GB/T 5581-1985 Technical requirements and test methods for 75 baud/180 Hz frequency modulated audio frequency telegraph
Some standard content:
National Standard of the People's Republic of China
GB/T5581—1985
75 baud/180 Hz frequency modulated audio frequency telegraph
Technical requirements and test methods
Specification and measuring method offrequency-modulated voice-frequencytelegraph set for a modulation rate of75 Bauds with channelsspaced at 180 HzPublished on November 12, 1985
National Bureau of Standards
Implementation on July 1, 1986
National Standard of the People's Republic of China
75 baud/180 Hz frequency modulated audio frequency telegraph
Technical requirements and test methods
Specification and measuring method offrequency-modulated voice-frequencytelegraph set for a modulation rate of75 Bauds with channelsspaced at 180 HzUDC621.394.6
:621.376.2
GB/T5581—1985
This standard applies to 75 baud, 180Hz frequency modulation audio frequency telegraph (hereinafter referred to as telegraph) fixedly installed on the carrier line.
This standard adopts CCITT Yellow Book (1980) R·35 Recommendation 1 Technical Requirements
1.1 Equipment working conditions:
Ambient temperature: +5~+40℃
Relative humidity: not more than 85% (at +25℃) Atmospheric pressure: 86～106kPa
1.2 Working power supply: DC 24±2.4V, two power supply groups, one positive pole is grounded, one negative pole is grounded, the deviation between the positive and negative power supplies is not more than 1.2V, or AC 220±22V, 50Hz. 1.3 Number of reporting channels: 16 channels
1.4 Modulation rate: 75 baud
1.5 Frequency interval of each channel: 180Hz
1.6 When the DC circuit of each reporting channel inputs positive current or no current, it should send a positive current signal frequency, and when it inputs negative current, it should send a negative current signal frequency. Its nominal value is calculated according to the following formula: F+=Fo+45
F_-Fo-45
Where: F. - The nominal center frequency of the reporting channel, Hz: - The nominal positive current signal frequency of the reporting channel, Hz, F+
F_——The nominal negative current signal frequency of the reporting channel, Hz. 1.7 The nominal center frequency of each reporting channel is calculated according to the following formula: F. =450+（n-1）X180
Wherein: Fo—nominal center, Hz: minimum 450Hz, maximum 3150Hz;
n——serial number of the reporting circuit.
1.8 Impedance: The impedance at the total audio transmission end and the receiving input end is 6002 balanced to ground. 1.9 The actual positive and negative current signal frequencies emitted by the telegraph shall meet the following requirements: (1)
1.9.1 The difference between the average value of the positive and negative current signal frequencies and the nominal center frequency shall be within the range of ±0.5Hz for crystal-controlled telegraphs and within the range of ±2Hz for non-crystal-controlled telegraphs. 1.9.2 The difference between the positive and negative current signal frequencies should be within the range of 90 ± 3 Hz. 1.9.3 When the room temperature is +5~+40℃ and when the room temperature is +25℃, the change in the positive and negative current signal frequencies should not exceed 3 Hz.
1.10 The working level relative to the zero level point at the total audio transmission output end: 1.10.1 The rated value of the signal level of the working frequency F+ and F- of each reporting channel is -21.3±1.7dBm0. 1.10.2 The signal level difference of the working frequency F+ and F- of the same reporting channel should not exceed 1.7dB. 1.11 Crosstalk within this machine: In the case of the total loop test of the terminal, except for the reported channel under test, all other channels are open, and the crosstalk level after the branch filter of each received reporting channel under test should be at least 34.7dB lower than the rated level of the signal at that point. 1.12 Reporting characteristics: Under rated conditions, the reporting rate is 75 baud, other reporting channels are open, and 1:1, 1:6, and 6:1 signals are transmitted.
