This standard is applicable to the measurement of the attenuation constant frequency characteristics of coaxial pairs by comparison method. GB 5441.8-1985 Communication cable test method Coaxial pair attenuation constant frequency characteristics test comparison method GB5441.8-1985 Standard download decompression password: www.bzxz.net

Scope of application
National Standard of the People's Republic of China
Test methods for communication cableTest fur freuuency characteristic ofattenuation coefficient of coaxial pairComparison melhod
This standard is applicable to the measurement of attenuation coefficient of coaxial pair by comparison method. UDC 621.315.2
+ 621.39 : 621
.317.3.08
GB5441.885
The test frequency is 0.06～70MHz, and the maximum value of test attenuation is 40dB. If the instrument performance allows, the attenuation value can be increased with a higher frequency.
When testing an attenuation of more than 10dB, the test accuracy is better than F+0.1. 2 Test equipment
The wiring diagram of the test system is shown in Figures 1, 2 and 3. Figure 1. Parallel comparison method
2. Parallel comparison method
Published by National Bureau of Standards on 198509-29
Implementation on 1986-06-01
In the figure: f-
Digital frequency meter
oscillator,
coaxial switch
variable attenuator
a fixed attenuator usually of 1dB;
GB 5441.8—85
Figure 3 Series-parallel comparison method
A and A type variable attenuator are used for fixed attenuation: D
-frequency selective level meter,
-variable distributor:
-digital voltmeter;
-axis pair under test:
1 coaxial short connection;
-7552 coaxial lead:
1 branch:
-2 branches,
The test instrument should meet the following requirements:
2.1 Oscillator: The output impedance is 752. Within the frequency band used, the mismatch attenuation of 759 circuit should not be less than 32dB, and the frequency can be locked in 0.1MHz or smaller steps. 2.2 Frequency-selective level meter: Input impedance is 75Ω, and within the required frequency band, the mismatch attenuation of the 7592 resistor should not be less than 32d. And at a certain input, the short-term change of the DC output level should not be less than 1×10-3H. 2.3 Variable attenuator;
2.3.1 The total attenuation of each gear should not be less than 40dB, and the resolution of the minimum gear should not be less than 0.1dB. 2.3.2 The required frequency band should be within the upper operating frequency band of the attenuator. If the attenuator is within the required frequency band, and the attenuation value of the attenuation frequency characteristic (i.e., the difference between the attenuation frequency characteristic correction value of the attenuation reading of the attenuator in Figure 1 in a comparison test, and the difference between the frequency characteristics of the two attenuators in Figures 2 and 3) is within ±1×10-~B, the frequency characteristic correction can be omitted and the DC correction can be adopted. Otherwise, the frequency characteristic correction of the attenuation value should be carried out. 2.3.3 Within the minimum and maximum temperature range of the test environment, the attenuation of each gear of the attenuator will change with the temperature. If the attenuation value of each gear of the attenuator changes within 1×10-“dB due to the temperature change, no temperature characteristic correction is required. Otherwise, the temperature characteristic correction of the attenuation value should be carried out.
2.3.4 When the attenuator input terminal is connected to 752 pure electric positive, the total mismatch attenuation of the attenuator should not be less than 32dB regardless of any gear position.
