This standard applies to interference measurement in simulated radio relay systems for transmitting television and frequency division multiplexing telephone. Interference may come from various signals in the same mixed baseband of a certain radio frequency channel itself, or from other radio frequency channels. GB/T 4958.13-1988 Measurement methods for equipment used in terrestrial radio relay systems Part 3: Measurement of simulated systems Section 5: Measurement of mutual interference GB/T4958.13-1988 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
GB/T4958.13—1988
idtIEC487-3-5:1982
Methods of measurement for equipment used in terrestrial radio-relay systems Part 3: Measurement of simulated systems
Section Five-Measurement of mutual interference
Methods of measurement for equipment Used in terrestrial radio-relay systems Part 3: Simulated systems
Section Five-Measurement of mutual interferencePromulgated 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: Measurement of simulated systems
Section Five-Measurement of mutual interference
Methods of measurement for equipment Used in terrestrial radio-relay systems Part 3: Simulated systems
Section FiveMeasurement of mutual interferenceUDC621.396
621.317.08
GB/T4958.13—1988
IEC487—3—5(1982)
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-—5(1982) "Measurement methods for equipment used in terrestrial radio-relay systems Part 3: Measurement of simulated systems Section 5 1 Scope of application
Measurement of mutual interference".
This standard applies to interference measurement in simulated radio-relay systems for transmitting television and frequency division multiplexing telephones. Interference may come from various signals in the same mixed baseband of a certain radio frequency channel itself, or from other radio frequency channels. In order to make the most appropriate evaluation of the noise that may appear in the operating radio relay system, according to GB4958·10-88 "Measurement methods for equipment used in terrestrial radio relay systems Part 3: Measurement of simulation systems Section 3 Measurement of black-and-white and color television transmission" and GB4958·11-88 "Measurement methods for equipment used in terrestrial radio relay systems Part 3: Measurement of simulation systems Section 4 Measurement of frequency division multiplexing transmission", when measuring the simulated radio relay system, it is necessary to consider the interference from other signals. In order to determine the noise increase caused by interference, measurements are usually carried out in two situations: with and without interference sources. 2 Interference in mixed baseband
2.1 Television transmission
When transmitting television, the typical mixed baseband includes video signals, continuous pilot signals and four subcarriers (at most), each subcarrier is modulated by a sound program, and the following forms of interference may occur. a. Video to sound program crosstalk;
subcarrier to video crosstalk;
sound program to video crosstalk;
sound channel to sound channel crosstalk (see GB4958·3-88 "Measurement methods for equipment used in terrestrial radio relay systems d.
Part 3: Measurement of simulation systems Section 6 Measurement of sound program transmission"). 2.1.1 Video to sound program crosstalk
2.1.1.1 Definition and general considerations
Video to sound program crosstalk is the increase in interference noise generated in the sound channel by the load of the video channel. In the hybrid television baseband, this is the most important form of interference. The evaluation method is to first add a load to the video channel and then remove the load, and measure the weighted and unweighted noise levels of each sound channel in these two situations. 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
2.1.1.2 Measurement method
GB/T4958.13—1988
When measuring video to sound program crosstalk, the video channel shall be loaded with the standard test signal described in Appendix AA, 1, and the carrier frequency deviation shall be adjusted to the value specified in the detailed equipment specification. After the sound channel is adjusted in accordance with the detailed equipment specification, the weighted and unweighted signal-to-noise ratios of the sound channel shall be measured with and without the video channel loaded.
2.1.1.3 Expression of results
The measurement results shall express the weighted and unweighted signal-to-noise ratios with and without the video channel loaded. 2.1.1.4 Details to be specified
In the detailed equipment specification, the following items shall be included as required: video load signal;
b. The minimum permissible signal-to-noise ratio when video is loaded, c. The minimum permissible signal-to-noise ratio when no video is loaded. 2.1.2 Crosstalk from subcarrier to video and audio program to video 2.1.2.1 Definition and general considerations
The result of the mutual modulation between the audio subcarrier, the color subcarrier and the pilot signal may produce periodic interference components in the video channel. When the audio channel is not loaded with a signal, because there is no modulation and no spectrum diffusion, the interference of the subcarrier to the video is more serious at this time, so the crosstalk should be measured under the condition of no load on the audio channel. In order to make all the larger crosstalk signals at different frequency points visible, the load added to the measured video channel should have a frequency equal to the color subcarrier frequency and an amplitude equivalent to the sine wave signal under operating conditions. The modulation of the audio subcarrier can also produce interference components in the video channel. This is the crosstalk of audio to video, which can be evaluated by measuring the frequency and amplitude of the interference components when the video channel is not loaded when the audio channel is appropriately loaded (see GB4958·1188).
