IEC TR 61156-1-2:2009/AMD1:2014

IEC TR 61156-1-2 ®
Edition 1.0 2014-09
TECHNICAL
REPORT
AMENDMENT 1
Multicore and symmetrical pair/quad cables for digital communications –
Part 1-2: Electrical transmission characteristics and test methods of
Symmetrical pair/quad cables
IEC TR 61156-1-2:2009-05/AMD1.2014-09(en)

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IEC TR 61156-1-2 ®
Edition 1.0 2014-09
TECHNICAL
REPORT
AMENDMENT 1
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
PRICE CODE
U
ICS 33.120.20 ISBN 978-2-8322-1787-0

– 2 – IEC TR 61156-1-2:2009/AMD1:2014

© IEC 2014
FOREWORD
This amendment has been prepared by subcommittee 46C: Wires and symmetric cables, of

IEC technical committee 46: Cables, wires, waveguides, R.F. connectors, R.F. and microwave

passive components and accessories.

The text of this amendment is based on the following documents:

Enquiry draft Report on voting

46C/993/DTR 46C/1000/RVC
Full information on the voting for the approval of this amendment can be found in the report
on voting indicated in the above table.
The committee has decided that the contents of this amendment and the base publication will
remain unchanged until the stability date indicated on the IEC web site under
"http://webstore.iec.ch" in the data related to the specific publication. At this date, the
publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

_____________
2 Normative references
Add, after IEC 60050-726, the following new references:
IEC 60169-15, Radio-frequency connectors – Part 15: R.F. coaxial connectors with inner
diameter of outer conductor 4,13 mm (0,163 in) with screw coupling – Characteristic
impedance 50 ohms (Type SMA)
IEC 61169-16, Radio-frequency connectors – Part 16: Sectional specification – RF coaxial
connectors with inner diameter of outer conductor 7 mm (0,276 in) with screw coupling –
Characteristics impedance 50 ohms (75 ohms) (type N)
3 Terms, definitions, symbols, units and abbreviated terms
3.1 Terms and definitions
Change the introductory wording as follows:
For the purposes of this document, the terms and definitions given in IEC 60050-726,
IEC TR 62152 and the following apply:

© IEC 2014
Add the following new definition:

3.1.1
single-ended
measurement with respect to a fixed potential, usually ground

8 Unbalance attenuation
8.3 Theoretical background
In Formula (140), replace T by T .

u,n u,f
In Formula (143), replace in the exponential term β ± β by β + β .
diff com diff com
Add, after Clause 8, the following new Clause 9:
9 Balunless test method
9.1   Overall test arrangement
9.1.1 Test instrumentation
The test procedures hereby described require the use of a vector network analyser or similar
test equipment. The analyser shall have the capability of full 4-port calibration and should
include isolation calibrations. The analyser should cover at least the full frequency range of
the cable or cabling under test (CUT).
Measurements are to be taken using a mixed mode test set-up, which is often referred to as
an unbalanced, modal decomposition or balun-less set-up. This allows measurements of
balanced devices without use of an RF balun in the signal path. With such a test set-up, all
balanced and unbalanced parameters can be measured over the full frequency range.
Such a configuration allows testing with both a common or differential mode stimulus and
responses, ensuring that intermodal parameters can be measured without reconnection.
A 16 port network analyser is required to measure all combinations of a 4 pair device without
external switching; however, the network analyser should have a minimum of 2 ports to
enable the data to be collated and calculated.
It should be noted that the use of a 4-port analyser will involve successive repositioning of the

measurement ports in order to measure any given parameter.
A 4-port network analyser is recommended as a minimum number of ports, as this will allow
the measurement of the full 16 term mixed mode S-parameter matrix on a given pair
combination without switching or reconnection in one direction.
In order to minimise the reconnection of the CUT for each pair combination, the use of an RF
switching unit is also recommended.
Each conductor of the pair or pair combination under test should be connected to a separate
port of the network analyser, and results are processed either by internal analysis within the
network analyser or by an external application.
Reference loads and through connections are needed for the calibration of the set-up.
Requirements for the reference loads are given in 9.1.5. Termination loads are needed for

– 4 – IEC TR 61156-1-2:2009/AMD1:2014

© IEC 2014
termination of pairs, used and unused, which are not terminated by the network analyser.

Requirements for the termination loads are given in 9.1.7.