2.3.5 The attenuator should have a good mechanical structure to ensure good recovery after frequent operation. 2.3.6 The current calibration and the AC calibration within the test frequency range should be carried out regularly at the upper and lower temperature limits of the test environment temperature to obtain the correction value of the attenuation value, the temperature coefficient of the correction value and the correction value of the frequency characteristic. The temperature coefficient of the correction value is calculated for every 3~5℃ as one gear. The correction of the frequency characteristic is carried out in steps of 5 to 10 MHz, and then the correction is carried out according to the specific conditions. 2.4 Watt switch: The impedance is 75 Ω, and the mismatch attenuation and band attenuation should meet the requirements of Articles 27 and 2.8. The contact resistance should be small and stable to ensure that there is no observable change in the output after frequent switching at constant input. Note: When appropriate back-off is provided, it is allowed to test by adopting new technical methods. 2.5 Digital voltmeter: It should have a filter device and can be 5 digits or less. Its stability should ensure that within the time of a comparative test, the change of the last digit does not exceed ±2. 2.6 Variable voltage divider:
2.6.1 The circuit of the variable voltage divider is shown in Figure 4, which can be made by yourself. Figure 10 R, R2, R, the value is selected according to the DC output voltage of the selected frequency-selective level meter and the range of the digital voltmeter. 2.6.2 When both ends of the input terminal of the frequency-selective level meter are not grounded, the ends a and b in Figure 4 can be connected arbitrarily. If one end is grounded, the grounding end is connected to b. 2.6.3 The components of the variable voltage divider, especially R2, and the potentiometer, should be well connected, and at least ensure that there is no observable change on the digital voltmeter within one comparison test time. 2.6.4 The connecting leads of the variable voltage divider and the frequency-selective level meter should be made of well-shielded wires. 2.7 From the output lead of the oscillator to the input lead of the frequency-selective level meter in Figures 1 to 3, the mismatch attenuation of the entire test system should not be less than 32dB, and 30dB can be allowed in the frequency band above 24MHz. 2.8 The crosstalk attenuation B value between the two plugs with leads of the coaxial pair under test (when terminating with a 759 resistor) connected to the I branch of the test system should not be lower than the calculated value of dry formula (1): B = X - 20lg (0.115 × 10 1. Ax) Where: B——crosstalk attenuation, dB,
Ax——attenuation value of the coaxial pair under test, dB. 3 Sample preparation
3.1 The sample is a finished cable of manufacturing length, and the coaxial pair is connected by ring connection or middle connection (it must be done with regular connection parts and connection methods). To meet the attenuation value of lndB or above at the test frequency. 3.2 Measure the length of each cable sample according to the provisions of GB5111.10-85 "Test methods for cables in communications - Sine wave method for measuring the unfolded length of coaxial pairs": or use a steel tape measure to measure the length. 1 Test steps
4.1 Select the type of test system from Figures 1.2 and 3. 4.2 Measure the fixed attenuation of the test system.
GB 5441.885
4.2.1 According to the selected test system wiring type, select the wiring type for measuring the mismatch attenuation of the test system according to Figures 5, 6, and 74, and connect the system.
coaxial short circuit
752 you power on
reflection bridge
Figure 5 Series comparison method system mismatch attenuation test wiring diagram 750 standard resistor
759 standard resistor
reflection bridge
parallel comparison method system mismatch attenuation test wiring diagram? Parallel comparison method system mismatch attenuation test wiring diagram coaxial short circuit
75 standard resistor
750 standard resistor
coaxial short circuit
75Q standard resistor
4.2.2 Measure on the two branches I and II respectively. During measurement, the variable attenuator should be placed in the "all zero" (or lowest value) position. 4.2.3 When the mismatch attenuation does not reach the 32dB value specified in Article 2.7, a buffer attenuator with a certain attenuation value should be added to make the mismatch attenuation reach 32dB.
.3 Measure the attenuation value of the affected part of the test system. 4.3.1 According to the selected test system wiring type, connect the system according to the requirements of Figures 1, 2, and 3. GB 5441.8—85
4.3.2 Or at the two lead ends of the sample, respectively terminate with a shielded 75Ω resistor, directly plug in or connect through a known coaxial pair.
4.3.3 The oscillator is connected to the zero-level input, and the variable attenuator is placed in the "all zero" (or lowest value) position. 4.3.4 Place the coaxial switch on branch 1 first, adjust the frequency and sensitivity of the frequency selector, so that the frequency selector indicates a minimum level, or a minimum level corresponding to the lowest value of the attenuator.
4.3.5 Place the coaxial switch on branch 1 again, increase the sensitivity of the frequency selector, read the receiving level, and the difference between the two levels is the crosstalk attenuation value of the system.