Note: The results of this measurement may not always correlate with subjective effects. 2.1.2.2 Measurement Method
The video channel is superimposed with a sine wave signal with an amplitude of 0.5V peak-to-peak and a frequency of the color subcarrier frequency. All sound subcarrier levels are adjusted to the levels given in the detailed equipment specification. When measuring subcarrier crosstalk to video, the subcarriers shall be unmodulated. The unweighted amplitude and frequency of the periodic components in the frequency range from 1kHz to the highest video frequency shall be measured using a frequency-selective level meter or baseband spectrum analyzer. The measured peak-to-peak levels are expressed in decibels relative to the luminance signal level. When measuring sound-to-video crosstalk, each subcarrier shall be modulated by a single tone with an amplitude of the sound program peak level and a frequency of 1kHz. The crosstalk shall be measured in the video channel from 1kHz to 10kHz using a frequency-selective level meter. In both cases, it is convenient to temporarily apply a sinusoidal signal of appropriate frequency and level equivalent to the peak white noise amplitude to the video channel to calibrate the reference level (0 dB) of the frequency-selective level meter or spectrum analyzer. 2.1.2.3 Presentation of results
The results of the measurement shall be presented in a narrative manner, indicating that the spurious signals do not exceed the specified maximum level within the specified bandwidth. 2.1.2.4 Details to be specified
The following items should be included in the detailed equipment specification: the peak-to-peak amplitude of the reference signal;
the maximum permissible level of each interference component, which varies with frequency, as shown in the following table: Frequency
1~20kHz
Maximum permissible level of interference component
(relative to the reference signal level)
—50dB
20kHz~1MHz
2.2 Transmission of frequency-division multiplexed telephone
GB/T4958.13—1988
Maximum permissible level of interference component
(relative to the reference signal level)
—50dB
When transmitting frequency-division multiplexed telephone, the typical mixed baseband includes the frequency-division multiplexed baseband and additional frequency bands below it (sub-baseband) and/or above it (super-baseband). Additional frequency bands can be used for a variety of purposes, such as official communications, data signals ("data below the call" and/or "data above the call"), protection channel switching signals or monitoring signals. The following crosstalk may be generated:
Frequency division multiplexing baseband to sub-baseband and/or super-baseband; sub-baseband and/or super-baseband to frequency division multiplexing baseband. 2.2.1 Crosstalk from frequency division multiplexing baseband to sub-baseband and/or super-baseband 2.2.1.1 Definition
The crosstalk of the frequency division multiplexing baseband to the sub-baseband or super-baseband is the noise measured in any part of the sub-baseband or super-baseband when a white noise load signal is added to the frequency division multiplexing baseband (Appendix AA2). 2.2.1.2 Measurement method
The noise of the sub-baseband or super-baseband is measured with and without a load on the frequency division multiplexing baseband. First, use white noise as the load. Adjust the load of the frequency division multiplexing baseband to the nominal value specified in GB4958·12-88, and the bandwidth of the white noise is appropriately limited to the capacity of the voice channel of the system under test. Use a frequency-selective level meter or baseband spectrum analyzer to measure the noise level in the sub-baseband or super-baseband at the output of the simulation system. Repeat the measurement after removing all input signals and auxiliary signals except the continuous pilot. Note: The permissible level of noise varies with the characteristics of the signals transmitted in the sub-baseband and/or super-baseband. 2.2.1.3 Presentation of results
The results shall show:
a. The effective bandwidth of the frequency-selective level meter or spectrum analyser; b. The maximum noise level and the corresponding frequency measured when the baseband is loaded, and the noise level measured at the same frequency when the baseband is unloaded
If required by the detailed equipment specification, the noise level at other frequencies measured both with and without the baseband loaded c.