1.12.1 When transmitting 1:1 signals, the isochronous distortion value should not be greater than 3% (4% is allowed for the 1st and 2nd channels). 1.12.2 When transmitting 1:6 and 6:1 signals, the isochronous distortion value should not be greater than 5%. 1.12.3 When the received signal level is 8.7dB higher or 17.4dB lower than the rated working level, the distortion value should not be greater than 7%. 1.12.4 When concentrated sinusoidal interference is introduced into the measured reporting channel, and its interference level is 20dB lower than the received signal level, and the interference frequency is F+ or F_, the distortion value should not be greater than 12%.
1.12.5 When the frequency deviation Af at both ends of the carrier voice channel of the open reporting channel is not greater than 5Hz, the distortion value should not be greater than (5+1.8△f)%. 1.12.6 When the DC power supply voltage changes by ±10%, the distortion value indicators in 1.12.1 to 1.12.5 are allowed to increase by 1%. Note: Rated conditions refer to the ambient temperature of +15~+35℃, relative humidity of 45%~75%, power supply voltage of ±24V, and the working level remains rated. bzxZ.net
1.13 The receiving adjustment range should not be less than 25%. 1.14 Return loss: At the total audio transmission output and receiving input, the return loss of 6002Q in the frequency band of 300~3400Hz should not be less than 20dB.
1.15 Alarm performance: When the total receiving signal level is low to a level that cannot work normally, a visible and audible alarm signal should be issued, and its level value and control method are selected by the manufacturer. 2 Test methods
2.1 Except for special provisions, all tests should be carried out under the conditions of +15~+35℃, relative humidity 45%~75%, using a regulated power supply (DC 24±0.48V, two power supply groups, one group of positive poles grounded, one group of negative poles grounded. AC 220±4.4V) and 4 hours after power on. 2.2 Test instrument and equipment requirements: The following test instruments must be calibrated with national secondary standard measuring instruments. 2.2.1 Level tester.
2.2.2 Frequency meter with more than four digits or more than four digits with decimal point. 2.2.3 Audio oscillator capable of sending 1Hz or 0.1Hz steps. 2.2.4 Isochronous signal distortion tester.
2.2.5 600Q balanced attenuator with variable more than 50dB and 0.1dB steps. 2.2.6 Carrier telephone circuit or equivalent modulation and demodulation equipment that conforms to relevant national standards. 2.3 Test of the frequency of each transmission signal: Use a digital frequency meter to test the frequency of the F+ or F- signal output by each reporting channel one by one, which should meet the indicators specified in 1.9.1 and 1.9.2 of this standard. 2.4 Test of working level:
When testing the working level of each transmission signal, send the F+ or F signal of the tested reporting channel to the main audio transmission end, and do not send out the signals of other reporting channels. Use the wide-band, 600 impedance terminal of the level meter to measure the levels of these two signals at the main audio transmission output end, which should meet the indicators specified in 1.10.1 and 1.10.2 of this standard. 2.5 Test of crosstalk within the machine: After adjusting the working level of each point of the machine under test according to the above 2.4, connect its total audio transmission output terminal and total audio receiving input terminal into a self-loop, and make each reporting channel a 75-baud amplifier point (in the analog working state). The signal of the reported channel under test is not sent out. The crosstalk level measured after the receiving branch filter of the reported channel under test should meet the indicators specified in Article 1.11 of this standard. 2.6 Test of reporting characteristics: First check the frequency and level of the tested telegraph according to the above 2.3 and 2.4. After meeting the requirements, perform this test. During the test, the total audio transmission output terminal and the receiving input terminal are connected through a balanced variable attenuator, the reporting rate is 75 baud, and other reporting channels are all 75 baud. The reported channel under test transmits 1:1, 1:6, and 6:1 signals. After adjusting to eliminate the partial distortion, the distortion value is read again. Under rated conditions:
2.6.1 The measured distortion value should meet the indicators specified in 1.12.1 and 1.12.2 of this standard. 2.6.2 Change the attenuation of the attenuator and adjust the internal receiving amplifier or other methods to increase the receiving level by 8.7dB or decrease it by 17.4dB, the measured distortion value shall meet the indicators specified in 1.12.3 of this standard. 2.6.3 The measured reporting line introduces concentrated interference. The introduction method is as follows: After connecting two 5.1kQ resistors in series to the output loop of an oscillator, cross-connect it to the total audio receiving end to send the interference signal (Figure 1). When testing the distortion value of a certain line, first send a 1:1 signal to measure the signal level value on the "receiving level" jack of the line (no interference signal is sent at this time); then short-circuit the "transmitting level" jack (that is, the signal is not sent out), and send an interference signal from the oscillator, whose frequency is the signal frequency F+ or F- of the measured line, adjust the oscillator output so that the interference signal level on the "receiving level" jack is 20dB lower than the signal level at this point, and then cancel the above short-circuit, and the measured distortion value shall meet the indicators specified in 1.12.4 of this standard.
