This section deals with some measurements made at the baseband of simulated radio-relay systems and not directly related to specific types of signals actually transmitted (e.g. frequency-division multiplexed telephone and television signals). The baseband measurements described in this standard are generally made at the input of the modulator and the output of the demodulator, excluding the associated terminal equipment, such as the pre-emphasis network and de-emphasis network associated with the specific type of baseband signal. This section does not include random noise, periodic noise and impulse noise measurements. This is because these noise levels can only be meaningfully evaluated by passing through the specific type of baseband signal to which they are related and using the corresponding de-emphasis network and weighting network. The various measurements related to frequency-division multiplexed telephone, television and sound programs are given in the corresponding single sections of Part 3 of this series of standards. GB/T 4958.2-1988 Measurement methods for equipment used in terrestrial radio-relay systems Part 3: Measurements on simulated systems Section 2: Baseband measurements GB/T4958.2-1988 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
GB/T4958.2—1988
idtIEC 487-2:1981
Methods of measurement for equipment used inTerrestrial radio-relay systemsPart 3:Simulated systemsSection 2-Measurements in the basebandPromulgated on February 10, 1988
Implemented on January 1, 1989
Ministry of Posts and Telecommunications of the People's Republic of China
National Standard of the People's Republic of China
Methods of measurement for equipment used inTerrestrial radio-relay systemsPart 3:Simulated systemsSection 2-Measurements in the baseband This standard is one of the national standards "Measurement methods for equipment used in terrestrial radio-relay systems" series. This standard is equivalent to the International Electrotechnical Commission (IEC) standard 487-3-2 (1981) "Measurement methods for equipment used in terrestrial radio-relay systems Part 3: Simulated systems Section 2 Baseband measurements". 1 Scope This section deals with some measurements on the simulated radio-relay system baseband and is not directly related to specific types of signals actually transmitted (such as frequency-division multiplexed telephone signals and television signals). The baseband measurements described in this standard are generally made at the modulator input and demodulator output, excluding the associated terminal equipment, such as pre-emphasis networks and de-emphasis networks associated with a specific type of baseband signal. This section does not include random noise, periodic noise and impulse noise measurements. This is because these noise levels can only be meaningfully evaluated by passing through the specific type of baseband signal to which they are associated and using the corresponding de-emphasis networks and weighting networks. The various measurements related to frequency division multiplexing telephone, television and sound programs are given in the corresponding chapters of Part 3 of this series of standards. 2 Measurement items
The following characteristics are usually measured:
Linear input and output characteristics: input and output impedance; input and output level;
Linear transfer characteristics: amplitude/baseband frequency characteristics, group delay/baseband frequency characteristics;
Non-linear transfer characteristics: differential gain/non-linearity, differential phase/group delay;
Standby switching characteristics www.bzxz.net
Before starting these measurements, all parts of the radio-relay system should be correctly adjusted and connected. In particular, all relevant impedances, levels and frequency deviations of the baseband and radio frequency parts should be checked according to the measurement methods given in the relevant chapters of Part 1 of this series of standards. All relevant impedances, levels and frequency deviations of the intermediate frequency part should be checked according to the measurement methods given in GB6662 "Measurement methods for equipment used in ground radio relay systems Part 1 Measurements common to subsystems and simulation systems Section 3 Measurements in the intermediate frequency range". For detailed provisions on power supply and environmental conditions, see Section 1 of Part 1 of this series of standards: General Provisions. Approved by the Ministry of Posts and Telecommunications of the People's Republic of China on February 10, 1988 and implemented on January 1, 1989
Impedance and level measurement
GB/T4958.2—1988
Impedance and level measurement
GB/T4958.2—1988
Impedance and level should be measured at all input and output ends of the simulation system under test. The measurement method is shown in Section 4 of Part 1 of this series of standards "Baseband measurement".
4 Linear transfer characteristics
Amplitude/baseband frequency characteristics and group delay/baseband frequency characteristics shall be measured in accordance with the method given in Section 4 of Part 1 of this series of standards. Above a certain baseband level, these characteristics become increasingly dependent on the input level. Therefore, these characteristics should be measured at or below the level at which the characteristics begin to change. Measurements may also be made at higher levels if the measurement results are appropriately explained. 5 Non-linear transfer characteristics
Differential gain/non-linear distortion and differential phase/group delay distortion shall be measured in accordance with the method given in Section 4 of Part 1 of this series of standards.
6 Standby switching characteristics
See Section 9 of Part 2 of this series of standards: Measurement of standby channel switching equipment. Additional notes:
This standard is under the jurisdiction of the Post and Telecommunications Industry Standardization Institute of the Ministry of Posts and Telecommunications. This standard was drafted by the Post and Telecommunications Industry Standardization Institute of the Ministry of Posts and Telecommunications2
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