The number of channels simulated by the noise load signal. d.
2.2.1.4 Details to be specified
The detailed equipment specification shall include the following items as required: the limits of the frequency band;
The maximum noise level allowed or the maximum noise level allowed increment. b.wwW.bzxz.Net
Note: The band-limited filter in the noise generator that provides the frequency division multiplexing channel noise load does not have sufficient attenuation in its stop band (i.e., in the sub-baseband and super-baseband regions) to make meaningful measurements. Therefore, if a band-limited filter is not connected to the modulator of the system under test, an additional band-limited filter must be connected.
2.2.2 Crosstalk of sub-baseband and/or super-baseband to frequency division multiplexing baseband. 2.2.2.1 Definition
Crosstalk of sub-baseband and/or super-baseband to frequency division multiplexing baseband; it is the noise measured in the frequency division multiplexing baseband when there is a signal in the sub-baseband and/or super-baseband.
2.2.2.2 Measurement method
GB/T4958.13—1988
Without loading the sub-baseband and/or super-baseband, the total noise is measured in the frequency division multiplexing band according to the noise loading test method in GB4958.12-1-88. Then, the signal given by the detailed equipment specification is added to the sub-baseband or super-baseband as a load, and the white noise load measurement is repeated. Note: If the crosstalk generated by the sub-baseband or super-baseband is masked by the inherent intermodulation noise in the frequency division multiplexing baseband, it is necessary to measure the basic noise in the frequency division multiplexing band (i.e. without white noise loading) instead of measuring the total noise. Some periodic noise components whose frequencies do not fall within the narrow measurement channel of the white noise measurement equipment should be identified, and their frequencies and levels should be measured using a frequency-selective level meter or baseband spectrum analyzer. These measurements are made both with and without loading the sub-baseband and/or super-baseband.
Note: Spurious periodic signals may be present in the frequency division multiplexed baseband even in the absence of crosstalk from sub- or super-baseband signals. 2.2.2.3 Presentation of results
The results shall be presented in tabular form showing the following: a. The basic noise and total noise levels measured in the narrow measurement channel of the frequency division multiplexed baseband with and without sub- and/or super-baseband loading
b. The frequencies and levels of any periodic components measured with and without sub- or super-baseband loading. 2.2.2.4 Details to be specified
The following items shall be included in the detailed equipment specification as required: a. The maximum noise or the maximum noise increase allowed when the baseband is unloaded;
The total noise or the maximum noise increase allowed when the baseband is loaded; the maximum level of any periodic signal allowed; c.
The signal and level of the load used for the sub- or super-baseband. d.
Note: When making all the above measurements, the sub-baseband or super-baseband signals (or both) required by the detailed equipment specification must be added to the terminal station and relay station of the simulated radio-relay system. 3 Interference between different radio-frequency channels
3.1 General considerations
When measuring and simulating a radio-relay system with multiple radio-frequency channels (for example: acceptance testing), some subsystems such as antennas and polarization filters are difficult to simulate for some practical reasons. In addition, it is generally customary to simulate the system only including odd or even radio-frequency channels, so some effects that may occur in the operating situation may not necessarily occur in the simulation situation (see GB4958·10-88). These effects must be taken into account when evaluating the noise performance of the actual radio-relay system. In many cases, the interference source can be simulated by connecting one or two external signals at appropriate points in the signal path, for example, at the input of the waveguide of the radio-frequency channel under test, using a combining network such as a hybrid connector to connect the interference source. Figure 1 shows a diagram of a waveguide connection system between a transmitter and a receiver including the above-mentioned combining network for simulating a multi-relay line. In other cases, when evaluating the total channel noise, it is more advantageous to use a calculation method instead of measuring the interference noise generated by other RF channels (see Appendix AA·3). In a multi-RF channel system, the interference noise caused by other RF channels can be divided into the following two categories: a. Adjacent channel interference and multi-carrier intermodulation products; b. Co-channel interference.
