GB/T 3974-1983 Interference tolerance for large capacity and long distance analog microwave communication trunk telephone transmission
Some standard content:
National Standard of the People's Republic of China
GB/T3974—1983
Telephone transmission interferenceallawances for long-distance high-capacityanaloguemicrowavecommunication systems1983-12-15Promulgated
National Bureau of Standards
Implementation on 1984-10-01
National Standard of the People's Republic of China
Telephone transmission interferenceallawances for long-distance high-capacityanaloguemicrowavecommunicationsystemsUDC
12:621
.391.82
GB/T3974-1983
This standard specifies the telephone transmission interference tolerance for large-capacity long-distance analogue microwave communication trunks in the national communication network. It is the basis for the overall design, equipment production, circuit construction and maintenance, and technical transformation of the analog microwave communication system. This standard is also the basis for the interference coordination between the analog microwave communication trunk system of the national communication network and other radio systems. 1 Limitation of interference
The design of the large-capacity and long-distance analog microwave communication system in the national communication network adopts the hypothetical reference circuit recommended by the International Radio Consultative Committee (CCIR) (see CCIR Recommendation 1-392). The reference circuit is 2,500 kilometers long, and the total length is divided into 9 modulation sections, each modulation section contains 6 relay sections.
In each modulation section of the hypothetical reference circuit, the total interference noise power generated by various interference sources of the system at the zero relative level point of the highest voice channel shall not exceed 450pW per minute average value (weighted but not weighted) for more than 20% of the time in any month. The interference limit for the system is divided into two parts: internal and external. The sum of the interference noise power inside the system shall not exceed 440pW, and the sum of the interference noise power outside the system shall not exceed 10pW. 2 Limitation of internal interference sources in the system
The maximum permissible interference noise power generated by various interference sources in the system is listed in the table below. At the same time, the total noise power generated by all interference sources in the system shall not exceed 440pW. 3 Limitation of external interference sources in the system
3.1 Radar interference
The permissible interference noise power of each radar interference source is 90pW. The permissible interference noise power of each modulation segment and the entire radar interference source is 90pW.
Interference source name
Front-to-back interference
Cross-station interference
Propagation distortion
Combined interference
Third-line interference
Microwave feeder echo interference
Intermediate frequency cable echo interference
Front-to-side interference
Single-amount interference
Adjacent channel interference
Published by the National Bureau of Standards on December 15, 1983
Allowable interference noise for each interference source Power (pw)
Allowable interference noise power per modulation segment
When the signal fades to the threshold level, the interference power level should be 6dB lower than the signal power level at the demodulator input of the receiver1984-10-01 implementation
3.2 Satellite earth station interference
GB/T3974—1983
In principle, the allowable value of interference noise power from satellite earth stations must be included in the allowable value of the total noise power of the system. In some cases, the total noise power value can be considered to be increased by 10% as the allowable value of interference noise power of satellite earth stations. At this time, the allowable value of interference noise power from satellite earth stations is at the zero relative level point of the highest voice channel of the 2500 km assumed reference circuit, and the average value per minute shall not exceed 1000pW for more than 20% of the time in any month. 3.3 Interference of sound broadcasting
Restrictions on the interference sources of sound broadcasting are proposed according to the following three indicators: The intelligible crosstalk shall not exceed:
The incomprehensible crosstalk shall not exceed:
—73.7dBmO,;
—68.7dBmo
The single-frequency interference noise shall not exceed:—73.0dBm0.3.4 Interference of TV broadcasting
The allowable value of the interference noise power of the TV broadcasting interference source is 10pW per modulation segment. For TV transmitters working on the second, third and fourth TV channels, when the transmission power is 10kW, the distance from the microwave station should not be less than 1 km, and when the transmission power is 1kW, the distance from the microwave station should not be less than 300m. 2
Working frequency band
Channel spacing
Frequency stability
(including inaccuracy)
Transmitting bandwidth
(±0.1dB)
Voice channel frequency deviation
(RMS value)
GB/T3974—1983
Appendix A
Typical transmitting parameters of microwave communication equipment
(reference)
4GHz microwave communication equipment
Low section 3400~3800
High section 3800~4200
Arrange 6 service
channels, 2 contact channels, service in 400MHz bandwidth Channel capacity is 960 telephone/color TV plus audio
less than 2×10-5
6GHz microwave communication equipment
5925~6425
Arrange 8 business
channels and 2 contact channels in 500MHz bandwidth, and the business channel capacity is 1800 telephone/color TV plus 4 audio29.65
less than 1×10-5
GB/T3974—1983
Appendix B
Interference sources in microwave communication systems
(reference)
The interference sources in microwave communication systems can be divided into two categories: internal interference sources and external interference sources. Internal interference refers to the interference generated in the same communication system during the transmission process. External interference refers to the interference not generated by this communication system or other radio systems.