9.1.2 Measurement precautions
To assure a high degree of reliability for transmission measurements, the following

precautions are required:
a) Consistent and stable resistor loads should be used throughout the test sequence.

b) Cable and adapter discontinuities, as introduced by physical flexing, sharp bends and

restraints should be avoided before, during and after the tests.

c) Consistent test methodology and termination resistors should be used at all stages of
transmission performance qualifications.
The relative spacing of conductors in the pairs should be preserved throughout the tests to
the greatest extent possible.
d) The balance of the cables should be maintained to the greatest extent possible by
consistent conductor lengths, pair twisting and lay up of the screen to the point of load.
e) The sensitivity to set-up variations for these measurements at high frequencies demands
attention to details for both the measurement equipment and the procedures.
9.1.3 Mixed mode S-parameter nomenclature
The test methods specified in this document are based on a balun-less test set-up in which all
terminals of a device under test are measured and characterized as single-ended (SE) ports,
i.e. signals (RF voltages and currents) are defined relative to a common ground. For a device
with 4 terminals, a diagram is given in Figure 14.
Port 1 Port 2
CUT
Port 3 Port 4
(single-ended)
IEC
Figure 14 – Diagram of a single-ended 4-port device

The 4-port device in Figure 14 is characterized by the 16 term SE S-matrix given in
Equation (146), in which the S-parameter S expresses the relation between a single-ended
ba
response on port “b” resulting from a single ended stimulus on port “a”.
S S S S
 
11 12 13 14
 
S S S S
21 22 23 24
 
S = (146)
 
S S S S
31 32 33 34
 
S S S S
 41 42 34 44 
For a balanced device, each port is considered to consist of a pair of terminals (= a balanced
port) as opposed to the SE ports defined above, see Figure 15.

© IEC 2014
Port 1
Port 2
CUT
(balanced)
IEC
Figure 15 – Diagram of a balanced 2-port device
In order to characterize the balanced device, both the differential mode and the common
mode signals on each balanced port shall be considered. The device can be characterized by
a mixed mode S-matrix that includes all combinations of modes and ports, e.g. the mixed
mode S-parameter S that expresses the relation between a differential mode response on
DC21
port 2 resulting from a common mode stimulus on port 1. Using this nomenclature, the full set
of mixed mode S -parameters for a 2-port can be presented as in Table 4.
Table 4 – Mixed mode S-parameter nomenclature
Differential mode Common mode
stimulus stimulus
Port 1 Port 2 Port 1 Port 2
Port 1 S S S S
DD11 DD12 DC11 DC12
Differential mode response
Port 2 S S S S
DD21 DD22 DC21 DC22
Port 1 S S S S
CD11 CD12 CC11 CC12
Common mode response
Port 2 S S S S
CD21 CD22 CC21 CC22
A 4-terminal device can be represented both as a 4-port SE device as in Figure 14
characterized by a single ended S-matrix (Equation (146)) and as a 2-port balanced device as
in Figure 15 characterized by a mixed mode S-matrix (see Table 4). As applying a SE signal to
a port is mathematically equivalent to applying superposed differential and common mode
signals, the SE and the mixed mode characterizations of the device are interrelated. The
conversion from SE to mixed mode S-parameters is given in Annex A. Making use of this
conversion, the mixed mode S-parameters may be derived from the measured SE S-matrix.
9.1.4 Coaxial cables and interconnect for network analysers
Assuming that the characteristic impedance of the network analyser is 50 Ω, coaxial cables
used to interconnect the network analyser, switching matrix and the test fixture should be of
50 Ω characteristic impedance and of low transfer impedance (double screen or more).
These coaxial cables should be as short as possible. (It is recommended that they do not
exceed 1 000 mm each.)
The screens of each cable shall be electrically bonded to a common ground plane, with the
screens of the cable bonded to each other at multiple points along their length.
To optimize dynamic range, the total interconnecting cable insertion loss should be minimised.
(It is recommended that the interconnecting cable loss does not exceed 3 dB at 1 000 MHz.)

– 6 – IEC TR 61156-1-2:2009/AMD1:2014

© IEC 2014
9.1.5 Reference loads for calibration

The N-nonnector shall be seen as a possible sample. Other connectors can be used for

similar purposes such as e.g. SMA-connectors. Some test equipment even use no

standardized fixtures.
To perform a one or 2-port calibration of the test equipment, a short circuit, an open circuit

and a reference load are required. These devices should be used to obtain a calibration.

