In order to ensure the transmission quality of voice-line fax (category 3 machines) in telephone networks or leased circuits, this standard specifies the total tolerance of various transmission impairment factors throughout the fax transmission circuit, and is the basis for the design, use and maintenance procedures of the fax communication system for class 3 machines. GB/T 5437-1985 Transmission requirements for voice-line fax (category 3 machines) GB/T5437-1985 standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
GB/T5437—1985
Document facsimile (group 3) transmission requirement
Published on September 29, 1985
National Bureau of Standardswww.bzxz.net
Implemented on June 1, 1986
1 Introduction
National Standard of the People's Republic of China
Document facsimile (group 3) transmission requirement requirement
UDC621.395.72
:621.391.6
GB/T5437=1985
In order to ensure the transmission quality of voice fax (category 3 machines) in the telephone network or leased circuit, this standard specifies the total tolerance of various transmission damage factors in the entire fax transmission circuit, which is the basis for the design, use and formulation of maintenance regulations for the fax communication system of the class 3 machine. 1.1 Fax transmission circuit
From the output point of the fax transmitter to the input point of the fax receiver, it is the entire fax transmission circuit (see Figure 1). The fax transmission circuit includes three basic parts: the local telephone circuit or dedicated line at the originating end, the long-distance circuit, and the local telephone circuit or dedicated line at the receiving end. Note: ① The local telephone circuit is the user line and long-distance city relay line that have passed the local telephone exchange. ② The long-distance circuit is the long-distance exchange circuit or leased circuit. A-fax transmitter output point: B-fax transmitter, four-wire conversion point (zero relative level point); two-wire conversion point, four-wire conversion point, D-fax receiver input point 1.2 Interface parameters
According to the relevant provisions of GB3384-1982 "Analog Carrier Communication System Network Interface Parameters", the maximum power level of the fax signal at point B is -13dBm0. The impedance is 600Q (balanced). 1.3 Fax communication quality
a. The original manuscript sent uses GB2683-1981 "Fax Test Sample", and the text quality of the received copy is evaluated according to the five-level quality score and text readability in the subjective evaluation method. b. The fax machine used for subjective assessment should comply with GB3382-1982 "Technical conditions for interoperability of Class 3 voice fax machines in telephone networks"; the quality of the copy of the terminal's self-loop should be above the subjective assessment average score of 4.5 points (including 4.5 points), and the text readability should reach 100%. When the transmission impairment factor is within the tolerance range, the message transmission establishment rate* of 4800 bit/s or 9600 bit/s is above 80%, and the average score of the copy text quality is: when the one-dimensional (MH) coding method is used, it is 3.5 points or more (including 3.5*message transmission establishment rate = the number of successful training at the specified rate, the total number of training at the specified rate
National Bureau of Standards 1985-09-29 Issued
1986-06-01 Implemented
GB/T5437-1985
points), and the text readability is above 99%. When the two-dimensional (MR) coding method is used, it is 3 points or more (including 3 points), and the text readability is 99%.
Note: The average scores of points b and c in Section 1.3 refer to the average scores obtained by subjectively evaluating the copy text quality using a scanning density of 7.7 lines/mm. When the scanning density is 3.85 lines/mm, the average score of point b is 3 points, and the text readability reaches 99.5%; when the one-dimensional (MH) encoding method is used, the average score of point c is 2.2 points, and the text readability reaches 99%. 24800 bits/second transmission rate fax communication full transmission damage factor tolerance 2.1 Full attenuation
The full attenuation of the carrier frequency 1800Hz is not more than 32dB. Note: The full attenuation of the frequency of 800Hz is not more than 24dB. 2.2 Group delay distortion
The tolerance of group delay distortion is given in Figure 2 and Table 1. The tolerance within the frequency band in the figure is expressed by the group delay value relative to 1800Hz.