In addition, there may be other interference signals caused by signal sources such as local oscillators. 3.2 Adjacent channel interference and multi-carrier intermodulation products 3.2.1 Definition and general considerations
The way in which adjacent channel interference is generated is shown in Figure 2. Study the "going" direction channel with frequency f2 at station B. The receiver of this channel will also receive:
a. The adjacent channel signals at 1 and f3 from the "going" direction transmitter of station A (far-end interference). This is because the polarization decoupling of the antenna and waveguide system is finite, and the receiver selectivity of channel f2 is also limited; b. The signals from the "return" direction transmission channels f\1, f'2 and f'3 of station B (near-end interference). This is due to the limited selectivity of the transmitter and receiver coupling network, as well as the reception of image frequencies. 4
GB/T4958.13—1988
Note: In some cases, multi-carrier intermodulation products generated by the "return" direction transmitter of station B, such as "2p-q" or \p+q-r" types (whose frequencies are within the "going" direction receiver band), can also cause near-end interference at station B. These products are caused by intermodulation between the transmitter signals in the "return" direction due to nonlinearities, such as poor waveguide connections, nonlinear components, etc. In modern radio-relay systems, when the receiver and transmitter use the same polarization but do not share the same antenna, and/or when the RF channels are configured to minimize the impact of multi-carrier intermodulation products, the above-mentioned near-end interference can generally be ignored. 3.2.2 Measurement method of adjacent channel interference
Adjacent channel interference can be simulated by introducing a signal into the merging network as shown in Figure 1. The introduced signal frequency should be the same as the adjacent channel frequency given in the detailed equipment specification. When two simulated interference signals (one higher than the measured channel frequency and the other lower than the measured channel frequency) are connected at the same time, the actual interference noise caused by them can be directly measured. When only one signal is connected at a time, first connect a signal higher than the measured channel frequency, and then connect a signal lower than the measured channel frequency. Measure the interference noise in both cases. From the measured values, the interference noise generated when two interference signals are connected can be calculated. Measure the interference noise at two levels of the useful signal, one level is equivalent to the level under free space propagation conditions. The other level is equivalent to the level under the deep drop (for example, 30dB) conditions given in the detailed equipment specification. The range of corresponding changes in the interference signal level should be determined by agreement between the buyer and the manufacturer. The load signal used to modulate the simulated interference signal is determined by the type of information that the channel is scheduled to transmit. When simulating frequency division multiplexing transmission, a white noise signal with bandwidth equivalent to the channel capacity should be used. When simulating television conditions, a conventional television load signal (Appendix A, A.1) is used for modulation.
When making interference measurements, it is assumed that the RF channel under test is suitable for transmitting frequency-division multiplexed telephone signals, because this implies stricter requirements than when transmitting television signals. Therefore, the interference noise of the measured channel is first measured using the white noise test meter described in GB4958.12-88, and it should be noted that the interference noise may be smaller than the intermodulation noise in the baseband. In the second step, use a frequency-selective level meter or a baseband spectrum analyzer to measure the frequency and level of any periodic components that do not fall within the narrow channel bandwidth of the white noise receiver. The measurement results listed above are the sum of intelligible crosstalk and incomprehensible crosstalk. If the intelligible crosstalk is to be determined separately, the interfering carrier can be modulated with a sine wave signal at different baseband frequencies (for example: at the high end, low end and center frequency of the baseband). If it is necessary to modulate with a frequency higher than the baseband, an unmodulated subcarrier and pilot signal can be used for modulation. The carrier of the useful signal should not be modulated. Use a frequency-selective level meter and a baseband spectrum analyzer to measure the signal level in the measured channel. The frequency of the signal is the same as the frequency of the signal used to modulate the interfering carrier. 3.2.3 Representation of results
The measurement results should show:
a. Carrier frequency of the useful signal,
b. Level of the useful carrier,
Carrier frequency of each interfering signal
Level of each interfering carrier,
Modulation type of each interfering carrier;
f. Level of each interfering noise.
It should be stated whether this result is total crosstalk (intelligible and intelligible) or only intelligible crosstalk. 3.2.4 Details to be specified
The detailed equipment specification should include the following items as required: a. Frequency, level and modulation data of the useful signal; b. Frequency, level and modulation data of each interfering signal; c. Permissible interference level.
3.3 Co-channel interference
The way co-channel interference is generated is shown in Figure 3. The receiver of the "going" direction channel 1 of station B can also receive: a.
