GB/T 4958.10-1988 Measurement methods for equipment used in terrestrial radio-relay systems Part 3: Measurements on simulation systems Section 1: General
Some standard content:
National Standard of the People's Republic of China
GB/T 4958.10—1988
idt IEC 487-3:1975
Methods of measurement for equipment used in terrestrial Radiorelay systems
Part 3: Simulated systems
Section One-General
Promulgated on March 28, 1988
Ministry of Posts and Telecommunications of the People's Republic of China
Implementation on February 1, 1989
National Standard of the People's Republic of China
Methods of measurement for equipment used in terrestrial Radio-relay systems
Part 3: Simulated systems
Section One-General
Promulgated on March 28, 1988
Ministry of Posts and Telecommunications of the People's Republic of China
Implementation on February 1, 1989 3: Simulated systemsbZxz.net
Section One-General
621.317.08
GB/T4958.10—1988
IEC487—3(1975)
This standard is one of the national standards "Measurement methods for equipment used in terrestrial radio-relay systems" series of standards. This standard is equivalent to the International Electrotechnical Commission (IEC) standard 487-3 (1975) "Measurement methods for equipment used in terrestrial radio-relay systems Part 3: Measurement of simulated systems Section 1 1 Purpose
General
The purpose of this standard is to specify the test methods for evaluating the overall technical performance of terrestrial radio-relay systems by simulated systems within the scope that the simulated system can represent.
2 Scope of application
The test methods described in Part 3 of this standard are general methods and are applicable to simulated systems consisting of two or more subsystems. The test methods described in the following sections are applicable to the transmission of frequency division multiplexing (FDM) telephones. Transmission characteristic tests for various systems of black-and-white and color television, sound programs, and baseband digital information.
Part III should be used together with Part I: "Common measurements for subsystems and simulation systems". 3 Terms and definitions
The definitions given below are supplementary to those in Section I of Part III. 3.1 Simulated System A simulated system consists of two or more subsystems. It partially represents an actual working radio-relay system. The results obtained by measuring the simulated system can, to a certain extent, make a meaningful evaluation of the performance of an actual system to be established (see Section 4.1).
3.2 Typical Simulated System A typical simulated system is a simulation system that can fully represent the actual system and is suitable for system finalization testing. This simulation system consists of subsystems with similar design features and manufacturing processes and conforming to the manufacturer's usual characteristic rating range. Note: Although there are many different types of radio-relay systems, the composition of a typical system can be selected from one of the basic configurations listed in Section 4.2. 3.3 System type test System type test refers to a series of tests specified for a typical simulation system. It is to determine whether the subsystems manufactured by a manufacturer can be combined into a complete radio relay system that meets the overall technical requirements. Approved by the Ministry of Posts and Telecommunications of the People's Republic of China on March 28, 1988 and implemented on February 1, 1989
4 General inspection of simulation system
GB/T4958.10—1988
The first part has given the common measurement methods for subsystems and simulation systems. The third part only involves those tests that are only applicable to simulation systems.
4.1 Limitations of simulation system tests
The tests conducted on simulation systems should be as close to real working conditions as possible. Due to some objective reasons, some subsystems contained in the actual system cannot be included in the simulation test configuration. Therefore, the results of the simulated direct system measurement are subject to the following limitations when applied to the actual system:
4.1.1 Some subsystems not included in the simulation system Due to practical reasons such as volume and price, the simulation system generally does not include the following subsystems: a. Antenna;
b. Feeder;
Orthogonal polarization separator;
Long lossy intermediate frequency cable;
e. Special power supply equipment.
4.1.2 Significant effects caused by the lack of certain subsystems The equipment configuration of the simulation test does not include the subsystems listed in Section 4.1.1. This will affect the test results, and this fact must be considered when evaluating the performance of the simulation system.
Some possible effects are given below as a guide There is no echo distortion and frequency pulling because there are no feeders and antennas; a.
No adjacent channel interference. Because the simulation system usually does not contain adjacent channels, it is necessary to consider the interference that may be caused by them; b.
No co-channel interference. Because the simulation system has no antenna, in principle, there will be no co-channel interference caused by co-frequency signals from other directions (such as at intermediate stations) c.
backlobe reception: d. There is no interference from the transmitter to the receiver at the same station caused by the following reasons: sidelobe coupling between adjacent antennas,
using a shared antenna equipped with an orthogonal polarization separator; e. Propagation effects cannot be simulated, except for non-selective fading, f. In the simulation system, in addition to the specified path, coupling of abnormal paths may also occur between the transmitter and receiver working at the same frequency.
