IEC TS 61156-1-2:2023

IEC TS 61156-1-2 ®
Edition 1.0 2023-11
TECHNICAL
SPECIFICATION
colour
inside
Multicore and symmetrical pair/quad cables for digital communications –
Part 1-2: Electrical transmission characteristics and test methods of symmetrical
pair/quad cables
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IEC TS 61156-1-2 ®
Edition 1.0 2023-11
TECHNICAL
SPECIFICATION
colour
inside
Multicore and symmetrical pair/quad cables for digital communications –

Part 1-2: Electrical transmission characteristics and test methods of

symmetrical pair/quad cables
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS  21.220 ISBN 978-2-8322-7881-9

– 2 – IEC TS 61156-1-2:2023 © IEC 2023
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms, definitions, symbols, units and abbreviated terms . 7
3.1 Terms and definitions . 7
3.2 Symbols, units and abbreviated terms . 8
4 Basic transmission line formulae. 8
4.1 Overview. 10
4.2 Complex characteristic impedance and propagation coefficient formulae . 11
4.2.1 General . 11
4.2.2 Propagation coefficient . 11
4.2.3 Complex characteristic impedance. 12
4.2.4 Phase and group velocity . 14
4.3 High frequency representation of secondary parameters . 15
4.4 Frequency dependence of the primary and secondary parameters . 17
4.4.1 Resistance . 17
4.4.2 Inductance . 17
4.4.3 Complex characteristic impedance. 17
4.4.4 Attenuation coefficient . 18
4.4.5 Phase delay and group delay . 18
5 Measurement of the complex characteristic impedance . 19
5.1 General . 19
5.2 Open/short circuit single-ended impedance measurement made with a balun
(reference method) . 20
5.2.1 Principle . 20
5.2.2 Test equipment . 21
5.2.3 Procedure . 21
5.2.4 Expression of results . 22
5.3 Function fitting the impedance magnitude and angle . 22
5.3.1 General . 22
5.3.2 Impedance magnitude . 22
5.3.3 Function fitting the angle of the complex characteristic impedance . 24
5.4 Complex characteristic impedance determined from measured phase
coefficient and capacitance . 25
5.4.1 General . 25
5.4.2 Formulae for all frequencies case and for high frequencies. 25
5.4.3 Procedure for the measurement of the phase coefficient . 26
5.4.4 Phase delay . 27
5.4.5 Phase velocity . 28
5.4.6 Procedure for the measurement of the capacitance . 28
5.5 Determination of the complex characteristic impedance using the terminated
measurement method . 28
5.6 Extended open/short circuit method using a balun but excluding the balun
performance . 29
5.6.1 Test equipment and cable-end preparation . 29
5.6.2 Basic formulae . 29
5.6.3 Measurement principle. 29

5.7 Extended open/short circuit method without using a balun . 32
5.7.1 Basic formulae and circuit diagrams . 32
5.7.2 Measurement principle. 34
5.8 Open/short impedance measurements at low frequencies with a balun . 35
5.9 Complex characteristic impedance and propagation coefficient obtained from

modal decomposition technique . 37
5.9.1 General . 37
5.9.2 Procedure . 37
5.9.3 Measurement principle. 38
5.9.4 Scattering matrix to impedance matrix . 40
5.9.5 Expression of results . 42
6 Measurement of return loss and structural return loss . 42
6.1 General . 42
6.2 Principle . 42
7 Propagation coefficient effects due to periodic structural variation related to the

effects appearing in the structural return loss . 43
7.1 General . 43
7.2 Formula for the forward echoes caused by periodic structural
inhomogeneities . 43
8 Unbalance attenuation . 45
8.1 General . 45
8.2 Unbalance attenuation near end and far end . 46
8.3 Theoretical background . 48
9 Balunless test method . 51
9.1 Overall test arrangement . 51
9.1.1 Test instrumentation . 51
9.1.2 Measurement precautions . 52
9.1.3 Mixed mode S-parameter nomenclature . 52
9.1.4 Coaxial cables and interconnect for network analysers . 54
9.1.5 Reference loads for calibration . 54
9.1.6 Calibration . 55
9.1.7 Termination loads for termination of conductor pairs . 56
9.1.8 Termination of screens . 57
9.1.9 Calibration . 57
9.1.10 Establishment of noise floor . 57
9.2 Cabling and cable measurements . 57
9.2.1 Insertion loss and EL TCTL . 57
9.2.2 NEXT . 59
9.2.3 ACR-F . 61
9.2.4 Return loss and TCL . 63
9.2.5 PS alien near-end crosstalk (PS ANEXT-Exogenous crosstalk) . 64
9.2.6 PS attenuation to alien crosstalk ratio, far-end crosstalk (PS AACR-F-
Exogenous crosstalk . 67
Annex A (informative) Example derivation of mixed mode parameters using the modal
decomposition technique . 70
Bibliography . 74

Figure 1 – Secondary parameters extending from 1 kHz to 1 GHz . 19
Figure 2 – Diagram of cable pair measurement circuit . 21

– 4 – IEC TS 61156-1-2:2023 © IEC 2023
Figure 3 – Determining the multiplier of 2π radians to add to the phase measurement . 27
Figure 4 – Measurement configurations . 30
Figure 5 – Measurement principle with four terminal network theory . 30
Figure 6 – Admittance measurement configurations . 34
Figure 7 – Admittance measurement principle . 34
Figure
...