4. Debug the test system.
4.4.1 According to the test system selected in the plan, connect the test system according to the requirements of Figure 1.2.3. 4.4.2 Select: - a shaft with the same structure as the sample and about 100mm long, replace the sample to connect to the test system. 4.4.3 Turn on the power, preheat the test instrument, and start debugging after it stabilizes. a. Place the shaft on the II branch. b. The output impedance of the oscillator is 752: the input level is adjusted to 16dB or -10dB; the output frequency is adjusted to the highest test frequency, the variable attenuator (A and A” in Figure 1, 2.3) is set to the "zero" (or minimum) position, the input impedance of the frequency-selective level meter is set to 752, and the intermediate frequency bandwidth is adjusted to an appropriate position to make the digital meter reading most stable, and select the oscillator frequency under low noise working conditions. c. Adjust the sensitivity of the oscillator input fine-tuning or frequency-selective level meter so that the level meter pointer is near 0dB and -10dB. d. Adjust the variable potentiometer and digital voltmeter so that the digital meter displays five digits. During a comparison test time, when the digital difference of the digital voltmeter reading does not exceed 1×10"dB, the system correction value can be measured. 4.5 Measuring the correction value of the system.
, 51 The measurement of system correction should be carried out at each frequency point of the sample. 4.5.2 When using the series comparison method of Figure 1 and the open-closed comparison method of Figure 2, set the variable attenuator to zero. When using the parallel comparison method of Figure 3, estimate the attenuation of the coaxial pair under test at the highest test frequency, and place both attenuators on a voltage slightly larger than this value.
4.5.3 Place the coaxial switch on branch II 1, adjust the variable voltage divider so that the digital small pressure meter displays an appropriate number, recorded as Vx. Then place the coaxial switch on branch T, read the digital small pressure meter, recorded as [4.5.4 The system correction value is based on the following formula: When using Figure 1,
Ay=20lg
When using Figure 2,
Ay = A uy+ A1 y+ 20lg
When using Figure 3,
4 = A ly+A 41x- 20lg
■ branch attenuator reading;
A1y——T branch attenuator reading;
一I branch attenuator reading correction value:
AAty-—I branch attenuator reading correction value. Wey
The above formula does not deduct the attenuation value of the 100mm long shaft pair, this value is processed in formula (11). 4.6 Measure the actual temperature of the sample.
（4）
4.6.1 Under the condition of a constant temperature room, place the cable sample in a relative humidity room until the point current resistance of the conductor in the sample sheath reaches stability, and then accurately measure the temperature of the room, which is the actual temperature of the sample. 4.6.2 When there is no constant temperature, use any of the following methods a and b to measure. Standard. Temperature measuring line method
GB5 441.8—85
In order to make full use of the electrical resolution, a wire core with an appropriate energy flow resistance value is selected in the sample (n conductors can be connected in series) as the temperature measuring line.
A thermometer with a resolution of 0.1°C is hung on the cable reel of the sample. It is recommended that when the sample is composed of ten-reel cables, there should be no less than 2 hygrometers, and the reading should be the average value of the temperature values. The DC resistance of the temperature measuring line is measured every 20-30 minutes: continuous measurement for 48 hours, at least four digits are read each time, and the temperature indicated by the thermometer and the measurement time are recorded.