Taking into account the limitations of the simulation system compared with the actual system, it is necessary to evaluate the effects that are not included in the evaluation of the simulation system test. This can be done by performing relevant measurements and calculations on the subsystem. The measurement method of the subsystem is described in Part 2: "Measurement of the Subsystem". The calculation method does not belong to the content of this standard and can be found in other technical documents. It can be inferred that as long as the above factors are taken into account, the inherent limitations of measuring the performance of the simulation system are allowed. The details of the simulation system and the test should be determined by negotiation between the relevant parties. 4.2 Examples of basic types of simulation systems
There are two types of simulation systems:
a. One type consists of several subsystems but cannot simulate the actual system, such as modulators and demodulators or transmitters and receivers. b. The other type simulates an actual system, such as a multi-relay segment/multi-channel system. This type of simulation system is a simulation segment of the CCIR hypothetical reference circuit. If it consists of several channels, this type of simulation system is more representative of the actual system. To facilitate the selection of applicable simulation systems, several examples are given below. Note: System finalization tests are often carried out in the early stages of development, when the number of subsystems available is not sufficient. In this case, a simpler configuration can be used.
Figure 1 is derived from Figure 1 in Section 1 of Part 1: "General Principles", which shows all the subsystems that make up a complex system. Most simulation systems do not require all the subsystems shown in the figure. The simplest case is a baseband loop or an intermediate frequency loop to interconnect the modulator and demodulator.
GB/T4958.10—1988
Figure 2 shows a one-way single-channel system with only one relay segment. It is the simplest simulation system that can represent the actual system. Its input and output ports can be at baseband or at intermediate frequency. This type of simulation system does not require the transceiver duplexer Y shown in Figure 1. Figure 3 shows a link with two relay segments. The switching between the two segments can be at baseband or at intermediate frequency. As shown in the figure. The RF frequencies f1 and f1 should select a pair of frequencies from the frequency allocation plan as the frequencies in the "going" and "coming" directions. Figure 4 is a six-relay segment simulation system consisting of three pairs of different RF frequencies. Since the orthogonal polarization separators are generally omitted in the simulation system, only odd channels or even channels can be used. In actual business, these separators can make use of the phase channels. The six-segment system shown in Figure 4 represents a real system with baseband or intermediate frequency input and output and intermediate frequency switching at the intermediate station. It simulates a 380km long equal-quality segment of the frequency division multiplexing/FM telephone hypothetical reference circuit recommended by CCIR. This equal-quality segment is considered to be the upper limit of the complete simulation of the multi-relay system. In fact, this upper limit depends on the number of available channels. The system shown in Figure 4 can be considered as simulating a real system composed of six segments of unidirectional links, as shown in the figure, or it can be used by using a different connection method from the figure and adding several modulators and demodulators to simulate a real system in which each relay segment includes three sets of bidirectional links. Therefore, the interference between odd (or even) channels working in the same transmission direction and between channels working in opposite transmission directions can be measured. When connected into a three-channel single-segment system, various tests of the two-way system can be carried out, including the test of the protection switching equipment. For radio relay systems transmitting television signals, a particularly important case is the simulation system containing more than one pair of modulators/demodulators. For example, using the structure of Figure 4, if each pair of modulators/demodulators is separated by three relay segments, a system containing two pairs of modulators/demodulators can be simulated.
Note: ① The equipment used for the link of two relay segments shown in Figure 3 and the link of six relay segments shown in Figure 4 can form a single-segment multi-channel link under working conditions.
In order to simulate the signal damage caused by multiple relay segments, it can be looped back at the intermediate frequency or at the baseband. In this way, the RF signal can be transmitted in alternating directions on the same path for a total of six times.
② When looping back at the intermediate frequency, the modulation polarity on each RF path should be determined. That is, it is determined whether the frequency increases or decreases when the signal level changes in the positive direction. The modulation polarity of each relay segment of the loopback simulation system does not have to be the same as that of the actual system, so that the intermodulation noise characteristics in the two cases are different. 4.3 Measured noise characteristics
The main purpose of conducting experiments on the simulation system is to determine the effect that can be achieved in the actual business as closely as possible. The most important of these is to measure the baseband to baseband transmission characteristics between points R and R' in the simulation system as shown in Figure 1. 4.3.1 Input test signals for noise measurements in simulation systems The input test signals for frequency division multiplexing systems are specified in Part 3, Section 4: "Measurements for frequency division multiplexing telephone transmission". The input test signals and test procedures for television transmission systems are specified in Part 3, Section 3: "Measurements for black-and-white and color television transmission systems". Other test signals and test procedures may be specified. 4.3.2 Noise evaluation of simulation systems There are three main types of noise in simulation systems: periodic noise, random noise (including intermodulation noise), and impulse noise (non-periodic). The power supply may introduce all three types of noise mentioned above. Usually, it is not only desirable to measure the total noise power generated in the simulation system, but also the proportion of noise power introduced by various sources, especially for random noise. Random noise may come from four sources;
random noise related to path loss;
basic random noise not related to path loss, intermodulation noise (caused by white noise loading); interference noise.