Signal f1 from the "return" direction transmitter of station C, because the antenna of station B still has a certain response to the signal from this direction;
b. Signal f1 from the "return" direction transmitter of station A, because the back radiation of the "return" direction antenna of station A. The interference generated by the transmitter of station C is usually more serious interference, because the fading of the useful signal and the useless signal is not related.
GB/T4958.13—1988
Co-channel interference may also occur under cross-station propagation conditions. At this time, a "going" direction receiver may respond to the co-channel signal directly from a station three relay sections away. This effect does not occur in the simulation system and can usually be ignored in the actual operating system if the site selection is appropriate.
Because none of the subsystems that make up the simulated radio-relay system under test will produce co-channel interference, it is best to use calculation methods instead of measurement methods to evaluate the effect of co-channel interference. Co-channel interference has two components: a. Interference noise generated by the modulation of the interfering carrier, and b. Baseband signal with a frequency equal to the difference between the interfering carrier frequencies. When calculating the noise, it is assumed that the interference signal level has been determined by the above system parameters. The receiver signal level and modulation characteristics are assumed to be the same as those given in 3.2.2 for adjacent channel interference measurements. GB/T4958.13—1988
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Figure 1 Typical transceiver waveguide system to which an interfering signal can be connected. Four West One
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Figure 2 shows an example of how adjacent channel interference is generated in a relay section of a line with three two-way radio frequency channels
Figure 3 shows an example of how co-channel interference is generated in two relay sections of a two-way channel line
GB/T4958.13-1988
Appendix A
Reference Documents
(Reference Documents))
A.1CCIR Recommendation 570 (Volume XI): Standard test signal for conventional load of television channels. A.2
CCIR Recommendation 3993 (Volume Area): Noise measurement of frequency division multiplexing telephone radio relay systems using continuous uniform spectrum signals. CCIR Report 388-3 (Volume Area): Methods for determining interference between terrestrial radio relay systems and fixed satellite service systems. A.3
CCIR Recommendation 567 (Volume XI): Transmission performance of television circuits used for international switching. A.4
Additional notes:
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 Fourth Research Institute of the Ministry of Posts and Telecommunications. The main drafter of this standard was Cai Yaocheng.Figure 1 Typical transceiver waveguide system into which interference signals can be connected. Figure 2 shows an example of how adjacent channel interference is generated in a relay section of a line with three bidirectional RF channels. Figure 3 shows an example of how co-channel interference is generated in two relay sections of a line with one bidirectional channel. GB/T 4958.13—1988 Appendix A Reference Documents (Reference Documents) A.1 CCIR Recommendation 570 (Volume XI): Standard test signal for conventional load of television channels. A.2
CCIR Recommendation 3993 (Volume Area): Measurement of noise in frequency division multiplexed telephone radio relay systems using continuous uniform spectrum signals. CCIR Report 388-3 (Volume Area): Methods for determining interference from terrestrial radio relay systems and fixed satellite service systems. A.3
CCIR Recommendation 567 (Volume XI): Transmission performance of television circuits used for international switching. A.4
Additional Notes:
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 Fourth Research Institute of the Ministry of Posts and Telecommunications. The main drafter of this standard is Cai Yaocheng.Figure 1 Typical transceiver waveguide system into which interference signals can be connected. Figure 2 shows an example of how adjacent channel interference is generated in a relay section of a line with three bidirectional RF channels. Figure 3 shows an example of how co-channel interference is generated in two relay sections of a line with one bidirectional channel. GB/T 4958.13—1988 Appendix A Reference Documents (Reference Documents) A.1 CCIR Recommendation 570 (Volume XI): Standard test signal for conventional load of television channels. A.2
CCIR Recommendation 3993 (Volume Area): Measurement of noise in frequency division multiplexed telephone radio relay systems using continuous uniform spectrum signals. CCIR Report 388-3 (Volume Area): Methods for determining interference from terrestrial radio relay systems and fixed satellite service systems. A.3
CCIR Recommendation 567 (Volume XI): Transmission performance of television circuits used for international switching. A.4
Additional Notes:
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 Fourth Research Institute of the Ministry of Posts and Telecommunications. The main drafter of this standard is Cai Yaocheng.
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