This standard specifies the measurement method and limit value of the immunity of 30MHz~1GHz sound and television signal cable distribution system. This standard applies to the evaluation of the system immunity during the design and acceptance of 30MHz~1GHz sound and television signal cable distribution system. GB 16788-1997 30MHz? 1GHz sound and television signal cable distribution system immunity measurement method and limit value GB16788-1997 Standard download decompression password: www.bzxz.net

GB16788-1997
This standard is formulated based on the content of "immunity" in the International Electrotechnical Commission standard IEC728-1:1986 "Cable distribution system for sound and television signals from 30MHz to 1GHz", and is consistent with the corresponding content of the international standard in terms of technical content. This standard is also a supplement and improvement to the measurement method and technical parameters of immunity in GB/T6510-1996 "Cable distribution system for sound and television signals from 30MHz to 1GHz". In this way, the standards of my country's cable television distribution system are basically consistent with international standards, which is conducive to improving the quality of my country's cable distribution system and maintaining the production of cable distribution systems. This standard is proposed and managed by the National Radio Interference Standardization Technical Committee. The drafting units of this standard are: Sichuan Provincial Radio and Television Bureau, Standardization Planning Institute of the Ministry of Radio, Film and Television, Xiwu Antenna Company of Southwest Institute of Technical Physics, and Chengdu Yinxing Radio Factory. The main drafters of this standard are: Luo Zhuwei, Wang Ximing, Li Xiang, and Liu Yanlong. 347
1 Scope
National Standard of the People's Republic of China
30MHz~1GHz Sound and Television Signals
Cable Distribution System Immunity
Measurement Methods and Limits
Measurements and limits of immunity of cabled distribution systems primarily intended for sound and television signals operating between 30 MHz and 1 GHzGB16788—1997
This standard specifies the measurement methods and limits of immunity of cabled distribution systems for sound and television signals between 30 MHz and 1 GHz. This standard is applicable to the evaluation of system immunity during the design and acceptance of cable distribution systems for sound and television signals between 30 MHz and 1 GHz.
2 Referenced Standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. When this standard is published, the versions shown are valid. All standards will be revised, and parties using this standard should explore the possibility of using the latest versions of the following standards. GB/T4365---1995 Electromagnetic compatibility terminology
GB/T6510-1996. Cable distribution system for 30MHz~1GHz sound and television signals 3 Definitions
In addition to the definitions in GB/T 4365, this standard adopts the following definitions. 3.1 External immunity external immunity The ability of a device, equipment or system to operate normally without performance degradation when electromagnetic interference invades through a path other than the conventional input terminal or antenna.
3.2 Figure of merit
For synchronous (frequency) operation, the ratio of the output port working signal level to the maximum level of the same output port pickup signal when all input ports of the system are terminated; for asynchronous operation, it is the ratio of the nearest working signal level to the maximum level of the pickup signal\. The quality factor can be used to characterize the external immunity of the system.
4 Measuring equipment
4.1 Selective frequency voltmeter
The immunity of the selective frequency voltmeter itself must be suitable for the measurement carried out in this standard. Main technical indicators:
1) If a higher working signal level is designed to obtain a larger immunity, the maximum value of these signal levels shall not exceed the provisions of Chapter 32 of GB65101996.
Approved by the State Administration of Technical Supervision on May 28, 1997 348
Implementation on June 1, 1998
a) Frequency range: 30 MHz～1GHz;
b) Level calibration error: less than 1dB;
c) Voltage measurement error: less than 2dB;
d) Measuring range: (5～120)dBμV;e) Detection method: effective value.
4.2 Load impedance
The load impedance is 75Ω.
GB167881997
The return loss should be greater than 17dB within the measured frequency range. 4.3 Antenna
Antenna suitable for the frequency range of cable distribution system. 4.4 Measurement accessories
Matching attenuators, various measurement cables and adapters used for measurement. 5 Measurement methodbzxz.net
5.1 Equipment connection
See Figure 1 for connecting equipment.
System under test
Figure 1 is used for the schematic diagram of the connection of the immunity measurement equipment5.2 Measurement procedure
Frequency-selective voltmeter
5.2.1 Disconnect the antenna and connect it to the system input port with a well-shielded load (see Figure 1). Measure the levels of all interference signals appearing at the output port of the system under test and record the results (signal level and frequency). 5.2.2 Disconnect the load at the input port of the system under test, connect the antenna, measure the signal level of all the assigned channels (rates) at the output port of the system under test and the level of the disturbance signal at any other frequency for which the result has been recorded in 5.2.1, and record all the measurement results. 5.2.3 Confirm that the frequency of the disturbance signal measured in 5.2.1 is the frequency of the external disturbance field, not the intermodulation product. The confirmation work can be assisted by installing a suitable antenna near the system under test to observe whether the frequency-selective voltmeter can receive any signal at the relevant frequency. 5.2.4 Repeat the operations from 5.2.1 to 5.2.3 at the output port of the system under test, and 5.2.3 only needs to be repeated where it is necessary to further confirm whether it is an external disturbance field. 5.2.5 In order to ensure the representativeness of the immunity measurement, the measurement should be carried out at enough points. In large broadband distribution cable networks, where broadband trunk amplifiers (with or without automatic gain control AGC or automatic level control ALC) are used at the intermediate amplification point, the measurement should also be carried out at the system output port after the above amplifier. ) 1) In large systems using AGC or ALC, the results may be unfavorable because the normal operating input signal level does not exist. In this case, other methods can be used to make the AGC or ALC work so that they are close to the normal operating gain value. 349
5.3 Result Expression
5.3.1 The measurement result is usually expressed as d1:
Where: Q-quality factor, that is, system immunity, dB; GB 16788--1997
A-—working signal level of normal operation of the system output port, dBμV; B-—the maximum interference level picked up by the output port when the system input port is terminated, dBuV. 5.3.2 The immunity of the output port of any measured system can be calculated from the results recorded in 5.2.1 and 5.2.2. When calculating the results of synchronous (frequency) immunity, the formula in 5.3.1 can be used to directly compare the results to obtain the immunity. When calculating the asynchronous (frequency) immunity results under external field interference, the group used the check in 5.2.3 to confirm that it was an external field disturbance signal. The disturbance signal level was compared with the normal operating level of the allocated channel with the closest frequency to obtain the immunity. 5.3.3 System output port immunity, different multiple immunity values ​​can be obtained at different measurement frequencies, and the worst value is the system (output port) immunity.
5.3.4 represents the complete immunity of the system under test, which can be obtained according to the results obtained at the different output ports of the system under test in Article 5.3.3, that is, the system (output port) immunity is the worst value of these immunity values. 6 System immunity limit
The system immunity requirement for TV channels is greater than or equal to 57dB; for FM channels, it is required to be greater than or equal to 60dB. 350
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