Figure 2 Tolerance of group delay value relative to 1800Hz in the frequency band of 500~3000Hz Table 1
Frequency range
500~600
600~800
800~1000
1000~2800
2800~3000
Group delay distortion
2.3 Attenuation distortion
The tolerance of attenuation distortion is given by Figure 3 and Table 2. Frequency range
5001300
1300~1600
1600~2000
2000~2200
2200~2500
2500~3000
GB/T5437—1985
Maximum deviation allowed relative to 800Hz attenuation (dB)
—1~+12.0
Figure 3 Tolerance of attenuation relative to 800Hz in the frequency band of 500~3000Hz 2.4 Signal-to-noise ratio
Signal-to-noise ratio S/N (unweighted) shall not be less than 24dB. 2.5 Received echo
Signal-to-echo ratio S/E shall not be less than 27dB.
2.6 Harmonic distortion
The attenuation of the second and third harmonics shall not be less than 25dB. 2.7 Phase jitter
The phase jitter shall not be greater than 10°.
2.8 Frequency deviation
The frequency deviation |Af| shall not be greater than 5Hz.
2.9 Single-frequency interference
The signal-to-interference ratio shall not be less than 30dB.
2.10 Impulse noise
GB/T5437—1985
The count of impulse noise with a peak value exceeding -16dBm0 shall not exceed 18 times within 15 minutes. 2.11 Phase mutation
The phase mutation exceeding the measurement threshold of 20° shall not occur more than 10 times within 15 minutes. 2.12 Level mutation
The level mutation exceeding the measurement threshold of 3dB shall not occur more than 8 times within 15 minutes. 2.13 Momentary interruption
Exceeding the measurement threshold by 6dB, the number of transient interruptions with a duration of no more than 3ms shall not exceed 8 times within 15 minutes. 39600 bit/s transmission rate fax communication full transmission damage factor tolerance 3.1 Full attenuation
The full attenuation of the carrier frequency 1700Hz is not more than 22dB Note: The full attenuation of the carrier frequency 800Hz is not more than 18dB. 3.2 Group delay distortion
The tolerance of group delay distortion is given in Figure 4 and Table 3.
The tolerance within the frequency band in the figure is shown in terms of group delay values ​​relative to 1800Hz. Table He
Figure 4 Tolerance of group delay values ​​relative to 1800Hz in the frequency band 500-3000Hz 3.3
Attenuation distortion
Frequency range
500~600
600~800
800~1000
1000~2800
2800~3000
The tolerance for attenuation distortion is given in Figure 5 and Table 4. ant
GB/T5437—1985
Group delay distortion
Tolerance diagram 5 of attenuation relative to 800Hz in the frequency band of 500~3000Hz
Frequency range
500~1200
1200~1700
1700~2000
2000~2400
2400~3000
Maximum deviation value allowed relative to attenuation of 800Hz (dB)
-1~+5.5
3.4 ​​Signal-to-noise ratio
GB/T5437—1985
Signal-to-noise ratio S/N (unweighted) shall not be less than 27dB. 3.5 Receive echo
Signal echo ratio S/E is not less than 29dB.
3.6 Harmonic distortion
The attenuation of the second and third harmonics is not less than 42dB. 3.7 Phase jitter
Phase jitter is not greater than 10°p.
3.8 Frequency deviation
Frequency deviation |Af| is not greater than 5Hz.
3.9 Single frequency interference
Signal interference ratio is not less than 30dB.
3.10 Impulse noise
The count of impulse noise with a peak value exceeding -21dBm0 shall not exceed 18 times within 15 minutes. 3.11 Phase mutation
The number of phase mutations exceeding the measurement threshold of 20° shall not exceed 10 times within 15 minutes. 3.12 Sudden level change
Sudden level change exceeding the measurement threshold by 3dB shall not occur more than 8 times within 15 minutes. 3.13 Momentary interruption
Momentary interruption exceeding the measurement threshold by 6dB and lasting no longer than 3ms shall not occur more than 8 times within 15 minutes. 6
GB/T5437—1985
Appendix A
Test method
(Supplement)
This appendix provides a unified test method for the transmission impairment factors specified in the standard. The accuracy of the instruments used must be calibrated with national secondary standard measuring instruments or devices.
A, 1 Fax signal interface level adjustment
When adjusting, connect as shown in Figure A1.