The reference load should be calibrated against a calibration reference, which should be a

50 Ω load, traceable to an international reference standard. One 50 Ω reference load should

be calibrated against the calibration reference. The reference load for calibration should be
placed in an N-type connector according to IEC 61169-16 or a SMA-connector according to
IEC 60169-15, meant for panel mounting, which is machined-flat on the back side, see
Figure 16. For frequencies higher than 1 GHz, a SMA-connector should be used.
The load should be fixed to the flat side of the connector. A network analyser should be
calibrated, 1-port full calibration, with the calibration reference. Thereafter, the return loss of
the reference load for calibration should be measured. The verified return loss should be
≥46 dB at frequencies up to 100 MHz and ≥40 dB at frequencies above 100 MHz and up to
the limit for which the measurements are to be carried out.
Machined flat
Load for calibration
N-type connector
IEC
Figure 16 – Possible solution for calibration of reference loads
For short and open, the inductance and capacitance should be minimised.
9.1.6 Calibration
Isolation measurements should be used as part of the calibration.

The calibration should be equivalent to a minimum of a full 4-port SE calibration for
measurements where the response and stimulus ports are the same (S and S ), and a
xx11 xx22
minimum of a full 4-port SE calibration for measurements where the response and stimulus
ports are different (S and S ).
xx12 xx21
An individual calibration should be performed for each signal path used for the measurements.
If a complete switching matrix and a 4-port network analyser test set-up is used, a full set of
measurements for a 4-pair device (i.e. 16 single-ended ports), will require 28 separate 4-port
calibrations, although many of the measurements within each calibration are in common with
other calibrations. A software or hardware package may be used to minimise the number of
calibration measurements required.
The calibration should be applied in such a way that the calibration plane should be at the
ends of the fixed connectors of the test fixture.

© IEC 2014
The calibration may be performed at the test interface using appropriate calibration artefacts,

or at the ends of the coaxial test cable using coaxial terminations.

Where calibration is performed at the test interface, open, short and load measurements

should be taken on each SE port concerned, and through and isolation measurements should

be taken on every pair combination of those ports.

Where calibration is performed at the end of the coaxial test cables, open, short and load

measurements should be taken on each port concerned, and through and isolation

measurements should be taken on every pair combination of those ports. In addition, the test

fixture shall then be de-embedded from the measurements. The de-embedding techniques

should incorporate a fully populated 16 port S-matrix. It is not acceptable to perform a de-
embedded calibration using only reflection terms (S , S , S , S ) or only near-end terms (S ,
11 22 33 44 11
S , S , S ).
21 12 22
De-embedding using reduced term S-matrices may be used for post processing of results.
9.1.7 Termination loads for termination of conductor pairs
9.1.7.1 General
When this document is used for the measurement of performance against standards, the
differential mode terminations applied to the device under test (DUT) shall provide the
differential mode and common mode reference termination impedances specified in standards
for the cabling system where the DUT is used.
50 Ω wires to ground terminations should be used on all active pairs under test. 50 Ω
differential mode to ground terminations should be used on all inactive pairs and on the
opposite ends of active pairs for near-end crosstalk (NEXT) and far-end crosstalk (FEXT)
testing. Inactive pairs for return loss testing should be terminated with 50 Ω differential mode
to ground terminations. See Figure 17.
50 Ω ± 0,1 % 50 Ω ± 0,1 %
50 Ω differential mode to
ground terminations
IEC
Figure 17 – Resistor termination networks

Small geometry chip resistors should be used for the construction of resistor terminations.
The two 50 Ω DM terminating resistors should be matched to within 0,1 % at DC, and 2 % at
1 000 MHz (corresponding to a 40 dB return loss requirement at 1 000 MHz). The length of
connections to impedance terminating resistors should be minimized. Use of soldered
connections without leads is recommended.
9.1.7.2 Verification of termination loads
The performance of impedance matching resistor termination networks should be verified by
measuring the return loss of the termination and the residual NEXT between any two resistor
termination networks at the calibration plane.
For the return loss measurement, a 2-port SE calibration is required using a reference load
verified according to 9.1.5.
– 8 – IEC TR 61156-1-2:2009/AMD1:2014

© IEC 2014
After calibration, connect the resistor termination network and perform a full 2-port SE

S-matrix measurement. The measured SE S-matrix should be transformed into the associated

mixed mode S-matrix to obtain the S-parameters S and S from which the differential
DD11 CC11
mode return loss RL and the common mode return loss RL are determined. The return
DM CM
loss of the resistor termination network should meet the requirements of Table 5.

For the residual NEXT measurement, a 4-port SE calibration is required. After calibration,

connect the resistor termination networks and perform a full 4-port SE S-matrix measurement.