Based on the resistance and temperature values ​​measured each time, a temperature change curve with time and a resistance change curve with time are drawn. The average temperature and average resistance R are calculated from the two curves respectively, and the resistance R20 of the temperature measuring line at 20 o'clock is calculated according to the following formula. R20 =
b. Temperature measuring cable method
1+0.00393(7
—20)
This method should be used in the case of periodic testing or large-scale testing. (5)
Take a cable with the same model and specification as the cable to be tested, with a basically similar length and wound on the same cable drum as the temperature measuring cable, and measure the resistance R20 of the temperature measuring wire in the cable according to the provisions of 4.6.2 item a. Then place the temperature measuring cable and the sample cable as close as possible for at least 6 hours. Measure the resistance of the temperature measuring wire in the temperature measuring cable and the resistance of the humidity measuring wire in the sample cable. Transplant the relationship between the resistance and temperature of the temperature measuring wire in the temperature measuring cable to the temperature measuring wire of the sample cable. The measurement and transplantation should be repeated several times at different times until they are consistent with each other before they can be adopted. 4.6,a At the ambient temperature of measuring the attenuation constant, the DC resistance R of the temperature measuring wire in the sheath of the sample cable is measured. 4,6.4 Calculate the actual temperature of the coaxial pair of the sample according to the following formula fx = 20 +
4.7 Measure the attenuation of the coaxial pair of the sample.
4.7.1 Series comparison method
(6)
a Connect the coaxial pair to be tested to the test system of Figure 1, set the coaxial switch to branch II, adjust the voltage oscillator to the required test frequency, and the output voltage is dB or -10dR.
b. Estimate the attenuation of the coaxial pair to be tested at the highest test frequency. Set the attenuator to a position slightly larger than this value, and use this value as the starting attenuation A
c Use the frequency selection level meter to select the frequency. Adjust the input attenuator so that the meter pointer points to the vicinity of dB, and if necessary, fine-tune the adjustable meter sensitivity.
d. Adjust the variable voltage divider so that the digital voltage represents a five-digit number, read the number, and record it as the cutoff. e. Set the coaxial switch to branch 1, keep the voltage divider unchanged, reduce the attenuation value of the variable attenuator, until the meter pointer of the selected level meter is near 0dB, so that the digital voltmeter displays the number close to 0dB, and read the variable attenuator reading as A and the digital meter reading as 0dB.
". Adjust the variable attenuator back to the starting attenuation A, and then put the coaxial switch on branch 2. At this time, the value displayed on the digital voltmeter should return to 0dB. The difference between the allowed numbers is equal to 1×10dB. If the difference exceeds this value, the test should be repeated. 4.7.2 Parallel comparison method
a. Connect the coaxial to be tested to the test system in Figure 2, and turn the coaxial switch to the working branch. Adjust the oscillator to the frequency required for the test, and the output level is dB or -10dB.
b. Use the frequency-selective meter to select the frequency. Adjust the input attenuator to make the meter pointer point to near 0dB: if necessary, adjust the sensitivity of the meter for fine adjustment.
c, adjust the variable divider to make the digital voltmeter decelerate and read the number. d, adjust the variable attenuator to a value close to the coaxial pair under test, then set the coaxial line to the "10,000" position, and further adjust the attenuation value of the attenuator to make the digital voltage meter's purple needle point to dB, and the digital voltage meter's number is close to the number on the screen, read GB. 5441.8-85
Take the reading of the variable attenuator as Au, and the reading of the digital voltmeter as . e. Place the coaxial line on the I branch, and the digital voltmeter will be small. The value of the digital voltmeter is allowed to be equivalent to 1×103dB. If the difference exceeds this value, the test should be repeated. 4.7.3 Parallel comparison method
a. Connect the coaxial line to be tested to the test system in Figure 3, and place the switch on the II branch. Adjust the oscillator to the frequency required for the test, and input the voltage to odB or -10d.
b. Variable attenuation on the III branch Place the attenuator in the same position as the attenuator of the test system. c. Use the frequency-selective level meter to select the frequency. Adjust the input attenuator so that the meter pointer points to the dB level. If necessary, adjust the level sensitivity.
d. Adjust the variable voltage divider so that the digital voltmeter displays a five-digit number. Read the number and record it as Ve. Place the coaxial switch S on the I branch and adjust the variable attenuator A so that the number displayed on the digital voltmeter is close to V. The reading of the variable attenuator is A and the reading of the digital voltmeter is VI. f. Place the coaxial switch S on the II branch. At this time, the digital meter should return to the V level. The difference in the allowed digits is equivalent to 1×10dB. If the value exceeds this value, the test should be repeated. 5
Test results and calculations
5.1 Calculation of the attenuation value A× of the coaxial pair under test. 5.1.1 In the case of the medium-link comparison method, Ax is calculated as follows: Ax = [(A, +AA)-(A, +AAI)) +A,-My+ Formula: A.