The adjustment steps are as follows:
Use an oscillator (impedance 600Q) to send a 1700Hz or 1800Hz signal at point A, and the sending level is 0dBm. At point B a.
Use the level meter 600α terminal to measure and directly read the absolute value of the measured signal level, which is the attenuation value bL of the AB section local telephone circuit or dedicated line to the 1700Hz or 1800Hz signal.
b. Adjust the variable attenuator of the Class III machine transmission branch to make the transmission level S=(-13+b)dBm, which can ensure that the fax signal interface level at point B is -13dBm0.
A.2 Group delay distortion
Long reverse telephone
Delay and co-education
GB/T5437—1985
The reference frequency is 1800Hz, and the test frequency is 500, 600, 800, 1.000, 1400, 1.700, 2.200, 2.600, 28002900, 3000Hz. The transmission level at point A is 0dBm, and the group delay value relative to 1800Hz is directly read at point D. A.3 Attenuation distortion and full-range attenuation
The schematic diagram of the tested circuit is the same as Figure A2.
Connect the oscillator at point A and the level meter at point D (impedance is 6002). A.3.1 Attenuation distortion
The transmission level at point A is 0dBm, and the test frequencies are 500, 600, 800, 1000, 1200, 1300, 1600, 1700, 1800, 2000, 2200, 2400, 2500, 2700, 3000Hz. b.
Read the level value directly at point D, and calculate the attenuation or gain difference between each test frequency and 800Hz in the frequency band of 500-3000Hz.
A.3.2 Full-range attenuation
In the test of A.3.1, the absolute value of the level of 1700Hz (carrier frequency at a rate of 9600 bits/second), 1800Hz (carrier frequency at a rate of 4800 bits/second) and 800Hz directly read at point D is the full-range attenuation. A.4 Signal-to-noise ratio
A.4.1 Signal reception level S
The schematic diagram of the circuit under test is the same as Figure A2.
a. Connect an oscillator (impedance 600Ω) at point A, send a carrier frequency of 1800Hz at a rate of 4800 bits/second, and send a carrier frequency of 1700Hz at a rate of 9600 bits/second, so that the level at point B is -13dBm0. b.: Connect a level meter (impedance 600Ω) at point D and directly read the signal reception level S. A.4.2 Noise level N (non-weighted)
The schematic diagram of the circuit under test is the same as Figure A2.
Connect a 600Ω resistor at the terminal A, connect a noise meter (impedance 600Ω) at point D, and directly read the noise level N (non-weighted). A.4.3: Signal-to-noise ratio
The difference between the signal receiving level S and the noise level N (non-weighted) is the signal-to-noise ratio. A.5 Signal-to-echo ratio
City telephone circuit
Digital dedicated line
Figure noa
Changtong Electric Appliance
Low frequency and frequency syndrome
E and F disconnection points are the audio four-wire interface points receiving end. a.
City telephone computer
Iron shore television
GB/T5437—1985
Output test signal level at point E is 0dBm, and the test frequency is 1000, 1400, 1800, b.
2200, 2600Hz at 4800 bit/s rate, and 500, 1100, 1700, 2300, 2900Hz at 9600 bit/s rate. c. Select the transmission attenuation bi of the test frequency through the E-B-C-F path at point F, and calculate the signal echo ratio according to the following formula: S/B=—101g (（10 yuan）
Wherein is the weighting coefficient selected by the fax signal spectrum, the value is shown in the table below. Transmission rate
(bit/second)
ft(Hz)
Weighting coefficient
A.6 Harmonic attenuation
The schematic diagram of the measured circuit is the same as Figure A2.
Connect an oscillator (impedance 600Q) at point B and send a 700Hz sinusoidal signal with a level of -13dBm0.a
23002.900
b. Connect a low-frequency frequency selector (impedance 600Q) at point C to measure the 700Hz fundamental signal level, the second harmonic (1400Hz) level and the third harmonic (2100Hz) level. The wave signal levels are respectively the same as A.7 Phase jitter
The schematic diagram of the circuit under test is the same as Figure A2. The difference between the second and third harmonic levels is the attenuation of the second and third harmonics. a: Connect the phase jitter meter transmitter or oscillator (impedance is 600Q) at point A, and send a sinusoidal signal with a frequency of 1020Hz to make the level at point B be -13dBm0.
b. Connect the phase jitter meter receiver (impedance 600Q) at point D and read the phase jitter value directly. A.8 Frequency deviation Af
The schematic diagram of the circuit under test is the same as Figure A2.
