GB 5441.7-1985 Test methods for communication cables - Attenuation constant test - Open-short circuit method

This standard is applicable to the measurement of the attenuation constant of high-frequency symmetrical communication cables (including high-frequency quads and high-frequency pairs in integrated cables) of manufactured lengths by the open-short circuit method (referred to as the arbitrary frequency method) at any frequency, and the measurement of the attenuation constant of coaxial pairs in coaxial communication cables by the open-short circuit method (referred to as the resonant frequency method) at resonant frequency. The attenuation range of the tested cable is within 10dB. The test frequency range is below 2.5MHz. If the test conditions permit, the frequency range can be expanded. GB 5441.7-1985 Communication cable test method Attenuation constant test Open-short circuit method GB5441.7-1985 Standard download decompression password: www.bzxz.net

1 Scope of application
National Standard of the People's Republic of China
Test methods for communication cable
Attenuation constant test Open and short circuit method
Test methods for communication cableAllenuation coefficient testOpen and short circuit methodUDC 621.815,2
: 621. 39 : 621
- 317.3.08
GB 5441.785
This standard is applicable to the measurement of the attenuation constant of the high-frequency symmetrical communication cable (including the high-frequency four-wire group and high-frequency line pair in the integrated cable) at any frequency by the open and short circuit method (referred to as the arbitrary frequency method) and the attenuation constant of the attenuation pair in the interaxial communication cable by the open and short circuit method (referred to as the harmonic frequency method) at the potential vibration frequency. The attenuation range of the tested cable is within 10dB. The test frequency range is below 2.5MHz. If the test conditions allow, the frequency pool can be cut. 2 Test equipment
The test system is as shown in the wiring schematic diagram: Figure: ——Digital frequency;
G——Oscillator:
B—High frequency impedance (admittance) bridge:
D——Frequency selective meter.
The test equipment should meet the following requirements:
2.1 Oscillator: The frequency stability of continuous operation for 4h is not less than ±0.5%. Input voltage: 0～20dB. 2.2 Bridge: The accuracy is +2%. When measuring the cable, a symmetrical impedance (admittance) bridge is used. When measuring the coaxial pair, a non-shifted impedance (admittance) bridge is used. bzxz.net
2.3 Frequency selective meter: The sensitivity is not low! .9)d3 (excluding the meter head). 2.4 Digital frequency F: The number of digits displayed is not less than 6, and the frequency stability is not less than -1.5×107/2h. 3 Sample preparation
The test sample is a finished cable of manufacturing length.
4 Test steps
4.1 Arbitrary frequency method
.1.1 Connect the test system according to the test system connection schematic diagram. Without connecting the sample cable, turn on the power supply and preheat the instrument. The National Bureau of Standards issued on September 29, 1985
Implementation on June 1, 1986
True to stability
GB 5441.7-85
4.1.2 Set the bridge's inductance (neutral resistance) and capacitance (inductance) to "zero". Set the "and angle" selection knob to the "capacitive" (inductive) position.
4.1.3 Adjust the oscillator to the required test frequency. After the indicator selects the frequency, gradually increase the sensitivity. Alternately adjust the zero balance knobs of the inductance (resistance) and capacitance (inductance) until the bridge is balanced. If the cable under test must be connected with a lead, zero balance should be performed with the lead wire. 4.1. Connect the cable under test with the end of the circuit to the test terminal or lead wire of the bridge, gradually increase the indicator sensitivity, and alternately adjust the conductance (resistance), capacitance (inductance) measurement knobs to adjust to the bridge balance. Read G (R), C (L)
4.1.5 Remove the cable, keep the oscillator output frequency unchanged, set the bridge "angle" selector to the "inductive" (capacitive) position, set each measurement gear to zero, and perform zero balance according to 4.1.3. Then connect the cable under test with the end of the short circuit to the test terminal or lead wire of the bridge, and test according to 4.1.4. Read G, (R,), C, (1.). 4.1.6 When the bridge cannot reach the balance point in step 4.1.4.4.1.5, change the position of the "phase angle" selection knob, re-balance the bridge and then avoid testing.
4.2 Resonance frequency method
4.2.1 According to the provisions of Article 4.2 of GB5441.5-85 "Communication Cable Test Method Coaxial Pair External 1 Impedance Real Half Mean Value Test Resonance Method", estimate the harmonic detection frequency and its interval, and select the value closest to the required test frequency as the test frequency. 4.2.2 Short-circuit the terminals of the sample and test according to the steps specified in Article 1.1 of GB5441.5-85, then read the resonant frequency nm from the digital frequency meter and read R from the resistance (or resistance) of the bridge. 4.2.3 Open the terminals of the sample and repeat the steps of Articles 4.3.2 and 4.3.3 of GB5441.5-85, then read the resonant frequency nm from the digital frequency meter and read R from the resistance (or resistance) of the bridge. 4.2.4 If Jmr\ (or fum) deviates greatly from the estimated value, the oscillator output must be set at a frequency of /nm (or /n) and repeat GB 5.441.585, Section 4.3.2.4.3.3, shall be repeated. 5. Test results and calculation
Arbitrary frequency method
27cus4r
(dB/km
,. The calculation shall be carried out according to the formulas listed in the following table for different equivalent circuits of the bridge balanced branch. Military branch equivalent electrical energy
Continental dimension nest
R (R. or)
Impedance and phase angle calculation formula
Balanced branch equivalent circuit
GB 54417--85
Test results
G (G, G)
G (u or C)
R (R. R))
G (G or G)
C (C or
Impedance and phase angle calculation formula
q= -arctg
When 9\」
p -arctg
When ?*90 2
-arcig
When →90, Z=
Note: When the impedance is "capacitive", the phase angle should be "negative"; when the impedance is "inductive", the phase angle should be "stop". In formula (1) and the table:
Length of the cable under test, km;
Attenuation value of the cable under test, dB/km
Reading of the electrical conductivity when the bridge is balanced (R when the terminal is short-circuited, Rx when the circuit is open), 2; Reading of the conductance when the bridge is balanced (terminal short-circuited) G: G when the circuit is parallel, S, inductance reading when the bridge is balanced (L when the terminal is short-circuited, L when the circuit is open), H, capacitance reading when the bridge is balanced, C when the terminal is short-circuited, C when the circuit is open), F: input impedance (when the terminal is short-circuited, ), angular frequency, rad/s;
-frequency, Hz.
5.2 Resonance frequency method
5.2.1 Calculation of actual resonant frequency:
famo+fn
The calculation formula for the attenuation constant during impedance bridge testing is: Ra
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