The measured S-matrix should be transformed into the associated mixed mode S-matrix to

obtain the S-parameter S from which the residual NEXT of the terminations,
DD21
NEXT , is determined. The residual NEXT should meet the requirements of Table 5.
residual_term
For the TCL measurement, a 2-port SE calibration is required using a reference load verified
according to 9.1.5.
After calibration, connect the resistor termination network and perform a full 2-port SE
S-matrix measurement. The measured SE S-matrix should be transformed into the associated
mixed mode S-matrix to obtain the S-parameter S from which the differential mode TCL is
CD11
determined. The TCL of the resistor termination network should meet the requirements of
Table 5.
Table 5 – Requirements for terminations at calibration plane
Frequency Requirement up to maximum
Parameter
MHz frequency
≥74-20 log(f) dB
SE port (50 Ω) return loss (dB)
40 dB max
20 dB min
≥74-20 log(f) dB
DM port (100 Ω) return loss (dB) 40 dB max
20 dB min
1 ≤ f ≤ f
max
≥140-20 log(f) dB
DM port to port residual NEXT (dB) 104 dB max
80 dB min
≥ 60-10 log(f) dB
DM port TCL of loads (dB)
50 dB max
20 dB min
9.1.8 Termination of screens
If the CUT is screened, screened measurement cables shall be applied.
The screen or screens of these cables should be fixed to the ground plane as close as
possible to the calibration plane.
9.2 Cabling and cable measurements
9.2.1 Insertion loss and EL TCTL
9.2.1.1 Object
When this document is used for the measurement of performance against standards, the
differential mode terminations applied to the DUT shall provide the differential mode and
common mode reference termination impedances specified in standards for the cabling
system where the DUT is used.
© IEC 2014
The object of this test is to measure the insertion loss (IL) and equal-level transverse

conversion transfer loss (EL TCTL) of a cable or cabling pair. Insertion loss is defined as the

attenuation that is caused by the cable or cabling pair. EL TCTL is defined as the unbalance

attenuation at far end.
9.2.1.2 Cable and cabling insertion loss and EL TCTL

Cable or cabling should be tested for insertion loss in one direction and EL TCTL in both

directions.
9.2.1.3 Test method
Insertion loss is evaluated from the mixed mode parameter S and EL TCTL is evaluated
DD21
from the mixed mode parameter S for each conductor pair. The mixed mode S-parameters
CD21
are derived by transformation of the SE S-matrix.
9.2.1.4 Test set-up
The test set-up consists of a network analyser and two test fixtures. An illustration of the test
set-up, which also shows the termination principles, is shown in Figure 18. Resistor
termination networks in accordance with 9.1.7 should be applied for all inactive pairs.
9.2.1.5 Procedure
9.2.1.5.1 Calibration
A full 4-port SE calibration should be performed at the calibration planes in accordance with
9.1.6. Reference loads used for calibration should be in accordance with 9.1.5.
9.2.1.5.2 Measurement
The CUT should be arranged in an appropriate test set-up according to Figure 18, including
proper termination of the active, inactive pairs and screen. A full SE S-matrix measurement
should be performed. The measured SE S-matrix should be transformed into the associated
mixed mode S-matrix to obtain the S-parameter S from which insertion loss is determined
DD21
and S from which TCTL is determined.
CD21
IL(𝑓) =−20∙ log (|𝑆 |) =−20∙ log �� (𝑆 −𝑆 −𝑆 +𝑆 )�� (147)
DD21 31 41 32 42
10 10
( )
TCTL(𝑓) =−20∙ log (|𝑆 |) =−20∙ log �� 𝑆 +𝑆 −𝑆 −𝑆 �� (148)
CD21 31 41 32 42
10 10
(𝑆 +𝑆 −𝑆 −𝑆 )
31 41 32 42
EL TCTL(𝑓)=TCTL(f)-IL(𝑓) =−20∙ log �� �� (149)
(𝑆 −𝑆 −𝑆 +𝑆 )
31 41 32 42
Test all conductor pairs and record the results.

– 10 – IEC TR 61156-1-2:2009/AMD1:2014

© IEC 2014
CUT
NA Port 1 NA Port 3
NA Port 2 NA Port 4
50 Ω
50 Ω
50 Ω
50 Ω
50 Ω
50 Ω
50 Ω
50 Ω
50 Ω
50 Ω
50 Ω
50 Ω
Screen (if applicable)
Calibration plane
Calibration plane Reference plane Reference plane

IEC
Figure 18 – Insertion loss and EL TCTL measurement
9.2.1.6 Test report
The test results should be reported in graphical or table format with the specification limits
shown on the graphs or in the table at the same frequencies as specified in the relevant detail
specification. Results for all pairs should be reported. It should be explicitly noted if the test
results exceed the test limits.
9.2.1.7 Accuracy
As there is no definition of accuracy in this document and there is no procedure defined to
determine the accuracy, the accuracy requirement is for further studies.
9.2.2 NEXT
9.2.2.1 Object
When this document is used for the measurement of performance against standards, the
differential mode terminations applied to the DUT shall provide the differential
...