Attenuation value, dB:
-Starting attenuation, dB,
-Correction value of A, dB:
The reading of the variable attenuator when the fixed axis switch is placed on the I branch, dB; A1
-Correction value of Ai, dB,
Ay--System correction value, calculated according to formula (2), dB,-Trend correction value, calculated according to formula (8), dR. A
A4x = 20lg-
Formula: When the switch is placed on the "" branch, the value of the electric escape read on the digital meter, V; Vir
When the axis switch is placed on the "" branch, the voltage value read on the digital voltmeter, V. 5.1.2 When using the parallel comparison method, Ax is calculated according to the following formula: Ax =Aμ+AAi+A-Aybzxz.net
Formula: Ax——attenuation value, dB,
variable attenuator reading, dB,
correction value of variable attenuator reading, dB; A,——system correction value, calculated according to formula (3), dB, A
-mantissa correction value, calculated according to formula (8), dB. 5.1.3 When using the parallel comparison method, Ax is calculated according to the following formula: Ax =Ay-(A.+AA) +A
Wherein: Ax——attenuation value, dB,
A1--When the coaxial switch is placed in the TI branch, the reading of the variable attenuator (A\), (B(7)
Correction of GB5441.8-85
, dB,
System correction value, calculated according to formula (4), dB, -When the coaxial switch is placed in the 1 branch, the mantissa correction value, calculated according to formula (8), dB. 5.2 The attenuation constant α of the measured return axis at the test environment temperature is calculated according to the following formula: 1000
Q =Ax*
(dB/km)
- the length of the coaxial pair being tested after deducting the length of the 100mm short-circuited coaxial pair, m; - the actual measured value of the attenuation of the coaxial pair with the missing length. 5.3 The attenuation constant α- at standard temperature is converted as follows: at
1+Kr(tT)
武T—is the marked temperature, C
- the temperature of the coaxial pair during the test, ℃;
(dB/km）
- the attenuation temperature coefficient of the coaxial pair at the standard temperature T. Kr-
5.4 The values ​​of each frequency converted to the standard temperature should be derived by the least square method to obtain the attenuation frequency characteristics shown in the following formula: ul=VT+f +C(dB/km)
It can also be expressed as:
C = 0.5429-
A+B/ (dB/km)
[2 (1-e-29)-- (1+e-5
(dB/km）
R is the DC resistance of the inner conductor at standard temperature, α;-=d/D, is the ratio of the inner conductor diameter d of the coaxial pair under test to the inner diameter D of the outer conductor, Z,=（60）In（D/d）, is the impedance of the coaxial pair under test at high frequency, R,-\, is determined according to GB5441.1085 "Communication Cable Test Method Coaxial Pair Length Measurement Sine Wave Method" A=α+S..C
(dB/km ·V MHz)
B -b+t.-C
(dB/km - MHz)
2号-21-2VT24
(dB/km-yMHz)
(dR/km. MHz)
GB5441.8-: 85
\，, that is, the ordinal number of the test frequency.