B.1 Internal interference sources of the system
B.1.1 Front-to-side interference
In the hub station (or branch station) of the microwave communication circuit, when the angle of the convergence circuit is small, the coupling of the antennas between different circuits will cause front-to-side interference. The interference path is shown in Figure B1. Assuming the number of convergence circuits is n, the number of interference sources is n-2. HO
B.1.2 Front-to-back interference
Front-to-side interference at the hub station
In the relay station of the microwave communication circuit, front-to-back interference is generated due to the back transmission and back reception of the antenna. The interference path is shown in Figure B2. The number of interference sources includes the number of front-to-back interference sources at the hub station in the communication direction. Figure B2 Front-to-back interference
B.1.3 Cross-station interference
In a microwave communication circuit using a dual-frequency system, each relay station may receive interference signals from the previous three stations in addition to the signal from the previous station. The latter is cross-station interference, and its interference path is shown in Figure B3. 4
B.1.4 Propagation distortion
GB/T3974-1983
Figure B3 Cross-station interference
On the path of microwave signal propagation, multipath reflection of the signal not only causes K-type fading, but also generates propagation distortion noise at the microwave receiver. This type of distortion is particularly obvious in large-capacity communication systems. B.1.5 Combined interference
This type of interference comes from the combination product of 2A-B type and A+B-C type between the RF signals of each channel in the microwave communication equipment. B.1.6 Third-line interference
In large-capacity microwave communication systems, third-line interference is generated in the radio frequency channel due to the conversion effect of the limiter. As shown in Figure B4, the three adjacent radio frequency channels, due to the conversion effect of the second channel receiver limiter, make the signal of the first channel interfere with the third channel, and at the same time may return to the first channel as an interference signal. Station A
￥Fan Dao
The main did not pass
B.1.7 Echo reflection interference
According to the receiver
To receive
Transmitter
Figure B4 Third line interferenceWww.bzxZ.net
According to the receiver
Receiver
In the transmission process of multi-channel signals, the impedance mismatch point in the microwave feeder and the intermediate frequency cable reflects the signal. When the time delay of the reflected wave relative to the signal wave is large, the noise generated at this time can be treated as interference noise. B.1.8 Single-frequency interference
In microwave communication circuits, when the interference signal is an unmodulated signal, or the carrier frequency beat of the modulated interference signal and the interfered signal, single-frequency interference can be generated. Single-frequency interference appears randomly in the circuit, and multiple single-frequency interference sources will not fall into the same channel at the same time, so the noise generated by single-frequency interference is not superimposed throughout the circuit. B.1.9 Adjacent channel interference
Microwave communication circuits are systems where multiple channel RF signals share antennas and feeders. During the transmission process, interference is easily generated due to the mutual coverage of the sidebands of adjacent channel signals. The impact of this interference is manifested in the increase of the noise suppression level of the interfered receiver and the reduction of the fading margin. The limitation of adjacent channel interference 5
GB/T3974-1983
is that when the signal fades to the threshold level, the ratio of the signal level at the input of the receiver demodulator to the interference level must be limited. B.2 External interference sources of the system
B.2.1 Radar interference
Radar interference is divided into two categories, one is the interference caused by the radar radiation component falling into the passband of the interfered microwave receiver, and the other is the interference caused by the radar fundamental wave falling outside the passband of the interfered receiver due to the nonlinearity of the mixer. The limitation of opponent radar interference is handled in accordance with the requirements of single-frequency interference limitation. In addition, this limitation is based on the premise that the radar machine must be equipped with a harmonic filter. B.2.2 Interference from satellite communication earth stations