Connect the frequency deviation tester transmitter (impedance 600Q) at point A, and send two test signals with harmonic relationship, 1020 and 2040Hz, and the sending level is 0dB m.
b. Connect the receiving end of the frequency deviation tester (impedance 600Ω) at point D and directly read the frequency deviation value Af. A.9 Single-frequency interference
The schematic diagram of the circuit under test is the same as Figure A2.
The signal receiving level measurement method is the same as A.4.1. a.
bConnect a 600Ω resistor at the terminal of point A and connect a low-frequency frequency selection meter (impedance 600Ω) at point D to measure the single-frequency interference level in the frequency band of 300~3400Hz. The difference between the signal receiving level and the single-frequency interference level is the signal-to-interference ratio. 9
A.10 Pulse noise
The schematic diagram of the circuit under test is the same as Figure A2.
GB/T5437—1985
Connect at point A Oscillator (impedance 6002), transmit carrier frequency 1800Hz at 4800 bit/s rate, transmit carrier frequency 1700Hz at 9600 bit/s rate a.
, make the level at point B be -13dBm0, connect level meter (impedance 600②) at point D to directly read signal receiving level S. bTerminate point A with 600Q resistor, connect impulse noise tester (impedance 600) at point D, set impulse noise threshold level 3dB (at 4800 bit/s) or 8dB (at 9600 bit/s) lower than signal receiving level at point D, take 15 minutes as one test unit, and directly read pulse count. A.11 Phase mutation
The schematic diagram of the circuit under test is the same as Figure A2.
a. Connect an oscillator or the transmitting end of a data circuit tester (impedance 600Q) at point A to send a sine signal with a frequency of 1020Hz, so that the level at point B is -13dBm0.
b. Connect the receiving end of a data circuit tester (impedance 600Q) at point D, set the phase mutation threshold to 20°, take 15 minutes as a test unit, and directly read the phase mutation count. A.12 Level mutation
The schematic diagram of the circuit under test is the same as Figure A2.
a. Connect an oscillator or the transmitting end of a data circuit tester (impedance 600Q) at point A to send a sine signal with a frequency of 1020Hz, so that the level at point B is -13dBm0.
b.: Connect the receiving end of a data circuit tester (impedance 600Q) at point D, set the level mutation threshold to 3dB, take 15 minutes as a test unit, and directly read the level mutation count. A.13 Momentary Interruptions
The schematic diagram of the circuit under test is the same as Figure A2.
a. Connect an oscillator or the transmitting end of a data circuit tester (impedance is 600Ω) at point A, and send a sinusoidal signal with a frequency of 1020 or 2000Hz, so that the level at point B is -13dBmo. b. Connect the receiving end of a data circuit tester (impedance is 600Ω, which can detect 0.3ms momentary interruptions) at point D, set the momentary interruption threshold to 6dB, take 15 minutes as a test unit, and read the momentary interruption count directly. Additional Notes:
This standard was proposed by the Ministry of Posts and Telecommunications of the People's Republic of China and is under the jurisdiction of the Telecommunications Transmission Research Institute of the Ministry of Posts and Telecommunications. This standard was drafted by the Telecommunications Transmission Research Institute of the Ministry of Posts and Telecommunications. The main drafters of this standard are Shi Xiaohui and Yang Zemin. 103ms interruption), the interruption threshold is set at 6dB, 15 minutes is used as a test unit, and the interruption count is directly read. Additional Notes:
This standard is proposed by the Ministry of Posts and Telecommunications of the People's Republic of China and is under the jurisdiction of the Telecommunications Transmission Research Institute of the Ministry of Posts and Telecommunications. This standard is drafted by the Telecommunications Transmission Research Institute of the Ministry of Posts and Telecommunications. The main drafters of this standard are Shi Xiaohui and Yang Zemin. 10
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