GB/T4958.10—1988
Generally, interference noise can be ignored in simulation systems (such as described in Section 4.2). Random noise related to path loss is caused by thermal noise generated at the input of the receiver. In an FM system, the baseband signal-to-noise ratio at the output of the receiver, which is normalized to the path loss, is proportional to the carrier-to-noise ratio at the input of the receiver over most of the carrier level range, but is not proportional at the low level end near the FM threshold and the high level end near the overload point. Basic random noise is caused by many factors, such as thermal noise of baseband stages, modulators and demodulators, traveling wave tubes, local oscillators, etc. Basic random noise and random noise related to path loss can be calculated by measuring the noise power at two locations of the RF attenuator that simulates the path loss.
Periodic noise may be caused by RF interference related to the channel allocation scheme, or it may be caused by stray baseband signals. When evaluating power supply noise, it is necessary to consider the wide spectrum of stray frequencies that may be generated by modern power supply units. Pulse noise is not important in simulation systems. 4.4 Crosstalk
In simulation systems, there may be two types of crosstalk: crosstalk between baseband devices caused by capacitive coupling or other unwanted coupling; and crosstalk between FM carriers (for example, crosstalk between adjacent FM carriers when the frequency spacing is not appropriate). 1-45 -EF
Simulation radio relay system
GB/T4958.10—1988
Simulation system:
One relay section, one-way, one channel
Figure 3 Simulation system: Two relay sections, one-way, intermediate frequency or baseband switching 5
Additional instructions:
GB/T4958.10—1988
Figure 4 Simulation system: Six relay sections, one-way, intermediate frequency switching This standard is under the jurisdiction of the Post and Telecommunications Industry Standardization Research Institute of the Ministry of Posts and Telecommunications. This standard was drafted by the Post and Telecommunications Industry Standardization Research Institute of the Ministry of Posts and Telecommunications. The main drafter of this standard: Liu Yunhai.2) can be ignored. The random noise related to the path loss is caused by the thermal noise generated at the receiver input. In FM systems, the baseband signal-to-noise ratio at the receiver output related to the path loss is proportional to the carrier-to-noise ratio at the receiver input in most of the carrier level range, but is not proportional at the low level end near the FM threshold and the high level end near the overload point. Basic random noise is caused by many factors, such as thermal noise of baseband stages, modulators and demodulators, traveling wave tubes, local oscillators, etc. The basic random noise and the random noise related to the path loss can be calculated by measuring the noise power at two locations of the RF attenuator that simulates the path loss.
periodic noise can be caused by RF interference related to the channel allocation scheme, or it can be caused by spurious baseband signals. When evaluating power supply noise, the wide spectrum of spurious frequencies that may be generated by new power supply units must be considered. Pulse noise is not important in the simulation system. 4.4 Crosstalk
There may be two types of crosstalk in the simulation system: crosstalk between baseband devices caused by capacitive coupling or other unnecessary coupling; crosstalk between FM carriers (for example, crosstalk between adjacent FM carriers when the frequency spacing is not appropriate). 1-45-EF
Simulation radio relay system
GB/T4958.10—1988
Simulation system:
One relay section, one-way, single channel
Figure 3 Simulation system: two relay sections, one-way, intermediate frequency or baseband transfer 5
Additional instructions:
GB/T4958.10—1988
Figure 4 Simulation system: six relay sections, one-way, intermediate frequency transfer 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 Telecommunications. The main drafter of this standard: Liu Yunhai.2) can be ignored. The random noise related to the path loss is caused by the thermal noise generated at the receiver input. In FM systems, the baseband signal-to-noise ratio at the receiver output related to the path loss is proportional to the carrier-to-noise ratio at the receiver input in most of the carrier level range, but is not proportional at the low level end near the FM threshold and the high level end near the overload point. Basic random noise is caused by many factors, such as thermal noise of baseband stages, modulators and demodulators, traveling wave tubes, local oscillators, etc. The basic random noise and the random noise related to the path loss can be calculated by measuring the noise power at two locations of the RF attenuator that simulates the path loss.
periodic noise can be caused by RF interference related to the channel allocation scheme, or it can be caused by spurious baseband signals. When evaluating power supply noise, the wide spectrum of spurious frequencies that may be generated by new power supply units must be considered. Pulse noise is not important in the simulation system. 4.4 Crosstalk
There may be two types of crosstalk in the simulation system: crosstalk between baseband devices caused by capacitive coupling or other unnecessary coupling; crosstalk between FM carriers (for example, crosstalk between adjacent FM carriers when the frequency spacing is not appropriate). 1-45-EF
Simulation radio relay system
GB/T4958.10—1988
Simulation system:
One relay section, one-way, single channel
Figure 3 Simulation system: two relay sections, one-way, intermediate frequency or baseband transfer 5
Additional instructions:
GB/T4958.10—1988
Figure 4 Simulation system: six relay sections, one-way, intermediate frequency transfer 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 Telecommunications. The main drafter of this standard: Liu Yunhai.
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