In the frequency bands shared by terrestrial microwave communications and satellite communications (for example, the 4GHz and 6GHz bands), due to the large uplink transmission power of satellite communication earth stations and the high sensitivity of downlink receiving systems, if coordination is not done properly, it is easy for satellite communication earth stations to interfere with microwave stations in terrestrial microwave communication systems, or for terrestrial microwave stations to interfere with satellite earth stations. Limits on interference from satellite earth stations are determined in accordance with the recommendations of the International Radio Consultative Committee (CCIR). B.2.3 Sound broadcast interference
This type of interference does not belong to the interference source of the microwave frequency band. It is the interference of sound broadcast signals to the baseband signal obtained after demodulation of the microwave signal in the microwave receiver.
B.2.4 TV broadcast interference
Some TV broadcast channel frequencies (for example, the second, third, and fourth channel frequencies) are close to the intermediate frequency (70MHz) of the microwave receiver. When the TV broadcast transmitter is close to the microwave station, for example, in large and medium-sized cities, the TV broadcast transmission signal will interfere with the intermediate frequency signal of the microwave machine, and the beat product of the two signals will fall into the baseband to form interference. 6
GB/T3974—1983
Appendix C
Instructions for use of interference standards
(reference)
This standard limits the interference source in the form of baseband allowable interference noise power. The allowable interference noise power listed in the standard is the allowable value of the noise power of various interference sources falling into the highest voice path in the baseband of the interfered receiver. In this standard, the limit of the interference noise power allowed by the internal interference source of the system is the minimum standard. When the system characteristics are better than this standard, the margin can be arranged separately, but the circuit design must be compatible with the system design.
The following explains the conversion relationship between the noise power unit used in this standard, the radio frequency interference power and the baseband interference noise power. C.1 Noise power unit
pW: picowatt, the absolute value unit of noise power. pWO: Zero relative level point noise meter weighted noise power. dBmO: The dB number of the zero relative level point noise meter weighted noise power level. C.2 Conversion relationship between baseband interference noise power and RF interference power Carrier frequency beat
Where:
2182So
+b(dB)
The power ratio of the baseband signal of the interfered receiver to the interference noise, in dB;The power ratio of the RF signal at the input end of the interfered receiver to the RF interference, in dB;8o—RMS value of the voice channel test audio deviation;
Afo—the absolute value of the frequency difference between the signal carrier frequency and the interference carrier frequency. The frequency difference Af. in the case of co-frequency interference is determined by the frequency stability of the transmitter. The frequency difference △f. in the case of different frequency interference is determined by the difference between the two carrier frequencies. When the frequency difference Af. is greater than the baseband highest frequency of the interfered receiver, the value of the frequency difference Af. should be equal to the baseband highest frequency, carrier frequency diffusion factor.
C.2.2 Sideband Beat
C.2.2.1 Co-channel Interference
When calculated with the test tone level, it is
(dB)
+17(dB)
C.2.2.2 Different-channel Interference
+a(dB)
Where: C-interference conversion factor, which is related to the carrier frequency difference △f. between the signal and the interference, and the unit is dB. The relationship between the conversion factor and the carrier frequency difference Af. is shown in the figure below.