The degree of fluctuation of the attenuation frequency characteristic can also be expressed by F. MIz
The apparent power factor F is calculated from the B value using the following formula: 183.22.B (μR)
6 Notes
6.1 is the calculation method. Formula (8) uses A, and the following formula can be used to calculate: A
(W-Vm) ×10 (dB)
Formula: The voltage value read on the digital voltmeter when the coaxial switch is placed in branch 1, V; the voltage value read on the digital voltmeter when the coaxial switch is placed in branch II, V; find the multiple of the digital voltmeter reading of 0.868~0.8692V, which is 2,1/2. During the test, the digital voltmeter reading is required to be within the 2,1/2 multiple range of 0.8630~0.8730, (21)
6.2 Formula (13) is used to represent the attenuation frequency characteristics of the solid axis pair under test, which is only applicable to the frequency band above the A frequency. Otherwise, the calculation result will have significant errors. Unless otherwise specified, the values ​​for coaxial pairs of different specifications are: 2.6/9.5mm coaxial pair.*.-f =2.5MHz 1.2/4.4mm coaxial pair..fA= 4MHz
6.3 When this method is used to test communication cables with impedances other than 752, impedance transformers should be added on both sides of the object under test. Correspondingly, when the test system is corrected, the test should be carried out with the impedance transformer connected. 6.4 When the test is carried out on a shorter sample length at a lower frequency (such as 1.2/4.4mm coaxial pair below 0.2MHz), the attenuation test error will occur due to impedance mismatch. At this time, the error can be estimated by the following formula and the test data can be corrected. 2 =8.6859 [mim2c0s (0 +P2) + Where:
Attenuation test error.
In the equation of m:
+(1 -e-211)
-Input impedance (complex effect) of the sample at the test frequency, 2,-Test system impedance, usually 759.
In the second equation:
β =a+jB
-Propagation constant of the sample.
αAttenuation constant, Np/km.
B——Phase shift constant, rad/km.
α, β can be the nominal value at standard temperature. (dB)
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This city machine share responsible person meeting2 Formula (13) is used to represent the attenuation frequency characteristics of the measured solid coaxial pair. It is only applicable to the frequency band above A frequency. Otherwise, the calculation result will have significant errors. Unless otherwise specified, the values ​​for coaxial pairs of different specifications are: 2.6/9.5mm coaxial pair.*.-f =2.5MHz 1.2/4.4mm coaxial pair..fA= 4MHz
6.3 When this method is used to test communication cables with impedances other than 752, impedance transformers should be added on both sides of the measured object. When the test system correction value is used, the test should be carried out with the impedance transformer connected. 6.4 When the test is carried out on a shorter sample length at a lower frequency (such as 1.2/4.4mm coaxial pair below 0.2MHz), the attenuation test error will occur due to impedance mismatch. At this time, the following formula can be used to estimate the error and correct the test data. 2 =8.6859 [mim2c0s (0 +P2) + In the formula:
Attenuation test error.
In the equation of m:
+(1 -e-211)
- Input impedance (complex effect) of the sample at the test frequency, 2, - Test system impedance, usually 759.
In the second equation:
β =a+jB
- Propagation constant of the sample.
α Attenuation constant, Np/km.
B——Phase shift constant, rad/km.
α, β can be the nominal value at standard temperature. (dB)
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This machine is the first place benefit,
This city machine share responsible person meeting2 Formula (13) is used to represent the attenuation frequency characteristics of the measured solid coaxial pair. It is only applicable to the frequency band above A frequency. Otherwise, the calculation result will have significant errors. Unless otherwise specified, the values ​​for coaxial pairs of different specifications are: 2.6/9.5mm coaxial pair.*.-f =2.5MHz 1.2/4.4mm coaxial pair..fA= 4MHz
6.3 When this method is used to test communication cables with impedances other than 752, impedance transformers should be added on both sides of the measured object. When the test system correction value is used, the test should be carried out with the impedance transformer connected. 6.4 When the test is carried out on a shorter sample length at a lower frequency (such as 1.2/4.4mm coaxial pair below 0.2MHz), the attenuation test error will occur due to impedance mismatch. At this time, the following formula can be used to estimate the error and correct the test data. 2 =8.6859 [mim2c0s (0 +P2) + In the formula:
Attenuation test error.
In the equation of m:
+(1 -e-211)
- Input impedance (complex effect) of the sample at the test frequency, 2, - Test system impedance, usually 759.
In the second equation:
β =a+jB
- Propagation constant of the sample.
α Attenuation constant, Np/km.
B——Phase shift constant, rad/km.
α, β can be the nominal value at standard temperature. (dB)
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This city machine share responsible person meeting
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