The output impedance of the oscillator is 02, balanced to the ground. 2.6.4 Open the total audio transmission output and receiving input of the telegraph through a carrier voice circuit. When the frequency deviation Af at both ends of the carrier voice circuit of the open voice circuit is not greater than 5Hz, the distortion will not be eliminated after the detuning. Test the distortion value of each channel, which should meet the calculation index specified in 1.12.5 of this standard.
Random start
Reduced total audio
Transmission mountain new chemical
Long total 6
Figure 1 Block diagram of concentrated interference test
2.6.5 When the DC power supply voltage supplied to the telegraph changes by ±10%, test the distortion value according to the methods of 2.6.1, 2.6.2, 2.6.3, and 2.6.4, which should meet the index specified in 1.12.6 of the standard. 2.7 Deviation range test: Under rated conditions, use an isochronous signal distortion tester to send a 1:1 signal, rotate the deviation potentiometer, and try to see the deviation range (this test can also be carried out simultaneously with 2.6.1). The measured results should meet the indicators specified in Article 1.13 of this standard. 2.8 Return loss test: The return loss of the total audio transmission output and the receiving input is tested using the bridge method as shown in Figure 2. When testing the return loss of the total audio transmission output, the oscillators of each transmission circuit should have no signal output. R is a resistor, whose resistance is equal to the characteristic impedance of the measured point. Here, the nominal resistance is 600 ± 62. Z is the measured impedance of the total audio transmission output or receiving input of the telegraph. The oscillator output impedance is 0, the signal level is 0dBm, balanced to ground, and the test frequency band is 300 to 3400Hz. The level meter is a high-impedance wide-band balanced type. During the test: first open the impedance Z to be tested, measure the level Po, then connect Z, measure the level P1, then the return loss value b. =(Po-P)dB.
Substitute the measurement results into the above formula, and you will get the return loss value of the total audio transmission output and receiving input, which should meet the indicators specified in Article 1.14 of this standard.
2.9 Frequency stability test: Put the tested machine (or unit chassis) into a constant temperature room (or box), turn on the power to preheat for 4 hours, adjust the temperature in the room (or box) to +25℃, keep it warm for 4 hours, adjust the frequency, then raise the temperature in the room (or box) to +40℃, keep it warm for 4 hours, test the frequency of each reporting circuit according to Article 2.3 of this standard, and its value should meet the indicators specified in Article 1.19.3 of this standard, then lower the temperature to +5℃, keep it warm for 4 hours, and repeat the above test. Domestic source type machine
Front impedance
Transformer construction
Untransformer layout
Figure 2 Block diagram of return loss test
2.10 Alarm performance test, connect the total audio transmission output terminal and receiving input terminal of the telegraph machine in series with a balanced variable attenuator, connect them into a self-loop loop, adjust the variable attenuator to make the total receiving signal level drop to the alarm level value, and a visible and audible alarm signal should be issued. 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 Post and Telecommunications Industry Standardization Research Institute. This standard was drafted by the Chongqing Communication Equipment Factory of the Ministry of Posts and Telecommunications. The main drafter of this standard is Liao Hongfu.
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