm interface version, a rectifier module, a power distribution module, Intelligent resonant high-frequency switching power supply composed of frame and frame. The principle of the power system is shown in Figure 6.

The working principle of the system is that the rectifier module converts the AC input into a DC output, and then sends it to the DC power distribution module and battery fuse module connected in parallel by the bus bar, and outputs the power to the load through the shunt switch or fuse output in the power distribution module It also charges the battery. When the mains power is interrupted, the battery supplies power to the load. The control module communicates with the alarm module and rectifier module via RS485. The data measurement and collection are the responsibility of the alarm module. Its objects include mains power, DC power distribution module, battery fuse module and battery. When the system is working, the control module monitors the various states of the system, adjusts its parameters, and automatically executes predetermined tasks. When the system is abnormal, it sends out an alarm signal, which is output through the alarm module and displayed on the control module.

3. Maintenance and maintenance of digital equipment.

In order to ensure the normal use and reliability of digital equipment, we first did the following two aspects: First, the grounding system of the original equipment room was transformed. The specific method is to increase the range of the ground wire into the pit, and add materials with good conductor characteristics in the pit, increase the area of ​​the ground wire, and change the original 12 square aluminum wire to 16 square copper wire as the ground wire; Decoration renovation. The specific method is to seal the doors and windows of the machine room, the ground is laid as a wooden floor, and the maintenance floor after the equipment rack is laid as a floor material with anti-static characteristics. On the other hand, we seal the entrance and exit of the waveguide, and the staff on duty ensure that the machine room environment is cleaned and inspected daily to minimize the damage of dust, rain and other harmful substances to the digital equipment. Because different digital devices have different working characteristics, this requires us to do a good job of maintaining and maintaining them in different categories.

1. Use and maintenance of SMART-2000 digital microwave communication equipment

The temperature of the equipment room should be controlled within the range of 0 degrees Celsius to 45 degrees Celsius. The optimal temperature should be maintained between 15 degrees Celsius and 25 degrees Celsius. According to the environment of the equipment room, regularly clean the upper and lower ducts of the plug-in panel and the chassis to prevent the accumulation of dust and affect the ventilation. .

Before checking the working status of the equipment or testing its performance, be sure to notify the staff on duty at the monitoring station to prepare for the corresponding treatment and maintenance. When repairing the equipment at work, the manual operation procedures must be strictly implemented without disconnection. Before the power tray outputs power, you cannot insert any plug-ins and cables. When pulling out the plug-in, you must use special tools to prevent damage to the plug-in. After the maintenance is completed, insert all the plug-ins into the hanging box, and connect the cables correctly, check the position of each switch according to the power-on procedure, turn on the power switch of the power disk (PS), and check whether all plug-in alarms (red) When the flame is off, only the green indicator light should be on when it is normal, and finally the monitoring station should be repaired.

When searching for faults, follow these steps:

Check the alarm signal lights of each plug-in to determine the component where the fault occurs;

Check whether the input and output of the power disk (PS) are normal;

Check the instructions of each unit with the meter header and compare with the factory records to find out the faulty plug-in;

Through standard testing, faults are found, and faulty plug-ins are found through analysis and judgment.

2. Use and maintenance of encoder, decoder and adapter

After daily use and maintenance of the encoder, decoder and adapter, the following work must be done:

Ensure that each device is reliably grounded to prevent damage from lightning strikes;

Do not block the ventilation holes of the device, and always pay attention to whether the device fan is working properly to facilitate heat dissipation of the device;

Since the device needs to be initialized at startup, the interval between each switch must be greater than 4 seconds;

The analog video and audio signals input by the encoder must be standard full TV signals, that is, with line and field synchronization, which meets the requirements of the radio and television standards; if it is a non-standard video and audio signal, it is necessary to add one before the analog video and audio signal is input to the encoder Time base corrector, synchronous processing of input signal source;

The encoder used to transmit TV news should also provide video signals in spare time to prevent the crash.

3. Use and maintenance of the electric system

The system must be reliably grounded to prevent the generation of dangerous voltages. The rack ground, three-phase four-wire ground, and -48 volt ground should be grounded separately, and finally connected to a ground plate;

Check the output voltage value every quarter to ensure that it does not exceed the error range, and the inspection results should be archived in order to find abnormalities.

Four conclusions

Over the past year, the digital transformation of Yuncheng ’s microwave transmission system has improved the quality of radio and television signal transmission, the reliability of the system, the reduction of microwave external radiation, the increase of the system transmission quality, the enhancement of anti-interference ability, and the maintenance of equipment. It has been reduced, but at the same time, it has put forward a new topic for technical personnel, that is, to continuously strengthen the learning of digital microwave transmission knowledge and digital TV knowledge. Only by constantly learning new knowledge and mastering new technologies can we truly achieve uninterrupted high-quality Transmit radio and television signals.

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