Additional Notes:
GB/T3974-1983
-No Warfare Plus
Interference Conversion Factor and Carrier Frequency Difference Af. Relationship Curve This standard was proposed by the Ministry of Posts and Telecommunications and was under the jurisdiction of the Telecommunications Transmission Institute. This standard was drafted by the Telecommunications Transmission Institute. The main drafter of this standard was Lu Huiju.1Unit of noise power
pW: picowatt, absolute value unit of noise power. pWO: Zero relative level point noise meter weighted noise power. dBmO: Zero relative level point noise meter weighted noise power level in dB. C.2 Conversion relationship between baseband interference noise power and RF interference power Carrier frequency beat
Where:
2182So
+b(dB)
The power ratio of the baseband signal of the interfered receiver to the interference noise, in dB; The power ratio of the RF signal at the input end of the interfered receiver to the RF interference, in dB; 8o—RMS value of the test audio frequency deviation of the voice channel;
Afo—The absolute value of the frequency difference between the signal carrier frequency and the interference carrier frequency. Frequency difference Af in case of co-frequency interference. Determined by the frequency stability of the transmitter. Frequency difference △f in case of different frequency interference. Determined by the difference between the two carrier frequencies. When the frequency difference Af. When the frequency difference Af is greater than the highest baseband frequency of the interfered receiver, the value of the frequency difference Af should be equal to the highest baseband frequency and the carrier frequency diffusion factor.
C.2.2 Sideband Beat
C.2.2.1 Co-channel Interference
When calculated with the test tone level, it is
(dB)
+17(dB)
C.2.2.2 Different-frequency Interference
+a(dB)
Where: C--interference conversion factor, which is related to the carrier frequency difference △f of the signal and the interference, and the unit is dB. The relationship between the conversion factor and the carrier frequency difference Af is shown in the figure below.
Additional Note:
GB/T3974-1983
-interference conversion factor and carrier frequency difference Af. This standard was proposed by the Ministry of Posts and Telecommunications and is under the jurisdiction of the Telecommunications Transmission Institute. This standard was drafted by the Telecommunications Transmission Institute. The main drafter of this standard was Lu Huiju.1Unit of noise power
pW: picowatt, absolute value unit of noise power. pWO: Zero relative level point noise meter weighted noise power. dBmO: Zero relative level point noise meter weighted noise power level in dB. C.2 Conversion relationship between baseband interference noise power and RF interference power Carrier frequency beat
Where:
2182So
+b(dB)
The power ratio of the baseband signal of the interfered receiver to the interference noise, in dB; The power ratio of the RF signal at the input end of the interfered receiver to the RF interference, in dB; 8o—RMS value of the test audio frequency deviation of the voice channel;
Afo—The absolute value of the frequency difference between the signal carrier frequency and the interference carrier frequency. Frequency difference Af in case of co-frequency interference. Determined by the frequency stability of the transmitter. Frequency difference △f in case of different frequency interference. Determined by the difference between the two carrier frequencies. When the frequency difference Af. When the frequency difference Af is greater than the highest baseband frequency of the interfered receiver, the value of the frequency difference Af should be equal to the highest baseband frequency and the carrier frequency diffusion factor.
C.2.2 Sideband Beat
C.2.2.1 Co-channel Interference
When calculated with the test tone level, it is
(dB)
+17(dB)
C.2.2.2 Different-frequency Interference
+a(dB)
Where: C--interference conversion factor, which is related to the carrier frequency difference △f of the signal and the interference, and the unit is dB. The relationship between the conversion factor and the carrier frequency difference Af is shown in the figure below.
Additional Note:
GB/T3974-1983
-interference conversion factor and carrier frequency difference Af. This standard was proposed by the Ministry of Posts and Telecommunications and is under the jurisdiction of the Telecommunications Transmission Institute. This standard was drafted by the Telecommunications Transmission Institute. The main drafter of this standard was Lu Huiju.
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